Evelo Biosciences (EVLO) 10-Q 31 Jul 20 2020 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2020	Jul. 27, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	001-38473
Entity Registrant Name	Evelo Biosciences, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-5594527
Entity Address, Address Line One	620 Memorial Drive
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	(617)
Local Phone Number	577-0300
Title of 12(b) Security	Common Stock,$0.001 par value per share
Trading Symbol	EVLO
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	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		46,136,643
Entity Central Index Key	0001694665
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 90,173	$ 77,833
Prepaid expenses and other current assets	2,544	3,176
Total current assets	92,717	81,009
Property and equipment, net	8,002	8,341
Right of use asset - operating lease	11,616
Other assets	1,570	1,570
Total assets	113,905	90,920
Current liabilities:
Accounts payable	3,439	620
Accrued expenses	7,986	8,758
Operating lease liability, current portion	1,788
Other current liabilities	395	365
Total current liabilities	13,608	9,743
Noncurrent liabilities:
Long-term debt	19,806	19,634
Operating lease liability, net of current portion	10,982
Deferred rent, net of current portion		1,148
Other noncurrent liabilities	303	198
Total liabilities	44,699	30,723
Commitments and contingencies
Stockholder’s equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding at June 30, 2020 and December 31, 2019, respectively	0	0
Common stock, $0.001 par value; 200,000,000 shares authorized; 46,173,415 and 32,232,258 shares issued and 46,136,643 and 32,170,605 shares outstanding at June 30, 2020 and December 31, 2019, respectively	46	32
Additional paid-in capital	311,706	259,018
Accumulated deficit	(242,546)	(198,853)
Total stockholders’ equity	69,206	60,197
Total liabilities and stockholders’ equity	$ 113,905	$ 90,920

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	46,173,415	32,232,258
Common stock, shares outstanding (in shares)	46,136,643	32,170,605

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 15,174,000	$ 15,464,000	$ 32,593,000	$ 31,141,000
General and administrative	5,071,000	5,923,000	10,913,000	11,050,000
Total operating expenses	20,245,000	21,387,000	43,506,000	42,191,000
Loss from operations	(20,245,000)	(21,387,000)	(43,506,000)	(42,191,000)
Other (expense) income:
Interest (expense) income, net	(458,000)	446,000	(639,000)	951,000
Other income, net	140,000	0	606,000	0
Other (expense) income, net	(318,000)	446,000	(33,000)	951,000
Loss before income taxes	(20,563,000)	(20,941,000)	(43,539,000)	(41,240,000)
Income tax expense	(89,000)	0	(154,000)	0
Net loss	$ (20,652,000)	$ (20,941,000)	$ (43,693,000)	$ (41,240,000)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.63)	$ (0.65)	$ (1.35)	$ (1.29)
Weighted-average number of common shares outstanding, basic and diluted (in shares)	32,634,468	32,041,401	32,442,259	31,983,558
Comprehensive loss:
Net loss	$ (20,652,000)	$ (20,941,000)	$ (43,693,000)	$ (41,240,000)
Other comprehensive loss:
Unrealized gain (loss) on investments, net of tax of $0	0	3,000	0	19,000
Comprehensive loss	(20,652,000)	(20,938,000)	(43,693,000)	(41,221,000)
Tax portion of unrealized loss on investments	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Tax portion of unrealized loss on investments	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Preferred Stock and Stockholders’ Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		0	31,825,769
Beginning balance at Dec. 31, 2018	$ 136,949	$ 0	$ 32	$ 250,316	$ (18)	$ (113,381)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted common stock (in shares)			23,345
Vesting of restricted common stock	7			7
Exercise of stock options (in shares)			181,521
Exercise of stock options	257			257
Stock-based compensation expense	1,953			1,953
Unrealized gain on investments	16				16
Net loss	(20,299)					(20,299)
Ending balance (in shares) at Mar. 31, 2019		0	32,030,635
Ending balance at Mar. 31, 2019	118,883	$ 0	$ 32	252,533	(2)	(133,680)
Beginning balance (in shares) at Dec. 31, 2018		0	31,825,769
Beginning balance at Dec. 31, 2018	136,949	$ 0	$ 32	250,316	(18)	(113,381)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Unrealized gain on investments	19
Net loss	(41,240)
Ending balance (in shares) at Jun. 30, 2019		0	32,045,706
Ending balance at Jun. 30, 2019	100,088	$ 0	$ 32	254,676	1	(154,621)
Beginning balance (in shares) at Mar. 31, 2019		0	32,030,635
Beginning balance at Mar. 31, 2019	118,883	$ 0	$ 32	252,533	(2)	(133,680)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted common stock (in shares)			13,692
Vesting of restricted common stock	7			7
Exercise of stock options (in shares)			1,379
Exercise of stock options	1			1
Stock-based compensation expense	2,135			2,135
Unrealized gain on investments	3				3
Net loss	(20,941)					(20,941)
Ending balance (in shares) at Jun. 30, 2019		0	32,045,706
Ending balance at Jun. 30, 2019	100,088	$ 0	$ 32	254,676	1	(154,621)
Beginning balance (in shares) at Dec. 31, 2019		0	32,170,605
Beginning balance at Dec. 31, 2019	60,197	$ 0	$ 32	259,018	0	(198,853)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted common stock (in shares)			13,390
Vesting of restricted common stock	7			7
Exercise of stock options (in shares)			137,213
Exercise of stock options	226			226
Stock-based compensation expense	1,955			1,955
Net loss	(23,041)					(23,041)
Ending balance (in shares) at Mar. 31, 2020		0	32,321,208
Ending balance at Mar. 31, 2020	39,344	$ 0	$ 32	261,206	0	(221,894)
Beginning balance (in shares) at Dec. 31, 2019		0	32,170,605
Beginning balance at Dec. 31, 2019	$ 60,197	$ 0	$ 32	259,018	0	(198,853)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	141,157
Unrealized gain on investments	$ 0
Net loss	(43,693)
Ending balance (in shares) at Jun. 30, 2020		0	46,136,643
Ending balance at Jun. 30, 2020	69,206	$ 0	$ 46	311,706	0	(242,546)
Beginning balance (in shares) at Mar. 31, 2020		0	32,321,208
Beginning balance at Mar. 31, 2020	39,344	$ 0	$ 32	261,206	0	(221,894)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of fees (in shares)			13,800,000
Issuance of common stock in public offering, net of fees	48,407		$ 14	48,393
Vesting of restricted common stock (in shares)			11,491
Vesting of restricted common stock	5			5
Exercise of stock options (in shares)			3,944
Exercise of stock options	9			9
Stock-based compensation expense	2,093			2,093
Unrealized gain on investments	0
Net loss	(20,652)					(20,652)
Ending balance (in shares) at Jun. 30, 2020		0	46,136,643
Ending balance at Jun. 30, 2020	$ 69,206	$ 0	$ 46	$ 311,706	$ 0	$ (242,546)

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (43,693)	$ (41,240)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,048	4,088
Depreciation expense	1,031	803
Net (accretion of discount)/amortization of premium on marketable securities	0	(161)
Non-cash interest expense	132	51
Non-cash lease expense	1,117
Gain on sale of fixed assets, net	(5)	0
Changes in assets and liabilities:
Prepaid expenses and other current assets	632	(144)
Accounts payable	2,812	1,324
Accrued expenses and other current liabilities	(1,001)	1,920
Operating lease liabilities	(1,111)
Other liabilities	147	10
Net cash used in operating activities	(35,891)	(33,349)
Investing activities
Proceeds from sales and maturities of investments	0	51,000
Purchases of property and equipment	(651)	(1,480)
Proceeds from sale of fixed assets	6	0
Net cash (used in)/provided by investing activities	(645)	49,520
Financing activities
Payment of deferred offering costs	0	(56)
Proceeds from issuance of common stock, net of issuance cost	48,641	0
Proceeds from the exercise of stock options	235	259
Net cash provided by financing activities	48,876	203
Net (decrease) increase in cash, cash equivalents and restricted cash	12,340	16,374
Cash, cash equivalents and restricted cash – beginning of period	79,333	94,351
Cash, cash equivalents and restricted cash – end of period	91,673	110,725
Supplemental disclosure of cash flow information
Cash paid for interest	875	436
Cash paid for taxes	20	0
Noncash investing and financing activities
Deferred financing and public offering costs in accounts payable and accrued expenses	234	46
Property and equipment additions in accounts payable and accrued expenses	$ 248	$ 211

Organization

Organization	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Evelo Biosciences, Inc. ("Evelo" or the "Company”) is a biotechnology company which was incorporated in Delaware on May 6, 2014. The Company is discovering and developing oral biologics designed to act on cells in the small intestine with systemic therapeutic effects. The Company is advancing these oral biologics with the aim of treating a broad range of immune mediated diseases with an initial focus on inflammatory diseases and oncology. The Company is headquartered in Cambridge, Massachusetts. Since inception, the Company has devoted substantially all of its efforts to research and development and raising capital. The Company has not generated any revenue related to its primary business purpose to date. The Company is subject to a number of risks similar to those of other development stage companies, including dependence on key individuals, the need to develop commercially viable products, competition from other companies, many of whom are larger and better capitalized, and the need to obtain adequate additional financing to fund the development of its products. In June 2020, the Company sold 13,800,000 shares of its common stock in an underwritten public offering at a public offering price of $3.75 per share, including the underwriters' exercise of their option to purchase 1,800,000 shares to cover over-allotment, generating gross proceeds of $51.8 million and estimated net proceeds of $48.4 million, after deducting underwriting discounts and commission and other offering expenses payable by the Company. Issuance costs totaling $0.2 million were unpaid as of June 30, 2020 and have been included in accounts payable and accrued expenses in the Company's unaudited condensed consolidated balance sheet. The Company has incurred operating losses since inception and expects such losses and negative operating cash flows to continue for the foreseeable future. The Company historically has funded its operations from the issuance of convertible notes, convertible preferred stock and common stock, and through debt financings. As of June 30, 2020, the Company had cash and cash equivalents of $90.2 million and an accumulated deficit of $242.5 million. Going Concern In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company's ability to continue as a going concern within one year after the date that the unaudited condensed consolidated financial statements are issued. The transition to profitability is dependent upon the successful development, approval, and commercialization of its products and product candidates and the achievement of a level of revenues adequate to support its cost structure. Based on the Company’s current operating plan and due to the uncertainty related to the impact of the COVID-19 and the nature of Evelo's business, the Company has substantial doubt that its cash and cash equivalents at June 30, 2020, together with the $10.0 million in additional debt drawdown in the third quarter of 2020, will be sufficient to fund operations and capital expenditures for at least the twelve months following the filing of this Quarterly Report on Form 10-Q, and the Company will need to obtain additional funding. The Company intends to pursue strategic partnerships and collaborations, or obtain additional funding through its available financing sources which include, additional public offerings of common stock and private financing of debt or equity. Management’s belief with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional funding sooner than would otherwise be expected. There can be no assurance that the Company will be able to obtain additional funding on acceptable terms, if at all. If the Company is unable to obtain sufficient funding, it could be required to delay its development efforts, limit activities and reduce research and development costs, which could adversely affect its business prospects. Because of the uncertainty in securing additional funding and the insufficient amount of cash and cash equivalent resources at June 30, 2020, management has concluded that substantial doubt exists with respect to the Company’s ability to continue as a going concern within one year after the date that the unaudited condensed consolidated financial statements are issued.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standard Codification (“ASC”) and ASU of the FASB. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019 and notes thereto. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of June 30, 2020, the results of its operations and stockholders' equity for the three and six months ended June 30, 2020 and 2019 and cash flows for the six months ended June 30, 2020 and 2019. Such adjustments are of a normal and recurring nature. The results for the three and six months ended June 30, 2020 are not necessarily indicative of the results for the year ending December 31, 2020, or for any future period. Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant estimates and assumptions reflected in these unaudited condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of stock-based awards. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Principles of Consolidation The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned, controlled subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Subsequent Event Considerations The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the unaudited condensed consolidated financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure in this Quarterly Report on Form 10-Q, except as disclosed in Note 6 to these unaudited condensed consolidated financial statements. Emerging Growth Company Status Evelo is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"), and it may take advantage of reduced reporting requirements that are otherwise applicable to public companies. Evelo may take advantage of these exemptions until it is no longer an emerging growth company. Section 107 of the JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. Evelo has elected to use the extended transition period for complying with new or revised accounting standards, and, as a result of this election, its consolidated financial statements may not be comparable to companies that comply with public company effective dates. Evelo may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of its IPO or such earlier time that it is no longer an emerging growth company. Evelo would cease to be an emerging growth company if it has more than $1.07 billion in annual revenue, it has more than $700.0 million in market value of its stock held by non-affiliates (and has been a public company for at least 12 months and has filed one annual report on Form 10-K), or it has issued more than $1.0 billion of non-convertible debt securities over a three-year period. Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are excluded from net loss. The Company's only element of other comprehensive loss is unrealized gains on available-for-sale investments. Comprehensive loss totaled $20.7 million and $43.7 million, respectively, for the three and six months ended June 30, 2020. For the three and six months ended June 30, 2019 comprehensive loss was $20.9 million and $41.2 million, respectively. Cash, Cash Equivalents, and Restricted Cash Cash equivalents are comprised of highly liquid investments that are readily convertible into cash with original maturities of three months or less. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Cash equivalents are stated at cost, which approximates market value. The Company’s restricted cash consists of restricted cash in connection with building leases for the Company’s office and laboratory premises and deposits held in relation to the company's credit card facility. Restricted cash totaled approximately $1.5 million at June 30, 2020 and December 31, 2019, and is classified within other assets on the accompanying condensed consolidated balance sheet. The following reconciles cash, cash equivalents and restricted cash as of June 30, 2020 and December 31, 2019, as presented on the Company's statements of cash flows, to its related balance sheet accounts (in thousands): June 30, 2020 December 31, 2019 Cash and cash equivalents: Cash $ 8,461 $ 1,634 Money market funds 81,712 76,199 Total cash and cash equivalents 90,173 77,833 Restricted cash 1,500 1,500 Cash, cash equivalents and restricted cash $ 91,673 $ 79,333 Fair Value of Financial Instruments ASC 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly; and • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in 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. An entity may choose to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in earnings. The Company did not elect to measure any additional financial instruments or other items at fair value. Research and Development Costs Research and development costs are expensed in the period incurred. Research and development expenses consist of both internal and external costs such as payroll, consulting, and manufacturing costs associated with the development of the Company’s product candidates. Costs for certain development activities, such as clinical trials and manufacturing development activities, are recognized based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, and information provided to the Company by its vendors on their actual costs incurred or level of effort expended. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued research and development expenses. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. The Company has and may continue to acquire the rights to develop and commercialize new product candidates from third parties. The upfront payments to acquire license, product or rights, as well as any future milestone payments, are immediately recognized as research and development expense provided that there is no alternative future use of the rights in other research and development projects. Any milestone payments made for Intellectual Property after regulatory approval, or that have alternative future use, are capitalized and amortized. Stock-Based Compensation The Company records stock-based compensation for options granted to employees and directors based on the grant date fair value of awards issued. The expense is recorded over the requisite service period, which is the vesting period, on a straight-line basis. The Company uses the Black-Scholes option-pricing model to determine the fair value of stock options. The determination of the fair value of stock options on the date of grant using an option-pricing model is affected by the Company’s common stock price, as well as a number of other assumptions. The Company records forfeitures as they occur. The Company accounts for stock-based compensation arrangements with non-employees based upon the fair value of the consideration received or the equity instruments issued, whichever is more reliably measurable. The measurement date for non-employee awards is generally the date performance of services required from the non-employee is complete. Stock-based compensation costs for non-employee awards are recognized as services are provided, which is generally the vesting period, on a straight-line basis. Segments The Company has one operating segment. The Company's chief operating decision maker, its Chief Executive Officer, manages the Company's operations on a consolidated basis for the purposes of allocating resources. Recently Adopted Accounting Pronouncements Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”), which supersedes the guidance in former ASC 840, Leases. The new accounting guidance requires recognition of all long-term lease assets and lease liabilities by lessees and sets forth new disclosure requirements for those lease assets and liabilities. It requires lessees to recognize right-of-use assets and lease liabilities on the balance sheet using a modified retrospective approach at the beginning of the earliest comparative period in the financial statements for all leases with a term of greater than 12 months regardless of classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases. The FASB subsequently issued several ASUs amending the new standard. This guidance is effective for annual reporting periods, and interim periods within those years, beginning after December 15, 2018 for most public entities. The Company adopted this new standard on January 1, 2020 using the required modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. ASU 2016-02 provides a number of optional practical expedients in transition. The Company elected to adopt the 'package of practical expedients', which permits the Company (i) not to reassess whether expired existing contracts are or contain leases, (ii) not to reassess the classification of expired or existing leases, and (iii) not to reassess initial direct costs for any existing leases. The Company will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance. Adoption of this standard resulted in the recognition of a right-of-use asset and a lease liability on the Company’s January 1, 2020 condensed consolidated balance sheet of $12.7 million and $13.9 million, respectively. There was no material impact resulting from the adoption on the Company’s unaudited condensed consolidated statement of operations for the three and six months ended June 30, 2020. For leases with terms greater than 12 months, the Company records the related right-of-use asset and lease liability at the present value of lease payments over the term. As the Company’s leases do not provide readily determinable implicit interest rates, the Company utilized its incremental borrowing rate, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. The application of the new standard required netting of unamortized balance of lease incentives and deferred lease obligation to the right-of-use asset at the adoption date. The Company’s operating leases include rental escalation clauses that are factored into the determination of lease payments when appropriate. The Company does not separate lease and non-lease components of contracts. Refer to Note 3, Leases within these unaudited condensed consolidated financial statements for additional information. Share-Based Compensation In June 2018, the FASB issued ASU No. 2018-07, Stock-based Compensation: Improvements to Nonemployee Share-based Payment Accounting (Topic 718) ("ASU 2018-07"), which amends the existing accounting standards for share-based payments to nonemployees. This ASU aligns much of the guidance on measuring and classifying nonemployee awards with that of awards to employees. Under the new guidance, the measurement of nonemployee equity awards is fixed on the grant date. Entities will apply the ASU by recognizing a cumulative-effect adjustment, if any, to retained earnings as of the beginning of the annual period of adoption. The Company adopted ASU 2018-07 on January 1, 2020. The adoption of this standard did not have a material impact on its condensed consolidated financial statements. Accounting Pronouncements Issued and Not Adopted as of June 30, 2020 Income Taxes In December 2019, the FASB issued ASU No. 2019 -12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The new standard includes several provisions which simplify accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and increasing consistency and clarity for the users of financial statements. This standard will be effective for the Company on January 1, 2021. Early adoption is permitted. The Company is currently evaluating the potential impact ASU 2019-12 may have on its financial position and results of operations upon adoption.

Leases

Leases	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Leases	Leases In January 2018, the Company entered into an operating sublease arrangement to lease approximately 40,765 square feet for its office and research development space at 620 Memorial Drive, Cambridge, MA 02139 from February 2018 to September 2025. The Company maintains an additional separate operating lease for office and laboratory space that expired in May 2020. The leases require security deposits, which the Company has primarily met with letters of credit from a financial institution that are secured with cash on deposit. In June 2018, the Company entered into a sublease arrangement with a third party to lease space subject to an operating lease that expired in April 2020. The minimum rental payments received under this agreement totaled $0.1 million and $0.2 million, respectively, for the three and six months ended June 30, 2020 and were equivalent to the minimum payments due from the Company to the landlord. For both the three months ended June 30, 2020 and June 30, 2019 and for both the six months ended June 30, 2020 and June 30, 2019, the Company recorded rent expense of $0.7 million and $1.4 million, respectively. Rent expense was net of sublease rental income of $0.1 million for both three months ended June 30, 2020 and June 30, 2019 and was net of $0.3 million sublease rental income for both six months ended June 30, 2020 and June 30, 2019. Sublease rental income is inclusive of rental payments, taxes and operating expenses. The minimum aggregate future lease commitments, exclusive of any offsetting sublease rental payments, at June 30, 2020, are as follows (in thousands): Amount 2020 (excluding six month ended June 30. 2020) $ 1,454 2021 2,973 2022 3,062 2023 3,154 2024 3,249 Thereafter 2,491 Total lease payments 16,383 Less imputed interest (3,613) $ 12,770 Other information: Operating cash flows used for operating leases $ 1,634 Weighted-average remaining lease term (in years) 5.25 Weighted-average discount rate 9.5 %

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value as of June 30, 2020 and December 31, 2019 (in thousands): Description June 30, 2020 Assets: Money market funds included within cash and cash equivalents $ 81,712 $ 81,712 $ — $ — Total $ 81,712 $ 81,712 $ — $ — Description December 31, 2019 Assets: Money market funds included within cash and cash equivalents $ 76,199 $ 76,199 $ — $ — Total $ 76,199 $ 76,199 $ — $ — As of June 30, 2020 and December 31, 2019, the Company's cash equivalents have been initially valued at the transaction price and subsequently valued utilizing a third party pricing service. The Company validates the prices provided by its third-party pricing service by understanding the models used and obtaining market values from other pricing sources.

Property and Equipment, Net

Property and Equipment, Net	6 Months Ended
	Jun. 30, 2020
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment consists of the following (in thousands): June 30, 2020 December 31, 2019 Property and equipment: Lab equipment $ 8,300 $ 7,479 Leasehold improvements 2,157 2,014 Furniture and fixtures 822 750 Computers and software 230 204 Office equipment 3 9 Construction-in-process 1,138 1,594 Property and equipment 12,650 12,050 Less: accumulated depreciation (4,648) (3,709) Property and equipment, net $ 8,002 $ 8,341 The Company recognized $0.5 million and $1.0 million of depreciation expense for the three and six months ended June 30, 2020, respectively and $0.4 million and $0.8 million for the three and six months ended June 30, 2019, respectively.

Loan and Security Agreements

Loan and Security Agreements	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Loan and Security Agreements	Loan and Security Agreements 2016 Credit Facility In 2016, the Company entered into a credit facility (the “2016 Credit Facility”) with a bank that allowed the Company to borrow up to $15.0 million. Borrowings under the 2016 Credit Facility were secured by a lien on all Company assets, excluding intellectual property. The Company borrowed the entire $15.0 million available under the 2016 Credit Facility prior to its extinguishment in July 2019 as discussed in further detail below. The 2016 Credit Facility contained negative covenants restricting the Company’s activities, including limitations on cash deposits, dispositions, mergers or acquisitions, incurring indebtedness or liens, paying dividends or making investments and certain other business transactions. There were no financial covenants associated with the agreement. 2019 Credit Facility On July 19, 2019, the Company entered into a loan and security agreement (as amended, the "2019 Credit Facility") with K2 HealthVentures LLC and others (collectively, "K2HV") pursuant to which the K2HV agreed to make term loans in an aggregate principal amount of up to $45.0 million available to the Company in three tranches. The initial tranche of $20.0 million was funded upon closing on July 19, 2019. As amended on May 15, 2020, the second tranche of $10.0 million was available to be funded between December 1, 2019 and July 15, 2020 and was drawdown on July 14, 2020. The third tranche of $15.0 million is available to be funded at the Company's election on or before January 15, 2021, subject to certain customary conditions and the achievement of certain clinical development milestones. Borrowings under the 2019 Credit Facility are collateralized by substantially all of the Company's personal property, excluding intellectual property, and the Company pledged its equity interests in its subsidiaries, subject to certain limitations with respect to its foreign subsidiaries. Interest on the outstanding loan balance will accrue at a variable annual rate equal to the greater of (i) 8.65% and (ii) the prime rate plus 3.15%. The Company is required to make interest-only payments on the loans on a monthly basis through February 28, 2022. If the Company elects to draw the third tranche, the interest-only period will be extended through August 31, 2022. Subsequent to the interest only periods, the Company is required to make equal monthly payments of principal plus interest until the loans mature on August 1, 2024. Upon final payment or prepayment of the loans, the Company must pay a final payment equal to 4.3% of the loans borrowed, which is being accrued to interest expense over the term of the loan using the effective-interest method. The Company incurred fees associated with establishing the 2019 Credit Facility of $0.4 million. The Company has an option to prepay the loans in whole, subject to a prepayment fee of 2% of the amount prepaid or, if the prepayment occurs after the 18-month anniversary of the funding date of the loans, 1% of the amount prepaid. The 2019 Credit Facility contains customary representations, warranties and covenants and also includes customary events of default, including payment defaults, breaches of covenants, change of control and occurrence of a material adverse effect. The Company has determined that the risk of subjective acceleration under the material adverse events clause was remote and therefore has classified the long-term portion of the outstanding principal in non-current liabilities. Upon the occurrence and continuation of an event of default, a default interest rate of an additional 5% per annum may be applied to the outstanding loan balances, and the administrative agent, collateral agent, and lenders may declare all outstanding obligations immediately due and payable and exercise all of their rights and remedies as set forth in the 2019 Credit Facility and under applicable law. As of June 30, 2020, the Company was in compliance with all covenants under the 2019 Credit Facility. The Company used the proceeds from the initial $20.0 million tranche to prepay on July 19, 2019 the full $15.0 million loan balance outstanding under the 2016 Credit Facility. The Company has the following minimum aggregate future loan payments at June 30, 2020 (in thousands). The table below excludes minimum future payments related to second tranche drawdown on July 14, 2020 in the total of $10.0 million. These payments will be made based on the same terms as the initial borrowing. Twelve month period ending June 30, Amount 2021 $ 1,754 2022 4,391 2023 9,199 2024 8,498 Thereafter 2,208 Total minimum payments 26,050 Less amounts representing interest and discount (6,244) Long-term debt $ 19,806 Interest expense related to the Company's 2016 Credit Facility was approximately $0.2 million and $0.4 million for the three and six months ended June 30, 2019. Interest expense related to the Company's 2019 Credit Facility was approximately $0.4 million and $0.8 million for the three and six months ended June 30, 2020.

In-License Agreements

In-License Agreements	6 Months Ended
	Jun. 30, 2020
Research and Development [Abstract]
In-License Agreements	In-License Agreements Mayo Foundation for Medical Education and Research On June 10, 2016, the Company entered into a Research and License Agreement, (the “2016 Mayo License Agreement”) with the Mayo Foundation for Medical Education and Research, an affiliate of Mayo Clinic (the “Mayo Clinic”). Under the 2016 Mayo License Agreement, the Mayo Clinic was entitled to certain participation rights in connection with the issuance and sale of preferred stock that was issued prior to the Company’s public offering and warrants which were issued in 2016 and exercised in 2018. On August 6, 2017, the Company and the Mayo Clinic entered into a license agreement (“2017 Mayo License Agreement”). Under the 2017 Mayo License Agreement, the Mayo Clinic granted the Company (i) an exclusive, worldwide, sublicensable license under the Mayo Clinic’s rights to certain intellectual property and microbial strains (ii) a non-exclusive, worldwide, sublicensable license to certain related know-how, in each case, to develop and commercialize certain microbial strains and licensed products incorporating any such strains. As consideration, the Company paid a nonrefundable upfront fee of $0.2 million and annual license maintenance fees. Nonrefundable upfront fees were expensed in full to research and development expense in 2017. Annual maintenance fees will be expensed as incurred over the term of the agreement. The Company may owe the Mayo Clinic milestone payments upon the achievement of certain development, regulatory, and commercial milestones, up to a maximum of $56.0 million in the aggregate, as well as royalties on net sales of licensed products in low single-digit percentages. As of June 30, 2020, the Company has incurred milestone payments to date totaling approximately $0.2 million under the agreement of which no amounts are currently due. University of Chicago On March 10, 2016, the Company and the University of Chicago entered into a patent license agreement (“2016 University of Chicago Agreement”). Under the 2016 University of Chicago Agreement, the University of Chicago granted the Company (i) an exclusive, royalty-bearing and sublicensable license under the Licensed Patents and (ii) a non-exclusive, royalty-bearing, sublicensable license to access the technical information to diligently develop and commercialize Licensed Products. As consideration, the Company paid a nonrefundable upfront fee of less than $0.5 million and will pay annual license maintenance fees. Nonrefundable upfront fees were expensed in full to research and development expense in 2016. Annual maintenance fees will be expensed as incurred over the term of the agreement. The Company may owe the University of Chicago milestone payments, totaling an aggregate of approximately $60.9 million upon the achievement of certain development, regulatory, and commercial milestones, as well as royalties on net sales of licensed products ranging from low to high single-digit percentages. As of June 30, 2020, the Company has incurred milestone payments to date totaling approximately $0.4 million.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Collaboration Agreement with Sacco S.r.l. In July 2019, the Company entered into an agreement with Sacco S.r.l. ("Sacco"), an affiliate of one of the Company’s existing contract manufacturing organizations, pursuant to which and subject to certain exceptions for pre-existing products for pre-existing customers, Sacco will manufacture and supply single strain, non-genetically modified microbes intended for oral delivery or oral use in pharmaceutical products exclusively for the Company for a period of five years. Sacco may terminate the agreement if the provision of manufacturing services has been, or is scheduled to be, inactive for a period of six Agreement with Biose Industrie On February 15, 2018, the Company entered into an agreement with Biose Industrie (“Biose”), a French corporation, in which Biose has agreed to exclusively manufacture certain microbial biotherapeutic products for the Company and reserve agreed upon manufacturing resources to conduct manufacturing runs for such products. Under the terms of this agreement, the Company agreed to annual fees in the mid-six digits in consideration of both exclusivity for the manufacture of monoclonal microbials and for a set minimum number of manufacturing runs per year. Exclusivity fees paid and any minimum commitments are expensed as incurred. As of June 30, 2020, aggregate minimum payments over the remaining contract life total approximately $1.1 million. Litigation and Other Proceedings The Company may periodically become subject to legal proceedings and claims arising in connection with on-going business activities, including claims or disputes related to patents that have been issued or that are pending in the field of research on which the Company is focused. The Company is not a party to any material litigation and does not have contingency reserves established for any litigation liabilities.

Stockholders_ Equity

Stockholders’ Equity	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock On June 3, 2019, the Company filed a Registration Statement on Form S-3 (File No. 333-231911) (the “Shelf”) with the SEC in relation to the registration of common stock, preferred stock, debt securities, warrants and/or units of any combination thereof in the aggregate amount of up to $200.0 million for a period of up to three years from the date of the filing. The Company also simultaneously entered into a sales agreement with Cowen and Company, LLC, as sales agent, providing for the offering, issuance and sale by the Company of up to an aggregate $50.0 million of its common stock from time to time in “at-the-market” offerings under the Shelf. As of June 30, 2020, no securities have been issued pursuant to the sales agreement. In June 2020, the Company sold 13,800,000 shares of its common stock pursuant to the Shelf in the 2020 Offering at public offering price of $3.75 per share, for gross proceeds of $51.8 million and estimated net proceeds of $48.4 million, after deducting underwriting discounts and commission and other offering expenses payable by the Company.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2018 Incentive Award Plan The Company’s board of directors adopted on April 18, 2018, and the Company’s stockholders approved, the 2018 Incentive Award Plan (the “2018 Plan”), which became effective May 8, 2018 and under which the Company may grant cash and equity-based incentive awards to the Company’s employees, officers, directors, consultants and advisors. Following the effectiveness of the 2018 Plan, the Company ceased making grants under the 2015 Stock Incentive Plan (as amended, the "2015 Plan"). The 2018 Plan initially allowed the Company to grant awards for up to 1,344,692 shares of common stock plus that number of shares of common stock subject to awards outstanding under the 2015 Plan that expire, lapse or become terminated or are exchanged for cash, surrendered, repurchased, canceled without having been fully exercised or forfeited following the effective date of the 2018 Plan. Each year starting with 2019 and ending in and including 2028, the number of shares available for grants of awards under the 2018 Plan will be increased automatically on January 1 by a number of shares of common stock equal to the lesser of 4% of the shares of common stock outstanding on the final day of the preceding calendar year or the number of shares determined by the Company’s board of directors. Accordingly, on January 1, 2019, the number of shares authorized for issuance under the 2018 Plan was increased by 1,273,031 shares, and on January 1, 2020 this number was further increased by 1,286,824 shares. The 2015 Plan continues to govern the terms and conditions of the outstanding awards granted under it. The exercise price of stock options granted under the 2018 Plan is not less than the fair market value of a share of the Company’s common stock on the grant date. Other terms of awards, including vesting requirements, are determined by the board of directors and are subject to the provisions of the 2018 Plan. Stock options granted to employees generally vest over a four-year period but may be granted with different vesting terms. Certain options provide for accelerated vesting in the event of a change in control. Awards granted to non-employee consultants generally vest monthly over a period of one 2015 Stock Incentive Plan Prior to the approval of the 2018 Plan, the Company granted equity awards under the 2015 Plan, which originally provided for grant of incentive stock options, non-qualified stock options, restricted stock awards ("RSAs"), and other stock-based awards to the Company’s employees, officers, directors, consultants and advisors. The terms of equity award agreements, including vesting requirements, were determined by the board of directors and are subject to the provisions of the 2015 Plan. Stock options granted to employees generally vest over a four-year period but may be granted with different vesting terms. A limited number of awards contain performance-based vesting criteria and for such awards that are deemed probable of vesting, the Company records expense in the period in which such determination is made through any estimated remaining vesting period. Certain options provide for accelerated vesting in the event of a change in control. Awards granted to non-employee consultants generally vest monthly over a period of one Under the 2015 Plan, the Company was authorized to grant equity awards up to an aggregate of 5,417,044 shares of common stock. As of June 30, 2020, an aggregate of 5,758,518 options and other equity awards had been granted under the 2015 Plan, of which 1,326,425 have been exercised, 1,247,620 have been canceled and 18,468 have been repurchased as of June 30, 2020. A total of 113,006 shares previously reserved under the 2015 Plan that had not been exercised or were otherwise subject to outstanding exercise awards were no longer authorized for issuance under the 2015 Plan as of May 8, 2018. Stock-Based Compensation Expense Stock-based compensation expense included in the Company’s condensed consolidated statements of operations and comprehensive loss is as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 General and administrative $ 1,010 $ 1,162 $ 1,899 $ 2,224 Research and development 1,083 973 2,149 1,864 Total stock-based compensation expense $ 2,093 $ 2,135 $ 4,048 $ 4,088 Stock Options A summary of the Company’s stock option activity and related information is as follows: Shares Weighted- Options outstanding at December 31, 2019 5,691,474 $ 6.99 Granted 1,616,718 6.51 Exercised (141,157) 1.67 Canceled (781,463) 9.85 Options outstanding at June 30, 2020 6,385,572 $ 6.63 Exercisable as of June 30, 2020 3,035,054 $ 5.12 The weighted-average fair value of options granted during the six months ended June 30, 2020 and 2019 was $4.45 and $8.19, respectively. As of June 30, 2020, total unrecognized stock-based compensation expense relating to unvested stock options was $17.8 million. This amount is expected to be recognized over a weighted average period of 2.73 years. 2018 Employee Stock Purchase Plan The Company's board of directors adopted on April 18, 2018, and the Company’s stockholders approved, the 2018 Employee Stock Purchase Plan (the “ESPP”), which became effective on May 8, 2018. A total of 336,356 shares of common stock were initially reserved for issuance under the ESPP. In addition, the number of shares of common stock that may be issued under the ESPP will automatically increase on the first day of each calendar year, beginning in 2020 and ending in and including 2028, by an amount equal to the lesser of (i) 1% of the number of shares of the Company’s common stock outstanding on the last day of the applicable preceding calendar year and (ii) an amount determined by the Company’s board of directors. The Company's board of directors determined not to increase the number of shares that may be issued under the ESPP on January 1, 2020. The Company's board of directors authorized an initial offering period under the ESPP commencing on February 1, 2020.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to losses incurred since inception and the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. The Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was enacted on March 27, 2020. The CARES Act contains several key provisions including: (i) five year carryback of net operating losses (“NOLs”), (ii) increasing Section 163(j) from 30% limitation to 50% for 2019 and 2020, (iii) delay of payment of employer payroll taxes, (iv) temporary refundable employee retention credit, (v) suspension of certain aviation and alcohol excise taxes and (vi) technical correction for qualified improvement property. As of June 30, 2020, the Company had deferred $0.2 million in employer payroll taxes in relation to the CARES Act, which is included in the other noncurrent liabilities in these unaudited condensed consolidated balance sheets. For the three and six months ended June 30, 2020, the Company has recorded a tax provision of $0.1 million and $0.2 million, respectively, primarily related to the Company's wholly-owned UK subsidiary. There were no significant income tax provisions or benefits for the three and six months ended June 30, 2019.

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic and diluted net loss per common share is determined by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding during the period. The Company has computed diluted net loss per common share after giving consideration to all potentially dilutive common shares, including options to purchase common stock, issuance of common stock under the ESPP, restricted common stock, convertible preferred stock and warrants to purchase convertible preferred stock, outstanding during the period determined using the if-converted and treasury stock methods, except where the effect of including such securities would be antidilutive. Because the Company has reported net losses since inception, these potential common shares have been anti-dilutive and therefore basic and diluted net loss per share have been equivalent. The following table presents securities that have been excluded from the computations of diluted weighted-average shares outstanding as they would be anti-dilutive: Six Months Ended June 30, 2020 2019 Unvested common stock from early exercise of options 36,772 88,744 Stock options to purchase common stock 6,385,572 5,865,247 Common stock offering from ESPP 23,492 — Total 6,445,836 5,953,991

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions The Company receives clinical advisory services from Weatherden Ltd. (“Weatherden”) under agreements that were entered into during 2017 and 2018. Duncan McHale, the Company’s Chief Medical Officer, is a part owner of Weatherden. During the six months ended June 30, 2020 and 2019, the Company paid Weatherden $0.4 million and $0.5 million, respectively. As of June 30, 2020 and 2019, the amounts due to Weatherden under the supply of service agreement were $0.1 million and $0.2 million, respectively. In June 2018, the Company entered into a subleasing arrangement with Ring Therapeutics (formerly VL46), an affiliate of one of its stockholders, Flagship Venture Funds. Under the terms of the sublease, the Company invoiced Ring Therapeutics for an aggregate $0.9 million in rent payments which were due during the period from July 1, 2018 through April 30, 2020, expiration date, plus any related taxes and lease operating costs. For the three and six months ended June 30, 2020, $0.1 million and $0.3 million, respectively, related to this sublease agreement, inclusive of rent payments, taxes, and operating expenses, has been recorded as an offset to operating expense within the unaudited condensed consolidated statements of operations and comprehensive loss. The Company entered into a consulting agreement with David Epstein (the "Consulting Agreement"), the Company's Chairman of the Board, effective September 16, 2019 pursuant to which Mr. Epstein will provide strategic advisory and other consulting services to the Company. The Consulting Agreement has a one year term and may be terminated earlier by either Mr. Epstein or the Company upon 30 days’ notice, or 24 hours’ notice by the non-breaching party in the event of a breach. In accordance with the terms of the Consulting Agreement, Mr. Epstein was granted an option to purchase 75,000 shares of the Company’s common stock, which award vests in 36 equal monthly installments subject to his continued provision of consulting services to the Company pursuant to the Consulting Agreement on the applicable vesting date. Under the Consulting Agreement, Mr. Epstein also is entitled to receive (i) an annual equity award on each anniversary of the effective date of the Consulting Agreement in the form of an option to purchase shares of the Company’s common stock having an aggregate grant date fair market value equal to approximately $0.2 million, as determined by the Board in its discretion based on customary option pricing methodologies, which award vests in full on the first anniversary of the grant date, subject to his continued provision of consulting services to the Company pursuant to the Consulting Agreement on the applicable vesting date, and (ii) an aggregate annual cash consulting fee of $0.3 million for his consulting services. All of the foregoing options, to the extent then outstanding, will be subject to accelerated vesting upon the occurrence of a change in control of the Company.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Going Concern	Going Concern In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company's ability to continue as a going concern within one year after the date that the unaudited condensed consolidated financial statements are issued. The transition to profitability is dependent upon the successful development, approval, and commercialization of its products and product candidates and the achievement of a level of revenues adequate to support its cost structure. Based on the Company’s current operating plan and due to the uncertainty related to the impact of the COVID-19 and the nature of Evelo's business, the Company has substantial doubt that its cash and cash equivalents at June 30, 2020, together with the $10.0 million in additional debt drawdown in the third quarter of 2020, will be sufficient to fund operations and capital expenditures for at least the twelve months following the filing of this Quarterly Report on Form 10-Q, and the Company will need to obtain additional funding. The Company intends to pursue strategic partnerships and collaborations, or obtain additional funding through its available financing sources which include, additional public offerings of common stock and private financing of debt or equity. Management’s belief with respect to its ability to fund operations is based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional funding sooner than would otherwise be expected. There can be no assurance that the Company will be able to obtain additional funding on acceptable terms, if at all. If the Company is unable to obtain sufficient funding, it could be required to delay its development efforts, limit activities and reduce research and development costs, which could adversely affect its business prospects. Because of the uncertainty in securing additional funding and the insufficient amount of cash and cash equivalent resources at June 30, 2020, management has concluded that substantial doubt exists with respect to the Company’s ability to continue as a going concern within one year after the date that the unaudited condensed consolidated financial statements are issued.
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standard Codification (“ASC”) and ASU of the FASB. Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2019 and notes thereto. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of June 30, 2020, the results of its operations and stockholders' equity for the three and six months ended June 30, 2020 and 2019 and cash flows for the six months ended June 30, 2020 and 2019. Such adjustments are of a normal and recurring nature. The results for the three and six months ended June 30, 2020 are not necessarily indicative of the results for the year ending December 31, 2020, or for any future period.
Use of Estimates	Use of Estimates The preparation of the unaudited condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant estimates and assumptions reflected in these unaudited condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of stock-based awards. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Principles of Consolidation	Principles of ConsolidationThe unaudited condensed consolidated financial statements include the accounts of the Company and its wholly owned, controlled subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Subsequent Event Considerations	Subsequent Event Considerations The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the unaudited condensed consolidated financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. The Company has evaluated all subsequent events and determined that there are no material recognized or unrecognized subsequent events requiring disclosure in this Quarterly Report on Form 10-Q, except as disclosed in Note 6 to these unaudited condensed consolidated financial statements.
Emerging Growth Company Status	Emerging Growth Company Status Evelo is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"), and it may take advantage of reduced reporting requirements that are otherwise applicable to public companies. Evelo may take advantage of these exemptions until it is no longer an emerging growth company. Section 107 of the JOBS Act provides that an emerging growth company can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. Evelo has elected to use the extended transition period for complying with new or revised accounting standards, and, as a result of this election, its consolidated financial statements may not be comparable to companies that comply with public company effective dates. Evelo may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of its IPO or such earlier time that it is no longer an emerging growth company. Evelo would cease to be an emerging growth company if it has more than $1.07 billion in annual revenue, it has more than $700.0 million in market value of its stock held by non-affiliates (and has been a public company for at least 12 months and has filed one annual report on Form 10-K), or it has issued more than $1.0 billion of non-convertible debt securities over a three-year period.
Comprehensive Loss	Comprehensive LossComprehensive loss includes net loss and certain changes in stockholders’ equity that are excluded from net loss.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents, and Restricted CashCash equivalents are comprised of highly liquid investments that are readily convertible into cash with original maturities of three months or less. Cash and cash equivalents include cash held in banks and amounts held in money market funds. Cash equivalents are stated at cost, which approximates market value. The Company’s restricted cash consists of restricted cash in connection with building leases for the Company’s office and laboratory premises and deposits held in relation to the company's credit card facility.
Fair Value of Financial Instruments	Fair Value of Financial Instruments ASC 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities; • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly; and • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in 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.
Research and Development Costs	Research and Development Costs Research and development costs are expensed in the period incurred. Research and development expenses consist of both internal and external costs such as payroll, consulting, and manufacturing costs associated with the development of the Company’s product candidates. Costs for certain development activities, such as clinical trials and manufacturing development activities, are recognized based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, and information provided to the Company by its vendors on their actual costs incurred or level of effort expended. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as prepaid or accrued research and development expenses. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. The Company has and may continue to acquire the rights to develop and commercialize new product candidates from third parties. The upfront payments to acquire license, product or rights, as well as any future milestone payments, are immediately recognized as research and development expense provided that there is no alternative future use of the rights in other research and development projects. Any milestone payments made for Intellectual Property after regulatory approval, or that have alternative future use, are capitalized and amortized.
Stock-Based Compensation	Stock-Based Compensation The Company records stock-based compensation for options granted to employees and directors based on the grant date fair value of awards issued. The expense is recorded over the requisite service period, which is the vesting period, on a straight-line basis. The Company uses the Black-Scholes option-pricing model to determine the fair value of stock options. The determination of the fair value of stock options on the date of grant using an option-pricing model is affected by the Company’s common stock price, as well as a number of other assumptions. The Company records forfeitures as they occur. The Company accounts for stock-based compensation arrangements with non-employees based upon the fair value of the consideration received or the equity instruments issued, whichever is more reliably measurable. The measurement date for non-employee awards is generally the date performance of services required from the non-employee is complete. Stock-based compensation costs for non-employee awards are recognized as services are provided, which is generally the vesting period, on a straight-line basis. Segments
Segments	The Company has one operating segment. The Company's chief operating decision maker, its Chief Executive Officer, manages the Company's operations on a consolidated basis for the purposes of allocating resources.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements Leases In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”), which supersedes the guidance in former ASC 840, Leases. The new accounting guidance requires recognition of all long-term lease assets and lease liabilities by lessees and sets forth new disclosure requirements for those lease assets and liabilities. It requires lessees to recognize right-of-use assets and lease liabilities on the balance sheet using a modified retrospective approach at the beginning of the earliest comparative period in the financial statements for all leases with a term of greater than 12 months regardless of classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases. The FASB subsequently issued several ASUs amending the new standard. This guidance is effective for annual reporting periods, and interim periods within those years, beginning after December 15, 2018 for most public entities. The Company adopted this new standard on January 1, 2020 using the required modified retrospective approach and utilizing the effective date as its date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. ASU 2016-02 provides a number of optional practical expedients in transition. The Company elected to adopt the 'package of practical expedients', which permits the Company (i) not to reassess whether expired existing contracts are or contain leases, (ii) not to reassess the classification of expired or existing leases, and (iii) not to reassess initial direct costs for any existing leases. The Company will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance. Adoption of this standard resulted in the recognition of a right-of-use asset and a lease liability on the Company’s January 1, 2020 condensed consolidated balance sheet of $12.7 million and $13.9 million, respectively. There was no material impact resulting from the adoption on the Company’s unaudited condensed consolidated statement of operations for the three and six months ended June 30, 2020. For leases with terms greater than 12 months, the Company records the related right-of-use asset and lease liability at the present value of lease payments over the term. As the Company’s leases do not provide readily determinable implicit interest rates, the Company utilized its incremental borrowing rate, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rates. The application of the new standard required netting of unamortized balance of lease incentives and deferred lease obligation to the right-of-use asset at the adoption date. The Company’s operating leases include rental escalation clauses that are factored into the determination of lease payments when appropriate. The Company does not separate lease and non-lease components of contracts. Refer to Note 3, Leases within these unaudited condensed consolidated financial statements for additional information. Share-Based Compensation In June 2018, the FASB issued ASU No. 2018-07, Stock-based Compensation: Improvements to Nonemployee Share-based Payment Accounting (Topic 718) ("ASU 2018-07"), which amends the existing accounting standards for share-based payments to nonemployees. This ASU aligns much of the guidance on measuring and classifying nonemployee awards with that of awards to employees. Under the new guidance, the measurement of nonemployee equity awards is fixed on the grant date. Entities will apply the ASU by recognizing a cumulative-effect adjustment, if any, to retained earnings as of the beginning of the annual period of adoption. The Company adopted ASU 2018-07 on January 1, 2020. The adoption of this standard did not have a material impact on its condensed consolidated financial statements. Accounting Pronouncements Issued and Not Adopted as of June 30, 2020 Income Taxes In December 2019, the FASB issued ASU No. 2019 -12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The new standard includes several provisions which simplify accounting for income taxes by removing certain exceptions to the general principles in Topic 740 and increasing consistency and clarity for the users of financial statements. This standard will be effective for the Company on January 1, 2021. Early adoption is permitted. The Company is currently evaluating the potential impact ASU 2019-12 may have on its financial position and results of operations upon adoption.
Income Taxes	Income TaxesDeferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to losses incurred since inception and the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets.

Income Taxes (Policies)

Income Taxes (Policies)	6 Months Ended
	Jun. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income TaxesDeferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to losses incurred since inception and the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following reconciles cash, cash equivalents and restricted cash as of June 30, 2020 and December 31, 2019, as presented on the Company's statements of cash flows, to its related balance sheet accounts (in thousands): June 30, 2020 December 31, 2019 Cash and cash equivalents: Cash $ 8,461 $ 1,634 Money market funds 81,712 76,199 Total cash and cash equivalents 90,173 77,833 Restricted cash 1,500 1,500 Cash, cash equivalents and restricted cash $ 91,673 $ 79,333

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Schedule of Minimum Aggregate Future Lease Commitments	The minimum aggregate future lease commitments, exclusive of any offsetting sublease rental payments, at June 30, 2020, are as follows (in thousands): Amount 2020 (excluding six month ended June 30. 2020) $ 1,454 2021 2,973 2022 3,062 2023 3,154 2024 3,249 Thereafter 2,491 Total lease payments 16,383 Less imputed interest (3,613) $ 12,770 Other information: Operating cash flows used for operating leases $ 1,634 Weighted-average remaining lease term (in years) 5.25 Weighted-average discount rate 9.5 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value	The following tables present information about the Company’s financial assets and liabilities that have been measured at fair value as of June 30, 2020 and December 31, 2019 (in thousands): Description June 30, 2020 Assets: Money market funds included within cash and cash equivalents $ 81,712 $ 81,712 $ — $ — Total $ 81,712 $ 81,712 $ — $ — Description December 31, 2019 Assets: Money market funds included within cash and cash equivalents $ 76,199 $ 76,199 $ — $ — Total $ 76,199 $ 76,199 $ — $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	6 Months Ended
	Jun. 30, 2020
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consists of the following (in thousands): June 30, 2020 December 31, 2019 Property and equipment: Lab equipment $ 8,300 $ 7,479 Leasehold improvements 2,157 2,014 Furniture and fixtures 822 750 Computers and software 230 204 Office equipment 3 9 Construction-in-process 1,138 1,594 Property and equipment 12,650 12,050 Less: accumulated depreciation (4,648) (3,709) Property and equipment, net $ 8,002 $ 8,341

Loan and Security Agreements (T

Loan and Security Agreements (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Schedule of Minimum Aggregate Future Loan Payments	The Company has the following minimum aggregate future loan payments at June 30, 2020 (in thousands). The table below excludes minimum future payments related to second tranche drawdown on July 14, 2020 in the total of $10.0 million. These payments will be made based on the same terms as the initial borrowing. Twelve month period ending June 30, Amount 2021 $ 1,754 2022 4,391 2023 9,199 2024 8,498 Thereafter 2,208 Total minimum payments 26,050 Less amounts representing interest and discount (6,244) Long-term debt $ 19,806

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Summary of Stock-based Compensation Expense	Stock-based compensation expense included in the Company’s condensed consolidated statements of operations and comprehensive loss is as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 General and administrative $ 1,010 $ 1,162 $ 1,899 $ 2,224 Research and development 1,083 973 2,149 1,864 Total stock-based compensation expense $ 2,093 $ 2,135 $ 4,048 $ 4,088
Summary of Stock Option Activity	A summary of the Company’s stock option activity and related information is as follows: Shares Weighted- Options outstanding at December 31, 2019 5,691,474 $ 6.99 Granted 1,616,718 6.51 Exercised (141,157) 1.67 Canceled (781,463) 9.85 Options outstanding at June 30, 2020 6,385,572 $ 6.63 Exercisable as of June 30, 2020 3,035,054 $ 5.12

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding	The following table presents securities that have been excluded from the computations of diluted weighted-average shares outstanding as they would be anti-dilutive: Six Months Ended June 30, 2020 2019 Unvested common stock from early exercise of options 36,772 88,744 Stock options to purchase common stock 6,385,572 5,865,247 Common stock offering from ESPP 23,492 — Total 6,445,836 5,953,991

Organization - Additional Infor

Organization - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Subsidiary, Sale of Stock [Line Items]
Gross proceeds from issuance of common stock		$ 48,641	$ 0
Deferred issuance costs, net	$ 200	200
Cash, cash equivalents and short-term investments	90,200	90,200
Accumulated deficit	$ 242,546	$ 242,546		$ 198,853
June Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares sold in public offering (in shares)	13,800,000
Price of shares sold in public offering (in dollars per share)	$ 3.75	$ 3.75
Gross proceeds from issuance of common stock	$ 51,800
Net proceeds from issuance of common stock	$ 48,400
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares sold in public offering (in shares)	1,800,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)segment	Jun. 30, 2019USD ($)	Jan. 01, 2020USD ($)	Dec. 31, 2019USD ($)
Accounting Policies [Abstract]
Comprehensive loss	$ 20,652	$ 20,938	$ 43,693	$ 41,221
Restricted cash	1,500		$ 1,500			$ 1,500
Number of operating segments | segment			1
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	11,616		$ 11,616
Operating lease liability	$ 12,770		$ 12,770
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets					$ 12,700
Operating lease liability					$ 13,900

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Cash and cash equivalents:
Cash	$ 8,461	$ 1,634
Money market funds	81,712	76,199
Total cash and cash equivalents	90,173	77,833
Restricted cash	1,500	1,500
Cash, cash equivalents and restricted cash	$ 91,673	$ 79,333	$ 110,725	$ 94,351

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jan. 31, 2018ft²
Leases [Abstract]
Area of leased office and research development space (in square feet) | ft²					40,765
Minimum rental payments received	$ 0.1		$ 0.2
Rent expense	0.7	$ 0.7	1.4	$ 1.4
Sublease rent income	$ 0.1	$ 0.1	$ 0.3	$ 0.3

Leases - Schedule of Minimum Ag

Leases - Schedule of Minimum Aggregate Future Lease Commitments (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2020USD ($)
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020 (excluding six month ended June 30. 2020)	$ 1,454
2021	2,973
2022	3,062
2023	3,154
2024	3,249
Thereafter	2,491
Total lease payments	16,383
Less imputed interest	(3,613)
Total operating lease liabilities	12,770
Other information:
Operating cash flows used for operating leases	$ 1,634
Weighted-average remaining lease term (in years)	5 years 3 months
Weighted-average discount rate	9.50%

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Total	$ 81,712	$ 76,199
Money market funds included within cash and cash equivalents
Assets:
Cash and cash equivalents, fair value disclosure	81,712	76,199
(Level 1)
Assets:
Total	81,712	76,199
(Level 1) | Money market funds included within cash and cash equivalents
Assets:
Cash and cash equivalents, fair value disclosure	81,712	76,199
(Level 2)
Assets:
Total	0	0
(Level 2) | Money market funds included within cash and cash equivalents
Assets:
Cash and cash equivalents, fair value disclosure	0	0
(Level 3)
Assets:
Total	0	0
(Level 3) | Money market funds included within cash and cash equivalents
Assets:
Cash and cash equivalents, fair value disclosure	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property and equipment:
Property and equipment	$ 12,650	$ 12,050
Less: accumulated depreciation	(4,648)	(3,709)
Property and equipment, net	8,002	8,341
Lab equipment
Property and equipment:
Property and equipment	8,300	7,479
Leasehold improvements
Property and equipment:
Property and equipment	2,157	2,014
Furniture and fixtures
Property and equipment:
Property and equipment	822	750
Computers and software
Property and equipment:
Property and equipment	230	204
Office equipment
Property and equipment:
Property and equipment	3	9
Construction-in-process
Property and equipment:
Property and equipment	$ 1,138	$ 1,594

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property, Plant and Equipment [Abstract]
Depreciation	$ 500	$ 400	$ 1,031	$ 803

Loan and Security Agreements -

Loan and Security Agreements - Narrative (Details)	Jul. 14, 2020USD ($)	Jul. 19, 2019USD ($)tranche	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)
2016 Credit Facility
Line of Credit Facility [Line Items]
Aggregate principal amount			$ 15,000,000		$ 15,000,000
Interest expense				$ 200,000		$ 400,000
2019 Credit Facility
Line of Credit Facility [Line Items]
Interest expense			400,000		800,000
Line of Credit | 2016 Credit Facility
Line of Credit Facility [Line Items]
Aggregate principal amount			$ 15,000,000		$ 15,000,000
Line of Credit | 2019 Credit Facility
Line of Credit Facility [Line Items]
Aggregate principal amount		$ 45,000,000
Loan and security agreement, interest rate		8.65%
Prepayment fee percentage		2.00%
Prepayment fee percentage after specified period		1.00%
Number of tranches | tranche		3
Final payment under agreement as a percentage of loans borrowed		4.30%
Fees incurred to establish facility		$ 400,000
Anniversary of funding date for determining prepayment fee percentage		18 months
Debt default interest rate per annum		5.00%
Line of Credit | Security And Loan Agreement, Tranche One | 2019 Credit Facility
Line of Credit Facility [Line Items]
Proceeds from Issuance of Long-term Debt		$ 20,000,000
Line of Credit | Security And Loan Agreement, Tranche Two | 2019 Credit Facility | Subsequent Event
Line of Credit Facility [Line Items]
Proceeds from Issuance of Long-term Debt	$ 10,000,000
Line of Credit | Security And Loan Agreement, Tranche Three | 2019 Credit Facility
Line of Credit Facility [Line Items]
Proceeds from Issuance of Long-term Debt		$ 15,000,000
Line of Credit | Prime Plus | 2019 Credit Facility
Line of Credit Facility [Line Items]
Loan and security agreement, basis spread on interest rate		3.15%

Loan and Security Agreements _2

Loan and Security Agreements - Schedule of Minimum Aggregate Future Loan Payments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Total minimum payments	$ 26,050
Long-term debt	19,806	$ 19,634
Line of Credit
Line of Credit Facility [Line Items]
2021	1,754
2022	4,391
2023	9,199
2024	8,498
Thereafter	2,208
Less amounts representing interest and discount	(6,244)
Long-term debt	$ 19,806

In-License Agreements - Narrati

In-License Agreements - Narrative (Details) - USD ($)	Aug. 06, 2017	Mar. 10, 2016	Jun. 30, 2020
2017 Mayo License Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-refundable upfront fee	$ 200,000
Milestone payments upon achievement of certain development, regulatory, and commercial events			$ 200,000
Amount due under license agreement			0
2017 Mayo License Agreement | Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments upon achievement of certain development, regulatory, and commercial events	$ 56,000,000
2016 University of Chicago Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments upon achievement of certain development, regulatory, and commercial events		$ 60,900,000
Milestone payments for development and commercialization of licensed products			$ 400,000
2016 University of Chicago Agreement | Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-refundable upfront fee		$ 500,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) € in Millions, $ in Millions	1 Months Ended
	Jul. 31, 2019EUR (€)	Jun. 30, 2020USD ($)
Sacco | Collaborative Arrangement
Commitment And Contingencies [Line Items]
Term of collaboration arrangement	5 years
Period of inactive manufacturing services causing termination under collaborative arrangement	6 months
Aggregate amount due under collaborative arrangement	€ 3
Annual amount due under collaborative arrangement	€ 0.6
Biose Industrie | Exclusivity and Commitment Agreement
Commitment And Contingencies [Line Items]
Aggregate amount due under collaborative arrangement | $		$ 1.1

Stockholders_ Equity (Details)

Stockholders’ Equity (Details) - USD ($)	Jun. 03, 2019	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Gross proceeds from issuance of common stock			$ 48,641,000	$ 0
June Offering
Class of Stock [Line Items]
Net proceeds from issuance of common stock		$ 48,400,000
Number of shares sold in public offering (in shares)		13,800,000
Price of shares sold in public offering (in dollars per share)		$ 3.75	$ 3.75
Gross proceeds from issuance of common stock		$ 51,800,000
Registration Statement
Class of Stock [Line Items]
Registration of equity instruments, aggregate authorized amount	$ 200,000,000
Sale of stock, term	3 years
Sales Agreement, Cowen And Company, LLC
Class of Stock [Line Items]
Registration of equity instruments, aggregate authorized amount	$ 50,000,000

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2020	Jan. 01, 2019	May 08, 2018	Apr. 18, 2018	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares canceled (in shares)					781,463
Number of shares exercised (in shares)					141,157
Weighted average fair value of options granted (in dollars per share)					$ 4.45	$ 8.19
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense					$ 17.8
Compensation cost not yet recognized, period for recognition					2 years 8 months 23 days
2018 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares authorized for issuance (in shares)				336,356
Number of shares canceled (in shares)					630,458
Number of shares exercised (in shares)					0
Number of common stock available for future grant (in shares)					1,515,072
Percentage of outstanding shares				1.00%
2018 Stock Incentive Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
2018 Stock Incentive Plan | Minimum | Non-Employee Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					1 year
2018 Stock Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares originally authorized for issuance (in shares)			1,344,692
Common stock outstanding percentage to be declared as an increase in grants					4.00%
Number of additional shares authorized for issuance (in shares)	1,286,824	1,273,031
Options granted, maximum expiration period					10 years
Number of shares issued for purchase (in shares)					3,831,544
2018 Stock Incentive Plan | Maximum | Non-Employee Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
2015 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares originally authorized for issuance (in shares)			0
Number of shares canceled (in shares)					811,611
Number of common stock available for future grant (in shares)					5,417,044
Number of shares, options and other equity awards granted (in shares)					5,758,518
Number of shares, options and other equity awards exercised (in shares)					1,326,425
Number of shares, options and other equity awards canceled (in shares)					1,247,620
Number of shares repurchased (in shares)					18,468
Number of shares no longer authorized (in shares)			113,006
2015 Stock Incentive Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
2015 Stock Incentive Plan | Minimum | Non-Employee Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					1 year
2015 Stock Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, maximum expiration period					10 years
2015 Stock Incentive Plan | Maximum | Non-Employee Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,093	$ 2,135	$ 4,048	$ 4,088
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,010	1,162	1,899	2,224
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,083	$ 973	$ 2,149	$ 1,864

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details) - $ / shares	6 Months Ended
	Jun. 30, 2020
Shares
Options outstanding, beginning balance (in shares)	5,691,474
Granted (in shares)	1,616,718
Exercised (in shares)	(141,157)
Canceled (in shares)	(781,463)
Options outstanding, ending balance (in shares)	6,385,572
Exercisable as of period end (in shares)	3,035,054
Weighted- Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 6.99
Granted (in dollars per share)	6.51
Exercised (in dollars per share)	1.67
Canceled (in dollars per share)	9.85
Options outstanding, ending balance (in dollars per share)	6.63
Exercisable as of period end (in dollars per share)	$ 5.12

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 89	$ 0	$ 154	$ 0
Deferred payroll taxes related to CARES Act	$ 200		$ 200

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Details) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of securities excluded from computation of diluted weighted-average shares outstanding (in shares)	6,445,836	5,953,991
Unvested common stock from early exercise of options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of securities excluded from computation of diluted weighted-average shares outstanding (in shares)	36,772	88,744
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of securities excluded from computation of diluted weighted-average shares outstanding (in shares)	6,385,572	5,865,247
Common stock offering from ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total number of securities excluded from computation of diluted weighted-average shares outstanding (in shares)	23,492	0

Related Party Transactions - Na

Related Party Transactions - Narrative (Details) $ in Millions	Sep. 16, 2019USD ($)installmentshares	Jun. 30, 2020USD ($)	Jun. 30, 2020USD ($)shares	Jun. 30, 2019USD ($)	Apr. 30, 2020USD ($)
Related Party Transaction [Line Items]
Offset to rent expense from sublease agreement		$ 0.1	$ 0.2
Number of stock options granted (in shares) | shares			1,616,718
Weatherden Ltd
Related Party Transaction [Line Items]
Payment to related party			$ 0.4	$ 0.5
Amounts due to related party		0.1	$ 0.1	$ 0.2
VL46
Related Party Transaction [Line Items]
Rent due from sublease agreement					$ 0.9
Offset to rent expense from sublease agreement		$ 0.1
Consulting Agreement | Mr. Epstein
Related Party Transaction [Line Items]
Consulting arrangement term	1 year
Termination notice period of consulting arrangement	30 days
Termination notice period by non-breaching party in event of a breach	24 hours
Number of stock options granted (in shares) | shares	75,000
Number of equal monthly installments | installment	36
Aggregate grant date fair value	$ 0.2
Aggregate annual cash consulting fee	$ 0.3