Human SH2D1A mutations resulting in X-linked lymphoproliferative syndrome type 1 (XLP1) are associated with a unique susceptibility to the Epstein-Barr virus (EBV), which may lead to fatal infectious mononucleosis (FIM). Many studies have attempted to elucidate an appropriate treatment for XLP1 that does not involve hematopoietic stem cell transplantation (HSCT); clinical evidence supporting such treatments has been minimal, until now.