Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2022

Summary of Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:

	March 31, 2022
Common stock warrants		13,760
Common stock options and restricted stock units		1,824,164
Shares available under the 2015 equity incentive plan		72,423
Shares available under the 2022 inducement plan		241,600
Shares available under the employee stock purchase plan		71,933
		2,223,880

Summary of Stock Option Activity

The following table summarizes our stock option activity under all equity incentive plans for the three months ended March 31, 2022:

	Number of Outstanding Stock Options			Weighted Average Exercise Price
Outstanding as of December 31, 2021		1,412,550		$	12.01
Granted		331,912		$	5.47
Exercises		(259	)	$	3.77
Canceled/forfeited/expired		(5,477	)	$	4.89
Outstanding as of March 31, 2022		1,738,726		$	10.79

Schedule of Restricted Stock Unit Activity

The following table summarizes our restricted stock unit activity under all equity incentive plans for the three months ended March 31, 2022:

	Number of Outstanding Restricted Stock Units			Weighted Average Grant Date Fair Value
Balance as of December 31, 2021		7,500		$	4.08
Granted		80,438		$	5.52
Released		(2,500	)	$	4.13
Balance as of March 31, 2022		85,438		$	5.43

Schedule of Allocation of Stock-Based Compensation for All Options and Restricted Stock Units and Stock Issued to Our Employee Stock Purchase Plan

The allocation of stock-based compensation for all options and restricted stock units and stock issued pursuant to our employee stock purchase plan is as follows (in thousands):

	March 31,
	2022		2021
Research and development	$	107	$	63
General and administrative		310		297
Total stock-based compensation expense	$	417	$	360

Employee Stock Option [Member]

Summary of Assumptions Used to Determine Fair Value of Employee Stock Option Grants and Performance Options with Market Condition

The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:

	March 31,
	2022			2021
Expected term (in years)	6.02 – 6.08			5.99 – 6.02
Risk-free interest rate	1.7% – 2.4		%	0.6% – 0.9		%
Expected volatility	85.8% – 86.5		%	104.0% – 104.8		%
Expected dividend yield		0.0	%		0.0	%