18. Related Party Transactions

Zenas BioPharma, Inc.

The Company considers Zenas to be a related party because (i) Tellus BioVentures LLC (“Tellus”), whose sole member is a significant shareholder in the Company and a member of the board of directors of the Company, is also a significant shareholder in Zenas and serves as Chief Executive Officer and Chairman of the board of directors of Zenas and (ii) Fairmount Healthcare Fund LP and Fairmount Healthcare Fund II LP (together, the “Fairmount Funds”), who are significant shareholders in the Company and whose investment manager is a member of the board of directors of the Company, are also significant shareholders in Zenas and have a seat on the board of directors of Zenas. As of December 31, 2024, Tellus and its affiliated entities and Fairmount Funds and its affiliated entities owned approximately 5% and 9% of the Company’s outstanding shares, respectively.

The Company was previously party to the Zenas Agreements, which were assigned to Zenas HK in October 2024. After the assignment, the Company entered into the Novation Agreement with Zenas HK and Tenacia, pursuant to which Tenacia replaced Zenas HK as a party to the Zenas Agreements. In connection with the Zenas Agreements, the Company recognized $5.9 million and $2.8 million of revenue from Zenas within the license revenue – related party line item in the consolidated statements of operations and comprehensive loss for the years ended December 31, 2024 and 2023, respectively. As of December 31, 2024, the Company recorded a related party receivable of $0.8 million on its consolidated balance sheet for activities related to Zenas. As of December 31, 2023, the Company recorded a related party receivable of $0.3 million, unbilled related party receivable of $0.2 million, current deferred related party revenue of $0.1 million and noncurrent deferred related party revenue of $0.7 million on its consolidated balance sheet for activities related to Zenas.

In September 2020, Zenas issued 156,848 common shares to the Company in exchange for the Zenas Option. Previously, the Company used the measurement alternative as the measurement attribute for accounting for the Zenas common stock which did not require it to assess the fair value of the common stock at each reporting period as the fair value of the Zenas common stock was not readily determinable nor was there a reliable source for observable transactions from which the Company could determine a fair value. On September 12, 2024, Zenas announced the pricing of its initial public offering (the “Zenas IPO”) of $17.00 per share, which also included a 1-for-8.6831 reverse stock split of its capital stock. Upon the Zenas IPO, the fair value of the Zenas common stock was deemed readily determinable. The Company reassesses the fair value of the investment at the end of each reporting period, with any adjustments to the fair value recorded as unrealized gains or losses within other income (loss) in the consolidated statements of operations and comprehensive loss. As of December 31, 2024, the fair value of the investment in Zenas was $0.1 million, which was included within other assets and restricted cash on the Company's consolidated balance sheet.

See Note 13 for more information on these agreements.

Fairmount Funds

On March 13, 2023, the Fairmount Funds issued promissory notes in the aggregate principal amount of $0.4 million to Former Dianthus at an interest rate of 4.5% per annum. On March 15, 2023, Former Dianthus repaid principal and interest in the amount of $0.4 million to the Fairmount Funds in satisfaction of its obligations under the promissory notes.