Boundless Bio and Serapha Bio announced that they have entered into a definitive merger agreement. Serapha Bio is a privately held biotechnology company developing an investigational in vivo base editing therapy for Alpha-1 Antitrypsin Deficiency.
Under the agreement, Serapha will combine with Boundless Bio in an all-stock merger.
After closing, the combined company plans to operate under the name Serapha Bio and is expected to trade on Nasdaq under the ticker symbol AATD.
Before the closing, Boundless Bio expects to declare a cash dividend to pre-merger Boundless stockholders.
In connection with the merger, Serapha has secured commitments for pre-closing private investments of about $230 million.
The private placement is co-led by RA Capital Management and RTW Investments.
Additional participating investors include Janus Henderson Investors, Decheng Capital, Vivo Capital, Casdin Capital, LifeSci Venture Partners, Logos Capital, Balyasny Asset Management, and Eventide Asset Management.
Of the $230 million private placement, about $138 million has already been funded through a Series A financing. The remaining $92 million is expected to close substantially concurrently with the merger, subject to customary closing conditions.
The combined company’s cash and cash equivalents at closing, including proceeds from the private placement, are expected to fund operations into the second half of 2029.
The financing is expected to provide runway through Phase 2 completion and Phase 3 initiation for SERP-01.
The combined company will focus on Serapha’s lead clinical-stage candidate, SERP-01, for the treatment of severe Alpha-1 Antitrypsin Deficiency.
SERP-01 is an investigational in vivo base editing therapy designed to correct the SERPINA1 E342K mutation at its source.
Serapha said the therapy has the potential to address both the liver and lung manifestations of the disease with a single administration by restoring functional M-AAT production while reducing toxic Z-AAT.
Serapha licensed SERP-01, developed as YOLT-202 in Greater China, from YolTech Therapeutics in June 2026.
Under the license agreement, YolTech received an upfront cash payment and a minority equity stake in Serapha. YolTech is also eligible to receive regulatory and commercial milestones totaling more than $2 billion, along with tiered royalties on net sales of SERP-01.
YolTech is enrolling Alpha-1 Antitrypsin Deficiency patients in an Investigator-Initiated Trial at Renji Hospital in Shanghai and retains development and commercialization rights for Greater China.
Alpha-1 Antitrypsin Deficiency is a hereditary disorder most commonly caused by the SERPINA1 E342K point mutation. This mutation causes the liver to produce a misfolded form of AAT known as Z-AAT instead of normal M-AAT.
The accumulation of Z-AAT polymers in the liver can lead to hepatitis, fibrosis, and cirrhosis. Reduced levels of functional AAT in circulation can also leave the lungs vulnerable to progressive emphysema and COPD.
There are estimated to be up to 100,000 people with the severe PiZZ genotype in the United States.
Current treatment options are limited to supportive care, liver transplantation for end-stage disease, and weekly intravenous augmentation therapy, which does not address the underlying liver pathology.
Under the terms of the merger agreement, pre-merger Boundless Bio stockholders are expected to own about 3.7% of the combined company. Pre-merger Serapha stockholders, including investors participating in the pre-closing financings, are expected to own about 96.3%.
Boundless Bio expects to distribute excess net cash of approximately $44 million to $48 million to pre-merger Boundless stockholders through the expected cash dividend, subject to adjustment.
The transaction has been unanimously approved by the Boards of Directors of both companies.
The merger is expected to close in the fourth quarter of 2026, subject to closing conditions including shareholder approvals, Nasdaq listing approval, effectiveness of a registration statement, applicable Hart-Scott-Rodino clearance, and other customary conditions.
Lucid Capital Markets is serving as exclusive financial advisor to Boundless Bio, and Latham & Watkins is serving as legal counsel.
Wedbush Securities is serving as exclusive financial advisor to Serapha, while Gibson Dunn and Goodwin Procter are serving as legal counsel.
KEY QUOTES:
“This transaction provides Serapha with the public-market platform and capital to advance SERP-01 through a U.S. clinical program with conviction. 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 in patients with the most severe form of this disease.”
Roderick Wong, MD, Managing Partner and Chief Investment Officer at RTW Investments
“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 – and many more around the world – who suffer from the life-threatening effects of severe AATD. Serapha will hit the ground running with company building support from RTW Investments and RA Capital, including RA Capital’s Blackbird clinical development accelerator.”
Rajeev Shah, Managing Partner at RA Capital
“Since our founding, Boundless has pioneered a novel approach rooted in extrachromosomal DNA biology to attempt to treat some of the most aggressive and difficult cancers. While we’ve deepened our understanding of ecDNA’s foundational role in certain cancers, the early clinical data for BBI-940 did not support continuing to advance this program. I am incredibly proud of our Boundless Bio team and their rigorous advancement of our novel science over the past seven years. 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
