Complications of Reduced Intensity Conditioning HSCT for XIAP Deficiency (Alloimmune Cytopenias and HLH) Successfully Managed With Donor Lymphocyte Infusion.

X-linked inhibitor of apoptosis protein deficiency is a rare illness and although stem cell transplant is curative, full intensity conditioning is associated with high mortality rates. We describe a child with unusual complications associated with residual host lymphocytes following reduced intensity stem cell transplant. Recipient derived, donor directed, antigranulocyte antibodies led to life-threatening and prolonged neutropenia and residual recipient lymphocytes reestablished hemophagocytic lymphohistiocytosis after withdrawal of immune suppression despite high levels of whole blood chimerism.