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Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2021

The following table summarizes the stock option activity during the six months ended June 30, 2021:


	Shares Subject to Options			Weighted- Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2020		2,463,317		$	3.71
Granted		1,750,580		$	5.35
Exercised		(295,028	)	$	2.72
Forfeitures and cancellations		(78,918	)	$	4.29
Options outstanding at June 30, 2021		3,839,951		$	4.53		8.83	$	5,898
Options exercisable at June 30, 2021		1,068,656		$	3.72		8.04	$	2,556

(a)

Aggregate intrinsic value in this table was calculated as the positive difference, if any, between the closing price per share of the Company’s common stock on June 30, 2021 of $5.89 and the price of the underlying options.

Summary of Non-cash Stock-based Compensation Expense

The non-cash stock-based compensation expense for all stock awards, net of forfeitures recognized as they occur, that was recognized in the condensed consolidated statements of operations is as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Research and development	$	462	$	488	$	936	$	902
General and administrative		602		862		1,172		1,235
Total	$	1,064	$	1,350	$	2,108	$	2,137

Summary of Reserved Shares of Common Stock for Future Issuance

Common stock reserved for future issuance at June 30, 2021 is as follows:


	June 30,		December 31,
	2021		2020
Stock options issued and outstanding		3,839,951		2,463,317
Warrants for common stock		1,366,141		80,428
Awards available under the 2018 Equity Incentive Plan		605,524		1,039,531
Employee stock purchase plan		811,094		612,529
Total		6,622,710		4,195,805