Mirum Pharmaceuticals completes acquisition of Bluejay Therapeutics to advance rare liver disease treatment

USA—Mirum Pharmaceuticals has finalized its acquisition of Bluejay Therapeutics, marking a significant expansion of the company’s capabilities in addressing rare and severe liver diseases.

The transaction positions Mirum to potentially become a leader in treating chronic hepatitis delta virus (HDV), a rare condition that currently has no approved therapies available in the United States.

Understanding Hepatitis Delta Virus

HDV represents one of the most severe forms of viral hepatitis known to medical science.

The virus occurs as a coinfection in select individuals who already have hepatitis B virus, creating a particularly dangerous combination.

Medical research indicates that HDV drives rapid progression toward life-threatening complications, including liver cirrhosis, liver cancer, and liver-related mortality.

Approximately 230,000 people in the United States live with HDV, with another 230,000 cases documented across Europe.

The prognosis remains grim for many patients, as studies suggest that more than half of individuals diagnosed with HDV will die from liver-related causes within a decade of their diagnosis.

Brelovitug’s strategic value

Through this acquisition, Mirum gains worldwide rights to brelovitug, a monoclonal antibody that has advanced to Phase III clinical development.

The company originally announced the transaction in December 2025, valuing the deal at up to USD 820 million.

Brelovitug represents a fully human antibody currently undergoing rigorous evaluation in clinical trials designed to assess its effectiveness against HDV.

The drug candidate has already earned breakthrough therapy designation from the US Food and Drug Administration and prime designation from the European Medicines Agency, reflecting regulatory recognition of both the urgent medical need and the compound’s promising characteristics.

How Brelovitug works

Brelovitug functions as an investigational immunoglobulin G1 (IgG1) antibody that targets hepatitis B Surface Antigen (HBsAg) present on both hepatitis B virus and HDV.

The molecule demonstrates potent pan-genotypic activity, meaning it shows effectiveness against multiple genetic variations of the virus.

This broad activity profile enhances its potential value as a therapeutic option for diverse patient populations affected by HDV.

Financial structure and investment

Mirum acquired all outstanding shares of Bluejay Therapeutics through a combination of cash payments and Mirum common stock.

The agreement also includes potential tiered sales-based milestone payments that could bring the total transaction value to the full USD820 million figure.

To support the acquisition and subsequent development activities, Mirum simultaneously completed private placement financings with existing and new healthcare investors.

These financing rounds raised nearly USD268.5 million, which the company has allocated toward commercialization activities and continued clinical development of brelovitug for HDV treatment.

Mirum continues to evaluate strategic options for other pipeline programs previously owned by Bluejay.

Clinical development continues

Chris Peetz, chief executive officer of Mirum, emphasized that the company’s attention now turns to execution following the completed transaction.

The integration includes welcoming the talented Bluejay team into Mirum’s organization as they work to complete the AZURE Phase III program for HDV.

The AZURE global Phase III registrational program encompasses multiple open-label trials that assess both biochemical and virologic response endpoints.

These trials will support regulatory filings in Europe and the United States, with Mirum targeting a potential biologics license application submission and product launch in 2027.

Peetz noted that the program aligns perfectly with Mirum’s core strengths in rare disease management and builds upon the company’s established expertise in rare liver conditions.

He expressed confidence that Mirum’s global development capabilities and commercial synergies position the organization to deliver meaningful outcomes for patients living with HDV.