Mirum Agrees to Acquire Bluejay Therapeutics

Rare Daily Staff

Mirum Pharmaceuticals has entered into a definitive agreement to acquire Bluejay Therapeutics, a privately held biotechnology company focused on viral and liver diseases.

The acquisition is expected to strengthen Mirum’s leadership in rare diseases, build on its expertise in rare liver disorders, and add a fourth potential registrational readout for the company over the next 18 months.

The transaction would add worldwide rights to brelovitug, a late-stage, fully human monoclonal antibody with Breakthrough Therapy and PRIME designations for chronic hepatitis delta virus (HDV), to Mirum’s portfolio of rare liver programs.

Brelovitug is being evaluated in the AZURE phase 3 registrational program for HDV, the most severe form of viral hepatitis. HDV occurs in people already infected with hepatitis B. Nearly half of those affected progress to liver-related death within 10 years of diagnosis due to rapid progression to fibrosis, cirrhosis, hepatic decompensation, and an increased risk of liver cancer.

In phase 2 studies, brelovitug demonstrated strong antiviral activity in HDV, achieving 100 percent HDV RNA response, along with improvements in liver enzyme levels and a favorable safety profile. The most common adverse event was injection-site erythema.

Beyond brelovitug for HDV, Mirum will evaluate strategic options for Bluejay’s additional experimental programs after closing.

Mirum will acquire all Bluejay shares for $250 million in cash and $370 million in stock, plus up to $200 million in potential milestone payments. The Mirum common stock issued to Bluejay security holders at closing will be priced at $71.21 per share.

The transaction has been approved by the boards of directors of both companies and is expected to close in the first quarter of 2026, subject to regulatory approval and other customary closing conditions.

Mirum has also entered into a definitive agreement with a syndicate of existing and new healthcare investors for the sale of Mirum common stock and, to certain investors, pre-funded warrants in lieu of stock, in a private placement. The private placement is expected to close concurrently with the acquisition and result in gross proceeds to Mirum of approximately $200 million before deducting placement agent and other offering expenses. The proceeds are intended to fund clinical development and commercial activities following the proposed acquisition.

“This acquisition fits squarely with what we do best—advancing high-impact medicines for patients with rare diseases through disciplined development, regulatory innovation, and commercial excellence,” said Chris Peetz, CEO of Mirum Pharmaceuticals. “Brelovitug in HDV leverages our deep expertise in rare liver disease and builds on the relationships we’ve established with key providers through the volixibat and LIVMARLI programs. The Bluejay team has done commendable work advancing brelovitug to this stage, and we look forward to building on that progress to bring this important new treatment to people living with HDV.”