GSK has finalised the previously announced acquisition of efimosfermin alfa, an investigational therapy targeting metabolic dysfunction-associated steatohepatitis (MASH), from Boston Pharmaceuticals.

Announced in May 2025, the deal is worth up to $2bn. It involves an upfront payment of $1.2bn, with up to $800m tied to future performance milestones.

This acquisition involved BP Asset IX, a subsidiary of Boston Pharmaceuticals, granting GSK access to the investigational medicine.

Efimosfermin is currently in phase III development as a monthly subcutaneous treatment for MASH, which is an advanced form of steatotic liver disease (SLD).

According to GSK, the investigational therapy also holds potential for tackling alcohol-related liver disease (ALD). Both conditions are significant contributors to liver transplant demand in the US due to limited treatment options.

GSK respiratory, immunology and inflammation research and development senior vice president and global head Kaivan Khavandi said: “The close of our acquisition for efimosfermin alfa represents a significant expansion of our hepatology pipeline aimed at addressing steatotic and viral drivers of liver disease.

“Efimosfermin is a key growth opportunity for GSK with multiple development options and potential first launch in 2029. We look forward to unlocking the potential of this medicine for patients.”

Data from a Phase II trial indicated that efimosfermin effectively reverses liver fibrosis and inhibits its progression, demonstrating manageable tolerability.

Findings suggest enhanced efficacy over existing therapies and potential benefits in triglyceride reduction and glycaemic control. These features are crucial for MASH patients, who often experience cardiometabolic comorbidities.

This once-monthly fibroblast growth factor 21 (FGF21) analogue aims to regulate metabolic pathways, reducing liver fat and inflammation while reversing fibrosis. Efimosfermin’s low immunogenicity and extended half-life could improve patient adherence by facilitating monthly dosing.

GSK intends to leverage efimosfermin’s antifibrotic mechanism as part of its broader strategy to combat advanced stages of SLD. Additionally, the company sees potential combinations with its siRNA therapeutic, GSK’990, for varied patient subsets.

This acquisition enhances GSK’s portfolio focused on fibroinflammatory diseases across liver, lung, and kidney domains.