Taysha Gene Therapies (TSHA) 10-K 19 Mar 24 2023 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 19, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	TSHA
Entity Registrant Name	Taysha Gene Therapies, Inc.
Entity Central Index Key	0001806310
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity File Number	001-39536
Entity Tax Identification Number	84-3199512
Entity Address, Address Line One	3000 Pegasus Park Dr
Entity Address Address Line2	Ste 1430
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75247
City Area Code	214
Local Phone Number	612-0000
Entity Common Stock, Shares Outstanding		187,018,275
Title of 12(b) Security	Common stock, par value $0.00001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes
Document Annual Report	true
Document Transition Report	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Public Float			$ 30.4
Auditor Name	Deloitte & Touche LLP
Auditor Location	Dallas, Texas
Auditor Firm ID	34
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement relating to the 2024 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K. The Proxy Statement will be filed with the Securities and Exchange Commission within 120 days after the year ended December 31, 2023.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 143,940	$ 87,880
Restricted cash	449
Prepaid expenses and other current assets	3,479	8,537
Assets held for sale	2,000
Total current assets	149,868	96,417
Restricted cash	2,151	2,637
Property, plant and equipment, net	10,826	14,963
Operating lease right-of-use assets	9,582	10,943
Other non-current assets	304	1,316
Total assets	172,731	126,276
Current liabilities
Accounts payable	6,366	10,946
Accrued expenses and other current liabilities	12,284	18,287
Deferred revenue	18,106	33,557
Total current liabilities	36,756	62,790
Term loan, net	40,508	37,967
Operating lease liability, net of current portion	18,953	20,440
Other non-current liabilities	1,577	4,130
Total liabilities	97,794	125,327
Commitments and contingencies - Note 13
Stockholders' equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of December 31, 2023 and December 31, 2022
Common stock, $0.00001 par value per share; 400,000,000 shares authorized and 186,960,193 issued and outstanding as of December 31, 2023 and 200,000,000 shares authorized and 63,207,507 issued and outstanding as of December 31, 2022.	2	1
Additional paid-in capital	587,942	402,389
Accumulated deficit	(513,007)	(401,441)
Total stockholders’ equity	74,937	949
Total liabilities and stockholders' equity	$ 172,731	$ 126,276

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value per share	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value per share	$ 0.00001	$ 0.00001
Common stock, shares authorized	400,000,000	200,000,000
Common stock, shares issued	186,960,193	63,207,507
Common stock, shares outstanding	186,960,193	63,207,507

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
Revenues	$ 15,451	$ 2,502
Operating expenses:
Research and development	56,778	91,169
General and administrative	30,047	37,360
Impairment of long-lived assets	1,065	36,420
Total operating expenses	87,890	164,949
Loss from operations	(72,439)	(162,447)
Other income (expense):
Change in fair value of warrant liability	(34,718)
Loss on debt extinguishment	(1,398)
Change in fair value of term loan	(1,538)
Interest income	3,572	249
Interest expense	(4,998)	(3,798)
Other expense	(47)	(18)
Total other expense, net	(39,127)	(3,567)
Net loss	$ (111,566)	$ (166,014)
Net loss per common share, basic	$ (0.96)	$ (3.78)
Net loss per common share, diluted	$ (0.96)	$ (3.78)
Weighted average common shares outstanding, basic	116,121,482	43,952,015
Weighted average common shares outstanding, diluted	116,121,482	43,952,015

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Offering to Astellas	Public Offering	At-the-Market Offering	Private Placement	Common Stock	Common Stock Offering to Astellas	Common Stock Public Offering	Common Stock At-the-Market Offering	Common Stock Private Placement	Additional Paid-in Capital	Additional Paid-in Capital Offering to Astellas	Additional Paid-in Capital Public Offering	Additional Paid-in Capital At-the-Market Offering	Additional Paid-in Capital Private Placement	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Balance at Dec. 31, 2021	$ 95,383	$ 222										$ 331,032					$ (235,649)	$ 222
Balance, shares at Dec. 31, 2021							38,473,945
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2016-02 [Member]
Stock-based compensation	$ 18,275											18,275
Issuance of common stock			$ 13,764	$ 27,457	$ 11,609					$ 1			$ 13,764	$ 27,457	$ 11,608
Issuance of common stock, shares								7,266,342	14,765,226	2,000,000
Issuance of common stock, upon vesting and settlement of restricted stock units, net, shares							628,921
Issuance of common stock under ESPP	253											253
Issuance of common stock under ESPP, shares							73,073
Net loss	(166,014)																(166,014)
Balance at Dec. 31, 2022	$ 949						$ 1					402,389					(401,441)
Balance, shares at Dec. 31, 2022	63,207,507						63,207,507
Stock-based compensation	$ 7,905											7,905
Issuance of common stock						$ 103,239					$ 1					$ 103,238
Issuance of common stock, shares											123,117,594
Issuance of common stock, upon vesting and settlement of restricted stock units, net, shares							566,772
Issuance of common stock under ESPP	68											68
Issuance of common stock under ESPP, shares							68,320
Reclassification of pre-funded warrants to equity classification	74,342											74,342
Net loss	(111,566)																(111,566)
Balance at Dec. 31, 2023	$ 74,937						$ 2					$ 587,942					$ (513,007)
Balance, shares at Dec. 31, 2023	186,960,193						186,960,193

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Payment of sales commissions and other offering costs		$ 392
Offering to Astellas
Offering costs		187
Public Offering
Underwriting discount and other offering costs		$ 2,072
Private Placement
Offering costs	$ 7,138

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities
Net loss	$ (111,566)	$ (166,014)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,371	1,172
Research and development license expense	3,500	1,250
Stock-based compensation	7,905	18,043
Change in fair value of warrant liability	34,718
Issuance costs for pre-funded warrant liability	2,567
Non-cash loss on debt extinguishment	1,366
Non-cash change in fair value of term loan	1,278
Debt issuance costs expensed under the fair value option	867
Impairment of long-lived assets	1,065	36,420
Non-cash lease expense	1,182	1,315
Other	741	906
Changes in operating assets and liabilities:
Prepaid expenses and other assets	6,011	2,088
Accounts payable	(2,295)	(7,804)
Accrued expenses and other liabilities	(6,277)	(9,323)
Deferred revenue	(15,451)	33,557
Net cash used in operating activities	(73,018)	(88,390)
Cash flows from investing activities
Purchase of research and development license	(3,500)	(4,250)
Purchase of property, plant and equipment	(3,869)	(20,619)
Other	17	(61)
Net cash used in investing activities	(7,352)	(24,930)
Cash flows from financing activities
Proceeds from Trinity term loan, net	39,550
Debt issuance costs for term loan	(399)
Repayment of SVB term loan	(43,000)
Proceeds from issuance of common stock and pre-funded warrants from private placement, net of placement agent commissions and other offering costs	140,290
Payment of offering costs	(387)	(358)
Proceeds from common stock issuances under ESPP	68	253
Other	(229)	(1,042)
Net cash provided by financing activities	136,393	52,097
Net increase (decrease) in cash, cash equivalents and restricted cash	56,023	(61,223)
Cash, cash equivalents and restricted cash at the beginning of the period	90,517	151,740
Cash, cash equivalents and restricted cash at the end of the period	146,540	90,517
Cash and cash equivalents	143,940	87,880
Restricted cash	2,600	2,637
Supplemental disclosure of cash flow information:
Cash paid for interest	4,952	2,775
Supplemental disclosure of noncash investing and financing activities:
Reclassification of warrants to additional paid-in capital	74,342
Allocation of proceeds to Success Fee liability	770
Recognition of asset retirement obligation	449
Property, plant and equipment in accounts payable and accrued expenses		4,002
Right-of-use assets obtained in exchange for lease liabilities		23,432
Offering costs not yet paid	18	387
Issuance of warrants in connection with private placement	252
Public Offering
Cash flows from financing activities
Net proceeds from issuance of common stock		27,717
Offering to Astellas
Cash flows from financing activities
Net proceeds from issuance of common stock		13,887
At-the-Market Offering
Cash flows from financing activities
Net proceeds from issuance of common stock		$ 11,640
Private Placement
Cash flows from financing activities
Net proceeds from issuance of common stock	$ 500

Organization and Description of

Organization and Description of Business Operations	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business Operations	Note 1—Organization and Description of Business Operations Taysha Gene Therapies, Inc. (the “Company” or “Taysha”) was originally formed under the laws of the State of Texas on September 20, 2019. Taysha converted to a Delaware corporation on February 13, 2020 , which had no impact to the Company’s par value or issued and authorized capital structure. Taysha is a clinical-stage biotechnology company focused on advancing AAV-based gene therapies for severe monogenic diseases of the central nervous system. Sales Agreement On October 5, 2021, the Company entered into a Sales Agreement (the “Sales Agreement”) with SVB Securities LLC (f/k/a SVB Leerink LLC) and Wells Fargo Securities, LLC (collectively, the “Sales Agents”), pursuant to which the Company may issue and sell, from time to time in its sole discretion, shares of its common stock having an aggregate offering price of up to $ 150.0 million through the Sales Agents. In March 2022, the Company amended the Sales Agreement to, among other things, include Goldman Sachs & Co. LLC as an additional Sales Agent. The Sales Agents may sell common stock by any method permitted by law deemed to be an “at-the-market offering” as defined in Rule 415(a)(4) of the Securities Act, including sales made directly on or through the Nasdaq Global Select Market or any other existing trade market for the common stock, in negotiated transactions at market prices prevailing at the time of sale or at prices related to prevailing market prices, or any other method permitted b y law. The Sales Agents are entitled to receive 3.0 % of the gross sales price per share of common stock sold under the Sales Agreement. In April 2022, the Company sold 2,000,000 shares of common stock under the Sales Agreement and received $ 11.6 million in net proceeds. No other shares of common stock have been issued and sold pursuant to the Sales Agreement as of December 31, 2023. Liquidity and Capital Resources The Company has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of December 31, 2023, the Company had an accumulated deficit of $ 513.0 million. Future capital requirements will depend on many factors, including the timing and extent of spending on research and development and the market acceptance of the Company’s products. The Company will need to obtain additional financing in order to complete clinical studies and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be on terms acceptable to the Company. As of December 31, 2023, the Company had cash and cash equivalents of $ 143.9 million which the Company believes will be sufficient to fund its planned operations for a period of at least twelve months from the date of issuance of these consolidated financial statements. The Company has based this estimate on assumptions that may prove to be wrong, and its operating plan may change as a result of many factors currently unknown to it. As a result, the Company could deplete its capital resources sooner than it currently expects. The Company expects to finance its future cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances or licensing arrangements. If the Company is unable to obtain funding, the Company would be forced to delay, reduce or eliminate some or all of its research and development programs, preclinical and clinical testing or commercialization efforts, which could adversely affect its business prospects.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Significant Accounting Policies	Note 2—Significant Accounting Policies Basis of Presentation The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented. Principles of Consolidation The accompanying consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Emerging Growth Company From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended, the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards, which delays the adoption of these accounting standards until they would apply to private companies. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to the determination of the fair value of the common stock prior to the IPO (as an input into stock-based compensation), estimating manufacturing accruals and accrued or prepaid research and development expenses, the measurement of impairment of long-lived assets, the valuation of the Trinity Term Loans that are carried at fair value, and the allocation of consideration received in connection with the Astellas Transactions. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected. Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development by the Company or its competitors of technological innovations, risks of failure of clinical studies, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to transition from preclinical manufacturing to commercial production of products. The Company’s product candidates require approvals from the FDA and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as a single operating segment, which is the business of developing AAV-based gene therapies for the treatment of rare monogenic diseases of the central nervous system. As of December 31, 2023 and 2022, the Company did no t have any significant long-lived assets located outside of the United States. Revenue Recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers . Revenues consist of activities in connection with the Astellas Transactions, including the exclusive option to license intellectual property and the performance of research and development activities. See Note 7 for additional information. The Company evaluates the agreement to determine if the other party is a customer, and then determines the units of account within the agreement to determine which promised goods or services are distinct. In order for a promised good or service to be considered "distinct” under ASC 606, the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (i.e., the good or service is capable of being distinct), and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (i.e., the promise to transfer the good or service is distinct within the context of the contract). For any units of account that fall within the scope of ASC 606, where the other party is a customer, the Company (i) evaluates the separate performance obligation(s) under each contract, (ii) determines the transaction price, (iii) allocates the transaction price to each performance obligation considering the estimated standalone selling prices of the services and (iv) recognizes revenue when, or as, the Company satisfies the performance obligation(s). At the inception of an arrangement that includes options for a customer to purchase additional services or products at agreed upon prices in the future, the Company evaluates whether each option provides a material right. An option that provides a material right will be accounted for as a separate performance obligation. As part of the accounting for arrangements under ASC 606, the Company must use significant judgment to determine the performance obligations, the transaction price, and the standalone selling price (“SSP”) for each performance obligation identified in the contract for the allocation of the transaction price. The SSP is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the SSP of each of the identified performance obligations, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis, the Company utilizes similar observable transactions in the marketplace or estimates the SSP of each performance obligation in its customer arrangements at contract inception based on either (1) its estimate of costs to be incurred to fulfill its obligations associated with the performance obligation, plus a reasonable margin, or (2) an estimate that reflects the discount that the customer would obtain when exercising its option adjusted for (i) any discount that the customer could receive without exercising the option and (ii) the likelihood that the option will be exercised. The Company allocates the transaction price to each performance obligation in proportion to its SSP. A performance obligation is satisfied and revenue is recognized when “control” of the promised good or service is transferred, either over time or at a point in time, to the customer. A customer obtains control of a good or service if it has the ability to (1) direct its use and (2) obtain substantially all of the remaining benefits from it. Amounts received prior to satisfying the revenue recognition criteria listed above are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue, including the amounts allocated to material rights which are subject to customer exercise at any point. Amounts not expected to be recognized as revenue within the following 12 months of the balance sheet date are classified as deferred revenue, net of current portion. The Company does not incur commission or other costs to fulfill customer contracts and as such, no capitalized contract costs are recorded on the consolidated balance sheets. Cash and Cash Equivalents Cash and cash equivalents consist of funds held in a standard checking account, a standard savings account and a money market fund. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of December 31, 2023, the Company had $ 142.4 million in cash equivalents. As of December 31, 2022, the Company had no cash equivalents. Restricted Cash Restricted cash consists of cash that the Company has placed in an escrow account which is pledged as collateral under certain lease agreements and letters of credit. Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. On March 10, 2023, the California Department of Financial Protection and Innovation closed the Silicon Valley Bank, Santa Clara, California (“SVB”), and appointed the FDIC as receiver. On March 12, 2023, the Treasury Department announced that depositors of SVB will have access to all of their money starting March 13, 2023. On March 14, 2023, the Company regained access to the full amount of its cash that was deposited with SVB. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management continues to believe to be of high credit quality. The Company has not experienced any losses on these deposits. Fair Value of Financial Instruments The Company’s financial assets and liabilities are accounted for in accordance with ASC 820, Fair Value Measurements which defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels: Level 1—Observable inputs, such as quoted prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life. Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying values reported in the Company’s consolidated balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities are reasonable estimates of their fair values due to the short-term nature of these items. Fair Value Option The fair value option provides an election that allows a company to irrevocably elect to record certain financial assets and liabilities at fair value on an instrument-by-instrument basis at initial recognition. The Company has elected to apply the fair value option to the Trinity Term Loans. The term loans accounted for under the fair value option election are each a debt host financial instrument containing embedded features that would otherwise be required to be bifurcated from the debt-host and recognized as separate derivative liabilities subject to initial and subsequent periodic estimated fair value measurements in accordance with GAAP. Notwithstanding, when the fair value option election is applied to financial liabilities, bifurcation of an embedded derivative is not required, and the financial liability is initially measured at its issue-date estimated fair value and then subsequently remeasured at estimated fair value on a recurring basis as of each reporting period date. The portion of the change in fair value attributed to a change in the instrument-specific credit risk is recognized as a component of other comprehensive income or loss if material and the remaining amount of the fair value adjustment is recognized as a component of other income (expense) in the consolidated statements of operations. Deferred Offering Costs The Company capitalizes costs directly associated with equity financings until such financings are consummated, at which time such costs are recorded in additional paid-in capital against the gross proceeds of the equity financings. Costs associated with the shelf registration statement on Form S-3, filed with the SEC on October 5, 2021 have been capitalized and will be reclassified to additional paid-in capital on a pro rata basis when the Company completes offerings under the shelf registration. At the end of the three-year term of the shelf registration, the remaining deferred offering costs, if any, will be charged to operations. Property, Plant and Equipment, net Property, plant and equipment, net are stated at cost less accumulated depreciation and consist of computer equipment, laboratory equipment and leasehold improvements. Directly identifiable payroll and payroll-related costs incurred in connection with the build-out of the Company’s cGMP manufacturing facility were capitalized into the cost basis of the asset to the extent that such costs had been incurred to bring the asset to the condition and location for its intended use. Depreciation expense is recognized using the straight-line method over its estimated useful life of three to seven years . Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred. Leases Effective January 1, 2022, the Company adopted ASC 842, Leases using the modified retrospective approach and utilizing the effective dates as its date of initial application. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. To estimate its incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets. Assets Held for Sale Assets and liabilities are classified as held for sale when all of the following criteria for a plan of sale have been met: (1) management, having the authority to approve the action, commits to a plan to sell the assets; (2) the assets are available for immediate sale, in their present condition, subject only to terms that are usual and customary for sales of such assets; (3) an active program to locate a buyer and other actions required to complete the plan to sell the assets have been initiated; (4) the sale of the assets is probable and is expected to be completed within one year; (5) the assets are being actively marketed for a price that is reasonable in relation to their current fair value; and (6) actions required to complete the plan indicate that it is unlikely that significant changes to the plan will be made or the plan will be withdrawn. When all of these criteria have been met, the assets and liabilities are classified as held for sale in the balance sheet. Assets classified as held for sale are reported at the lower of their carrying value or fair value less costs to sell. The Company recorded a partial impairment of $ 0.6 million during the year ended December 31, 2023 in connection with the classification of certain assets to assets held for sale. Depreciation and amortization of assets ceases upon designation as held for sale. Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property, plant and equipment as well as right-of-use assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. In November 2022, the Company decided not to continue the build-out of the North Carolina manufacturing facility, resulting in a change in use of this asset group. The Company performed an undiscounted cash flow analysis over the long-lived assets associated with the manufacturing facility and determined that the carrying value of the asset group is not recoverable. Significant assumptions used to determine this non-recurring fair value measurement include the time to sublease the facility, the amount of sublease income expected to be generated over the remaining lease term, and the discount rate used to measure the present value of the net cash flows associated with this asset group. The impairment charge represented the entire amount of the asset group’s carrying amount as of the date of impairment. The Company recorded a non-cash impairment charge of $ 36.4 million (see Note 4) in connection with the North Carolina manufacturing facility which was allocated on a pro rata basis across the assets within the asset group. Debt Issuance Costs Debt issuance costs associated with the Term Loan Agreement (as defined in Note 6) are deferred and presented as a reduction to long-term debt. Debt issuance costs are amortized using the effective interest rate method over the term of the loan. Amortization of deferred debt issuance costs are included in interest expense in the consolidated statements of operations. Debt issuance costs related to the Trinity Term Loans are expensed as incurred due to the election of the fair value option. Research and Development The Company has entered into research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued expenses. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Research and development costs primarily consist of payroll, stock-based compensation, certain manufacturing costs, laboratory costs and other supplies, and the cost to acquire third-party licenses. Costs incurred in obtaining technology licenses through asset acquisitions are charged to research and development expense if the licensed technology has not reached technological feasibility and has no alternative future use. Payments of such upfront license fees and subsequent development milestones are included as investing cash outflows in the consolidated statements of cash flows. Stock-Based Compensation The Company accounts for all stock-based payments to employees and non-employees, including grants of stock options, restricted stock awards, or RSAs, and restricted stock units, or RSUs, based on their respective grant date fair values. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, which is affected principally by the estimated fair value of shares of the Company’s common stock and requires management to make a number of other assumptions, including the expected life of the option, the volatility of the underlying shares, the risk-free interest rate and expected dividends. Expected volatility is based on the historical share volatility of a set of comparable publicly traded companies over a period of time equal to the expected term of the options. Due to the lack of historical exercise history, the expected term of the Company’s stock options is determined using the “simplified” method. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Prior to September 23, 2020, the fair value of common stock underlying the Company’s stock options, RSAs and RSUs was estimated by the Company’s board of directors considering, among other things, contemporaneous valuations of the Company’s common stock prepared by unrelated third-party valuation firms. After the IPO, the fair value of common stock is based on the closing price of the Company’s common stock as reported on the date of the grant. The RSAs and RSUs are valued based on the fair value of the Company’s common stock on the date of grant. The Company expenses stock-based compensation related to stock options, RSAs and RSUs which contain only service-based vesting conditions over the requisite service period using the straight-line method. For awards with both performance and service conditions, the Company recognizes expense based on the fair value of the performance awards over the estimated service period using the accelerated attribution method to the extent the achievement of the related performance criteria is estimated to be probable. At each reporting date, the Company evaluates whether any performance conditions related to a performance-based award have changed. The effect of any change in performance conditions is recognized as a cumulative catch-up adjustment in the period such change occurs. Stock-based compensation costs are initially recorded in research and development expense or general and administrative expense in the consolidated statements of operations in a manner consistent with the classification of the respective employee’s payroll costs. A portion of stock-based compensation expense that relates to employees who were directly involved in the buildout of the Company’s cGMP manufacturing facility have been capitalized into the cost basis of that asset to the extent that such costs were incurred to bring the asset to the condition and location for its intended use, prior to the Company's decision to cease continued build-out of this manufacturing facility. Forfeitures are recorded as they occur. Warrants The Company accounts for warrants as either equity-classified or liability-classified instruments based on an assessment of the warrant’s specific terms and applicable authoritative guidance in FASB ASC 480, Distinguishing Liabilities from Equity (“ASC 480”) and ASC 815, Derivatives and Hedging (“ASC 815”). The assessment considers whether the warrants are freestanding financial instruments pursuant to ASC 480, meet the definition of a liability pursuant to ASC 480, and whether the warrants meet all of the requirements for equity classification under ASC 815, including whether the warrants are indexed to the Company’s own common shares and whether the warrant holders could potentially require “net cash settlement” in a circumstance outside of the Company’s control, among other conditions for equity classification. This assessment, which requires the use of professional judgment, is conducted at the time of warrant issuance and as of each subsequent reporting period while the warrants are outstanding. For issued or modified warrants that meet all of the criteria for equity classification, the warrants are required to be recorded as a component of additional paid-in capital at the time of issuance, or when the conditions for equity classification are met, and are not remeasured. For issued or modified warrants that do not meet all the criteria for equity classification, the warrants are required to be recorded at their initial fair value on the date of issuance, and each balance sheet date thereafter. Liability-classified warrants are recorded at their fair value, and the Company adjusts such warrants to fair value at each reporting period. This liability is subject to remeasurement at each balance sheet date until the warrants are exercised or expire, and any change in fair value is recognized in the Company’s consolidated statements of operations. Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse, and net operating loss (“NOL”) carryforwards and research and development tax credit (“R&D Credit”) carryforwards. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has recorded a full valuation allowance to reduce its net deferred income tax assets to zero. In the event the Company were to determine that it would be able to realize some or all of its deferred income tax assets in the future, an adjustment to the deferred income tax asset valuation allowance would increase income in the period such determination was made. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit would more likely than not be realized assuming examination by the taxing authority. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. During the years ended December 31, 2023 and 2022, the Company recorded increases in the amount of gross unrecognized tax benefits of $ 0.4 million and $ 3.1 million, respectively. The Company also reduced its uncertain tax positions during 2023 by $ 7.8 million related to prior year positions largely as a result of the Section 382 ownership shift analysis performed during 2023 (see Note 12). The gross unrecognized tax benefits recorded as of December 31, 2023 were not material. The unrecognized tax benefits, if recognized, would not affect the effective income tax rate due to the valuation allowance that currently offsets deferred tax assets. The Company does no t expect the unrecognized tax benefits to change significantly over the next 12 months. The Company would recognize any corresponding interest and penalties associated with its income tax positions in income tax expense. There was no income tax interest or penalties incurred for the years ended December 31, 2023 and 2022. Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying consolidated statements of operations. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) ("ASU 2016-02"), as amended, with guidance regarding the accounting for and disclosure of leases. This update requires lessees to recognize the liabilities related to all leases, including operating leases, with a term greater than 12 months on the balance sheets. This update also requires lessees and lessors to disclose key information about their leasing transactions. Effective January 1, 20 22 , the Company adopted ASU 2016-02 using the modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. The Company elected the following practical expedients, which must be elected as a package and applied consistently to all of its leases at the transition date (including those for which the entity is a lessee or a lessor): i) the Company did not reassess whether any expired or existing contracts are or contain leases; ii) the Company did not reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases, and all existing leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases); and iii) the Company did not reassess initial direct costs for any existing leases. For leases that existed prior to the date of initial application of ASC 842 (which were previously classified as operating leases), a lessee may elect to use either the total lease term measured at lease inception under ASC 840 or the remaining lease term as of the date of initial application of ASC 842 in determining the period for which to measure its incremental borrowing rate. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. The adoption of th is standard re

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 3—Fair Value Measurements The Company's financial instruments that are measured at fair value on a recurring basis consist of money market funds, the Trinity Term Loans, a success fee derivative liability and certain of the Company's warrant liabilities. The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values (in thousands): December 31, 2023 Total Level 1 Level 2 Level 3 Assets: Cash equivalents – money market funds $ 142,425 $ 142,425 $ — $ — Total assets $ 142,425 $ 142,425 $ — $ — Liabilities: Trinity Term Loans $ 40,508 $ — $ — $ 40,508 Success Fee Derivative liability 800 — — 800 SSI Warrant liability 454 — — 454 Total liabilities $ 41,762 $ — $ — $ 41,762 The Company classifies its money market funds, which are valued based on quoted market prices in an active market with no valuation adjustment, as Level 1 assets within the fair value hierarchy. The Company's Trinity Term Loans and Success Fee liability are classified as Level 3 measurements under the fair value hierarchy as the fair values were determined based on significant inputs not observable in the market. The fair values were determined utilizing a probability-weighted income approach, including variables for the timing of a success event and other probability estimates. See Note 6 for additional information on the Trinity Term Loans and Success Fee. The Company uses the Black-Scholes-Merton option pricing model to determine the fair value of the SSI Warrants (as defined below). The Company classified its Pre-Funded Warrants (as defined below), which were valued using quoted prices of similar financial instruments in the market, as Level 2 liabilities at their issue date and through their reclassification date. During the year ended December 31, 2023, the Pre-Funded Warrants were reclassified to equity. See Note 10 for additional information on the SSI Warrants and the Pre-Funded Warrants.

Supplemental Financial Informat

Supplemental Financial Information	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Supplemental Financial Information	Note 4—Supplemental Financial Information Property, plant and equipment, net consisted of the following (in thousands): December 31, December 31, Leasehold improvements $ 2,117 $ 2,091 Laboratory equipment 2,868 2,868 Computer equipment 1,133 1,115 Furniture and fixtures 864 898 Construction in progress 6,823 9,633 13,805 16,605 Accumulated depreciation ( 2,979 ) ( 1,642 ) Property, plant and equipment, net $ 10,826 $ 14,963 In November 2022, the Company recognized a non-cash impairment charge of $ 36.4 million for the manufacturing facility asset group, of which $ 26.3 million relates to construction in progress and finance lease right-of-use assets. The impairment charge was estimated using a discounted cash flow model and recorded in the consolidated statements of operations for the year ended December 31, 2022. Property, plant and equipment, net includes $ 1.0 million and $ 1.3 million of assets capitalized as finance leases as of December 31, 2023 and December 31, 2022, respectively. De preciation expense was $ 1.4 million and $ 1.2 million for the years ended December 31, 2023 and 2022, respectively. During the year ended December 31, 2023, the Company committed to a plan to sell specific pieces of equipment originally intended for use in the Company’s manufacturing facility in Durham, NC. The Company determined that this equipment met the requirements to be classified as held for sale. The sale is expected to be completed within one year. During the year ended December 31, 2023, the Company recorded an impairment loss of $ 0.6 million which was the difference between the carrying value and its estimated fair value less cost to sell. Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, December 31, Accrued research and development $ 3,467 $ 8,190 Accrued compensation 3,423 2,519 Accrued clinical trial 1,851 1,473 Lease liabilities, current portion 1,646 1,521 Warrant liability 454 — Accrued severance 390 1,463 Accrued professional and consulting fees 330 390 Accrued property, plant and equipment — 2,081 Other 723 650 Total accrued expenses and other current liabilities $ 12,284 $ 18,287 Prepaid expenses and other current assets consisted of the following (in thousands): December 31, December 31, Prepaid research and development $ 1,412 $ 4,840 Prepaid clinical trial 802 2,119 Deferred offering costs 681 724 Prepaid insurance 292 388 Other 292 466 Total prepaid expenses and other current assets $ 3,479 $ 8,537

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Leases	Note 5— Leases The Company leases certain office, laboratory, and manufacturing space. Dallas Lease On January 11, 2021, the Company entered into a lease agreement (the “Dallas Lease”) with Pegasus Park, LLC, a Delaware limited liability company (the “Dallas Landlord”), pursuant to which the Company agreed to lease approximately 15,000 square feet of office space at 3000 Pegasus Park Drive, Dallas, Texas 75247 (the “Office Space”). The Dallas Lease commenced on May 27, 2021 , and has a term of approximately ten years . The Company has an option to extend the term of the Dallas Lease for one additional period of five years . The Dallas Landlord has the right to terminate the Dallas Lease, or the Company’s right to possess the Office Space without terminating the Dallas Lease, upon specified events of default, including the Company’s failure to pay rent in a timely manner and upon the occurrence of certain events of insolvency with respect to the Company. Dallas Lease Expansion On December 14, 2021, the Company amended the Dallas Lease (the “Dallas Lease Amendment”) with the Dallas Landlord, pursuant to which the Company agreed to lease approximately 18,000 square feet of office space adjacent to the Office Space at 3000 Pegasus Park Drive, Dallas, Texas 75247 (the “Expansion Premises”). The Dallas Lease Amendment commenced on July 1, 2022, and has a term of ten years . The Company is obligated to pay operating costs and utilities applicable to the Expansion Premises. Total future minimum lease payments under the Dallas Lease Amendment over the initial 10 year term are $ 6.0 million. The Company will be responsible for costs of constructing interior improvements within the Expansion Premises that exceed a $ 40.00 per rentable square foot construction allowance provided by the Dallas Landlord. The Company has a right of first refusal with respect to certain additional office space on the 15 th floor at 3000 Pegasus Park Drive, Dallas, Texas 75247 before the Dallas Landlord accepts any offer for such space. Durham Lease On December 17, 2020, the Company entered into a lease agreement (the “Durham Lease”) with Patriot Park Partners II, LLC, a Delaware limited liability company (the “Durham Landlord”), pursuant to which the Company agreed to lease approximately 187,500 square feet of a manufacturing facility located at 5 National Way, Durham, North Carolina (the “Facility”). The Durham Lease commenced on April 1, 2021 and is expected to have a term of approximately fifteen years and six months . The Company has two options to extend the term of the Durham Lease, each for a period of an additional five years . The Company was not required to provide a security deposit in connection with its entry into the Durham Lease. The Company will be responsible for constructing interior improvements within the Facility. The Company was required to place $ 2.6 million in an escrow account which was to be released when the improvements were substantially complete. In December 2023, the Company entered into an agreement with the landlord whereby the Company agreed to remove specified leasehold improvements which will be funded by the escrowed funds. The escrow funds are recorded as restricted cash on the consolidated balance sheets as of December 31, 2023 with $ 0.5 million recorded in current assets and $ 2.1 million in noncurrent assets. The Durham Landlord has the right to terminate the Durham Lease upon specified events of default, including the Company’s failure to pay rent in a timely manner and upon the occurrence of certain events of insolvency with respect to the Company. Summary of all lease costs recognized under ASC 842 The following table summarizes the lease costs recognized under ASC 842 and other information pertaining to the Company's operating leases for the year ended December 31, 2023 and 2022 (in thousands): For the Year Ended December 31, 2023 2022 Operating lease cost $ 2,770 $ 2,873 Variable lease cost 960 452 Total lease cost $ 3,730 $ 3,325 Supplemental information related to the remaining lease term and discount rate are as follows: December 31, 2023 December 31, 2022 Weighted average remaining lease term (in years) – Finance leases 2.88 3.88 Weighted average remaining lease term (in years) – Operating leases 10.75 11.45 Weighted average discount rate – Finance leases 10.52 % 10.51 % Weighted average discount rate – Operating leases 7.80 % 7.72 % Supplemental cash flow information related to the Company's operating leases are as follows (in thousands): For the Year Ended December 31, 2023 2022 Operating cash flows for operating leases $ 2,824 $ 2,486 As of December 31, 2023, future minimum commitments under ASC 842 under the Company's operating and finance leases were as follows (in thousands): Year Ending December 31, Operating Finance 2024 $ 2,810 $ 454 2025 2,910 454 2026 2,485 325 2027 2,577 73 2028 2,673 — Thereafter 17,045 — Total lease payments 30,500 1,306 Less: imputed interest ( 10,255 ) ( 174 ) Total lease liabilities $ 20,245 $ 1,132 Lease liabilities, current 1,292 354 Lease liabilities, non-current 18,953 778 Total lease liabilities $ 20,245 $ 1,132

Term Loans

Term Loans	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Term Loans	Note 6 – Term Loans Loan with Trinity Capital On November 13, 2023 (the “Trinity Closing Date”), the Company entered into a Loan and Security Agreement (the “Trinity Term Loan Agreement”), by and among the Company, the lenders party thereto from time to time (the “Trinity Lenders”) and Trinity Capital Inc., as administrative agent and collateral agent for the Trinity Lenders (“Trinity”). The Trinity Term Loan Agreement provides for, on the Trinity Closing Date, $ 40.0 million aggregate principal amount of term loans (collectively, the “Trinity Term Loans”). The Company drew the Trinity Term Loans in full on the Trinity Closing Date. The interest rate applicable to the Trinity Term Loans is the greater of (a) the WSJ Prime Rate plus 4.50 % or (b) 12.75 % per annum. The Trinity Term Loans are interest only from the Trinity Closing Date through 36 months from the Trinity Closing Date, which may be extended to 48 months from the Trinity Closing Date upon the satisfaction of certain milestones set forth in the Trinity Term Loan Agreement, after which the Company is required to pay equal monthly installments of principal through November 13, 2028 (the “Maturity Date”). As of December 31, 2023, $ 40.0 million was outstanding on the Term Loan, recorded as Term Loan, net on the consolidated balance sheet. Future principal debt payments on the Term Loan Agreement as of December 31, 2023 are as follows (in thousands): Year Ending December 31, 2024 $ — 2025 — 2026 — 2027 18,709 2028 21,291 Total principal payments $ 40,000 The Trinity Term Loans may be prepaid in full (i) from the Trinity Closing Date through November 13, 2024, with payment of a 3.00 % prepayment premium, (ii) from November 13, 2024 through November 13, 2025, with payment of a 2 % prepayment premium, and (iii) from November 13, 2025 through, but excluding, the Maturity Date, with payment of a 1 % prepayment premium. On the Trinity Closing Date, the Company paid to Trinity a commitment fee of 1.00 % of the original principal amount of the Trinity Term Loans. Upon repayment in full of the Trinity Term Loans, the Company will pay to Trinity an end of term payment equal to 5.00 % of the original principal amount of the Trinity Term Loans. The obligations under the Trinity Term Loan Agreement are secured by a perfected security interest in all of the Company’s assets except for certain customarily excluded property pursuant to the terms of the Trinity Term Loan Agreement. There are no financial covenants and no warrants associated with the Trinity Term Loan Agreement. The Trinity Term Loan Agreement contains various covenants that limit the Company’s ability to engage in specified types of transactions without the consent of Trinity and the Trinity Lenders which include, among others, incurring or assuming certain debt; merging, consolidating or acquiring all or substantially all of the capital stock or property of another entity; changing the nature of the Company’s business; changing the Company’s organizational structure or type; licensing, transferring or disposing of certain assets; granting certain types of liens on the Company’s assets; making certain investments; and paying cash dividends. As of December 31, 2023, the Company is in compliance with all covenants of the Trinity Term Loans. The Trinity Term Loan Agreement also contains customary representations and warranties, and also includes customary events of default, including payment default, breach of covenants, change of control, and material adverse effects. Upon the occurrence of an event of default, a default interest rate of an additional 5 % per annum may be applied to the outstanding loan balances, and the Trinity Lenders may declare all outstanding obligations immediately due and payable and exercise all of its rights and remedies as set forth in the Trinity Term Loan Agreement and under applicable law. The proceeds of the Trinity Term Loans were used to repay the Company’s obligations under the Term Loan Agreement with Silicon Valley Bank in full. The Term Loan Agreement with Silicon Valley Bank was terminated concurrently with entry into the Trinity Term Loan Agreement. The Company assessed the terms and features of the Trinity Term Loans and determined that the Company is eligible to elect the fair value option under ASC 825, Financial Instruments . Th e Trinity Term Loans contains various embedded features and the election of the fair value option allows the Company to bypass analysis of potential embedded derivatives and further analysis of bifurcation of any recognized financial liabilities. Under the fair value option, the financial liability is initially measured at its fair value on the issue date and subsequently remeasured at estimated fair value on a recurring basis at each reporting date. Changes in the fair value of the Trinity Term Loans, which include accrued interest, if any, are recorded as a component of other expense (income) in the consolidated statements of operations. The Company has not elected to present interest expense separately from changes in fair value and therefore will not present interest expense associated with the Trinity Term Loans. Any changes in fair value caused by instrument-specific credit risk are presented separately in other comprehensive income or loss if material. Under the fair value option, debt issuance costs are expensed as incurred. The Company incurred $ 0.9 million of debt issuance costs, which were recorded within general and administrative expense in the consolidated statements of operations for the year ended December 31, 2023. In connection with the Trinity Term Loans, the Company entered into a Success Fee Agreement with Trinity which specifies the terms regarding a fee in the amount of 10 % of the principal amount of the funded Trinity Term Loans (the "Success Fee"). The Success Fee is payable upon the achievement of certain corporate development value-inflection milestones. The Success Fee survives the termination of the Trinity Term Loans and expires on the earlier of ten years , or payment in full in cash of the Success Fee. The Company determined that the Success Fee represents a freestanding financial instrument and should be accounted for as a derivative liability under ASC 815 and recorded a liability within other non-current liabilities on the consolidated balance sheet, at fair value on the Trinity Closing Date and will be marked-to-market at the end of each reporting period with gains and losses recognized as a component of other income (expense) in the consolidated statements of operations. The proceeds from the Trinity Term Loans were allocated to the Success Fee and Trinity Term Loans based on their respective fair values on the Trinity Closing Date. The fair values were determined utilizing a probability-weighted income approach, including variables for the timing of a success event and other probability estimates. The Company determined the fair value of the Trinity Term Loans and the Success Fee using a probability-weighted income approach and recorded the loan at fair value of $ 39.2 million and the Success Fee liability at fair value of $ 0.8 million in the consolidated balance sheet at issuance. The Company calculated the discounted cash flows of the Trinity Term Loans using a discount rate of 15.68 % and adjusted for the probability of various repayment scenarios. The Company calculated the discounted cash flows of the Success Fee liability, using a discount rate of 15.68 % then adjusted for the probability of achievement of certain corporate development value-inflection milestones. The following table reconciles the change in fair value of the Trinity Term Loans during the year ended December 31, 2023 (in thousands): Trinity Term Loans Beginning fair value balance on November 13, 2023 $ 39,230 Principal payments — Change in fair value reported in statements of operations 1,278 Ending fair value balance as of December 31, 2023 $ 40,508 The following table reconciles the change in fair value of the Success Fee liability during the year ended December 31, 2023 (in thousands): Success Fee Beginning fair value balance on November 13, 2023 $ 770 Change in fair value of Success Fee 30 Ending fair value balance as of December 31, 2023 $ 800 Loan with Silicon Valley Bank On August 12, 2021 (the “Closing Date”), the Company entered into a Loan and Security Agreement (the “Term Loan Agreement”), by and among the Company, the lenders party thereto from time to time (the “Lenders”) and Silicon Valley Bank, as administrative agent and collateral agent for the Lenders (“Agent”). The Term Loan Agreement provided for (i) on the Closing Date, $ 40.0 million aggregate principal amount of term loans available through December 31, 2021 , (ii) from January 1, 2022 until September 30, 2022 , an additional $ 20.0 million term loan facility available at the Company’s option upon having three distinct and active clinical stage programs, determined at the discretion of the Agent, at the time of draw, (iii) from October 1, 2022 until March 31, 2023 , an additional $ 20.0 million term loan facility available at the Company’s option upon having three distinct and active clinical stage programs, determined at the discretion of the Agent, at the time of draw and (iv) from April 1, 2023 until December 31, 2023 , an additional $ 20.0 million term loan facility available upon approval by the Agent and the Lenders (collectively, the “Term Loans”). The Company drew $ 30.0 million in term loans on the Closing Date and $ 10.0 million in term loans in December 2021. The Company did no t draw on the two additional $ 20.0 million tranches prior to expiration on September 30, 2022 and March 31, 2023 . The Term Loan Agreement with Silicon Valley Bank was terminated concurrently with entry into the Trinity Term Loan Agreement in November 2023. The interest rate applicable to the Term Loans was the greater of (a) the WSJ (“Wall Street Journal”) Prime Rate plus 3.75 % or (b) 7.00 % per annum. The Term Loans were interest only from the Closing Date through August 31, 2024, after which the Company was required to pay equal monthly installments of principal through August 1, 2026 , the maturity date. The Term Loans could have been prepaid in full through August 12, 2023, with payment of a 1.00 % prepayment premium, after which they could be prepaid in full with no prepayment premium. An additional final payment of 7.5 % of the amount of Terms Loans advanced by the Lenders (“Exit Fee”) was due upon prepayment or repayment of the Term Loans in full. The Exit Fee of $ 3.0 million was recorded as debt discount. The debt discount was being accreted using the effective interest method over the term of the Term Loans within interest expense in the consolidated statements of operations. The obligations under the Term Loan Agreement were secured by a perfected security interest in all of the Company’s assets except for intellectual property and certain other customarily excluded property pursuant to the terms of the Term Loan Agreement. Upon termination of the Term Loan Agreement with Silicon Valley Bank, the Company made a prepayment of $ 43.2 million to satisfy the Company's principal and interest obligations and related fees under the Term Loan Agreement. The payoff amount paid by the Company in connection with the Term Loans included payment of the Exit Fee of $ 3.0 million and accrued interest of $ 0.2 million. In connection with the repayment of the Term Loans, the remaining balance of debt discount of $ 1.4 million was recognized as a component of other income (expense) in the consolidated statements of operations for the year ended December 31, 2023. During the years ended December 31, 2023 and 2022, the Company recognized interest expense related to the Term Loans of $ 4.9 million and $ 3.7 million, respectively.

Astellas Agreements

Astellas Agreements	12 Months Ended
	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Astellas Agreements	Note 8—Research, Collaboration, Grant and License Agreements UT Southwestern Agreement On November 19, 2019, the Company entered into a research, collaboration and license agreement (“UT Southwestern Agreement”) with the Board of Regents of the University of Texas System on behalf of The University of Southwestern Medical Center (“UT Southwestern”). Under the UT Southwestern Agreement, UT Southwestern is primarily responsible for preclinical development activities with respect to licensed products for use in certain specified indications (up to IND-enabling studies), and the Company is responsible for all subsequent clinical development and commercialization activities with respect to the licensed products. UT Southwestern will conduct such preclinical activities for a two-year period under mutually agreed upon sponsored research agreements that were entered into beginning in April 2020. During the initial research phase, the Company has the right to expand the scope of specified indications under the UT Southwestern Agreement. In connection with the UT Southwestern Agreement, the Company obtained an exclusive, worldwide, royalty-free license under certain patent rights of UT Southwestern and a non-exclusive, worldwide, royalty-free license under certain know-how of UT Southwestern, in each case to make, have made, use, sell, offer for sale and import licensed products for use in certain specified indications. Additionally, the Company obtained a non-exclusive, worldwide, royalty-free license under certain patents and know-how of UT Southwestern for use in all human uses, with a right of first refusal to obtain an exclusive license under certain of such patent rights and an option to negotiate an exclusive license under other of such patent rights. The Company is required to use commercially reasonable efforts to develop, obtain regulatory approval for, and commercialize at least one licensed product. On April 2, 2020, the Company amended the UT Southwestern Agreement to include the addition of another licensed product and certain indications, and a right of first refusal to the Company over certain patient dosing patents. No additional consideration was transferred in connection with this amendment. In March 2022, the Company and UT Southwestern mutually agreed to revise the payment schedules and current performance expectations of the current sponsored research agreements under the UT Southwestern Agreement and defer payments by fifteen mo nths. In December 2023, the Company and UT Southwestern mutually agreed to terminate specific sponsored research agreements. There are no outstanding payments due for these terminated programs as of December 31, 2023. The UT Southwestern Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last valid claim of a licensed patent in such country for such licensed product. After the initial research term, the Company may terminate the agreement, on an indication-by-indication and licensed product-by-licensed product basis, at any time upon specified written notice to UT Southwestern. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. In December 2023, the Company transferred rights to specific indications back to UT Southwestern. In November 2019, as partial consideration for the license rights granted under the UT Southwestern Agreement, the Company issued 2,179,000 shares of its common stock, or 20 % of its then outstanding fully-diluted common stock, to UT South western. The Company does not have any future milestone or royalty obligations to UT Southwestern under the UT Southwestern Agreement other than costs related to maintenance of patents. Queen’s Agreement On February 21, 2020, the Company entered into a license agreement with Queen’s (the “Queen’s Agreement”) to obtain the exclusive perpetual, royalty-bearing license, with the right to sublicense through multiple tiers, under certain patent rights and know-how of Queen’s, including certain improvements to such patent rights and know-how, to develop products in any field which use one or more valid claims of the patents licensed under the Queen’s Agreement (the “Licensed Patents”), or the technology, information and intellectual property related to the patents licensed under the Queen’s Agreement (together with the Licensed Patents, the “Licensed Products”), and to make, have made, use, sell, offer for sale, import and export Licensed Products and otherwise exploit such patents and know-how for use in certain specified indications. In exchange for the rights granted to the Company, the Company made a cash payment of $ 3.0 million in April 2020 which is recorded in research and development expenses in the consolidated statements of operations since the acquired license does not have an alternative future use. The Company is obligated to make aggregate cash payments of up to $ 10.0 million upon the completion of a combination of regulatory milestones and up to $ 10.0 million upon the completion of a combination of commercial milestones. In further consideration of the rights granted, beginning with the Company’s first commercial sale of the Licensed Products, the Company will also pay an annual earned royalty in the low single digits on net sales of Licensed Products, subject to certain customary reductions, and a percentage of non-royalty sublicensing revenue ranging in the low double digits. Royalties are payable, on a Licensed Products-by-Licensed Products and a country-by-country basis, until expiration of the last valid claim of a Licensed Patent covering such Licensed Products in such country and the expiration of any regulatory exclusivity for such Licensed Products in such country. No additional milestone payments were made in connection with the Queen’s Agreement during the years ended December 31, 2023 and 2022. In January 2024, the Company transferred rights back to Queen’s for the Licensed Patents. Abeona CLN1 Agreements In August 2020, the Company entered into license and inventory purchase agreements with Abeona Therapeutics Inc. (“Abeona”) for worldwide exclusive rights to certain intellectual property rights and know-how relating to the research, development and manufacture of ABO-202, an AAV-based gene therapy for CLN1 disease (also known as infantile Batten disease). Under the terms of the agreements, the Company made initial cash payments to Abeona of $ 3.0 million for the license fee and $ 4.0 million for purchase of clinical materials and reimbursement for previously incurred development costs in October 2020. In exchange for the license rights, the Company recorded an aggregate of $ 7.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license or acquired inventory do not have an alternative future use. The Company is obligated to make up to $ 26.0 million in regulatory-related milestones and up to $ 30.0 million in sales-related milestones per licensed CLN1 product. The Company will also pay an annual earned royalty in the high single digits on net sales of any licensed CLN1 products. The license agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the license agreement for convenience upon specified prior written notice to Abeona. In December 2021, a regulatory milestone was triggered in connection with this agreement and therefore the Company recorded $ 3.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2021. The milestone fee was paid in January 2022 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. No additional milestone payments were triggered in connection with this agreement during the years ended December 31, 2023 and 2022. Abeona Rett Agreement On October 29, 2020, the Company entered into a license agreement (the “Abeona Rett Agreement”) with Abeona pursuant to which the Company obtained an exclusive, worldwide, royalty-bearing license, with the right to grant sublicenses under certain patents, know-how and materials originally developed by the University of North Carolina at Chapel Hill, the University of Edinburgh and Abeona to research, develop, manufacture, have manufactured, use, and commercialize licensed products for gene therapy and the use of related transgenes for Rett syndrome. Subject to certain obligations of Abeona, the Company is required to use commercially reasonable efforts to develop at least one licensed product and commercialize at least one licensed product in the United States. In connection with the Abeona Rett Agreement, the Company paid Abeona a one-time upfront license fee of $ 3.0 million which is recorded in research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license does not have an alternative future use. The Company is obligated to pay Abeona up to $ 26.5 million in regulatory-related milestones and up to $ 30.0 million in sales-related milestones per licensed Rett product and high single-digit royalties on net sales of licensed Rett products. Royalties are payable on a licensed product-by-licensed product and country-by-country basis until the latest of the expiration or revocation or complete rejection of the last licensed patent covering such licensed product in the country where the licensed product is sold, the loss of market exclusivity in such country where the product is sold, or, if no licensed product exists in such country and no market exclusivity exists in such country, ten years from first commercial sale of such licensed product in such country. The Abeona Rett Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the agreement for convenience upon specified prior written notice to Abeona. In March 2022, the Company’s CTA filing for TSHA-102 for the treatment of Rett Syndrome was approved by Health Canada and therefore triggered a regulatory milestone payment in connection with this agreement. The Company recorded $ 1.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2022. The $ 1.0 million regulatory milestone fee was paid in July 2022 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. In May 2023, the Company dosed the first patient with TSHA-102 in the Phase 1/2 REVEAL trial evaluating the safety and preliminary efficacy of TSHA-102 in adult patients with Rett syndrome and therefore triggered a milestone payment in connection with the Abeona Rett Agreement. The Company recorded $ 3.5 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2023. This milestone fee was paid in August 2023 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2023. No additional milestone payments were made or triggered in connection with the Abeona Rett Agreement during the years ended December 31, 2023 and 2022. Acquisition of Worldwide Rights for TSHA-120 for the treatment of GAN In March 2021, the Company acquired the exclusive worldwide rights to a clinical-stage AAV9 gene therapy program, now known as TSHA-120, for the treatment of Giant Axonal Neuropathy (“GAN”) pursuant to a license agreement with Hannah’s Hope Fund (“HHF”) for Giant Axonal Neuropathy, Inc. TSHA-120 is an intrathecally dosed AAV9 gene therapy currently being evaluated in a clinical trial for the treatment of GAN. Under the terms of the agreement, in exchange for granting the Company the exclusive worldwide rights to TSHA-120, HHF received an upfront payment of $ 5.5 million and will be eligible to receive clinical, regulatory and commercial milestones totaling up to $ 19.3 million, as well as a low, single-digit royalty on net sales upon commercialization of the product. In exchange for the license rights, the Company recorded an aggregate of $ 5.5 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2021, since the acquired license does not have an alternative future use. No additional milestone payments were made or triggered in connection with this agreement during the years ended December 31, 2023 and 2022. License Agreement for CLN7 In March 2022, the Company entered into a license agreement with UT Southwestern (the “CLN7 Agreement”) pursuant to which the Company obtained an exclusive worldwide, royalty-bearing license with right to grant sublicenses to develop, manufacture, use, and commercialize licensed products for gene therapy for CLN7, a form of Batten Disease. In connection with the CLN7 Agreement, the Company paid a one-time upfront license fee of $ 0.3 million. The Company recorded the upfront license fee in research and development expense in the consolidated statements of operations since the acquired license does not have an alternative future use. The upfront license fee was classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. The Company is obligated to pay UT Southwestern up to $ 7.7 million in regulatory-related milestones and up to $ 7.5 million in sales-related milestones, as well as a low, single-digit royalty on net sales upon commercialization of the product. No additional milestone payments were made in connection with this agreement during the years ended December 31, 2023 and 2022.
Astellas
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Astellas Agreements	Note 7—Astellas Agreements On October 21, 2022 (the “Effective Date”), the Company entered into the Option Agreement with Astellas, pursuant to which the Company granted to Astellas an exclusive option to obtain an exclusive, worldwide, royalty and milestone-bearing right and license (A) to research, develop, make, have made, use, sell, offer for sale, have sold, import, export and otherwise exploit, or, collectively, exploit, the product known, as of the Effective Date, as TSHA-120 (the “120 GAN Product”), and any backup products with respect thereto for use in the treatment of GAN or any other gene therapy product for use in the treatment of GAN that is controlled by Taysha or any of its affiliates or with respect to which the Company or any of its affiliates controls intellectual property rights covering the exploitation thereof, or a GAN Product, and (B) under any intellectual property rights controlled by Taysha or any of its affiliates with respect to such exploitation (the “GAN Option”). Subject to certain extensions, the GAN Option is exercisable from the Effective Date through a specified period of time following Astellas’ receipt of (i) the formal minutes from the Type B end-of-Phase 2 meeting between Taysha and the FDA in response to the Company’s meeting request sent to the FDA on September 19, 2022 for the 120 GAN Product (the “Type B end-of-Phase 2 Meeting”), (ii) all written feedback from the FDA with respect to the Type B end-of-Phase 2 Meeting, and (iii) all briefing documents sent by Taysha to the FDA with respect to the Type B end-of-Phase 2 Meeting. Under the Option Agreement, the Company also granted to Astellas an exclusive option to obtain an exclusive, worldwide, royalty and milestone-bearing right and license (A) to exploit any Rett Product (as defined below), and (B) under any intellectual property rights controlled by Taysha or any of its affiliates with respect to such exploitation (the “Rett Option,” and together with the GAN Option, each, an “Option”). Subject to certain extensions, the Rett Option is exercisable from the Effective Date through a specified period of time following Astellas’ receipt of (i) certain clinical data from the female pediatric trial and (ii) certain specified data with respect to TSHA-102, such period, the Rett Option Period, related to (i) the product known, as of the Effective Date, as TSHA-102 and any backup products with respect thereto for use in the treatment of Rett syndrome, and (ii) any other gene therapy product for use in the treatment of Rett syndrome that is controlled by Taysha or any of its affiliates or with respect to which the Company or any of its affiliates controls intellectual property rights covering the exploitation thereof (a “Rett Product”). The parties have agreed that, if Astellas exercises an Option, the parties will, for a specified period, negotiate a license agreement in good faith on the terms and conditions outlined in the Option Agreement, including payments by Astellas of a to be determined upfront payment, certain to be determined milestone payments, and certain to be determined royalties on net sales of GAN Products and/or Rett Products, as applicable. During the Rett Option Period, the Company has agreed to (A) not solicit or encourage any inquiries, offers or proposals for, or that could reasonably be expected to lead to, a Change of Control (as defined in the Option Agreement), or (B) otherwise initiate a process for a potential Change of Control, in each case, without first notifying Astellas and offering Astellas the opportunity to submit an offer or proposal to the Company for a transaction that would result in a Change of Control. If Astellas fails or declines to submit any such offer within a specified period after the receipt of such notice, the Company will have the ability to solicit third party bids for a Change of Control transaction. If Astellas delivers an offer to the Company for a transaction that would result in a Change of Control, the Company and Astellas will attempt to negotiate in good faith the potential terms and conditions for such potential transaction that would result in a Change of Control for a specified period, which period may be shortened or extended by mutual agreement. As partial consideration for the rights granted to Astellas under the Option Agreement, Astellas paid the Company the Upfront Payment, which is $ 20.0 million. Astellas or any of its affiliates shall have the right, in its or their discretion and upon written notice to the Company, to offset the amount of the Upfront Payment (in whole or in part, until the full amount of the Upfront Payment has been offset) against (a) any payment(s) owed to Taysha or any of its affiliates (or to any third party on behalf of the Company) under or in connection with any license agreement entered into with respect to any GAN Product or Rett Product, including, any upfront payment, milestone payment or royalties owed to Taysha or any of its affiliates (or to any third party on behalf of the Company) under or in connection with any such license agreement or (b) any amount owed to Taysha or any of its affiliates in connection with a Change of Control transaction with Astellas or any of its affiliates. As further consideration for the rights granted to Astellas under the Option Agreement, the Company and Astellas also entered into the Securities Purchase Agreement. Securities Purchase Agreement On October 21, 2022, the Company entered into the Securities Purchase Agreement with Astellas, pursuant to which the Company agreed to issue and sell to Astellas in a private placement (the “Private Placement”), an aggregate of 7,266,342 shares (the “Private Placement Shares”), of its common stock, for aggregate gross proceeds of $ 30.0 million. The Private Placement closed on October 24, 2022. Pursuant to the Securities Purchase Agreement, in connection with the Private Placement, Astellas has the right to designate one individual to attend all meetings of the Board in a non-voting observer capacity. The Company also granted Astellas certain registration rights with respect to the Private Placement Shares. Accounting Treatment In October 2022, upon closing of the Private Placement and transferring the 7,266,342 shares to Astellas, the Company recorded the issuance of shares at fair value. Fair value of the shares transferred to Astellas was calculated in accordance with ASC 820, Fair Value Measurement by analyzing the Company's stock price for a short period of time prior to and after the transaction date as traded on the NASDAQ. The NASDAQ trading data is considered an active market and a Level 1 measurement under ASC 820. The fair value was determined to be approximately $ 13.95 million or $ 1.92 per share. The $ 16.1 million difference between the $ 30.0 million paid by Astellas and the fair market value of shares issued was allocated to the transaction price of the Option Agreement. The Company determined that the Option Agreement falls within the scope of ASC 606, Revenue from Contracts with Customers as the development of TSHA-102 for the treatment of Rett Syndrome and TSHA-120 for the treatment of GAN are considered ordinary activities for the Company. In accordance with ASC 606, the Company evaluated the Option Agreement and identified three separate performance obligations: (1) option to obtain licensing right to GAN, (2) option to obtain licensing right to Rett and (3) performance of research and development activities in the Rett development plan. The transaction price is determined to be $ 36.1 million which is comprised of the $ 20.0 million Upfront Payment and the $ 16.1 million allocated from the Private Placement. To determine the standalone selling price ("SSP") of the Rett and GAN options, which the Company concluded to be material rights, the Company utilized the probability-weighted expected return (PWERM) method. The PWERM method contemplates the probability and timing of an option exercise. At contract inception, the Company estimated that the probability of exercise was 50 % for each of the GAN and Rett options. The SSP of the Rett research and development activities was estimated using an expected cost plus margin approach. The standalone selling prices of the material rights and Rett research and development activities were then used to proportionately allocate the $ 36.1 million transaction price to the three performance obligations. The $ 36.1 million transaction price was recorded as deferred revenue on the consolidated balance sheet at the inception of the Astellas Transactions. The following table summarizes the allocation of the transaction price to the three performance obligations at contract inception (amounts in thousands): Transaction Price Allocation Option to obtain license for Rett $ 5,485 Option to obtain license for GAN 2,317 Rett research and development activities 28,257 Total $ 36,059 Revenue allocated to the material rights will be recognized at a point in time when each option period expires or when a decision is made by Astellas to exercise or not exercise each option. Revenue from the Rett research and development activities will be recognized as activities are performed using an input method, according to the costs incurred as related to the total costs expected to be incurred to satisfy the performance obligation. The transfer of control occurs over this time period and is a reliable measure of progress towards satisfying the performance obligation. During the year ended December 31, 2023, the Company determined that the total estimated costs to be incurred to satisfy the performance obligation associated with Rett research and development activities had increased from the cost estimate used for the year ended December 31, 2022. The Company recognized revenue of $ 13.2 million and $ 2.5 million from Rett research and development activities for the year ended December 31, 2023 and 2022, respectively. In September 2023, Astellas provided written notice of its decision not to exercise the GAN Option. The Company recognized revenue of $ 2.3 million from the GAN Option during the year ended December 31, 2023. As of December 31, 2023, the Company recorded deferred revenue of $ 18.1 million within current liabilities in the accompanying consolidated balance sheet. The Company will recognize revenues for these performance obligations as they are satisfied.

Research, Collaboration, Grant

Research, Collaboration, Grant and License Agreements	12 Months Ended
	Dec. 31, 2023
Research Collaboration And License Agreements [Abstract]
Research, Collaboration, Grant and License Agreements	Note 8—Research, Collaboration, Grant and License Agreements UT Southwestern Agreement On November 19, 2019, the Company entered into a research, collaboration and license agreement (“UT Southwestern Agreement”) with the Board of Regents of the University of Texas System on behalf of The University of Southwestern Medical Center (“UT Southwestern”). Under the UT Southwestern Agreement, UT Southwestern is primarily responsible for preclinical development activities with respect to licensed products for use in certain specified indications (up to IND-enabling studies), and the Company is responsible for all subsequent clinical development and commercialization activities with respect to the licensed products. UT Southwestern will conduct such preclinical activities for a two-year period under mutually agreed upon sponsored research agreements that were entered into beginning in April 2020. During the initial research phase, the Company has the right to expand the scope of specified indications under the UT Southwestern Agreement. In connection with the UT Southwestern Agreement, the Company obtained an exclusive, worldwide, royalty-free license under certain patent rights of UT Southwestern and a non-exclusive, worldwide, royalty-free license under certain know-how of UT Southwestern, in each case to make, have made, use, sell, offer for sale and import licensed products for use in certain specified indications. Additionally, the Company obtained a non-exclusive, worldwide, royalty-free license under certain patents and know-how of UT Southwestern for use in all human uses, with a right of first refusal to obtain an exclusive license under certain of such patent rights and an option to negotiate an exclusive license under other of such patent rights. The Company is required to use commercially reasonable efforts to develop, obtain regulatory approval for, and commercialize at least one licensed product. On April 2, 2020, the Company amended the UT Southwestern Agreement to include the addition of another licensed product and certain indications, and a right of first refusal to the Company over certain patient dosing patents. No additional consideration was transferred in connection with this amendment. In March 2022, the Company and UT Southwestern mutually agreed to revise the payment schedules and current performance expectations of the current sponsored research agreements under the UT Southwestern Agreement and defer payments by fifteen mo nths. In December 2023, the Company and UT Southwestern mutually agreed to terminate specific sponsored research agreements. There are no outstanding payments due for these terminated programs as of December 31, 2023. The UT Southwestern Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last valid claim of a licensed patent in such country for such licensed product. After the initial research term, the Company may terminate the agreement, on an indication-by-indication and licensed product-by-licensed product basis, at any time upon specified written notice to UT Southwestern. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. In December 2023, the Company transferred rights to specific indications back to UT Southwestern. In November 2019, as partial consideration for the license rights granted under the UT Southwestern Agreement, the Company issued 2,179,000 shares of its common stock, or 20 % of its then outstanding fully-diluted common stock, to UT South western. The Company does not have any future milestone or royalty obligations to UT Southwestern under the UT Southwestern Agreement other than costs related to maintenance of patents. Queen’s Agreement On February 21, 2020, the Company entered into a license agreement with Queen’s (the “Queen’s Agreement”) to obtain the exclusive perpetual, royalty-bearing license, with the right to sublicense through multiple tiers, under certain patent rights and know-how of Queen’s, including certain improvements to such patent rights and know-how, to develop products in any field which use one or more valid claims of the patents licensed under the Queen’s Agreement (the “Licensed Patents”), or the technology, information and intellectual property related to the patents licensed under the Queen’s Agreement (together with the Licensed Patents, the “Licensed Products”), and to make, have made, use, sell, offer for sale, import and export Licensed Products and otherwise exploit such patents and know-how for use in certain specified indications. In exchange for the rights granted to the Company, the Company made a cash payment of $ 3.0 million in April 2020 which is recorded in research and development expenses in the consolidated statements of operations since the acquired license does not have an alternative future use. The Company is obligated to make aggregate cash payments of up to $ 10.0 million upon the completion of a combination of regulatory milestones and up to $ 10.0 million upon the completion of a combination of commercial milestones. In further consideration of the rights granted, beginning with the Company’s first commercial sale of the Licensed Products, the Company will also pay an annual earned royalty in the low single digits on net sales of Licensed Products, subject to certain customary reductions, and a percentage of non-royalty sublicensing revenue ranging in the low double digits. Royalties are payable, on a Licensed Products-by-Licensed Products and a country-by-country basis, until expiration of the last valid claim of a Licensed Patent covering such Licensed Products in such country and the expiration of any regulatory exclusivity for such Licensed Products in such country. No additional milestone payments were made in connection with the Queen’s Agreement during the years ended December 31, 2023 and 2022. In January 2024, the Company transferred rights back to Queen’s for the Licensed Patents. Abeona CLN1 Agreements In August 2020, the Company entered into license and inventory purchase agreements with Abeona Therapeutics Inc. (“Abeona”) for worldwide exclusive rights to certain intellectual property rights and know-how relating to the research, development and manufacture of ABO-202, an AAV-based gene therapy for CLN1 disease (also known as infantile Batten disease). Under the terms of the agreements, the Company made initial cash payments to Abeona of $ 3.0 million for the license fee and $ 4.0 million for purchase of clinical materials and reimbursement for previously incurred development costs in October 2020. In exchange for the license rights, the Company recorded an aggregate of $ 7.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license or acquired inventory do not have an alternative future use. The Company is obligated to make up to $ 26.0 million in regulatory-related milestones and up to $ 30.0 million in sales-related milestones per licensed CLN1 product. The Company will also pay an annual earned royalty in the high single digits on net sales of any licensed CLN1 products. The license agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the license agreement for convenience upon specified prior written notice to Abeona. In December 2021, a regulatory milestone was triggered in connection with this agreement and therefore the Company recorded $ 3.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2021. The milestone fee was paid in January 2022 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. No additional milestone payments were triggered in connection with this agreement during the years ended December 31, 2023 and 2022. Abeona Rett Agreement On October 29, 2020, the Company entered into a license agreement (the “Abeona Rett Agreement”) with Abeona pursuant to which the Company obtained an exclusive, worldwide, royalty-bearing license, with the right to grant sublicenses under certain patents, know-how and materials originally developed by the University of North Carolina at Chapel Hill, the University of Edinburgh and Abeona to research, develop, manufacture, have manufactured, use, and commercialize licensed products for gene therapy and the use of related transgenes for Rett syndrome. Subject to certain obligations of Abeona, the Company is required to use commercially reasonable efforts to develop at least one licensed product and commercialize at least one licensed product in the United States. In connection with the Abeona Rett Agreement, the Company paid Abeona a one-time upfront license fee of $ 3.0 million which is recorded in research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license does not have an alternative future use. The Company is obligated to pay Abeona up to $ 26.5 million in regulatory-related milestones and up to $ 30.0 million in sales-related milestones per licensed Rett product and high single-digit royalties on net sales of licensed Rett products. Royalties are payable on a licensed product-by-licensed product and country-by-country basis until the latest of the expiration or revocation or complete rejection of the last licensed patent covering such licensed product in the country where the licensed product is sold, the loss of market exclusivity in such country where the product is sold, or, if no licensed product exists in such country and no market exclusivity exists in such country, ten years from first commercial sale of such licensed product in such country. The Abeona Rett Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the agreement for convenience upon specified prior written notice to Abeona. In March 2022, the Company’s CTA filing for TSHA-102 for the treatment of Rett Syndrome was approved by Health Canada and therefore triggered a regulatory milestone payment in connection with this agreement. The Company recorded $ 1.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2022. The $ 1.0 million regulatory milestone fee was paid in July 2022 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. In May 2023, the Company dosed the first patient with TSHA-102 in the Phase 1/2 REVEAL trial evaluating the safety and preliminary efficacy of TSHA-102 in adult patients with Rett syndrome and therefore triggered a milestone payment in connection with the Abeona Rett Agreement. The Company recorded $ 3.5 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2023. This milestone fee was paid in August 2023 and classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2023. No additional milestone payments were made or triggered in connection with the Abeona Rett Agreement during the years ended December 31, 2023 and 2022. Acquisition of Worldwide Rights for TSHA-120 for the treatment of GAN In March 2021, the Company acquired the exclusive worldwide rights to a clinical-stage AAV9 gene therapy program, now known as TSHA-120, for the treatment of Giant Axonal Neuropathy (“GAN”) pursuant to a license agreement with Hannah’s Hope Fund (“HHF”) for Giant Axonal Neuropathy, Inc. TSHA-120 is an intrathecally dosed AAV9 gene therapy currently being evaluated in a clinical trial for the treatment of GAN. Under the terms of the agreement, in exchange for granting the Company the exclusive worldwide rights to TSHA-120, HHF received an upfront payment of $ 5.5 million and will be eligible to receive clinical, regulatory and commercial milestones totaling up to $ 19.3 million, as well as a low, single-digit royalty on net sales upon commercialization of the product. In exchange for the license rights, the Company recorded an aggregate of $ 5.5 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2021, since the acquired license does not have an alternative future use. No additional milestone payments were made or triggered in connection with this agreement during the years ended December 31, 2023 and 2022. License Agreement for CLN7 In March 2022, the Company entered into a license agreement with UT Southwestern (the “CLN7 Agreement”) pursuant to which the Company obtained an exclusive worldwide, royalty-bearing license with right to grant sublicenses to develop, manufacture, use, and commercialize licensed products for gene therapy for CLN7, a form of Batten Disease. In connection with the CLN7 Agreement, the Company paid a one-time upfront license fee of $ 0.3 million. The Company recorded the upfront license fee in research and development expense in the consolidated statements of operations since the acquired license does not have an alternative future use. The upfront license fee was classified as an investing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2022. The Company is obligated to pay UT Southwestern up to $ 7.7 million in regulatory-related milestones and up to $ 7.5 million in sales-related milestones, as well as a low, single-digit royalty on net sales upon commercialization of the product. No additional milestone payments were made in connection with this agreement during the years ended December 31, 2023 and 2022.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	Note 9—Stock-Based Compensation On July 1, 2020, the Company’s board of directors approved the 2020 Equity Incentive Plan (“Previous Plan”) which permits the granting of incentive stock options, non-statutory stock options, stock appreciation rights, restricted stock awards (“RSAs”), restricted stock units (“RSUs”) and other stock-based awards to employees, directors, officers and consultants. As of September 16, 2020, the approval date of the New Plan (as defined below), no additional awards will be granted under the Previous Plan. The terms of the Previous Plan will continue to govern the terms of outstanding equity awards that were granted prior to approval of the New Plan. On September 16, 2020, the Company’s stockholders approved the 2020 Stock Incentive Plan (“New Plan”), which became effective upon the execution of the underwriting agreement in connection with the IPO. The number of shares of common stock reserved for issuance under the New Plan automatically increases on January 1 of each year, for a period of ten years , from January 1, 2021 , continuing through January 1, 2030 , by 5 % of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors. On January 1, 2023, the Company’s board of directors increased the number of shares of common stock reserved for issuance under the New Plan by 3,160,375 shares. Furthermore, on September 16, 2020, the Company’s stockholders approved the Employee Stock Purchase Plan (“ESPP”), which became effective upon the execution of the underwriting agreement in connection with the IPO. The maximum number of shares of common stock that may be issued under the ESPP will not exceed 362,000 shares of common stock, plus the number of shares of common stock that are automatically added on January 1st of each year for a period of up to ten years , commencing on the first January 1 following the IPO and ending on (and including) January 1, 2030 , in an amount equal to the lesser of (i) one percent ( 1.0 %) of the total number of shares of capital stock outstanding on December 31st of the preceding calendar year, and (ii) 724,000 shares of common stock. No shares were added to the ESPP in 2021. On January 1, 2022 and 2023, the Company’s board of directors increased the number of shares of common stock reserved for issuance under the ESPP by 384,739 and 632,075 respectively. The Company has issued an aggregate of 141,393 shares of common stock under the ESPP as of December 31, 2023. On December 15, 2023, the Company's board of directors adopted the Taysha Gene Therapies, Inc. 2023 Inducement Plan (the “Inducement Plan”). The Inducement Plan was adopted without stockholder approval pursuant to Nasdaq Listing Rule 5635(c)(4). The Board reserved 4,000,000 shares of the Company’s common stock for issuance under the Inducement Plan. The only persons eligible to receive grants of Inducement Awards (as defined below) under the Inducement Plan are individuals who satisfy the standards for inducement grants under Nasdaq Listing Rule 5635(c)(4). The Inducement Plan will be administered by the Board and the Company’s Compensation Committee. Inducement Awards may only be granted by: (i) the Compensation Committee, provided such committee is comprised solely of “independent directors” (as defined by Nasdaq Listing Rule 5605(a)(2)) or (ii) a majority of the Company’s “independent directors.” An “Inducement Award” means any right to receive the Company’s common stock, cash or other property granted under the Inducement Plan (including nonstatutory stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards, performance cash awards or other stock-based awards). No grants have been issued under the Inducement Plan as of December 31, 2023. The number of shares available for grant under the Company’s incentive plans were as follows: Previous New Inducement Plan Plan Plan Total Available for grant - January 1, 2022 — 1,652,101 — 1,652,101 Plan adjustments and amendments — 1,923,697 — 1,923,697 Grants — ( 4,775,676 ) — ( 4,775,676 ) Forfeitures — 2,267,560 — 2,267,560 Available for grant - December 31, 2022 — 1,067,682 — 1,067,682 Plan adjustments and amendments ( 667,828 ) 3,828,203 4,000,000 7,160,375 Grants — ( 5,447,757 ) — ( 5,447,757 ) Forfeitures 667,828 3,714,597 — 4,382,425 Available for grant - December 31, 2023 — 3,162,725 4,000,000 7,162,725 Stock Options During the year ended December 3 1, 2023, 2,726,871 sh ares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $ 0.71 . The stock options vest over one to four years and have a ten-year contractual term. The following weighted-average assumptions were used to estimate the fair value of time-based vesting stock options that were granted during the years ended December 31, 2023 and 2022: Year Ended December 31, 2023 2022 Risk-free interest rate 3.68 % 2.95 % Expected dividend yield — — Expected term (in years) 5.5 6.1 Expected volatility 82 % 78 % The following table summarizes time-based vesting stock option activity, during the years ended December 31, 2023 and 2022: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at January 1, 2022 3,649,962 $ 24.13 9.2 $ — Options granted 4,775,676 4.48 Options cancelled or forfeited ( 2,048,192 ) 15.25 Options expired ( 219,368 ) 24.36 Outstanding at December 31, 2022 6,158,078 $ 11.84 8.9 $ 62 Options granted 2,726,871 0.99 Options cancelled or forfeited ( 2,050,562 ) 10.70 Options expired ( 873,465 ) 22.21 Outstanding at December 31, 2023 5,960,922 $ 5.75 8.7 $ 1,960 Options exercisable at December 31, 2023 1,580,373 $ 13.51 7.6 $ 8 The aggregate intrinsic value in the above table is calculated as the difference between the fair value of the Company’s common stock at the respective reporting date and the exercise price of the stock options. As of December 31, 2023, the total unrecognized compensation related to unvested time-based vesting stock option awards granted was $ 8.4 million, which the Company expects to recognize over a weighted-average period of approximate ly 1.9 ye ars. No stock options were exercised during the years ended December 31, 2023 and 2022. Performance Stock Options In February 2023, the Company issued options to purchase 70,235 shares of common stock to employees under the New Plan that contain performance-based vesting conditions, subject to continued employment through each anniversary and achievement of the performance conditions. The grant date fair value of these awards was not material. As of December 31, 2023, 58,346 of the shares subject to the performance-based options were outstanding, all of which vested during the period. No stock options were exercised during the period. In May 2023, the Company issued options to purchase 2,166,653 shares of common stock to employees under the New Plan that contain both service and performance-based vesting conditions (the "Original Options"), with a weighted average grant date fair value per share of $ 0.50 . These Original Options were expected to vest over a 3.6 year term if a combination of clinical, regulatory and financing performance conditions were achieved . No compensation expense was recognized in 2023 related to the Original Options as achievement of the performance conditions was not considered probable. The following weighted-average assumptions were used to estimate the fair value of the options granted in February 2023 and the Original Options that were granted in May 2023: Risk-free interest rate 4.02 % Expected dividend yield — Expected term (in years) 6.0 Expected volatility 81 % In December 2023, the Company modified all of the Original Options to amend the clinical and regulatory performance conditions and decreased the number of options granted to 1,516,655 (the “Modified Options”). The Company accounted for the changes in award terms as a modification in accordance with ASC 718, Compensation - Stock Compensation . Total compensation cost is equal to the modification date fair value. The Modified Options have a grant date fair value per share of $ 1.28 . The following assumptions were used to estimate the fair value of the Modified Options: Risk-free interest rate 3.90 % Expected dividend yield — Expected term (in years) 5.8 Expected volatility 88 % The Modified Options will vest over 3.0 years. The Company recognized stock-based compensation expense of $ 0.1 million in 2023 related to the Modified Options. As of December 31, 2023, the total unrecognized compensation expense related to the Modified Options was $ 1.9 million, which the Company expects to recognize over a weighted average period of approximately 2.0 years using the accelerated attribution method. As of December 31, 2023, 1,516,655 of the Modified Options were outstanding. No stock options vested or were exercised during the period. Market-based Stock Options In February 2023, the Company issued options to purchase 70,233 shares of common stock to employees under the New Plan that contain a market-based vesting condition, subject to continued employment through each anniversary and achievement of the market condition. The grant date fair value of the stock options that contain market-based vesting conditions was not material. As of December 31, 2023, the market condition was not met and all 70,233 shares were forfeited. Restricted Stock Units In February 2023, the Company issued 81,236 RSUs to employees under the New Plan. The RSUs are subject to a service-based vesting condition. The service-based RSUs vest in equal annual installments over a four-year period. The Company at any time may accelerate the vesting of the RSUs. Such shares are not accounted for as outstanding until they vest. The Company’s default tax withholding method for RSUs granted prior to 2023 is the sell-to-cover method, in which shares with a market value equivalent to the tax withholding obligation are sold on behalf of the holder of the RSUs upon vesting and settlement to cover the tax withholding liability and the cash proceeds from such sales are remitted by the Company to taxing authorities. For RSUs granted in 2023, the Company’s tax withholding policy allows the RSU holder to choose to either pay cash to the Company for the tax withholding obligation or elect the net withholding method, in which shares with a market equivalent to the tax withholding obligation are withheld and the net shares are issued to the RSU holder. In March 2023, the Company issued 251,296 RSUs to the former President and Chief Executive officer of the Company in connection with his resignation from the Company and Board of Directors. The RSUs vested immediately. The Company’s RSU activity for the years ended December 31, 2023 and 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at January 1, 2022 1,886,765 $ 6.52 Restricted units granted — — Vested ( 628,921 ) 6.52 Cancelled or forfeited — — Nonvested at December 31, 2022 1,257,844 $ 6.52 Restricted units granted 332,532 1.06 Vested ( 556,989 ) 4.78 Cancelled or forfeited ( 658,343 ) 5.18 Nonvested at December 31, 2023 375,044 $ 6.63 As of December 31, 2023, the total unrecognized compensation related to unvested RSUs granted was $ 1.4 million which is expected to be amortized on a straight-line basis over a weighted-average period of approximately 0.7 years. Performance and Market-based Restricted Stock Units In February 2023, the Company issued 81,233 RSUs to employees under the New Plan that contain a combination of performance and market-based vesting conditions, subject to continued employment through each anniversary and achievement of market and performance conditions. The grant date fair value of the RSUs that contain performance and market-based vesting conditions was not material. As of December 31, 2023, 46,562 of the RSUs were forfeited and 34,671 RSUs vested and were settled during the period. Restricted Stock Awards The Company’s former President and Chief Executive Officer, was awarded 769,058 RSAs under the Existing Plan on July 1, 2020, which vested over a three-year term, subject to continuous employment. The fair value of these RSAs at the grant date of July 1, 2020, was $ 5.28 per share. On March 2, 2023, the Company’s former President and Chief Executive Officer resigned from the Board of Directors, therefore cancelling any remaining unvested tranches. The Company’s RSA activity for the years ended December 31, 2023 and 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at January 1, 2022 341,975 $ 5.28 Restricted stock granted — — Vested ( 256,481 ) 5.28 Nonvested at December 31, 2022 85,494 $ 5.28 Restricted stock granted — — Vested ( 64,120 ) 5.28 Cancelled or forfeited ( 21,374 ) 5.28 Nonvested at December 31, 2023 — $ — Employee Stock Purchase Plan In February 2022, the Company’s board of directors authorized the first offering under the ESPP. Under the ESPP, eligible employees may purchase shares of Taysha common stock through payroll deductions at a price equal to 85 % of the lower of the fair market values of the stock as of the beginning or the end of six-month offering periods. An employee’s payroll deductions under the ESPP are limited to 15 % of the employee’s compensation and employees may not purchase more than 1,800 of shares of Taysha common stock during any offering period. During the years ended December 31, 2023 and 2022, stock-based compensation expense related to the ESPP was not material. Stock-based Compensation Expense The following table summarizes the total stock-based compensation expense for the stock options, ESPP, RSAs and RSUs recorded in the consolidated statements of operations for the years ended December 31, 2023 and 2022 (in thousands): For the Year Ended December 31, 2023 2022 Research and development expense $ 2,225 $ 7,608 General and administrative expense 5,680 10,435 Total $ 7,905 $ 18,043

Warrants

Warrants	12 Months Ended
	Dec. 31, 2023
Warrants and Rights Note Disclosure [Abstract]
Warrants	Note 10—Warrants Pre-Funded Warrants On August 14, 2023, the Company entered into a Securities Purchase Agreement (the “August 2023 Purchase Agreement”) with certain institutional and other accredited investors (the “Purchasers”), pursuant to which the Company agreed to sell and issue to the Purchasers in a private placement transaction (the “August 2023 Private Placement”) (i) 122,412,376 shares (the “PIPE Shares”) of the Company’s common stock, and (ii) with respect to certain Purchasers, pre-funded warrants to purchase 44,250,978 shares of the Company’s common stock (the “Pre-Funded Warrants”) in lieu of shares of the Company’s common stock. The purchase price per share of common stock was $ 0.90 per share (the “Purchase Price”), and the purchase price for the Pre-Funded Warrants was the Purchase Price minus $ 0.001 per Pre-Funded Warrant. The Pre-Funded Warrants have a per share exercise price of $ 0.001 , subject to proportional adjustments in the event of stock splits or combinations or similar events. The Pre-Funded Warrants will not expire until exercised in full. The Pre-Funded Warrants may not be exercised if the aggregate number of shares of common stock beneficially owned by the holder thereof immediately following such exercise would exceed a specified beneficial ownership limitation; provided, however, that a holder may increase or decrease the beneficial ownership limitation by giving 61 days’ notice to the Company, but not to any percentage in excess of 19.99 %. The exercise of the Pre-Funded Warrants was also contingent upon receipt of stockholder approval of an increase in the authorized shares of the Company’s common stock (the “Stockholder Approval”), which the Company obtained at a special meeting of stockholders held on November 15, 2023. The closing of the August 2023 Private Placement occurred on August 16, 2023 (the “Closing”). The total gross proceeds to the Company at the Closing were $ 150.0 million, and after deducting placement agent commissions and offering expenses payable by the Company, net proceeds were $ 140.3 million. The Company used the with-and-without method to allocate the total gross proceeds by first allocating the portion of the proceeds equal to the fair value of the Pre-Funded Warrants on the Closing date with the remaining proceeds allocated to the PIPE Shares on a residual basis. The Company concluded that at the closing of the Private Placement in August 2023, the Pre-Funded Warrants did not meet the criteria for equity classification under the guidance of ASC 815 as the Company did not have sufficient authorized and unissued shares to satisfy the warrants if exercised. The Company recorded the Pre-Funded Warrants as liabilities at their fair value. This liability is subject to remeasurement at each balance sheet date and any change in fair value is recognized in the Company’s consolidated statements of operations. The Company incurred $ 9.7 million of placement agent commissions and other issuance costs in connection with the August 2023 Private Placement. The placement agent commissions and other issuance costs were allocated between the PIPE Shares and the Pre-Funded Warrants on a systematic basis. The Company allocated $ 7.1 million to the PIPE Shares which was recorded as a deduction to additional paid-in capital. The remaining $ 2.6 million allocated to the Pre-Funded Warrants were recorded within general and administrative expense in the consolidated statements of operations for the year ended December 31, 2023. The issuance costs allocated to the Pre-Funded Warrants have been added back to net loss when deriving cash flows used in operations, and have been classified as a financing cash outflow in the consolidated statements of cash flows for the year ended December 31, 2023. The Company measured the fair value of the PIPE Shares and Pre-Funded Warrants based on the $ 0.90 per share Purchase Price. The Company used the relative fair value method to allocate the net proceeds received from the sales of the PIPE Shares and the Pre-Funded Warrants on the consolidated balance sheet as follows (in thousands): Purchase Price Allocation PIPE Shares $ 110,127 Pre-Funded Warrants 39,826 Total $ 149,953 The Company remeasured the fair value of the Pre-Funded Warrants using the closing price of the Company’s common stock on the Nasdaq Global Market as of November 15, 2023 o f $ 1.68 per c ommon share upon receipt of Stockholder Approval. The Company recorded a fair value adjustment o f $ 34.5 million in the consolidated statements of operations for the year ended December 31, 2023 and the warrant liability of $ 74.3 million was reclassified into equity as an increase to additional paid-in capital upon receipt of Stockholder Approval. SSI Warrants In April 2023, the Company entered into a securities purchase agreement (the “SSI Securities Purchase Agreement”), with two affiliates of SSI Strategy Holdings LLC (“SSI”), named therein (the “SSI Investors”) pursuant to which the Company agreed to issue and sell to the SSI Investors in a private placement (the “SSI Private Placement”), 705,218 shares of its common stock (the “SSI Shares”) and warrants (the “SSI Warrants”) to purchase an aggregate of 525,000 shares of the Company’s common stock (the “Warrant Shares”). SSI provides certain consulting services to the Company. Each SSI Warrant has an exercise price of $ 0.7090 per Warrant Share, which was the closing price of the Company’s common stock on the Nasdaq Global Market on April 4, 2023. The SSI Warrants issued in the SSI Private Placement provide that the holder of the SSI Warrants will not have the right to exercise any portion of its SSI Warrants until the achievement of certain clinical and regulatory milestones related to the Company’s clinical programs. The SSI Private Placement closed on April 5, 2023. Gross proceeds of the SSI Private Placement were $ 0.5 million. The Company concluded that the SSI Warrants do not meet the criteria for equity classification under the guidance of ASC 815 due to settlement provisions that permit the holder to receive a variable number of shares in the event of a specified fundamental transaction as well as provisions that permit the holder to participate in dividends. As the SSI Warrants do not meet the criteria for equity classification, the Company recorded the warrants as liabilities at their fair value. This liability is subject to remeasurement at each balance sheet date until the warrants are exercised or expire, and any change in fair value is recognized in the Company’s consolidated statements of operations. The Company determined the fair value of the SSI Warrants at issuance was $ 0.3 million using the Black-Scholes-Merton option pricing model. The following assumptions were used to estimate the fair value of the warrants at issuance: Risk-free interest rate 3.46 % Expected dividend yield — Expected term (in years) 5.2 Expected volatility 81 % Market value of common stock (per share) $ 0.71 The fair value adjustment as of December 31, 2023 w as $ 0.2 m illion using the Black-Scholes-Merton option pricing model with probability weights applied to each of the SSI Warrants where vesting is contingent upon the achievement of certain clinical and regulatory milestones related to the Company’s clinical programs. As of December 31, 2023, 316,667 of the SSI Warrants have vested and are exercisable. No warrants were exercised during the period. The Company estimated the fair value of the SSI Warrant liability using the following assumptions as of December 31, 2023: Risk-free interest rate 3.84 % Expected dividend yield — Expected term (in years) 4.5 Expected volatility 88 % Market value of common stock (per share) $ 1.77 The following table summarizes changes in the Company's warrant liability during the year ended December 31, 2023 (in thousands): Warrant Liability Balance at January 1, 2023 $ — Issuance of SSI Warrants 252 Issuance of Pre-Funded Warrants 39,826 Change in fair value 34,718 Reclass of Pre-Funded Warrants to equity ( 74,342 ) Balance at December 31, 2023 $ 454

Net Loss Per Common Share

Net Loss Per Common Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss Per Common Share	Note 11—Net Loss Per Common Share Basic net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. Since the Company had a net loss in both periods presented, basic and diluted net loss per common share are the same. In August 2023, the Company issued liability-classified Pre-Funded Warrants with a nominal exercise price of $ 0.001 per share (see Note 10). In accordance with ASC 260, Earnings Per Share (ASC 260), shares issuable for little to no cash consideration should be included in the number of outstanding shares used to calculate basic loss per share as long as all conditions necessary for exercise are met. The conditions for exercise were met on November 15, 2023, at which time the Pre-Funded Warrants were reclassified into equity. The Pre-Funded Warrants are therefore included as outstanding shares as of November 15, 2023 to calculate the weighted average number of shares outstanding to calculate basic loss per share. The following table represents the calculation of basic and di luted net loss per common share for the years ended December 31, 2023 and 2022, respectively (in thousands, except share and per share data): For the Year Ended December 31, 2023 2022 Net loss $ ( 111,566 ) $ ( 166,014 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 116,121,482 43,952,015 Net loss per common share, basic and diluted $ ( 0.96 ) $ ( 3.78 ) The following common stock equivalents outstanding as of December 31, 2023 and 2022, respectively, were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been anti‑dilutive: December 31, December 31, Unvested RSUs 375,044 1,257,844 Unvested RSAs — 85,494 Stock options 7,535,924 6,158,078 SSI Warrants 316,667 — Total 8,227,635 7,501,416

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Note 12—Income Taxes Provision for income taxes There is no provision for income taxes because the Company has incurred operating losses and capitalized certain items for income tax purposes since its inception and maintains a full valuation allowance against its net deferred tax assets. The reported amount of income tax expense for the period differs from the amount that would result from applying the federal statutory tax rate to net loss before taxes primarily because of the change in valuation allowance. Beginning in 2022, the 2017 Tax Cuts and Jobs Act amended Section 174 to eliminate current-year deductibility of research and experimentation (R&E) expenditures and software development costs (collectively, R&E expenditures) and instead require taxpayers to charge their R&E expenditures to a capital account amortized over five years ( 15 years for expenditures attributable to R&E activity performed outside the United States). The Company generated a deferred tax asset for capitalized R&E expenditures for the years ended December 31, 2023 and 2022 which are fully offset by valuation allowances for each period. On August 16, 2022, President Biden signed the Inflation Reduction Act of 2022, or the Inflation Act, into law. The Inflation Act contains certain tax measures, including a corporate alternative minimum tax of 15 % on some large corporations and an excise tax of 1 % on corporate stock buy-backs. The various provisions of the Inflation Act do not have a material impact on the Company’s consolidated financial statements. The effective tax rate of the Company's provision (benefit) for income taxes differs from the federal statutory rate as follows: For the Year Ended December 31, 2023 2022 Statutory rate 21.00 % 21.00 % State tax 0.33 % 0.25 % Research and development tax credits ( 18.98 )% 4.91 % Other permanent differences ( 0.67 )% ( 0.55 )% Change in valuation allowance 8.10 % ( 25.61 )% Change in fair value of warrant liability ( 6.55 )% ( 0.00 )% Change in fair value of term loan ( 0.30 )% ( 0.00 )% Stock-based compensation ( 2.93 )% ( 0.00 )% Income tax provision (benefit) 0.00 % 0.00 % Deferred tax assets and valuation allowance Deferred tax assets reflect the tax effects of NOLs, tax credit carryovers, and temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. At December 31, 2023 and 2022, the significant components of the Company’s net deferred tax assets and liabilities are as follows (in thousands): For the Year Ended December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 47,373 $ 45,609 Tax credit carryforwards 1,961 23,216 Accruals and reserves 1,020 689 Other 3,978 1 Intangibles 4,888 4,607 Non-qualified stock options 2,585 3,647 R&E expenditures 22,497 15,563 Lease liabilities 4,452 4,574 Impairment of long-lived assets 5,509 5,525 Total deferred tax assets 94,263 103,431 Deferred tax liabilities Right-of-use assets ( 2,224 ) ( 2,308 ) Fixed assets ( 2 ) ( 47 ) Total deferred tax liabilities ( 2,226 ) ( 2,355 ) Valuation allowance ( 92,037 ) ( 101,076 ) Net deferred taxes $ — $ — The valuation allowance is equal to the total net deferred tax asset amounts as of December 31, 2023 and 2022. ASC 740 requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is "more likely than not." Realization of the future tax benefits is dependent on the Company's ability to generate sufficient taxable income within the carryforward period. Because of the Company's recent history of operating losses, management believes that recognition of the deferred tax assets net of liabilities arising from the above-mentioned future tax benefits is currently not likely to be realized and, accordingly, has provided a valuation allowance. The valuation allowance decreased by $ 9.0 million during the year ended December 31, 2023, due to the write-off of certain worthless deferred tax assets, and increased by $ 42.8 million during the year ended December 31, 2022. As of December 31, 2023, there were gross federal NOLs of $ 222.1 million, gross state NOLs of $ 11.9 million, federal tax credit carryforward of $ 28.6 million, and state tax credit carryforward of $ 1.2 million. The net operating losses and state tax credit carryforward do not expire. As of December 31, 2022, there were gross federal NOLs of $ 216.3 million, gross state NOLs of $ 4.5 million, federal tax credit carryforward of $ 30.2 million, and state tax credit carryforward of $ 1.3 million. The federal tax credit carryforward will expire in 2040 . The Company files federal, foreign and state income tax returns and, in the normal course of business, the Company is subject to examination by these taxing authorities. All periods since Inception are subject to examination by these taxing authorities, where applicable. There are currently no pending income tax examinations. Pursuant to Section 382 of the Internal Revenue Code, certain substantial changes in the Company's ownership may result in a limitation on the amount of NOL carryforwards and tax credit carryforwards that may be used in future years. Utilization of the NOL and tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL and tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. The Company has completed studies to assess whether an ownership change has occurred through December 31, 2023. Based on these analyses, several ownership changes were identified in 2020 and an additional ownership change occurred in 2023. As a result of the ownership shift that occurred in August 2023, the Company has determined that $ 217.9 million of its gross federal NOLs are subject to an annual utilization limitation of $ 3.1 million, which can be increased in the five year period post change date for any realized built-in gain. Additionally, there were $ 27.1 million of research credits that will expire due to such limitations, resulting in a write-off of the related deferred tax assets and reversal of the corresponding uncertain tax positions and valuation allowance in 2023. The Company will continue to monitor equity movement and its impact on the utilization of the NOLs and credits as the Company could experience additional ownership changes subsequent to December 31, 2023, which may result in additional limitations on the utilization of NOL carryforwards and credits.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 13—Commitments and Contingencies Litigation From time to time, the Company may be subject to various legal proceedings and claims that arise in the ordinary course of its business activities. The Company records a liability when a particular contingency is probable and estimable. In January 2024, the Company was named a nominal defendant in a putative stockholder derivative action filed by a stockholder of the Company in the Court of Chancery of the State of Delaware. The complaint asserts claims against certain of the Company’s current and former directors for breach of fiduciary duty and unjust enrichment relating to the Company’s August 2023 Private Placement. The complaint seeks an unspecified award of damages in the Company’s favor, plus pre-judgment and post-judgement interest, and an award to the plaintiff for the costs and disbursement of the action, including fees for his attorneys, experts, and accountants. The Company has not recorded a liability related to this lawsuit because, at this time, the Company is unable to reasonably estimate possible losses or gains or determine whether an unfavorable outcome is either probable or remote. Commitments In the normal course of business, the Company enters into contracts that contain a variety of indemnifications with its directors, officers, employees, licensors, suppliers and service providers. The Company’s maximum exposure under these arrangements is unknown at December 31, 2023. The Company does not anticipate recognizing any significant losses relating to these arrangements.

Strategic Reprioritization

Strategic Reprioritization	12 Months Ended
	Dec. 31, 2023
Restructuring and Related Activities [Abstract]
Strategic Reprioritization	Note 14— Strategic Reprioritization In March 2022, the Company implemented changes to the Company’s organizational structure as well as a broader operational cost reduction plan to enable the Company to focus on specific clinical-stage programs for GAN and Rett syndrome. Substantially all other research and development activities have been paused to increase operational efficiency. In connection with prioritization of programs, the Company reduced headcount by approximately 35 % across all functions in March 2022. In accordance with ASC 420, Exit and Disposal Activities , the Company recorded one-time severance and termination-related costs of $ 2.6 million in the consolidated statements of operations for the year ended December 31, 2022, primarily within research and development expenses. In December 2022, the Company further reduced headcount and recorded additional one-time severance and termination related costs of $ 1.5 million within research and development and general and administrative expenses. Throughout the first quarter of 2023, the Company further reduced headcount and recorded additional one-time severance and termination related costs of $ 2.7 million within research and development and general and administrative expenses. The Company expects payment of these costs to be complete by March 31, 2024. The change in accrued severance during the years ended December 31, 2023 and 2022 is as follows (amounts in thousands): Accrued Severance Accrued severance as of January 1, 2022 $ — Severance recorded 4,035 Severance paid ( 2,572 ) Accrued severance as of December 31, 2022 $ 1,463 Severance recorded 2,691 Severance paid ( 3,764 ) Accrued severance as of December 31, 2023 $ 390

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
Retirement Plan	Note 15– Retirement Plan In July 2021, the Company adopted a 401(k) retirement savings plan that provides retirement benefits to all full-time employees. Eligible employees may contribute a percentage of their annual compensation, subject to Internal Revenue Service limitations. The Company contribu ted $ 0.3 million an d $ 0.7 million to the 401(k) retirement savings plan for the years ended December 31, 2023 and 2022, respectively.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Note 16—Subsequent Events In January and February 2024, the Company granted options under the New Plan to purchase an aggregate of 7.0 million shares of its common stock at an exercise price of $ 1.71 per share, and also granted 4.3 million restricted stock units. These equity awards generally vest over a four year period and are subject to service-based vesting conditions. In January, February and March 2024, the Company granted options under the Inducement Plan to purchase an aggregate 0.8 million shares of its common stock at a weighted-average exercise price of $ 2.35 per share. These equity awards generally vest over a four year period and are subject to service-based vesting conditions.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Emerging Growth Company	Emerging Growth Company From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s financial statements upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended, the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards, which delays the adoption of these accounting standards until they would apply to private companies.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to the determination of the fair value of the common stock prior to the IPO (as an input into stock-based compensation), estimating manufacturing accruals and accrued or prepaid research and development expenses, the measurement of impairment of long-lived assets, the valuation of the Trinity Term Loans that are carried at fair value, and the allocation of consideration received in connection with the Astellas Transactions. These estimates and assumptions are based on current facts, historical experience and various other factors believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities and the recording of expenses that are not readily apparent from other sources. Actual results may differ materially from these estimates. To the extent there are material differences between the estimates and actual results, the Company’s future results of operations will be affected.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, development by the Company or its competitors of technological innovations, risks of failure of clinical studies, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and ability to transition from preclinical manufacturing to commercial production of products. The Company’s product candidates require approvals from the FDA and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.
Segments	Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as a single operating segment, which is the business of developing AAV-based gene therapies for the treatment of rare monogenic diseases of the central nervous system. As of December 31, 2023 and 2022, the Company did no t have any significant long-lived assets located outside of the United States.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in accordance with ASC 606, Revenue from Contracts with Customers . Revenues consist of activities in connection with the Astellas Transactions, including the exclusive option to license intellectual property and the performance of research and development activities. See Note 7 for additional information. The Company evaluates the agreement to determine if the other party is a customer, and then determines the units of account within the agreement to determine which promised goods or services are distinct. In order for a promised good or service to be considered "distinct” under ASC 606, the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer (i.e., the good or service is capable of being distinct), and the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract (i.e., the promise to transfer the good or service is distinct within the context of the contract). For any units of account that fall within the scope of ASC 606, where the other party is a customer, the Company (i) evaluates the separate performance obligation(s) under each contract, (ii) determines the transaction price, (iii) allocates the transaction price to each performance obligation considering the estimated standalone selling prices of the services and (iv) recognizes revenue when, or as, the Company satisfies the performance obligation(s). At the inception of an arrangement that includes options for a customer to purchase additional services or products at agreed upon prices in the future, the Company evaluates whether each option provides a material right. An option that provides a material right will be accounted for as a separate performance obligation. As part of the accounting for arrangements under ASC 606, the Company must use significant judgment to determine the performance obligations, the transaction price, and the standalone selling price (“SSP”) for each performance obligation identified in the contract for the allocation of the transaction price. The SSP is the price at which an entity would sell a promised good or service separately to a customer. Management estimates the SSP of each of the identified performance obligations, maximizing the use of observable inputs. Because the Company has not sold the same goods or services in its contracts separately to any customers on a standalone basis, the Company utilizes similar observable transactions in the marketplace or estimates the SSP of each performance obligation in its customer arrangements at contract inception based on either (1) its estimate of costs to be incurred to fulfill its obligations associated with the performance obligation, plus a reasonable margin, or (2) an estimate that reflects the discount that the customer would obtain when exercising its option adjusted for (i) any discount that the customer could receive without exercising the option and (ii) the likelihood that the option will be exercised. The Company allocates the transaction price to each performance obligation in proportion to its SSP. A performance obligation is satisfied and revenue is recognized when “control” of the promised good or service is transferred, either over time or at a point in time, to the customer. A customer obtains control of a good or service if it has the ability to (1) direct its use and (2) obtain substantially all of the remaining benefits from it. Amounts received prior to satisfying the revenue recognition criteria listed above are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts expected to be recognized as revenue within 12 months of the balance sheet date are classified as current deferred revenue, including the amounts allocated to material rights which are subject to customer exercise at any point. Amounts not expected to be recognized as revenue within the following 12 months of the balance sheet date are classified as deferred revenue, net of current portion. The Company does not incur commission or other costs to fulfill customer contracts and as such, no capitalized contract costs are recorded on the consolidated balance sheets.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of funds held in a standard checking account, a standard savings account and a money market fund. The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of December 31, 2023, the Company had $ 142.4 million in cash equivalents. As of December 31, 2022, the Company had no cash equivalents.
Restricted Cash	Restricted Cash Restricted cash consists of cash that the Company has placed in an escrow account which is pledged as collateral under certain lease agreements and letters of credit.
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash and cash equivalents. Periodically, the Company may maintain deposits in financial institutions in excess of government insured limits. On March 10, 2023, the California Department of Financial Protection and Innovation closed the Silicon Valley Bank, Santa Clara, California (“SVB”), and appointed the FDIC as receiver. On March 12, 2023, the Treasury Department announced that depositors of SVB will have access to all of their money starting March 13, 2023. On March 14, 2023, the Company regained access to the full amount of its cash that was deposited with SVB. Management believes that the Company is not exposed to significant credit risk as the Company’s deposits are held at financial institutions that management continues to believe to be of high credit quality. The Company has not experienced any losses on these deposits.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial assets and liabilities are accounted for in accordance with ASC 820, Fair Value Measurements which defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. The fair value hierarchy requires an entity to maximize the use of observable inputs when measuring fair value and classifies those inputs into three levels: Level 1—Observable inputs, such as quoted prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the instrument’s anticipated life. Level 3—Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The carrying values reported in the Company’s consolidated balance sheets for cash and cash equivalents, prepaid expenses and other current assets, accounts payable, accrued expenses and other current liabilities are reasonable estimates of their fair values due to the short-term nature of these items. Fair Value Option The fair value option provides an election that allows a company to irrevocably elect to record certain financial assets and liabilities at fair value on an instrument-by-instrument basis at initial recognition. The Company has elected to apply the fair value option to the Trinity Term Loans. The term loans accounted for under the fair value option election are each a debt host financial instrument containing embedded features that would otherwise be required to be bifurcated from the debt-host and recognized as separate derivative liabilities subject to initial and subsequent periodic estimated fair value measurements in accordance with GAAP. Notwithstanding, when the fair value option election is applied to financial liabilities, bifurcation of an embedded derivative is not required, and the financial liability is initially measured at its issue-date estimated fair value and then subsequently remeasured at estimated fair value on a recurring basis as of each reporting period date. The portion of the change in fair value attributed to a change in the instrument-specific credit risk is recognized as a component of other comprehensive income or loss if material and the remaining amount of the fair value adjustment is recognized as a component of other income (expense) in the consolidated statements of operations.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes costs directly associated with equity financings until such financings are consummated, at which time such costs are recorded in additional paid-in capital against the gross proceeds of the equity financings. Costs associated with the shelf registration statement on Form S-3, filed with the SEC on October 5, 2021 have been capitalized and will be reclassified to additional paid-in capital on a pro rata basis when the Company completes offerings under the shelf registration. At the end of the three-year term of the shelf registration, the remaining deferred offering costs, if any, will be charged to operations.
Property Plant and Equipment, net	Property, Plant and Equipment, net Property, plant and equipment, net are stated at cost less accumulated depreciation and consist of computer equipment, laboratory equipment and leasehold improvements. Directly identifiable payroll and payroll-related costs incurred in connection with the build-out of the Company’s cGMP manufacturing facility were capitalized into the cost basis of the asset to the extent that such costs had been incurred to bring the asset to the condition and location for its intended use. Depreciation expense is recognized using the straight-line method over its estimated useful life of three to seven years . Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.
Leases	Leases Effective January 1, 2022, the Company adopted ASC 842, Leases using the modified retrospective approach and utilizing the effective dates as its date of initial application. At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets and short-term and long-term lease liabilities, as applicable. Operating lease liabilities and their corresponding right-of-use assets are initially recorded based on the present value of lease payments over the expected remaining lease term. Certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate to discount lease payments, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. To estimate its incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. The Company has elected not to recognize leases with an original term of one year or less on the balance sheet. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. Assumptions made by the Company at the commencement date are re-evaluated upon occurrence of certain events, including a lease modification. A lease modification results in a separate contract when the modification grants the lessee an additional right of use not included in the original lease and when lease payments increase commensurate with the standalone price for the additional right of use. When a lease modification results in a separate contract, it is accounted for in the same manner as a new lease. The Company has elected to account for lease and non-lease components together as a single lease component for all underlying assets.
Assets Held for Sale	Assets Held for Sale Assets and liabilities are classified as held for sale when all of the following criteria for a plan of sale have been met: (1) management, having the authority to approve the action, commits to a plan to sell the assets; (2) the assets are available for immediate sale, in their present condition, subject only to terms that are usual and customary for sales of such assets; (3) an active program to locate a buyer and other actions required to complete the plan to sell the assets have been initiated; (4) the sale of the assets is probable and is expected to be completed within one year; (5) the assets are being actively marketed for a price that is reasonable in relation to their current fair value; and (6) actions required to complete the plan indicate that it is unlikely that significant changes to the plan will be made or the plan will be withdrawn. When all of these criteria have been met, the assets and liabilities are classified as held for sale in the balance sheet. Assets classified as held for sale are reported at the lower of their carrying value or fair value less costs to sell. The Company recorded a partial impairment of $ 0.6 million during the year ended December 31, 2023 in connection with the classification of certain assets to assets held for sale. Depreciation and amortization of assets ceases upon designation as held for sale.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist of property, plant and equipment as well as right-of-use assets, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. In November 2022, the Company decided not to continue the build-out of the North Carolina manufacturing facility, resulting in a change in use of this asset group. The Company performed an undiscounted cash flow analysis over the long-lived assets associated with the manufacturing facility and determined that the carrying value of the asset group is not recoverable. Significant assumptions used to determine this non-recurring fair value measurement include the time to sublease the facility, the amount of sublease income expected to be generated over the remaining lease term, and the discount rate used to measure the present value of the net cash flows associated with this asset group. The impairment charge represented the entire amount of the asset group’s carrying amount as of the date of impairment. The Company recorded a non-cash impairment charge of $ 36.4 million (see Note 4) in connection with the North Carolina manufacturing facility which was allocated on a pro rata basis across the assets within the asset group.
Debt Issuance Costs	Debt Issuance Costs Debt issuance costs associated with the Term Loan Agreement (as defined in Note 6) are deferred and presented as a reduction to long-term debt. Debt issuance costs are amortized using the effective interest rate method over the term of the loan. Amortization of deferred debt issuance costs are included in interest expense in the consolidated statements of operations. Debt issuance costs related to the Trinity Term Loans are expensed as incurred due to the election of the fair value option.
Research and Development	Research and Development The Company has entered into research and development contracts with research institutions and other companies. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued expenses. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Research and development costs primarily consist of payroll, stock-based compensation, certain manufacturing costs, laboratory costs and other supplies, and the cost to acquire third-party licenses. Costs incurred in obtaining technology licenses through asset acquisitions are charged to research and development expense if the licensed technology has not reached technological feasibility and has no alternative future use. Payments of such upfront license fees and subsequent development milestones are included as investing cash outflows in the consolidated statements of cash flows.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for all stock-based payments to employees and non-employees, including grants of stock options, restricted stock awards, or RSAs, and restricted stock units, or RSUs, based on their respective grant date fair values. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model, which is affected principally by the estimated fair value of shares of the Company’s common stock and requires management to make a number of other assumptions, including the expected life of the option, the volatility of the underlying shares, the risk-free interest rate and expected dividends. Expected volatility is based on the historical share volatility of a set of comparable publicly traded companies over a period of time equal to the expected term of the options. Due to the lack of historical exercise history, the expected term of the Company’s stock options is determined using the “simplified” method. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Prior to September 23, 2020, the fair value of common stock underlying the Company’s stock options, RSAs and RSUs was estimated by the Company’s board of directors considering, among other things, contemporaneous valuations of the Company’s common stock prepared by unrelated third-party valuation firms. After the IPO, the fair value of common stock is based on the closing price of the Company’s common stock as reported on the date of the grant. The RSAs and RSUs are valued based on the fair value of the Company’s common stock on the date of grant. The Company expenses stock-based compensation related to stock options, RSAs and RSUs which contain only service-based vesting conditions over the requisite service period using the straight-line method. For awards with both performance and service conditions, the Company recognizes expense based on the fair value of the performance awards over the estimated service period using the accelerated attribution method to the extent the achievement of the related performance criteria is estimated to be probable. At each reporting date, the Company evaluates whether any performance conditions related to a performance-based award have changed. The effect of any change in performance conditions is recognized as a cumulative catch-up adjustment in the period such change occurs. Stock-based compensation costs are initially recorded in research and development expense or general and administrative expense in the consolidated statements of operations in a manner consistent with the classification of the respective employee’s payroll costs. A portion of stock-based compensation expense that relates to employees who were directly involved in the buildout of the Company’s cGMP manufacturing facility have been capitalized into the cost basis of that asset to the extent that such costs were incurred to bring the asset to the condition and location for its intended use, prior to the Company's decision to cease continued build-out of this manufacturing facility. Forfeitures are recorded as they occur.
Warrants	Warrants The Company accounts for warrants as either equity-classified or liability-classified instruments based on an assessment of the warrant’s specific terms and applicable authoritative guidance in FASB ASC 480, Distinguishing Liabilities from Equity (“ASC 480”) and ASC 815, Derivatives and Hedging (“ASC 815”). The assessment considers whether the warrants are freestanding financial instruments pursuant to ASC 480, meet the definition of a liability pursuant to ASC 480, and whether the warrants meet all of the requirements for equity classification under ASC 815, including whether the warrants are indexed to the Company’s own common shares and whether the warrant holders could potentially require “net cash settlement” in a circumstance outside of the Company’s control, among other conditions for equity classification. This assessment, which requires the use of professional judgment, is conducted at the time of warrant issuance and as of each subsequent reporting period while the warrants are outstanding. For issued or modified warrants that meet all of the criteria for equity classification, the warrants are required to be recorded as a component of additional paid-in capital at the time of issuance, or when the conditions for equity classification are met, and are not remeasured. For issued or modified warrants that do not meet all the criteria for equity classification, the warrants are required to be recorded at their initial fair value on the date of issuance, and each balance sheet date thereafter. Liability-classified warrants are recorded at their fair value, and the Company adjusts such warrants to fair value at each reporting period. This liability is subject to remeasurement at each balance sheet date until the warrants are exercised or expire, and any change in fair value is recognized in the Company’s consolidated statements of operations.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse, and net operating loss (“NOL”) carryforwards and research and development tax credit (“R&D Credit”) carryforwards. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company has recorded a full valuation allowance to reduce its net deferred income tax assets to zero. In the event the Company were to determine that it would be able to realize some or all of its deferred income tax assets in the future, an adjustment to the deferred income tax asset valuation allowance would increase income in the period such determination was made. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit would more likely than not be realized assuming examination by the taxing authority. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. During the years ended December 31, 2023 and 2022, the Company recorded increases in the amount of gross unrecognized tax benefits of $ 0.4 million and $ 3.1 million, respectively. The Company also reduced its uncertain tax positions during 2023 by $ 7.8 million related to prior year positions largely as a result of the Section 382 ownership shift analysis performed during 2023 (see Note 12). The gross unrecognized tax benefits recorded as of December 31, 2023 were not material. The unrecognized tax benefits, if recognized, would not affect the effective income tax rate due to the valuation allowance that currently offsets deferred tax assets. The Company does no t expect the unrecognized tax benefits to change significantly over the next 12 months. The Company would recognize any corresponding interest and penalties associated with its income tax positions in income tax expense. There was no income tax interest or penalties incurred for the years ended December 31, 2023 and 2022.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying consolidated statements of operations.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) ("ASU 2016-02"), as amended, with guidance regarding the accounting for and disclosure of leases. This update requires lessees to recognize the liabilities related to all leases, including operating leases, with a term greater than 12 months on the balance sheets. This update also requires lessees and lessors to disclose key information about their leasing transactions. Effective January 1, 20 22 , the Company adopted ASU 2016-02 using the modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. The Company elected the following practical expedients, which must be elected as a package and applied consistently to all of its leases at the transition date (including those for which the entity is a lessee or a lessor): i) the Company did not reassess whether any expired or existing contracts are or contain leases; ii) the Company did not reassess the lease classification for any expired or existing leases (that is, all existing leases that were classified as operating leases in accordance with ASC 840 are classified as operating leases, and all existing leases that were classified as capital leases in accordance with ASC 840 are classified as finance leases); and iii) the Company did not reassess initial direct costs for any existing leases. For leases that existed prior to the date of initial application of ASC 842 (which were previously classified as operating leases), a lessee may elect to use either the total lease term measured at lease inception under ASC 840 or the remaining lease term as of the date of initial application of ASC 842 in determining the period for which to measure its incremental borrowing rate. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. The adoption of th is standard resulted in the recognition of operating lease right-of-use assets and operating lease liabilities of $ 18.4 million and $ 19.1 million, respectively, on the Company’s consolidated balance sheet at adoption relating to its operating leases. The lease liabilities were determined based on the present value of the remaining minimum lease payments. Upon adoption of ASC 842, the Company also (i) derecognized the build-to-suit lease asset of $ 26.3 million previously presented in property, plant and equipment, (ii) derecognized the build-to-suit lease liability of $ 26.5 million, and (iii) eliminated $ 0.7 million of deferred rent liabilities and tenant improvement allowances as of January 1, 2022 as these liabilities are reflected in the operating lease right-of-use assets. In adopting ASU 2016-02, the Company recorded a total one-time adjustment of $ 0.2 million to the opening balance of accumulated deficit as of January 1, 2022 related to the de-recognition of the build-to-suit lease asset and related build-to-suit lease obligation. The adoption did not have a material impact on accumulated deficit or on the consolidated statements of operations and cash flows.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting - Improvements to Reportable Segment Disclosures , to improve segment disclosure requirements under ASC 280, Segment Reporting , through enhancing disclosures about significant segment expenses. The guidance requires entities to provide significant segment expenses that are regularly provided to the chief operating decision maker and other segment expenses included in each reported measure of segment profitability. The ASU also enhances interim segment reporting requirements by aligning interim disclosures with information that must be disclosed annually in accordance with ASC 280. The guidance is effective for annual periods beginning after December 15, 2023, and interim periods beginning after December 15, 2024, applied retrospectively with early adoption permitted. The Company is still evaluating the impact this ASU will have on its consolidated financial statements and related disclosures.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values (in thousands): December 31, 2023 Total Level 1 Level 2 Level 3 Assets: Cash equivalents – money market funds $ 142,425 $ 142,425 $ — $ — Total assets $ 142,425 $ 142,425 $ — $ — Liabilities: Trinity Term Loans $ 40,508 $ — $ — $ 40,508 Success Fee Derivative liability 800 — — 800 SSI Warrant liability 454 — — 454 Total liabilities $ 41,762 $ — $ — $ 41,762

Supplemental Financial Inform_2

Supplemental Financial Information (Tables)	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Schedule of Property, Plant and Equipment	Property, plant and equipment, net consisted of the following (in thousands): December 31, December 31, Leasehold improvements $ 2,117 $ 2,091 Laboratory equipment 2,868 2,868 Computer equipment 1,133 1,115 Furniture and fixtures 864 898 Construction in progress 6,823 9,633 13,805 16,605 Accumulated depreciation ( 2,979 ) ( 1,642 ) Property, plant and equipment, net $ 10,826 $ 14,963
Schedule of Accrued Expenses and Other Current Labilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, December 31, Accrued research and development $ 3,467 $ 8,190 Accrued compensation 3,423 2,519 Accrued clinical trial 1,851 1,473 Lease liabilities, current portion 1,646 1,521 Warrant liability 454 — Accrued severance 390 1,463 Accrued professional and consulting fees 330 390 Accrued property, plant and equipment — 2,081 Other 723 650 Total accrued expenses and other current liabilities $ 12,284 $ 18,287
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, December 31, Prepaid research and development $ 1,412 $ 4,840 Prepaid clinical trial 802 2,119 Deferred offering costs 681 724 Prepaid insurance 292 388 Other 292 466 Total prepaid expenses and other current assets $ 3,479 $ 8,537

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Lease Cost	The following table summarizes the lease costs recognized under ASC 842 and other information pertaining to the Company's operating leases for the year ended December 31, 2023 and 2022 (in thousands): For the Year Ended December 31, 2023 2022 Operating lease cost $ 2,770 $ 2,873 Variable lease cost 960 452 Total lease cost $ 3,730 $ 3,325
Schedule of Supplemental Information Related to Remaining Lease Term and Discount Rate	Supplemental information related to the remaining lease term and discount rate are as follows: December 31, 2023 December 31, 2022 Weighted average remaining lease term (in years) – Finance leases 2.88 3.88 Weighted average remaining lease term (in years) – Operating leases 10.75 11.45 Weighted average discount rate – Finance leases 10.52 % 10.51 % Weighted average discount rate – Operating leases 7.80 % 7.72 %
Schedule of Supplemental Cash Flow Information Related to Operating Leases	Supplemental cash flow information related to the Company's operating leases are as follows (in thousands): For the Year Ended December 31, 2023 2022 Operating cash flows for operating leases $ 2,824 $ 2,486
Schedule of Future Minimum Commitments Under Company's Operating and Finance Leases	As of December 31, 2023, future minimum commitments under ASC 842 under the Company's operating and finance leases were as follows (in thousands): Year Ending December 31, Operating Finance 2024 $ 2,810 $ 454 2025 2,910 454 2026 2,485 325 2027 2,577 73 2028 2,673 — Thereafter 17,045 — Total lease payments 30,500 1,306 Less: imputed interest ( 10,255 ) ( 174 ) Total lease liabilities $ 20,245 $ 1,132 Lease liabilities, current 1,292 354 Lease liabilities, non-current 18,953 778 Total lease liabilities $ 20,245 $ 1,132

Term Loans (Tables)

Term Loans (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Schedule of Reconcile of Change in Fair Value of Debt	The following table reconciles the change in fair value of the Trinity Term Loans during the year ended December 31, 2023 (in thousands): Trinity Term Loans Beginning fair value balance on November 13, 2023 $ 39,230 Principal payments — Change in fair value reported in statements of operations 1,278 Ending fair value balance as of December 31, 2023 $ 40,508 The following table reconciles the change in fair value of the Success Fee liability during the year ended December 31, 2023 (in thousands): Success Fee Beginning fair value balance on November 13, 2023 $ 770 Change in fair value of Success Fee 30 Ending fair value balance as of December 31, 2023 $ 800
Schedule of Future Principal Debt Payments on Term Loan Agreement	Future principal debt payments on the Term Loan Agreement as of December 31, 2023 are as follows (in thousands): Year Ending December 31, 2024 $ — 2025 — 2026 — 2027 18,709 2028 21,291 Total principal payments $ 40,000

Astellas Agreements (Tables)

Astellas Agreements (Tables)	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Summary of Allocation for Transaction Price to the Three Performance Obligations	The following table summarizes the allocation of the transaction price to the three performance obligations at contract inception (amounts in thousands): Transaction Price Allocation Option to obtain license for Rett $ 5,485 Option to obtain license for GAN 2,317 Rett research and development activities 28,257 Total $ 36,059

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2023
Schedule of Share Based Compensation Available for Grant under Incentive Plans	The number of shares available for grant under the Company’s incentive plans were as follows: Previous New Inducement Plan Plan Plan Total Available for grant - January 1, 2022 — 1,652,101 — 1,652,101 Plan adjustments and amendments — 1,923,697 — 1,923,697 Grants — ( 4,775,676 ) — ( 4,775,676 ) Forfeitures — 2,267,560 — 2,267,560 Available for grant - December 31, 2022 — 1,067,682 — 1,067,682 Plan adjustments and amendments ( 667,828 ) 3,828,203 4,000,000 7,160,375 Grants — ( 5,447,757 ) — ( 5,447,757 ) Forfeitures 667,828 3,714,597 — 4,382,425 Available for grant - December 31, 2023 — 3,162,725 4,000,000 7,162,725
Schedule of Restricted Stock Units Activity	The Company’s RSU activity for the years ended December 31, 2023 and 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at January 1, 2022 1,886,765 $ 6.52 Restricted units granted — — Vested ( 628,921 ) 6.52 Cancelled or forfeited — — Nonvested at December 31, 2022 1,257,844 $ 6.52 Restricted units granted 332,532 1.06 Vested ( 556,989 ) 4.78 Cancelled or forfeited ( 658,343 ) 5.18 Nonvested at December 31, 2023 375,044 $ 6.63
Schedule of Restricted Stock Awards Activity	The Company’s RSA activity for the years ended December 31, 2023 and 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at January 1, 2022 341,975 $ 5.28 Restricted stock granted — — Vested ( 256,481 ) 5.28 Nonvested at December 31, 2022 85,494 $ 5.28 Restricted stock granted — — Vested ( 64,120 ) 5.28 Cancelled or forfeited ( 21,374 ) 5.28 Nonvested at December 31, 2023 — $ —
Schedule of Total Stock-Based Compensation Expense for Stock Options, ESPP, RSAs and RSUs	The following table summarizes the total stock-based compensation expense for the stock options, ESPP, RSAs and RSUs recorded in the consolidated statements of operations for the years ended December 31, 2023 and 2022 (in thousands): For the Year Ended December 31, 2023 2022 Research and development expense $ 2,225 $ 7,608 General and administrative expense 5,680 10,435 Total $ 7,905 $ 18,043
Stock Options
Schedule of Assumptions Used to Estimate Fair Value of Stock Options	The following weighted-average assumptions were used to estimate the fair value of time-based vesting stock options that were granted during the years ended December 31, 2023 and 2022: Year Ended December 31, 2023 2022 Risk-free interest rate 3.68 % 2.95 % Expected dividend yield — — Expected term (in years) 5.5 6.1 Expected volatility 82 % 78 %
Schedule of Stock Option Activity	The following table summarizes time-based vesting stock option activity, during the years ended December 31, 2023 and 2022: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at January 1, 2022 3,649,962 $ 24.13 9.2 $ — Options granted 4,775,676 4.48 Options cancelled or forfeited ( 2,048,192 ) 15.25 Options expired ( 219,368 ) 24.36 Outstanding at December 31, 2022 6,158,078 $ 11.84 8.9 $ 62 Options granted 2,726,871 0.99 Options cancelled or forfeited ( 2,050,562 ) 10.70 Options expired ( 873,465 ) 22.21 Outstanding at December 31, 2023 5,960,922 $ 5.75 8.7 $ 1,960 Options exercisable at December 31, 2023 1,580,373 $ 13.51 7.6 $ 8
Performance Stock Options | Initial Options and Original Options
Schedule of Assumptions Used to Estimate Fair Value of Stock Options	The following weighted-average assumptions were used to estimate the fair value of the options granted in February 2023 and the Original Options that were granted in May 2023: Risk-free interest rate 4.02 % Expected dividend yield — Expected term (in years) 6.0 Expected volatility 81 %
Performance Stock Options | Modified Options
Schedule of Assumptions Used to Estimate Fair Value of Stock Options	The following assumptions were used to estimate the fair value of the Modified Options: Risk-free interest rate 3.90 % Expected dividend yield — Expected term (in years) 5.8 Expected volatility 88 %

Warrants (Tables)

Warrants (Tables)	12 Months Ended
	Dec. 31, 2023
Warrants and Rights Note Disclosure [Abstract]
Schedule of Fair Value Method to Allocate Net Proceeds Received from Sale of Common Stock and Pre-funded Warrants	The Company used the relative fair value method to allocate the net proceeds received from the sales of the PIPE Shares and the Pre-Funded Warrants on the consolidated balance sheet as follows (in thousands): Purchase Price Allocation PIPE Shares $ 110,127 Pre-Funded Warrants 39,826 Total $ 149,953
Schedule Of Assumptions Used To Estimate Fair Value Of Warrants	The following assumptions were used to estimate the fair value of the warrants at issuance: Risk-free interest rate 3.46 % Expected dividend yield — Expected term (in years) 5.2 Expected volatility 81 % Market value of common stock (per share) $ 0.71 The Company estimated the fair value of the SSI Warrant liability using the following assumptions as of December 31, 2023: Risk-free interest rate 3.84 % Expected dividend yield — Expected term (in years) 4.5 Expected volatility 88 % Market value of common stock (per share) $ 1.77
Schedule of Warrant Liability	The following table summarizes changes in the Company's warrant liability during the year ended December 31, 2023 (in thousands): Warrant Liability Balance at January 1, 2023 $ — Issuance of SSI Warrants 252 Issuance of Pre-Funded Warrants 39,826 Change in fair value 34,718 Reclass of Pre-Funded Warrants to equity ( 74,342 ) Balance at December 31, 2023 $ 454

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Net Loss Per Common Share	The following table represents the calculation of basic and di luted net loss per common share for the years ended December 31, 2023 and 2022, respectively (in thousands, except share and per share data): For the Year Ended December 31, 2023 2022 Net loss $ ( 111,566 ) $ ( 166,014 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 116,121,482 43,952,015 Net loss per common share, basic and diluted $ ( 0.96 ) $ ( 3.78 )
Schedule of Common Stock Equivalents Outstanding Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders	The following common stock equivalents outstanding as of December 31, 2023 and 2022, respectively, were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been anti‑dilutive: December 31, December 31, Unvested RSUs 375,044 1,257,844 Unvested RSAs — 85,494 Stock options 7,535,924 6,158,078 SSI Warrants 316,667 — Total 8,227,635 7,501,416

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of Federal Statutory Income Tax Rate	The effective tax rate of the Company's provision (benefit) for income taxes differs from the federal statutory rate as follows: For the Year Ended December 31, 2023 2022 Statutory rate 21.00 % 21.00 % State tax 0.33 % 0.25 % Research and development tax credits ( 18.98 )% 4.91 % Other permanent differences ( 0.67 )% ( 0.55 )% Change in valuation allowance 8.10 % ( 25.61 )% Change in fair value of warrant liability ( 6.55 )% ( 0.00 )% Change in fair value of term loan ( 0.30 )% ( 0.00 )% Stock-based compensation ( 2.93 )% ( 0.00 )% Income tax provision (benefit) 0.00 % 0.00 %
Schedule of Significant Components of Net Deferred Tax Asset	At December 31, 2023 and 2022, the significant components of the Company’s net deferred tax assets and liabilities are as follows (in thousands): For the Year Ended December 31, 2023 2022 Deferred tax assets: Net operating loss carryforwards $ 47,373 $ 45,609 Tax credit carryforwards 1,961 23,216 Accruals and reserves 1,020 689 Other 3,978 1 Intangibles 4,888 4,607 Non-qualified stock options 2,585 3,647 R&E expenditures 22,497 15,563 Lease liabilities 4,452 4,574 Impairment of long-lived assets 5,509 5,525 Total deferred tax assets 94,263 103,431 Deferred tax liabilities Right-of-use assets ( 2,224 ) ( 2,308 ) Fixed assets ( 2 ) ( 47 ) Total deferred tax liabilities ( 2,226 ) ( 2,355 ) Valuation allowance ( 92,037 ) ( 101,076 ) Net deferred taxes $ — $ —

Strategic Reprioritization (Tab

Strategic Reprioritization (Tables)	12 Months Ended
	Dec. 31, 2023
Restructuring and Related Activities [Abstract]
Summary of Accrued Severance Activity Recorded	The Company expects payment of these costs to be complete by March 31, 2024. The change in accrued severance during the years ended December 31, 2023 and 2022 is as follows (amounts in thousands): Accrued Severance Accrued severance as of January 1, 2022 $ — Severance recorded 4,035 Severance paid ( 2,572 ) Accrued severance as of December 31, 2022 $ 1,463 Severance recorded 2,691 Severance paid ( 3,764 ) Accrued severance as of December 31, 2023 $ 390

Organization and Description _2

Organization and Description of Business Operations - Additional Information (Details) - USD ($)		1 Months Ended	12 Months Ended
	Oct. 05, 2021	Apr. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Organization and Description of Business Operations [Line Items]
Date of incorporation			Feb. 13, 2020
Accumulated deficit			$ (513,007,000)	$ (401,441,000)
Cash and cash equivalents			$ 143,940,000	$ 87,880,000
Sales Agreement
Organization and Description of Business Operations [Line Items]
Number of shares issued		2,000,000
Net proceeds from issuance of common stock		$ 11,600,000
Common stock shares issued and sold			0
Sales Agreement | Sales Agents
Organization and Description of Business Operations [Line Items]
Percentage of gross sales price per share of common stock	3%
Sales Agreement | Sales Agents | Maximum
Organization and Description of Business Operations [Line Items]
Aggregate offering price from sale of common stock	$ 150,000,000

Significant Accounting Polici_3

Significant Accounting Policies - Additional Information (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 0	$ 0

Significant Accounting Polici_4

Significant Accounting Policies - Additional Information (Details 1) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Significant Accounting Policies [Line Items]
Cash equivalents		$ 142,400,000	$ 0
Shelf Registration,term		3 years
Non-cash impairment charge	$ 36,400,000	$ 600,000
Impairment losses		1,065,000	36,420,000
Accumulated Deficit		200,000
Increase in the amount of gross unrecognized tax benefits		400,000	3,100,000
Reduced uncertain tax positions related to prior year positions		7,800,000
Unrecognized tax benefits to change significantly over next 12 months		0
Interest and penalties associated with income tax positions		0	0
Derecognized build to suite lease asset		26,300,000
Deferred rent liabiilities and tenant improvement allowances		700,000
Operating Lease, Right-of-Use Asset		9,582,000	$ 10,943,000
Operating Lease, Liability		20,245,000
Derecognized build to suit lease liablility		$ 26,500,000
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Jan. 01, 2022
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		false
Operating Lease, Right-of-Use Asset		$ 18,400,000
Operating Lease, Liability		$ 19,100,000
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, useful life		3 years
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, useful life		7 years

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 142,425
Trinity Term Loans	40,508
Success Fee Derivative liability	800
SSI Warrant liability	454
Total liabilities	41,762
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents - money market funds	142,425
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	142,425
Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents - money market funds	142,425
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trinity Term Loans	40,508
Success Fee Derivative liability	800
SSI Warrant liability	454
Total liabilities	$ 41,762

Supplemental Financial Inform_3

Supplemental Financial Information - Schedule of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 13,805	$ 16,605
Accumulated depreciation	(2,979)	(1,642)
Property, plant and equipment, net	10,826	14,963
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,117	2,091
Laboratory Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,868	2,868
Computer Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,133	1,115
Furniture and Fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	864	898
Construction in Progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 6,823	$ 9,633

Supplemental Financial Inform_4

Supplemental Financial Information - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Non-cash impairment charge	$ 36,400	$ 600
Impairment charges to construction in process and finance lease right of use assets	$ 26,300
Depreciation expense		1,371	$ 1,172
Impairment loss on sale of assets		600
Property, plant and equipment, net		10,826	14,963
Assets Capitalized as Finance Leases
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 1,000	$ 1,300

Supplemental Financial Inform_5

Supplemental Financial Information - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 3,467	$ 8,190
Accrued compensation	3,423	2,519
Accrued clinical trial	1,851	1,473
Lease liabilities, current portion	1,646	1,521
Warrant liability, Current	454
Accrued severance	390	1,463
Accrued professional and consulting fees	330	390
Accrued property, plant and equipment		2,081
Other	723	650
Total accrued expenses and other current liabilities	$ 12,284	$ 18,287

Supplemental Financial Inform_6

Supplemental Financial Information - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 1,412	$ 4,840
Prepaid clinical trial	802	2,119
Deferred offering costs	681	724
Prepaid insurance	292	388
Other	292	466
Total prepaid expenses and other current assets	$ 3,479	$ 8,537

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands				12 Months Ended
	Dec. 14, 2021 USD ($) ft²	Jan. 11, 2021 ft²	Dec. 17, 2020 ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Future minimum remianing lease payments				$ 30,500
Restricted cash, current				449
Restricted cash, noncurrent				$ 2,151	$ 2,637
Durham Lease
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility | ft²			187,500
Operating lease commencement date			Apr. 01, 2021
Operating lease term of contract			15 years 6 months
Lease, option to extend description				The Company has two options to extend the term of the Durham Lease, each for a period of an additional five years.
Operating lease extend term of contract			5 years
Amount required to place in escrow account				$ 2,600
Restricted cash, current				500
Restricted cash, noncurrent				$ 2,100
Pegasus Park L L C | Dallas Lease
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility | ft²		15,000
Operating lease commencement date		May 27, 2021
Operating lease term of contract		10 years
Lease, option to extend description		Company has an option to extend the term of the Dallas Lease for one additional period of five years
Operating lease extend term of contract		5 years
Pegasus Park L L C | Dallas Lease Amendment
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility | ft²	18,000
Operating lease term of contract	10 years
Future minimum remianing lease payments	$ 6,000
Pegasus Park L L C | Dallas Lease Amendment | Minimum
Lessee, Lease, Description [Line Items]
Maximum construction allowance provided by landlord per rentable square foot | ft²	40

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lease, Cost [Abstract]
Operating lease cost	$ 2,770	$ 2,873
Variable lease cost	960	452
Total lease cost	$ 3,730	$ 3,325

Leases - Supplemental Informati

Leases - Supplemental Information Related to Remaining Lease Term and Discount Rate (Details)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term (in years) - Finance leases	2 years 10 months 17 days	3 years 10 months 17 days
Weighted average remaining lease term (in years) - Operating leases	10 years 9 months	11 years 5 months 12 days
Weighted average discount rate - Finance leases	10.52%	10.51%
Weighted average discount rate - Operating leases	7.80%	7.72%

Leases - Schedule of Supplement

Leases - Schedule of Supplemental Cash Flow Information Related to Operating Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash Flow, Operating Activities, Lessee [Abstract]
Operating cash flows for operating leases	$ 2,824	$ 2,486

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Commitments Under Company's Operating and Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Operating Lease
2024	$ 2,810
2025	2,910
2026	2,485
2027	2,577
2028	2,673
Thereafter	17,045
Total lease payments	30,500
Less: imputed interest	(10,255)
Total lease liabilities	20,245
Operating lease liabilities, current	$ 1,292
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Operating lease liabilities, non-current	$ 18,953	$ 20,440
Total lease liabilities	20,245
Finance Lease
2024	454
2025	454
2026	325
2027	73
Total lease payments	1,306
Less: imputed interest	(174)
Total lease liabilities	1,132
Finance lease liabilities, current	$ 354
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Finance, lease liabilities, non-current	$ 778
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Noncurrent
Total lease liabilities	$ 1,132
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities

Term Loans - Additional Informa

Term Loans - Additional Information (Details)			12 Months Ended
	Nov. 13, 2023 USD ($)	Aug. 12, 2021 USD ($) Program	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Debt instrument, maturity date		Aug. 01, 2026
Success fee liability at fair value			$ 800,000
Percentage of interest rate		7%
Percentage of prepayment of facility		7.50%
Exit fee recorded as debt discount			3,000,000
Interest expense related to term loan			4,900,000	$ 3,700,000
Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		3.75%
Term Loan
Debt Instrument [Line Items]
Current borrowing capacity		$ 30,000,000			$ 10,000,000
Prepayment of long term debt			43,200,000
Payment of exit fee			3,000,000
Accrued interest			200,000
Remaining balance of debt discount			1,400,000
Trinity Term Loans
Debt Instrument [Line Items]
Fair value of loan at issuance	$ 39,230,000		$ 40,508,000
Trinity Term Loan Agreement
Debt Instrument [Line Items]
Percentage of calculated discounted cash flows of discount rate			15.68%
Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 40,000,000
Interest rate terms description	The interest rate applicable to the Trinity Term Loans is the greater of (a) the WSJ Prime Rate plus 4.50% or (b) 12.75% per annum. The Trinity Term Loans are interest only from the Trinity Closing Date through 36 months from the Trinity Closing Date, which may be extended to 48 months from the Trinity Closing Date upon the satisfaction of certain milestones set forth in the Trinity Term Loan Agreement, after which the Company is required to pay equal monthly installments of principal through November 13, 2028 (the “Maturity Date”).
Interest rate period	36 months
Interest rate extension period	48 months
Debt outstanding			$ 40,000,000
Debt instrument, maturity date	Nov. 13, 2028
Debt instrument, basis spread on variable rate	12.75%
Commitment fee percentage	1%
End of term payment percentage	5%
Warrants associated with loan facility	$ 0
Percentage of annual default interest rate	5%
Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | Closing Date through November 13, 2024
Debt Instrument [Line Items]
Percentage of prepayment premium	3%
Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | November 13, 2024 through November 13, 2025
Debt Instrument [Line Items]
Percentage of prepayment premium	2%
Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | November 13, 2025 through, but excluding, the Maturity Date
Debt Instrument [Line Items]
Percentage of prepayment premium	1%
Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | General and Administrative Expense
Debt Instrument [Line Items]
Debt issuance costs			$ 900,000
Trinity Term Loan Agreement | Trinity Term Loans | Prime Rate | Trinity Lenders
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate	4.50%
Success Fee Agreement
Debt Instrument [Line Items]
Percentage of calculated discounted cash flows of discount rate			15.68%
Success Fee Agreement | Trinity Term Loans | Trinity Lenders
Debt Instrument [Line Items]
Success fee liability at fair value			$ 800,000
Fair value of loan at issuance			39,200,000
Percentage of principal amount of terms regarding fee	10%
Expiration Period	10 years
Through December 31, 2021 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 40,000,000
Debt instrument, maturity date		Dec. 31, 2021
January 1, 2022 until September 30, 2022 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 20,000,000	$ 20,000,000
Debt instrument, maturity start date		Jan. 01, 2022
Debt instrument, maturity end date		Sep. 30, 2022	Sep. 30, 2022
Number of distinct and active clinical stage | Program		3
Proceeds from term loan			$ 0
January 1, 2022 until March 31, 2023 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 20,000,000
Debt instrument, maturity end date			Mar. 31, 2023
Proceeds from term loan			$ 0
October 1, 2022 until March 31, 2023 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 20,000,000
Debt instrument, maturity start date		Oct. 01, 2022
Debt instrument, maturity end date		Mar. 31, 2023
Number of distinct and active clinical stage | Program		3
April 1, 2023 until December 31, 2023 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 20,000,000
Debt instrument, maturity start date		Apr. 01, 2023
Debt instrument, maturity end date		Dec. 31, 2023
Through August 13, 2023
Debt Instrument [Line Items]
Percentage of prepayment premium		1%

Term Loans - Schedule of Reconc

Term Loans - Schedule of Reconcile of Change in Fair Value of Debt (Details) $ in Thousands	2 Months Ended
	Dec. 31, 2023 USD ($)
Trinity Term Loans
Debt Instrument [Line Items]
Beginning fair value balance	$ 39,230
Change in fair value	1,278
Ending fair value balance	40,508
Success Fee Liability
Debt Instrument [Line Items]
Beginning fair value balance	770
Change in fair value	30
Ending fair value balance	$ 800

Term Loans - Schedule of Future

Term Loans - Schedule of Future Principal Debt Payments on Term Loan Agreement (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
2027	$ 18,709
2028	21,291
Total principal payments	$ 40,000

Astellas Agreements - Additiona

Astellas Agreements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		12 Months Ended
	Oct. 21, 2022	Oct. 31, 2022	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued				186,960,193	63,207,507
Deferred revenue				$ 18,106	$ 33,557
Probability of option exercise		50%
Revenues				15,451	2,502
TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment			$ 5,500
Rett research and development activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				13,200	$ 2,500
Option Agreement for GAN
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				2,300
Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment	$ 20,000
Transaction price		$ 36,100		36,059
Deferred revenue		$ 36,100
Astellas | Securities Purchase Agreement | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued	7,266,342	7,266,342
Aggregate gross proceeds	$ 30,000
Fair value of shares transferred, Value		$ 13,950
Share price		$ 1.92
Difference of market value paid		$ 30,000
Transaction price		$ 16,100
Astellas | TSHA-120
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront Payment				20,000
Transaction price				36,100
Astellas | TSHA-120 | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price				16,100
Astellas | Rett research and development activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price				$ 28,257

Astellas Transaction - Summary

Astellas Transaction - Summary of Allocation for Transaction Price to the Three Performance Obligations (Details) - Astellas - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2022	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction Price Allocation	$ 36,100	$ 36,059
Option to obtain license for Rett
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction Price Allocation		5,485
Option to obtain license for GAN
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction Price Allocation		2,317
Rett research and development activities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Transaction Price Allocation		$ 28,257

Research, Collaboration, Gran_2

Research, Collaboration, Grant and License Agreements - Additional Information (Details)

1 Months Ended

12 Months Ended

Jul. 31, 2022 USD ($)

Mar. 31, 2022 USD ($)

Mar. 31, 2021 USD ($)

Oct. 31, 2020 USD ($)

Aug. 31, 2020 USD ($)

Apr. 30, 2020 USD ($) Product

Dec. 31, 2023 USD ($) shares

Dec. 31, 2022 USD ($) shares

Dec. 31, 2021 USD ($)

Dec. 31, 2020 USD ($)

Oct. 29, 2020 USD ($)

Feb. 21, 2020 USD ($)

Nov. 30, 2019 shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Common stock, shares issued | shares

186,960,193

63,207,507

Research and development

$ 56,778,000

$ 91,169,000

License Agreement for CLN7

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

0

Payment of one-time upfront license fee

$ 300,000

License agreement regulatory related milestones maximum amount payable

7,700,000

License agreement sales-related milestones maximum amount payable

$ 7,500,000

TSHA-120

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

0

Research and development

$ 5,500,000

Upfront payment

$ 5,500,000

Clinical, regulatory and commercial milestones to be received

$ 19,300,000

UT Southwestern Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Preclinical activities period under sponsored research agreements

2 years

Minimum licensed product to develop obtain regulatory approval for and commercialize | Product

1

Common stock, shares issued | shares

2,179,000

Percentage of fully diluted common stock shares outstanding

20%

Outstanding payments due

0

Queens Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

0

Queens Agreement | Research and Development Expense

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Cash payment to acquire license agreement

$ 3,000,000

Queens Agreement | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License agreement regulatory milestones payment

$ 10,000,000

License agreement commercial milestones payment

$ 10,000,000

Abeona CLN1 Agreements

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

0

License fee payment

$ 3,000,000

Purchase of clinical materials and reimbursement incurred development costs

$ 4,000,000

Research and development

$ 3,000,000

$ 7,000,000

Abeona CLN1 Agreements | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License and inventory purchase agreement regulatory related milestones payment

26,000,000

License and inventory purchase agreement sales related milestones payment

$ 30,000,000

Abeona | Abeona Rett Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

0

Research and development

$ 3,500,000

$ 1,000,000

Regulatory milestone fee paid

$ 1,000,000

Payment of one-time upfront license fee

$ 3,000,000

Abeona | Maximum | Abeona Rett Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Regulatory related milestones obligation payable

$ 26,500,000

Sale-related milestones per licensed product and royalties on net sales of licensed products payable

$ 30,000,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)

1 Months Ended

12 Months Ended

Feb. 28, 2023

Sep. 16, 2020

Jul. 01, 2020

May 31, 2023

Mar. 31, 2023

Feb. 28, 2023

Feb. 28, 2022

Dec. 31, 2023

Dec. 31, 2022

Jan. 01, 2023

Jan. 01, 2022

Dec. 31, 2021

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Stock-based compensation expense

$ 7,905,000

$ 18,043,000

Percentage of common stock price purchased through payroll deductions

85%

Percentage of payroll deductions of employee's compensation during offering period

15%

Maximum number of shares employees may purchase during offering period

1,800

Employee Stock Purchase Plan (ESPP)

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, terms of award issuance

the number of shares of common stock that are automatically added on January 1st of each year for a period of up to ten years, commencing on the first January 1 following the IPO and ending on (and including) January 1, 2030, in an amount equal to the lesser of (i) one percent (1.0%) of the total number of shares of capital stock outstanding on December 31st of the preceding calendar year, and (ii) 724,000 shares of common stock.

Common stock reserved for future issuance

724,000

632,075

384,739

Share-based payment award, expiration period

10 years

Share-based payment award, expiration date

Jan. 01, 2030

Percentage of automatic increase every year in common stock shares reserved for future issuance

1%

Number of shares of common stock issued under ESPP

0

141,393

Restricted Stock Units

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition

8 months 12 days

Share-based payment award, RSU/RSA granted

332,532

Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized

$ 1,400,000

Share-based payment award, RSU/RSA granted, weighted average grant date fair value

$ 1.06

Performance and market-based restricted stock units of other option forfeited during period

658,343

Performance and market-based restricted stock units of other option vested during period

556,989

628,921

Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, options granted

2,726,871

4,775,676

Options forfeited

2,050,562

2,048,192

Stock options were exercised during the period

$ 0

$ 0

Share-based payment award, options, compensation cost not yet recognized

$ 8,400,000

Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition

1 year 10 months 24 days

Outstanding performance and market-based options

5,960,922

6,158,078

3,649,962

Restricted Stock Awards

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, RSU/RSA granted, weighted average grant date fair value

$ 5.28

Performance and market-based restricted stock units of other option forfeited during period

21,374

Performance and market-based restricted stock units of other option vested during period

64,120

256,481

Maximum | Employee Stock Purchase Plan (ESPP)

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Number of shares authorized for issuance

362,000

Existing Plan | Restricted Stock Awards | Former President and Chief Executive Officer

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, RSU/RSA granted

769,058

Award requisite service vesting period

3 years

Existing Plan | Minimum | Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Award vesting period

1 year

New Plan

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, terms of award issuance

The number of shares of common stock reserved for issuance under the New Plan automatically increases on January 1 of each year, for a period of ten years, from January 1, 2021, continuing through January 1, 2030, by 5% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by the Company’s board of directors.

Common stock reserved for future issuance

3,160,375

Share-based payment award, expiration period

10 years

Share-based payment award, commencement date

Jan. 01, 2021

Share-based payment award, expiration date

Jan. 01, 2030

Percentage of automatic increase every year in common stock shares reserved for future issuance

5%

New Plan | Restricted Stock Units

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Award vesting period

4 years

Share-based payment award, RSU/RSA granted

81,236

New Plan | Restricted Stock Units | Former President and Chief Executive Officer

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, RSU/RSA granted

251,296

New Plan | Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, expiration period

10 years

Share-based payment award, options granted

2,726,871

Share-based payment award, options, weighted-average grant date fair value

$ 0.71

New Plan | Performance Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, options granted

70,235

Stock options were exercised during the period

$ 0

Outstanding performance and market-based options

58,346

New Plan | Market Based Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, options granted

70,233

Options forfeited

70,233

New Plan | Performance and Market-based Restricted Stock Units

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, RSU/RSA granted

81,233

Performance and market-based restricted stock units of other option forfeited during period

46,562

Performance and market-based restricted stock units of other option vested during period

34,671

New Plan | Maximum | Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Award vesting period

4 years

Inducement Plan

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Common stock reserved for future issuance

4,000,000

Original Options | Performance Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, options granted

2,166,653

Award vesting period

3 years 7 months 6 days

Share-based payment award, options, weighted-average grant date fair value

$ 0.5

Stock-based compensation expense

$ 0

Modified Options | Performance Stock Options

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Share-based payment award, options granted

1,516,655

Award vesting period

3 years

Share-based payment award, options, weighted-average grant date fair value

$ 1.28

Stock options were exercised during the period

$ 0

Share-based payment award, options, compensation cost not yet recognized

$ 1,900,000

Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition

2 years

Outstanding performance and market-based options

1,516,655

Stock-based compensation expense

$ 100,000

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Share Based Compensation Available for Grant under Incentive Plans (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for grant beginning of period	1,067,682	1,652,101
Plan adjustments and amendments	7,160,375	1,923,697
Grants	(5,447,757)	(4,775,676)
Forfeitures	4,382,425	2,267,560
Available for grant end of period	7,162,725	1,067,682
Previous Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan adjustments and amendments	(667,828)
Forfeitures	667,828
New Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Available for grant beginning of period	1,067,682	1,652,101
Plan adjustments and amendments	3,828,203	1,923,697
Grants	(5,447,757)	(4,775,676)
Forfeitures	3,714,597	2,267,560
Available for grant end of period	3,162,725	1,067,682
Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan adjustments and amendments	4,000,000
Available for grant end of period	4,000,000

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Options (Details)	1 Months Ended	12 Months Ended
	May 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate		3.68%	2.95%
Expected term (in years)		5 years 6 months	6 years 1 month 6 days
Expected volatility		82%	78%
Performance Stock Options | Initial Options and Original Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	4.02%
Expected term (in years)	6 years
Expected volatility	81%
Performance Stock Options | Modified Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate		3.90%
Expected term (in years)		5 years 9 months 18 days
Expected volatility		88%

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance	6,158,078	3,649,962
Options granted, Stock Options	2,726,871	4,775,676
Options cancelled or forfeited, Stock Options	(2,050,562)	(2,048,192)
Options expired, Stock Options	(873,465)	(219,368)
Outstanding. Stock Options, Ending Balance	5,960,922	6,158,078	3,649,962
Options exercisable at December 31, 2023	1,580,373
Outstanding, Weighted Average Exercise Price, Beginning balance	$ 11.84	$ 24.13
Options granted, Weighted Average Exercise Price	0.99	4.48
Options cancelled or forfeited, Weighted Average Exercise Price	10.7	15.25
Options expired, Weighted Average Exercise Price	22.21	24.36
Outstanding, Weighted Average Exercise Price, Ending balance	5.75	$ 11.84	$ 24.13
Options exercisable at December 31, 2023, Weighted Average Exercise Price	$ 13.51
Outstanding, Weighted Average Remaining Contractual Life	8 years 8 months 12 days	8 years 10 months 24 days	9 years 2 months 12 days
Weighted Average Remaining Contractual Life, Options exercisable at December 31, 2023	7 years 7 months 6 days
Outstanding, Aggregate Intrinsic Value, Beginning Balance	$ 62
Outstanding, Aggregate Intrinsic Value, Ending Balance	1,960	$ 62
Options exercisable at December 31, 2023, Aggregate Intrinsic Value	$ 8

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance	1,257,844	1,886,765
Restricted units/stock granted, Number of Shares	332,532
Vested, Number of Shares	(556,989)	(628,921)
Cancelled or forfeited, Number of Shares	(658,343)
Nonvested, Number of Shares, Ending Balance	375,044	1,257,844
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance	$ 6.52	$ 6.52
Restricted units/stock granted, Weighted Average Grant Date Fair Value per Share	1.06
Vested, Weighted Average Grant Date Fair Value per Share	4.78	6.52
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share	5.18
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance	$ 6.63	$ 6.52

Stock-Based Compensation - Sc_5

Stock-Based Compensation - Schedule of Restricted Stock Awards Activity (Details) - Restricted Stock Awards - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance	85,494	341,975
Vested, Number of Shares	(64,120)	(256,481)
Cancelled or forfeited, Number of Shares	(21,374)
Nonvested, Number of Shares, Ending Balance		85,494
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance	$ 5.28	$ 5.28
Vested, Weighted Average Grant Date Fair Value per Share	5.28	5.28
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share	$ 5.28
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance		$ 5.28

Stock-Based Compensation - Sc_6

Stock-Based Compensation - Schedule of Total Remaining Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 7,905	$ 18,043
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,225	7,608
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,680	$ 10,435

Warrants - Additional Informati

Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended
	Aug. 16, 2023	Aug. 14, 2023	Apr. 05, 2023	Apr. 30, 2023	Dec. 31, 2023	Dec. 31, 2022	Nov. 15, 2023
Class of Warrant or Right [Line Items]
Common stock, shares issued					186,960,193	63,207,507
Common stock, par value per share					$ 0.00001	$ 0.00001
General and administrative					$ 30,047	$ 37,360
Warrant liability fair value adjustment					34,718
Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Warrant liability fair value adjustment					34,500
Warrant liability reclassified into equity					$ 74,342
Common Stock
Class of Warrant or Right [Line Items]
Share price							$ 1.68
Securities Purchase Agreement | Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Common stock, par value per share		$ 0.001
Exercise price of warrants		$ 0.001
SSI Warrants
Class of Warrant or Right [Line Items]
Issuance of fair value warrant			$ 300
Class of warrant or right vested and exercisable shares					316,667
Warrant liability fair value adjustment					$ 200
Warrants Exercised					0
Private Placement
Class of Warrant or Right [Line Items]
Gross proceeds from issuance of common stock					$ 500
Private Placement | Securities Purchase Agreement
Class of Warrant or Right [Line Items]
Beneficial ownership limitation notice period (in days)		61 days
Increase or decrease in beneficial ownership limitation percentage		19.99%
Gross proceeds from issuance of common stock	$ 150,000
Net proceeds from issuance of common stock	$ 140,300
Private Placement | Securities Purchase Agreement | Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Purchase price per share of common stock		$ 0.9
Incurred placement agent commissions and other issuance costs					9,700
Allocated to shares, deduction to Additional paid-In capital					7,100
General and administrative					$ 2,600
August 2023 Private Placement | Securities Purchase Agreement
Class of Warrant or Right [Line Items]
Common stock, shares issued		122,412,376
August 2023 Private Placement | Securities Purchase Agreement | Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Warrants issued		44,250,978
Purchase price per share of common stock		$ 0.9
Exercise price of warrants		$ 0.001
SSI Strategy Holdings LLC | Private Placement | Securities Purchase Agreement
Class of Warrant or Right [Line Items]
Common stock, shares issued				705,218
Aggregate gross proceeds				$ 500
Warrants issued				525,000
Exercise price of warrants				$ 0.709

Warrants - Schedule of Fair Val

Warrants - Schedule of Fair Value Method to Allocate Net Proceeds Received from Sale of Common Stock and Pre-funded Warrants (Details)	Dec. 31, 2023 USD ($)
Class of Warrant or Right [Line Items]
Common stock and warrants fair value disclosure	$ 149,953
PIPE Shares
Class of Warrant or Right [Line Items]
Common stock and warrants fair value disclosure	110,127
Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Common stock and warrants fair value disclosure	$ 39,826

Warrants - Schedule Of Assumpti

Warrants - Schedule Of Assumptions Used To Estimate Fair Value Of Warrants (Details)	Dec. 31, 2023 USD ($) yr	Apr. 05, 2023 yr USD ($)
Risk-free interest rate
Class of Warrant or Right [Line Items]
Warrants, measurement input	3.84	3.46
Expected term (in years)
Class of Warrant or Right [Line Items]
Warrants, measurement input | yr	4.5	5.2
Expected volatility
Class of Warrant or Right [Line Items]
Warrants, measurement input	88	81
Market value of common stock (per share)
Class of Warrant or Right [Line Items]
Warrants, measurement input | $	1.77	0.71

Warrants - Schedule of Warrant

Warrants - Schedule of Warrant Liability (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Class of Warrant or Right [Line Items]
Change in fair value	$ 34,718
Balance at December 31, 2023	454
SSI Warrants
Class of Warrant or Right [Line Items]
Issuance of Warrants	252
Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Issuance of Warrants	39,826
Reclass of Pre-Funded Warrants to equity	$ (74,342)

Net Loss Per Common Share - Add

Net Loss Per Common Share - Additional Information (Details)	Aug. 14, 2023 $ / shares
Pre-Funded Warrants | Securities Purchase Agreement
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Exercise price of warrants Per Share	$ 0.001

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Calculation of Basic and Diluted Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Net loss	$ (111,566)	$ (166,014)
Weighted average common shares outstanding, basic	116,121,482	43,952,015
Weighted average common shares outstanding, diluted	116,121,482	43,952,015
Net loss per common share, basic	$ (0.96)	$ (3.78)
Net loss per common share, diluted	$ (0.96)	$ (3.78)

Net Loss Per Common Share - S_2

Net Loss Per Common Share - Schedule of Common Stock Equivalents Outstanding Excluded from Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	8,227,635	7,501,416
Unvested RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	375,044	1,257,844
Unvested RSAs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share		85,494
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	7,535,924	6,158,078
SSI Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	316,667

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Line Items]
Provision for income taxes	$ 0
Corporate alternative minimum tax on large corporations	15%
Excise tax rate on corporate buy-backs	1%
Valuation allowance increased (decreased)	$ (9,000,000)	$ 42,800,000
Gross operating loss carryforward	$ 217,900,000
Net operating loss carryforwards, limitations on use	federal NOLs are subject to an annual utilization limitation of $3.1 million, which can be increased in the five year period post change date for any realized built-in gain.
Net operating loss carryforward annual utilization limitation	$ 3,100,000
Tax credit carryforwards	1,961,000	23,216,000
Research credits	$ 27,100,000
United States
Income Tax Disclosure [Line Items]
Research and experimentation expenditures amortized period	5 years
Outside the United States
Income Tax Disclosure [Line Items]
Research and experimentation expenditures amortized period	15 years
Federal
Income Tax Disclosure [Line Items]
Gross operating loss carryforward	$ 222,100,000	216,300,000
Tax credit carryforwards	$ 28,600,000	30,200,000
Tax credit carryforward expiration or due date year	2040
State
Income Tax Disclosure [Line Items]
Gross operating loss carryforward	$ 11,900,000	4,500,000
Tax credit carryforwards	$ 1,200,000	$ 1,300,000

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Statutory rate	21%	21%
State tax	0.33%	0.25%
Research and development tax credits	(18.98%)	4.91%
Other permanent differences	(0.67%)	(0.55%)
Change in valuation allowance	8.10%	(25.61%)
Change in fair value of warrant liability	(6.55%)	0%
Change in fair value of term loan	(0.30%)	(0.00%)
Stock-based compensation	(2.93%)	0%
Income tax provision (benefit)	0%	0%

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Components of Deferred Tax Assets [Abstract]
Net operating loss carryforwards	$ 47,373	$ 45,609
Tax credit carryforwards	1,961	23,216
Accruals and reserves	1,020	689
Other	3,978	1
Intangibles	4,888	4,607
Non-qualified stock options	2,585	3,647
R&E expenditures	22,497	15,563
Lease liabilities	4,452	4,574
Impairment of long-lived assets	5,509	5,525
Total deferred tax assets	94,263	103,431
Right-of-use assets	(2,224)	(2,308)
Fixed assets	(2)	(47)
Total deferred tax liabilities	(2,226)	(2,355)
Valuation allowance	(92,037)	(101,076)
Net deferred taxes	$ 0	$ 0

Strategic Reprioritization - Ad

Strategic Reprioritization - Additional Information (Details) - Exit and Disposal Activities - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Percentage of headcount reduced			35%
Severance and termination-related costs	$ 1.5	$ 2.7		$ 2.6

Strategic Reprioritization - Su

Strategic Reprioritization - Summary of Accrued Severance Activity Recorded (Details) - Employee Severance - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Accrued severance, Beginning	$ 1,463
Severance recorded	2,691	$ 4,035
Severance paid	(3,764)	(2,572)
Accrued severance, Ending	$ 390	$ 1,463

Retirement Plan - Additional In

Retirement Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Retirement Benefits [Abstract]
Contribution to retirement savings plan	$ 0.3	$ 0.7

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - $ / shares	1 Months Ended	2 Months Ended	3 Months Ended	12 Months Ended
	Feb. 28, 2023	Feb. 29, 2024	Mar. 31, 2024	Dec. 31, 2023
Restricted Stock Units
Subsequent Event [Line Items]
Restricted units/stock granted, Number of Shares				332,532
Restricted Stock Units | New Plan
Subsequent Event [Line Items]
Restricted units/stock granted, Number of Shares	81,236
Award vesting period	4 years
Subsequent Events | New Plan
Subsequent Event [Line Items]
Options granted for purchase an aggregate share of common stock		7,000,000
Weighted-average exercise price		$ 1.71
Award vesting period		4 years
Subsequent Events | Inducement Plan
Subsequent Event [Line Items]
Options granted for purchase an aggregate share of common stock			800,000
Weighted-average exercise price			$ 2.35
Award vesting period			4 years
Subsequent Events | Restricted Stock Units | New Plan
Subsequent Event [Line Items]
Restricted units/stock granted, Number of Shares		4,300,000