GSK has concluded the acquisition of efimosfermin alfa, an investigational therapeutic for serious liver disease (SLD), from Boston Pharmaceuticals in a $2bn deal.

The transaction includes an upfront payment of $1.2bn and potential milestone payments of $800m.

The acquisition, announced in May 2025, saw GSK purchase Boston Pharmaceuticals' subsidiary BP Asset IX.

This strategic move expands GSK's pipeline to include treatments for liver, lung and kidney conditions.

Efimosfermin, now in Phase III clinical development, is a once-monthly subcutaneous injection designed to treat and prevent the progression of SLD.

GSK respiratory, immunology and inflammation research and development senior vice-president and global head Kaivan Khavandi stated: “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.”

The new fibroblast growth factor 21 (FGF21) analog therapeutic targets metabolic dysfunction-associated steatohepatitis (MASH), including cirrhosis, and potentially alcohol-related liver disease (ALD). These conditions, which currently have limited treatment options, are leading causes of liver transplants in the US and pose a significant healthcare burden.

GSK's expertise in human genetics and disease phenotyping suggests that efimosfermin has the potential to treat advanced stages of SLD due to its direct antifibrotic mechanism.

The therapy may also be used in combination with GSK’990, an siRNA therapeutic under development for different patient subsets with SLD.

In June 2025, the US Food and Drug Administration approved GSK’s 200 mg/ml autoinjector of Benlysta for individuals aged five years and above with active lupus nephritis.