Clinical course of XIAP-deficient patient with active HLH treated with antibody-based minimal-intensity conditioned stem cell transplant. Time course of conditioning, immunosuppression, neutrophil engraftment, donor chimerism, fevers, and significant complications during the first 140 days following stem cell transplant are shown. Total doses of conditioning drugs were as follows: alemtuzumab, 1 mg/kg; fludarabine, 150 mg/m²; cyclophosphamide, 1 g/m²; anti-CD45 monoclonal antibodies, 1600 µg/kg each of YTH24/54 antibodies; and etoposide, 150 mg/m². AV, adenoviremia requiring treatment with cidofovir; HSV, herpes simplex virus stomatitis and viremia; mAbs, monoclonal antibodies; PO, pulmonary edema as part of a capillary leak syndrome requiring ventilatory support; Sk2, grade 2 skin graft-versus-host disease treated by increased prednisolone dose; syn, syndrome.