Boundless Bio (Nasdaq: BOLD) and privately held Serapha Bio have entered into a definitive merger agreement under which the two companies will combine in an all-stock transaction, according to a joint statement released June 23, 2026.

The combined company plans to operate under the Serapha Bio name and is expected to trade on Nasdaq under the ticker symbol "AATD." Under the merger terms, pre-merger Boundless Bio stockholders are expected to own approximately 3.7% of the combined company, while pre-merger Serapha stockholders are expected to own approximately 96.3%.

Prior to closing, Boundless Bio expects to declare a cash dividend to its existing stockholders of approximately $44 million to $48 million, subject to adjustment based on net cash at closing.

Concurrent with the merger announcement, Serapha has secured approximately $230 million in private placement commitments co-led by RTW Investments and RA Capital Management. Additional participants include Janus Henderson Investors, Decheng Capital, Vivo Capital, Casdin Capital, LifeSci Venture Partners, Logos Capital, Balyasny Asset Management, and Eventide Asset Management. Of the total, approximately $138 million has already been funded through a Series A financing, with the remaining $92 million expected to close alongside the merger.

The combined company's cash position at closing is expected to fund operations into the second half of 2029, covering Phase 2 completion and Phase 3 initiation for its lead candidate, SERP-01.

SERP-01 is an investigational in vivo base editing therapy targeting the SERPINA1 E342K mutation, which causes Alpha-1 Antitrypsin Deficiency (AATD). Serapha licensed SERP-01 from YolTech Therapeutics in June 2026, in exchange for an upfront cash payment and a minority equity stake. YolTech is eligible to receive regulatory and commercial milestones totaling over $2 billion and tiered royalties on net sales.

The transaction has received unanimous approval from the boards of both companies and is expected to close in the fourth quarter of 2026, subject to stockholder approval, Nasdaq listing approval, SEC registration effectiveness, and other customary conditions.