Surprisingly, although lymphoproliferative aberrations were also observed in the trials of HSC gene therapy for Wiskott–Aldrich syndrome (Braun et al., 2014) and for chronic granulomatous disease (CGD, Stein et al., 2010), no case of leukemic events for ADA-SCID in the context of clinical trials has been recorded, despite the fact that all the aforementioned indications employed oncoretroviral vectors. This evidence concerns the gene ADA and chronic granulomatous disease.