CD34 and acute lymphoblastic leukemia: First, LMO2 ectopic activation caused by retroviral insertion in the CD34+ HSCs of X‐SCID patients specifically triggered T‐ALL development, but no other hematopoietic tumors (Hacein‐Bey‐Abina et al, 2008; Howe et al, 2008), although it is considered that LMO2 expression in BM progenitors is not relevant per se (Ruggero et al, 2016).