Emapalumab is a fully human immunoglobulin G1 monoclonal antibody directed 
against interferon-γ (IFN-γ), which in November 2018 received the first global 
approval for the treatment of pediatric and adult patients with primary 
hemophagocytic lymphohistiocytosis (HLH) with refractory, recurrent, or 
progressive disease or intolerance to HLH therapy. This review will highlight 
the pathophysiology of primary HLH, the therapeutic rationale for use of 
IFN-γ-targeting therapy, and potential limitations to its broader use in the 
treatment of HLH.