Stoke Therapeutics (STOK) 10-Q 12 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 05, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity File Number	001-38938
Entity Registrant Name	Stoke Therapeutics, Inc.
Entity Central Index Key	0001623526
Entity Tax Identification Number	47-1144582
Entity Address, Address Line One	45 Wiggins Ave
Entity Address, City or Town	Bedford
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01730
City Area Code	781
Local Phone Number	430-8200
Trading Symbol	STOK
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 Common Stock, Shares Outstanding		33,470,262
Entity Incorporation State Country Code	DE
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false

Condensed consolidated balance

Condensed consolidated balance sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 191,461	$ 222,471
Prepaid expenses and other current assets	3,615	3,281
Deferred financing costs	378
Interest receivable	2	281
Total current assets	195,456	226,033
Restricted cash	205	205
Operating lease right-of-use assets	1,381
Property and equipment, net	2,893	2,512
Total assets	199,935	228,750
Current liabilities:
Accounts payable	1,095	751
Accrued and other current liabilities	5,640	3,350
Total current liabilities	6,735	4,101
Long term liabilities	665	221
Total liabilities	7,400	4,322
Commitments and contingencies (Note 5)
Stockholders’ equity
Common stock, par value of $0.0001 per share; 300,000,000 shares authorized, 33,361,188 and 32,861,842 shares issued and outstanding as of September 30, 2020 and December 31, 2019, respectively	3	3
Additional paid-in capital	288,249	282,460
Accumulated deficit	(95,717)	(58,035)
Total stockholders’ equity	192,535	224,428
Total liabilities and stockholders’ equity	$ 199,935	$ 228,750

Condensed consolidated balanc_2

Condensed consolidated balance sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	33,361,188	32,861,842
Common stock, shares outstanding	33,361,188	32,861,842

Condensed consolidated statemen

Condensed consolidated statements of operations and comprehensive loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development	$ 8,109	$ 6,518	$ 23,293	$ 16,675
General and administrative	5,602	3,324	15,165	7,935
Total operating expenses	13,711	9,842	38,458	24,610
Loss from operations	(13,711)	(9,842)	(38,458)	(24,610)
Other income:
Interest income	11	1,236	734	2,447
Other income (expense), net	16	2	42	(2)
Total other income	27	1,238	776	2,445
Net loss and comprehensive loss	$ (13,684)	$ (8,604)	$ (37,682)	$ (22,165)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.41)	$ (0.26)	$ (1.14)	$ (1.71)
Weighted-average common shares outstanding, basic and diluted	33,273,597	32,707,647	32,954,727	12,991,672

Condensed consolidated statem_2

Condensed consolidated statements of stockholders' equity - USD ($) $ in Thousands	Total	Initial Public Offering	Convertible Preferred Stock	Common Stock	Common StockInitial Public Offering	Additional Paid-in Capital	Additional Paid-in CapitalInitial Public Offering	Accumulated Deficit
Balance at Dec. 31, 2018	$ 105,068		$ 2			$ 130,776		$ (25,710)
Balance, Shares at Dec. 31, 2018			22,677,585	727,413
Net loss	(5,742)							(5,742)
Stock-based compensation	181					181
Issuance of common stock upon exercise of stock options	74					74
Issuance of common stock upon exercise of stock options, Shares				164,810
Balance at Mar. 31, 2019	99,581		$ 2			131,031		(31,452)
Balance, Shares at Mar. 31, 2019			22,677,585	892,223
Balance at Dec. 31, 2018	105,068		$ 2			130,776		(25,710)
Balance, Shares at Dec. 31, 2018			22,677,585	727,413
Net loss	(22,165)
Balance at Sep. 30, 2019	233,683			$ 3		281,555		(47,875)
Balance, Shares at Sep. 30, 2019				32,724,153
Balance at Mar. 31, 2019	99,581		$ 2			131,031		(31,452)
Balance, Shares at Mar. 31, 2019			22,677,585	892,223
Net loss	(7,819)							(7,819)
Stock-based compensation	298					298
Issuance of common stock upon exercise of stock options	27					27
Issuance of common stock upon exercise of stock options, Shares				29,981
Issuance of common stock upon initial public offering, net of underwriting discounts, commissions, and offering costs		$ 149,449			$ 1		$ 149,448
Issuance of common stock upon initial public offering, net of underwriting discounts, commissions, and offering costs, Shares					9,074,776
Conversion of preferred stock to common stock			$ (2)	$ 2
Conversion of preferred stock to common stock, Shares			(22,677,585)	22,677,585
Balance at Jun. 30, 2019	241,536			$ 3		280,804		(39,271)
Balance, Shares at Jun. 30, 2019				32,674,565
Net loss	(8,604)							(8,604)
Stock-based compensation	731					731
Issuance of common stock upon exercise of stock options	20					20
Issuance of common stock upon exercise of stock options, Shares				49,588
Balance at Sep. 30, 2019	233,683			$ 3		281,555		(47,875)
Balance, Shares at Sep. 30, 2019				32,724,153
Balance at Dec. 31, 2019	224,428			$ 3		282,460		(58,035)
Balance, Shares at Dec. 31, 2019				32,861,842
Net loss	(11,039)							(11,039)
Stock-based compensation	754					754
Issuance of common stock upon exercise of stock options	199					199
Issuance of common stock upon exercise of stock options, Shares				105,508
Balance at Mar. 31, 2020	214,342			$ 3		283,413		(69,074)
Balance, Shares at Mar. 31, 2020				32,967,350
Balance at Dec. 31, 2019	224,428			$ 3		282,460		(58,035)
Balance, Shares at Dec. 31, 2019				32,861,842
Net loss	(37,682)
Balance at Sep. 30, 2020	192,535			$ 3		288,249		(95,717)
Balance, Shares at Sep. 30, 2020				33,361,188
Balance at Mar. 31, 2020	214,342			$ 3		283,413		(69,074)
Balance, Shares at Mar. 31, 2020				32,967,350
Net loss	(12,959)							(12,959)
Stock-based compensation	1,649					1,649
Issuance of common stock upon exercise of stock options	368					368
Issuance of common stock upon exercise of stock options, Shares				245,194
Balance at Jun. 30, 2020	203,400			$ 3		285,430		(82,033)
Balance, Shares at Jun. 30, 2020				33,212,544
Net loss	(13,684)							(13,684)
Stock-based compensation	1,785					1,785
Issuance of common stock upon exercise of stock options	682					682
Issuance of common stock upon exercise of stock options, Shares				131,253
Issuance of common stock related to employee stock purchase plan	352					352
Issuance of common stock related to employee stock purchase plan, Shares				17,391
Balance at Sep. 30, 2020	$ 192,535			$ 3		$ 288,249		$ (95,717)
Balance, Shares at Sep. 30, 2020				33,361,188

Condensed consolidated statem_3

Condensed consolidated statements of cash flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (37,682)	$ (22,165)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	651	311
Stock-based compensation	4,188	1,210
Loss on disposal of property and equipment	3	3
Reduction in the carrying amount of right of use assets	772
Changes in assets and liabilities:
Prepaid expenses and other current assets	(55)	(2,887)
Accounts payable and accrued liabilities	833	2,652
Deferred rent		22
Net cash used in operating activities	(31,290)	(20,854)
Cash flows from investing activities:
Purchases of property and equipment	(960)	(1,067)
Proceeds from sale of property and equipment		2
Net cash used in investing activities	(960)	(1,065)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of stock options	1,248	121
Proceeds from Employee Stock Purchase Plan	352
Deferred Financing Costs	(360)
Proceeds from the issuance of common stock upon initial public offering		151,912
Payments of initial public offering costs		(2,463)
Net cash provided by financing activities	1,240	149,570
Net increase (decrease) in cash, cash equivalents and restricted cash	(31,010)	127,651
Cash, cash equivalents and restricted cash—beginning of period	222,676	105,603
Cash, cash equivalents and restricted cash—end of period	191,666	$ 233,254
Supplemental Disclosure of Non-Cash Investing and Financing Activities:
Right-of-use assets recognized in exchange for operating leases upon adoption of Topic 842	2,153
Property and equipment included in accrued expense and accounts payable	76
Deferred offering costs not yet paid	$ 17

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Nature of the business and basis of presentation	1. Nature of the business and basis of presentation Organization Stoke Therapeutics, Inc. (the “Company”) was founded in June 2014 and was incorporated under the laws of the State of Delaware. The Company is an early-stage biopharmaceutical company pioneering a new way to treat the underlying causes of severe genetic diseases by precisely upregulating protein expression. Initial public offering On June 21, 2019, the Company completed an initial public offering (“IPO”) of its common stock and issued and sold 9,074,776 shares of common stock at a public offering price of $18.00 per share, which included 1,183,666 shares sold upon full exercise of the underwriters’ option to purchase additional shares, resulting in net proceeds of approximately $149.4 million after deducting underwriting discounts, commissions and offering costs of $13.9 million. Upon closing of the IPO, the Company’s outstanding convertible preferred stock automatically converted into shares of common stock (see Note 6). Upon conversion of the convertible preferred stock, the Company reclassified the carrying value of the convertible preferred stock to common stock and additional paid-in capital. On June 6, 2019, in connection with the IPO, the Company effected a one-for-9.95 reverse split of the Company’s issued and outstanding common and convertible preferred stock. Upon the effectiveness of the reverse stock split, (i) all shares of outstanding common stock and convertible preferred stock were adjusted; (ii) the number of shares of common stock for which each outstanding option to purchase common stock is exercisable were adjusted; and (iii) the exercise price of each outstanding option to purchase common stock were adjusted. All of the outstanding common stock share numbers (including shares of common stock subject to the Company’s options and as converted for the outstanding convertible preferred stock shares), share prices, exercise prices and per share amounts contained in the interim condensed consolidated financial statements have been retroactively adjusted in the interim condensed consolidated financial statements to reflect this reverse stock split for all periods presented. The par value per share and the authorized number of shares of common stock and convertible preferred stock were not adjusted as a result of the reverse stock split. On June 21, 2019, the Company filed an amended and restated certificate of incorporation with the Secretary of State of the State of Delaware to authorize the issuance of up to 300 million shares of common stock, $0.0001 par value per share, and 10 million shares of undesignated preferred stock, $0.0001 par value per share. Shelf Registration In July 2020, the Company filed a universal Shelf Registration statement on Form S-3 (the “Registration Statement”) with the Securities and Exchange Commission (the “SEC”). The Registration Statement was declared effective by the SEC on July 20, 2020, and contains two prospectuses: a base prospectus, which covers the offering, issuance and sale by the Company of up to a maximum aggregate offering price of $400,000,000 of our common stock, preferred stock, debt securities, warrants to purchase our common stock, preferred stock or debt securities, subscription rights to purchase our common stock, preferred stock or debt securities and/or units consisting of some or all of these securities; and a sales agreement prospectus covering the offering, issuance and sale by us of up to a maximum aggregate offering price of $150,000,000 of our common stock that may be issued and sold under a Controlled Equity Offering Sales Agreement. The specific terms of any securities to be offered pursuant to the base prospectus will be specified in a prospectus supplement to the base prospectus. The $150,000,000 of common stock that may be offered, issued and sold under the sales agreement prospectus is included in the $400,000,000 of securities that may be offered, issued and sold by the Company under the base prospectus. As of September 30, 2020, the Company has not issued any securities in connection with Registration Statement. Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. 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. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. Liquidity The Company expects that its operating losses and negative cash flows will continue for the foreseeable future. As of the issuance date of these unaudited condensed consolidated financial statements the Company expects that its cash and cash equivalents will be sufficient to fund its operating expenses and capital expenditure requirements through at least twelve months from the issuance date of these unaudited condensed consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary of significant accounting policies and recent accounting pronouncements	2. Summary of significant accounting policies and recent accounting pronouncements Basis of presentation and consolidation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”),and include the accounts of the Company and its wholly-owned subsidiary. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). All intercompany transactions between and among its consolidated subsidiary have been eliminated. Unaudited interim financial information The accompanying interim unaudited condensed consolidated financial statements and related disclosures are unaudited and have been prepared in accordance with GAAP for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Company’s consolidated financial statements and related footnotes as of and for the year ended December 31, 2019, which was filed with the SEC on March 23, 2020. The Company’s financial information as of September 30, 2020, and for the three and nine months ended September 30, 2020 and 2019 is unaudited, but in the opinion of management, all adjustments, consisting only of normal recurring adjustments, considered necessary for a fair presentation of the financial position, results of operations and cash flows at the dates and for the periods presented of the results of these interim periods have been included. The balance sheet information as of December 31, 2019 was derived from audited financial statements. The results of the Company’s operations for any interim period are not necessarily indicative of the results that may be expected for any other interim period or for a full fiscal year. Use of estimates The preparation of unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from those estimates. Cash and cash equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. The Company deposits its cash in checking, sweep and money market accounts. Restricted cash At September 30, 2020, restricted cash consisted of money market accounts collateralizing letters of credit issued as security deposits in connection with the Company’s leases of its corporate facilities. The following table reconciles cash and cash equivalents and restricted cash per the condensed consolidated balance sheets to the condensed consolidated statements of cash flows (in thousands): As of September 30, 2020 2019 Cash and cash equivalents $ 191,461 $ 233,049 Restricted cash $ 205 $ 205 Total cash, cash equivalents and restricted cash $ 191,666 $ 233,254 Fair value of financial instruments ASC Topic 820, Fair Value Measurement Level 1—Quoted market prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the condensed consolidated statement of stockholders’ equity as a reduction of additional paid-in capital. 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. The Company considers its convertible preferred stock (“Preferred Stock”) to be participating securities as in the event a dividend is paid on common stock, the holders of Preferred Stock would be entitled to receive dividends on a basis consistent with the common stockholders. Under the two-class method, the net loss attributable to common stockholders is not allocated to the Preferred Stock as the holders of the Preferred Stock do not have a contractual obligation to share in losses. Under the two-class method, basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock. Emerging growth company and smaller reporting 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 is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, the Company’s unaudited condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company will remain an emerging growth company until the earliest of (1) the last day of its first fiscal year (a) in which the Company has total annual gross revenues of at least $1.07 billion, or (b) in which the Company is deemed to be a large accelerated filer, which means the market value of its common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30 th The Company is also a “smaller reporting company,” meaning that as of the date of its initial public offering, the market value of its stock held by non-affiliates is less than $700 million and our annual revenue is less than $100 million during the most recently completed fiscal year. The Company may continue to be a smaller reporting company as long as either (i) the market value of its stock held by non-affiliates is less than $250 million or (ii) its annual revenue is less than $100 million during the most recently completed fiscal year and the market value of its stock held by non-affiliates is less than $700 million. If the Company is a smaller reporting company at the time it ceases to be an emerging growth company, the Company may continue to rely on exemptions from certain disclosure requirements that are available to smaller reporting companies. Specifically, as a smaller reporting company, the Company may choose to present only the two most recent fiscal years of audited financial statements in its Annual Report on Form 10-K and, similar to emerging growth companies, smaller reporting companies have reduced disclosure obligations regarding executive compensation. Recently adopted accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases In July 2017, the FASB issued ASU 2017-11, Earnings Per Share I. Accounting for Certain Financial Instruments with Down Round Features; II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Fair value measurements	3. Fair value measurements The following tables present 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 (in thousands): Fair value measurements as of September 30, 2020 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 191,461 $ — $ — $ 191,461 Total $ 191,461 $ — $ — $ 191,461 Fair value measurements as of December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 222,471 $ — $ — $ 222,471 Total $ 222,471 $ — $ — $ 222,471 The Company’s assets with fair value categorized as Level 1 within the fair value hierarchy include money market funds. Money market funds are publicly traded mutual funds and are presented as cash equivalents on the condensed consolidated balance sheets as of September 30, 2020 and December 31, 2019. There were no transfers among Level 1, Level 2, or Level 3 categories in the periods presented. The carrying value of cash, cash equivalents, accounts payable and accrued expenses that are reported on the condensed consolidated balance sheets approximate their fair value due to the short-term nature of these assets and liabilities.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	9 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Accrued and other current liabilities	4. Accrued and other current liabilities Accrued and other current liabilities consisted of the following (in thousands): September 30, December 31, 2020 2019 Accrued employee compensation costs $ 2,409 $ 2,053 Accrued professional 559 228 Accrued research and development costs 1,231 959 Current portion of operating lease liabilities 1,119 — Accrued Other 67 56 Other Current Liabilities 255 54 $ 5,640 $ 3,350

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and contingencies	5. Commitments and contingencies Operating lease In February 2016, the FASB issued ASU No. 2016-02, Leases Upon adoption of Topic 842 on January 1, 2020, the Company recorded right-of-use assets of $2.2 million, operating lease liabilities of $2.2 million and the elimination of deferred rent of $0.03 million. Adoption of the standard did not result in the Company recording a cumulative effect adjustment. The Company determines whether an arrangement is a lease at inception. The Company accounts for a lease when it has the right to control the leased asset for a period of time while obtaining substantially all of the assets’ economic benefits. The Company determined that it held operating leases for office and laboratory space as of January 1, 2020. Operating lease right-of-use assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at the lease commencement date. The discount rate used to determine the present value of the lease payments is the Company’s incremental borrowing rate based on the information available at lease inception, as the Company did not have information to determine the rate implicit in the leases. Lease expense for operating leases is recognized on a straight-line basis over the reasonably assured lease term based on the total lease payments (which include initial direct costs and lease incentives). The expense is included in operating expenses in the condensed consolidated statements of operations. The Company’s lease agreements also contain variable payments, primarily maintenance-related costs, which are expensed as incurred and not included in the measurement of the right-of-use assets and lease liabilities. In August 2018, the Company entered into an agreement to lease approximately 23,000 square feet of space for a term of three years. Lease terms are triple net lease commencing at $0.9 million per year, then with 3% annual base rent increases plus operating expenses, real estate taxes, utilities and janitorial fees. The lease commencement date was December 10, 2018. In December 2018, the Company entered into an agreement to lease 2,485 square feet of space for an initial term of three years. The lease includes one renewal option for an additional two years, however, any time after the initial term the landlord may relocate the Company from the premises to a space reasonably comparable in size and utility. As the Company does not have the right to control the use of the identified asset after the initial term, the renewal option was excluded from the lease liability calculation. Lease terms commence at $0.2 million per annum, with 2.5% annual base rent increases plus operating expenses, real estate taxes, utilities and janitorial fees. The lease commencement date was May 1, 2019. Future minimum lease payments under non-cancellable leases as of September 30, 2020 are as follows (in thousands): 2020 $ 290 2021 1,102 2022 81 Total lease payments 1,473 Less imputed interest (58 ) Present value of lease liabilities $ 1,415 Future minimum lease payments under non-cancellable leases as of December 31, 2019 are as follows (in thousands): 2020 $ 1,149 2021 1,102 2022 81 2023 — Thereafter — $ 2,332 Lease balances as of September 30, 2020 are as follows (in thousands): Operating right-of-use assets $ 1,381 Current Portion of operating lease liabilities $ 1,119 Non-current portion of operating lease liabilities 296 Total operating lease liabilities $ 1,415 The weighted average remaining lease term and weighted average discount rate of our operating leases as of September 30, 2020 are as follows: Weighted average remaining lease term in years 1.3 Weighted average discount rate 7.02 % Rent expense incurred under operating leases was approximately Consulting agreement In October 2014, the Company entered into a consulting agreement with a member of the Company’s board of directors, who is also an employee of Cold Spring Harbor Laboratory (“CSHL”), to provide consulting services related to scientific research related to the development of antisense-based drugs, therapies, diagnostic and research tools, products, services and intellectual property. The Company recognized expenses of $0.02 million for the three-month period ended March 31, 2020 and did not recognize any additional expense in the nine-month period ended September 30, 2020. The Company recognized expenses of $0.02 million in the three-month period ending September 30, 2019 and $0.07 million in the nine-month period ending September 30, 2019, for such consulting services. The initial term of this agreement was five years and the parties mutually agreed not to extend the consulting agreement in April 2020. Scientific Advisory Board Agreement In June 2020, the Company entered into a scientific advisory board agreement with a member of the Company’s board of directors, who is also an employee of CSHL, to provide scientific advisory services related to the Company’s Targeted Augmentation of Nuclear Gene Output (“TANGO”) antisense oligonucleotide technology and other antisense oligonucleotide technologies, as well as current and future therapeutic targets and programs. The Company recognized expense of $0.01 million in the three-month period ended September 30, 2020 and $0.04 million in the nine-month period ended September 30, 2020, for such scientific advisory services. The term of this agreement is 12 months. License and research agreements In July 2015, the Company entered into a worldwide license agreement (the “CSHL Agreement”), with CSHL, with respect to TANGO patents. Under the CSHL Agreement, the Company receives an exclusive (except with respect to certain government rights and non-exclusive licenses), worldwide license under certain patents and applications relating to TANGO. As part of the CSHL Agreement, the Company granted CSHL 164,927 shares of common stock valued based on an independent appraisal at approximately $0.07 million. The CSHL Agreement obligates the Company to make additional payments that are contingent upon certain milestones being achieved. The Company is also required to pay royalties, tiered based on the scope of patent coverage for each licensed product, ranging from a low-single digit percentage to a mid-single digit percentage on annual net sales. These royalty obligations apply on a licensed product-by-licensed product and country-by-country basis until the latest of (i) the expiration of the last valid claim of a CSHL patent covering the applicable licensed product or (ii) the expiration of any regulatory exclusivity for the applicable licensed product. In addition, if the Company sublicenses the rights under the CSHL Agreement, the Company is required to pay a maximum of twenty percent of the sublicense revenue to CSHL, which may be reduced to a mid-teens or a mid-single digit percentage upon achievement of certain clinical milestones for the applicable licensed product. Finally, the Company is required to pay an annual license maintenance fee of $0.01 million, which amount is creditable against any owed royalty or milestone payments. The maximum aggregate potential milestone payments payable total approximately $0.9 million. Additionally, certain licenses under the CSHL Agreement require the Company to reimburse CSHL for certain past and ongoing patent related expenses, however there were no expenses related to these reimbursable patent costs during the three months and nine months ended September 30, 2020 and 2019. In April 2016, the Company entered into an exclusive, worldwide license agreement with the University of Southampton, (the “Southampton Agreement”), whereby the Company acquired rights to foundational technologies related to the Company’s TANGO technology. Under the Southampton Agreement, the Company receives an exclusive, worldwide license under certain licensed patents and applications relating to TANGO. As part of the Southampton Agreement, the Company paid 0.06 million pounds sterling (approximately $0.07 million as of the date thereof) as an up-front license fee. Under the Southampton Agreement, the Company may be obligated to make additional payments that are contingent upon certain milestones being achieved, as well as royalties on future product sales. These royalty obligations survive until the latest of (i) the expiration of the last valid claim of a licensed patent covering a subject product or (ii) the expiration of any regulatory exclusivity for the subject product in a country. In addition, if the Company sublicenses its rights under the Southampton Agreement, the Company is required to pay a mid-single digit percentage of the sublicense revenue to the University of Southampton. The maximum aggregate potential milestone payments payable by the Company totaled approximately 0.4 million pounds sterling (approximately $0.5 million as of September 30, 2020). As of September 30, 2020, and December 31, 2019, the Company had recorded no liabilities under the Southampton Agreement.

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2020
Stockholders Equity Note [Abstract]
Convertible preferred stock	6. Convertible preferred stock On June 6, 2019, the Company’s stockholders approved an amendment to the Company’s Amended and Restated Certificate of Incorporation which became effective on June 21, 2019 upon which the authorized capital stock of the Corporation consisted of 300 million shares of common stock, $0.0001 per share par value, and 10 million shares of undesignated preferred stock, $0.0001 per share par value. On June 21, 2019, the Company completed its IPO and in conjunction therewith, all outstanding convertible preferred stock was converted into common stock. Accordingly, as of September 30, 2020, there was no preferred stock outstanding.

Equity Incentive Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity incentive plans	7. Equity incentive plans In June 2019, the Company’s board of directors and stockholders approved the 2019 Equity Incentive Plan (the “2019 Plan”) which became effective on June 17, 2019 and replaced the Company’s 2014 Equity Incentive Plan (the “2014 Plan”). In addition to the shares of common stock reserved for future issuance under the 2014 Plan that were added to the 2019 Plan upon its effective date, the Company initially reserved 2,200,000 shares of common stock for issuance under the 2019 Plan. The number of shares reserved for issuance under the Company’s 2019 Plan will increase automatically on January 1 of each of 2020 through 2029 by the number of shares equal to 4% of the aggregate number of outstanding shares of the Company’s common stock as of the immediately preceding December 31, or a lesser number as may be determined by the Company’s board of directors. As of September 30, 2020, there were no shares available for future issuance under the 2014 Plan and During the three-months ended September 30, 2020, the Company granted options to purchase 168,255 shares of common stock to certain of its employees and 1,138,657 shares for the nine-months ended September 30, 2020. The options vest over four years and are exercisable at a per share price equal to the fair value of the common stock on the grant date. Stock-based compensation As of September 30, 2020, there was $18.8 million of unrecognized compensation cost related to unvested stock-based compensation arrangements granted under the 2014 and 2019 Plans. The compensation is expected to be recognized over a weighted average period of 3.01 years as of September 30, 2020. Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying condensed consolidated statements of operations and comprehensive loss is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 499 $ 134 $ 1,237 $ 330 General and administrative 1,286 597 2,951 880 $ 1,785 $ 731 $ 4,188 $ 1,210 2019 Employee stock purchase plan In June 2019, the Company adopted the 2019 Employee Stock Purchase Plan (the “ESPP”), which became effective on June 18, 2019. The Company initially reserved 315,000 shares of common stock for sale under the ESPP. At September 30, 2020, the Company had 297,609 shares available for issuance under the plan. The average grant date fair value per share under the plan was $26.54 for 2020. The total ESPP stock-based compensation expense for the nine-months ended September 30, 2020 was $0.2 million. The number of shares reserved for issuance under the ESPP will increase automatically on January 1st of each of the first ten calendar years following the first offering date by the number of shares equal to the lesser of 1% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31 or a lower amount determined by the Company’s board of directors. The aggregate number of shares issued over the term of the ESPP will not exceed 3,150,000 shares of the Company’s common stock.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss per share attributable to common stockholders	8. Net loss per share attributable to common stockholders The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Numerator: Net loss $ (13,684 ) $ (8,604 ) $ (37,682 ) $ (22,165 ) Denominator: Weighted-average number of common shares, basic and diluted 33,273,597 32,707,647 32,954,727 12,991,672 Net loss per common share attributable to common stockholders, basic and diluted $ (0.41 ) $ (0.26 ) $ (1.14 ) $ (1.71 ) The Company’s potential dilutive securities, which include Preferred Stock and common stock options, have been excluded from the computation of diluted net loss per share as the effect would be anti-dilutive. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential common shares, presented based on amounts outstanding at period end, from the computation of diluted net loss per share attributable to common stockholders for the period indicated because including them would have had an anti-dilutive effect: September 30, 2020 2019 Preferred Stock — — Outstanding options to purchase common stock 4,894,249 4,218,937 4,894,249 4,218,937

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income taxes	9. Income taxes The Company did not record an income tax benefit in its condensed consolidated statement of operations and comprehensive loss for the three months and nine months ended September 30, 2020 and 2019 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 had net deferred tax assets and liabilities of $17.9 million at December 31, 2019. The Company has provided a valuation allowance for the full amount of its net deferred tax assets and liabilities as of September 30, 2020 and December 31, 2019, 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. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (“CARES Act”) was enacted in response to the COVID-19 pandemic. The CARES Act, among other things, permits net operating loss (“NOL”) carryovers and carrybacks to offset 100% of taxable income for taxable years beginning before 2021. In addition, the CARES Act allows NOLs incurred in 2018, 2019, and 2020 to be carried back to each of the five preceding taxable years to generate a refund of previously paid income taxes. The Company has evaluated the impact of the CARES Act, and at present, the Company does not expect that the NOL carryback provision of the CARES Act would result in a cash benefit to us. The Company did not record any amounts for unrecognized tax benefits as of September 30, 2020 or December 31, 2019.

Employee Benefits

Employee Benefits	9 Months Ended
	Sep. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Employee benefits	10. Employee benefits In 2016, the Company established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pretax basis. On January 1, 2020, the Company began to make matching contributions up to 4% of annual salary for those employees who are participating in the 401(k) Plan. For the three and nine months ended September 30, 2020, the Company made matching contributions of $0.08 million and $0.24 million, respectively. The Company was not required to make and did not make any contributions to the 401(k) Plan for the three and nine months ended September 30, 2019.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent events	11. Subsequent events The Company has evaluated subsequent events through the issuance date of these interim condensed consolidated financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of presentation and consolidation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”),and include the accounts of the Company and its wholly-owned subsidiary. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). All intercompany transactions between and among its consolidated subsidiary have been eliminated.
Unaudited Interim Financial Information	Unaudited interim financial information The accompanying interim unaudited condensed consolidated financial statements and related disclosures are unaudited and have been prepared in accordance with GAAP for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all the information and footnotes required by GAAP for complete financial statements and should be read in conjunction with the Company’s consolidated financial statements and related footnotes as of and for the year ended December 31, 2019, which was filed with the SEC on March 23, 2020. The Company’s financial information as of September 30, 2020, and for the three and nine months ended September 30, 2020 and 2019 is unaudited, but in the opinion of management, all adjustments, consisting only of normal recurring adjustments, considered necessary for a fair presentation of the financial position, results of operations and cash flows at the dates and for the periods presented of the results of these interim periods have been included. The balance sheet information as of December 31, 2019 was derived from audited financial statements. The results of the Company’s operations for any interim period are not necessarily indicative of the results that may be expected for any other interim period or for a full fiscal year.
Use of Estimates	Use of estimates The preparation of unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, expenses and disclosure of contingent assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and cash equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. The Company deposits its cash in checking, sweep and money market accounts.
Restricted Cash	Restricted cash At September 30, 2020, restricted cash consisted of money market accounts collateralizing letters of credit issued as security deposits in connection with the Company’s leases of its corporate facilities. The following table reconciles cash and cash equivalents and restricted cash per the condensed consolidated balance sheets to the condensed consolidated statements of cash flows (in thousands): As of September 30, 2020 2019 Cash and cash equivalents $ 191,461 $ 233,049 Restricted cash $ 205 $ 205 Total cash, cash equivalents and restricted cash $ 191,666 $ 233,254
Fair Value of Financial Instruments	Fair value of financial instruments ASC Topic 820, Fair Value Measurement Level 1—Quoted market prices in active markets for identical assets or liabilities. Level 2—Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves. Level 3—Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use. To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.
Deferred Offering Costs	Deferred offering costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in the condensed consolidated statement of stockholders’ equity as a reduction of additional paid-in capital.
Net Loss per Share	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. The Company considers its convertible preferred stock (“Preferred Stock”) to be participating securities as in the event a dividend is paid on common stock, the holders of Preferred Stock would be entitled to receive dividends on a basis consistent with the common stockholders. Under the two-class method, the net loss attributable to common stockholders is not allocated to the Preferred Stock as the holders of the Preferred Stock do not have a contractual obligation to share in losses. Under the two-class method, basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock.
Emerging Growth Company and Smaller Reporting Company Status	Emerging growth company and smaller reporting 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 is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, the Company’s unaudited condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company will remain an emerging growth company until the earliest of (1) the last day of its first fiscal year (a) in which the Company has total annual gross revenues of at least $1.07 billion, or (b) in which the Company is deemed to be a large accelerated filer, which means the market value of its common stock that is held by non-affiliates exceeds $700.0 million as of the prior June 30 th The Company is also a “smaller reporting company,” meaning that as of the date of its initial public offering, the market value of its stock held by non-affiliates is less than $700 million and our annual revenue is less than $100 million during the most recently completed fiscal year. The Company may continue to be a smaller reporting company as long as either (i) the market value of its stock held by non-affiliates is less than $250 million or (ii) its annual revenue is less than $100 million during the most recently completed fiscal year and the market value of its stock held by non-affiliates is less than $700 million. If the Company is a smaller reporting company at the time it ceases to be an emerging growth company, the Company may continue to rely on exemptions from certain disclosure requirements that are available to smaller reporting companies. Specifically, as a smaller reporting company, the Company may choose to present only the two most recent fiscal years of audited financial statements in its Annual Report on Form 10-K and, similar to emerging growth companies, smaller reporting companies have reduced disclosure obligations regarding executive compensation.
Recently Adopted Accounting Pronouncements	Recently adopted accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases In July 2017, the FASB issued ASU 2017-11, Earnings Per Share I. Accounting for Certain Financial Instruments with Down Round Features; II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception In August 2018, the FASB issued ASU 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement”.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Schedule of Cash and Cash Equivalents and Restricted Cash	The following table reconciles cash and cash equivalents and restricted cash per the condensed consolidated balance sheets to the condensed consolidated statements of cash flows (in thousands): As of September 30, 2020 2019 Cash and cash equivalents $ 191,461 $ 233,049 Restricted cash $ 205 $ 205 Total cash, cash equivalents and restricted cash $ 191,666 $ 233,254

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Schedule of Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Utilized	The following tables present 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 (in thousands): Fair value measurements as of September 30, 2020 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 191,461 $ — $ — $ 191,461 Total $ 191,461 $ — $ — $ 191,461 Fair value measurements as of December 31, 2019 Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 222,471 $ — $ — $ 222,471 Total $ 222,471 $ — $ — $ 222,471

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consisted of the following (in thousands): September 30, December 31, 2020 2019 Accrued employee compensation costs $ 2,409 $ 2,053 Accrued professional 559 228 Accrued research and development costs 1,231 959 Current portion of operating lease liabilities 1,119 — Accrued Other 67 56 Other Current Liabilities 255 54 $ 5,640 $ 3,350

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases	Future minimum lease payments under non-cancellable leases as of September 30, 2020 are as follows (in thousands): 2020 $ 290 2021 1,102 2022 81 Total lease payments 1,473 Less imputed interest (58 ) Present value of lease liabilities $ 1,415
Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases	Future minimum lease payments under non-cancellable leases as of December 31, 2019 are as follows (in thousands): 2020 $ 1,149 2021 1,102 2022 81 2023 — Thereafter — $ 2,332
Summary of Lease Balances	Lease balances as of September 30, 2020 are as follows (in thousands): Operating right-of-use assets $ 1,381 Current Portion of operating lease liabilities $ 1,119 Non-current portion of operating lease liabilities 296 Total operating lease liabilities $ 1,415
Summary of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Operating Leases	The weighted average remaining lease term and weighted average discount rate of our operating leases as of September 30, 2020 are as follows: Weighted average remaining lease term in years 1.3 Weighted average discount rate 7.02 %

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-based Compensation Expense	Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying condensed consolidated statements of operations and comprehensive loss is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Research and development $ 499 $ 134 $ 1,237 $ 330 General and administrative 1,286 597 2,951 880 $ 1,785 $ 731 $ 4,188 $ 1,210

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Numerator: Net loss $ (13,684 ) $ (8,604 ) $ (37,682 ) $ (22,165 ) Denominator: Weighted-average number of common shares, basic and diluted 33,273,597 32,707,647 32,954,727 12,991,672 Net loss per common share attributable to common stockholders, basic and diluted $ (0.41 ) $ (0.26 ) $ (1.14 ) $ (1.71 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at period end, from the computation of diluted net loss per share attributable to common stockholders for the period indicated because including them would have had an anti-dilutive effect: September 30, 2020 2019 Preferred Stock — — Outstanding options to purchase common stock 4,894,249 4,218,937 4,894,249 4,218,937

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Details)	Jun. 21, 2019USD ($)$ / sharesshares	Jun. 06, 2019$ / sharesshares	Jul. 31, 2020USD ($)	Jun. 30, 2019shares	Sep. 30, 2020USD ($)$ / sharesshares	Dec. 31, 2019$ / sharesshares
Nature Of Business And Basis Of Presentation [Line Items]
Entity incorporation state name					DE
Reverse stock split, description					On June 6, 2019, in connection with the IPO, the Company effected a one-for-9.95 reverse split of the Company’s issued and outstanding common and convertible preferred stock.
Reverse stock split		0.1005
Common stock, shares authorized | shares	300,000,000	300,000,000			300,000,000	300,000,000
Common stock, per share par value | $ / shares	$ 0.0001	$ 0.0001			$ 0.0001	$ 0.0001
Undesignated preferred stock, shares authorized | shares	10,000,000	10,000,000
Undesignated preferred stock, per share par value | $ / shares	$ 0.0001	$ 0.0001
Securities issued in connection with shelf registration					$ 0
Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from initial public offering	$ 149,400,000
Initial Public Offering | Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares | shares	9,074,776			9,074,776
Stock issued, price per share | $ / shares	$ 18
Offering costs	$ 13,900,000
Underwriters' Option | Common Stock
Nature Of Business And Basis Of Presentation [Line Items]
Stock issued during period, shares | shares	1,183,666
Base Prospectus
Nature Of Business And Basis Of Presentation [Line Items]
Maximum aggregate offering price			$ 400,000,000
Sales Agreement Prospectus
Nature Of Business And Basis Of Presentation [Line Items]
Maximum aggregate offering price			$ 150,000,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 191,461	$ 222,471	$ 233,049
Restricted cash	205		205
Total cash, cash equivalents and restricted cash	$ 191,666	$ 222,676	$ 233,254	$ 105,603

Summary of Significant Accoun_5

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details)	Sep. 30, 2020
ASU 2016-02
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
ASU 2017-11
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect	true
ASU 2018-13
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect	true

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Recurring Basis and Level of Fair Value Hierarchy Utilized (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 191,461	$ 222,471
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	191,461	222,471
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	191,461	222,471
Money Market Funds | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total cash equivalents	$ 191,461	$ 222,471

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair value assets, transfers between level 1, level 2 and level 3, amount	$ 0	$ 0
Fair value liabilities, transfers between level 1, level 2 and level 3, amount	$ 0	$ 0

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued employee compensation costs	$ 2,409	$ 2,053
Accrued professional	559	228
Accrued research and development costs	1,231	959
Current portion of operating lease liabilities	1,119
Accrued Other	67	56
Other Current Liabilities	255	54
Total accrued and other current liabilities	$ 5,640	$ 3,350

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended					3 Months Ended			9 Months Ended
	Dec. 31, 2018USD ($)ft²Option	Aug. 31, 2018USD ($)ft²	Jul. 31, 2015USD ($)shares	Jun. 30, 2014USD ($)	Jun. 30, 2014GBP (£)	Sep. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020GBP (£)	Jun. 30, 2020USD ($)	Jan. 01, 2020USD ($)	Dec. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets						$ 1,381,000			$ 1,381,000
Operating lease, liabilities						1,415,000			1,415,000
Cumulative effect adjustment	$ 105,068,000					192,535,000	$ 214,342,000	$ 233,683,000	192,535,000	$ 233,683,000		$ 203,400,000		$ 224,428,000	$ 241,536,000	$ 99,581,000
Area of space subject to operating lease | ft²	2,485	23,000
Operating lease term	3 years	3 years
Operating lease cost per year	$ 200,000	$ 900,000
Annual base rent increase percentage for operating lease	2.50%	3.00%
Operating lease commencement date	May 1, 2019	Dec. 10, 2018
Number of options to renewal operating lease term | Option	1
Operating lease, renewal term	2 years
Operating leases, rent expense						300,000			900,000
Liabilities recorded under agreement						7,400,000			7,400,000					4,322,000
CSHL Agreement
Commitments And Contingencies [Line Items]
Stock issued during period, shares | shares			164,927
Shares of common stock granted, value			$ 70,000
Percentage of maximum required payment of sublicense revenue			20.00%
Annual license maintenance fee									10,000
Maximum aggregate potential milestone payments payable						900,000			900,000
Expenses related to reimbursable patent costs						0		0	0	0
Southampton Agreement
Commitments And Contingencies [Line Items]
Maximum aggregate potential milestone payments payable						500,000			500,000		£ 400,000
Payment of up-front license fee				$ 70,000	£ 60,000
Liabilities recorded under agreement						0			0					$ 0
Member of Board of Directors
Commitments And Contingencies [Line Items]
Consulting services expenses							$ 20,000	$ 20,000	$ 0	$ 70,000
Consulting services agreement term									5 years
Scientific advisory services expenses						$ 10,000			$ 40,000
Scientific advisory services agreement term									12 months
ASU 2016-02
Commitments And Contingencies [Line Items]
Operating lease right-of-use assets													$ 2,200,000
Operating lease, liabilities													2,200,000
Deferred rent													30,000
ASU 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Commitments And Contingencies [Line Items]
Cumulative effect adjustment													$ 0

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases (Details) $ in Thousands	Sep. 30, 2020USD ($)
Future minimum lease payments under non-cancellable leases
2020	$ 290
2021	1,102
2022	81
Total lease payments	1,473
Less imputed interest	(58)
Present value of lease liabilities	$ 1,415

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-Cancellable Leases Before the Adoption of Topic 842 (Details) $ in Thousands	Dec. 31, 2019USD ($)
Future minimum payments for operating leases
2020	$ 1,149
2021	1,102
2022	81
Total	$ 2,332

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Lease Balances (Details) $ in Thousands	Sep. 30, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating lease right-of-use assets	$ 1,381
Current portion of operating lease liabilities	1,119
Non-current portion of operating lease liabilities	296
Total operating lease liabilities	$ 1,415

Commitments and Contingencies_5

Commitments and Contingencies - Summary of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Operating Leases (Details)	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Weighted average remaining lease term in years	1 year 3 months 18 days
Weighted average discount rate	7.02%

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - $ / shares	Sep. 30, 2020	Dec. 31, 2019	Jun. 21, 2019	Jun. 06, 2019
Stockholders Equity Note [Abstract]
Common stock, shares authorized	300,000,000	300,000,000	300,000,000	300,000,000
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, shares authorized			10,000,000	10,000,000
Preferred stock, par value			$ 0.0001	$ 0.0001
Preferred stock, shares outstanding	0

Equity Incentive Plans - Additi

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option granted to purchase shares		168,255		1,138,657
Options vest over period				4 years
Unrecognized compensation cost		$ 18,800		$ 18,800
Expected weighted average period				3 years 3 days
Stock based compensation expense		$ 1,785	$ 731	$ 4,188	$ 1,210
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	2,200,000
Percentage of increase in reserved common shares	4.00%
Number of common shares available for future issuance		2,358,296		2,358,296
The 2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares available for future issuance		0		0
2019 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	315,000
Number of common shares available for future issuance		297,609		297,609
Average grant date fair value per share under the plan				$ 26.54
Stock based compensation expense				$ 200
2019 ESPP | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock reserved for issuance	3,150,000
Percentage of increase in reserved common shares	1.00%

Equity Incentive Plans - Summar

Equity Incentive Plans - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 1,785	$ 731	$ 4,188	$ 1,210
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	499	134	1,237	330
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock based compensation expense	$ 1,286	$ 597	$ 2,951	$ 880

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Schedule of Computation of Basic and Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (13,684)	$ (12,959)	$ (11,039)	$ (8,604)	$ (7,819)	$ (5,742)	$ (37,682)	$ (22,165)
Denominator:
Weighted-average number of common shares, basic and diluted	33,273,597			32,707,647			32,954,727	12,991,672
Net loss per common share attributable to common stockholders, basic and diluted	$ (0.41)			$ (0.26)			$ (1.14)	$ (1.71)

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	4,894,249	4,218,937
Outstanding Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	4,894,249	4,218,937

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	Mar. 27, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax benefit		$ 0	$ 0	$ 0	$ 0
Deferred tax assets and liabilities, net						$ 17,900,000
Percentage of net operating loss carryovers and carrybacks to offset of taxable income	100.00%
NOL carryback provision CARES Act would result in cash benefit		0		0
Unrecognized tax benefits		$ 0		$ 0		$ 0

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Contribution Plan Disclosure [Line Items]
Contributions to 401(k) Plan	$ 80,000	$ 0	$ 240,000	$ 0
Maximum
Defined Contribution Plan Disclosure [Line Items]
Maximum matching contribution percentage of employees salary			4.00%