Serapha Bio launched Tuesday via a reverse merger with Boundless Bio, backed by $230 million in funding to advance SERP-01, an in vivo base editing therapy for Alpha-1 Antitrypsin Deficiency that has shown proof-of-concept data restoring serum AAT to normal levels.
Serapha Bio, a clinical-stage biotechnology company developing an in vivo base editing therapy for Alpha-1 Antitrypsin Deficiency, launched Tuesday through a reverse merger with Boundless Bio Inc. (Nasdaq: BOLD) backed by $230 million in concurrent private financing, the companies said.
The combined company will operate as Serapha Bio and trade on Nasdaq under the ticker "AATD," with a focus on advancing SERP-01, a one-time treatment designed to correct the SERPINA1 E342K mutation — the most common genetic cause of severe AATD. The mutation, known as PiZZ, causes the liver to produce misfolded Z-AAT protein instead of functional M-AAT, leading to toxic accumulation in the liver and leaving the lungs vulnerable to progressive emphysema.
"SERP-01 has a highly differentiated clinical profile, and, with this financing and merger agreement, Serapha is well positioned to deliver meaningful benefit for the up to 100,000 Americans who suffer from the life-threatening effects of severe AATD," Rajeev Shah, Managing Partner at RA Capital Management, said.
The financing was co-led by RTW Investments and RA Capital Management, with participation from Janus Henderson Investors, Decheng Capital, Vivo Capital, Casdin Capital, LifeSci Venture Partners, Logos Capital, Balyasny Asset Management, and Eventide Asset Management. Of the total, $138 million has already been funded as a Series A round, with the remaining $92 million expected to close concurrently with the merger, subject to customary conditions.
How the base editing therapy works
SERP-01 is an investigational in vivo base editing therapy designed to correct the single-point mutation in the SERPINA1 gene at its source. Unlike augmentation therapy — the current standard of care that requires weekly intravenous infusions of AAT protein and does not address liver pathology — SERP-01 aims to restore the liver's ability to produce functional M-AAT while reducing toxic Z-AAT accumulation with a single administration.
Serapha licensed the program from YolTech Therapeutics in June 2026 in exchange for an upfront cash payment and a minority equity stake. YolTech, which developed the therapy as YOLT-202 in Greater China, is eligible for regulatory and commercial milestones totaling more than $2 billion plus tiered royalties on net sales. The Chinese biotech has been enrolling AATD patients in an investigator-initiated trial at Renji Hospital in Shanghai and retains development and commercialization rights for Greater China.
Proof-of-concept data for SERP-01 demonstrated restoration of serum AAT to normal levels, according to the company. AATD affects up to 100,000 people in the US with the severe PiZZ genotype, and current treatment options are limited to supportive care, liver transplantation for end-stage disease, and weekly augmentation therapy that does not address the underlying liver damage.
Deal structure and cash runway
Under the merger agreement, pre-merger Boundless Bio stockholders are expected to own approximately 3.7% of the combined company, while pre-merger Serapha stockholders — including investors in the pre-closing financings — will own about 96.3%. Boundless Bio expects to declare a cash dividend of approximately $44 million to $48 million to its pre-merger stockholders before closing.
The combined company's cash position is expected to fund operations into the second half of 2029, providing runway through Phase 2 completion and Phase 3 initiation for SERP-01. The merger is expected to close in the fourth quarter of 2026, subject to stockholder approvals, Nasdaq listing approval, SEC registration statement effectiveness, and other customary conditions.
Boundless Bio, founded in 2019, had been developing therapies targeting extrachromosomal DNA in cancer but discontinued its lead program BBI-940 after early clinical data did not support continued advancement. "We believe this transaction represents a strong opportunity to deliver meaningful value for our stakeholders, while providing Serapha with a public-market platform to advance novel therapies for people with rare diseases," Zachary Hornby, President and CEO of Boundless Bio, said.
"This transaction provides Serapha with the public-market platform and capital to advance SERP-01 through a US clinical program with conviction," Roderick Wong, MD, Managing Partner and Chief Investment Officer at RTW Investments, said. "The early clinical data generated with SERP-01 give us confidence that this is a potentially best-in-class base editing therapy that can restore AAT to physiologic levels."
Lucid Capital Markets served as exclusive financial advisor to Boundless Bio, with Latham & Watkins LLP as legal counsel. Wedbush Securities Inc. served as exclusive financial advisor to Serapha, with Gibson, Dunn & Crutcher LLP and Goodwin Procter LLP as legal counsel.
For investors, the deal creates a well-capitalized public biotech with a clear path to clinical data. The $230 million financing — one of the larger private placements in the gene editing space this year — provides Serapha with the resources to generate proof-of-concept data in US patients. The company's focus on a single, well-validated genetic target with a large addressable population reduces some of the binary risk typical of early-stage biotech, though clinical data from the US program will determine whether SERP-01 can replicate the preclinical results in a broader patient population.
This article is for informational purposes only and does not constitute investment advice.
