Taysha Gene Therapies (TSHA) 10-Q 8 Nov 22 2022 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2022	Nov. 08, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2022
Document Fiscal Year Focus	2022
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		62,442,281
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, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 34,306	$ 149,103
Prepaid expenses and other current assets	8,696	10,499
Total current assets	43,002	159,602
Restricted cash	2,637	2,637
Deferred lease asset	630	667
Property, plant and equipment, net	63,954	50,610
Other non-current assets	1,245	440
Total assets	111,468	213,956
Current liabilities
Accounts payable	15,251	21,763
Accrued expenses and other current liabilities	17,888	29,983
Total current liabilities	33,139	51,746
Build-to-suit lease liability	25,496	25,900
Term loan, net	37,773	37,192
Other non-current liabilities	3,934	3,735
Total liabilities	100,342	118,573
Commitments and contingencies - Note 9
Stockholders' equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of September 30, 2022 and December 31, 2021
Common stock, $0.00001 par value per share; 200,000,000 shares authorized and 41,175,939 and 38,473,945 issued and outstanding as of September 30, 2022 and December 31, 2021, respectively	1
Additional paid-in capital	357,065	331,032
Accumulated deficit	(345,940)	(235,649)
Total stockholders’ equity	11,126	95,383
Total liabilities and stockholders' equity	$ 111,468	$ 213,956

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2022	Dec. 31, 2021
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	41,175,939	38,473,945
Common stock, shares outstanding	41,175,939	38,473,945

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Operating expenses:
Research and development	$ 16,391	$ 39,528	$ 77,308	$ 94,025
General and administrative	8,683	11,153	30,019	29,518
Total operating expenses	25,074	50,681	107,327	123,543
Loss from operations	(25,074)	(50,681)	(107,327)	(123,543)
Other income (expense):
Interest income	9	37	50	143
Interest expense	(1,241)	(543)	(3,002)	(737)
Other expense	(1)		(12)
Total other expense, net	(1,233)	(506)	(2,964)	(594)
Net loss	$ (26,307)	$ (51,187)	$ (110,291)	$ (124,137)
Net loss per common share, basic	$ (0.64)	$ (1.35)	$ (2.77)	$ (3.31)
Net loss per common share, diluted	$ (0.64)	$ (1.35)	$ (2.77)	$ (3.31)
Weighted average common shares outstanding, basic	40,937,808	38,003,954	39,761,764	37,495,537
Weighted average common shares outstanding, diluted	40,937,808	38,003,954	39,761,764	37,495,537

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2020	$ 251,302		$ 312,428	$ (61,126)
Balance, shares at Dec. 31, 2020		37,761,435
Stock-based compensation	13,229		13,229
Issuance of common stock upon vesting and settlement of restricted stock units		712,510
Net loss	(124,137)			(124,137)
Balance at Sep. 30, 2021	140,394		325,657	(185,263)
Balance, shares at Sep. 30, 2021		38,473,945
Balance at Jun. 30, 2021	186,495		320,571	(134,076)
Balance, shares at Jun. 30, 2021		38,391,165
Stock-based compensation	5,086		5,086
Issuance of common stock upon vesting and settlement of restricted stock units		82,780
Net loss	(51,187)			(51,187)
Balance at Sep. 30, 2021	140,394		325,657	(185,263)
Balance, shares at Sep. 30, 2021		38,473,945
Balance at Dec. 31, 2021	$ 95,383		331,032	(235,649)
Balance, shares at Dec. 31, 2021	38,473,945	38,473,945
Stock-based compensation	$ 14,172		14,172
Issuance of common stock, net of sales commissions and other offering costs	11,609	$ 1	11,608
Issuance of common stock, net of sales commissions and other offering costs, shares		2,000,000
Issuance of common stock upon vesting and settlement of restricted stock units		628,921
Issuance of common stock under ESPP	253		253
Issuance of common stock under ESPP, Shares		73,073
Net loss	(110,291)			(110,291)
Balance at Sep. 30, 2022	$ 11,126	$ 1	357,065	(345,940)
Balance, shares at Sep. 30, 2022	41,175,939	41,175,939
Balance at Jun. 30, 2022	$ 32,710	$ 1	352,342	(319,633)
Balance, shares at Jun. 30, 2022		41,020,086
Stock-based compensation	4,470		4,470
Issuance of common stock upon vesting and settlement of restricted stock units		82,780
Issuance of common stock under ESPP	253		253
Issuance of common stock under ESPP, Shares		73,073
Net loss	(26,307)			(26,307)
Balance at Sep. 30, 2022	$ 11,126	$ 1	$ 357,065	$ (345,940)
Balance, shares at Sep. 30, 2022	41,175,939	41,175,939

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) $ in Thousands	9 Months Ended
	Sep. 30, 2022 USD ($)
Statement Of Stockholders Equity [Abstract]
Payment of sales commissions and other offering costs	$ 392

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities
Net loss	$ (110,291)	$ (124,137)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	808	283
Research and development license expense	1,250	6,750
Stock-based compensation	13,940	13,229
Other	616	450
Changes in operating assets and liabilities:
Prepaid expenses and other assets	1,980	(1,530)
Accounts payable	(3,217)	16,000
Accrued expenses and other liabilities	(7,753)	12,179
Due to related party		(8)
Net cash used in operating activities	(102,667)	(76,784)
Cash flows from investing activities
Purchase of research and development license	(4,250)	(6,000)
Purchase of property, plant and equipment	(18,310)	(7,034)
Net cash used in investing activities	(22,560)	(13,034)
Cash flows from financing activities
Proceeds from Term Loan, net		29,978
Proceeds from issuance of common stock, net of sales commissions	11,640
Payment of shelf registration costs	(319)
Proceeds from common stock issuances under ESPP	253
Other	(1,144)
Net cash provided by financing activities	10,430	29,978
Net decrease in cash, cash equivalents and restricted cash	(114,797)	(59,840)
Cash, cash equivalents and restricted cash at the beginning of the period	151,740	251,253
Cash, cash equivalents and restricted cash at the end of the period	36,943	191,413
Cash and cash equivalents	34,306	188,785
Restricted cash	2,637	2,628
Supplemental disclosure of cash flow information:
Cash paid for interest	1,758	110
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	3,366	6,658
Acquisition of property, plant and equipment funded by landlord		606
Deferred offering costs not yet paid	$ 40	204
Purchase of research and development license not yet paid		750
Build-to-suit lease liability		$ 26,607

Organization and Description of

Organization and Description of Business Operations	9 Months Ended
	Sep. 30, 2022
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business Operations	Note 1—Organization and Description of Business Operations Taysha Gene Therapies, Inc. (the “Company” or “Taysha”) was originally formed under the laws of the State of Texas on September 20, 2019 (“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. 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, 2022. 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 In October 2022, the Company entered into a securities purchase agreement (the “Securities Purchase Agreement”) and an option agreement (the “Option Agreement,” together with the Securities Purchase Agreement the “Astellas Transactions”) with Audentes Therapeutics, Inc. (d/b/a Astellas Gene Therapy) (“Astellas”), pursuant to which the Company agreed to issue and sell 7,266,342 shares of its common stock for aggregate proceeds of $30.0 million and received a one-time payment in the amount of $20.0 million (the “Upfront Payment”), respectively, for total gross proceeds of $50.0 million. Also in October 2022, the Company entered into an underwriting agreement (the “Underwriting Agreement”) with Goldman Sachs & Co. LLC (the "Underwriter”) to issue and sell 14,000,000 shares of common stock for at a price of $2.00 per share. The Underwriter has an option, for a period of 30 days, to purchase up to an additional 2,100,000 shares of the Company’s common stock at a price of $1.88 per share. The net proceeds are expected be approximately $25.6 million, or approximately $29.6 million if the Underwriter exercises in full its option to purchase additional shares of Common Stock, in each case after deducting underwriting discounts and commissions and estimated offering expenses. See Note 12 for additional information. The Company has concluded that these additional cash flows provide the Company with 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, 2022, the Company had an accumulated deficit of $345.9 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. The Company will need to obtain additional financing in order to complete clinical studies and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be on terms acceptable to the Company.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2022
Accounting Policies [Abstract]
Summary of 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, 2021, filed with the Securities and Exchange Commission ("SEC") on March 31, 2022 (the “2021 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, 2021 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 2021 Annual Report. Principles of Consolidation The accompanying interim condensed consolidated financial statements include the accounts of Taysha and its inactive wholly owned U.S. subsidiaries as well as t wo foreign subsidiaries incorporated during 2021 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 Company’s initial public offering (“IPO”) in September 2020 (as an input into stock-based compensation), and estimating preclinical manufacturing accruals and accrued or prepaid research and development expenses. 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 2021 Annual Report. Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying condensed consolidated statements of operations. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) The new standard requires the use of one of the following two approaches, either (1) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (2) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. The Company commenced its implementation efforts of this new accounting standard during the quarter and concluded that the cumulative impact of the adoption will be recorded as an adjustment to accumulated deficit as of January 1, 2022, and prior periods will not be adjusted. Upon adoption, the Company expects to recognize right-of-use assets and lease liabilities in the consolidated balance sheet related to operating leases. Additionally, upon adoption, the Company expects to derecognize the build-to-suit asset and obligation (see Note 9) related to the construction-in-progress as the Company does not control the building during the construction period.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2022
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Note 3—Balance Sheet Components Prepaid expenses and other current assets consisted of the following (in thousands): September 30, 2022 December 31, 2021 Prepaid research and development $ 5,182 $ 5,218 Prepaid clinical trial 2,284 3,298 Deferred offering costs 722 545 Prepaid insurance 74 148 Prepaid bonus 54 427 Other 380 863 Total prepaid expenses and other current assets $ 8,696 $ 10,499 Property, plant and equipment, net consisted of the following (in thousands): September 30, 2022 December 31, 2021 Leasehold improvements $ 2,091 $ 2,067 Laboratory equipment 2,069 1,095 Computer equipment 1,127 1,098 Furniture and fixtures 897 845 Construction in progress 59,058 46,004 65,242 51,109 Accumulated depreciation (1,288 ) (499 ) Property, plant and equipment, net $ 63,954 $ 50,610 Included in construction in progress at September 30, 2022 was $59.0 million of costs associated with the Build-to-Suit lease (see Note 9), which includes $3.1 million of capitalized payroll and payroll-related costs. Depreciation expense was $0.3 million and $0.8 million for the three and nine months ended September 30, 2022, respectively. Depreciation expense was $0.2 million and $0.3 million for the three and nine months ended September 30, 2021, respectively. Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, 2022 December 31, 2021 Accrued research and development $ 8,027 $ 11,895 Accrued compensation 4,914 7,703 Accrued license fees — 3,500 Accrued property, plant and equipment 1,655 2,644 Accrued clinical trial 889 1,659 Accrued professional and consulting fees 823 1,091 Other 1,580 1,491 Total accrued expenses and other current liabilities $ 17,888 $ 29,983

Loan with Silicon Valley Bank

Loan with Silicon Valley Bank	9 Months Ended
	Sep. 30, 2022
Debt Disclosure [Abstract]
Loan with Silicon Valley Bank	Note 4—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 provides 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 additional $ 20.0 million tranche prior to its expiration on September 30, 2022 . The interest rate applicable to the Term Loans is the greater of (a) the WSJ Prime Rate plus 3.75% or (b) 7.00% per annum. The Term Loans are interest only from the Closing Date through August 31, 2024, after which the Company is required to pay equal monthly installments of principal through August 1, 2026, the maturity date. The Term Loans may be prepaid in full through August 12, 2023 with payment of a 1.00% prepayment premium, after which they may 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”) will be 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, 2022. The debt discount is 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 are 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 are no financial covenants and no warrants associated with the Term Loan Agreement. The Term Loan Agreement contains various covenants that limit the Company’s ability to engage in specified types of transactions without the consent of the 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 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. The Company was in compliance with all covenants under the Term Loan Agreement as of September 30, 2022. 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 Lenders may declare all outstanding obligations immediately due and payable and exercise all of its rights and remedies as set forth in the Term Loan Agreement and under applicable law. During the nine months ended September 30, 2022, the Company recognized interest expense related to the Term Loan of $2.5 million. Future principal debt payments on the loan payable as of September 30, 2022 are as follows (in thousands): Year Ending December 31, 2022 — 2023 — 2024 6,667 2025 20,000 2026 13,333 Total principal payments 40,000 Unamortized debt discount (2,227 ) Term Loan, net $ 37,773

Research, Collaboration and Lic

Research, Collaboration and License Agreements	9 Months Ended
	Sep. 30, 2022
Research Collaboration And License Agreements [Abstract]
Research, Collaboration and License Agreements	Note 5—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 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. As additional consideration, UT Southwestern was entitled to receive additional shares if their holdings fell below 10% on a fully-diluted basis before or as a result of the completion of a qualified financing. In March 2020, following the initial closing of the Series A convertible preferred stock agreement, which met the definition of such qualified financing, the anti-dilution feature expired and no additional shares were issued. UT Southwestern no longer owns such shares of common stock as of January 2022. The Company does not have any future milestone or royalty obligations to UT Southwestern under the UT Southwestern Agreement other than costs related to maintenance of patents. Queen’s Agreement On February 21, 2020, the Company entered into a license agreement with Queen’s (the “Queen’s Agreement”) to obtain the exclusive perpetual, royalty-bearing license, with the right to sublicense through multiple tiers, under certain patent rights and know-how of Queen’s, including certain improvements to such patent rights and know-how, to develop products in any field which use one or more valid claims of the patents licensed under the Queen’s Agreement (the “Licensed Patents”), or the technology, information and intellectual property related to the patents licensed under the Queen’s Agreement (together with the Licensed Patents, the “Licensed Products”), and to make, have made, use, sell, offer for sale, import and export Licensed Products and otherwise exploit such patents and know-how for use in certain specified indications. In exchange for the rights granted to the Company, the Company made a cash payment of $3.0 million in April 2020 which was recorded within 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 make aggregate cash payments of up to $10.0 million upon the completion of a combination of regulatory milestones and up to $10.0 million upon the completion of a combination of commercial milestones. In further consideration of the rights granted, beginning with the Company’s first commercial sale of the Licensed Products, the Company will also pay an annual earned royalty in the low single digits on net sales of Licensed Products, subject to certain customary reductions, and a percentage of non-royalty sublicensing revenue ranging in the low double digits. Royalties are payable, on a Licensed Products-by-Licensed Products and a country-by-country basis, until expiration of the last valid claim of a Licensed Patent covering such Licensed Products in such country and the expiration of any regulatory exclusivity for such Licensed Products in such country. No additional milestone payments were made in connection with the Queen’s Agreement during the nine months ended September 30, 2022. 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, the Company’s Clinical Trial Application (“CTA”) filing for TSHA-118 for the treatment of CLN1 disease was approved by Health Canada and therefore triggered a regulatory milestone payment in connection with this agreement. 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. 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 CTA filing for TSHA-102 for the treatment of Rett Syndrome was approved by Health Canada and therefore triggered a regulatory milestone payment in connection with this agreement. T he 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 and classified as an investing cash outflow in the condensed consolidated statements of cash flows for the nine months ended September 30, 2022 . Acquisition of Worldwide Rights for TSHA-120 for the treatment of GAN In March 2021, the Company acquired the exclusive worldwide rights to a clinical-stage AAV9 gene therapy program, now known as TSHA-120, for the treatment of Giant Axonal Neuropathy (“GAN”). 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. In exchange for the license rights, the Company recorded an aggregate of $5.5 million within research and development expenses in the condensed consolidated statements of operations for the nine months ended September 30, 2021, since the acquired license does not have an alternative future use. This license fee was paid in April 2021 and has been classified as an investing outflow in the condensed consolidated statements of cash flows for the nine months ended September 30, 2021 . No additional milestone payments were made in connection with the GAN Agreement during the nine months ended September 30, 2022. License Agreement for CLN7 In March 2022, the Company entered into a license agreement with UT Southwestern (the “CLN7 Agreement”) pursuant to which the Company obtained an exclusive worldwide, royalty-bearing license with right to grant sublicenses to develop, manufacture, use, and commercialize licensed products for gene therapy for CLN7, a form of Batten Disease. In connection with the CLN7 Agreement, the Company paid a one-time upfront license fee of $0.3 million. The Company recorded the upfront license fee in research and development expense in the condensed consolidated statements of operations since the acquired license does not have an alternative future use. The upfront license fee was classified as an investing cash outflow in the condensed consolidated statements of cash flows for the nine months ended September 30, 2022. The Company is obligated to pay UT Southwestern up to $7.7 million in regulatory-related milestones and up to $7.5 million in sales-related milestones, as well as a low, single-digit royalty on net sales upon commercialization of the product.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2022
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note 6—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, RSAs, RSUs and other stock-based awards to employees, directors, officers and consultants. On July 1, 2020, 3,529,412 shares of common stock were authorized for issuance under the Existing Plan. On September 16, 2020, the Company increased the number of shares of common stock authorized for issuance under the Existing Plan to 3,845,294. 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. Initially, the number of shares available for future issuance under the New Plan was the sum of (1) 3,390,168 new shares of common stock, (2) 209,841 remaining shares of common stock reserved under the Existing Plan that became available for issuance upon the effectiveness of the New Plan and (3) the number of shares of common stock subject to outstanding awards under the Existing Plan when the New Plan became effective that thereafter expire or are forfeited, canceled, withheld to satisfy tax withholding or to purchase or exercise an award, repurchased by the Company or are otherwise terminated . The number of shares of common stock reserved for issuance under the New Plan automatically increase s 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, 2021 , the Company’s board of directors increased the number of shares of common stock reserved for issuance under the New Plan by 1,434,934 shares. On January 1, 2022 , the Company’s board of directors increased the number of shares of common stock reserved for issuance under the New Plan by 1,923,697 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, the Company’s board of directors increased the number of shares of common stock reserved for issuance under the ESPP by 384,739. The Company has issued 73,073 shares of common stock under the ESPP as of September 30, 2022. Stock Options On July 1, 2020, options to purchase 2,896,782 shares of common stock under the Existing Plan were awarded to certain employees and consultants of the Company with an exercise price per share of $0.80, which were expected to vest over a four-year four-year Compensation – Stock Compensation For the three months ended September 30, 2022, no shares of common stock under the New Plan were awarded. For the nine months ended September 30, 2022, 2,679,952 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $4.21. The stock options vest over one to four years and have a ten-year The following weighted-average assumptions were used to estimate the fair value of stock options that were granted during the three and nine months ended September 30, 2022 and 2021: Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 Risk-free interest rate — 1.02 % 2.16 % 0.83 % Expected dividend yield — — — — Expected term in years — 6.1 6.1 6.0 Expected volatility — 75 % 76 % 75 % The following table summarizes stock option activity, during the nine months ended September 30, 2022: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at December 31, 2021 3,649,962 $ 24.13 9.2 $ — Options granted 2,679,952 6.24 — $ — Options cancelled or forfeited (1,684,140 ) 15.38 — $ — Options expired (98,041 ) 24.72 — $ — Outstanding at September 30, 2022 4,547,733 $ 16.82 8.6 $ — Vested and expected to vest at September 30, 2022 4,547,733 $ 16.82 8.6 $ — Options exercisable at September 30, 2022 1,199,900 $ 24.86 7.5 $ — The aggregate intrinsic value in the above table is calculated as the difference between the fair value of the Company’s common stock as of September 30, 2022 and the exercise price of the stock options. As of September 30, 2022, the total unrecognized compensation related to unvested stock option awards granted was $29.2 million, which the Company expects to recognize over a weighted-average period of approximately 2.9 years. No stock options were exercised during the period. Restricted Stock Units On September 2, 2020, the Company issued 331,121 RSUs to an employee under the Existing Plan; 25% of the shares of common stock underlying the RSUs vest at each anniversary over a four-year As of September 30, 2022, the total unrecognized compensation related to unvested RSUs granted, including the remaining compensation cost associated with the RSUs granted on September 2, 2020 in exchange for the Cancelled Options, was $7.5 million which is expected to be amortized on a straight-line basis over a weighted-average period of approximately 1.7 years. The Company's default tax withholding method for RSUs 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. The Company’s RSU activity for the nine months ended September 30, 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at December 31, 2021 1,886,765 $ 6.52 Restricted units granted — — Vested (628,921 ) 6.52 Cancelled or forfeited — — Nonvested at September 30, 2022 1,257,844 $ 6.52 Restricted Stock Awards RA Session II, the Company’s President and Chief Executive Officer, was awarded 769,058 RSAs under the Existing Plan on July 1, 2020, which are expected to vest over a three-year The Company’s RSA activity for the nine months ended September 30, 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at December 31, 2021 341,975 $ 5.28 Restricted stock granted — — Vested (192,361 ) 5.28 Nonvested at September 30, 2022 149,614 $ 5.28 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, 2022, stock-based compensation expense related to the ESPP was not material. During the nine months ended September 30, 2022, $0.2 million of stock-based compensation expense was capitalized as part of construction in process (see Note 3). 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, net of the amounts capitalized, for the three and nine months ended September 30, 2022 and 2021 (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2022 2021 2022 2021 Research and development expense $ 2,001 $ 2,305 $ 5,894 $ 6,098 General and administrative expense 2,469 2,781 8,046 7,131 Total $ 4,470 $ 5,086 $ 13,940 $ 13,229

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2022
Earnings Per Share [Abstract]
Net Loss Per Common Share	Note 7—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. 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, 2022 2021 2022 2021 Net loss $ (26,307 ) $ (51,187 ) $ (110,291 ) $ (124,137 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 40,937,808 38,003,954 39,761,764 37,495,537 Net loss per common share, basic and diluted $ (0.64 ) $ (1.35 ) $ (2.77 ) $ (3.31 ) The following common stock equivalents outstanding as of September 30, 2022 and 2021 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, 2022 September 30, 2021 Unvested RSUs 1,257,844 1,886,765 Unvested RSAs 149,614 406,095 Stock options 4,547,733 3,516,992 Total 5,955,191 5,809,852

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Income Taxes	Note 8—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, 2022, 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, 2021.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2022
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 9—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, 2022. The Company does not anticipate recognizing any significant losses relating to these arrangements. Total lease expense, inclusive of lease incentives, under all operating lease agreements amounted to $0.4 million and $0.1 million for the three months ended September 30, 2022 and 2021, respectively, and $1.0 million and $0.1 million for the nine months ended September 30, 2022 and 2021, respectively. 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 is 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, 2022. 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. The Company incurred initial direct costs to enter into the Durham Lease of approximately $0.8 million. The costs have been recorded on the condensed consolidated balance sheets as a deferred lease asset and are being amortized into earnings over the term of the Durham Lease. In accordance with ASC Topic 840, Leases

Strategic Reprioritization

Strategic Reprioritization	9 Months Ended
	Sep. 30, 2022
Restructuring And Related Activities [Abstract]
Strategic Reprioritization	Note 10 – 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. The Company will conduct small proof-of-concept studies in CLN1 disease and SLC13A5 deficiency. Development of the CLN7 program will continue in collaboration with existing partners with future clinical development to focus on the first-generation construct. 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, in the condensed consolidated statements of operations for the nine months ended September 30, 2022, primarily within research and development expenses.

Retirement Plan

Retirement Plan	9 Months Ended
	Sep. 30, 2022
Compensation And Retirement Disclosure [Abstract]
Retirement Plan	Note 11 – 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 $0.7 million to the 401(k) retirement savings plan for the three and nine months ended September 30, 2022, respectively. The Company contributed less than $0.1 million and $0.1 million to the 401(k) retirement savings plan for the three and nine months ended September 30, 2021, respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2022
Subsequent Events [Abstract]
Subsequent Events	Note 12– Subsequent Events Astellas Transactions On October 21, 2022, or the Effective Date, the Company entered into the Option Agreement with Astellas, pursuant to which the Company granted to Astellas an exclusive option to obtain an exclusive, worldwide, royalty and milestone-bearing right and license (A) to research, develop, make, have made, use, sell, offer for sale, have sold, import, export and otherwise exploit, or, collectively, Exploit, the product known, as of the Effective Date, as TSHA-120, or the 120 GAN Product, and any backup products with respect thereto for use in the treatment of GAN or any other gene therapy product for use in the treatment of GAN that is controlled by Taysha or any of its affiliates or with respect to which the Company or any of its affiliates controls intellectual property rights covering the Exploitation thereof, or a GAN Product, and (B) under any intellectual property rights controlled by Taysha or any of its affiliates with respect to such Exploitation, or the GAN Option. Subject to certain extensions, the GAN Option is exercisable from the Effective Date through a specified period of time following Astellas’ receipt of (i) the formal minutes from the Type B end-of-Phase 2 meeting between Taysha and the FDA in response to the Company’s meeting request sent to the FDA on September 19, 2022 for the 120 GAN Product, or 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, or 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, or 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 will pay the Company the Upfront Payment, which is $20.0 million, within 30 days after receipt of an invoice for such payment, which invoice will be delivered by the Company on or after the Effective Date. Astellas or any of its affiliates shall have the right, in its or their discretion and upon written notice to the Company, to offset the amount of the Upfront Payment (in whole or in part, until the full amount of the Upfront Payment has been offset) against (a) any payment(s) owed to Taysha or any of its affiliates (or to any third party on behalf of the Company) under or in connection with any license agreement entered into with respect to any GAN Product or Rett Product, including, any upfront payment, milestone payment or royalties owed to Taysha or any of its affiliates (or to any third party on behalf of the Company) under or in connection with any such license agreement or (b) any amount owed to Taysha or any of its affiliates in connection with a Change of Control transaction with Astellas or any of its affiliates. As further consideration for the rights granted to Astellas under the Option Agreement, the Company and Astellas also entered into the Securities Purchase Agreement. Securities Purchase Agreement On October 21, 2022, the Company entered into the Securities Purchase Agreement with Astellas, pursuant to which the Company agreed to issue and sell to Astellas in a private placement, or the Private Placement, an aggregate of 7,266,342 shares, or the Private Placement Shares, of its common stock, for aggregate gross proceeds of $30.0 million. The Private Placement closed on October 24, 2022. Pursuant to the Securities Purchase Agreement, in connection with the Private Placement, Astellas has the right to designate one individual to attend all meetings of the Board in a non-voting observer capacity. The Company also granted Astellas certain registration rights with respect to the Private Placement Shares. October 2022 Follow-On Offering On October 26, 2022, the Company entered into the Underwriting Agreement with the Underwriter to issue and sell 14,000,000 shares of the Company’s common stock of the Company, par value $0.00001 per share, in an underwritten public offering pursuant to an effective registration statement on Form S-3 (File No. 333-260069) and a related prospectus and prospectus supplement, in each case filed with the SEC. The offering price to the public was $2.00 per share of the Company’s common stock, and the Underwriter agreed to purchase the shares from the Company pursuant to the Underwriting Agreement at a price of $1.88 per share. In addition, the Company granted the Underwriter an option to purchase, for a period of 30 days, up to an additional 2,100,000 shares of the Company’s common stock, which such option had not been exercised as of the date of this Quarterly Report on Form 10-Q. The offering closed on October 31, 2022 and the Company received net proceeds of $25.6 million after deducting underwriting discounts, commissions and estimated offering expenses. The Company estimates that the net proceeds from the Offering will be approximately $29.6 million if the Underwriter exercises in full its option to purchase additional shares of the Company’s common stock after deducting underwriting discounts and commissions and estimated offering expenses.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2022
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, 2021, filed with the Securities and Exchange Commission ("SEC") on March 31, 2022 (the “2021 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, 2021 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 2021 Annual Report.
Principles of Consolidation	Principles of Consolidation The accompanying interim condensed consolidated financial statements include the accounts of Taysha and its inactive wholly owned U.S. subsidiaries as well as t wo foreign subsidiaries incorporated during 2021
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 Company’s initial public offering (“IPO”) in September 2020 (as an input into stock-based compensation), and estimating preclinical manufacturing accruals and accrued or prepaid research and development expenses. 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.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is equal to net loss as presented in the accompanying condensed consolidated statements of operations.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) The new standard requires the use of one of the following two approaches, either (1) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (2) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. The Company commenced its implementation efforts of this new accounting standard during the quarter and concluded that the cumulative impact of the adoption will be recorded as an adjustment to accumulated deficit as of January 1, 2022, and prior periods will not be adjusted. Upon adoption, the Company expects to recognize right-of-use assets and lease liabilities in the consolidated balance sheet related to operating leases. Additionally, upon adoption, the Company expects to derecognize the build-to-suit asset and obligation (see Note 9) related to the construction-in-progress as the Company does not control the building during the construction period.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2022
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, 2022 December 31, 2021 Prepaid research and development $ 5,182 $ 5,218 Prepaid clinical trial 2,284 3,298 Deferred offering costs 722 545 Prepaid insurance 74 148 Prepaid bonus 54 427 Other 380 863 Total prepaid expenses and other current assets $ 8,696 $ 10,499
Schedule of Property Plant and Equipment Net	Property, plant and equipment, net consisted of the following (in thousands): September 30, 2022 December 31, 2021 Leasehold improvements $ 2,091 $ 2,067 Laboratory equipment 2,069 1,095 Computer equipment 1,127 1,098 Furniture and fixtures 897 845 Construction in progress 59,058 46,004 65,242 51,109 Accumulated depreciation (1,288 ) (499 ) Property, plant and equipment, net $ 63,954 $ 50,610
Schedule of Accrued Expense and Other Current Labilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, 2022 December 31, 2021 Accrued research and development $ 8,027 $ 11,895 Accrued compensation 4,914 7,703 Accrued license fees — 3,500 Accrued property, plant and equipment 1,655 2,644 Accrued clinical trial 889 1,659 Accrued professional and consulting fees 823 1,091 Other 1,580 1,491 Total accrued expenses and other current liabilities $ 17,888 $ 29,983

Loan with Silicon Valley Bank (

Loan with Silicon Valley Bank (Tables)	9 Months Ended
	Sep. 30, 2022
Debt Disclosure [Abstract]
Schedule of Future Principal Debt Payments on Loan Payable	Future principal debt payments on the loan payable as of September 30, 2022 are as follows (in thousands): Year Ending December 31, 2022 — 2023 — 2024 6,667 2025 20,000 2026 13,333 Total principal payments 40,000 Unamortized debt discount (2,227 ) Term Loan, net $ 37,773

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2022
Schedule of Restricted Stock Units Activity	The Company’s RSU activity for the nine months ended September 30, 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at December 31, 2021 1,886,765 $ 6.52 Restricted units granted — — Vested (628,921 ) 6.52 Cancelled or forfeited — — Nonvested at September 30, 2022 1,257,844 $ 6.52
Schedule of Restricted Stock Awards Activity	The Company’s RSA activity for the nine months ended September 30, 2022 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at December 31, 2021 341,975 $ 5.28 Restricted stock granted — — Vested (192,361 ) 5.28 Nonvested at September 30, 2022 149,614 $ 5.28
Schedule of Total Stock-Based Compensation Expense for Stock Options, ESPP, RSAs and RSUs	During the nine months ended September 30, 2022, $0.2 million of stock-based compensation expense was capitalized as part of construction in process (see Note 3). 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, net of the amounts capitalized, for the three and nine months ended September 30, 2022 and 2021 (in thousands): For the Three Months Ended September 30, For the Nine Months Ended September 30, 2022 2021 2022 2021 Research and development expense $ 2,001 $ 2,305 $ 5,894 $ 6,098 General and administrative expense 2,469 2,781 8,046 7,131 Total $ 4,470 $ 5,086 $ 13,940 $ 13,229
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 stock options that were granted during the three and nine months ended September 30, 2022 and 2021: Three Months Ended September 30, Nine Months Ended September 30, 2022 2021 2022 2021 Risk-free interest rate — 1.02 % 2.16 % 0.83 % Expected dividend yield — — — — Expected term in years — 6.1 6.1 6.0 Expected volatility — 75 % 76 % 75 %
Schedule of Stock Option Activity	The following table summarizes stock option activity, during the nine months ended September 30, 2022: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at December 31, 2021 3,649,962 $ 24.13 9.2 $ — Options granted 2,679,952 6.24 — $ — Options cancelled or forfeited (1,684,140 ) 15.38 — $ — Options expired (98,041 ) 24.72 — $ — Outstanding at September 30, 2022 4,547,733 $ 16.82 8.6 $ — Vested and expected to vest at September 30, 2022 4,547,733 $ 16.82 8.6 $ — Options exercisable at September 30, 2022 1,199,900 $ 24.86 7.5 $ —

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2022
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, 2022 2021 2022 2021 Net loss $ (26,307 ) $ (51,187 ) $ (110,291 ) $ (124,137 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 40,937,808 38,003,954 39,761,764 37,495,537 Net loss per common share, basic and diluted $ (0.64 ) $ (1.35 ) $ (2.77 ) $ (3.31 )
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, 2022 and 2021 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, 2022 September 30, 2021 Unvested RSUs 1,257,844 1,886,765 Unvested RSAs 149,614 406,095 Stock options 4,547,733 3,516,992 Total 5,955,191 5,809,852

Organization and Description _2

Organization and Description of Business Operations - Additional Information (Details) - USD ($)					1 Months Ended		9 Months Ended
	Oct. 31, 2022	Oct. 26, 2022	Oct. 21, 2022	Oct. 05, 2021	Oct. 31, 2022	Apr. 30, 2022	Sep. 30, 2022	Dec. 31, 2021
Organization and Description of Business Operations [Line Items]
Date of incorporation							Feb. 13, 2020
Net proceeds from issuance of common stock							$ 11,640,000
Common stock, shares issued							41,175,939	38,473,945
Common stock, par value per share							$ 0.00001	$ 0.00001
Astellas
Organization and Description of Business Operations [Line Items]
Upfront payment			$ 20,000,000		$ 20,000,000
Gross proceeds including upfront payments					50,000,000
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
Securities Purchase Agreement | Private Placement [Member] | Astellas
Organization and Description of Business Operations [Line Items]
Net proceeds from issuance of common stock					$ 30,000,000
Common stock, shares issued	7,266,342		7,266,342		7,266,342
Underwriting Agreement
Organization and Description of Business Operations [Line Items]
Net proceeds from issuance of common stock	$ 25,600,000				$ 25,600,000
Common stock, shares issued	14,000,000	14,000,000			14,000,000
Common stock, par value per share	$ 2	$ 2			$ 2
Underwriter period for option to purchase additional share		30 days			30 days
Option to purchase additional number of shares	2,100,000	2,100,000			2,100,000
Underwriter agreed to purchase share price of per share	$ 1.88	$ 1.88			$ 1.88
Estimated net proceeds from offering if underwriter exercises options	$ 29,600,000				$ 29,600,000

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 5,182	$ 5,218
Prepaid clinical trial	2,284	3,298
Deferred offering costs	722	545
Prepaid insurance	74	148
Prepaid bonus	54	427
Other	380	863
Total prepaid expenses and other current assets	$ 8,696	$ 10,499

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property, Plant and Equipment Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 65,242	$ 51,109
Accumulated depreciation	(1,288)	(499)
Property, plant and equipment, net	63,954	50,610
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	2,091	2,067
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	2,069	1,095
Computer Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	1,127	1,098
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	897	845
Construction in Progress
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 59,058	$ 46,004

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Property Plant And Equipment [Line Items]
Depreciation expense	$ 300	$ 200	$ 808	$ 283
Build-to-Suit Lease
Property Plant And Equipment [Line Items]
Construction in progress	59,000		59,000
Payroll and Payroll Related Costs
Property Plant And Equipment [Line Items]
Construction in progress	$ 3,100		$ 3,100

Balance Sheet Components - Sc_3

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 8,027	$ 11,895
Accrued compensation	4,914	7,703
Accrued license fees		3,500
Accrued property, plant and equipment	1,655	2,644
Accrued clinical trial	889	1,659
Accrued professional and consulting fees	823	1,091
Other	1,580	1,491
Total accrued expenses and other current liabilities	$ 17,888	$ 29,983

Loan with Silicon Valley Bank -

Loan with Silicon Valley Bank - Additional Information (Details) $ in Thousands		9 Months Ended
	Aug. 12, 2021 USD ($) Program	Sep. 30, 2022 USD ($)	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
Percentage of annual default interest rate	5%
Interest expense related to term loan		2,500
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	0	$ 10,000
Through December 31, 2021 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 40,000
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	$ 20,000
Debt instrument, maturity start date	Jan. 01, 2022
Debt instrument, maturity end date	Sep. 30, 2022	Sep. 30, 2022
October 1, 2022 until March 31, 2023 | Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 20,000
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
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) $ in Thousands	Sep. 30, 2022 USD ($)
Debt Disclosure [Abstract]
2024	$ 6,667
2025	20,000
2026	13,333
Total principal payments	40,000
Unamortized debt discount	(2,227)
Term Loan, net	$ 37,773

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 USD ($) Product

Sep. 30, 2022 USD ($) shares

Sep. 30, 2021 USD ($)

Sep. 30, 2022 USD ($) shares

Sep. 30, 2021 USD ($)

Dec. 31, 2021 USD ($) shares

Dec. 31, 2020 USD ($)

Oct. 29, 2020 USD ($)

Mar. 31, 2020 shares

Feb. 21, 2020 USD ($)

Nov. 30, 2019 shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Common stock, shares issued | shares

41,175,939

41,175,939

38,473,945

Research and development

$ 16,391,000

$ 39,528,000

$ 77,308,000

$ 94,025,000

TSHA-120

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

Research and development

$ 5,500,000

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]

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

0

2,179,000

Percentage of fully diluted common stock shares outstanding

20%

Percentage of entitled to receive additional shares on fully diluted basis

10%

Queens Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

Queens Agreement | Research and Development Expense

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Cash payment to acquire license agreement

$ 3,000,000

Queens Agreement | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License agreement regulatory milestones payment

$ 10,000,000

License agreement commercial milestones payment

$ 10,000,000

Abeona CLN1 Agreements

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License fee payment

$ 3,000,000

Purchase of clinical materials and reimbursement incurred development costs

$ 4,000,000

Research and development

$ 3,000,000

$ 7,000,000

Abeona CLN1 Agreements | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License and inventory purchase agreement regulatory related milestones payment

26,000,000

License and inventory purchase agreement sales related milestones payment

$ 30,000,000

Abeona | Abeona Rett Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research and development

$ 1,000,000

Payment of one-time upfront license fee

$ 3,000,000

Regulatory milestone fee paid

$ 1,000,000

Abeona | Maximum | Abeona Rett Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Regulatory related milestones obligation payable

$ 26,500,000

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

$ 30,000,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)				1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 16, 2020	Sep. 02, 2020	Jul. 01, 2020	Feb. 28, 2022	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Jan. 01, 2022	Jan. 01, 2021
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					$ 4,470,000	$ 5,086,000	$ 13,940,000	$ 13,229,000
Construction in Progress
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense							$ 200,000
Employee Stock Purchase Plan (ESPP)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	724,000								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						73,073
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]
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition							1 year 8 months 12 days
Share-based payment award, RSU/RSA granted
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					7,500,000		$ 7,500,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted							2,679,952
Share-based payment award, options granted, exercise price per share							$ 6.24
Share-based payment award, options, compensation cost not yet recognized					29,200,000		$ 29,200,000
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition							2 years 10 months 24 days
Stock options were exercised during the period							$ 0
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition							6 months
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 700,000		$ 700,000
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					73,073		73,073
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	209,841
Share-based payment award, plan modification, incremental cost							$ 0
2020 Equity Incentive Plan | Cancelled Options | Certain Employees and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted			2,896,782
Share-based payment award, options granted, exercise price per share			$ 0.80
Award vesting period			4 years
Share-based payment award, options grant date fair value			$ 13,800,000
2020 Equity Incentive Plan | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period		4 years
Number of shares awarded		2,518,932
Share-based payment award, RSU/RSA granted		331,121
2020 Equity Incentive Plan | Restricted Stock Units | Share-based Payment Arrangement, Tranche One
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25%
2020 Equity Incentive Plan | Restricted Stock Units | Share-based Payment Arrangement, Tranche Two
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25%
2020 Equity Incentive Plan | Restricted Stock Units | Share-based Payment Arrangement, Tranche Three
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25%
2020 Equity Incentive Plan | Restricted Stock Units | Share-based Payment Arrangement, Tranche Four
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, vesting rights percentage		25%
2020 Equity Incentive Plan | Restricted Stock Awards | RA Session II
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, RSU/RSA granted			769,058
Award requisite service vesting period			3 years
2020 Equity Incentive Plan | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance	3,845,294		3,529,412
New Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance	3,390,168								1,923,697	1,434,934
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 | 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					0		2,679,952
Share-based payment award, options, weighted-average grant date fair value							$ 4.21
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 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period							1 year

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Assumptions Used to Estimate Fair Value of Stock Options and Cancelled Options (Details) - Stock Options	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.02%	2.16%	0.83%
Expected term in years	6 years 1 month 6 days	6 years 1 month 6 days	6 years
Expected volatility	75%	76%	75%

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options	9 Months Ended	12 Months Ended
	Sep. 30, 2022 $ / shares shares	Dec. 31, 2021 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance | shares	3,649,962
Options granted, Stock Options | shares	2,679,952
Options cancelled or forfeited, Stock Options | shares	(1,684,140)
Options expired, Stock Options | shares	(98,041)
Outstanding. Stock Options, Ending Balance | shares	4,547,733	3,649,962
Vested and expected to vest at September 30, 2022, Stock Options | shares	4,547,733
Options exercisable at September 30, 2022, Stock Options | shares	1,199,900
Outstanding, Weighted Average Exercise Price, Beginning balance | $ / shares	$ 24.13
Options granted, Weighted Average Exercise Price | $ / shares	6.24
Options cancelled or forfeited, Weighted Average Exercise Price | $ / shares	15.38
Options expired, Weighted Average Exercise Price | $ / shares	24.72
Outstanding, Weighted Average Exercise Price, Ending balance | $ / shares	16.82	$ 24.13
Vested and expected to vest at September 30, 2022, Weighted Average Exercise Price | $ / shares	16.82
Options exercisable at September 30, 2022, Weighted Average Exercise Price | $ / shares	$ 24.86
Outstanding, Weighted Average Remaining Contractual Life	8 years 7 months 6 days	9 years 2 months 12 days
Vested and expected to vest at September 30, 2022, Weighted Average Remaining Contractual Life	8 years 7 months 6 days
Options exercisable at September 30, 2022, Weighted Average Remaining Contractual Life	7 years 6 months

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2022 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance | shares	1,886,765
Restricted units/stock granted, Number of Shares | shares
Vested, Number of Shares | shares	(628,921)
Cancelled or forfeited, Number of Shares | shares
Nonvested, Number of Shares, Ending Balance | shares	1,257,844
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
Vested, Weighted Average Grant Date Fair Value per Share | $ / shares	6.52
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share | $ / shares
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance | $ / shares	$ 6.52

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Restricted Stock Awards Activity (Details) - Restricted Stock Awards - $ / shares		9 Months Ended
	Jul. 01, 2020	Sep. 30, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance		341,975
Vested, Number of Shares		(192,361)
Nonvested, Number of Shares, Ending Balance		149,614
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
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance		$ 5.28

Stock-Based Compensation - Sc_5

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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 4,470	$ 5,086	$ 13,940	$ 13,229
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,001	2,305	5,894	6,098
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,469	$ 2,781	$ 8,046	$ 7,131

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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net loss	$ (26,307)	$ (51,187)	$ (110,291)	$ (124,137)
Weighted average common shares outstanding, basic	40,937,808	38,003,954	39,761,764	37,495,537
Weighted average common shares outstanding, diluted	40,937,808	38,003,954	39,761,764	37,495,537
Net loss per common share, basic	$ (0.64)	$ (1.35)	$ (2.77)	$ (3.31)
Net loss per common share, diluted	$ (0.64)	$ (1.35)	$ (2.77)	$ (3.31)

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, 2022	Sep. 30, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	5,955,191	5,809,852
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	1,257,844	1,886,765
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	406,095
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	4,547,733	3,516,992

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	9 Months Ended
	Sep. 30, 2022 USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions		3 Months Ended		9 Months Ended
	Dec. 17, 2020 ft²	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Loss Contingencies [Line Items]
Lease expense		$ 0.4	$ 0.1	$ 1	$ 0.1
Durham Lease
Loss Contingencies [Line Items]
Number of operating lease landlord square feet manufacturing facility | ft²	187,500
Operating lease commencement date	Apr. 01, 2021
Operating lease term of contract	15 years 6 months
Operating lease extend term of contract	5 years
Amount required to place in escrow account		2.6		2.6
Operating leases initial direct costs				0.8
Build-to-suit asset		26.3		26.3
Build-to-suit lease liability		$ 26.3		26.3
Equipment purchases and build-out of leased Facility				$ 13.2

Strategic Reprioritization - Ad

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

Retirement Plan - Additional In

Retirement Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Defined Benefit Plan Disclosure [Line Items]
Contribution to retirement savings plan	$ 0.1		$ 0.7	$ 0.1
Maximum
Defined Benefit Plan Disclosure [Line Items]
Contribution to retirement savings plan		$ 0.1

Subsequent - Events - Additiona

Subsequent - Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	9 Months Ended
	Oct. 31, 2022	Oct. 26, 2022	Oct. 21, 2022	Oct. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Common stock, shares issued					41,175,939	38,473,945
Common stock, par value per share					$ 0.00001	$ 0.00001
Net proceeds after deducting underwriting discounts and commission					$ 11,640
Underwriting Agreement
Subsequent Event [Line Items]
Common stock, shares issued	14,000,000	14,000,000		14,000,000
Common stock, par value per share	$ 2	$ 2		$ 2
Underwriter agreed to purchase share price of per share	$ 1.88	$ 1.88		$ 1.88
Underwriter period for option to purchase additional share		30 days		30 days
Option to purchase additional number of shares	2,100,000	2,100,000		2,100,000
Net proceeds after deducting underwriting discounts and commission	$ 25,600			$ 25,600
Estimated net proceeds from offering if underwriter exercises options	$ 29,600			29,600
Underwritten Public Offering | Underwriting Agreement
Subsequent Event [Line Items]
Common stock, par value per share		$ 0.00001
Astellas
Subsequent Event [Line Items]
Upfront payment			$ 20,000	$ 20,000
Upfront payment period			30 days
Astellas | Private Placement [Member] | Securities Purchase Agreement
Subsequent Event [Line Items]
Common stock, shares issued	7,266,342		7,266,342	7,266,342
Aggregate gross proceeds			$ 30,000
Net proceeds after deducting underwriting discounts and commission				$ 30,000