Emapalumab, sold under the brand name Gamifant, is an anti-interferon-gamma (IFNγ) antibody medication used for the treatment of hemophagocytic lymphohistiocytosis (HLH), which has no cure.

The most common side effects include infections, hypertension, infusion-related reactions, and pyrexia.

The U.S. Food and Drug Administration (FDA) considers it to be a first-in-class medication.

In June 2025, the U.S. Food and Drug Administration (FDA) approved emapalumab-lzsg for the treatment of macrophage activation syndrome (MAS) in patients with Still’s disease.

Emapalumab is used to treat primary hemophagocytic lymphohistiocytosis (HLH) with refractory, recurrent or progressive disease or intolerance with conventional HLH therapy.

In the clinical trials that lead to emapalumab's FDA approval, the most commonly reported adverse effects were infections (56%), high blood pressure (41%), infusion reactions (27%), and fever (24%). Serious adverse effects occurred in about half of the subjects studied in the clinical trial that led to its FDA approval.

In the setting of HLH, over-secretion of IFN-γ is thought to contribute to the pathogenesis of the disease. Emapalumab binds and neutralizes IFN-γ, preventing it from inducing pathological effects.

Like other antibody-based medications, which are made of amino acid chains called polypeptides, emapalumab is broken down into smaller peptides via the body's normal catabolism.