Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory disorder driven by interferon-gamma (IFN-γ). Emapalumab, an anti-IFN-γ antibody, is approved for the treatment of patients with primary HLH. Hematopoietic stem cell transplantation (HSCT) is required for cure of HLH. Reduced intensity conditioning (RIC) HSCT is associated with improved survival but higher incidences of mixed chimerism and secondary graft failure. To understand the potential impact of emapalumab on post-HSCT …