Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity and Related Information

The following table summarizes the stock option activity and related information for 2022:

	Number of Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (Years)		Total Intrinsic Value (in thousands)
Outstanding as of December 31, 2021		6,161,901		$	11.77		6.4	$	53
Granted		4,087,350			2.09
Forfeited		(1,158,386	)		14.43
Outstanding as of December 31, 2022		9,090,865		$	7.08		7.1	$	—
Options vested and exercisable as of December 31, 2022		4,262,287		$	11.32		4.9	$	—

Summary of Restricted Stock Units and Related Information

The following table summarizes RSU activity and related information for 2022:

	Number of RSUs			Weighted Average Fair Value Per RSU at Grant Price
Nonvested as of December 31, 2021		970,339		$	7.04
Granted		1,255,275			2.06
Vested		(249,376	)		8.88
Forfeited		(276,474	)		5.26
Nonvested as of December 31, 2022		1,699,764		$	3.39

Summary of Assumptions Used to Estimate Fair Values of Stock Options Grants

A summary of the assumptions used to estimate the fair values of stock options grants for the years presented is as follows:

	Year Ended December 31,
	2022	2021
Exercise price	$1.53 - $2.45	$2.24 - $5.79
Expected volatility	78.49% - 81.72%	79.74% - 91.18%
Risk-free rate	1.41% - 4.15%	0.50% - 1.37%
Expected term (years)	5.5 - 7.5	5.5 - 7.5
Expected dividend yield	0%	0%

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense included in the consolidated statement of operations and comprehensive loss for the years presented (in thousands):

	Year Ended December 31,
	2022		2021
Research and development	$	3,024	$	548	(1)
General and administrative		3,569		4,689
Total stock-based compensation expense	$	6,593	$	5,237

(1) Includes the reversal of previously recognized stock-based compensation expense of $4.8 million related to forfeited awards of terminated employees, $2.7 million of which resulted from the wind-down of the Company’s Microbiome program in January 2021.