FDA Approves Gamifant for Treating Macrophage Activation Syndrome in Still's Disease

On June 28, 2025, Sobi® announced that its drug Gamifant® (emapalumab-lzsg) has gained approval from the U.S. Food and Drug Administration (FDA) for treating a severe medical condition known as macrophage activation syndrome (MAS), which is associated with Still's disease. This condition affects both adults and children, including newborns, and is characterized by an inadequate response to traditional treatments like glucocorticoids or recurrent MAS episodes.

Gamifant, already established in treating primary hemophagocytic lymphohistiocytosis (HLH), offers a new therapeutic option for MAS patients, providing hope for improved management of this life-threatening complication. MAS is noted for severe hyperinflammation that can lead to multi-organ failure if not managed effectively. The drug's approval stems from the pooled results of two pivotal studies, EMERALD and NI-0501-06, demonstrating significant efficacy in controlling the disease. In one of the studies, 54% of patients achieved a complete response by the eighth week, with 82% showing clinical MAS remission.

The safety profile of Gamifant was consistent with previous clinical findings, with the most common adverse events being viral infections and rashes. Dr. Alexei A. Grom, a professor of pediatrics, highlighted the importance of this approval, as MAS poses significant challenges in both pediatric and adult patients. With Gamifant, there is now a viable treatment that can reduce reliance on high-dose glucocorticoids, which have been the primary approach until now.

Gamifant functions as an interferon gamma (IFNγ)–blocking antibody, targeting the underlying hyperinflammation driving MAS and HLH. This drug is the first FDA-approved treatment specifically for this condition, and it works by neutralizing the effects of IFNγ, which, when uncontrolled, can cause damaging inflammation throughout the body.

HLH/MAS is a rare systemic disorder often associated with rheumatic diseases like systemic juvenile idiopathic arthritis and adult-onset Still’s disease. It manifests in symptoms such as persistent high fever, elevated ferritin levels, and cytopenias, among others. The approval of Gamifant marks a significant advancement in the treatment of this challenging condition, providing a new avenue for patients who have not responded well to conventional therapies.

Sobi, the company behind Gamifant, is known for its focus on biopharmaceutical innovations that address rare diseases. With nearly 1,900 employees globally, Sobi continues to transform the lives of those affected by rare medical conditions through its commitment to breakthrough treatments. The company's share (STO:SOBI) is listed on Nasdaq Stockholm, and its revenue figures reflect its impactful presence in the biopharma industry.

The introduction of Gamifant into the treatment regime for MAS in Still's disease represents a promising development in the field of rare diseases. It offers a critical tool for clinicians and patients alike, aiming to enhance patient outcomes and reduce the reliance on traditional therapies that may not be effective in all cases. With this FDA approval, Gamifant is set to make a meaningful difference for those struggling with the serious implications of MAS.