Taysha Gene Therapies (TSHA) 10-Q 14 Nov 23 2023 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 14, 2023
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
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 Drive
Entity Address, Address Line Two	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		186,960,193
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 Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 164,278	$ 87,880
Prepaid expenses and other current assets	5,529	8,537
Assets held for sale	2,000
Total current assets	171,807	96,417
Restricted cash	2,637	2,637
Property, plant and equipment, net	11,169	14,963
Operating lease right-of-use assets	9,852	10,943
Other non-current assets	304	1,316
Total assets	195,769	126,276
Current liabilities
Accounts payable	7,520	10,946
Accrued expenses and other current liabilities	13,638	18,287
Deferred revenue	18,759	33,557
Warrant liability	140,534
Total current liabilities	180,451	62,790
Deferred revenue, net of current portion	2,951
Term loan, net	38,548	37,967
Operating lease liability, net of current portion	19,101	20,440
Other non-current liabilities	3,832	4,130
Total liabilities	244,883	125,327
Commitments and contingencies - Note 13
Stockholders' (deficit) equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of September 30, 2023 and December 31, 2022
Common stock, $0.00001 par value per share; 200,000,000 shares authorized and 186,960,193 and 63,207,507 issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	2	1
Additional paid-in capital	511,632	402,389
Accumulated deficit	(560,748)	(401,441)
Total stockholders' (deficit) equity	(49,114)	949
Total liabilities and stockholders' (deficit) equity	$ 195,769	$ 126,276

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 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	200,000,000	200,000,000
Common stock, shares issued	186,960,193	63,207,507
Common stock, shares outstanding	186,960,193	63,207,507

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Statement [Abstract]
Revenue	$ 4,746		$ 11,847
Operating expenses:
Research and development	11,791	$ 16,774	44,096	$ 78,462
General and administrative	8,589	8,683	23,328	30,019
Impairment of long-lived assets	616		616
Total operating expenses	20,996	25,457	68,040	108,481
Loss from operations	(16,250)	(25,457)	(56,193)	(108,481)
Other income (expense):
Change in fair value of warrant liability	(100,456)		(100,456)
Interest income	1,109	9	1,651	50
Interest expense	(1,471)	(1,078)	(4,285)	(2,493)
Other expense	(19)	(1)	(24)	(12)
Total other income (expense), net	(100,837)	(1,070)	(103,114)	(2,455)
Net loss	$ (117,087)	$ (26,527)	$ (159,307)	$ (110,936)
Net loss per common share, basic	$ (0.93)	$ (0.65)	$ (1.88)	$ (2.79)
Net loss per common share, diluted	$ (0.93)	$ (0.65)	$ (1.88)	$ (2.79)
Weighted average common shares outstanding, basic	125,700,799	40,937,808	84,630,796	39,761,764
Weighted average common shares outstanding, diluted	125,700,799	40,937,808	84,630,796	39,761,764

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Private Placement	Common Stock	Common Stock Private Placement	Additional Paid-in Capital	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	$ 14,172					14,172
Issuance of common stock	11,609			$ 1		11,608
Issuance of common stock, shares				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	(110,936)							(110,936)
Balance at Sep. 30, 2022	10,703			$ 1		357,065		(346,363)
Balance, shares at Sep. 30, 2022				41,175,939
Balance at Jun. 30, 2022	$ 32,507			$ 1		352,342		(319,836)
Balance, shares at Jun. 30, 2022				41,020,086
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2016-02 [Member]
Stock-based compensation	$ 4,470					4,470
Issuance of common stock upon vesting and settlement of restricted stock units, net, shares				82,780
Issuance of common stock under ESPP	253					253
Issuance of common stock under ESPP, shares				73,073
Net loss	(26,527)							(26,527)
Balance at Sep. 30, 2022	10,703			$ 1		357,065		(346,363)
Balance, shares at Sep. 30, 2022				41,175,939
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	$ 5,937					5,937
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
Net loss	(159,307)							(159,307)
Balance at Sep. 30, 2023	$ (49,114)			$ 2		511,632		(560,748)
Balance, shares at Sep. 30, 2023	186,960,193			186,960,193
Balance at Jun. 30, 2023	$ (37,114)			$ 1		406,546		(443,661)
Balance, shares at Jun. 30, 2023				64,432,637
Stock-based compensation	2,040					2,040
Issuance of common stock			$ 103,029		$ 1		$ 103,028
Issuance of common stock, shares					122,412,376
Issuance of common stock upon vesting and settlement of restricted stock units, net, shares				82,780
Issuance of common stock under ESPP	18					18
Issuance of common stock under ESPP, shares				32,400
Net loss	(117,087)							(117,087)
Balance at Sep. 30, 2023	$ (49,114)			$ 2		$ 511,632		$ (560,748)
Balance, shares at Sep. 30, 2023	186,960,193			186,960,193

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' (Deficit) Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022
Payment of sales commissions and other offering cost			$ 392
Private Placement
Offering costs	$ 7,098	$ 7,138

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities
Net loss	$ (159,307)	$ (110,936)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,005	810
Research and development license expense	3,500	1,250
Stock-based compensation	5,937	13,940
Change in fair value of warrant liability	100,456
Issuance costs for pre-funded warrant liability	2,567
Impairment of long-lived assets	616
Non-cash lease expense	908	1,031
Other	581	616
Changes in operating assets and liabilities:
Prepaid expenses and other assets	4,008	1,980
Accounts payable	(1,065)	(3,217)
Accrued expenses and other liabilities	(4,260)	(8,576)
Deferred revenue	(11,847)
Net cash used in operating activities	(56,901)	(103,102)
Cash flows from investing activities
Purchase of research and development license	(3,500)	(4,250)
Purchase of property, plant and equipment	(3,852)	(18,310)
Other	10
Net cash used in investing activities	(7,342)	(22,560)
Cash flows from financing activities
Proceeds from issuance of common stock, net of sales commissions		11,640
Proceeds from issuance of common stock and pre-funded warrants from private placement, net of placement agent commissions and other offering costs	140,713
Payment of shelf registration costs	(387)	(319)
Proceeds from common stock issuances under ESPP	68	253
Other	(253)	(709)
Net cash provided by financing activities	140,641	10,865
Net increase (decrease) in cash, cash equivalents and restricted cash	76,398	(114,797)
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	166,915	36,943
Cash and cash equivalents	164,278	34,306
Restricted cash	2,637	2,637
Supplemental disclosure of cash flow information:
Cash paid for interest	3,665	1,758
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	45	3,366
Right-of-use assets obtained in exchange for lease liabilities		23,035
Offering costs not yet paid	423	$ 40
Issuance of warrants in connection with private placement	252
Private Placement
Cash flows from financing activities
Proceeds from issuance of common stock, net of sales commissions	$ 500

Organization and Description of

Organization and Description of Business Operations	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business Operations	Note 1—Organization and Descr iption 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 (“Inception”). 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 patient-centric gene therapy company focused on developing and commercializing AAV-based gene therapies for the treatment of monogenic diseases of the central nervous system in both rare and large patient populations. 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 by law. Any shares of the Company’s common stock will be issued pursuant to the Company’s shelf registration statement on Form S-3 (File No. 333-260069) (the “Shelf Registration Statement”), which the Securities and Exchange Commission (“SEC”) declared effective on October 14, 2021; however the Company’s use of the Shelf Registration Statement will be limited for so long as the Company is subject to General Instruction I.B.6 of Form S-3, which limits the amounts that the Company may sell under the Shelf Registration Statement and in accordance with the Sales Agreement. 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 September 30, 2023. Liquidity and Capital Resources The accompanying condensed consolidated financial statements are prepared in accordance with generally accepted accounting principles applicable to a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. Pursuant to ASC 205, Presentation of Financial Statements , the Company is required to and does evaluate at each annual and interim period whether there are conditions or events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that the condensed consolidated financial statements are issued. In its Quarterly Report on Form 10-Q for the quarter ended June 30, 2023, the Company concluded that due to inherent uncertainties in the Company’s forecast, and after considering both quantitative and qualitative factors that were known or reasonably knowable as of the date that such condensed consolidated financial statements were issued, there were conditions present in the aggregate that raised substantial doubt about the Company’s ability to continue as a going concern. Following the closing of the Private Placement (as defined below) in August 2023 (see Note 10), the Company has concluded that after considering both qualitative and quantitative factors, there are no longer conditions present in the aggregate that raise substantial doubt about the Company’s ability to continue as a going concern. The Company has sufficient liquidity to satisfy its obligations for at least twelve months following the date of the issuance of these condensed consolidated financial statements. Accordingly, the Company has concluded that there is no longer substantial doubt about the Company’s ability to continue as a going concern. 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 September 30, 2023, the Company had an accumulated deficit of $ 560.7 million. Losses are expected to continue as the Company continues to invest in its research and development activities. 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. As of September 30, 2023, the Company had cash and cash equivalents of $ 164.3 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 condensed consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Significant Accounting Policies	Note 2—Summary of Significant Accounting Policies Basis of Presentation The unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X and are consistent in all material respects with those included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the SEC on March 28, 2023 (the “2022 Annual Report”). In the opinion of management, the unaudited condensed consolidated financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the balances and results for the periods presented. The consolidated balance sheet as of December 31, 2022, is derived from audited financial statements, however, it does not include all of the information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes in the Company’s 2022 Annual Report. Principles of Consolidation The accompanying interim condensed consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. 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 initial public offering ("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 fair value of the warrant liability, and the allocation of consideration received in connection with the Astellas Transactions (as defined below) at contract inception. 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. Significant Accounting Policies There have been no changes in the Company’s significant accounting policies as disclosed in Note 2 to the audited consolidated financial statements included in the 2022 Annual Report, except as described below. 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. 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 three months ended September 30, 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. 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. 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. The Company classifies the warrants as liabilities at their fair value and adjusts the 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 condensed consolidated statement of operations. Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying condensed consolidated statements of operations. Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), 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. On December 31, 2022 , the Company adopted ASU 2016-02 using the modified retrospective approach and utilizing the effective date as its date of initial application. The Company has retrospectively changed its previously issued condensed consolidated financial statements as of September 30, 2022 as presented within the Company’s September 30, 2022 Quarterly Report on Form 10-Q to reflect the adoption of ASC 842 on January 1, 2022. The condensed consolidated financial statements for the three and nine months ended September 30, 2022 presented herein differ from the Company’s condensed consolidated financial statements included in the Company’s September 30, 2022 Quarterly Report on Form 10-Q as those condensed consolidated financial statements were prepared using the former accounting standard referred to as ASC Topic 840, Leases. 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 this 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 condensed 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 and on the condensed consolidated statements of operations and cash flows. The following table summarizes the effect of the adoption of ASC 842 on the condensed consolidated statement of operations and statement of cash flows for the nine months ended September 30, 2022 (in thousands): Pre ASC 842 Nine Months Ended ASC 842 Adjustments After ASC 842 Nine Months Ended Condensed Consolidated Statement of Operations Operating expenses: Research and development $ 77,308 $ 1,154 $ 78,462 Other income (expense): Interest expense ( 3,002 ) 509 ( 2,493 ) Net loss ( 110,291 ) ( 645 ) ( 110,936 ) Condensed Consolidated Statement of Cash Flows Adjustments to reconcile net loss to net cash used in operating activities: Depreciation expense $ 808 $ 2 $ 810 Non-cash lease expense — 1,031 1,031 Changes in operating assets and liabilities: Accrued expenses and other current liabilities ( 7,753 ) ( 823 ) ( 8,576 ) Cash flows from financing activities Other ( 1,144 ) 435 ( 709 ) Supplemental disclosure of noncash investing and financing activities: Right-of-use assets obtained in exchange for lease liabilities — 23,035 23,035 The following table summarizes the effect of the adoption of ASC 842 on the condensed consolidated statement of operations for the three months ended September 30, 2022 (in thousands): Pre ASC 842 Three Months Ended ASC 842 Adjustments After ASC 842 Three Months Ended Condensed Consolidated Statement of Operations Operating expenses: Research and development $ 16,391 $ 383 $ 16,774 Other income (expense): Interest expense ( 1,241 ) 163 ( 1,078 ) Net loss ( 26,307 ) ( 220 ) ( 26,527 )

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 3—Fair Value Measurements 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): September 30, 2023 Total Level 1 Level 2 Level 3 Assets: Cash equivalents – money market funds $ 150,514 $ 150,514 $ — $ — $ 150,514 $ 150,514 $ — $ — Liabilities: Warrant liability SSI Warrants $ 701 $ — $ — $ 701 Pre-funded warrants 139,833 — 139,833 — Total liabilities $ 140,534 $ — $ 139,833 $ 701 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 uses the Black-Scholes-Merton option pricing model to determine the fair value of the SSI Warrants (as defined below). The Company classifies its Pre-Funded Warrants (as defined below), which are valued using quoted prices of similar financial instruments in the market, as Level 2 liabilities. S ee Note 10 for additional information on the SSI Warrants and the Pre-Funded Warrants.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2023
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Note 4—Balance Sheet Components Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, Prepaid research and development $ 2,672 $ 4,840 Prepaid clinical trial 1,392 2,119 Deferred offering costs 724 724 Prepaid insurance 337 388 Other 404 466 Total prepaid expenses and other current assets $ 5,529 $ 8,537 Property, plant and equipment, net consisted of the following (in thousands): September 30, December 31, Leasehold improvements $ 2,091 $ 2,091 Laboratory equipment 2,868 2,868 Computer equipment 1,115 1,115 Furniture and fixtures 864 898 Construction in progress 6,874 9,633 13,812 16,605 Accumulated depreciation ( 2,643 ) ( 1,642 ) Property, plant and equipment, net $ 11,169 $ 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 $ 1.1 mi llion and $ 1.3 million of assets capitalized as finance leases as of September 30, 2023 and December 31, 2022, respectively. Depreciation expense w as $ 0.3 million and $ 0.3 million for the three months ended September 30, 2023 and 2022, respectively. Depreciation expense was $ 1.0 milli on and $ 0.8 million for the nine months ended September 30, 2023 and 2022, respectively. During the three months ended September 30, 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 three and nine months ended September 30, 2023, the Company recorded an impairment loss of $ 0.6 million which was the difference between the carrying value and fair value less cost to sell. Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, Accrued research and development $ 5,699 $ 8,190 Accrued compensation 2,745 2,519 Lease liabilities, current portion 1,538 1,521 Accrued clinical trial 1,359 1,473 Accrued severance 992 1,463 Accrued professional and consulting fees 579 390 Accrued property, plant and equipment 45 2,081 Other 681 650 Total accrued expenses and other current liabilities $ 13,638 $ 18,287

Leases

Leases	9 Months Ended
	Sep. 30, 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 will 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 will 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 approximately 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 approximately $ 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 will be released when the improvements are substantially complete. The escrow funds are recorded as restricted cash on the condensed consolidated balance sheet as of September 30, 2023. 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 three and nine months ended September 30, 2023 and 2022 (in thousands): Three Months Ended September 30, For the Nine Months Ended September 30, 2023 2022 2023 2022 Operating lease cost $ 696 $ 794 $ 2,088 $ 2,079 Variable lease cost 243 229 729 617 Total lease cost $ 939 $ 1,023 $ 2,817 $ 2,696 Supplemental information related to the remaining lease term and discount rate are as follows: September 30, 2023 December 31, 2022 Weighted average remaining lease term (in years) – Finance leases 3.13 3.88 Weighted average remaining lease term (in years) – Operating leases 10.97 11.45 Weighted average discount rate – Finance leases 10.52 % 10.51 % Weighted average discount rate – Operating leases 7.79 % 7.72 % Supplemental cash flow information related to the Company’s operating leases are as follows (in thousands): For the Nine Months Ended September 30, 2023 2022 Operating cash flows for operating leases $ 2,109 $ 847 As of September 30, 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 2023 $ 686 $ 114 2024 2,810 454 2025 2,910 454 2026 2,485 399 2027 2,577 — Thereafter 19,721 — Total lease payments 31,189 1,421 Less: imputed interest ( 10,895 ) ( 242 ) Total lease liabilities $ 20,294 $ 1,179 Lease liabilities, current 1,193 345 Lease liabilities, non-current 19,101 834 Total lease liabilities $ 20,294 $ 1,179

Astellas Agreements

Astellas Agreements	9 Months Ended
	Sep. 30, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Astellas Agreements	Note 8—Research, Collaboration 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 Texas 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 investigational new drug application-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 months. 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 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 Southwestern. 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. Abeona CLN1 Agreements In August 2020, the Company entered into license and inventory purchase agreements (collectively, the “Abeona 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 Abeona 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 with Abeona (the “Abeona 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 Abeona License Agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the Abeona 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 condensed consolidated statements of cash flows for the nine months ended September 30, 2022. No additional milestone payments were made or triggered in connection with this agreement during the nine months ended September 30, 2023. 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 was 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 clinical trial application (“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 the Abeona Rett Agreement. The Company recorded $ 1.0 million within research and development expenses in the condensed consolidated statements of operations for the nine months ended September 30, 2022. The $ 1.0 million regulatory milestone fee was paid in July 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 condensed consolidated statements of operations for the nine months ended September 30, 2023. This milestone fee was paid in August 2023 and classified as an investing cash outflow in the condensed consolidated statements of cash flows for the nine months ended September 30, 2023. No additional milestone payments were made or triggered in connection with the Abeona Rett Agreement during the nine months ended September 30, 2023. 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 GAN. TSHA-120 is an intrathecally dosed AAV9 gene therapy currently being evaluated in a clinical trial for the treatment of GAN. The trial is being conducted by the National Institutes of Health (“NIH”) in close collaboration with a leading patient advocacy group focused on finding treatments and cures for GAN. TSHA-120 has received rare pediatric disease and orphan drug designations from the U.S. Food and Drug Administration for the treatment of GAN. The worldwide rights were acquired through a license agreement, effective March 29, 2021, between Hannah’s Hope Fund for Giant Axonal Neuropathy, Inc. (“HHF”) and the Company (the “GAN Agreement”). Under the terms of the GAN 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. No additional milestone payments were made or triggered in connection with the GAN Agreement during the nine months ended September 30, 2023. 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 condensed consolidated statements of operations since the acquired license does not have an alternative future use. 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 or triggered in connection with the CLN7 Agreement during the nine months ended September 30, 2023.
Astellas
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Astellas Agreements	Note 6—Astellas Agreements On October 21, 2022 (the “Effective Date”), the Company entered into the Option Agreement (the “Option Agreement”) with Audentes Therapeutics, Inc. (d/b/a Astellas Gene Therapy)(“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 Giant Axonal Neuropathy (“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 was 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 an upfront payment of $ 20.0 million (the “Upfront Payment”). 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 Astellas Securities Purchase Agreement (as defined below). Astellas Securities Purchase Agreement On October 21, 2022, the Company entered into a securities purchase agreement with Astellas (the “Astellas Securities Purchase Agreement” and, together with the Option Agreement, the “Astellas Transactions”), pursuant to which the Company agreed to issue and sell to Astellas in a private placement (the “Astellas Private Placement”), an aggregate of 7,266,342 shares (the “Astellas Private Placement Shares”), of its common stock, for aggregate gross proceeds of $ 30.0 million. The Astellas Private Placement closed on October 24, 2022. Pursuant to the Astellas Securities Purchase Agreement, in connection with the Astellas 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 Astellas Private Placement Shares. Accounting Treatment In October 2022, upon closing of the Astellas 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 Astellas 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 condensed 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 (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 three and six months ended June 30, 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, and the three months ended March 31, 2023. The cumulative impact of this change would have resulted in a $ 3.1 million decrease related to revenue previously recognized based on prior cost estimates. Subsequent changes during the three months ended September 30, 2023 to total estimated costs were not material, and did not have a material impact on cumulative revenue earned. The Company recognized revenue of $ 2.4 million and $ 9.5 million from Rett research and development activities for the three and nine months ended September 30, 2023, 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 three and nine months ended September 30, 2023. As of September 30, 2023, the Company recorded deferred revenue of $ 18.8 million within current liabilities and $ 3.0 million within long-term liabilities in the accompanying consolidated balance sheet. The Company will recognize revenues for these performance obligations as they are satisfied.

Loan with Silicon Valley Bank

Loan with Silicon Valley Bank	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Loan with Silicon Valley Bank	Note 7—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 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 and has also been fully accrued within non-current liabilities as of September 30, 2023. The debt discount was being accreted using the effective interest method over the term of the Term Loans within interest expense in the condensed 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. There were no financial covenants and no warrants associated with the Term Loan Agreement. The Term Loan Agreement contained various covenants that limited the Company’s ability to engage in specified types of transactions without the consent of the Lenders which included, 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. The Term Loan Agreement also contained customary representations and warranties, and also included customary events of default, including payment default, breach of covenants, change of control, and material adverse effects. The Company was in compliance with all covenants under the Term Loan Agreement as of September 30, 2023. Upon the occurrence of an event of default, a default interest rate of an additional 5 % per annum could have been applied to the outstanding loan balances, and the Lenders could have declared all outstanding obligations immediately due and payable and exercised all of its rights and remedies as set forth in the Term Loan Agreement and under applicable law. During the three and nine months ended September 30, 2023, the Company recognized interest expense related to the Term Loan of $ 1.4 mi llion and $ 4.2 million, respectively. During the three and nine months ended September 30, 2022, the Company recognized interest expense related to the Term Loan of $ 1.1 million and $ 2.5 million, respectively. Future principal debt payments on the loan payable as of September 30, 2023 are as follows (in thousands): Year Ending December 31, 2023 $ — 2024 6,667 2025 20,000 2026 13,333 Total principal payments 40,000 Unamortized debt discount ( 1,452 ) Term Loan, net $ 38,548 The Term Loan is considered long-term debt because it has been refinanced on a long-term basis, subsequent to September 30, 2023 but before the issuance of these condensed consolidated financial statements, using the proceeds of the Trinity Term Loan Agreement (as defined in Note 16). On March 10, 2023, Silicon Valley Bank, based in Santa Clara, California, was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation (“FDIC”) as receiver. On March 27, 2023, First Citizens Bank purchased the remaining assets, deposits and loans of Silicon Valley Bank. As a result, the portion of the Company’s term loans previously held by Silicon Valley Bank is now held by Silicon Valley Bank as a division of First-Citizen’s Bank & Trust Company. The remaining portion of the Company’s term loans are still held by SVB Capital, which is currently in bankruptcy proceedings.

Research, Collaboration and Lic

Research, Collaboration and License Agreements	9 Months Ended
	Sep. 30, 2023
Research Collaboration And License Agreements [Abstract]
Research, Collaboration and License Agreements	Note 8—Research, Collaboration 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 Texas 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 investigational new drug application-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 months. 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 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 Southwestern. 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. Abeona CLN1 Agreements In August 2020, the Company entered into license and inventory purchase agreements (collectively, the “Abeona 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 Abeona 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 with Abeona (the “Abeona 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 Abeona License Agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the Abeona 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 condensed consolidated statements of cash flows for the nine months ended September 30, 2022. No additional milestone payments were made or triggered in connection with this agreement during the nine months ended September 30, 2023. 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 was 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 clinical trial application (“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 the Abeona Rett Agreement. The Company recorded $ 1.0 million within research and development expenses in the condensed consolidated statements of operations for the nine months ended September 30, 2022. The $ 1.0 million regulatory milestone fee was paid in July 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 condensed consolidated statements of operations for the nine months ended September 30, 2023. This milestone fee was paid in August 2023 and classified as an investing cash outflow in the condensed consolidated statements of cash flows for the nine months ended September 30, 2023. No additional milestone payments were made or triggered in connection with the Abeona Rett Agreement during the nine months ended September 30, 2023. 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 GAN. TSHA-120 is an intrathecally dosed AAV9 gene therapy currently being evaluated in a clinical trial for the treatment of GAN. The trial is being conducted by the National Institutes of Health (“NIH”) in close collaboration with a leading patient advocacy group focused on finding treatments and cures for GAN. TSHA-120 has received rare pediatric disease and orphan drug designations from the U.S. Food and Drug Administration for the treatment of GAN. The worldwide rights were acquired through a license agreement, effective March 29, 2021, between Hannah’s Hope Fund for Giant Axonal Neuropathy, Inc. (“HHF”) and the Company (the “GAN Agreement”). Under the terms of the GAN 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. No additional milestone payments were made or triggered in connection with the GAN Agreement during the nine months ended September 30, 2023. 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 condensed consolidated statements of operations since the acquired license does not have an alternative future use. 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 or triggered in connection with the CLN7 Agreement during the nine months ended September 30, 2023.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 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 (“Existing 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 Existing Plan. The terms of the Existing 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 incre ased 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 September 30, 2023. The number of shares available for grant under the Company’s incentive plans were as follows: Existing New Plan Plan Total Available for grant - December 31, 2022 — 1,067,682 1,067,682 Plan adjustments and amendments ( 667,828 ) 3,828,203 3,160,375 Grants — ( 5,241,357 ) ( 5,241,357 ) Forfeitures 667,828 2,918,614 3,586,442 Available for grant - September 30, 2023 — 2,573,142 2,573,142 Stock Options For the three months ended September 30, 2023, 50,000 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per sh are of $ 0.50 . For the nine months ended September 30, 2023, 2,520,471 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $ 0.64 . The stoc k 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 three and nine months ended September 30, 2023 and 2022: Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Risk-free interest rate 4.22 % — 3.61 % 2.16 % Expected dividend yield — — — — Expected term (in years) 5.5 — 5.5 6.1 Expected volatility 81 % — 81 % 76 % The following table summarizes time-based vesting stock option activity, during the nine months ended September 30, 2023: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at December 31, 2022 6,158,078 $ 11.84 8.9 $ 62 Options granted 2,520,471 0.90 Options cancelled or forfeited ( 2,013,500 ) 10.88 Options expired ( 857,557 ) 22.26 Outstanding at September 30, 2023 5,807,492 $ 5.89 8.9 $ 6,851 Options exercisable at September 30, 2023 1,036,300 $ 18.48 7.5 $ 49 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 September 30, 2023, the total unrecognized compensation related to unvested time-based vesting stock option awards granted was $ 9.3 million, which the Company expects to recognize over a weighted-average period of approximately 2.1 y ears. No stock options were exercised during the period. 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 c onditions. The grant date fair value of these awards was not material. As of September 30, 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 with a weighted average grant date fair value per share of $ 0.50 . T he stock options have a 10-year contractual term and vest over 3.6 years if a combination of clinical, regulatory and financing performance conditions are achieved. As of September 30, 2023, no compensation expense was recorded related to the awards as achievement of the performance conditions was not considered probable. The following assumptions were used to estimate the fair value of performance and service-based stock options that were granted during the nine months ended September 30, 2023: For the nine months ended September 30, 2023 Risk-free interest rate 4.02 % Expected dividend yield — Expected term (in years) 6.0 Expected volatility 81 % 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 c ondition. The grant date fair value of the stock options that contain market-based vesting conditions was not material. As of September 30, 2023, 58,344 of the shares subject to the stock options that contain a market-based vesting condition were outstanding, and no options vested during the period. Restricted Stock Units In February 2023, the Company issued 81,236 RSUs to employees under the New Plan. T he 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 out standing 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 nine months ended September 30, 2023 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share 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 September 30, 2023 375,044 $ 6.63 As of September 30, 2023, the total unrecognized compensation related to unvested RSUs granted was $ 2.0 million which is expected to be amortized on a straight-line basis over a weighted-average period of approximately 0.9 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 September 30, 2023, 34,673 of the RSUs were unvested and still outstanding 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 nine months ended September 30, 2023 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share 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 September 30, 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 nine months ended September 30, 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 condensed consolidated statements of operations for the three and nine months ended September 30, 2023 and 2022 (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2023 2022 2023 2022 Research and development expense $ 705 $ 2,001 $ 1,524 $ 5,894 General and administrative expense 1,335 2,469 4,413 8,046 Total $ 2,040 $ 4,470 $ 5,937 $ 13,940

Warrants

Warrants	9 Months Ended
	Sep. 30, 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 Pre-Funded Warrants will only be exercisable upon receipt of stockholder approval of an increase in the authorized shares of the Company’s common stock (the “Stockholder Approval”), which the Company will first seek to obtain at a special meeting of stockholders scheduled to be held on November 15, 2023. If the Company does not obtain Stockholder Approval by December 31, 2023, it is required to pay liquidated damages of 2.0 % of the aggregate purchase price paid by each holder of Pre-Funded Warrants. For any subsequent failure to obtain Stockholder Approval, the Company is required to pay an additional 2.0 % as liquidated damages. 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 approximately $ 150.0 million, and after deducting placement agent commissions and offering expenses payable by the Company, net proceeds were approximately $ 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 the Pre-Funded Warrants do not meet the criteria for equity classification under the guidance of ASC 815 as the Company does 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 condensed consolidated statement 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 nine months ended September 30, 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 condensed consolidated statement of cash flows for the nine months ended September 30, 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 condensed 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 September 30, 2023 of $ 3.16 per common share. The Company recorded a fair value adjustment of $ 100.0 million in the condensed consolidated statements of operations for the three and nine months ended September 30, 2023. 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 condensed consolidated statement 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 $ 0.71 The fair value adjustment as of September 30, 2023 was $ 0.5 million 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 September 30, 2023, 200,000 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 September 30, 2023: Risk-free interest rate 3.46 % Expected dividend yield — Expected term (in years) 4.8 Expected volatility 81 % Market value of common stock $ 3.16 The following table summarizes the Company’s warrant liability (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 100,456 Balance at September 30, 2023 $ 140,534

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 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 all 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, shares issuable for little to no cash consideration should be included in the number of outstanding shares used to calculate basic earnings per share as long as all conditions necessary for exercise are met. As the Company does not have enough authorized shares to satisfy the warrants, the requirement that all conditions necessary for exercise are not met, and the Pre-Funded Warrants are not included in the calculation of basic net loss per share for the three and nine months ended September 30, 2023. The following table represents the calculation of basic and diluted net loss per common share (in thousands, except share and per share data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2023 2022 2023 2022 Net loss $ ( 117,087 ) $ ( 26,527 ) $ ( 159,307 ) $ ( 110,936 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 125,700,799 40,937,808 84,630,796 39,761,764 Net loss per common share, basic and diluted $ ( 0.93 ) $ ( 0.65 ) $ ( 1.88 ) $ ( 2.79 ) The following common stock equivalents outstanding as of September 30, 2023 and 2022 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: September 30, September 30, Unvested RSUs 409,717 1,257,844 Unvested RSAs — 149,614 Stock options 8,090,835 4,547,733 SSI Warrants 525,000 — Pre-Funded Warrants 44,250,978 — Total 53,276,530 5,955,191

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Note 12—Income Taxes 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. 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 evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. 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. As of September 30, 2023, there were no material changes to either the nature or the amounts of the uncertain tax positions previously determined for the year ended December 31, 2022.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 13—Commitments and Contingencies Litigation The Company is not a party to any material legal proceedings and is not aware of any pending or threatened claims. 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. Commitments In the normal course of business, the Company enters into contracts that contain a variety of indemnifications with its employees, licensors, suppliers and service providers. The Company’s maximum exposure under these arrangements is unknown at September 30, 2023. The Company does not anticipate recognizing any significant losses relating to these arrangements.

Strategic Reprioritization

Strategic Reprioritization	9 Months Ended
	Sep. 30, 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 condensed consolidated statements of operations for the nine months ended September 30, 2022, primarily within research and development 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 amount of accrued severance recorded as of September 30, 2023 is as follows (in thousands): As of September 30, 2023 Accrued severance balance as of December 31, 2022 $ 1,463 Severance recorded 2,691 Severance paid ( 3,162 ) Accrued severance balance as of September 30, 2023 $ 992

Retirement Plan

Retirement Plan	9 Months Ended
	Sep. 30, 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 contributed $ 0.1 million and $ 0.1 million to the 401(k) retirement savings plan for the three months ended September 30, 2023 and 2022, respectively. The Company contributed $ 0.3 million and $ 0.7 million to the 401(k) retirement savings plan for the nine months ended September 30, 2023 and 2022, respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2023
Subsequent Events [Abstract]
Subsequent Events	Note 16– Subsequent Events 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”). 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. 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.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“GAAP”) as determined by the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X and are consistent in all material respects with those included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022, filed with the SEC on March 28, 2023 (the “2022 Annual Report”). In the opinion of management, the unaudited condensed consolidated financial statements reflect all adjustments, which include only normal recurring adjustments necessary for the fair statement of the balances and results for the periods presented. The consolidated balance sheet as of December 31, 2022, is derived from audited financial statements, however, it does not include all of the information and footnotes required by GAAP for complete financial statements. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes in the Company’s 2022 Annual Report.
Principles of Consolidation	Principles of Consolidation The accompanying interim condensed consolidated financial statements include the accounts of Taysha and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
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 initial public offering ("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 fair value of the warrant liability, and the allocation of consideration received in connection with the Astellas Transactions (as defined below) at contract inception. 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.
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.
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 three months ended September 30, 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.
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. 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. The Company classifies the warrants as liabilities at their fair value and adjusts the 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 condensed consolidated statement of operations.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying condensed 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), 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. On December 31, 2022 , the Company adopted ASU 2016-02 using the modified retrospective approach and utilizing the effective date as its date of initial application. The Company has retrospectively changed its previously issued condensed consolidated financial statements as of September 30, 2022 as presented within the Company’s September 30, 2022 Quarterly Report on Form 10-Q to reflect the adoption of ASC 842 on January 1, 2022. The condensed consolidated financial statements for the three and nine months ended September 30, 2022 presented herein differ from the Company’s condensed consolidated financial statements included in the Company’s September 30, 2022 Quarterly Report on Form 10-Q as those condensed consolidated financial statements were prepared using the former accounting standard referred to as ASC Topic 840, Leases. 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 this 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 condensed 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 and on the condensed consolidated statements of operations and cash flows. The following table summarizes the effect of the adoption of ASC 842 on the condensed consolidated statement of operations and statement of cash flows for the nine months ended September 30, 2022 (in thousands): Pre ASC 842 Nine Months Ended ASC 842 Adjustments After ASC 842 Nine Months Ended Condensed Consolidated Statement of Operations Operating expenses: Research and development $ 77,308 $ 1,154 $ 78,462 Other income (expense): Interest expense ( 3,002 ) 509 ( 2,493 ) Net loss ( 110,291 ) ( 645 ) ( 110,936 ) Condensed Consolidated Statement of Cash Flows Adjustments to reconcile net loss to net cash used in operating activities: Depreciation expense $ 808 $ 2 $ 810 Non-cash lease expense — 1,031 1,031 Changes in operating assets and liabilities: Accrued expenses and other current liabilities ( 7,753 ) ( 823 ) ( 8,576 ) Cash flows from financing activities Other ( 1,144 ) 435 ( 709 ) Supplemental disclosure of noncash investing and financing activities: Right-of-use assets obtained in exchange for lease liabilities — 23,035 23,035 The following table summarizes the effect of the adoption of ASC 842 on the condensed consolidated statement of operations for the three months ended September 30, 2022 (in thousands): Pre ASC 842 Three Months Ended ASC 842 Adjustments After ASC 842 Three Months Ended Condensed Consolidated Statement of Operations Operating expenses: Research and development $ 16,391 $ 383 $ 16,774 Other income (expense): Interest expense ( 1,241 ) 163 ( 1,078 ) Net loss ( 26,307 ) ( 220 ) ( 26,527 )

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Summary of Effect of the Adoption of ASC 842 on Statement of Operations and Cash Flows	The following table summarizes the effect of the adoption of ASC 842 on the condensed consolidated statement of operations and statement of cash flows for the nine months ended September 30, 2022 (in thousands): Pre ASC 842 Nine Months Ended ASC 842 Adjustments After ASC 842 Nine Months Ended Condensed Consolidated Statement of Operations Operating expenses: Research and development $ 77,308 $ 1,154 $ 78,462 Other income (expense): Interest expense ( 3,002 ) 509 ( 2,493 ) Net loss ( 110,291 ) ( 645 ) ( 110,936 ) Condensed Consolidated Statement of Cash Flows Adjustments to reconcile net loss to net cash used in operating activities: Depreciation expense $ 808 $ 2 $ 810 Non-cash lease expense — 1,031 1,031 Changes in operating assets and liabilities: Accrued expenses and other current liabilities ( 7,753 ) ( 823 ) ( 8,576 ) Cash flows from financing activities Other ( 1,144 ) 435 ( 709 ) Supplemental disclosure of noncash investing and financing activities: Right-of-use assets obtained in exchange for lease liabilities — 23,035 23,035 The following table summarizes the effect of the adoption of ASC 842 on the condensed consolidated statement of operations for the three months ended September 30, 2022 (in thousands): Pre ASC 842 Three Months Ended ASC 842 Adjustments After ASC 842 Three Months Ended Condensed Consolidated Statement of Operations Operating expenses: Research and development $ 16,391 $ 383 $ 16,774 Other income (expense): Interest expense ( 1,241 ) 163 ( 1,078 ) Net loss ( 26,307 ) ( 220 ) ( 26,527 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 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): September 30, 2023 Total Level 1 Level 2 Level 3 Assets: Cash equivalents – money market funds $ 150,514 $ 150,514 $ — $ — $ 150,514 $ 150,514 $ — $ — Liabilities: Warrant liability SSI Warrants $ 701 $ — $ — $ 701 Pre-funded warrants 139,833 — 139,833 — Total liabilities $ 140,534 $ — $ 139,833 $ 701

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2023
Balance Sheet Related Disclosures [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): September 30, December 31, Prepaid research and development $ 2,672 $ 4,840 Prepaid clinical trial 1,392 2,119 Deferred offering costs 724 724 Prepaid insurance 337 388 Other 404 466 Total prepaid expenses and other current assets $ 5,529 $ 8,537
Schedule of Property Plant and Equipment Net	Property, plant and equipment, net consisted of the following (in thousands): September 30, December 31, Leasehold improvements $ 2,091 $ 2,091 Laboratory equipment 2,868 2,868 Computer equipment 1,115 1,115 Furniture and fixtures 864 898 Construction in progress 6,874 9,633 13,812 16,605 Accumulated depreciation ( 2,643 ) ( 1,642 ) Property, plant and equipment, net $ 11,169 $ 14,963
Schedule of Accrued Expense and Other Current Labilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, December 31, Accrued research and development $ 5,699 $ 8,190 Accrued compensation 2,745 2,519 Lease liabilities, current portion 1,538 1,521 Accrued clinical trial 1,359 1,473 Accrued severance 992 1,463 Accrued professional and consulting fees 579 390 Accrued property, plant and equipment 45 2,081 Other 681 650 Total accrued expenses and other current liabilities $ 13,638 $ 18,287

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 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 three and nine months ended September 30, 2023 and 2022 (in thousands): Three Months Ended September 30, For the Nine Months Ended September 30, 2023 2022 2023 2022 Operating lease cost $ 696 $ 794 $ 2,088 $ 2,079 Variable lease cost 243 229 729 617 Total lease cost $ 939 $ 1,023 $ 2,817 $ 2,696
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: September 30, 2023 December 31, 2022 Weighted average remaining lease term (in years) – Finance leases 3.13 3.88 Weighted average remaining lease term (in years) – Operating leases 10.97 11.45 Weighted average discount rate – Finance leases 10.52 % 10.51 % Weighted average discount rate – Operating leases 7.79 % 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 Nine Months Ended September 30, 2023 2022 Operating cash flows for operating leases $ 2,109 $ 847
Schedule of Future Minimum Commitments Under Company's Operating and Finance Leases	As of September 30, 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 2023 $ 686 $ 114 2024 2,810 454 2025 2,910 454 2026 2,485 399 2027 2,577 — Thereafter 19,721 — Total lease payments 31,189 1,421 Less: imputed interest ( 10,895 ) ( 242 ) Total lease liabilities $ 20,294 $ 1,179 Lease liabilities, current 1,193 345 Lease liabilities, non-current 19,101 834 Total lease liabilities $ 20,294 $ 1,179

Astellas Agreements (Tables)

Astellas Agreements (Tables)	9 Months Ended
	Sep. 30, 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 (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

Loan with Silicon Valley Bank (

Loan with Silicon Valley Bank (Tables)	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Schedule of Future Principal Debt Payments on Loan Payable	Future principal debt payments on the loan payable as of September 30, 2023 are as follows (in thousands): Year Ending December 31, 2023 $ — 2024 6,667 2025 20,000 2026 13,333 Total principal payments 40,000 Unamortized debt discount ( 1,452 ) Term Loan, net $ 38,548

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 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: Existing New Plan Plan Total Available for grant - December 31, 2022 — 1,067,682 1,067,682 Plan adjustments and amendments ( 667,828 ) 3,828,203 3,160,375 Grants — ( 5,241,357 ) ( 5,241,357 ) Forfeitures 667,828 2,918,614 3,586,442 Available for grant - September 30, 2023 — 2,573,142 2,573,142
Schedule of Restricted Stock Units Activity	The Company’s RSU activity for the nine months ended September 30, 2023 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share 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 September 30, 2023 375,044 $ 6.63 As of September 30, 2023, the total unrecognized compensation related to unvested RSUs granted was $ 2.0 million which is expected to be amortized on a straight-line basis over a weighted-average period of approximately 0.9 years.
Schedule of Restricted Stock Awards Activity	The Company’s RSA activity for the nine months ended September 30, 2023 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share 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 September 30, 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 condensed consolidated statements of operations for the three and nine months ended September 30, 2023 and 2022 (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2023 2022 2023 2022 Research and development expense $ 705 $ 2,001 $ 1,524 $ 5,894 General and administrative expense 1,335 2,469 4,413 8,046 Total $ 2,040 $ 4,470 $ 5,937 $ 13,940
Stock Options
Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options	The following weighted-average assumptions were used to estimate the fair value of time-based vesting stock options that were granted during the three and nine months ended September 30, 2023 and 2022: Three Months Ended September 30, Nine Months Ended September 30, 2023 2022 2023 2022 Risk-free interest rate 4.22 % — 3.61 % 2.16 % Expected dividend yield — — — — Expected term (in years) 5.5 — 5.5 6.1 Expected volatility 81 % — 81 % 76 %
Schedule of Stock Option Activity	The following table summarizes time-based vesting stock option activity, during the nine months ended September 30, 2023: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at December 31, 2022 6,158,078 $ 11.84 8.9 $ 62 Options granted 2,520,471 0.90 Options cancelled or forfeited ( 2,013,500 ) 10.88 Options expired ( 857,557 ) 22.26 Outstanding at September 30, 2023 5,807,492 $ 5.89 8.9 $ 6,851 Options exercisable at September 30, 2023 1,036,300 $ 18.48 7.5 $ 49
Performance Stock Options
Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options	The following assumptions were used to estimate the fair value of performance and service-based stock options that were granted during the nine months ended September 30, 2023: For the nine months ended September 30, 2023 Risk-free interest rate 4.02 % Expected dividend yield — Expected term (in years) 6.0 Expected volatility 81 %

Warrants (Tables)

Warrants (Tables)	9 Months Ended
	Sep. 30, 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 condensed consolidated balance sheet as follows (in thousands): Purchase Price Allocation PIPE Shares $ 110,127 Pre-Funded Warrants 39,826 Total $ 149,953
Schedule of Warrant Liability	The following table summarizes the Company’s warrant liability (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 100,456 Balance at September 30, 2023 $ 140,534
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 $ 0.71 The Company estimated the fair value of the SSI Warrant liability using the following assumptions as of September 30, 2023: Risk-free interest rate 3.46 % Expected dividend yield — Expected term (in years) 4.8 Expected volatility 81 % Market value of common stock $ 3.16

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 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 diluted net loss per common share (in thousands, except share and per share data): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2023 2022 2023 2022 Net loss $ ( 117,087 ) $ ( 26,527 ) $ ( 159,307 ) $ ( 110,936 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 125,700,799 40,937,808 84,630,796 39,761,764 Net loss per common share, basic and diluted $ ( 0.93 ) $ ( 0.65 ) $ ( 1.88 ) $ ( 2.79 )
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 September 30, 2023 and 2022 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: September 30, September 30, Unvested RSUs 409,717 1,257,844 Unvested RSAs — 149,614 Stock options 8,090,835 4,547,733 SSI Warrants 525,000 — Pre-Funded Warrants 44,250,978 — Total 53,276,530 5,955,191

Strategic Reprioritization (Tab

Strategic Reprioritization (Tables)	9 Months Ended
	Sep. 30, 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 amount of accrued severance recorded as of September 30, 2023 is as follows (in thousands): As of September 30, 2023 Accrued severance balance as of December 31, 2022 $ 1,463 Severance recorded 2,691 Severance paid ( 3,162 ) Accrued severance balance as of September 30, 2023 $ 992

Organization and Description _2

Organization and Description of Business Operations - Additional Information (Details) - USD ($)		1 Months Ended	9 Months Ended
	Oct. 05, 2021	Apr. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Organization and Description of Business Operations [Line Items]
Date of incorporation			Feb. 13, 2020
Net proceeds from issuance of common stock				$ 11,640,000
Accumulated deficit			$ (560,748,000)		$ (401,441,000)
Cash and cash equivalents			$ 164,278,000	$ 34,306,000	$ 87,880,000
Sales Agreement
Organization and Description of Business Operations [Line Items]
Common stock shares issued and sold			0
Number of shares issued		2,000,000
Net proceeds from issuance of common stock		$ 11,600,000
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 Policies

Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Significant Accounting Policies [Line Items]
Impairment of assets held for sale	$ 616	$ 616
Operating Lease, Right-of-Use Asset	9,852	9,852	$ 10,943
Operating Lease, Liability	20,294	20,294
Derecognized build to suite lease asset	26,300	26,300
Derecognized build to suit lease liablility	26,500	26,500
Deferred rent liabiilities and tenant improvement allowances	700	700
Accumulated Deficit	$ 200	$ 200
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Dec. 31, 2022	Dec. 31, 2022
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true	true
Operating Lease, Right-of-Use Asset	$ 18,400	$ 18,400
Operating Lease, Liability	$ 19,100	$ 19,100
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	false	false

Significant Accounting Polici_2

Significant Accounting Policies - Summary of Effect of the Adoption of ASC 842 on Statement of Operations and Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
Research and development	$ 11,791	$ 16,774	$ 44,096	$ 78,462
Other income (expense):
Interest expense	(1,471)	(1,078)	(4,285)	(2,493)
Net loss	(117,087)	(26,527)	(159,307)	(110,936)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	$ 300	$ 300	1,005	810
Non-cash lease expense			908	1,031
Changes in operating assets and liabilities:
Accrued expenses and other current liabilities				(8,576)
Cash flows from financing activities
Other			$ (253)	(709)
Supplemental disclosure of noncash investing and financing activities:
Right-of-use assets obtained in exchange for lease liabilities				$ 23,035
Accounting Standards Update [Extensible Enumeration]		Accounting Standards Update 2016-02 [Member]		Accounting Standards Update 2016-02 [Member]
Previously ASC 842
Operating expenses:
Research and development		$ 16,391		$ 77,308
Other income (expense):
Interest expense		(1,241)		(3,002)
Net loss		(26,307)		(110,291)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense				808
Changes in operating assets and liabilities:
Accrued expenses and other current liabilities				(7,753)
Cash flows from financing activities
Other				(1,144)
ASC 842 Adjustments
Operating expenses:
Research and development		383		1,154
Other income (expense):
Interest expense		163		509
Net loss		$ (220)		(645)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense				2
Non-cash lease expense				1,031
Changes in operating assets and liabilities:
Accrued expenses and other current liabilities				(823)
Cash flows from financing activities
Other				435
Supplemental disclosure of noncash investing and financing activities:
Right-of-use assets obtained in exchange for lease liabilities				$ 23,035

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	$ 150,514
SSI Warrants	701
Pre-funded warrants	139,833
Total liabilities	140,534
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents - money market funds	150,514
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	150,514
Level 1 | Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents - money market funds	150,514
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Pre-funded warrants	139,833
Total liabilities	139,833
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
SSI Warrants	701
Total liabilities	$ 701

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 2,672	$ 4,840
Prepaid clinical trial	1,392	2,119
Deferred offering costs	724	724
Prepaid insurance	337	388
Other	404	466
Total prepaid expenses and other current assets	$ 5,529	$ 8,537

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property, Plant and Equipment Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 13,812	$ 16,605
Accumulated depreciation	(2,643)	(1,642)
Property, plant and equipment, net	11,169	14,963
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	2,091	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	1,115	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	$ 6,874	$ 9,633

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Depreciation expense		$ 300	$ 300	$ 1,005	$ 810
Non-cash impairment charge	$ 36,400
Impairment charges to construction in process and finance lease right of use assets	$ 26,300
Property, plant and equipment, net		11,169		11,169		$ 14,963
Impairment loss on sale of assets		600		600
Assets Capitalized As Finance Leases
Property Plant And Equipment [Line Items]
Property, plant and equipment, net		$ 1,100		$ 1,100		$ 1,300

Balance Sheet Components - Sc_3

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 5,699	$ 8,190
Accrued compensation	2,745	2,519
Lease liabilities, current portion	1,538	1,521
Accrued clinical trial	1,359	1,473
Accrued severance	992	1,463
Accrued professional and consulting fees	579	390
Accrued property, plant and equipment	45	2,081
Other	681	650
Total accrued expenses and other current liabilities	$ 13,638	$ 18,287

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands				9 Months Ended
	Dec. 14, 2021 USD ($) ft²	Jan. 11, 2021 ft²	Dec. 17, 2020 ft²	Sep. 30, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Future minimum remianing lease payments | $				$ 31,189
Durham Lease
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility			187,500
Operating lease commencement date			Apr. 01, 2021
Operating lease term of contract			15 years 6 months
Lease, option to extend description				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
Pegasus Park L L C | Dallas Lease
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility		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.
Pegasus Park L L C | Dallas Lease Amendment
Lessee, Lease, Description [Line Items]
Number of operating lease landlord square feet manufacturing facility	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	40

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Lease, Cost [Abstract]
Operating lease cost	$ 696	$ 794	$ 2,088	$ 2,079
Variable lease cost	243	229	729	617
Total lease cost	$ 939	$ 1,023	$ 2,817	$ 2,696

Leases - Supplemental Informati

Leases - Supplemental Information Related to Remaining Lease Term and Discount Rate (Details)	Sep. 30, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted average remaining lease term (in years) - Finance leases	3 years 1 month 17 days	3 years 10 months 17 days
Weighted average remaining lease term (in years) - Operating leases	10 years 11 months 19 days	11 years 5 months 12 days
Weighted average discount rate - Finance leases	10.52%	10.51%
Weighted average discount rate - Operating leases	7.79%	7.72%

Leases - Schedule of Supplement

Leases - Schedule of Supplemental Cash Flow Information Related to Operating Leases (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash Flow, Operating Activities, Lessee [Abstract]
Operating cash flows for operating leases	$ 2,109	$ 847

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Commitments Under Company's Operating and Finance Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Operating Lease
2023	$ 686
2024	2,810
2025	2,910
2026	2,485
2027	2,577
Thereafter	19,721
Total lease payments	31,189
Less: imputed interest	(10,895)
Total lease liabilities	20,294
Operating lease liabilities, current	$ 1,193
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Operating lease liabilities, non-current	$ 19,101	$ 20,440
Total lease liabilities	20,294
Finance Lease
2023	114
2024	454
2025	454
2026	399
Total lease payments	1,421
Less: imputed interest	(242)
Total lease liabilities	1,179
Finance lease liabilities, current	$ 345
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Accrued Liabilities and Other Liabilities
Finance, lease liabilities, non-current	$ 834
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Noncurrent
Total lease liabilities	$ 1,179
Finance Lease, Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities

Astellas Agreements - Additiona

Astellas Agreements - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended
	Oct. 21, 2022	Oct. 31, 2022	Mar. 31, 2021	Sep. 30, 2023	Jun. 30, 2023	Jun. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock, shares issued				186,960,193			186,960,193	63,207,507
Probability of option exercise		50%
Decrease in revenue previously recognized					$ 3,100	$ 3,100
Revenues				$ 4,746			$ 11,847
Deferred revenue recorded within current liabilities				18,759			18,759	$ 33,557
Deferred revenue recorded within long-term liabilities				2,951			2,951
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				2,400			9,500
Option Agreement for GAN
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues				$ 2,300			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 | Astellas Securities Purchase Agreement | Astellas 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
Transaction price		$ 16,100
Difference of market value paid		$ 30,000
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 Agreements - Summary o

Astellas Agreements - Summary of Allocation for Transaction Price to the Three Performance Obligations (Details) - Astellas - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Oct. 31, 2022	Sep. 30, 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

Loan with Silicon Valley Bank -

Loan with Silicon Valley Bank - Additional Information (Details)		3 Months Ended		9 Months Ended
	Aug. 12, 2021 USD ($) Program	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Instrument [Line Items]
Debt instrument, maturity date	Aug. 01, 2026
Percentage of interest rate	7%
Percentage of prepayment of facility	7.50%
Warrants associated with loan facility	$ 0
Exit fee recorded as debt discount		$ 3,000,000		$ 3,000,000
Percentage of annual default interest rate	5%
Interest expense related to term loan		1,400,000	$ 1,100,000	4,200,000	$ 2,500,000
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
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		$ 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		$ 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%

Loan with Silicon Valley Bank_2

Loan with Silicon Valley Bank - Schedule of Future Principal Debt Payments on Loan Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
2024	$ 6,667
2025	20,000
2026	13,333
Total principal payments	40,000
Unamortized debt discount	(1,452)
Term Loan, net	$ 38,548	$ 37,967

Research, Collaboration and L_2

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

1 Months Ended

3 Months Ended

9 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 Product

Sep. 30, 2023 USD ($) shares

Sep. 30, 2022 USD ($)

Sep. 30, 2023 USD ($) shares

Sep. 30, 2022 USD ($)

Dec. 31, 2021 USD ($)

Dec. 31, 2020 USD ($)

Dec. 31, 2022 shares

Oct. 29, 2020 USD ($)

Nov. 30, 2019 shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Common stock, shares issued | shares

186,960,193

186,960,193

63,207,507

Research and development

$ 11,791,000

$ 16,774,000

$ 44,096,000

$ 78,462,000

TSHA-120

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

Upfront payment

$ 5,500,000

Clinical, regulatory and commercial milestones to be received

$ 19,300,000

License Agreement for CLN7

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

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

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%

Abeona CLN1 Agreements

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

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 | Rett Research and Development Activities

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

Research and development

$ 3,500,000

$ 1,000,000

Payment of one-time upfront license fee

$ 3,000,000

Regulatory milestone fee paid

$ 1,000,000

Abeona | Maximum | Rett Research and Development Activities

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

3 Months Ended

9 Months Ended

Sep. 16, 2020

Jul. 01, 2020

May 31, 2023

Feb. 28, 2023

Feb. 28, 2022

Sep. 30, 2023

Mar. 31, 2023

Sep. 30, 2022

Sep. 30, 2023

Sep. 30, 2022

Jan. 01, 2023

Dec. 31, 2022

Jan. 01, 2022

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

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

Stock-based compensation expense

$ 2,040,000

$ 4,470,000

$ 5,937,000

$ 13,940,000

Employee Stock Purchase Plan (ESPP)

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

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%

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.

Number of shares of common stock issued under ESPP

0

141,393

Employee Stock Purchase Plan (ESPP) | Maximum

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

Number of shares authorized for issuance

362,000

Restricted Stock Units

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

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

556,989

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

10 months 24 days

Share-based payment award, RSU/RSA granted

332,532

Outstsanding performance and market-based RSU's

375,044

375,044

1,257,844

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

$ 2,000,000

$ 2,000,000

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

$ 1.06

Stock Options

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

Share-based payment award, options granted

2,520,471

Share-based payment award, options granted, exercise price per share

$ 0.9

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

$ 9,300,000

$ 9,300,000

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

2 years 1 month 6 days

Stock options were exercised during the period

$ 0

Outstanding performance and market-based options

5,807,492

5,807,492

6,158,078

Restricted Stock Awards

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

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

64,120

Outstsanding performance and market-based RSU's

85,494

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

$ 5.28

Common Stock

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

Number of shares of common stock issued under ESPP

32,400

73,073

68,320

73,073

2020 Equity Incentive 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

251,296

Award requisite service vesting period

3 years

New Plan

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

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%

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.

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 | Performance and Market-based Restricted Stock Units

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

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

34,671

Share-based payment award, RSU/RSA granted

81,233

Outstsanding performance and market-based RSU's

34,673

34,673

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

50,000

2,520,471

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

$ 0.5

$ 0.64

New Plan | Stock Options | Maximum

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

Award vesting period

4 years

New Plan | Stock Options | Minimum

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

Award vesting period

1 year

New Plan | Performance 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

2,166,653

70,235

Award vesting period

3 years 7 months 6 days

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

$ 0.5

Stock options were exercised during the period

$ 0

Stock-based compensation expense

$ 0

Outstanding performance and market-based options

58,346

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

Outstanding performance and market-based options

58,344

58,344

Market-based Stock Options vested during period

0

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Share Based Compensation Available for Grant under Incentive Plans (Details)	9 Months Ended
	Sep. 30, 2023 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Available for grant beginning of period	1,067,682
Plan adjustments and amendments	3,160,375
Grants	(5,241,357)
Forfeitures	3,586,442
Available for grant ending of period	2,573,142
Existing 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
Plan adjustments and amendments	3,828,203
Grants	(5,241,357)
Forfeitures	2,918,614
Available for grant ending of period	2,573,142

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value Time Based Vesting of Stock Options, Performance and Service-based Stock Options (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	4.22%	3.61%	2.16%
Expected term in years	5 years 6 months	5 years 6 months	6 years 1 month 6 days
Expected volatility	81%	81%	76%
Performance Stock 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%

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance | shares	6,158,078
Options granted, Stock Options | shares	2,520,471
Options cancelled or forfeited, Stock Options | shares	(2,013,500)
Options expired, Stock Options | shares	(857,557)
Outstanding. Stock Options, Ending Balance | shares	5,807,492	6,158,078
Options exercisable at September 30, 2023, Stock Options | shares	1,036,300
Outstanding, Weighted Average Exercise Price, Beginning balance | $ / shares	$ 11.84
Options granted, Weighted Average Exercise Price | $ / shares	0.9
Options cancelled or forfeited, Weighted Average Exercise Price | $ / shares	10.88
Options expired, Weighted Average Exercise Price | $ / shares	22.26
Outstanding, Weighted Average Exercise Price, Ending balance | $ / shares	5.89	$ 11.84
Options exercisable at September 30, 2023, Weighted Average Exercise Price | $ / shares	$ 18.48
Outstanding, Weighted Average Remaining Contractual Life	8 years 10 months 24 days	8 years 10 months 24 days
Options exercisable at September 30, 2023, Weighted Average Remaining Contractual Life	7 years 6 months
Outstanding, Aggregate Intrinsic Value, Beginning Balance | $	$ 62
Outstanding, Aggregate Intrinsic Value, Ending Balance | $	6,851	$ 62
Options exercisable at Sepember 30, 2023, Aggregate Intrinsic Value | $	$ 49

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2023 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance | shares	1,257,844
Restricted units/stock granted, Number of Shares | shares	332,532
Vested, Number of Shares | shares	(556,989)
Cancelled or forfeited, Number of Shares | shares	(658,343)
Nonvested, Number of Shares, Ending Balance | shares	375,044
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance | $ / shares	$ 6.52
Restricted units/stock granted, Weighted Average Grant Date Fair Value per Share | $ / shares	1.06
Vested, Weighted Average Grant Date Fair Value per Share | $ / shares	4.78
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share | $ / shares	5.18
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance | $ / shares	$ 6.63

Stock-Based Compensation - Sc_5

Stock-Based Compensation - Schedule of Restricted Stock Awards Activity (Details) - Restricted Stock Awards - $ / shares		9 Months Ended
	Jul. 01, 2020	Sep. 30, 2023
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance		85,494
Vested, Number of Shares		(64,120)
Cancelled or forfeited, Number of Shares		(21,374)
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance		$ 5.28
Restricted units/stock granted, Weighted Average Grant Date Fair Value per Share	$ 5.28
Vested, Weighted Average Grant Date Fair Value per Share		5.28
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share		$ 5.28

Stock-Based Compensation - Sc_6

Stock-Based Compensation - Schedule of Total Stock-Based Compensation Expense for Stock Options, ESPP, RSAs and RSUs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,040	$ 4,470	$ 5,937	$ 13,940
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	705	2,001	1,524	5,894
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,335	$ 2,469	$ 4,413	$ 8,046

Warrants - Additional Informati

Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 16, 2023	Aug. 14, 2023	Apr. 05, 2023	Apr. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Class of Warrant or Right [Line Items]
Common stock, shares issued					186,960,193		186,960,193		63,207,507
Common stock, par value per share					$ 0.00001		$ 0.00001		$ 0.00001
General and administrative					$ 8,589	$ 8,683	$ 23,328	$ 30,019
Warrant liability fair value adjustment							100,456
Gross proceeds from issuance of common stock								$ 11,640
Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Warrant liability fair value adjustment					$ 100,000		$ 100,000
Common Stock
Class of Warrant or Right [Line Items]
Share price					$ 3.16		$ 3.16
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
Payments to investors as liquidated damages		2%
Payments to investors as additional liquidated damages percentage		2%
SSI Warrants
Class of Warrant or Right [Line Items]
Issuance of fair value warrant			$ 300
Class of warrant or right vested and exercisable shares					200,000		200,000
Warrant liability fair value adjustment							$ 500
Warrants Exercised					0		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)	Sep. 30, 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 Warrant

Warrants - Schedule of Warrant Liability (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Class of Warrant or Right [Line Items]
Change in fair value	$ 100,456
Balance at September 30, 2023	140,534
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

Warrants - Schedule Of Assumpti

Warrants - Schedule Of Assumptions Used To Estimate Fair Value Of Warrants (Details)	Sep. 30, 2023 USD ($) yr	Apr. 05, 2023 USD ($) yr
Risk-free interest rate
Class of Warrant or Right [Line Items]
Warrants, measurement input	3.46	3.46
Expected term (in years)
Class of Warrant or Right [Line Items]
Warrants, measurement input | yr	4.8	5.2
Expected volatility
Class of Warrant or Right [Line Items]
Warrants, measurement input	81	81
Market value of common stock
Class of Warrant or Right [Line Items]
Warrants, measurement input | $	3.16	0.71

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	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net loss	$ (117,087)	$ (26,527)	$ (159,307)	$ (110,936)
Weighted average common shares outstanding, basic	125,700,799	40,937,808	84,630,796	39,761,764
Weighted average common shares outstanding, diluted	125,700,799	40,937,808	84,630,796	39,761,764
Net loss per common share, basic	$ (0.93)	$ (0.65)	$ (1.88)	$ (2.79)
Net loss per common share, diluted	$ (0.93)	$ (0.65)	$ (1.88)	$ (2.79)

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	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	53,276,530	5,955,191
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	409,717	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		149,614
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	8,090,835	4,547,733
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	525,000
Pre-Funded Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	44,250,978

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	9 Months Ended
	Sep. 30, 2023 USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0

Strategic Reprioritization - Ad

Strategic Reprioritization - Additional Information (Details) - Exit and Disposal Activities - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022
Restructuring Cost And Reserve [Line Items]
Percentage of headcount reduced		35%
Severance and termination-related costs	$ 2.7		$ 2.6

Strategic Reprioritization - Su

Strategic Reprioritization - Summary of Accrued Severance Activity Recorded (Details) - Employee Severance $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Accrued severance balance as of December 31, 2022	$ 1,463
Severance recorded	2,691
Severance paid	(3,162)
Accrued severance balance as of September 30, 2023	$ 992

Retirement Plan - Additional In

Retirement Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items]
Contribution to retirement savings plan	$ 0.1	$ 0.1	$ 0.3	$ 0.7

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)	Nov. 13, 2023	Aug. 12, 2021
Subsequent Event [Line Items]
Percentage of interest rate		7%
Debt instrument, maturity date		Aug. 01, 2026
Warrants associated with loan facility		$ 0
Percentage of annual default interest rate		5%
Prime Rate
Subsequent Event [Line Items]
Debt instrument, basis spread on variable rate		3.75%
Subsequent Event | Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders
Subsequent Event [Line Items]
Aggregate principal amount	$ 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”).
Percentage of interest rate	12.75%
Interest rate period	36 months
Interest rate extension period	48 months
Debt instrument, maturity date	Nov. 13, 2028
Commitment fee percentage	1%
End of term payment percentage	5%
Warrants associated with loan facility	$ 0
Percentage of annual default interest rate	5%
Subsequent Event | Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | Closing Date through November 13, 2024
Subsequent Event [Line Items]
Percentage of prepayment premium	3%
Subsequent Event | Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | November 13, 2024 through November 13, 2025
Subsequent Event [Line Items]
Percentage of prepayment premium	2%
Subsequent Event | Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | November 13, 2025 through, but excluding, the Maturity Date
Subsequent Event [Line Items]
Percentage of prepayment premium	1%
Subsequent Event | Trinity Term Loan Agreement | Trinity Term Loans | Trinity Lenders | Prime Rate
Subsequent Event [Line Items]
Debt instrument, basis spread on variable rate	4.50%