Abbreviations: allo-HSCT, allogeneic hematopoietic stem cell transplantation; CD, cluster of differentiation; CTL, cytotoxic T cell; EBV, Epstein-Barr virus; Hgb, hemoglobin; NK, natural killer cell; pHLH, primary hemophagocytic lymphohistiocytosis; WBC, white blood cell; XIAP, X-linked inhibitor of apoptosis protein; XLP-2, X-linked lymphoproliferative disease 2.Abstract XLP-2 is known as a rare primary immunodeficiency disease, which is characterized by the susceptibility to EBV infection and potential development into the pHLH. The existing studies believe that the dysfunction of XIAP represents one of the most significant pathogenic mechanisms of XLP-2, and allo-HSCT is regarded as a crucial treatment for the long-term survival in XLP-2 patients. In our present study, a 2-year-