Evelo Biosciences (EVLO) 10-Q/A 29 Oct 21 2021 Q3 Quarterly report (amended) Financial data

Cover Page

Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Oct. 26, 2021
Cover [Abstract]
Document Type	10-Q/A
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
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	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		53,459,948
Amendment Flag	true
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001694665
Current Fiscal Year End Date	--12-31
Amendment Description	EXPLANATORY NOTEThis Amendment No. 1 on Form 10-Q/A (this “Amended Filing”) amends the Quarterly Report on Form 10-Q for the period ended September 30, 2021, filed on October 28, 2021 (the “Original Filing”) by Evelo Biosciences, Inc. (the “Company”). The purpose of this Amended Filing is to revise Part I, Item 4 and Part II, Item 1A of the Original Filing to reflect management’s conclusion that the Company's disclosure controls and procedures were not effective due to a material weakness in the Company’s internal control over financial reporting identified subsequent to the Original Filing.Except as expressly set forth herein, this Amended Filing does not modify, amend, or update in any way the financial statements and other disclosures set forth in the Company’s Original Filing. As such, this Amended Filing speaks as of the date of the Original Filing and, except to revise the Original Filing as described above, the Company has not undertaken to supplement or update any information contained in the Original Filing to give effect to subsequent events, and the Company’s unaudited condensed consolidated financial statements as of and for the three and nine-months ended September 30, 2021, which were included in the Original Filing, have not changed as a result of the identification of the material weakness. This Amended Filing should be read in conjunction with the Original Filing and the Company’s reports filed with the SEC subsequent to the Original Filing, including any amendments to those filings.As required by Rule 12b-15 under the Securities and Exchange Act of 1934, as amended, we are also filing currently dated certifications by the Company’s Principal Executive Officer and Principal Financial Officer.

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 95,938	$ 68,857
Prepaid expenses and other current assets	1,977	2,123
Total current assets	97,915	70,980
Property and equipment, net	7,762	7,478
Right of use asset - operating lease	9,389	10,757
Other assets	1,392	1,424
Total assets	116,458	90,639
Current liabilities:
Accounts payable	2,517	1,442
Accrued expenses	15,641	16,254
Operating lease liability, current portion	1,877	1,674
Other current liabilities	692	463
Total current liabilities	20,727	19,833
Noncurrent liabilities:
Long-term debt	46,520	30,048
Operating lease liability, net of current portion	8,372	9,989
Deferred revenue	7,500	0
Other noncurrent liabilities	263	284
Total liabilities	83,382	60,154
Commitments and contingencies
Stockholder’s equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding as of September 30, 2021 and December 31, 2020, respectively	0	0
Common stock, $0.001 par value; 200,000,000 shares authorized; 53,472,345 and 47,488,505 shares issued and 53,453,959 and 47,470,119 shares outstanding as of September 30, 2021 and December 31, 2020, respectively	53	47
Additional paid-in capital	419,066	322,957
Accumulated deficit	(386,043)	(292,519)
Total stockholders’ equity	33,076	30,485
Total liabilities and stockholders’ equity	$ 116,458	$ 90,639

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
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)	53,472,345	47,488,505
Common stock, shares outstanding (in shares)	53,453,959	47,470,119

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 22,599	$ 14,910	$ 64,762	$ 47,503
General and administrative	10,111	5,272	23,075	16,185
Total operating expenses	32,710	20,182	87,837	63,688
Loss from operations	(32,710)	(20,182)	(87,837)	(63,688)
Other (expense) income:
Interest expense, net	(1,023)	(713)	(2,602)	(1,353)
Loss on extinguishment of debt	0	0	(3,226)	0
Other income, net	159	39	472	646
Total other expense	(864)	(674)	(5,356)	(707)
Loss before income taxes	(33,574)	(20,856)	(93,193)	(64,395)
Income tax expense	(156)	(67)	(331)	(221)
Net loss	$ (33,730)	$ (20,923)	$ (93,524)	$ (64,616)
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (0.63)	$ (0.45)	$ (1.77)	$ (1.74)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (0.63)	$ (0.45)	$ (1.77)	$ (1.74)
Weighted-average number of common shares outstanding, basic (in shares)	53,430,333	46,168,013	52,704,470	37,050,907
Weighted-average number of common shares outstanding, diluted (in shares)	53,430,333	46,168,013	52,704,470	37,050,907

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders’ Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		32,170,605
Beginning balance at Dec. 31, 2019	$ 60,197	$ 32	$ 259,018	$ (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		32,321,208
Ending balance at Mar. 31, 2020	39,344	$ 32	261,206	(221,894)
Beginning balance (in shares) at Dec. 31, 2019		32,170,605
Beginning balance at Dec. 31, 2019	60,197	$ 32	259,018	(198,853)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock warrants	0
Net loss	(64,616)
Ending balance (in shares) at Sep. 30, 2020		46,184,087
Ending balance at Sep. 30, 2020	50,430	$ 46	313,853	(263,469)
Beginning balance (in shares) at Mar. 31, 2020		32,321,208
Beginning balance at Mar. 31, 2020	39,344	$ 32	261,206	(221,894)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net (in shares)		13,800,000
Issuance of common stock, net	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
Net loss	(20,652)			(20,652)
Ending balance (in shares) at Jun. 30, 2020		46,136,643
Ending balance at Jun. 30, 2020	69,206	$ 46	311,706	(242,546)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under Employee Stock Purchase Plan (in shares)		28,603
Issuance of common stock under Employee Stock Purchase Plan	92		92
Exercise of stock options (in shares)		18,841
Exercise of stock options	11		11
Stock-based compensation expense	2,045		2,045
Fees associated with public offering of common stock	(1)		(1)
Net loss	(20,923)			(20,923)
Ending balance (in shares) at Sep. 30, 2020		46,184,087
Ending balance at Sep. 30, 2020	50,430	$ 46	313,853	(263,469)
Beginning balance (in shares) at Dec. 31, 2020		47,470,119
Beginning balance at Dec. 31, 2020	30,485	$ 47	322,957	(292,519)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net (in shares)		5,814,734
Issuance of common stock, net	81,961	$ 6	81,955
Issuance of common stock under Employee Stock Purchase Plan (in shares)		27,587
Issuance of common stock under Employee Stock Purchase Plan	90		90
Exercise of stock options (in shares)		45,299
Exercise of stock options	235		235
Stock-based compensation expense	3,264		3,264
Net loss	(28,196)			(28,196)
Ending balance (in shares) at Mar. 31, 2021		53,357,739
Ending balance at Mar. 31, 2021	87,839	$ 53	408,501	(320,715)
Beginning balance (in shares) at Dec. 31, 2020		47,470,119
Beginning balance at Dec. 31, 2020	$ 30,485	$ 47	322,957	(292,519)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	112,898
Issuance of common stock warrants	$ 1,750
Net loss	(93,524)
Ending balance (in shares) at Sep. 30, 2021		53,453,959
Ending balance at Sep. 30, 2021	33,076	$ 53	419,066	(386,043)
Beginning balance (in shares) at Mar. 31, 2021		53,357,739
Beginning balance at Mar. 31, 2021	87,839	$ 53	408,501	(320,715)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		40,532
Exercise of stock options	330		330
Stock-based compensation expense	3,772		3,772
Issuance of common stock warrants	1,750		1,750
Net loss	(31,598)			(31,598)
Ending balance (in shares) at Jun. 30, 2021		53,398,271
Ending balance at Jun. 30, 2021	62,093	$ 53	414,353	(352,313)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted common stock (in shares)		9,850
Issuance of common stock under Employee Stock Purchase Plan (in shares)		18,771
Issuance of common stock under Employee Stock Purchase Plan	147		147
Exercise of stock options (in shares)		27,067
Exercise of stock options	125		125
Stock-based compensation expense	4,441		4,441
Net loss	(33,730)			(33,730)
Ending balance (in shares) at Sep. 30, 2021		53,453,959
Ending balance at Sep. 30, 2021	$ 33,076	$ 53	$ 419,066	$ (386,043)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net loss	$ (93,524)	$ (64,616)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	11,477	6,093
Depreciation expense	1,678	1,493
Non-cash interest expense	218	250
Non-cash lease expense	1,368	1,541
Loss on extinguishment of debt	3,226	0
Gain on sale of fixed assets, net	5	(5)
Changes in assets and liabilities:
Prepaid expenses and other current assets	(63)	267
Accounts payable	1,075	2,105
Accrued expenses and other current liabilities	(404)	263
Operating lease liabilities	(1,414)	(1,771)
Deferred revenue	7,500	0
Other liabilities	(21)	270
Net cash used in operating activities	(68,879)	(54,110)
Investing activities
Purchases of property and equipment	(1,962)	(912)
Proceeds from sale of fixed assets	6	6
Net cash used in investing activities	(1,956)	(906)
Financing activities
Proceeds from issuance of common stock, net of issuance cost	81,961	48,424
Proceeds from the issuance of long-term debt, net of issuance costs	14,778	10,000
Proceeds from issuance of common stock under employee stock purchase plan and exercise of stock options	927	339
Net cash provided by financing activities	97,666	58,763
Net increase in cash, cash equivalents and restricted cash	26,831	3,747
Cash, cash equivalents and restricted cash – beginning of period	70,420	79,333
Cash, cash equivalents and restricted cash – end of period	97,251	83,080
Supplemental disclosure of cash flow information
Cash paid for interest	2,383	1,509
Cash paid for Tax	9	20
Noncash investing and financing activities
Deferred financing and public offering costs in accounts payable and accrued expenses	0	19
Property and equipment additions in accrued expenses	198	33
Issuance of common stock warrants	$ 1,750	$ 0

Organization

Organization	9 Months Ended
	Sep. 30, 2021
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 a new class of oral biologics that are intended to act on cells in the small intestine to produce therapeutic effects throughout the body. 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. To date, the Company has financed operations primarily with the proceeds from the issuance of common stock combined with proceeds from previous sales of convertible preferred stock to equity investors and debt financing. On June 3, 2019, the Company filed a Registration Statement on Form S-3 (File No. 333-231911) (the “2019 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 its effectiveness on June 6, 2019. The Company also simultaneously entered into a sales agreement (the "ATM") 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 2019 Shelf. For the three and nine months ended September 30, 2021, the Company sold no shares and 139,734 shares, respectively, under the ATM with offering prices ranging between $12.54 and $13.17 per share for gross proceeds of $1.8 million, and net proceeds of $1.7 million, after deducting commission and other offering expenses payable by the Company. On February 2, 2021, the Company sold 5,175,000 shares of its common stock in an underwritten public offering at a public offering price of $15.00 per share, including the underwriters' exercise of their option to purchase 675,000 shares to cover over-allotment, generating gross proceeds of $77.6 million and net proceeds of underwriting discounts and commission of $72.7 million, after deducting underwriting discounts and commission and other offering expenses paid by the Company. On January 28, 2021, the Company entered into a stock purchase agreement with ALJ Health Care & Life Science Company Limited ("ALJ Health Care"), pursuant to which on February 2, 2021, ALJ Health Care purchased $7.5 million of our common stock in a private placement at a purchase price of $15.00 per share, equal to the public offering price per share at which our common stock was sold to the public as referred above. The sale of such shares was not registered under the Securities Act. On August 23, 2021, the Company filed a Registration Statement on Form S-3 (File No. 333-259005) (the “2021 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 million for a period of up to three years from the date of its effectiveness on August 30, 2021. 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 September 30, 2021, the Company had cash and cash equivalents of $95.9 million and an accumulated deficit of $386.0 million. 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

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
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, 2020 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 September 30, 2021, the results of its operations and stockholders' equity for the three and nine months ended September 30, 2021 and 2020 and cash flows for the nine months ended September 30, 2021 and 2020. Such adjustments are of a normal and recurring nature. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results for the year ending December 31, 2021, 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, estimates related to the application of ASC 606, Revenue from Contracts with Customers ("ASC 606") to our collaboration agreement, 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. 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 Income or Loss Comprehensive income (loss) consists of net income (loss) and changes in equity during a period from transactions and other equity and circumstances generated from non-owner sources. The Company’s net loss equals comprehensive loss for all periods presented. 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. As of September 30, 2021 and December 31, 2020 the Company had $0 and $0.3 million in current restricted cash within prepaid expenses, respectively, and other current assets. As of September 30, 2021 and December 31, 2020 the Company had $1.3 million in noncurrent restricted cash which were included within other assets in the unaudited condensed consolidated balance sheets. The following reconciles cash, cash equivalents and restricted cash as of September 30, 2021 and December 31, 2020, as presented on the Company's statements of cash flows, to its related balance sheet accounts (in thousands): September 30, 2021 December 31, 2020 Cash and cash equivalents: Cash $ 3,359 $ 4,487 Money market funds 92,579 64,370 Total cash and cash equivalents 95,938 68,857 Restricted cash 1,313 1,563 Cash, cash equivalents and restricted cash $ 97,251 $ 70,420 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. Collaboration Agreements The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements ("ASC 808") to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. To the extent the arrangement is within the scope of ASC 808, the Company assesses whether aspects of the arrangement between the Company and its collaboration partner are within the scope of other accounting literature, including ASC 606. If it is concluded that some or all aspects of the arrangement represent a transaction with a customer, the Company will account for those aspects of the arrangement within the scope of ASC 606. ASC 808 provides guidance for the presentation and disclosure of transactions in collaborative arrangements, but it does not provide recognition or measurement guidance. Therefore, if the Company concludes a counterparty to a transaction is not a customer or otherwise not within the scope of ASC 606, the Company considers the guidance in other accounting literature, including the guidance in ASC 606, as applicable or by analogy to account for such transaction. The classification of transactions under the Company’s arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants. Revenue Recognition The Company analyzes its collaboration arrangements to assess whether they are within the scope of Accounting Standards Codification ASC 808, to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. If the Company concludes that some or all aspects of the arrangement represent a transaction with a customer, the Company accounts for those aspects of the arrangement within the scope of ASC 606. To determine the appropriate amount of revenue to be recognized for arrangements that the Company determines are within the scope of ASC 606, it performs the following steps: (i) identify the contract(s) with the customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) each performance obligation is satisfied. ASC 606 requires significant judgment and estimates and results in changes to, but not limited to: (i) the determination of the transaction price, including estimates of variable consideration, (ii) the allocation of the transaction price, including the determination of estimated selling price, and (iii) the pattern of recognition, including the application of proportional performance as a measure of progress on service-related promises and application of point-in-time recognition for supply-related promises. The promised good or services in the Company’s arrangement may consist of license rights to the Company’s intellectual property or research and development services. The Company also may have optional additional items in contracts, which are considered marketing offers and are accounted for as separate contracts with the customer if such option is elected by the customer, unless the option provides a material right which would not be provided without entering into the contract. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer. Promised goods or services are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources or (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own or whether the required expertise is readily available. The transaction price may be comprised of fixed payments, often an upfront payment due at contract inception, or other types of variable consideration in the form of payments for the Company’s services and materials and milestone payments due upon the achievement of specified events. Other payments the Company could be entitled to include tiered royalties earned when customers recognize net sales of licensed products. The Company considers the existence of any significant financing component within its arrangements to the extent there is a significant difference between the timing of payment and the transfer of control of the performance obligations. In making that determination, the Company considers whether substantive business purposes exist to support the payment structure other than to provide a significant benefit of financing. The Company measures the transaction price based on the amount of consideration to which it expects to be entitled in exchange for transferring the promised goods and/or services to the customer. The Company utilizes either the expected value method or the most likely amount method to estimate the amount of variable consideration, depending on which method is expected to better predict the amount of consideration to which the Company will be entitled. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. With respect to arrangements that include payments for a development or regulatory milestone payment, the Company evaluates whether the associated event is considered probable of achievement and estimates the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within the Company’s or the licensee’s control, such as those dependent upon receipt of regulatory approval, are not considered to be probable of achievement until the triggering event occurs. At the end of each reporting period, the Company re-evaluates the probability of achievement of each milestone and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based upon the achievement of a certain level of product sales, wherein the license is deemed to be the sole or predominant item to which the payments relate, the Company recognizes revenue upon the later of: (i) when the related sales occur or (ii) when the performance obligation to which some or all of the payment has been allocated has been satisfied (or partially satisfied). Consideration that would be received for optional goods and/or services is excluded from the transaction price at contract inception. For arrangements with more than one performance obligation, the Company generally allocates the transaction price to each performance obligation based on a relative standalone selling price basis. The Company develops assumptions that require judgment to determine the standalone selling price for each performance obligation in consideration of applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated research and development costs. However, in certain instances, the Company may allocate variable consideration entirely to one or more performance obligation if the terms of the variable consideration relate to the satisfaction of the respective performance obligation and the amount allocated is consistent with the amount the Company would expect to receive for the satisfaction of the respective performance obligation. The Company recognizes revenue based on the amount of the transaction price that is allocated to each respective performance obligation when or as the performance obligation is satisfied by transferring a promised good or service to the customer. For performance obligations that are satisfied at a point in time, the Company recognizes revenue when control of the goods and/or services is transferred to the customer. For performance obligations that are satisfied over time, the Company recognizes revenue by measuring the progress toward complete satisfaction of the performance obligation using a single method of measuring progress which depicts the performance in transferring control of the associated goods and/or services to the customer. With respect to arrangements containing a license to its intellectual property that is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from amounts allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations under an arrangement. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. Contract Liabilities The Company records a contract liability, classified as deferred revenue on its condensed consolidated balance sheet, when it has received payment but has not yet satisfied the related performance obligations. In the event of an early termination of a contract with a customer, any contract liabilities would be recognized in the period in which all Company obligations under the agreement have been fulfilled. 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 unaudited condensed 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 licenses, products 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 equity awards 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 options. The determination of the fair value of 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 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 was effective for the Company on January 1, 2021 and it 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. The Company adopted ASU No. 2019-12 on January 1, 2021 and has concluded the adoption did not have a material impact on its unaudited condensed consolidated financial statements. Accounting Pronouncements Issued and Not Adopted as of September 30, 2021 Financial Instruments - Credit Losses In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments, which has been subsequently amended by ASU No. 2018-19, ASU No. 2019-04, ASU No. 2019-05, ASU No. 2019-10, ASU No. 2019-11 and ASU No. 2020-03 (“ASU 2016-13”). The provisions of ASU 2016-13 modify the impairment model to utilize an expected loss methodology in place of the currently used incurred loss methodology and require a consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company on January 1, 2023, with early adoption permitted. The Company is currently evaluating the potential impact that this standard may have on its financial position and results of operations, as well as the timing of its adoption of this standard. Debt with Conversion and Other Options On August 5, 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU-2020-06”), which simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. ASU 2020-06 eliminates the beneficial conversion and cash conversion accounting models in ASC 470-20 that require separate accounting for embedded conversion features from convertible instruments. As a result, after adopting the ASU’s guidance, entities will not separately present in equity an embedded conversion feature in such debt. Additionally, the guidance simplifies the evaluation of whether a contract in the issuer’s own equity can be classified in equity or an embedded feature qualifies for the derivative scope exception. Although the guidance is not effective until 2022, early adoption of ASU 2020-06 is permitted for all entities for fiscal years beginning after December 15, 2020. The Company is currently evaluating the impact of this new guidance on the Company’s condensed consolidated financial statements and related disclosures.

ALJ Commercialization and Licen

ALJ Commercialization and License Agreement	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
ALJ Commercialization and License Agreement	ALJ Commercialization and License Agreement On March 17, 2021, the Company entered into a commercialization and license agreement (the “ALJ Agreement”) with ALJ. Pursuant to the ALJ Agreement, the Company granted to ALJ an exclusive, non-transferable, sublicensable license to the Company’s product candidate, EDP1815 (together with any replacement or second products of the Company described below, the “Products”) solely (i) to conduct development activities relating to the Products allocated to ALJ in a development plan agreed with the Company, (ii) to conduct manufacturing activities relating to the Products in all therapeutic uses in humans (the “Field”) throughout the world, subject to certain conditions and requirements, and (iii) to commercialize the Products in the Field in all countries of Africa and the Middle East-Turkey, excluding certain restricted countries (the “Territory”). If the Company ceases development of EDP1815 prior to receipt of regulatory approval required for commercialization of EDP1815 in any one of the United States, the United Kingdom, France, Germany, Spain, Italy, China or Japan, then ALJ will have the right to designate another product candidate of the Company as a replacement to EDP1815 or terminate the ALJ Agreement, subject to certain conditions and requirements. Further, for the first two years of the term, ALJ has the option to negotiate with the Company to add a second product candidate of the Company subject to certain conditions and requirements, for an additional license fee not to exceed $7.5 million. In consideration for the rights the Company granted under the ALJ Agreement, ALJ obligated to pay to the Company a one-time, non-refundable upfront payment of $7.5 million. The parties will also share the future operating profits and losses for all Products in the Territory equally (50:50) as well as certain development, regulatory and commercialization costs. The Company concluded that the delivery of the license to ALJ, should be accounted for under ASC 606. The development, regulatory and commercialization activities within the Territory will be accounted for under ASC 808. The Company has not recognized any revenue under the ALJ Agreement to date as they have not completed any performance obligation within the agreement. As of September 30, 2021, the Company has recognized $7.5 million of deferred revenue, which is classified as a non-current liability in the accompanying unaudited condensed consolidated balance sheets as the performance obligation is not expected to be completed within the next twelve months. The Company anticipates that payments under the costs share or profit and loss sharing arrangements, will be classified in the statement of operations consistent with the guidance in ASC 808. To date, the Company has not received or made any costs sharing or profit and loss payments. 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 and (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 will pay 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 September 30, 2021, the Company has incurred milestone payments to date totaling approximately $0.3 million under the agreement of which no amounts are currently due. 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 September 30, 2021, the Company has incurred milestone payments to date totaling approximately $0.4 million under the agreement of which no amounts are currently due.

Leases

Leases	9 Months Ended
	Sep. 30, 2021
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 maintained 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 is 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 and $0.2 million, respectively, for the three months and nine months ended September 30, 2020 and were equivalent to the minimum payments due from the Company to the landlord. For the three months and nine months ended September 30, 2021, the Company recorded rent expense of $0.7 million and $2.2 million, respectively. For the three months and nine months ended September 30, 2020, the Company recorded rent expense of $0.7 million and $2.1 million, respectively. There was no sublease rental income for the three months and nine months ended September 30, 2021. There was no sublease rental income for the three months ended September 30, 2020. Sublease rental income is inclusive of rental payments, taxes and operating expenses. The minimum aggregate future lease commitments at September 30, 2021, are as follows (in thousands): Amount 2021 ( excluding amounts paid or in Accounts Payable as of 9/30/2021) $ 507 2022 3,062 2023 3,154 2024 3,249 2025 2,491 Total lease payments 12,463 Less imputed interest (2,214) Total $ 10,249 Other information: Operating cash flows used for operating leases $ 1,967 Weighted-average remaining lease term (in years) 4.0 Weighted-average discount rate 9.5 %

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 (in thousands): Description September 30, 2021 (Level 1) (Level 2) (Level 3) Assets: Money market funds included within cash and cash equivalents $ 92,579 $ 92,579 $ — $ — Total $ 92,579 $ 92,579 $ — $ — Description December 31, 2020 (Level 1) (Level 2) (Level 3) Assets: Money market funds included within cash and cash equivalents $ 64,370 $ 64,370 $ — $ — Total $ 64,370 $ 64,370 $ — $ — As of September 30, 2021 and December 31, 2020, 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	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment consists of the following (in thousands): September 30, 2021 December 31, 2020 Property and equipment: Lab equipment $ 10,050 $ 8,831 Leasehold improvements 2,157 2,157 Furniture and fixtures 822 822 Computers and software 252 230 Office equipment 21 3 Construction-in-process 1,577 1,078 Property and equipment 14,879 13,121 Less: accumulated depreciation (7,117) (5,643) Property and equipment, net $ 7,762 $ 7,478 The Company recognized $0.6 million and $1.7 million of depreciation expense for the three and nine months ended September 30, 2021, respectively, and $0.5 million and $1.5 million of depreciation expense for the three and nine months ended September 30, 2020, respectively.

Loan and Security Agreements

Loan and Security Agreements	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Loan and Security Agreements	Loan and Security Agreements 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 drawn down on July 14, 2020. The availability of the third tranche of $15.0 million expired on January 15, 2021. On June 16, 2021 (the "Amended Credit Facility Effective Date"), the parties further amended the 2019 Credit Facility (as so amended, the “Amended Credit Facility”) to, among other things, replace and supersede the existing $15.0 million third tranche commitment with a new $15.0 million fourth tranche commitment, which the Company drew down on June 16, 2021. In connection with the Amended Credit Facility, the Company issued to K2 HealthVentures Equity Trust LLC, an affiliate of K2HV, a warrant to purchase up to 139,770 shares of the Company’s common stock with an exercise price of $13.30 per share, subject to customary per share adjustments that are within the Company's control (the "Warrant”). In addition, under the Amended Credit Facility, K2HV has the option, exercisable at any time, to convert up to $5.0 million of principal outstanding into shares of the Company’s common stock at a conversion price of $13.30 per share, subject to customary per share adjustments within the Company's control (the "Conversion Option”). 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, 2023 , which was extended from February 28, 2022 pursuant to the Amended Credit Facility . 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. 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 Amended Credit Facility Effective Date but prior to the maturity date, 1% of the amount prepaid. Pursuant to the Amended Credit Facility, the Company has the option at any point prior to January 1, 2022 to elect to adjust the repayment schedule (the “Modified Repayment Schedule”) such that commencing on March 1, 2023, the Company can make consecutive equal monthly payments of principal and accrued and unpaid interest based on a notional thirty month repayment period. Under the Modified Repayment Schedule, the loan maturity date remains August 1, 2024. Any outstanding principal and unpaid interest is due at maturity. Upon final payment or prepayment of the loans, the Company must pay a final payment equal to 4.3% (or 4.8% if the Company elects the Modified Repayment Schedule) of the aggregate original principal amount of the loans borrowed. The Company incurred fees associated with establishing the 2019 Credit Facility and fees related to the Amended Credit Facility of $0.4 million and $0.3 million, respectively. Borrowings under the Amended 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. The Amended 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 Amended Credit Facility and under applicable law. As of September 30, 2021, the Company was in compliance with all covenants under the Amended Credit Facility. The Company has concluded the Amended Credit Facility is a debt extinguishment for accounting purposes because the terms of the modified debt are considered substantially different than the terms of the debt prior to the amendment. As such, the Amended Credit Facility was recorded at its estimated fair value of $46.6 million which was determined using a combination of a discounted cash flow model and a binomial lattice model. The Company utilized the following significant unobservable inputs (Level 3 inputs) to determine the estimated fair value of its debt as of the amendment date: Expected volatility 70.00 % Expected yield 11.50 % Significant increases (decreases) in either of these inputs could result in a significantly lower or higher fair value measurement. The Warrant was deemed to be a freestanding financial instrument as it is legally detachable and separately exercisable from the debt obligations. The Company evaluated the terms and conditions of the warrant and concluded it met the criteria to be classified within equity. As such, the Company recorded the warrant as additional paid in capital at its issuance date fair value of $1.8 million. The Company utilized the Black-Scholes valuation method to determine the fair value of the warrant which utilized the following assumptions: Fair value of underlying common stock $ 16.13 Exercise price $ 13.30 Risk-free interest rate 1.56 % Expected volatility 70.0 % Expected term (years) 10.0 Expected dividend yield — % The Company recorded a loss on the extinguishment of the existing debt of $3.2 million which equaled the difference between the reacquisition cost of the new debt, inclusive of the fair value of the Warrant and lender fees, and the carrying amount of the existing debt. The difference between (i) the carrying amount of the debt and (ii) the par value of the debt and the amount of the final payment due at maturity will be amortized as interest expense using the effective interest rate method. The Company has the following minimum aggregate future loan payments at September 30, 2021 (in thousands). Twelve month period ending September 30, Amount 2022 $ 3,947 2023 20,377 2024 31,389 Total minimum payments 55,713 Less amounts representing interest and discount (9,193) Total Debt $ 46,520

In-License Agreements

In-License Agreements	9 Months Ended
	Sep. 30, 2021
Research and Development [Abstract]
In-License Agreements	ALJ Commercialization and License Agreement On March 17, 2021, the Company entered into a commercialization and license agreement (the “ALJ Agreement”) with ALJ. Pursuant to the ALJ Agreement, the Company granted to ALJ an exclusive, non-transferable, sublicensable license to the Company’s product candidate, EDP1815 (together with any replacement or second products of the Company described below, the “Products”) solely (i) to conduct development activities relating to the Products allocated to ALJ in a development plan agreed with the Company, (ii) to conduct manufacturing activities relating to the Products in all therapeutic uses in humans (the “Field”) throughout the world, subject to certain conditions and requirements, and (iii) to commercialize the Products in the Field in all countries of Africa and the Middle East-Turkey, excluding certain restricted countries (the “Territory”). If the Company ceases development of EDP1815 prior to receipt of regulatory approval required for commercialization of EDP1815 in any one of the United States, the United Kingdom, France, Germany, Spain, Italy, China or Japan, then ALJ will have the right to designate another product candidate of the Company as a replacement to EDP1815 or terminate the ALJ Agreement, subject to certain conditions and requirements. Further, for the first two years of the term, ALJ has the option to negotiate with the Company to add a second product candidate of the Company subject to certain conditions and requirements, for an additional license fee not to exceed $7.5 million. In consideration for the rights the Company granted under the ALJ Agreement, ALJ obligated to pay to the Company a one-time, non-refundable upfront payment of $7.5 million. The parties will also share the future operating profits and losses for all Products in the Territory equally (50:50) as well as certain development, regulatory and commercialization costs. The Company concluded that the delivery of the license to ALJ, should be accounted for under ASC 606. The development, regulatory and commercialization activities within the Territory will be accounted for under ASC 808. The Company has not recognized any revenue under the ALJ Agreement to date as they have not completed any performance obligation within the agreement. As of September 30, 2021, the Company has recognized $7.5 million of deferred revenue, which is classified as a non-current liability in the accompanying unaudited condensed consolidated balance sheets as the performance obligation is not expected to be completed within the next twelve months. The Company anticipates that payments under the costs share or profit and loss sharing arrangements, will be classified in the statement of operations consistent with the guidance in ASC 808. To date, the Company has not received or made any costs sharing or profit and loss payments. 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 and (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 will pay 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 September 30, 2021, the Company has incurred milestone payments to date totaling approximately $0.3 million under the agreement of which no amounts are currently due. 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 September 30, 2021, the Company has incurred milestone payments to date totaling approximately $0.4 million under the agreement of which no amounts are currently due.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
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 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. A Notice of Opposition (the "Opposition") was filed against European Patent No. 3223834, which is held by the Company. In July 2021, the Company filed its reply to the Opposition. The patent at issue does not relate to any of the Company’s current product candidates, and any subsequent proceeding is not expected to affect any of the Company’s current development plans.

Stockholders_ Equity

Stockholders’ Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Common Stock On June 3, 2019, the Company filed the 2019 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 the ATM, 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 2019 Shelf. For the three and nine months ended September 30, 2021, the Company sold no common shares and 139,734 common shares, respectively, under the ATM with offering prices ranging between $12.54 and $13.17 per share for gross proceeds of net proceeds of $1.7 million, after deducting commission and other offering expenses payable by the Company. On February 2, 2021, the Company sold 5,175,000 shares of its common stock in an underwritten public offering at a public offering price of $15.00 per share, including the underwriters' exercise of their option to purchase 675,000 shares to cover over-allotment, generating gross proceeds of $77.6 million and net proceeds of underwriting discounts and commission of $72.7 million, after deducting underwriting discounts and commission and other offering expenses paid by the Company. On January 28, 2021, the Company entered into a stock purchase agreement with ALJ Health Care & Life Science Company Limited ("ALJ Health Care"), pursuant to which on February 2, 2021, ALJ Health Care purchased $7.5 million of the Company's common stock in a private placement at a purchase price of $15.00 per share, equal to the public offering price per share at which the Company's common stock was sold to the public as referred above. The sale of such shares was not registered under the Securities Act. In connection with the entry into the Amended Credit Facility, the Company issued to K2 HealthVentures Equity Trust LLC, an affiliate of K2HV, a warrant to purchase up to 139,770 shares of the Company’s common stock, with an exercise price of $13.30 per share, subject to customary per share adjustments. The Warrant is exercisable immediately and expires on June 16, 2031, provided that, under certain circumstances, the Warrant may terminate and expire earlier in connection with the closing of certain acquisition transactions involving the Company. The Warrant provides that the holder thereof may elect to exercise the Warrant on a net “cashless” basis at any time prior to the expiration thereof. The fair market value of one share of the Company’s common stock in connection with any cashless exercise shall be the closing price or last sale price per share of the Company’s common stock on a nationally recognized securities exchange, inter-dealer quotation system or over-the-counter market on which the Company’s common stock is traded on the business day immediately prior to the date the holder elects to exercise the Warrant on a cashless basis. In addition, under the Amended Credit Facility, K2HV has the option, exercisable at any time, to convert up to $5.0 million of principal outstanding into shares of the Company’s common stock at a conversion price of $13.30 per share, subject to customary per share adjustments.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation 2021 Inducement Plan On May 27, 2021, the Company’s board of directors adopted the Evelo Biosciences, Inc. 2021 Employment Inducement Award Plan (the “Inducement Award Plan”) without stockholder approval pursuant to Rule 5635(c)(4) of the Nasdaq Stock Market LLC listing rules (“Rule 5635(c)(4)”). In accordance with Rule 5635(c)(4), cash and equity-based incentive awards under the Inducement Award Plan may only be made to a newly hired employee who has not previously been a member of the Company’s board of directors, or an employee who is being rehired following a bona fide period of non-employment by the Company or a subsidiary, as a material inducement to the employee’s entering into employment with the Company or its subsidiary. An aggregate of 1,250,000 shares of the Company’s common stock have been reserved for issuance under the Inducement Award Plan. The Company will continue to grant awards under the 2018 Incentive Award Plan (the “2018 Plan”) pursuant to the terms thereof. The exercise price of stock options granted under the Inducement Award Plan will not be 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 Company’s board of directors and are subject to the provisions of the Inducement Award Plan. Stock options granted to employees generally vest over a four-year period but may be granted with different vesting terms. Certain options may provide for accelerated vesting in the event of a change in control. Stock options granted under the Inducement Award Plan expire no more than 10 years from the date of grant. As of September 30, 2021, stock option awards covering up to 800,000 shares of the Company’s common stock have been issued under the Inducement Award Plan, none of which have been exercised or canceled. As of September 30, 2021, restricted stock unit (“RSU”) awards covering up to 4,545 shares of the Company’s common stock have been granted under the Inducement Award Plan, none of which have vested or been forfeited. As of September 30, 2021, 445,455 shares of common stock are available for future grant under the Inducement Award Plan. 2018 Incentive Award Plan The Company’s board of directors adopted on April 18, 2018, and the Company’s stockholders approved, 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, 2021 and 2020, the number of shares authorized for issuance under the 2018 Plan was increased by 1,898,805 shares and 1,286,824 shares, respectively. 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 will not be 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, 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 September 30, 2021, an aggregate of 5,758,536 options and other equity awards had been granted under the 2015 Plan, of which 1,454,079 have been exercised, 1,280,445 have been canceled and 18,468 have been repurchased as of September 30, 2021. 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 unaudited condensed consolidated statements of operations is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 General and administrative $ 2,388 $ 969 $ 5,552 $ 2,868 Research and development 2,053 1,076 5,925 3,225 Total stock-based compensation expense $ 4,441 $ 2,045 $ 11,477 $ 6,093 Stock Options A summary of the Company’s stock option activity and related information is as follows: Shares Weighted- Options outstanding at December 31, 2020 6,610,662 $ 6.55 Granted 3,472,149 14.63 Exercised (112,898) 6.12 Canceled (218,628) 11.10 Options outstanding at September 30, 2021 9,751,285 9.30 Exercisable as of September 30, 2021 4,724,499 $ 6.48 The weighted-average fair value of options granted during the nine months ended September 30, 2021 and 2020 was $10.81 and $4.17, respectively. As of September 30, 2021, total unrecognized stock-based compensation expense relating to unvested stock options was $40.3 million. This amount is expected to be recognized over a weighted average period of 2.78 years. Restricted Stock Units A summary of the restricted stock unit ("RSU") activity and related information is as follows: Shares Weighted- Unvested balance at December 31, 2020 284,000 $ 4.41 Granted 172,450 15.50 Vested (14,777) 13.74 Forfeited (39,192) 7.20 Unvested balance at September 30, 2021 402,481 $ 8.54 Stock-based compensation expense related to RSUs was $0.4 million and $0.7 million, respectively, for the three months and nine months ended September 30, 2021. 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 authorized an initial offering period under the ESPP commencing on February 1, 2020. Accordingly, on January 1, 2021, the number of shares authorized for issuance under the ESPP was increased by 474,701 shares. The compensation expense recognized related to the ESPP for the three and nine ended September 30, 2021 and 2020 was not material. There was a total of 18,771 shares and 46,358 shares, respectively, purchased under the ESPP during the three and nine months ended September 30, 2021. There were 28,603 shares purchased under the ESPP during both the three months and nine months ended September 30, 2020.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
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 contained several key provisions including: (i) five year carryback of net operating losses (“NOLs”), (ii) increase in amount of business interest expense deductible under Section 163(j) of the Internal Revenue Code from 30% to 50% for tax years 2019 and 2020, (iii) deferral 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 September 30, 2021, the Company had deferred $0.4 million in employer payroll taxes pursuant to the CARES Act, of which $0.2 million is included in the accrued expenses and $0.2 million is included in the other noncurrent liabilities in these unaudited condensed consolidated balance sheets. For the nine months ended September 30, 2021 and 2020 the Company recorded a tax provision of $0.3 million and $0.2 million, respectively, primarily related to the Company's wholly-owned UK subsidiary.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
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 and restricted common stock, and exercise of the Warrant and Conversion Option under the Amended Credit Facility, outstanding during the period determined using the 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: Nine Months Ended September 30, 2021 2020 Unvested common stock from early exercise of options 18,386 36,772 Stock options to purchase common stock 9,716,285 6,577,620 Warrant 139,770 — Conversion option 375,939 — Common stock offering from ESPP 13,152 12,482 Total 10,263,532 6,626,874

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
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 nine months ended September 30, 2021 and 2020, the Company paid Weatherden $0.2 million and $0.5 million, respectively. As of September 30, 2021 and 2020, the amounts due to Weatherden under the supply of service agreement were each less than $0.1 million, respectively. In June 2018, the Company entered into a subleasing arrangement with Ring Therapeutics, Inc. (formerly VL46, Inc.), 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, the sublease expiration date, plus related taxes and lease operating costs. For the nine months ended September 30, 2020, $0.3 million related to this sublease, 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. 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 provides strategic advisory and other consulting services to the Company. The Consulting Agreement was amended on October 15, 2020 and again on April 9, 2021, and now has a term that is scheduled to end on June 30, 2022 unless 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, on September 16, 2019, 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 dates. Under the Consulting Agreement as amended on October 15, 2020, 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 12 equal monthly installments following 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. In the event the Consulting Agreement is renewed for a term of less than one year, the aggregate grant date fair value of the corresponding annual equity award and the resulting number of shares of the Company’s common stock purchasable under such annual equity award and the vesting schedule shall be adjusted proportionately to the length of the renewal term. On October 11, 2020, in connection with the commencement of his second year of service as a consultant to the Company, Mr. Epstein was granted an annual equity award in the form of an option to purchase 44,743 shares of the Company’s common stock, which award vests in nine equal monthly installments, in each case subject to his continued provision of consulting services to the Company pursuant to the Consulting Agreement on the applicable vesting dates. Under the Consulting Agreement as amended on April 9, 2021, effective on June 30, 2021, Mr. Epstein is entitled to receive restricted stock units having an aggregate grant date fair value of approximately $0.5 million, as determined by our Board of Directors in its discretion based on a 10-day trailing average of the closing price of our common stock on the Nasdaq Global Select Market, as his sole compensation for the provision of consulting services to the Company. The restricted stock units will vest in 12 substantially equal monthly installments following June 30, 2021, such that the restricted stock units shall be fully vested on June 30, 2022, subject to his continued provision of consulting services to the Company pursuant to the Consulting Agreement on the applicable vesting date. All of the foregoing options and restricted stock units, 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)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
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, 2020 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 September 30, 2021, the results of its operations and stockholders' equity for the three and nine months ended September 30, 2021 and 2020 and cash flows for the nine months ended September 30, 2021 and 2020. Such adjustments are of a normal and recurring nature. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results for the year ending December 31, 2021, 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, estimates related to the application of ASC 606, Revenue from Contracts with Customers ("ASC 606") to our collaboration agreement, 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.
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 Income or Loss	Comprehensive Income or Loss Comprehensive income (loss) consists of net income (loss) and changes in equity during a period from transactions and other equity and circumstances generated from non-owner sources. The Company’s net loss equals comprehensive loss for all periods presented.
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. 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.
Collaborative Agreements	Collaboration Agreements The Company analyzes its collaboration arrangements to assess whether they are within the scope of ASC 808, Collaborative Arrangements ("ASC 808") to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. To the extent the arrangement is within the scope of ASC 808, the Company assesses whether aspects of the arrangement between the Company and its collaboration partner are within the scope of other accounting literature, including ASC 606. If it is concluded that some or all aspects of the arrangement represent a transaction with a customer, the Company will account for those aspects of the arrangement within the scope of ASC 606. ASC 808 provides guidance for the presentation and disclosure of transactions in collaborative arrangements, but it does not provide recognition or measurement guidance. Therefore, if the Company concludes a counterparty to a transaction is not a customer or otherwise not within the scope of ASC 606, the Company considers the guidance in other accounting literature, including the guidance in ASC 606, as applicable or by analogy to account for such transaction. The classification of transactions under the Company’s arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants.
Revenue Recognition and Contract Liabilities	Revenue Recognition The Company analyzes its collaboration arrangements to assess whether they are within the scope of Accounting Standards Codification ASC 808, to determine whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. If the Company concludes that some or all aspects of the arrangement represent a transaction with a customer, the Company accounts for those aspects of the arrangement within the scope of ASC 606. To determine the appropriate amount of revenue to be recognized for arrangements that the Company determines are within the scope of ASC 606, it performs the following steps: (i) identify the contract(s) with the customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) each performance obligation is satisfied. ASC 606 requires significant judgment and estimates and results in changes to, but not limited to: (i) the determination of the transaction price, including estimates of variable consideration, (ii) the allocation of the transaction price, including the determination of estimated selling price, and (iii) the pattern of recognition, including the application of proportional performance as a measure of progress on service-related promises and application of point-in-time recognition for supply-related promises. The promised good or services in the Company’s arrangement may consist of license rights to the Company’s intellectual property or research and development services. The Company also may have optional additional items in contracts, which are considered marketing offers and are accounted for as separate contracts with the customer if such option is elected by the customer, unless the option provides a material right which would not be provided without entering into the contract. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer. Promised goods or services are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources or (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own or whether the required expertise is readily available. The transaction price may be comprised of fixed payments, often an upfront payment due at contract inception, or other types of variable consideration in the form of payments for the Company’s services and materials and milestone payments due upon the achievement of specified events. Other payments the Company could be entitled to include tiered royalties earned when customers recognize net sales of licensed products. The Company considers the existence of any significant financing component within its arrangements to the extent there is a significant difference between the timing of payment and the transfer of control of the performance obligations. In making that determination, the Company considers whether substantive business purposes exist to support the payment structure other than to provide a significant benefit of financing. The Company measures the transaction price based on the amount of consideration to which it expects to be entitled in exchange for transferring the promised goods and/or services to the customer. The Company utilizes either the expected value method or the most likely amount method to estimate the amount of variable consideration, depending on which method is expected to better predict the amount of consideration to which the Company will be entitled. Amounts of variable consideration are included in the transaction price to the extent that it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. With respect to arrangements that include payments for a development or regulatory milestone payment, the Company evaluates whether the associated event is considered probable of achievement and estimates the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within the Company’s or the licensee’s control, such as those dependent upon receipt of regulatory approval, are not considered to be probable of achievement until the triggering event occurs. At the end of each reporting period, the Company re-evaluates the probability of achievement of each milestone and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. For arrangements that include sales-based royalties, including milestone payments based upon the achievement of a certain level of product sales, wherein the license is deemed to be the sole or predominant item to which the payments relate, the Company recognizes revenue upon the later of: (i) when the related sales occur or (ii) when the performance obligation to which some or all of the payment has been allocated has been satisfied (or partially satisfied). Consideration that would be received for optional goods and/or services is excluded from the transaction price at contract inception. For arrangements with more than one performance obligation, the Company generally allocates the transaction price to each performance obligation based on a relative standalone selling price basis. The Company develops assumptions that require judgment to determine the standalone selling price for each performance obligation in consideration of applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated research and development costs. However, in certain instances, the Company may allocate variable consideration entirely to one or more performance obligation if the terms of the variable consideration relate to the satisfaction of the respective performance obligation and the amount allocated is consistent with the amount the Company would expect to receive for the satisfaction of the respective performance obligation. The Company recognizes revenue based on the amount of the transaction price that is allocated to each respective performance obligation when or as the performance obligation is satisfied by transferring a promised good or service to the customer. For performance obligations that are satisfied at a point in time, the Company recognizes revenue when control of the goods and/or services is transferred to the customer. For performance obligations that are satisfied over time, the Company recognizes revenue by measuring the progress toward complete satisfaction of the performance obligation using a single method of measuring progress which depicts the performance in transferring control of the associated goods and/or services to the customer. With respect to arrangements containing a license to its intellectual property that is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from amounts allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations under an arrangement. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenue and net loss in the period of adjustment. Contract Liabilities The Company records a contract liability, classified as deferred revenue on its condensed consolidated balance sheet, when it has received payment but has not yet satisfied the related performance obligations. In the event of an early termination of a contract with a customer, any contract liabilities would be recognized in the period in which all Company obligations under the agreement have been fulfilled.
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 unaudited condensed 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 licenses, products 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 equity awards 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 options. The determination of the fair value of 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 and Accounting Pronouncements Issued and Not Adopted	Recently Adopted Accounting Pronouncements 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 was effective for the Company on January 1, 2021 and it 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. The Company adopted ASU No. 2019-12 on January 1, 2021 and has concluded the adoption did not have a material impact on its unaudited condensed consolidated financial statements. Accounting Pronouncements Issued and Not Adopted as of September 30, 2021 Financial Instruments - Credit Losses In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326)—Measurement of Credit Losses on Financial Instruments, which has been subsequently amended by ASU No. 2018-19, ASU No. 2019-04, ASU No. 2019-05, ASU No. 2019-10, ASU No. 2019-11 and ASU No. 2020-03 (“ASU 2016-13”). The provisions of ASU 2016-13 modify the impairment model to utilize an expected loss methodology in place of the currently used incurred loss methodology and require a consideration of a broader range of reasonable and supportable information to inform credit loss estimates. ASU 2016-13 is effective for the Company on January 1, 2023, with early adoption permitted. The Company is currently evaluating the potential impact that this standard may have on its financial position and results of operations, as well as the timing of its adoption of this standard. Debt with Conversion and Other Options On August 5, 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU-2020-06”), which simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. ASU 2020-06 eliminates the beneficial conversion and cash conversion accounting models in ASC 470-20 that require separate accounting for embedded conversion features from convertible instruments. As a result, after adopting the ASU’s guidance, entities will not separately present in equity an embedded conversion feature in such debt. Additionally, the guidance simplifies the evaluation of whether a contract in the issuer’s own equity can be classified in equity or an embedded feature qualifies for the derivative scope exception. Although the guidance is not effective until 2022, early adoption of ASU 2020-06 is permitted for all entities for fiscal years beginning after December 15, 2020. The Company is currently evaluating the impact of this new guidance on the Company’s condensed consolidated financial statements and related disclosures.
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)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following reconciles cash, cash equivalents and restricted cash as of September 30, 2021 and December 31, 2020, as presented on the Company's statements of cash flows, to its related balance sheet accounts (in thousands): September 30, 2021 December 31, 2020 Cash and cash equivalents: Cash $ 3,359 $ 4,487 Money market funds 92,579 64,370 Total cash and cash equivalents 95,938 68,857 Restricted cash 1,313 1,563 Cash, cash equivalents and restricted cash $ 97,251 $ 70,420
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following reconciles cash, cash equivalents and restricted cash as of September 30, 2021 and December 31, 2020, as presented on the Company's statements of cash flows, to its related balance sheet accounts (in thousands): September 30, 2021 December 31, 2020 Cash and cash equivalents: Cash $ 3,359 $ 4,487 Money market funds 92,579 64,370 Total cash and cash equivalents 95,938 68,857 Restricted cash 1,313 1,563 Cash, cash equivalents and restricted cash $ 97,251 $ 70,420

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Schedule of Minimum Aggregate Future Lease Commitments	The minimum aggregate future lease commitments at September 30, 2021, are as follows (in thousands): Amount 2021 ( excluding amounts paid or in Accounts Payable as of 9/30/2021) $ 507 2022 3,062 2023 3,154 2024 3,249 2025 2,491 Total lease payments 12,463 Less imputed interest (2,214) Total $ 10,249 Other information: Operating cash flows used for operating leases $ 1,967 Weighted-average remaining lease term (in years) 4.0 Weighted-average discount rate 9.5 %

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
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 September 30, 2021 and December 31, 2020 (in thousands): Description September 30, 2021 (Level 1) (Level 2) (Level 3) Assets: Money market funds included within cash and cash equivalents $ 92,579 $ 92,579 $ — $ — Total $ 92,579 $ 92,579 $ — $ — Description December 31, 2020 (Level 1) (Level 2) (Level 3) Assets: Money market funds included within cash and cash equivalents $ 64,370 $ 64,370 $ — $ — Total $ 64,370 $ 64,370 $ — $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property, Plant and Equipment [Abstract]
Summary of Property and Equipment	Property and equipment consists of the following (in thousands): September 30, 2021 December 31, 2020 Property and equipment: Lab equipment $ 10,050 $ 8,831 Leasehold improvements 2,157 2,157 Furniture and fixtures 822 822 Computers and software 252 230 Office equipment 21 3 Construction-in-process 1,577 1,078 Property and equipment 14,879 13,121 Less: accumulated depreciation (7,117) (5,643) Property and equipment, net $ 7,762 $ 7,478

Loan and Security Agreements (T

Loan and Security Agreements (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Fair Value Measurement Inputs and Valuation Techniques	The Company utilized the following significant unobservable inputs (Level 3 inputs) to determine the estimated fair value of its debt as of the amendment date: Expected volatility 70.00 % Expected yield 11.50 % Fair value of underlying common stock $ 16.13 Exercise price $ 13.30 Risk-free interest rate 1.56 % Expected volatility 70.0 % Expected term (years) 10.0 Expected dividend yield — %
Schedule of Minimum Aggregate Future Loan Payments	The Company has the following minimum aggregate future loan payments at September 30, 2021 (in thousands). Twelve month period ending September 30, Amount 2022 $ 3,947 2023 20,377 2024 31,389 Total minimum payments 55,713 Less amounts representing interest and discount (9,193) Total Debt $ 46,520

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock-based Compensation Expense	Stock-based compensation expense included in the Company’s unaudited condensed consolidated statements of operations is as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 General and administrative $ 2,388 $ 969 $ 5,552 $ 2,868 Research and development 2,053 1,076 5,925 3,225 Total stock-based compensation expense $ 4,441 $ 2,045 $ 11,477 $ 6,093
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, 2020 6,610,662 $ 6.55 Granted 3,472,149 14.63 Exercised (112,898) 6.12 Canceled (218,628) 11.10 Options outstanding at September 30, 2021 9,751,285 9.30 Exercisable as of September 30, 2021 4,724,499 $ 6.48
Summary of Restricted Stock Unit Activity	A summary of the restricted stock unit ("RSU") activity and related information is as follows: Shares Weighted- Unvested balance at December 31, 2020 284,000 $ 4.41 Granted 172,450 15.50 Vested (14,777) 13.74 Forfeited (39,192) 7.20 Unvested balance at September 30, 2021 402,481 $ 8.54

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
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: Nine Months Ended September 30, 2021 2020 Unvested common stock from early exercise of options 18,386 36,772 Stock options to purchase common stock 9,716,285 6,577,620 Warrant 139,770 — Conversion option 375,939 — Common stock offering from ESPP 13,152 12,482 Total 10,263,532 6,626,874

Organization - Narrative (Detai

Organization - Narrative (Details) - USD ($)	Aug. 23, 2021	Feb. 02, 2021	Jun. 03, 2019	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Subsidiary, Sale of Stock [Line Items]
Sale of stock, term (up to)	3 years		3 years
Cash and cash equivalents				$ 95,938,000	$ 95,938,000	$ 68,857,000
Accumulated deficit				$ 386,043,000	$ 386,043,000	$ 292,519,000
Registration Statement
Subsidiary, Sale of Stock [Line Items]
Maximum value of shares issued in transaction (up to)	$ 200,000,000		$ 200,000,000
At-the-market
Subsidiary, Sale of Stock [Line Items]
Maximum value of shares issued in transaction (up to)			$ 50,000,000
Number of shares sold in public offering (in shares)				0	139,734
Gross proceeds from transactions				$ 1,800,000	$ 1,800,000
Net proceeds from issuance of common stock				$ 1,700,000	$ 1,700,000
At-the-market | Minimum
Subsidiary, Sale of Stock [Line Items]
Price of shares sold in public offering (in dollars per share)				$ 12.54	$ 12.54
At-the-market | Maximum
Subsidiary, Sale of Stock [Line Items]
Price of shares sold in public offering (in dollars per share)				$ 13.17	$ 13.17
Public Stock Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares sold in public offering (in shares)		5,175,000
Price of shares sold in public offering (in dollars per share)		$ 15
Gross proceeds from transactions		$ 77,600,000
Net proceeds from issuance of common stock		$ 72,700,000
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares sold in public offering (in shares)		675,000
Private Placement
Subsidiary, Sale of Stock [Line Items]
Price of shares sold in public offering (in dollars per share)		$ 15
Net proceeds from issuance of common stock		$ 7,500,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)segment	Dec. 31, 2020USD ($)
Accounting Policies [Abstract]
Current restricted cash	$ 0	$ 0.3
Noncurrent restricted cash	$ 1.3	$ 1.3
Number of operating segments | segment	1

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash and cash equivalents:
Cash	$ 3,359	$ 4,487
Money market funds	92,579	64,370
Total cash and cash equivalents	95,938	68,857
Restricted cash	1,313	1,563
Cash, cash equivalents and restricted cash	$ 97,251	$ 70,420	$ 83,080	$ 79,333

ALJ Commercialization and Lic_2

ALJ Commercialization and License Agreement (Details) - USD ($) $ in Thousands	Mar. 17, 2021	Sep. 30, 2021	Dec. 31, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue recognized		$ 7,500	$ 0
Transaction with party to collaborative arrangement | ALJ
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Negotiation period for second product candidate	2 years
Maximum fee for second product option	$ 7,500
Deferred revenue recognized		$ 7,500
Share of operating profits and losses and development, regulatory and commercialization costs.	50.00%

Leases - Narrative (Details)

Leases - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Jan. 31, 2018ft²
Sale Leaseback Transaction [Line Items]
Area of leased office and research development space (in square feet) | ft²					40,765
Minimum rental payments received		$ 0		$ 200,000
Rent expense	$ 700,000	$ 700,000	$ 2,200,000	2,100,000
Sublease rental income	$ 0		$ 0
VL46
Sale Leaseback Transaction [Line Items]
Sublease rental income				$ 300,000

Leases - Schedule of Minimum Ag

Leases - Schedule of Minimum Aggregate Future Lease Commitments (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Leases [Abstract]
2021 (excluding amounts paid or in Accounts Payable as of 9/30/2021)	$ 507
2022	3,062
2023	3,154
2024	3,249
2025	2,491
Total lease payments	12,463
Less imputed interest	(2,214)
Total	10,249
Other information:
Operating cash flows used for operating leases	$ 1,967
Weighted-average remaining lease term (in years)	4 years
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	Sep. 30, 2021	Dec. 31, 2020
Assets:
Total	$ 92,579	$ 64,370
Money market funds included within cash and cash equivalents
Assets:
Cash and cash equivalents, fair value disclosure	92,579	64,370
(Level 1)
Assets:
Total	92,579	64,370
(Level 1) | Money market funds included within cash and cash equivalents
Assets:
Cash and cash equivalents, fair value disclosure	92,579	64,370
(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	Sep. 30, 2021	Dec. 31, 2020
Property and equipment:
Property and equipment	$ 14,879	$ 13,121
Less: accumulated depreciation	(7,117)	(5,643)
Property and equipment, net	7,762	7,478
Lab equipment
Property and equipment:
Property and equipment	10,050	8,831
Leasehold improvements
Property and equipment:
Property and equipment	2,157	2,157
Furniture and fixtures
Property and equipment:
Property and equipment	822	822
Computers and software
Property and equipment:
Property and equipment	252	230
Office equipment
Property and equipment:
Property and equipment	21	3
Construction-in-process
Property and equipment:
Property and equipment	$ 1,577	$ 1,078

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 600	$ 500	$ 1,678	$ 1,493

Loan and Security Agreements -

Loan and Security Agreements - Narrative (Details)	Jul. 19, 2019USD ($)tranche	Sep. 30, 2021USD ($)$ / shares	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)$ / shares	Sep. 30, 2020USD ($)	Jun. 16, 2021USD ($)$ / sharesshares
Line of Credit Facility [Line Items]
Common stock exercise prices (in dollars per share) | $ / shares		$ 13.30		$ 13.30
Additional paid in capital at its issuance date fair value		$ 1,800,000		$ 1,800,000
Loss on extinguishment of debt		0	$ 0	3,226,000	$ 0
Estimate of Fair Value Measurement
Line of Credit Facility [Line Items]
Credit Facility estimate fair value		46,600,000		46,600,000
2019 Credit Facility
Line of Credit Facility [Line Items]
Interest expense		$ 1,000,000	$ 600,000	2,600,000	$ 1,500,000
Line of Credit | 2019 Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 45,000,000
Number of tranches | tranche	3
Loan and security agreement, interest rate	8.65%
Prepayment fee percentage	2.00%
Anniversary of funding date for determining prepayment fee percentage	18 months
Prepayment fee percentage after specified period	1.00%
Final payment under agreement as a percentage of loans borrowed	4.30%
Fees incurred to establish facility	$ 400,000
Debt default interest rate per annum	5.00%
Line of Credit | 2019 Credit Facility | Security And Loan Agreement, Tranche One
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 20,000,000
Line of Credit | 2019 Credit Facility | Security And Loan Agreement, Tranche Two
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	10,000,000
Line of Credit | 2019 Credit Facility | Security And Loan Agreement, Tranche Three
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)	$ 15,000,000					$ 15,000,000
Line of Credit | 2019 Credit Facility | Security And Loan Agreement, Tranche Four
Line of Credit Facility [Line Items]
Maximum borrowing capacity (up to)						$ 15,000,000
Line of Credit | 2019 Credit Facility | Prime Plus
Line of Credit Facility [Line Items]
Loan and security agreement, basis spread on interest rate	3.15%
Line of Credit | Amended Credit Facility
Line of Credit Facility [Line Items]
Number of shares called by warrants (in shares) (up to) | shares						139,770
Common stock exercise prices (in dollars per share) | $ / shares						$ 13.30
Convertible debt (up to)						$ 5,000,000
Common stock at a conversion price (in dollars per share) | $ / shares						$ 13.30
Final payment under agreement as a percentage of loans borrowed	4.80%
Fees incurred to establish facility	$ 300,000
Loss on extinguishment of debt				$ 3,200,000

Loan and Security Agreements _2

Loan and Security Agreements - Significant Unobservable Inputs (level 3 Inputs) (Details) - (Level 3) - Fair Value, Recurring	Sep. 30, 2021
Expected volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, measurement input	0.7000
Expected yield
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, measurement input	0.1150

Loan and Security Agreements _3

Loan and Security Agreements - Fair Value of Warrant (Details)	Sep. 30, 2021$ / shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Exercise price (in dollars per share)	$ 13.30
Fair value of underlying common stock | (Level 3) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	16.13
Risk-free interest rate | (Level 3) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.0156
Expected volatility | (Level 3) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0.700
Expected term (years) | (Level 3) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	10
Expected dividend yield | (Level 3) | Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement input	0

Loan and Security Agreements _4

Loan and Security Agreements - Schedule of Minimum Aggregate Future Loan Payments (Details) - Line of Credit $ in Thousands	Sep. 30, 2021USD ($)
Line of Credit Facility [Line Items]
2022	$ 3,947
2023	20,377
2024	31,389
Total minimum payments	55,713
Less amounts representing interest and discount	(9,193)
Total minimum payments	$ 46,520

In-License Agreements - Narrati

In-License Agreements - Narrative (Details) - USD ($)	Sep. 30, 2021	Aug. 06, 2017	Mar. 10, 2016
Mayo Clinic
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 (up to)	$ 300,000
Amount due under license agreement	0
Mayo Clinic | Maximum
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Milestone payments upon achievement of certain development, regulatory, and commercial events (up to)		$ 56,000,000
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 (up to)			$ 60,900,000
Amount due under license agreement	0
Milestone payments for development and commercialization of licensed products	$ 400,000
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) - Sacco - Collaborative Arrangement - EUR (€) € in Millions	1 Months Ended	27 Months Ended
	Jul. 31, 2019	Sep. 30, 2021
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
Fee incurred under collaborative arrangement		€ 1.8

Stockholders_ Equity (Details)

Stockholders’ Equity (Details) - USD ($)	Aug. 23, 2021	Feb. 02, 2021	Jun. 03, 2019	Sep. 30, 2021	Sep. 30, 2021	Jun. 16, 2021
Class of Stock [Line Items]
Sale of stock, term (up to)	3 years		3 years
Line of Credit | Amended Credit Facility
Class of Stock [Line Items]
Number of shares called by warrants (in shares) (up to)						139,770
Common stock at a conversion price (in dollars per share)						$ 13.30
Convertible debt (up to)						$ 5,000,000
Registration Statement
Class of Stock [Line Items]
Maximum value of shares issued in transaction (up to)	$ 200,000,000		$ 200,000,000
At-the-market
Class of Stock [Line Items]
Maximum value of shares issued in transaction (up to)			$ 50,000,000
Number of shares sold in public offering (in shares)				0	139,734
Net proceeds from issuance of common stock				$ 1,700,000	$ 1,700,000
Gross proceeds from transactions				$ 1,800,000	$ 1,800,000
At-the-market | Minimum
Class of Stock [Line Items]
Price of shares sold in public offering (in dollars per share)				$ 12.54	$ 12.54
At-the-market | Maximum
Class of Stock [Line Items]
Price of shares sold in public offering (in dollars per share)				$ 13.17	$ 13.17
Public Stock Offering
Class of Stock [Line Items]
Number of shares sold in public offering (in shares)		5,175,000
Price of shares sold in public offering (in dollars per share)		$ 15
Net proceeds from issuance of common stock		$ 72,700,000
Gross proceeds from transactions		$ 77,600,000
Over-Allotment Option
Class of Stock [Line Items]
Number of shares sold in public offering (in shares)		675,000
Private Placement
Class of Stock [Line Items]
Price of shares sold in public offering (in dollars per share)		$ 15
Net proceeds from issuance of common stock		$ 7,500,000

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2021	May 27, 2021	Jan. 01, 2021	Jan. 01, 2020	May 08, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2015	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options granted (up to, in shares)								3,472,149
Number of shares exercised (in shares)								112,898
Number of shares canceled (in shares)								218,628
Weighted average fair value of options granted (in dollars per share)								$ 10.81	$ 4.17
Stock-based compensation expense						$ 4,441	$ 2,045	$ 11,477	$ 6,093
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 40,300					40,300		$ 40,300			$ 40,300
Compensation cost not yet recognized, period for recognition								2 years 9 months 10 days
Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted in period (in shares)								172,450
Stock-based compensation expense						$ 400		$ 700
2021 Stock Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares originally authorized for issuance (in shares)		1,250,000
Number of common stock available for future grant (in shares)	445,455					445,455		445,455			445,455
Number of shares, options and other equity awards exercised (in shares)											1,454,079
Number of shares, options and other equity awards canceled (in shares)											1,280,445
2021 Stock Inducement Plan | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Options granted, maximum expiration period (no more than)		10 years
Number of stock options granted (up to, in shares)	800,000
2021 Stock Inducement Plan | Warrant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted in period (in shares)	4,545
2018 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares originally authorized for issuance (in shares)					1,344,692
Number of stock options granted (up to, in shares)	7,048,331
Number of common stock available for future grant (in shares)	268,200					268,200		268,200			268,200
Percentage of outstanding shares					4.00%
Number of additional shares authorized for issuance (in shares)			1,898,805	1,286,824
Number of shares exercised (in shares)	39,600
Number of shares canceled (in shares)	1,081,458
2018 Stock Incentive Plan | Stock Options | Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
2018 Stock Incentive Plan | Maximum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, maximum expiration period (no more than)					10 years
2018 Stock Incentive Plan | Maximum | Stock Options | Nonemployee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					4 years
2018 Stock Incentive Plan | Minimum | Stock Options | Nonemployee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period					1 year
2015 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock available for future grant (in shares)										5,417,044
Number of shares, options and other equity awards granted (in shares)											5,758,536
Number of shares repurchased (in shares)											18,468
Number of shares no longer authorized (in shares)										113,006
2015 Stock Incentive Plan | Stock Options | Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period										4 years
2015 Stock Incentive Plan | Maximum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, maximum expiration period (no more than)										10 years
2015 Stock Incentive Plan | Maximum | Stock Options | Nonemployee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period										4 years
2015 Stock Incentive Plan | Minimum | Stock Options | Nonemployee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period										1 year
2018 Employee Stock Purchase Plan | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of outstanding shares					1.00%
Number of additional shares authorized for issuance (in shares)			474,701		336,356
Number of shares issued for purchase (in shares)						18,771	28,603	46,358	28,603

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 4,441	$ 2,045	$ 11,477	$ 6,093
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	2,388	969	5,552	2,868
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,053	$ 1,076	$ 5,925	$ 3,225

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021
Shares
Options outstanding, beginning balance (in shares)	6,610,662
Granted (in shares)	3,472,149
Exercised (in shares)	(112,898)
Canceled (in shares)	(218,628)
Options outstanding, ending balance (in shares)	9,751,285
Exercisable as of period end (in shares)	4,724,499
Weighted- Average Exercise Price
Options outstanding, beginning balance (in dollars per share)	$ 6.55
Granted (in dollars per share)	14.63
Exercised (in dollars per share)	6.12
Canceled (in dollars per share)	11.10
Options outstanding, ending balance (in dollars per share)	9.30
Weighted-Average Exercise Price, Exercisable as of period end (in dollars per share)	$ 6.48

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Restricted Stock Unit Activity (Details) - Warrant	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Shares
Unvested beginning balance (in shares) | shares	284,000
Granted (in shares) | shares	172,450
Vested (in shares) | shares	(14,777)
Forfeited (in shares) | shares	(39,192)
Unvested ending balance (in shares) | shares	402,481
Weighted- Average Grant Date Fair Value
Unvested beginning balance (in dollars per share) | $ / shares	$ 4.41
Granted (in dollars per share) | $ / shares	15.50
Vested (in dollars per share) | $ / shares	13.74
Forfeited (in dollars per share) | $ / shares	7.20
Unvested ending balance (in dollars per share) | $ / shares	$ 8.54

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Examination [Line Items]
Deferred payroll taxes related to CARES Act	$ 400		$ 400
Provision for income taxes	156	$ 67	331	$ 221
Subsidiaries | UK
Income Tax Examination [Line Items]
Provision for income taxes			300	$ 200
Prepaid Expenses and Other Current Assets
Income Tax Examination [Line Items]
Deferred payroll taxes related to CARES Act	200		200
Other Noncurrent Liabilities
Income Tax Examination [Line Items]
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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
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)	10,263,532	6,626,874
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)	18,386	36,772
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)	9,716,285	6,577,620
Warrant
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)	139,770	0
Conversion option
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)	375,939	0
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)	13,152	12,482

Related Party Transactions - Na

Related Party Transactions - Narrative (Details)	Sep. 30, 2021USD ($)installment	Apr. 09, 2021	Oct. 15, 2020USD ($)installment	Oct. 11, 2020installmentshares	Sep. 16, 2019installmentshares	Sep. 30, 2021USD ($)	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Jun. 30, 2021USD ($)	Apr. 30, 2020USD ($)
Related Party Transaction [Line Items]
Sublease rental income						$ 0	$ 0
Number of stock options granted (in shares) | shares							3,472,149
Weatherden Ltd
Related Party Transaction [Line Items]
Payment to related party							$ 200,000	$ 500,000
Amounts due to related party	$ 100,000					$ 100,000	$ 100,000	100,000
VL46
Related Party Transaction [Line Items]
Rent due from sublease agreement										$ 900,000
Sublease rental income								$ 300,000
Mr. Epstein | Warrant
Related Party Transaction [Line Items]
Aggregate grant date fair value for restricted stock units									$ 500,000
Mr. Epstein | Consulting Agreement
Related Party Transaction [Line Items]
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				44,743	75,000
Option to purchase shares, vesting period, number of equal monthly installments | installment					36
Aggregate grant date fair value			$ 200,000
Annual equity award, vesting period, number of equal monthly installments | installment			12	9
Aggregate annual cash consulting fee			$ 300,000
Renewal term			1 year
Mr. Epstein | Consulting Agreement | Warrant
Related Party Transaction [Line Items]
Option to purchase shares, vesting period, number of equal monthly installments | installment	12
Period for trailing average closing common stock price									10 days