On March 31, 2021, the Company filed a prospectus and prospectus supplement (the “2021 Prospectus”) under which the Company may offer and sell, from time to time, pursuant to an equity distribution agreement with Jeffries LLC, up to $75.0 million in shares of its common stock. During the six months ended June 30, 2021, no shares were sold under the 2021 Prospectus.

As of June 30, 2021, a total of 846,939 warrants were exercisable into common stock. The shares of common stock underlying the warrants are registered for offer and sale under the Securities Act of 1933, as amended (the “Securities Act”), pursuant to the Company’s effective registration statements on Form S-1.

	Rollforward of Warrant Activity
	Registered direct warrants, placement agent		Private placement warrants		Private placement warrants, placement agent		Warrants exchanged for common stock		Total
Balance as of December 31, 2020		9,581		319,064		9,177		—		337,822
Issued		—		—		—		509,117		509,117
Exercised		—		—		—		—		—
Cancelled/Expired		—		—		—		—		—
Balance as of June 30, 2021		9,581		319,064		9,177		509,117		846,939

As of June 30, 2021, 55,853.875 warrants were exercisable into Series X¹ Preferred Stock. Each share of Series X¹ Preferred Stock is convertible into approximately 55.5556 shares of common stock.

	Rollforward of Warrant Activity
		Warrants assumed and replaced in acquisition		Total
Balance as of December 31, 2020			55,583.875		55,583.875
Assumed and replaced			—		—
Exercised			—		—
Cancelled/Expired			—		—
Balance as of June 30, 2021			55,583.875		55,583.875

On December 31, 2020, the Company entered into an exchange agreement (the “Series X Exchange Agreement”) with Biotechnology Value Fund, L.P., Biotechnology Value Fund II, L.P., Biotechnology Value Trading Fund OS, L.P. , MSI BVF SPV, L.L.C. (collectively, the “BVF Exchanging Stockholders”) and Cormorant Global Healthcare Master Fund, LP (together with the BVF Exchanging Stockholders, the “Series X Exchanging Stockholders”), pursuant to which the Series X Exchanging Stockholders exchanged (the “Series X Exchange”) 344,666 shares of the Company’s common stock for 6,203.98 shares of Series X Convertible Preferred Stock.

In addition, on December 31, 2020 the Company entered into an exchange agreement (the “Warrant Exchange Agreement,” and together with the Series X Exchange Agreement, the “Exchange Agreements”) with the BVF Exchanging Stockholders, pursuant to which the BVF Exchanging Stockholders exchanged (the “Warrant Exchange,” and together with the Series X Exchange, “the Exchanges”) 509,117 shares of the Common Stock for one or more pre-funded warrants to purchase an aggregate of 509,117 shares of the Common Stock at a nominal exercise price (the “Warrants”).

The Company recorded the shares of Series X Convertible Preferred Stock and Warrants issuable as preferred stock and warrant subscriptions at December 31, 2020 since the physical settlement of the Exchanges was made on January 5, 2021, whereby the transfer agent recorded the exchange of common stock for the issuance of preferred stock and warrants.

Following the Exchanges, the Company had 6,203.98 shares of Series X Preferred Stock outstanding, which are convertible into 344,663 shares of Common Stock (after rounding for fractional shares).

As of June 30, 2021, a total of 509,117 warrants were available for exercise. The shares of common stock underlying the registered direct placement agent warrants are registered for offer and sale under the Securities Act, pursuant to the Company’s effective registration statements on Form S-1.

Total stock-based compensation expense was recognized in our condensed consolidated statements of operations and comprehensive loss as follows (in thousands):

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
	2021		2020		2021		2020
Research and development	$	785	$	49	$	1,470	$	203
General and administrative		1,249		148		2,338		431
Total stock-based compensation	$	2,034	$	197	$	3,808	$	634