Real-World Treatment Patterns and Outcomes in Patients with Hemophagocytic Lymphohistiocytosis (HLH) and Other Clinical Conditions Treated with Emapalumab: The Real-HLH Study Design

Introduction: Hemophagocytic lymphohistiocytosis (HLH) is a rare, life-threatening hyperinflammatory syndrome characterized by overactivation of the immune system due to systemic release of proinflammatory cytokines, especially of interferon gamma (IFNγ), and persistent activation of macrophages/histiocytes and T cells. Emapalumab, a fully human, anti-IFNγ monoclonal antibody that binds to both free and receptor-bound IFNy, neutralizing its biologic activity, was approved by the Food and Drug Administration (FDA) in 2018 for the treatment of adult and pediatric patients with primary HLH with refractory, recurrent or progressive disease or intolerance with conventional HLH therapy. The safety and efficacy of emapalumab was based on results from a pivotal phase 2/3 trial which reported a 63% overall response in patients treated with emapalumab. Since approval, no study has evaluated the use of emapalumab in a larger cohort of patients in the real-world clinical setting.