Taysha Gene Therapies (TSHA) 10-Q 16 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 16, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
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		38,391,165
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	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 197,370	$ 251,253
Prepaid expenses and other current assets	9,932	6,626
Total current assets	207,302	257,879
Deferred lease asset	691	715
Property, plant and equipment, net	33,867	287
Total assets	241,860	258,881
Current liabilities:
Accounts payable	6,355	1,994
Accrued expenses and other current liabilities	22,036	5,135
Total current liabilities	28,391	7,129
Build-to-suit lease liability	26,209
Other non-current liabilities	765	450
Total liabilities	55,365	7,579
Commitments and contingencies - Note 10
Stockholders' equity
Preferred stock, $0.00001 par value per share; 10,000,000 shares authorized and no shares issued and outstanding as of June 30, 2021 and December 31, 2020
Common stock, $0.00001 par value per share; 200,000,000 shares authorized and 38,391,165 and 37,761,435 issued and outstanding as of June 30, 2021 and December 31, 2020, respectively
Additional paid-in capital	320,571	312,428
Accumulated deficit	(134,076)	(61,126)
Total stockholders’ equity	186,495	251,302
Total liabilities and stockholders' equity	$ 241,860	$ 258,881

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
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	38,391,165	37,761,435
Common stock, shares outstanding	38,391,165	37,761,435

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating expenses:
Research and development	$ 30,643	$ 3,062	$ 54,497	$ 8,576
General and administrative	10,129	948	18,365	1,018
Total operating expenses	40,772	4,010	72,862	9,594
Loss from operations	(40,772)	(4,010)	(72,862)	(9,594)
Other income (expense):
Change in fair value of preferred stock tranche liability		(17,210)		(17,030)
Interest income	40		106
Interest expense	(194)		(194)	(27)
Total other expense, net	(154)	(17,210)	(88)	(17,057)
Net loss	$ (40,926)	$ (21,220)	$ (72,950)	$ (26,651)
Net loss per common share, basic and diluted	$ (1.09)	$ (1.95)	$ (1.96)	$ (2.45)
Weighted average common shares outstanding, basic and diluted	37,479,164	10,894,999	37,237,115	10,894,999

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2019	$ (135)			$ 980	$ (1,115)
Balance, shares at Dec. 31, 2019			10,894,999
Issuance of convertible preferred stock		$ 17,110
Issuance of convertible preferred stock, shares		6,200,000
Reclassification of preferred stock tranche liability upon issuance of Series A milestone shares		$ 904
Net loss	(26,651)				(26,651)
Balance at Jun. 30, 2020	(26,786)			980	(27,766)
Balance, shares at Jun. 30, 2020			10,894,999
Convertible preferred stock balance, shares at Jun. 30, 2020		6,200,000
Convertible preferred stock balance at Jun. 30, 2020		$ 18,014
Balance at Mar. 31, 2020	(5,566)			980	(6,546)
Convertible preferred stock balance, shares at Mar. 31, 2020		6,000,000
Convertible preferred stock balance at Mar. 31, 2020		$ 16,520
Balance, shares at Mar. 31, 2020			10,894,999
Issuance of convertible preferred stock		$ 590
Issuance of convertible preferred stock, shares		200,000
Reclassification of preferred stock tranche liability upon issuance of Series A milestone shares		$ 904
Net loss	(21,220)				(21,220)
Balance at Jun. 30, 2020	(26,786)			980	(27,766)
Balance, shares at Jun. 30, 2020			10,894,999
Convertible preferred stock balance, shares at Jun. 30, 2020		6,200,000
Convertible preferred stock balance at Jun. 30, 2020		$ 18,014
Balance at Dec. 31, 2020	$ 251,302			312,428	(61,126)
Balance, shares at Dec. 31, 2020	37,761,435		37,761,435
Stock-based compensation	$ 8,143			8,143
Issuance of common stock upon vesting and settlement of restricted stock units, shares			629,730
Net loss	(72,950)				(72,950)
Balance at Jun. 30, 2021	$ 186,495			320,571	(134,076)
Balance, shares at Jun. 30, 2021	38,391,165		38,391,165
Balance at Mar. 31, 2021	$ 222,872			316,022	(93,150)
Balance, shares at Mar. 31, 2021			37,761,435
Stock-based compensation	4,549			4,549
Issuance of common stock upon vesting and settlement of restricted stock units, shares			629,730
Net loss	(40,926)				(40,926)
Balance at Jun. 30, 2021	$ 186,495			$ 320,571	$ (134,076)
Balance, shares at Jun. 30, 2021	38,391,165		38,391,165

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Issuance of preferred stock tranche liability		$ 1,050
Series A Convertible Preferred Stock
Issuance of convertible preferred stock, offering costs	$ 10	$ 440

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities
Net loss	$ (72,950,000)	$ (26,651,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	117,000	0
Change in fair value of preferred stock tranche liability		17,030,000
Research and development license expense	5,500,000	3,000,000
Stock-based compensation	8,143,000
Other	194,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(3,282,000)	(9,000)
Accounts payable	2,382,000	1,237,000
Accrued expenses and other liabilities	15,053,000	1,214,000
Due to related party	(8,000)	14,000
Net cash used in operating activities	(44,851,000)	(4,165,000)
Cash flows from investing activities
Purchase of research and development license	(5,500,000)	(3,000,000)
Purchase of property, plant and equipment	(3,532,000)
Net cash used in investing activities	(9,032,000)	(3,000,000)
Cash flows from financing activities
Proceeds from issuances of Series A convertible preferred stock		18,600,000
Payment of Series A convertible preferred stock issuance costs		(263,000)
Proceeds from note payable to related party		1,673,000
Repayment of note payable to related party		(1,645,000)
Net cash provided by financing activities		18,365,000
Net (decrease) increase in cash and cash equivalents	(53,883,000)	11,200,000
Cash at the beginning of the period	251,253,000
Cash at the end of the period	197,370,000	11,200,000
Supplemental disclosure of cash flow information:
Cash paid for interest		27,000
Supplemental disclosure of noncash investing and financing activities:
Property, plant and equipment in accounts payable and accrued expenses	3,308,000	19,000
Acquisition of property, plant and equipment funded by landlord	606,000
Build-to-suit lease liability	$ 26,250,000
Deferred offering costs not yet paid		90,000
Reclassification of preferred stock tranche liability		904,000
Allocation of preferred stock tranche liability		1,050,000
Series A convertible preferred stock issuance costs not yet paid		$ 177,000

Organization and Description of

Organization and Description of Business Operations	6 Months Ended
	Jun. 30, 2021
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. Stock Split On September 16, 2020, the Company effected a 1.0895-for-one stock split of its authorized, issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s convertible preferred stock as discussed in Note 5. Accordingly, all share and per share amounts for the periods presented in the accompanying condensed consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the convertible preferred stock conversion ratios. On September 16, 2020, the Company also increased the number of shares of common stock authorized for issuance under the 2020 Equity Incentive Plan (the “Existing Plan”) to 3,845,294. Initial Public Offering On September 23, 2020, the Company’s registration statement on Form S-1 (File No. 333-248559) related to the initial public offering (“IPO”) of its common stock became effective and on September 28, 2020, the IPO closed. Pursuant to the IPO, the Company issued and sold 9,050,000 shares of common stock at a public offering price of $20.00 per share, which included 1,180,434 shares of common stock issued upon the exercise in full of the underwriters’ option to purchase additional shares. The Company received net proceeds of $165.9 million after deducting underwriting discounts and commissions and other offering costs of $2.5 million. The shares began trading on the Nasdaq Global Select Market on September 24, 2020. On September 28, 2020, in connection with the closing of the IPO, 10,000,000 shares of Series A and 5,647,048 shares of Series B convertible preferred stock automatically converted into an aggregate of 17,047,378 shares of common stock with a conversion ratio of 1.0895 shares of common stock for each share of Series A and Series B convertible preferred stock. As a result of the IPO, including the underwriters’ exercise in full of their option to purchase additional shares, and the conversions of the Series A and B convertible preferred stock, the Company’s total number of outstanding shares increased by 26,097,378 immediately following the closing of the IPO. Upon the effectiveness of the Company’s registration statement related to the IPO, the Company’s 2020 Stock Incentive Plan (the “New Plan”) and 2020 Employee Stock Purchase Plan became effective. At that time, all shares reserved for issuance under the Existing Plan ceased to be available for issuance under such plan and became available for issuance under the New Plan. Liquidity and Capital Resources The Company has incurred operating losses since inception and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of June 30, 2021, the Company had an accumulated deficit of $134.1 million. Prior to the closing of the Company’s IPO, between March and July 2020, the Company closed on the sale of an aggregate of 10,000,000 shares of Series A convertible preferred stock for gross proceeds of $30.0 million. Between July and August 2020, the Company closed on the sale of an aggregate of 5,647,048 shares of Series B convertible preferred stock for gross proceeds of $96.0 million. Future capital requirements will depend on many factors, including the timing and extent of spending on research and development and the market acceptance of the Company’s products. The Company will need to obtain additional financing in order to complete clinical studies and launch and commercialize any product candidates for which it receives regulatory approval. There can be no assurance that such financing will be available or will be on terms acceptable to the Company. As of June 30, 2021, the Company had cash of million which the Company believes will be sufficient to fund its planned operations for a period of at least twelve months from the date of issuance of these condensed consolidated financial statements. In December 2019 , the novel coronavirus that causes the disease COVID-19 emerged and has subsequently spread worldwide. The World Health Organization has declared the COVID-19 outbreak a global pandemic , resulting in federal, state and local governments and private entities implementing various restrictions , including travel restrictions, restrictions on public gatherings, stay at home orders, other advisories and quarantines of people who may have been exposed to the virus. The Company has been actively monitoring COVID - 19 and its impact globally. Management believes the financial results for the six months ended June 3 0 , 2021 were not significantly impacted by the COVID-19 pandemic . In addition, management believes the remote working arrangements and travel restrictions imposed by various governmental jurisdictions have had limited impact on the Company’s ability to maintain internal operations during the six months ended June 30, 2021 . The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat COVID-19.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
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, 2020, filed with the Securities and Exchange Commission ("SEC") on March 3, 2021 (the “2020 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, 2020 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 2020 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 that were incorporated during 2020, and one inactive foreign subsidiary incorporated in June 2021. All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to the determination of the fair value of the common stock prior to the IPO (as an input into stock-based compensation), estimating preclinical manufacturing accruals and accrued or prepaid research and development expenses, and the valuation of the preferred stock tranche liability. 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. In response to the ongoing and rapidly evolving COVID-19 pandemic, management considered the impact of the estimated economic implications on the Company’s critical and significant accounting estimates, including assessment of impairment of long-lived assets. 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 2020 Annual Report, except as described below. Build-to-Suit Lease In the Company’s recent lease arrangement (as described in Note 10), the Company was involved in the construction of the build-out. To the extent the Company is involved with the structural improvements of the construction project or takes construction risk prior to the commencement of a lease, accounting guidance requires the Company to be considered the owner for accounting purposes of these types of projects during the construction period. In such cases, the Company records an asset in property, plant and equipment on its consolidated balance sheet equal to the fair value of the building shell, and a corresponding build-to-suit lease obligation on its consolidated balance sheet representing the amounts paid by the lessor. Upon completion of construction, the Company will consider the requirements for sale-leaseback accounting treatment, including evaluating whether all risks of ownership have been transferred back to the landlord. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), as amended, with guidance regarding the accounting for and disclosure of leases. This update requires lessees to recognize the liabilities related to all leases, including operating leases, with a term greater than 12 months on the balance sheets. This update also requires lessees and lessors to disclose key information about their leasing transactions. This guidance will become effective for the Company for annual reporting periods beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. 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 has not yet concluded which approach will be utilized to adopt the new standard and is currently evaluating the impact of this standard on its consolidated financial statements.

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2021
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): June 30, 2021 December 31, 2020 Prepaid research and development $ 6,716 $ 2,462 Prepaid bonus 1,192 409 Prepaid insurance 826 2,480 Prepaid clinical trial 184 944 Other 1,014 331 Total prepaid expenses and other current assets $ 9,932 $ 6,626 Property, plant and equipment, net consisted of the following (in thousands): June 30, 2021 December 31, 2020 Leasehold improvements 1,863 — Furniture and fixtures 676 — Computer equipment 529 95 Laboratory equipment 460 — Construction in progress 30,465 201 33,993 296 Accumulated depreciation (126 ) (9 ) Property, plant and equipment, net $ 33,867 $ 287 Included in construction in progress at June 30, 2021 was $30.3 million of costs associated with the Build-to-Suit lease (see Note 10). Depreciation expense was $85,000 and $117,000 for the three and six months ended June 30, 2021, respectively. There was no depreciation expense for the three and six months ended June 30, 2020. Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Accrued research and development $ 14,508 $ 2,106 Accrued compensation 3,210 1,766 Accrued professional and consulting fees 1,372 999 Accrued property, plant, and equipment 1,309 173 Accrued clinical trial 959 — Other 678 91 Total accrued expenses and other current liabilities $ 22,036 $ 5,135

Research, Collaboration and Lic

Research, Collaboration and License Agreements	6 Months Ended
	Jun. 30, 2021
Research Collaboration And License Agreements [Abstract]
Research, Collaboration and License Agreements	Note 4—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. 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. 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 In late December 2019, the Company entered into a research grant agreement (“RGA”) with Queen’s University at Kingston (“Queen’s”), for certain research and development activities related to the generation of AAV9 vector. The Company committed to fund $3.8 million under the RGA with Queen’s. The Company issued Queen’s a promise-to-pay note whereby any amounts paid directly by Queen’s for the manufacture of the vector for use in the funded research activities, to the extent such amounts had not already been funded by the Company to Queen’s, would become a loan obligation for the Company (the “Note”), subject to an interest rate of 6 %. Any amounts outstanding under the Note were required to be repaid, along with any accrued interest, by or before June 30, 2020. In the event of default, any amount outstanding was deemed immediately payable by RA Session II, the Company’s President and Chief Executive Officer, as a personal guarantor (see Note 8 ). For the period from Inception through December 31, 2019, the Company did not incur any expenses associated with the Queen’s RGA, and no amounts were due or outstanding under the Note as of December 31, 2019. For the year ended December 31, 2020, the Company paid all expenses associated with the Queen’s RGA, thus no amounts were due or outstanding under the Note as of December 31, 2020, and the promise-to-pay has therefore expired. On February 21, 2020, the Company entered into a license agreement with Queen’s (the “Queen’s Agreement”) to obtain the exclusive perpetual, royalty-bearing license, with the right to sublicense through multiple tiers, under certain patent rights and know-how of Queen’s, including certain improvements to such patent rights and know-how, to develop products in any field which use one or more valid claims of the patents licensed under the Queen’s Agreement (the “Licensed Patents”), or the technology, information and intellectual property related to the patents licensed under the Queen’s Agreement (together with the Licensed Patents, the “Licensed Products”), and to make, have made, use, sell, offer for sale, import and export Licensed Products and otherwise exploit such patents and know-how for use in certain specified indications. In exchange for the rights granted to the Company, the Company made a cash payment of $3.0 million in April 2020 which is recorded in research and development expenses in the condensed consolidated statements of operations and included as an investing cash outflow in the condensed consolidated statements of cash flows since the acquired license does not have an alternative future use No additional milestone payments were made in connection with the Queen’s Agreement during the six months ended June 30, 2021. Abeona CLN1 Agreements In August 2020, the Company entered into license and inventory purchase agreements with Abeona Therapeutics Inc. (“Abeona”) for worldwide exclusive rights to certain intellectual property rights and know-how relating to the research, development and manufacture of ABO-202, an AAV-based gene therapy for CLN1 disease (also known as infantile Batten disease). Under the terms of the agreements, the Company made initial cash payments to Abeona of $3.0 million for the license fee and $4.0 million for purchase of clinical materials and reimbursement for previously incurred development costs in October 2020. In exchange for the license rights, the Company recorded an aggregate of $7.0 million within research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license or acquired inventory do not have an alternative future use. The Company is obligated to make up to $26.0 million in regulatory-related milestones and up to $30.0 million in sales-related milestones per licensed CLN1 product. The Company will also pay an annual earned royalty in the high single digits on net sales of any licensed CLN1 products. The license agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the license agreement for convenience upon specified prior written notice to Abeona. No additional milestone payments were made in connection with this agreement during the six months ended June 30, 2021. Abeona Rett Agreement On October 29, 2020, the Company entered into a license agreement (the “Abeona Rett Agreement”) with Abeona pursuant to which the Company obtained an exclusive, worldwide, royalty-bearing license, with the right to grant sublicenses under certain patents, know-how and materials originally developed by the University of North Carolina at Chapel Hill, the University of Edinburgh and Abeona to research, develop, manufacture, have manufactured, use, and commercialize licensed products for gene therapy and the use of related transgenes for Rett syndrome. Subject to certain obligations of Abeona, the Company is required to use commercially reasonable efforts to develop at least one licensed product and commercialize at least one licensed product in the United States. In connection with the Abeona Rett Agreement, the Company paid Abeona a one-time upfront license fee of $3.0 million which is recorded in research and development expenses in the consolidated statements of operations for the year ended December 31, 2020 since the acquired license does not have an alternative future use. The Company is obligated to pay Abeona up to $26.5 million in regulatory-related milestones and up to $30.0 million in sales-related milestones per licensed Rett product and high single-digit royalties on net sales of licensed Rett products. Royalties are payable on a licensed product-by-licensed product and country-by-country basis until the latest of the expiration or revocation or complete rejection of the last licensed patent covering such licensed product in the country where the licensed product is sold, the loss of market exclusivity in such country where the product is sold, or, if no licensed product exists in such country and no market exclusivity exists in such country, ten years from first commercial sale of such licensed product in such country. The Abeona Rett Agreement expires on a country-by-country and licensed product-by-licensed product basis upon the expiration of the last royalty term of a licensed product. Either party may terminate the agreement upon an uncured material breach of the agreement or insolvency of the other party. The Company may terminate the agreement for convenience upon specified prior written notice to Abeona. No additional milestone payments were made in connection with the Abeona Rett Agreement during the six months ended June 30, 2021. 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 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. Under the terms of the agreement, in exchange for granting the Company the exclusive worldwide rights to TSHA-120, HHF received an upfront payment of $5.5 million and will be eligible to receive clinical, regulatory and commercial milestones totaling up to $19.3 million, as well as a low, single-digit royalty on net sales upon commercialization of the product. In exchange for the license rights, the Company recorded an aggregate of $5.5 million within research and development expenses in the condensed consolidated statements of operations 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 six months ended June 30, 2021 No

Stockholders' Equity (Deficit),

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability	Note 5—Stockholders’ Equity (Deficit), Convertible Preferred Stock and Tranche Liability Authorized Shares The Company amended its certificate of incorporation on March 4, 2020, July 2, 2020 and again on July 28, 2020 such that the total number of shares of common stock authorized to be issued was increased to 32,685,000, and the total number of shares of preferred stock authorized to be issued was increased to 15,647,052, of which 10,000,000 preferred shares were designated Series A convertible preferred stock and 5,647,052 were designated Series B convertible preferred stock. On September 28, 2020, the Company amended its certificate of incorporation such that the total number of shares of common stock authorized to be issued was increased to 200,000,000, and the total number of shares of new preferred stock authorized to be issued was 10,000,000. As of June 30, 2021 and December 31, 2020, no shares of preferred stock were issued or outstanding. IPO On September 28, 2020, the Company issued an aggregate of 7,869,566 shares of common stock in the IPO, and on September 29, 2020, the Company issued an aggregate of 1,180,434 shares of common stock upon the underwriters’ exercise in full of their option to purchase additional shares, each at the public offering price of $20.00 per share less underwriting discounts and commissions. In connection with the IPO, the Company received gross proceeds of $181.0 million, which was offset by issuance costs, including underwriters’ discounts and commissions, of approximately $15.1 million. Series A and B convertible preferred stock On March 4, 2020, the Company entered into a purchase agreement (the “Series A Purchase Agreement”) providing for a private placement of up to 10,000,000 shares of Series A convertible preferred stock at an original issuance price of $3.00 per share, subject to separate closings, including: (1) 6,000,000 shares at the initial closing on March 4, 2020, and (2) 2,000,000 shares at each of two subsequent closings triggered by the achievement of specific clinical milestones. The Series A Purchase Agreement obligated the Company to issue and sell and the Series A investors to purchase up to a total of 4,000,000 additional shares of Series A convertible preferred stock (the “Milestone Shares”) at the same price per share upon the achievement of certain defined clinical milestones (the “tranche liability”). The determination as to whether the milestone events had been met was subject to certification by the Board of Directors. Each Series A investor had the right, but not the obligation, to purchase all or any portion of the Milestone Shares at any time in its sole option and in its sole and absolute discretion, whether or not the Company had achieved the applicable clinical milestone. On June 30, 2020, several affiliated Series A investors elected to exercise in full their options to purchase 200,000 shares, representing all of their remaining pro-rata portion of the Milestone Shares, prior to the Company’s achievement of the clinical milestones for gross proceeds of $0.6 million. The remainder of the Series A investors exercised in full their options to purchase 3,800,000 shares, representing all of their remaining pro-rata portion of the Milestone Shares, prior to the Company’s achievement of the clinical milestones, for gross proceeds of $11.4 million between July 1, 2020 and July 2, 2020. As part of this issuance, the Company issued and sold 3,266,667 shares to PBM TGT Holdings, LLC and 400,000 shares to Nolan Capital, LLC, which stockholders are controlled by certain members of the Company’s board of directors. On July 2, 2020, the Company entered into a purchase agreement (the “Series B Purchase Agreement”), as later amended on July 28, 2020, providing for a private placement of up to 5,647,052 shares of Series B convertible preferred stock. The Company sold 5,647,048 shares of Series B convertible preferred stock at a price of $17.00 per share in multiple closings in July and August 2020 for gross proceeds of $96.0 million. The majority of investors that participated in the Series B Purchase Agreement were new investors. As described above, in connection with the closing of the IPO, all shares of Series A and Series B convertible preferred stock were automatically converted into an aggregate of 17,047,378 shares of common stock with a conversion ratio, which was adjusted for the stock split, of 1.0895 shares of common stock for each share of Series A and Series B convertible preferred stock then outstanding. Series A convertible preferred stock tranche liability The Company concluded that the tranche liability met the definition of a freestanding financial instrument, as it was legally detachable and separately exercisable from the initial closing of the Series A convertible preferred stock. The estimated fair value of the tranche liability was determined using a Monte Carlo simulation at the initial issuance date. As of March 4, 2020, the simulations occurred based on the implied aggregate equity value of the Company derived from the Series A convertible preferred stock offering price of $3.00 per share, along with, in part, the following subjective assumptions: risk-free rate of 0.59%, an expected volatility of 80%, the expected term to a liquidity event of 1 year, and a 60% probability of achieving the clinical milestones and timing thereof. Subsequently, the estimated fair value of the tranche liability was determined using a backsolve approach at June 30, 2020, immediately prior to the issuance of the Milestone Shares, which was calculated based on the aggregate equity value of the Company derived from the Series B convertible preferred stock offering price of $17.00 per share. The subsequent remeasurement also considered, in part, a risk-free rate of 0.17%, an expected volatility of 80%, and the expected term to a liquidity event of 0.5 years. Based on the analysis, the Company recorded a preferred stock tranche liability of $1.1 million at the issue date to account for the obligation to issue the Milestone Shares at a predetermined fixed price at a future settlement date. At June 30, 2020, ahead of the anticipated closing of the Series B Purchase Agreement for $17.00 per share that occurred on July 2, 2020, certain investors elected to exercise in full their options to purchase their pro-rata portion of the Milestone Shares prior to the Company’s achievement of the clinical milestones and purchased 200,000 shares of Series A convertible preferred stock. The Company remeasured the fair value of the entire tranche liability at June 30, 2020, and recognized a non-cash expense of $17.0 million in the condensed consolidated statement of operations for the six months ended June 30, 2020. As 200,000 of the Milestone Shares were also issued to certain investors on June 30, 2020, the related tranche liability was extinguished, and the Company reclassified $0.9 million to convertible preferred stock on the condensed consolidated balance sheet as of June 30, 2020. The Company concluded that no beneficial conversion feature (“BCF”) existed as the effective conversion price of the Series A convertible preferred stock exceeded the fair value of the Company’s common stock at each of the commitment dates. Specifically at the commitment date of June 30, 2020, when 200,000 Milestone Shares were issued, the deemed proceeds were equal to the cash proceeds received for the shares of Series A convertible preferred stock and the fair value of the tranche liability that related to the Milestone Shares, or $7.52 per share. As the effective conversion price exceeded the fair value of the Company’s common stock, no BCF existed.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2021
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 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. On September 16, 2020, the Company’s stockholders approved the New Plan, which became effective upon the execution of the underwriting agreement in connection with the IPO. The number of shares available for future issuance under the New Plan is 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. At December 31, 2020, there were 2,941,509 shares available for future grant under the New Plan. The number of shares of common stock reserved for issuance under the New Plan will automatically increase 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 board of directors increased the number of common stock reserved for issuance under the New Plan by 1,434,934 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 date 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 as of January 1, 2021 and no issuances have been made under the ESPP as of June 30, 2021. 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 For the three months ended June 30, 2021, options to purchase 964,750 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $14.73. For the six months ended June 30, 2021, options to purchase 2,586,650 shares of common stock under the New Plan were awarded with a weighted-average grant date fair value per share of $17.25. 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 six months ended June 30, 2021: Three months ended June 30, 2021 Six months ended June 30, 2021 Risk-free interest rate 1.07 % 0.80 % Expected dividend yield — — Expected term in years 6.0 6.0 Expected volatility 76 % 75 % The following table summarizes stock option activity, during the six months ended June 30, 2021: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at December 31, 2020 674,842 20.68 9.8 $ 3,953 Options granted 2,586,650 26.41 Options cancelled or forfeited (47,800 ) 28.61 Outstanding at June 30, 2021 3,213,692 $ 25.18 9.6 $ 786 Vested and expected to vest at June 30, 2021 3,213,692 $ 25.18 9.6 $ 786 Options exercisable at June 30, 2021 43,054 $ 20.50 9.3 $ 37 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 June 30, 2021 and the exercise price of the stock options. As of June 30, 2021, the total unrecognized compensation related to unvested stock option awards granted was $47.5 million, which the Company expects to recognize over a weighted-average period of approximately 3.5 years. 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 June 30, 2021, 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 $13.3 million which is expected to be amortized on a straight-line basis over the weighted-average remaining vesting period of approximately 1.5 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 six months ended June 30, 2021 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at January 1, 2021 2,850,053 $ 6.37 Restricted units granted — — Vested (629,730 ) 5.25 Cancelled or forfeited (167,186 ) 5.25 Nonvested at June 30, 2021 2,053,137 $ 6.80 Restricted Stock Awards RA Session II, the Company’s founder, 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 six months ended June 30, 2021 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at December 31, 2020 769,058 $ 5.28 Restricted stock granted — — Vested (298,843 ) 5.28 Nonvested at June 30, 2021 470,215 $ 5.28 The following table summarizes the total stock-based compensation expense for the stock options, RSAs and RSUs recorded in the condensed consolidated statements of operations for the three and six months ended June 30, 2021 (in thousands): For the Three Months Ended June 30, 2021 For the Six Months Ended June 30, 2021 Research and development expense $ 2,214 $ 3,793 General and administrative expense 2,335 4,350 Total $ 4,549 $ 8,143

Net Loss Per Common Share

Net Loss Per Common Share	6 Months Ended
	Jun. 30, 2021
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 June 30, For the Six Months Ended June 30, 2021 2020 2021 2020 Net loss $ (40,926 ) $ (21,220 ) $ (72,950 ) $ (26,651 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 37,479,164 10,894,999 37,237,115 10,894,999 Net loss per common share, basic and diluted $ (1.09 ) $ (1.95 ) $ (1.96 ) $ (2.45 ) The following common stock equivalents outstanding as of June 30, 2021 and 2020 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: June 30, 2021 June 30, 2020 Unvested RSUs 2,053,137 — Unvested RSAs 470,215 — Stock options 3,213,692 — Series A convertible preferred stock — 6,200,000 Total 5,737,044 6,200,000

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Note 8—Related Party Transactions RA Session II, founder, President and Chief Executive Officer and a member of the Company’s board of directors, was a guarantor under the Guaranty and Security Agreement between himself, Queen’s and the Company, and in the event of the Company’s failure to fund its obligations under the RGA with Queen’s, had personally guaranteed payments due by the Company to Queen’s. In addition, the Company entered into two secured promissory notes with Mr. Session in January 2020 for an aggregate of $1.67 million, with 10% interest. The Company secured the notes with a first priority security interest in certain assets of the Company. During March 2020, the Company repaid $1.65 million of the notes, and the remaining balance was repaid in July 2020. In March 2020, the Company entered into a services agreement with PBM Capital Group, LLC (“PBM”), an affiliate of PBM TGT Holdings, LLC whereby PBM provides accounting and other administrative and management services related to payroll administration, human resources, bookkeeping, preparation of financial statements and tax returns, accounts payable and receivable, and other similar functions for a fee of $2,500 per month. Paul B. Manning, a member of the Company’s board of directors and a holder of more than 5% of the Company’s capital stock, is the Chief Executive Officer of PBM Capital Group, LLC and has sole voting and investment power with respect to the shares held by PBM TGT Holdings, LLC. In September 2020, PBM TGT Holdings, LLC distributed all of the shares of Series A convertible preferred stock it previously held to its beneficial owners, including Mr. Manning and entities controlled by Mr. Manning, for no additional consideration in accordance with the terms of its operating agreement. In April 2021, the PBM services agreement was terminated and all outstanding amounts due have been paid.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Note 9—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 June 30, 2021, 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, 2020.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 10—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 June 30, 2021. The Company does not anticipate recognizing any significant losses relating to these arrangements. Durham Lease On December 17, 2020, the Company entered into a lease agreement (the “Durham Lease”) with Patriot Park Partners II, LLC, a Delaware limited liability company (the “Durham Landlord”), pursuant to which the Company agreed to lease approximately 187,500 square feet of a manufacturing facility located at 5 National Way, Durham, North Carolina (the “Facility”). The Durham Lease commenced on April 1, 2021 and is expected to have a term of approximately fifteen years and six months. The Company has two options to extend the term of the Durham Lease, each for a period of an additional five years. The Company was not required to provide a security deposit in connection with its entry into the Durham Lease. The Company will be responsible for constructing interior improvements within the Facility. The 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 in December 2020. 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 Dallas Lease On January 11, 2021, the Company entered into a lease agreement (the “Dallas Lease”) with Pegasus Park, LLC, a Delaware limited liability company (the “Dallas Landlord”), pursuant to which the Company will lease approximately 15,000 square feet of office space at 3000 Pegasus Park Drive, Dallas, Texas 75247 (the “Office Space”). The Dallas Lease commenced on May 27, 2021, and has a term of approximately ten years. The Company has an option to extend the term of the Dallas Lease for one additional period of five years. The Company’s obligation for the payment of base rent for the Office Space is initially approximately $32,500 per month and will increase annually, up to an estimated monthly base rent of $50,000 during the term of the Lease. The Company is obligated to pay operating costs and utilities applicable to the Office Space. The Company was required to provide a security deposit of $32,500 in connection with its entry into the Dallas Lease. Total future minimum lease payments under the Dallas Lease over the initial 10 year term are approximately $4.9 million. The Company has a right of first refusal with respect to certain additional adjacent office space before the Dallas Landlord accepts any offer for such space. The Dallas Landlord has the right to terminate the Lease, or the Company’s right to possess the Office Space without terminating the Dallas Lease, upon specified events of default, including the Company’s failure to pay rent in a timely manner and upon the occurrence of certain events of insolvency with respect to the Company. As of June 30, 2021, the Company recognized approximately $0.6 million of lease construction incentive based on the construction allowance provided. The construction incentive has been recorded on the condensed consolidated balance sheets as a deferred lease incentive obligation and is being amortized into earnings as a deduction of rent expense over the term of the Dallas Lease.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Note 11—Subsequent Events 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 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 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. 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, 2022 with payment of a 2.00% prepayment premium, after which they 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 will be due upon prepayment or repayment of the Term Loans in full. 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.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
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, 2020, filed with the Securities and Exchange Commission ("SEC") on March 3, 2021 (the “2020 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, 2020 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 2020 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 that were incorporated during 2020, and one inactive foreign subsidiary incorporated in June 2021. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. The most significant estimates and assumptions in the Company’s financial statements relate to the determination of the fair value of the common stock prior to the IPO (as an input into stock-based compensation), estimating preclinical manufacturing accruals and accrued or prepaid research and development expenses, and the valuation of the preferred stock tranche liability. 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. In response to the ongoing and rapidly evolving COVID-19 pandemic, management considered the impact of the estimated economic implications on the Company’s critical and significant accounting estimates, including assessment of impairment of long-lived assets.
Build-to-Suit Lease	Build-to-Suit Lease In the Company’s recent lease arrangement (as described in Note 10), the Company was involved in the construction of the build-out. To the extent the Company is involved with the structural improvements of the construction project or takes construction risk prior to the commencement of a lease, accounting guidance requires the Company to be considered the owner for accounting purposes of these types of projects during the construction period. In such cases, the Company records an asset in property, plant and equipment on its consolidated balance sheet equal to the fair value of the building shell, and a corresponding build-to-suit lease obligation on its consolidated balance sheet representing the amounts paid by the lessor. Upon completion of construction, the Company will consider the requirements for sale-leaseback accounting treatment, including evaluating whether all risks of ownership have been transferred back to the landlord.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), as amended, with guidance regarding the accounting for and disclosure of leases. This update requires lessees to recognize the liabilities related to all leases, including operating leases, with a term greater than 12 months on the balance sheets. This update also requires lessees and lessors to disclose key information about their leasing transactions. This guidance will become effective for the Company for annual reporting periods beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. 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 has not yet concluded which approach will be utilized to adopt the new standard and is currently evaluating the impact of this standard on its consolidated financial statements.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2021
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): June 30, 2021 December 31, 2020 Prepaid research and development $ 6,716 $ 2,462 Prepaid bonus 1,192 409 Prepaid insurance 826 2,480 Prepaid clinical trial 184 944 Other 1,014 331 Total prepaid expenses and other current assets $ 9,932 $ 6,626
Schedule of Property Plant and Equipment, Net	Property, plant and equipment, net consisted of the following (in thousands): June 30, 2021 December 31, 2020 Leasehold improvements 1,863 — Furniture and fixtures 676 — Computer equipment 529 95 Laboratory equipment 460 — Construction in progress 30,465 201 33,993 296 Accumulated depreciation (126 ) (9 ) Property, plant and equipment, net $ 33,867 $ 287
Schedule of Accrued Expense and Other Current Labilities	Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Accrued research and development $ 14,508 $ 2,106 Accrued compensation 3,210 1,766 Accrued professional and consulting fees 1,372 999 Accrued property, plant, and equipment 1,309 173 Accrued clinical trial 959 — Other 678 91 Total accrued expenses and other current liabilities $ 22,036 $ 5,135

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Schedule of Restricted Stock Units Activity	The Company’s RSU activity for the six months ended June 30, 2021 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at January 1, 2021 2,850,053 $ 6.37 Restricted units granted — — Vested (629,730 ) 5.25 Cancelled or forfeited (167,186 ) 5.25 Nonvested at June 30, 2021 2,053,137 $ 6.80
Schedule of Restricted Stock Awards Activity	The Company’s RSA activity for the six months ended June 30, 2021 was as follows: Weighted Average Grant Date Number Fair Value of Shares per Share Nonvested at December 31, 2020 769,058 $ 5.28 Restricted stock granted — — Vested (298,843 ) 5.28 Nonvested at June 30, 2021 470,215 $ 5.28
Schedule of Total Stock-Based Compensation Expense for Stock Options, RSAs and RSUs (Detail)	The following table summarizes the total stock-based compensation expense for the stock options, RSAs and RSUs recorded in the condensed consolidated statements of operations for the three and six months ended June 30, 2021 (in thousands): For the Three Months Ended June 30, 2021 For the Six Months Ended June 30, 2021 Research and development expense $ 2,214 $ 3,793 General and administrative expense 2,335 4,350 Total $ 4,549 $ 8,143
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 six months ended June 30, 2021: Three months ended June 30, 2021 Six months ended June 30, 2021 Risk-free interest rate 1.07 % 0.80 % Expected dividend yield — — Expected term in years 6.0 6.0 Expected volatility 76 % 75 %
Schedule of Stock Option Activity	The following table summarizes stock option activity, during the six months ended June 30, 2021: Weighted Weighted Average Aggregate Average Remaining Intrinsic Stock Exercise Contractual Value Options Price Life (in years) (in thousands) Outstanding at December 31, 2020 674,842 20.68 9.8 $ 3,953 Options granted 2,586,650 26.41 Options cancelled or forfeited (47,800 ) 28.61 Outstanding at June 30, 2021 3,213,692 $ 25.18 9.6 $ 786 Vested and expected to vest at June 30, 2021 3,213,692 $ 25.18 9.6 $ 786 Options exercisable at June 30, 2021 43,054 $ 20.50 9.3 $ 37

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	6 Months Ended
	Jun. 30, 2021
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 June 30, For the Six Months Ended June 30, 2021 2020 2021 2020 Net loss $ (40,926 ) $ (21,220 ) $ (72,950 ) $ (26,651 ) Weighted-average shares of common stock outstanding used to compute net loss per common share, basic and diluted 37,479,164 10,894,999 37,237,115 10,894,999 Net loss per common share, basic and diluted $ (1.09 ) $ (1.95 ) $ (1.96 ) $ (2.45 )
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 June 30, 2021 and 2020 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: June 30, 2021 June 30, 2020 Unvested RSUs 2,053,137 — Unvested RSAs 470,215 — Stock options 3,213,692 — Series A convertible preferred stock — 6,200,000 Total 5,737,044 6,200,000

Organization and Description _2

Organization and Description of Business Operations - Additional Information (Details) $ / shares in Units, $ in Thousands	Sep. 29, 2020shares	Sep. 28, 2020USD ($)$ / sharesshares	Sep. 16, 2020shares	Aug. 31, 2020USD ($)shares	Jun. 30, 2021USD ($)$ / sharesshares	Jul. 31, 2020USD ($)shares	Jun. 30, 2021USD ($)$ / sharesshares	Jun. 30, 2020USD ($)$ / shares	Dec. 31, 2020USD ($)	Jul. 01, 2020shares
Organization and Description of Business Operations [Line Items]
Date of incorporation							Feb. 13, 2020
Share issue price per share | $ / shares								$ 7.52
Accumulated deficit | $					$ (134,076)		$ (134,076)		$ (61,126)
Gross proceeds from sale of convertible preferred stock | $								$ 18,600
Cash | $					$ 197,400		$ 197,400
Series A Convertible Preferred Stock
Organization and Description of Business Operations [Line Items]
Conversion of convertible preferred stock to common stock, shares		10,000,000
Aggregate shares sold						10,000,000
Gross proceeds from sale of convertible preferred stock | $						$ 30,000
Series B Convertible Preferred Stock
Organization and Description of Business Operations [Line Items]
Conversion of convertible preferred stock to common stock, shares		5,647,048
Aggregate shares sold				5,647,048
Gross proceeds from sale of convertible preferred stock | $				$ 96,000
Underwriters’ Option to Purchase Additional Shares
Organization and Description of Business Operations [Line Items]
Issuance of shares of common stock, shares	1,180,434	1,180,434
IPO
Organization and Description of Business Operations [Line Items]
Issuance of shares of common stock, shares		7,869,566					9,050,000
Share issue price per share | $ / shares		$ 20			$ 20		$ 20
Net proceeds from issuance of common stock | $		$ 165,900
Underwriting discounts and commissions and other offering costs | $		$ 2,500
Increase in outstanding shares		26,097,378
2020 Equity Incentive Plan
Organization and Description of Business Operations [Line Items]
Number of common stock authorized for issuance			3,845,294
Common Stock
Organization and Description of Business Operations [Line Items]
Conversion ratio		1.0895	1.0895
Issuance of shares of common stock, shares					629,730		629,730
Conversion of stock, shares issued		17,047,378
Common Stock | 2020 Equity Incentive Plan
Organization and Description of Business Operations [Line Items]
Number of common stock authorized for issuance			3,845,294							3,529,412

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Prepaid research and development	$ 6,716	$ 2,462
Prepaid bonus	1,192	409
Prepaid insurance	826	2,480
Prepaid clinical trial	184	944
Other	1,014	331
Total prepaid expenses and other current assets	$ 9,932	$ 6,626

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 33,993	$ 296
Accumulated depreciation	(126)	(9)
Property, plant and equipment, net	33,867	287
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	1,863
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	676
Computer Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	529	95
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	460
Construction in Progress
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 30,465	$ 201

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property Plant And Equipment [Line Items]
Depreciation expense	$ 85,000	$ 0	$ 117,000	$ 0
Build-to-Suit Lease
Property Plant And Equipment [Line Items]
Construction in progress	$ 30,300,000		$ 30,300,000

Balance Sheet Components - Sc_3

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Accrued research and development	$ 14,508	$ 2,106
Accrued compensation	3,210	1,766
Accrued professional and consulting fees	1,372	999
Accrued property, plant, and equipment	1,309	173
Accrued clinical trial	959
Other	678	91
Total accrued expenses and other current liabilities	$ 22,036	$ 5,135

Research, Collaboration and L_2

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

1 Months Ended

3 Months Ended

6 Months Ended

12 Months Ended

Mar. 31, 2021USD ($)

Oct. 31, 2020USD ($)

Aug. 31, 2020USD ($)

Apr. 30, 2020Product

Dec. 31, 2019USD ($)

Jun. 30, 2021USD ($)shares

Jun. 30, 2020USD ($)

Mar. 31, 2020USD ($)shares

Jun. 30, 2021USD ($)shares

Jun. 30, 2020USD ($)

Dec. 31, 2020USD ($)shares

Oct. 29, 2020USD ($)

Feb. 21, 2020USD ($)

Nov. 30, 2019shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Common stock, shares issued | shares

38,391,165

38,391,165

37,761,435

Research and development

$ 30,643,000

$ 3,062,000

$ 54,497,000

$ 8,576,000

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

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

20.00%

Percentage of entitled to receive additional shares on fully diluted basis

10.00%

Queen's Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Research grant of committed fund amount

$ 3,800,000

Percentage of interest rate

6.00%

Research grant outstanding fund amount

$ 0

Additional milestone payments

0

Queen's Agreement | Research and Development Expense

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Cash payment to acquire license agreement

$ 3,000,000

Queen's Agreement | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License agreement regulatory milestones payment

$ 10,000,000

License agreement commercial milestones payment

$ 10,000,000

Abeona CLN1 Agreements

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

0

License fee payment

$ 3,000,000

Purchase of clinical materials and reimbursement incurred development costs

$ 4,000,000

Research and development

7,000,000

Abeona CLN1 Agreements | Maximum

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

License and inventory purchase agreement regulatory related milestones payment

26,000,000

License and inventory purchase agreement sales related milestones payment

$ 30,000,000

Abeona | Abeona Rett Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payments

$ 0

Payment of one-time upfront license fee

$ 3,000,000

Abeona | Maximum | Abeona Rett Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Regulatory related milestones obligation payable

$ 26,500,000

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

$ 30,000,000

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit), Convertible Preferred Stock and Tranche Liability - Additional Information (Details) $ / shares in Units, $ in Thousands	Sep. 29, 2020shares	Sep. 28, 2020USD ($)$ / sharesshares	Sep. 16, 2020	Jul. 28, 2020$ / sharesshares	Jul. 02, 2020USD ($)$ / sharesshares	Jun. 30, 2020USD ($)$ / sharesshares	Mar. 05, 2020shares	Mar. 04, 2020USD ($)$ / sharesshares	Aug. 31, 2020USD ($)	Jun. 30, 2021$ / sharesshares	Jun. 30, 2020USD ($)$ / shares	Jul. 31, 2020USD ($)	Jun. 30, 2021$ / sharesshares	Jun. 30, 2020USD ($)$ / shares	Dec. 31, 2020shares
Class Of Stock [Line Items]
Common stock, shares authorized		200,000,000		32,685,000						200,000,000			200,000,000		200,000,000
Convertible preferred stock, shares authorized				15,647,052
Convertible preferred stock, shares authorized		10,000,000								10,000,000			10,000,000		10,000,000
Preferred stock, shares issued										0			0		0
Preferred stock, shares outstanding										0			0		0
Share issue price per share | $ / shares						$ 7.52					$ 7.52			$ 7.52
Stock issuance costs, including underwriters’ discounts and commissions | $														$ 263
Proceeds from issuances of Series A convertible preferred stock | $														18,600
Preferred stock tranche liability | $								$ 1,100
Non cash expenses due to remeasured fair value of tranche liability | $						$ 17,000					$ (17,210)			(17,030)
Mile stone shares issued during the period						200,000
Tranche liability amount reclassified to convertible preferred stock | $						$ 900					$ 900			$ 900
Common Stock
Class Of Stock [Line Items]
Shares issued during period										629,730			629,730
Conversion of stock, shares issued		17,047,378
Conversion ratio		1.0895	1.0895
IPO
Class Of Stock [Line Items]
Shares issued during period		7,869,566											9,050,000
Share issue price per share | $ / shares		$ 20								$ 20			$ 20
Gross proceeds from issuance of common stock | $		$ 181,000
Stock issuance costs, including underwriters’ discounts and commissions | $		$ 15,100
Underwriters' Option to Purchase Additional Shares
Class Of Stock [Line Items]
Shares issued during period	1,180,434	1,180,434
Series A Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized				10,000,000
Number of share options exercised					3,800,000	200,000
Clinical milestones for gross proceeds | $					$ 11,400	$ 600
Proceeds from issuances of Series A convertible preferred stock | $												$ 30,000
Convertible preferred stock tranche liability, offering price | $ / shares								$ 3
Convertible preferred stock tranche liability, term								1 year
Milestone pro-rate shares issued during the period						200,000
Series A Convertible Preferred Stock | Risk Free Rate
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input								0.0059
Series A Convertible Preferred Stock | Expected Volatility
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input								0.80
Series A Convertible Preferred Stock | Probability of Achieving Clinical Milestones and Timing
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input								0.60
Series A Convertible Preferred Stock | PBM TGT Holdings, LLC
Class Of Stock [Line Items]
Shares issued during period						3,266,667
Series A Convertible Preferred Stock | Nolan Capital, LLC
Class Of Stock [Line Items]
Shares issued during period						400,000
Series A Convertible Preferred Stock | Private Placement | Series A Purchase Agreement
Class Of Stock [Line Items]
Share issue price per share | $ / shares								$ 3
Series A Convertible Preferred Stock | Private Placement | Series A Purchase Agreement | Maximum
Class Of Stock [Line Items]
Shares issued during period								10,000,000
Series A Convertible Preferred Stock | Private Placement | Initial Closing
Class Of Stock [Line Items]
Shares issued during period								6,000,000
Series A Convertible Preferred Stock | Private Placement | Achievement of Specific Clinical Milestone One
Class Of Stock [Line Items]
Shares issued during period							2,000,000
Series A Convertible Preferred Stock | Private Placement | Achievement of Specific Clinical Milestone Two
Class Of Stock [Line Items]
Shares issued during period							2,000,000
Series A Convertible Preferred Stock | Private Placement | Upon Achievement of Certain Defined Clinical Milestones
Class Of Stock [Line Items]
Shares issued during period								4,000,000
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized				5,647,052
Proceeds from issuances of Series A convertible preferred stock | $									$ 96,000
Convertible preferred stock tranche liability, offering price | $ / shares						$ 17					$ 17			$ 17
Convertible preferred stock tranche liability, term						6 months
Series B Convertible Preferred Stock | Risk Free Rate
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input						0.0017					0.0017			0.0017
Series B Convertible Preferred Stock | Expected Volatility
Class Of Stock [Line Items]
Convertible preferred stock tranche liability, measurement input						0.80					0.80			0.80
Series B Convertible Preferred Stock | Series B Purchase Agreement
Class Of Stock [Line Items]
Share issue price per share | $ / shares					$ 17
Series B Convertible Preferred Stock | Private Placement | Series B Purchase Agreement
Class Of Stock [Line Items]
Shares issued during period				5,647,048
Share issue price per share | $ / shares				$ 17
Proceeds from issuances of Series A convertible preferred stock | $									$ 96,000
Series B Convertible Preferred Stock | Private Placement | Series B Purchase Agreement | Maximum
Class Of Stock [Line Items]
Shares issued during period				5,647,052

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	Jan. 01, 2021	Sep. 16, 2020	Sep. 02, 2020	Jul. 01, 2020	Jun. 30, 2021	Jun. 30, 2021
Employee Stock Purchase Plan (“ESPP”)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		724,000
Share-based payment award, expiration period		10 years
Share-based payment award, expiration date		Jan. 1, 2030
Percentage of automatic increase every year in common stock shares reserved for future issuance		1.00%
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 date 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.
Share-based payment award, options granted	0
Number of shares of common stock issued under ESPP						0
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 6 months
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 13,300,000	$ 13,300,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, options granted						2,586,650
Share-based payment award, options granted, exercise price per share						$ 26.41
Share-based payment award, options, compensation cost not yet recognized					47,500,000	$ 47,500,000
Share-based payment award, compensation cost not yet recognized, weighted-average period of recognition						3 years 6 months
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						1 year 9 months 18 days
Share-based payment award, unvested RSU/RSA granted, compensation cost not yet recognized					$ 2,600,000	$ 2,600,000
Share-based payment award, RSU/RSA granted, weighted average grant date fair value				$ 5.28
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance		3,845,294
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			25.00%
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			25.00%
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			25.00%
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			25.00%
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	1,434,934	3,390,168
Share-based payment award, expiration period		10 years
Share-based payment award, commencement date		Jan. 1, 2021
Share-based payment award, expiration date		Jan. 1, 2030
Percentage of automatic increase every year in common stock shares reserved for future issuance		5.00%
Share-based payment award, terms of award issuance						At December 31, 2020, there were 2,941,509 shares available for future grant under the New Plan. The number of shares of common stock reserved for issuance under the New Plan will automatically increase 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 board of directors increased the number of common stock reserved for issuance under the New Plan by 1,434,934 shares.
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					964,750	2,586,650
Share-based payment award, options, weighted-average grant date fair value					$ 14.73	$ 17.25
New Plan | Stock Options | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					4 years
New Plan | Stock Options | Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					1 year

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	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.07%	0.80%
Expected term in years	6 years	6 years
Expected volatility	76.00%	75.00%

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Stock Option Activity (Details) - Stock Options $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding. Stock Options, Beginning Balance | shares	674,842
Options granted, Stock Options | shares	2,586,650
Options cancelled or forfeited, Stock Options | shares	(47,800)
Outstanding. Stock Options, Ending Balance | shares	3,213,692	674,842
Vested and expected to vest at June 30, 2021, Stock Options | shares	3,213,692
Options exercisable at June 30, 2021, Stock Options | shares	43,054
Outstanding, Weighted Average Exercise Price, Beginning balance | $ / shares	$ 20.68
Options granted, Weighted Average Exercise Price | $ / shares	26.41
Options cancelled or forfeited, Weighted Average Exercise Price | $ / shares	28.61
Outstanding, Weighted Average Exercise Price, Ending balance | $ / shares	25.18	$ 20.68
Vested and expected to vest at June 30, 2021, Weighted Average Exercise Price | $ / shares	25.18
Options exercisable at June 30, 2021, Weighted Average Exercise Price | $ / shares	$ 20.50
Outstanding, Weighted Average Remaining Contractual Life	9 years 7 months 6 days	9 years 9 months 18 days
Vested and expected to vest at June 30, 2021, Weighted Average Exercise Price	9 years 7 months 6 days
Options exercisable at June 30, 2021, Weighted Average Exercise Price	9 years 3 months 18 days
Outstanding, Aggregate Intrinsic Value, Beginning Balance | $	$ 3,953
Outstanding, Aggregate Intrinsic Value, Ending Balance | $	786	$ 3,953
Vested and expected to vest at June 30, 2021, Aggregate Intrinsic Value | $	786
Options exercisable at June 30, 2021, Aggregate Intrinsic Value | $	$ 37

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Restricted Stock Units Activity (Details) - Restricted Stock Units	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance | shares	2,850,053
Vested, Number of Shares | shares	(629,730)
Cancelled or forfeited, Number of Shares | shares	(167,186)
Nonvested, Number of Shares, Ending Balance | shares	2,053,137
Nonvested, Weighted Average Grant Date Fair Value per Share, Beginning Balance | $ / shares	$ 6.37
Vested, Weighted Average Grant Date Fair Value per Share | $ / shares	5.25
Cancelled or forfeited, Weighted Average Grant Date Fair Value per Share | $ / shares	5.25
Nonvested, Weighted Average Grant Date Fair Value per Share, Ending Balance | $ / shares	$ 6.80

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Restricted Stock Awards Activity (Details) - Restricted Stock Awards - $ / shares	Jul. 01, 2020	Jun. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested, Number of Shares, Beginning Balance		769,058
Vested, Number of Shares		(298,843)
Nonvested, Number of Shares, Ending Balance		470,215
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, RSAs and RSUs (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 4,549	$ 8,143
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,214	3,793
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,335	$ 4,350

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (40,926)	$ (21,220)	$ (72,950)	$ (26,651)
Weighted average common shares outstanding, basic and diluted	37,479,164	10,894,999	37,237,115	10,894,999
Net loss per common share, basic and diluted	$ (1.09)	$ (1.95)	$ (1.96)	$ (2.45)

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	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	5,737,044	6,200,000
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	2,053,137
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	470,215
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	3,213,692
Series A Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share		6,200,000

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)	1 Months Ended
	Mar. 31, 2020USD ($)	Jan. 31, 2020USD ($)PromissoryNote	Sep. 30, 2020USD ($)
PBM Capital Group, LLC | Services Agreement
Related Party Transaction [Line Items]
Accounting and other administrative and management services fee per month	$ 2,500
PBM TGT Holdings, LLC
Related Party Transaction [Line Items]
Additional consideration payable under operating agreement			$ 0
RA Session II
Related Party Transaction [Line Items]
Number of secured promissory notes | PromissoryNote		2
Paul B. Manning | Services Agreement
Related Party Transaction [Line Items]
Ownership percentage more than capital stock	5.00%
Secured Promissory Notes | RA Session II
Related Party Transaction [Line Items]
Aggregate amount, related party transaction		$ 1,670,000
Percentage of interest rate		10.00%
Repayments of debt	$ 1,650,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details)	6 Months Ended
	Jun. 30, 2021USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Jan. 11, 2021USD ($)ft²	Dec. 17, 2020ft²	Jun. 30, 2021USD ($)	Dec. 31, 2020USD ($)
Loss Contingencies [Line Items]
Build-to-suit lease liability			$ 26,209,000
Dallas Lease
Loss Contingencies [Line Items]
Lease construction incentive			600,000
Durham Lease
Loss Contingencies [Line Items]
Number of operating lease landlord square feet manufacturing facility | ft²		187,500
Operating lease commencement date		Apr. 1, 2021
Operating lease term of contract		15 years 6 months
Operating lease extend term of contract		5 years
Operating leases initial direct costs				$ 800,000
Build-to-suit asset			26,300,000
Build-to-suit lease liability			26,300,000
Equipment purchases and build-out of leased Facility			$ 4,000,000
Dallas Lease | Pegasus Park L L C
Loss Contingencies [Line Items]
Number of operating lease landlord square feet manufacturing facility | ft²	15,000
Operating lease commencement date	May 27, 2021
Operating lease term of contract	10 years
Operating lease extend term of contract	5 years
Lease, option to extend description	Company has an option to extend the term of the Dallas Lease for one additional period of five years.
Lease, option to extend	true
Obligation for payment of initial base rent for office space	$ 32,500,000
Maximum estimated monthly base rent increase annually during term of lease	50,000,000
Security deposit	$ 32,500,000
Maximum construction allowance provided by landlord per rentable square foot | ft²	40
Future minimum lease payments	$ 4,900,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event	Aug. 12, 2021USD ($)Program
Subsequent Event [Line Items]
Debt instrument, maturity date	Aug. 1, 2026
Percentage of interest rate	7.00%
Percentage of prepayment of facility	7.50%
Warrants associated with loan facility	$ 0
Prime Rate
Subsequent Event [Line Items]
Debt instrument, basis spread on variable rate	3.75%
Term Loan
Subsequent Event [Line Items]
Current borrowing capacity	$ 30,000,000
Through December 31, 2021 | Term Loan
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 40,000,000
Debt instrument, maturity date	Dec. 31, 2021
January 1, 2022 until September 30, 2022 | Term Loan
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 20,000,000
Debt instrument, maturity start date	Jan. 1, 2022
Debt instrument, maturity end date	Sep. 30, 2022
October 1, 2022 until March 31, 2023 | Term Loan
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 20,000,000
Debt instrument, maturity start date	Oct. 1, 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
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 20,000,000
Debt instrument, maturity start date	Apr. 1, 2023
Debt instrument, maturity end date	Dec. 31, 2023
Through August 13, 2022
Subsequent Event [Line Items]
Percentage of prepayment premium	2.00%
Through August 13, 2023
Subsequent Event [Line Items]
Percentage of prepayment premium	1.00%