In February 2023, we completed an underwritten follow-on public offering of 23,125,000 shares of our common stock, including the partial exercise of the underwriters’ option to purchase additional shares, at a price to the public of $2.25 per share. The total net proceeds from the offering were approximately $48.1 million, after deducting underwriting discounts, commissions and offering expenses payable by us.

In April 2022, we entered into an Open Market Sale AgreementSM with Jefferies LLC (Jefferies) implementing an “at-the-market” offering program (the Jefferies ATM Offering Program), pursuant to which we may offer and sell, from time to time and at our option, up to an aggregate of $65.0 million of shares of our common stock through Jefferies, acting as sales agent. Jefferies is entitled to a fixed commission rate of up to 3.0% of the gross sales proceeds of shares sold under the Jefferies ATM Offering Program. During 2022, we sold an aggregate of 1,421,627 shares of common stock at a weighted-average price of $3.09 per share for net proceeds of approximately $4.0 million under the Jefferies ATM Offering Program. During the three months ended March 31, 2023, we sold an aggregate of 694,012 shares of common stock at a weighted-average price of $2.30 per share for net proceeds of approximately $1.5 million under the Jefferies ATM Offering Program.

Common Stock Reserved for Future Issuance

Common stock reserved for future issuance was as follows:


	March 31, 2023
Common stock warrants		13,760
Common stock options and restricted stock units		3,922,930
Shares available under the 2015 equity incentive plan		83,313
Shares available under the 2022 inducement plan		109,833
Shares available under the employee stock purchase plan		801,321
		4,931,157

The following table summarizes our stock option activity under all equity incentive plans for the three months ended March 31, 2023:


	Number of Outstanding Stock Options			Weighted- Average Exercise Price
Outstanding as of December 31, 2022		2,956,170		$	7.45
Granted		938,485		$	2.20
Canceled/forfeited/expired		(71,052	)	$	4.37
Outstanding as of March 31, 2023		3,823,603		$	6.22

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,
	2023			2022
Expected term (in years)	$	6.02		6.02 – 6.08
Risk-free interest rate		4.0	%	1.7% – 2.4%
Expected volatility		82.0	%	85.8% – 86.5%
Expected dividend yield		0.0	%		0.0	%

The following table summarizes our restricted stock unit activity under all equity incentive plans for the three months ended March 31, 2023:


	Number of Outstanding Restricted Stock Units			Weighted-Average Grant Date Fair Value
Balance as of December 31, 2022		121,438		$	5.09
Released		(22,111	)	$	5.39
Balance as of March 31, 2023		99,327		$	5.02

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):


	Three Months Ended March 31,
	2023		2022
Research and development	$	129	$	107
General and administrative		490		310
Total stock-based compensation expense	$	619	$	417