Cabaletta Bio (CABA) 10-Q 1 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 29, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	CABA
Entity Registrant Name	CABALETTA BIO, INC.
Entity Current Reporting Status	Yes
Entity Central Index Key	0001759138
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		28,331,638
Entity File Number	001-39103
Entity Tax Identification Number	82-1685768
Entity Address, Address Line One	2929 Arch Street
Entity Address, Address Line Two	Suite 600
Entity Address, City or Town	Philadelphia
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19104
City Area Code	267
Local Phone Number	759-3100
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, par value $0.00001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 118,260	$ 101,429
Short-term investments	1,000	7,233
Prepaid expenses and other current assets	1,592	4,873
Total current assets	120,852	113,535
Property and equipment, net	1,462	890
Other assets	324	299
Total Assets	122,638	114,724
Current liabilities:
Accounts payable	1,707	1,243
Accrued and other current liabilities	4,316	3,937
Total current liabilities	6,023	5,180
Commitments and Contingencies (see Note 6)
Stockholders’ equity:
Preferred stock, $0.00001 par value: 10,000,000 shares authorized as of September 30, 2021 and December 31, 2020, respectively; no shares issued or outstanding at September 30, 2021 and December 31, 2020
Voting and non-voting common stock, $0.00001 par value: 150,000,000 (143,590,481 voting and 6,409,519 non-voting) shares authorized as of September 30, 2021 and December 31, 2020, respectively; 27,731,638 (23,419,138 voting and 4,312,500 non-voting) and 24,062,775 (19,387,160 voting and 4,675,615 non-voting) shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	0	0
Additional paid-in capital	215,314	175,836
Accumulated other comprehensive income		6
Accumulated deficit	(98,699)	(66,298)
Total stockholders’ equity	116,615	109,544
Total liabilities and stockholders’ equity	$ 122,638	$ 114,724

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, authorized shares	10,000,000	10,000,000
Preferred stock, issued shares	0	0
Preferred stock, outstanding shares	0	0
Common stock, authorized shares	150,000,000	150,000,000
Common stock, issued shares	27,731,638	24,062,775
Common stock, outstanding shares	27,731,638	24,062,775
Voting Common Stock
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, authorized shares	143,590,481	143,590,481
Common stock, issued shares	23,419,138	19,387,160
Common stock, outstanding shares	23,419,138	19,387,160
Non-voting Common Stock
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, authorized shares	6,409,519	6,409,519
Common stock, issued shares	4,312,500	4,675,615
Common stock, outstanding shares	4,312,500	4,675,615

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 8,169	$ 5,650	$ 22,575	$ 15,601
General and administrative	3,394	2,766	9,845	8,902
Total operating expenses	11,563	8,416	32,420	24,503
Loss from operations	(11,563)	(8,416)	(32,420)	(24,503)
Other income:
Interest income	3	23	19	473
Net loss	(11,560)	(8,393)	(32,401)	(24,030)
Other comprehensive income:
Net unrealized (loss) income on available-for-sale investments, net of tax	(1)	1	(6)	12
Net comprehensive loss	$ (11,561)	$ (8,392)	$ (32,407)	$ (24,018)
Net loss per share of voting and non-voting common stock, basic and diluted	$ (0.45)	$ (0.36)	$ (1.31)	$ (1.09)

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 138,321		$ 171,280		$ (32,959)
Beginning balance, Shares at Dec. 31, 2019		24,034,022
Stock-based compensation	873		873
Net loss	(7,485)				(7,485)
Ending balance at Mar. 31, 2020	131,709		172,153		(40,444)
Ending balance, Shares at Mar. 31, 2020		24,034,022
Beginning balance at Dec. 31, 2019	138,321		171,280		(32,959)
Beginning balance, Shares at Dec. 31, 2019		24,034,022
Net loss	(24,030)
Ending balance at Sep. 30, 2020	117,505		174,482	$ 12	(56,989)
Ending balance, Shares at Sep. 30, 2020		24,055,467
Beginning balance at Mar. 31, 2020	131,709		172,153		(40,444)
Beginning balance, Shares at Mar. 31, 2020		24,034,022
Stock-based compensation	1,067		1,067
Net unrealized gains (losses) on available-for-sale securities	11			11
Net loss	(8,152)				(8,152)
Ending balance at Jun. 30, 2020	124,635		173,220	11	(48,596)
Ending balance, Shares at Jun. 30, 2020		24,034,022
Stock-based compensation	1,127		1,127
Issuance of common stock in connection with exercise of stock options	135		135
Issuance of common stock in connection with exercise of stock options, Shares		21,445
Net unrealized gains (losses) on available-for-sale securities	1			1
Net loss	(8,393)				(8,393)
Ending balance at Sep. 30, 2020	117,505		174,482	12	(56,989)
Ending balance, Shares at Sep. 30, 2020		24,055,467
Beginning balance at Dec. 31, 2020	$ 109,544		175,836	6	(66,298)
Beginning balance, Shares at Dec. 31, 2020	24,062,775	24,062,775
Stock-based compensation	$ 1,310		1,310
Common stock issuance, net of issuance costs	2,165		2,165
Common stock issuance, net of issuance costs, Shares		194,189
Net unrealized gains (losses) on available-for-sale securities	(3)			(3)
Net loss	(9,702)				(9,702)
Ending balance at Mar. 31, 2021	103,314		179,311	3	(76,000)
Ending balance, Shares at Mar. 31, 2021		24,256,964
Beginning balance at Dec. 31, 2020	$ 109,544		175,836	6	(66,298)
Beginning balance, Shares at Dec. 31, 2020	24,062,775	24,062,775
Net loss	$ (32,401)
Ending balance at Sep. 30, 2021	$ 116,615		215,314		(98,699)
Ending balance, Shares at Sep. 30, 2021	27,731,638	27,731,638
Beginning balance at Mar. 31, 2021	$ 103,314		179,311	3	(76,000)
Beginning balance, Shares at Mar. 31, 2021		24,256,964
Stock-based compensation	1,385		1,385
Common stock issuance, net of issuance costs	7,665		7,665
Common stock issuance, net of issuance costs, Shares		701,469
Issuance of common stock in connection with exercise of stock options	60		60
Issuance of common stock in connection with exercise of stock options, Shares		9,563
Issuance of common stock under employee stock purchase plan	46		46
Issuance of common stock under employee stock purchase plan, Shares		4,834
Net unrealized gains (losses) on available-for-sale securities	(2)			(2)
Net loss	(11,139)				(11,139)
Ending balance at Jun. 30, 2021	101,329		188,467	1	(87,139)
Ending balance, Shares at Jun. 30, 2021		24,972,830
Stock-based compensation	1,508		1,508
Common stock issuance, net of issuance costs	24,880		24,880
Common stock issuance, net of issuance costs, Shares		2,710,347
Issuance of common stock in connection with exercise of stock options	459		459
Issuance of common stock in connection with exercise of stock options, Shares		48,461
Net unrealized gains (losses) on available-for-sale securities	(1)			$ (1)
Net loss	(11,560)				(11,560)
Ending balance at Sep. 30, 2021	$ 116,615		$ 215,314		$ (98,699)
Ending balance, Shares at Sep. 30, 2021	27,731,638	27,731,638

Condensed Statements of Stock_2

Condensed Statements of Stockholders' Equity (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Common Stock
Issuance costs	$ 769	$ 237	$ 67

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (32,401)	$ (24,030)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	4,203	3,067
Amortization of premium on investments	62	81
Depreciation	499	244
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	3,280	1,871
Other assets	(25)	(138)
Accounts payable	409	59
Accrued and other current liabilities	379	1,249
Net cash used in operating activities	(23,594)	(17,597)
Cash flows from investing activities:
Purchases of property and equipment	(1,015)	(408)
Purchases of investments		(11,097)
Proceeds from maturities of investments	6,165	1,633
Net cash provided by (used in) investing activities	5,150	(9,872)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	34,710	(191)
Proceeds from issuance of common stock in connection with the exercise of stock options	519	135
Proceeds from the issuance of common stock under employee stock purchase plan	46
Net cash provided by (used in) financing activities	35,275	(56)
Net increase (decrease) in cash and cash equivalents	16,831	(27,525)
Cash and cash equivalents—beginning of period	101,429	136,204
Cash and cash equivalents—end of period	118,260	108,679
Supplemental disclosures of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable	$ 76	$ 227

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Basis of Presentation	1. Basis of Presentation Cabaletta Bio, Inc. (the Company or Cabaletta) was incorporated in April 2017 in the State of Delaware as Tycho Therapeutics, Inc. and, in August 2018, changed its name to Cabaletta Bio, Inc. The Company is headquartered in Philadelphia, Pennsylvania. Cabaletta is a clinical-stage biotechnology company focused on the discovery and development of engineered T cell therapies for B cell-mediated autoimmune diseases. Principal operations commenced in April 2018, when the Company executed sponsored research agreements with the Trustees of the University of Pennsylvania (Penn). On October 29, 2019, the Company completed its initial public offering (IPO) of 6,800,000 shares of common stock at an offering price of $11.00 per share. The Company received net proceeds of $66,156 after deducting underwriting discounts, commissions and estimated offering expenses. In connection with the IPO, the Company’s outstanding shares of Convertible Preferred Stock were automatically converted into 12,904,534 shares of common stock. In November 2019, the underwriters partially exercised their option and purchased an additional 475,501 shares of common stock resulting in net proceeds to the Company of approximately $4,864, after deducting underwriting discounts and commissions. Risks and Uncertainties The Company does not expect to generate revenue from sales of engineered T cell therapies for B cell-mediated autoimmune diseases or any other revenue unless and until the Company completes preclinical and clinical development and obtains regulatory approval for one or more product candidates. If the Company seeks to obtain regulatory approval for any of its product candidates, the Company expects to incur significant commercialization expenses. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. As a result, the Company is unable to predict the timing or amount of increased expenses or when or if the Company will be able to achieve or maintain profitability. Further, the Company is currently dependent on the University of Pennsylvania (Penn) for much of its preclinical research, clinical research and development activities and initial manufacturing activities (Note 5). Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. Even if the Company is able to generate revenues from the sale of its product candidates, if approved, it may not become profitable. If the Company fails to become profitable or is unable to sustain profitability on a continuing basis, then it may be unable to continue its operations at planned levels and be forced to reduce its operations. In December 2019, a novel strain of coronavirus (COVID-19) surfaced in Wuhan, China and has since reached multiple other regions and countries. The COVID-19 pandemic continues to evolve and to date has led to the implementation of various responses, including government-imposed quarantines, travel restrictions and other public health safety measures, which have delayed the commencement of non-COVID-19-related clinical trials, among other restrictions. The extent to which COVID-19 impacts the Company’s operations or those of its third party partners will depend on future developments, which are highly uncertain and cannot be predicted with confidence, including new information that may emerge concerning the severity of COVID-19, the impact of new strains of the virus, the effectiveness, availability and utilization of vaccines and the actions to contain COVID-19 or treat its impact, among others. The Company’s financial results to date have not been significantly impacted by COVID-19, however, the Company cannot at this time predict the specific extent, duration, or full impact that the ongoing COVID-19 pandemic will have on its financial condition, operations, and business plans, including its ability to raise additional capital, the timing and enrollment of patients in its ongoing and planned clinical trials, future financings and other expected milestones of its product candidates. Liquidity The Company has sustained annual operating losses since inception and expects to continue to generate operating losses for the foreseeable future. The Company’s ultimate success depends on the outcome of its research and development activities. The Company has cash and cash equivalents and investments of $119,260 as of September 30, 2021. Through September 30, 2021, the Company has incurred an accumulated deficit of $98,699. Management expects to incur additional losses in the future as it continues its research and development and will need to raise additional capital to fully implement its business plan and to fund its operations. The Company intends to raise such additional capital through a combination of equity offerings, debt financings, government funding arrangements, strategic alliances or other sources. However, if such financing is not available at adequate levels and on a timely basis, or such agreements are not available on favorable terms, or at all, as and when needed, the Company will need to reevaluate its operating plan and may be required to delay or discontinue the development of one or more of its product candidates or operational initiatives. The Company expects that its cash and cash equivalents as of September 30, 2021, will be sufficient to fund its projected operations for at least 12 months following the date the Company files this Quarterly Report on Form 10-Q with the Securities and Exchange Commission (SEC).

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Financial Information The accompanying unaudited interim financial statements have been prepared in conformity with generally accepted accounting principles (GAAP) and the applicable rules and regulations of the SEC regarding interim financial reporting. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB). As permitted under these rules, certain footnotes and other financial information that are normally required by GAAP have been condensed or omitted. In the opinion of management, the accompanying unaudited interim financial statements include all normal and recurring adjustments (which consist primarily of accruals and estimates that impact the financial statements) considered necessary to present fairly the Company’s financial position as of September 30, 2021 and the results of its operations and its cash flows for the three and nine months ended September 30, 2021 and 2020. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period. The balance sheet as of December 31, 2020 included herein was derived from the audited financial statements as of that date. The unaudited interim financial statements, presented herein, do not contain the required disclosures under GAAP for annual financial statements. These unaudited financial statements should be read in conjunction with the Company’s audited financial statements, which are included in the Company’s 2020 Annual Report on Form 10-K, filed with the SEC on March 16, 2021 (2020 Annual Report). 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 as of the date of the financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying financial statements include, but are not limited to, the fair value of stock-based compensation, the valuation allowance on the Company’s deferred tax assets and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates. Off-Balance Sheet Risk and Concentrations of Credit Risk Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents, which are primarily invested in U.S. treasury-based money market funds, and available-for-sale debt securities, which are invested in investment grade corporate bonds with high credit quality issuers Significant Accounting Policies There have been no significant changes to the Company’s accounting policies during the three months ended September 30, 2021, as compared to the significant accounting policies described in Note 2 of the “Notes to the Financial Statements” in the Company’s audited financial statements included in its 2020 Annual Report. Fair Value Measurement Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs (other than quoted prices included in Level 1) that are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act, until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases Revenue from Contracts with Customers and Leases

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Fair value of financial instruments At September 30, 2021 and December 31, 2020, the Company’s financial instruments included cash and cash equivalents, accounts payable and accrued expenses. The carrying amounts reported in the Company's financial statements for these instruments approximate their respective fair values because of the short-term nature of these instruments. The following tables present financial information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: September 30, 2021 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash and Cash equivalents: Money market funds $ 118,260 $ 118,260 $ — $ — Short-term investments: Corporate bonds 1,000 — 1,000 — Total $ 119,260 $ 118,260 $ 1,000 $ — December 31, 2020 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash and Cash equivalents: Money market funds $ 101,429 $ 101,429 $ — $ — Short-term investments: Corporate bonds 7,233 — 7,233 — Total $ 108,662 $ 101,429 $ 7,233 $ — Money market funds are measured at fair value on a recurring basis using quoted prices and are classified as Level 1 inputs. Investments are measured at fair value based on inputs other than quoted prices that are derived from observable market data and are classified as Level 2 inputs. There were no transfers of assets between the fair value measurement levels during the three or nine months ended September 30, 2021 or 2020. For debt securities classified as available-for-sale investments, the Company records unrealized gains or losses resulting from changes in fair value between measurement dates as a component of other comprehensive income. September 30, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair value Financial assets Money market funds Included in cash and cash equivalents $ 118,260 $ — $ — $ 118,260 Corporate bonds - due in one year or less Included in short-term investments 1,000 — — 1,000 Total $ 119,260 $ — $ — $ 119,260 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair value Financial assets Money market funds Included in cash and cash equivalents $ 101,429 $ — $ — $ 101,429 Corporate bonds - due in one year or less Included in short-term investments 7,227 6 — 7,233 Total $ 108,656 $ 6 $ — $ 108,662

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Accrued and Other Current Liabilities	4. Accrued and Other Current Liabilities Accrued and other current liabilities consist of the following: September 30, 2021 December 31, 2020 Research and development services $ 2,446 $ 1,294 General and administrative services 108 160 Compensation expense 1,710 2,445 Other 52 38 $ 4,316 $ 3,937

Collaborations, Licensing Agree

Collaborations, Licensing Agreements and other Agreements	9 Months Ended
	Sep. 30, 2021
Collaborations Licensing Agreements And Other Agreements [Abstract]
Collaborations, Licensing Agreements and Other Agreements	5. Collaborations, Licensing Agreements and Other Agreements Research Service Agreement In February 2021, the Company entered into a research service agreement with the Children’s Hospital of Philadelphia (CHOP) for vector manufacturing. In May 2021, this agreement was amended to provide additional vector manufacturing services. Research and development expense related to this research service agreement with CHOP recognized in the accompanying statements of operations was $250 and $822 for the three and nine months ended September 30, 2021, respectively. No expense was recognized for the three and nine months ended September 30, 2020. There was $250 due under this agreement as of September 30, 2021 for services performed. This agreement has a remaining cost of approximately $900, expected to be incurred through the first half of 2023. Amended and Restated License Agreement with the Trustees of the University of Pennsylvania and Children’s Hospital of Philadelphia In August 2018, the Company entered into a license agreement with Penn, as amended and restated in July 2019 to include CHOP as a party, and as amended in May 2020 and October 2021 (the License Agreement) pursuant to which the Company obtained (a) a non-exclusive, non-sublicensable worldwide license to certain of Penn’s intellectual property to conduct research, product development, clinical trials, cell manufacturing and other activities, and (b) an exclusive, worldwide, royalty-bearing right and license, with a right to sublicense, on a target-by-target basis, under certain of Penn’s intellectual property to make, use, sell, offer for sale, import, and otherwise commercialize products for the treatment of autoimmune and alloimmune diseases. Unless earlier terminated, the License Agreement expires on the expiration or abandonment or other termination of the last valid claim in Penn’s intellectual property licensed by the Company. The Company may terminate the License Agreement at any time for convenience upon 60 days written notice. In the event of an uncured, material breach, Penn may terminate the License Agreement upon 60 days written notice. Under the terms of the License Agreement, the Company was obligated to pay $2,000 annually for three years beginning August 2018 for funding to the laboratories of each of Drs. Milone and Payne (see Sponsored Research Agreements The Company is required to pay certain milestone payments upon the achievement of specified clinical and commercial milestones. Milestone payments are reduced by a certain percentage for the second product that achieves a milestone, by an additional percentage for the third product that achieves a milestone, and so on, for each subsequent product that achieves a milestone. In the event that the Company is able to successfully develop and launch multiple products under the License Agreement, total milestone payments could be approximately $21,000. Penn is also eligible to receive tiered royalties at percentage rates in the low single-digits, subject to an annual minimum royalty, on annual worldwide net sales of any products that are commercialized by the Company or its sublicensees that contain or incorporate, or are covered by, the intellectual property licensed by the Company. To the extent the Company sublicenses its license rights under the License Agreement, Penn would be eligible to receive tiered sublicense income at percentage rates in the mid-single to low double-digits. There were no amounts due under the License Agreement as of September 30, 2021. Sponsored Research Agreements The Company has sponsored research agreements with two faculty members at Penn, who are also scientific co-founders of the Company and members of the Company’s scientific advisory board. In May 2020, one of the agreements was amended to expand the scope of sponsored research. In August 2020, this agreement was further amended to extend the term of the original research plan. In April and October 2021, the other sponsored research agreement was amended to extend the term of the original research plan. Under the amended agreements, the Company has committed to funding a defined research plan through February 2023. The total estimated cost of $12,290 under the agreements satisfies the Company’s annual obligation under the License Agreement (see Amended and Restated License Agreement with the Trustees of the University of Pennsylvania Master Translational Research Services Agreement In October 2018, the Company entered into a services agreement (the Services Agreement) with Penn for additional research and development services from various laboratories within Penn. The research and development activities are detailed in separately executed Penn organization-specific addenda. In May 2020, the Company amended its Addendum with the Center for Advanced Retinal and Ocular Therapeutics (CAROT) to expand access to vector manufacturing. Research and development expense related to executed addenda under the master translational research service agreement with Penn recognized in the accompanying statements of operations for the three and nine months ended September 30, 2021 and 2020 was $418 and $1,441, respectively, and $259 and $1,997 for the three and nine months ended September 30, 2020, respectively. The Company may incur additional expenses up to $1,360 through the remaining term of the CAROT Amended Addendum. Subscription and Technology Transfer Agreement In July 2019, the Company entered into a subscription and technology transfer agreement pursuant to which the Company owed Penn an upfront subscription fee, which was paid in the third quarter of 2019, and a nominal non-refundable royalty on the net sales of products, a portion of which will be credited toward milestone payments and royalties, respectively, under the Amended License Agreement. Technology transfer activities will be at the Company’s cost and subject to agreement as to the technology to be transferred. Expense recognized under this agreement was $0 and $150 during the three and nine months ended September 30, 2021, respectively. No expense was recognized in the three and nine months ended September 30, 2020. Collaboration and License Agreement In July 2020, the Company entered into a collaboration and license agreement with Artisan Bio, Inc. (Artisan), wherein the Company and Artisan agreed to collaborate to potentially enhance certain pipeline products of the Company at specific targets using Artisan’s gene editing and engineering technology. If the Artisan technology is applied to any of the Company’s products, the Company will be responsible for the development, manufacturing, and commercialization of any such products. Under the terms of the agreement, the Company was required to pay Artisan a nominal upfront fee, as well as costs associated with research and development activities. Artisan is eligible to receive future research, development and regulatory milestones, and is also eligible to receive sales milestones and tiered royalties on net sales of products that incorporate the Artisan technology. The Company can terminate the agreement at will upon advance written notice with payment of a nominal cancellation fee. Manufacturing Agreements In January 2021, the Company entered into a Development and Manufacturing Services Agreement (WuXi Agreement) with WuXi Advanced Therapies, Inc. (WuXi) to serve as the Company’s cell processing manufacturing partner for the anticipated MuSK-CAART Phase 1 clinical trial. The Company has the right to terminate the WuXi Agreement for convenience or other reasons specified in the WuXi Agreement upon prior written notice. If the Company terminates the WuXi Agreement, it will be obligated to pay an early termination fee of $1,500. In August and October 2021, the Company entered into agreements with a contract manufacturing organization for the purchase of plasmids to be used in vector manufacturing for a total cost of approximately $1,620, expected to be incurred during 2021 and 2022. As of September 30, 2021, $469 of expense related to these agreements has been recognized in the accompanying statements of operations.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Operating Lease Agreement In February 2019, the Company entered into an operating lease agreement for new office space in Philadelphia, Pennsylvania. The lease term commenced in May 2019 and will expire in July 2022. The initial annual base rent is $261, and such amount will increase by 2% annually on each anniversary of the commencement date. The Company records rent expense on a straight-line basis over the lease term. Rent expense related to this lease agreement recognized in the accompanying statements of operations was $69 and $205 for the three and nine months ended September 30, 2021 and $67 and $200 for the three and nine months ended September 30, 2020, respectively. As of September 30, 2021, the future minimum payments for operating leases are as follows: October 1, 2021 to December 31, 2021 $ 68 2022 158 $ 226 Other Purchase Commitments In the normal course of business, the Company enters into various purchase commitments with third-party contract manufacturers for the manufacture and processing of its product candidates and related raw materials, contracts with contract research organizations for clinical trials and agreements with vendors for other services and products for operating purposes. These agreements generally provide for termination or cancellation, other than for costs already incurred. Indemnification The Company enters into certain types of contracts that contingently require the Company to indemnify various parties against claims from third parties. These contracts primarily relate to (i) the Company’s Amended and Restated Bylaws (bylaws) under which the Company must indemnify directors and executive officers, and may indemnify other officers and employees, for liabilities arising out of their relationship, (ii) contracts under which the Company must indemnify directors and certain officers and consultants for liabilities arising out of their relationship, (iii) contracts under which the Company may be required to indemnify partners against certain claims, including claims from third parties asserting, among other things, infringement of their intellectual property rights, and (iv) procurement, consulting, or license agreements under which the Company may be required to indemnify vendors, consultants or licensors for certain claims, including claims that may be brought against them arising from the Company’s acts or omissions with respect to the supplied products, technology or services. From time to time, the Company may receive indemnification claims under these contracts in the normal course of business. In addition, under these contracts, the Company may have to modify the accused infringing intellectual property and/or refund amounts received. In the event that one or more of these matters were to result in a claim against the Company, an adverse outcome, including a judgment or settlement, may have a material adverse effect on the Company’s future business, operating results or financial condition. It is not possible to determine the maximum potential amount under these contracts due to the limited history of prior indemnification claims and the unique facts and circumstances involved in each particular agreement.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Common Stock	7. Common Stock Common Stock Pursuant to the Company’s Third Amended and Restated Certificate of Incorporation (the amended and restated certificate of incorporation) filed in October 2019, the Company is authorized to issue 143,590,481 shares of voting common stock and 6,409,519 shares of non-voting common stock. Holders of voting common stock shall have the exclusive right to vote for the election of directors of the Company and on all other matters requiring stockholder action. Each share of the Company’s non-voting common stock may be converted at any time into one share of common stock at the option of its holder by providing 61 days written notice to the Company, subject to certain limitations, as described in the amended and restated certificate of incorporation. The Company has a Sales Agreement with Cowen and Company, LLC, to provide for the offering, issuance and sale of up to an aggregate amount of $75.0 million of common stock from time to time in “at-the-market” offerings (the ATM Program) pursuant to its shelf registration statement on Form S-3 (File No. 333-250006) and subject to the limitations thereof. During the nine months ended September 30, 2021, the Company sold 3,606,005 shares pursuant to the ATM Program for net proceeds of $34.7 million, after deducting commissions of $1.1 million. Subsequent to September 30, 2021, the Company sold an additional 600,000 shares pursuant to the ATM Program for net proceeds of $6.3 million. 2018 Stock Option and Grant Plan In September 2018, the Company adopted the 2018 Stock Option and Grant Plan (the 2018 Plan), which provided for the Company to sell or issue common stock, or other stock-based awards, to employees, members of the board of directors and consultants of the Company. The Company generally granted stock-based awards with service conditions only (service-based awards), although there was one grant with performance conditions. Currently, there are no unvested options with performance conditions. Stock options granted under the 2018 Plan generally vest over three to four years. There were 1,959,411 options granted under the 2018 Plan prior to the Company’s IPO in October 2019. No further grants may be made under the 2018 Plan subsequent to the IPO. 2019 Stock Option and Incentive Plan The 2019 Stock Option and Incentive Plan (2019 Plan) was approved by the Company’s board of directors on October 14, 2019, and became effective on October 23, 2019. The 2019 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, directors and consultants. The number of shares initially reserved for issuance under the 2019 Plan was 2,342,288, and such number of shares will be increased each January 1 thereafter by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors. On January 1, 2021, the total number of shares under the 2019 Plan was increased by 962,511 shares. As of September 30, 2021, there were 2,080,288 shares remaining available for issuance. A summary of stock option activity is presented below: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding as of January 1, 2021 2,900,479 $ 7.33 8.5 $ 16,303 Granted 1,429,233 11.20 Exercised (58,024 ) 8.94 81 Forfeited/Cancelled (232,707 ) 10.87 Outstanding as of September 30, 2021 4,038,981 $ 8.47 8.3 $ 16,484 Options Exercisable at September 30, 2021 1,603,995 $ 5.70 7.6 $ 10,983 The aggregate intrinsic value of options granted is calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock. The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2021 and 2020 was $7.68 and $8.25, respectively. The fair value of each award is estimated using Black-Scholes based on the following assumptions: Nine Months Ended September 30, 2021 2020 Risk-free interest rate 0.63%—1.15% 0.28%—1.48% Expected term 5.5—6.1 years 5.7—6.1 years Expected volatility 79%—81% 70%—79% Expected dividend yield 0% 0% Black-Scholes requires the use of subjective assumptions which determine the fair value of stock-based awards. These assumptions include: Fair value of common stock —Prior to the Company’s IPO in October 2019, the fair value of the Company’s common stock underlying stock-based awards was estimated on each grant date by the Company’s board of directors. In order to determine the fair value of the Company’s common stock underlying stock-based awards, the Company’s board of directors considered, among other things, a valuation of the Company’s common stock prepared by an unrelated third-party valuation firm in accordance with the guidance provided by the American Institute of Certified Public Accountants Practice Guide, . Expected term —The expected term represents the period that stock-based awards are expected to be outstanding. The expected term for option grants is determined using the simplified method, which is the midpoint between the vesting period and the contractual term of the option. Expected volatility —As a privately held company prior to the Company’s IPO in October 2019, the Company has limited trading history for its common stock and, as such, the expected volatility is estimated based on the average volatility for comparable publicly traded biotechnology companies over a period equal to the expected term of the stock-based awards. The comparable companies were chosen based on their similar size, stage in the life cycle or area of specialty. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Risk-free interest rate —The risk-free interest rate is based on the U.S. Treasury zero coupon issues in effect at the time of grant for periods corresponding with the expected term of a stock-based award. Expected dividend —The Company has never paid dividends on its common stock and has no plans to pay dividends on its common stock. Therefore, the Company used an expected dividend yield of zero. Stock-based Compensation The Company has recorded stock-based compensation in the accompanying statements of operations as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 683 $ 539 $ 2,003 $ 1,449 General and administrative 825 588 2,200 1,618 Total $ 1,508 $ 1,127 $ 4,203 $ 3,067 As of September 30, 2021, there was $15,151 of unrecognized compensation cost related to unvested option awards, which is expected to be recognized over a weighted-average period of 2.8 years. 2019 Employee Stock Purchase Plan The 2019 Employee Stock Purchase Plan (2019 ESPP) was approved by the Company’s board of directors on October 14, 2019, and became effective on October 23, 2019. A total of 234,229 shares of common stock were initially reserved for issuance under the 2019 ESPP, and such number of shares will be increased each January 1 thereafter through January 1, 2029 by the least of (i) 234,229 shares of common stock, (ii) 1% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or (iii) such lesser number of shares determined by the 2019 ESPP’s administrator. On January 1, 2021, the total number of shares under the 2019 ESPP was increased by 234,229 shares. Employee contributions are made through payroll deductions of up to 15% of eligible compensation over the offering period. A participant may not accrue rights to purchase more than $25 worth of the Company’s common stock for each calendar year in which such right is outstanding. At the end of each offering period, shares of the Company’s common stock may be purchased at 85% of the lesser of the Company’s common stock on (i) the first trading day of the relevant offering period and (ii) the last trading day of the relevant offering period. The first offering period commenced on July 1, 2020 and ended on November 30, 2020. Thereafter, offerings will be six months in duration and will commence on each December 1 and June 1.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	8. Income Taxes The Company did not record an income tax benefit in its statements of operations for the three and nine months ended September 30, 2021 and 2020 as it is more likely than not that the Company will not recognize the federal and state deferred tax benefits generated by its losses. The Company has provided a valuation allowance for the full amount of its net deferred tax assets and liabilities as of September 30, 2021 and December 31, 2020, as management has determined it is more likely than not that any future benefit from deductible temporary differences and net operating loss and tax credit carryforwards would not be realized. The Company has not recorded any amounts for unrecognized tax benefits as of September 30, 2021 and December 31, 2020.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share The Company calculates basic and diluted net loss per share attributable to common stockholders in conformity with the two-class method required for participating securities. As of September 30, 2021 and 2020, the Company had voting and non-voting common stock outstanding. Since the rights of the voting and non-voting common stock are identical, except with respect to voting, the undistributed losses of the Company have been allocated on a proportionate basis to the two classes. Diluted net loss per share is calculated using the if-converted method, which assumes conversion of all non-voting common stock to voting common stock. Three months ended September 30, 2021 Nine months ended September 30, 2021 Voting common stock Non-voting common stock Voting common stock Non-voting common stock Basic net loss per share: Numerator Allocation of undistributed losses attributable to common stockholders $ (9,631 ) $ (1,929 ) $ (26,651 ) $ (5,750 ) Denominator Weighted average number of shares used in basic per share computation 21,534,342 4,312,500 20,389,242 4,398,437 Net loss per share, basic $ (0.45 ) $ (0.45 ) $ (1.31 ) $ (1.31 ) Diluted net loss per share: Numerator Allocation of undistributed losses for basic computation $ (9,631 ) $ (1,929 ) $ (26,651 ) $ (5,750 ) Reallocation of undistributed losses as a result of conversion of non-voting to voting common shares (1,929 ) — (5,750 ) — Allocation of undistributed losses $ (11,560 ) $ (1,929 ) $ (32,401 ) $ (5,750 ) Denominator Weighted average number of shares used in basic per share computation 21,534,342 4,312,500 20,389,242 4,398,437 Add: conversion of non-voting to voting common shares outstanding 4,312,500 — 4,398,437 — Weighted average number of shares used in diluted per share computation 25,846,842 4,312,500 24,787,679 4,398,437 Net loss per share, diluted $ (0.45 ) $ (0.45 ) $ (1.31 ) $ (1.31 ) Three months ended September 30, 2020 Nine months ended September 30, 2020 Voting common stock Non-voting common stock Voting common stock Non-voting common stock Basic net loss per share: Numerator Allocation of undistributed losses attributable to common stockholders $ (6,434 ) $ (1,959 ) $ (18,393 ) $ (5,637 ) Denominator Weighted average number of shares used in basic per share computation 17,828,169 5,429,486 16,943,599 5,193,114 Net loss per share, basic $ (0.36 ) $ (0.36 ) $ (1.09 ) $ (1.09 ) Diluted net loss per share: Numerator Allocation of undistributed losses for basic computation $ (6,434 ) $ (1,959 ) $ (18,393 ) $ (5,637 ) Reallocation of undistributed losses as a result of conversion of non-voting to voting common shares (1,959 ) — (5,637 ) — Allocation of undistributed losses $ (8,393 ) $ (1,959 ) $ (24,030 ) $ (5,637 ) Denominator Weighted average number of shares used in basic per share computation 17,828,169 5,429,486 16,943,599 5,193,114 Add: conversion of non-voting to voting common shares outstanding 5,429,486 — 5,193,114 — Weighted average number of shares used in diluted per share computation 23,257,655 5,429,486 22,136,713 5,193,114 Net loss per share, diluted $ (0.36 ) $ (0.36 ) $ (1.09 ) $ (1.09 ) The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share, as their effect is anti-dilutive: As of September 30, 2021 2020 Stock options to purchase common stock 4,038,981 2,889,045 Non-vested common stock 2,110 696,595 4,041,091 3,585,640

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying unaudited interim financial statements have been prepared in conformity with generally accepted accounting principles (GAAP) and the applicable rules and regulations of the SEC regarding interim financial reporting. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB). As permitted under these rules, certain footnotes and other financial information that are normally required by GAAP have been condensed or omitted. In the opinion of management, the accompanying unaudited interim financial statements include all normal and recurring adjustments (which consist primarily of accruals and estimates that impact the financial statements) considered necessary to present fairly the Company’s financial position as of September 30, 2021 and the results of its operations and its cash flows for the three and nine months ended September 30, 2021 and 2020. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period. The balance sheet as of December 31, 2020 included herein was derived from the audited financial statements as of that date. The unaudited interim financial statements, presented herein, do not contain the required disclosures under GAAP for annual financial statements. These unaudited financial statements should be read in conjunction with the Company’s audited financial statements, which are included in the Company’s 2020 Annual Report on Form 10-K, filed with the SEC on March 16, 2021 (2020 Annual Report).
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 as of the date of the financial statements and the reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying financial statements include, but are not limited to, the fair value of stock-based compensation, the valuation allowance on the Company’s deferred tax assets and certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ from those estimates.
Off-Balance Sheet Risk and Concentrations of Credit Risk	Off-Balance Sheet Risk and Concentrations of Credit Risk Financial instruments, which potentially subject the Company to significant concentrations of credit risk, consist primarily of cash and cash equivalents, which are primarily invested in U.S. treasury-based money market funds, and available-for-sale debt securities, which are invested in investment grade corporate bonds with high credit quality issuers
Fair Value Measurement	Fair Value Measurement Assets and liabilities recorded at fair value on a recurring basis in the balance sheets are categorized based upon the level of judgment associated with the inputs used to measure their fair values. Fair value is defined as the exchange price that would be received for an asset or an exit price that would be paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements as follows: Level 1—Observable inputs such as unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs (other than quoted prices included in Level 1) that are either directly or indirectly observable for the asset or liability. These include quoted prices for similar assets or liabilities in active markets and quoted prices for identical or similar assets or liabilities in markets that are not active. Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Emerging Growth Company Status	Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (the JOBS Act). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act, until such time as those standards apply to private companies. The Company has elected to use this extended transition period for complying with new or revised accounting standards that have different effective dates for public and private companies until the earlier of the date that it (i) is no longer an emerging growth company or (ii) affirmatively and irrevocably opts out of the extended transition period provided in the JOBS Act. As a result, these financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU 2016-02, Leases Revenue from Contracts with Customers and Leases

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Financial Assets Measured at Fair Value on Recurring Basis	The following tables present financial information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: September 30, 2021 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash and Cash equivalents: Money market funds $ 118,260 $ 118,260 $ — $ — Short-term investments: Corporate bonds 1,000 — 1,000 — Total $ 119,260 $ 118,260 $ 1,000 $ — December 31, 2020 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Financial assets Cash and Cash equivalents: Money market funds $ 101,429 $ 101,429 $ — $ — Short-term investments: Corporate bonds 7,233 — 7,233 — Total $ 108,662 $ 101,429 $ 7,233 $ —
Schedule of Debt Securities Classified as Available-for-Sale Investments	For debt securities classified as available-for-sale investments, the Company records unrealized gains or losses resulting from changes in fair value between measurement dates as a component of other comprehensive income. September 30, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair value Financial assets Money market funds Included in cash and cash equivalents $ 118,260 $ — $ — $ 118,260 Corporate bonds - due in one year or less Included in short-term investments 1,000 — — 1,000 Total $ 119,260 $ — $ — $ 119,260 December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair value Financial assets Money market funds Included in cash and cash equivalents $ 101,429 $ — $ — $ 101,429 Corporate bonds - due in one year or less Included in short-term investments 7,227 6 — 7,233 Total $ 108,656 $ 6 $ — $ 108,662

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following: September 30, 2021 December 31, 2020 Research and development services $ 2,446 $ 1,294 General and administrative services 108 160 Compensation expense 1,710 2,445 Other 52 38 $ 4,316 $ 3,937

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments for Operating Leases	As of September 30, 2021, the future minimum payments for operating leases are as follows: October 1, 2021 to December 31, 2021 $ 68 2022 158 $ 226

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Summary of Stock Option Activity	A summary of stock option activity is presented below: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding as of January 1, 2021 2,900,479 $ 7.33 8.5 $ 16,303 Granted 1,429,233 11.20 Exercised (58,024 ) 8.94 81 Forfeited/Cancelled (232,707 ) 10.87 Outstanding as of September 30, 2021 4,038,981 $ 8.47 8.3 $ 16,484 Options Exercisable at September 30, 2021 1,603,995 $ 5.70 7.6 $ 10,983
Schedule of Assumptions Used to Estimate Fair Value of Stock Options	The fair value of each award is estimated using Black-Scholes based on the following assumptions: Nine Months Ended September 30, 2021 2020 Risk-free interest rate 0.63%—1.15% 0.28%—1.48% Expected term 5.5—6.1 years 5.7—6.1 years Expected volatility 79%—81% 70%—79% Expected dividend yield 0% 0%
Summary of Stock-Based Compensation	The Company has recorded stock-based compensation in the accompanying statements of operations as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Research and development $ 683 $ 539 $ 2,003 $ 1,449 General and administrative 825 588 2,200 1,618 Total $ 1,508 $ 1,127 $ 4,203 $ 3,067

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Earnings Per Share	Three months ended September 30, 2021 Nine months ended September 30, 2021 Voting common stock Non-voting common stock Voting common stock Non-voting common stock Basic net loss per share: Numerator Allocation of undistributed losses attributable to common stockholders $ (9,631 ) $ (1,929 ) $ (26,651 ) $ (5,750 ) Denominator Weighted average number of shares used in basic per share computation 21,534,342 4,312,500 20,389,242 4,398,437 Net loss per share, basic $ (0.45 ) $ (0.45 ) $ (1.31 ) $ (1.31 ) Diluted net loss per share: Numerator Allocation of undistributed losses for basic computation $ (9,631 ) $ (1,929 ) $ (26,651 ) $ (5,750 ) Reallocation of undistributed losses as a result of conversion of non-voting to voting common shares (1,929 ) — (5,750 ) — Allocation of undistributed losses $ (11,560 ) $ (1,929 ) $ (32,401 ) $ (5,750 ) Denominator Weighted average number of shares used in basic per share computation 21,534,342 4,312,500 20,389,242 4,398,437 Add: conversion of non-voting to voting common shares outstanding 4,312,500 — 4,398,437 — Weighted average number of shares used in diluted per share computation 25,846,842 4,312,500 24,787,679 4,398,437 Net loss per share, diluted $ (0.45 ) $ (0.45 ) $ (1.31 ) $ (1.31 ) Three months ended September 30, 2020 Nine months ended September 30, 2020 Voting common stock Non-voting common stock Voting common stock Non-voting common stock Basic net loss per share: Numerator Allocation of undistributed losses attributable to common stockholders $ (6,434 ) $ (1,959 ) $ (18,393 ) $ (5,637 ) Denominator Weighted average number of shares used in basic per share computation 17,828,169 5,429,486 16,943,599 5,193,114 Net loss per share, basic $ (0.36 ) $ (0.36 ) $ (1.09 ) $ (1.09 ) Diluted net loss per share: Numerator Allocation of undistributed losses for basic computation $ (6,434 ) $ (1,959 ) $ (18,393 ) $ (5,637 ) Reallocation of undistributed losses as a result of conversion of non-voting to voting common shares (1,959 ) — (5,637 ) — Allocation of undistributed losses $ (8,393 ) $ (1,959 ) $ (24,030 ) $ (5,637 ) Denominator Weighted average number of shares used in basic per share computation 17,828,169 5,429,486 16,943,599 5,193,114 Add: conversion of non-voting to voting common shares outstanding 5,429,486 — 5,193,114 — Weighted average number of shares used in diluted per share computation 23,257,655 5,429,486 22,136,713 5,193,114 Net loss per share, diluted $ (0.36 ) $ (0.36 ) $ (1.09 ) $ (1.09 )
Schedule of Antidilutive Shares Excluded from Calculation of Diluted Net Loss Per Share	The following outstanding potentially dilutive shares have been excluded from the calculation of diluted net loss per share, as their effect is anti-dilutive: As of September 30, 2021 2020 Stock options to purchase common stock 4,038,981 2,889,045 Non-vested common stock 2,110 696,595 4,041,091 3,585,640

Basis of Presentation - Additio

Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 29, 2019	Nov. 30, 2019	Sep. 30, 2021	Dec. 31, 2020
Basis Of Presentation [Line Items]
Cash and cash equivalents and investments			$ 119,260
Accumulated deficit			$ (98,699)	$ (66,298)
Initial Public Offering
Basis Of Presentation [Line Items]
Issuance of common stock, shares	6,800,000
Common stock issued, per share	$ 11
Net proceeds from initial public offering	$ 66,156	$ 4,864
Conversion of convertible preferred stock to common stock	12,904,534
Number of additional common stock purchased by underwriters upon partial exercise of option		475,501

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Investments maturity year	2021

Fair Value Measurements - Finan

Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Short-term investments:
Short-term investments	$ 1,000	$ 7,233
Fair Value, Measurements, Recurring
Financial assets
Total	119,260	108,662
Fair Value, Measurements, Recurring | Money Market Funds
Cash and Cash equivalents:
Money market funds	118,260	101,429
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
Total	118,260	101,429
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Money Market Funds
Cash and Cash equivalents:
Money market funds	118,260	101,429
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Financial assets
Total	1,000	7,233
Fair Value, Measurements, Recurring | Short-term Investments - Corporate Bonds
Short-term investments:
Short-term investments	1,000	7,233
Fair Value, Measurements, Recurring | Short-term Investments - Corporate Bonds | Significant Other Observable Inputs (Level 2)
Short-term investments:
Short-term investments	$ 1,000	$ 7,233

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair value, assets, level 1 to level 2 transfers, amount	$ 0	$ 0	$ 0	$ 0
Fair value, assets, level 2 to level 1 transfers, amount	0	0	0	0
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, transfers, net	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Debt Securities Classified as Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 119,260	$ 108,656
Gross Unrealized Gains		6
Fair value	119,260	108,662
Money Market Funds Included in Cash and Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	118,260	101,429
Fair value	118,260	101,429
Corporate Bonds - due in One Year or Less
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,000	7,227
Gross Unrealized Gains		6
Fair value	$ 1,000	$ 7,233

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Research and development services	$ 2,446	$ 1,294
General and administrative services	108	160
Compensation expense	1,710	2,445
Other	52	38
Accrued and other current liabilities	$ 4,316	$ 3,937

Collaborations, Licensing Agr_2

Collaborations, Licensing Agreements and other Agreements - Additional Information (Details)	3 Months Ended			9 Months Ended
	Oct. 31, 2021USD ($)	Sep. 30, 2021USD ($)Faculty	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)Faculty	Sep. 30, 2020USD ($)	Jan. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Research and development expense		$ 8,169,000	$ 5,650,000	$ 22,575,000	$ 15,601,000
Research Service Agreement | Children's Hospital of Philadelphia
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Research and development expense		250,000	0	822,000	0
Amounts due to agreement		250,000		250,000
Remaining cost				900,000
License Agreement
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Amounts due to agreement		0		0
Obligation to be paid		2,000,000		$ 2,000,000
Payment term				3 years
Payment commencement date				2018-08
License maintenance fee				$ 10,000
Total milestone payments				21,000,000
Sponsored Research Agreements | Penn
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Research and development expense		625,000	624,000	2,260,000	1,960,000
Obligation to be paid		$ 12,290,000		$ 12,290,000
Number of faculty member | Faculty		2		2
Funding term end date				2023-02
Cost incurred		$ 9,350,000		$ 9,350,000
Sponsored Research Agreements | Penn | Prepaid Expenses and Other Current Assets
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Advance payments		720,000		720,000			$ 1,851,000
Sponsored Research Agreements | Penn | Accrued and Other Current Liabilities
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Obligation to be paid		0		0			$ 217,000
Master Translational Research Services Agreement
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Research and development expense		418,000	259,000	1,441,000	1,997,000
Maximum research and development additional expense incurred				1,360,000
Subscription and Technology Transfer Agreement
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Expense related to agreement		$ 0	$ 0	150,000	$ 0
Wuxi Agreement | WuXi Advanced Therapies
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Early termination fee						$ 1,500,000
Agreement with Contract Manufacturing Organization
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Expense related to agreement				$ 469,000
Agreement with Contract Manufacturing Organization | Subsequent Event
Collaborations, Licensing Agreements And Other Agreements [Line Items]
Total cost	$ 1,620,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - Operating Lease Agreement - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commitments and Contingencies [Line Items]
Operating lease, description			The lease term commenced in May 2019 and will expire in July 2022.
Lease commencement period			2019-05
Lease expiration period			2022-07
Initial annual base rent			$ 261,000
Percentage of annual increase of base rent			2.00%
Rent expense	$ 69,000	$ 67,000	$ 205,000	$ 200,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments for Operating Leases (Details) $ in Thousands	Sep. 30, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
October 1, 2021 to December 31, 2021	$ 68
2022	158
Total	$ 226

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)

Oct. 01, 2021

Oct. 23, 2019

Oct. 31, 2019

Sep. 30, 2021

Jun. 30, 2021

Mar. 31, 2021

Sep. 30, 2021

Sep. 30, 2020

Jan. 01, 2021

Dec. 31, 2020

Oct. 30, 2019

Jan. 31, 2019

Class Of Stock [Line Items]

Common stock, authorized shares

150,000,000

150,000,000

150,000,000

Non-voting common stock, Terms of conversion

Each share of the Company’s non-voting common stock may be converted at any time into one share of common stock at the option of its holder by providing 61 days written notice to the Company

Issuance and sale of common stock

$ 24,880,000

$ 7,665,000

$ 2,165,000

Net proceeds

$ 34,710,000

$ (191,000)

Unrecognized compensation cost related to unvested stock-based awards

$ 15,151,000

$ 15,151,000

Unrecognized compensation cost, period for recognition

2 years 9 months 18 days

2019 Plan

Class Of Stock [Line Items]

Shares reserved for issuance

2,342,288

962,511

Increase in share reserved percentage

4.00%

Share-based compensation, number of shares available for grant

2,080,288

2,080,288

2019 ESPP

Class Of Stock [Line Items]

Shares reserved for issuance

234,229

234,229

Stock Options | 2018 Plan

Class Of Stock [Line Items]

Share-based compensation unvested number of shares

0

0

Number of options granted

1,959,411

Stock Options | 2019 Plan

Class Of Stock [Line Items]

Number of options granted

1,429,233

Weighted average grant-date fair value of stock options granted

$ 7.68

$ 8.25

Maximum | Stock Options | 2018 Plan

Class Of Stock [Line Items]

Share-based compensation, vesting period

4 years

Minimum | 2019 ESPP

Class Of Stock [Line Items]

Shares reserved for issuance

234,229

Increase in share reserved percentage

1.00%

Payroll deduction percentage of eligible compensation

15.00%

Employee stock purchase plan maximum annual rights to purchase common stock

$ 25,000

Percentage of shares to be purchased

85.00%

Minimum | Stock Options | 2018 Plan

Class Of Stock [Line Items]

Share-based compensation, vesting period

3 years

ATM Program

Class Of Stock [Line Items]

Issuance of common stock, shares

3,606,005

Net proceeds

$ 34,700,000

Commissions

1,100,000

ATM Program | Maximum

Class Of Stock [Line Items]

Issuance and sale of common stock

$ 75,000,000

ATM Program | Subsequent Event

Class Of Stock [Line Items]

Number of additional shares sold

600,000

Net proceeds

$ 6,300,000

Voting Common Stock

Class Of Stock [Line Items]

Common stock, authorized shares

143,590,481

143,590,481

143,590,481

143,590,481

Non-voting Common Stock

Class Of Stock [Line Items]

Common stock, authorized shares

6,409,519

6,409,519

6,409,519

6,409,519

Common Stock - Summary of Stock

Common Stock - Summary of Stock Option Activity (Details) - Stock Options - 2019 Plan - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Number of Shares
Number of Shares, Beginning Balance	2,900,479
Number of Shares, Granted	1,429,233
Number of Shares, Exercised	(58,024)
Number of shares, Forfeited/Cancelled	(232,707)
Number of Shares, Ending Balance	4,038,981	2,900,479
Number of Shares, Options Exercisable	1,603,995
Weighted Average Exercise Price
Weighted Average Exercise Price, Beginning Balance	$ 7.33
Weighted Average Exercise Price, Granted	11.20
Weighted Average Exercise Price, Exercised	8.94
Weighted Average Exercise Price, Forfeited/Cancelled	10.87
Weighted Average Exercise Price, Ending Balance	8.47	$ 7.33
Weighted Average Exercise Price, Options Exercisable	$ 5.70
Weighted Average Remaining Contractual Term (years)
Term (years)	8 years 3 months 18 days	8 years 6 months
Weighted Average Remaining Contractual Term (years), Options Exercisable	7 years 7 months 6 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Beginning Balance	$ 16,303
Aggregate Intrinsic Value, Exercised	81
Aggregate Intrinsic Value, Ending Balance	16,484	$ 16,303
Aggregate Intrinsic Value, Options Exercisable	$ 10,983

Common Stock - Schedule of Assu

Common Stock - Schedule of Assumptions Used to Estimate Fair Value of Stock Options (Details)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	0.63%	0.28%
Risk-free interest rate, maximum	1.55%	1.48%
Expected volatility, minimum	79.00%	70.00%
Expected volatility, maximum	81.00%	79.00%
Expected dividend yield	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	5 years 6 months	5 years 8 months 12 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	6 years 1 month 6 days	6 years 1 month 6 days

Common Stock - Summary of Sto_2

Common Stock - Summary of Stock-Based Compensation (Details) - Stock Options - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stock-based compensation	$ 1,508	$ 1,127	$ 4,203	$ 3,067
Research and Development
Stock-based compensation	683	539	2,003	1,449
General and Administrative
Stock-based compensation	$ 825	$ 588	$ 2,200	$ 1,618

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income tax benefit	$ 0	$ 0	$ 0	$ 0
Unrecognized tax benefits	$ 0		$ 0		$ 0

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Voting Common Stock
Basic net loss per share:
Allocation of undistributed losses attributable to common stockholders	$ (9,631)	$ (6,434)	$ (26,651)	$ (18,393)
Weighted average number of shares used in basic per share computation	21,534,342	17,828,169	20,389,242	16,943,599
Net loss per share, basic	$ (0.45)	$ (0.36)	$ (1.31)	$ (1.09)
Diluted net loss per share:
Allocation of undistributed losses for basic computation	$ (9,631)	$ (6,434)	$ (26,651)	$ (18,393)
Reallocation of undistributed losses as a result of conversion of non-voting to voting common shares	(1,929)	(1,959)	(5,750)	(5,637)
Allocation of undistributed losses	$ (11,560)	$ (8,393)	$ (32,401)	$ (24,030)
Weighted average number of shares used in basic per share computation	21,534,342	17,828,169	20,389,242	16,943,599
Add: conversion of non-voting to voting common shares outstanding	4,312,500	5,429,486	4,398,437	5,193,114
Weighted average number of shares used in diluted per share computation	25,846,842	23,257,655	24,787,679	22,136,713
Net loss per share, diluted	$ (0.45)	$ (0.36)	$ (1.31)	$ (1.09)
Non-voting Common Stock
Basic net loss per share:
Allocation of undistributed losses attributable to common stockholders	$ (1,929)	$ (1,959)	$ (5,750)	$ (5,637)
Weighted average number of shares used in basic per share computation	4,312,500	5,429,486	4,398,437	5,193,114
Net loss per share, basic	$ (0.45)	$ (0.36)	$ (1.31)	$ (1.09)
Diluted net loss per share:
Allocation of undistributed losses for basic computation	$ (1,929)	$ (1,959)	$ (5,750)	$ (5,637)
Allocation of undistributed losses	$ (1,929)	$ (1,959)	$ (5,750)	$ (5,637)
Weighted average number of shares used in basic per share computation	4,312,500	5,429,486	4,398,437	5,193,114
Weighted average number of shares used in diluted per share computation	4,312,500	5,429,486	4,398,437	5,193,114
Net loss per share, diluted	$ (0.45)	$ (0.36)	$ (1.31)	$ (1.09)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Antidilutive Shares Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares have been excluded from calculation of diluted net loss per share	4,041,091	3,585,640
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares have been excluded from calculation of diluted net loss per share	4,038,981	2,889,045
Non-vested Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive shares have been excluded from calculation of diluted net loss per share	2,110	696,595