20 SCID-X1 patients were successfully treated with autologous bone marrow CD34+ hematopoietic stem cells transduced ex-vivo with an MLV vector expressing the therapeutic gene IL2RG. 5 of these patients developed T cell leukemia and 4 possessed insertional mutations from the MLV vector at LMO2[24]–[28], a T cell oncogene [95]. Here, IL2RG is linked to T-cell leukemia.