3. CASH, CASH EQUIVALENTS, AND RESTRICTED CASH

The Company considers only those investments which are highly liquid, readily convertible to cash, and that mature within 90 days from the date of purchase to be cash equivalents. At June 30, 2024 and December 31, 2023, cash equivalents were comprised of money market funds and corporate debt securities with maturities less than 90 days from the date of purchase.

Restricted cash as of June 30, 2024 included security for a stand-by letter of credit issued in favor of a landlord for $0.7 million of which $0.3 million was classified in current assets and $0.4 million was classified in noncurrent assets as of June 30, 2024.

As of June 30, 2024, the Company’s cash and cash equivalents held in the U.S. was approximately $19.4 million and approximately $4.3 million of cash was held in its subsidiaries in the United Kingdom and Australia. As of December 31, 2023, all of the Company’s cash was held in the U.S., except for approximately $3.8 million of cash which was held in its subsidiaries in the United Kingdom and Australia.

Our foreign subsidiaries in the United Kingdom and Australia may qualify for refundable research and development tax credits in the form of cash that were earned on certain research and development expenses incurred primarily outside of the U.S. The Company received no refundable research and development credits from foreign tax authorities for the three months ended June 30, 2024 and 2023 and $2.5 million for the six months ended June 30, 2024 recorded in other income (expense), net. No future conditions impact the recognition of these tax credits.