Study to Investigate the Pharmacokinetics, Pharmacodynamics and Assess the Efficacy and Safety to Support Dose Selection of Emapalumab in Pre-empting Graft Failure in Patients at High Risk After HSCT.

"Emapalumab is a fully human immunoglobulin G1 (IgG1) anti-IFNγ monoclonal antibody that binds to and neutralizes IFNγ. Emapalumab binds to both soluble and receptor (IFNγR1)-bound forms of IFNγ.~Emapalumab is in development for treatment of primary and secondary HLH. The benefit expected from the targeted neutralization of IFNγ by emapalumab has been validated by the recent FDA approval of emapalumab for treatment of patients with pHLH who have refractory, recurrent or progressive disease or intolerance with conventional HLH therapy. The safety profile has been assessed as acceptable.~Emapalumab will be administered by intravenous infusion over 1 to 2 hours, depending on the volume of the infusion. The first infusion must be performed within 12 hours after CXCL9 levels have been measured above defined threshold. Treatment will last until maximum dose 15 (up to 56 days) or until evidence of engraftment, whichever comes first."