Hematopoietic Stem Cell Transplantation for XIAP Deficiency in Japan

X-linked inhibitor of apoptosis protein (XIAP) deficiency is a rare immunodeficiency that is characterized by recurrent hemophagocytic lymphohistiocytosis (HLH) and splenomegaly and sometimes associated with refractory inflammatory bowel disease (IBD). Although hematopoietic stem cell transplantation (HSCT) is the only curative therapy, the outcomes of HSCT for XIAP deficiency remain unsatisfactory compared with those for SLAM-associated protein deficiency and familial HLH. To investigate the outcomes and adverse events of HSCT for patients with XIAP deficiency, a national survey was conducted. A spreadsheet questionnaire was sent to physicians who had provided HSCT treatment for patients with XIAP deficiency in Japan. Up to the end of September 2016, 10 patients with XIAP deficiency had undergone HSCT in Japan, 9 of whom (90%) had survived. All surviving patients had received a fludarabine-based reduced intensity conditioning (RIC) regimen. Although 5 patients developed post-HSCT HLH, 4 of them survived after etoposide administration. In addition, the IBD associated with XIAP deficiency improved remarkably after HSCT in all affected cases. The RIC regimen and HLH control might be important factors for successful HSCT outcomes, with improved IBD, in patients with XIAP deficiency.