Srivastava et al. [41] showed that CD34+ hematopoietic stem cells transduced with LVs carrying a codon-optimized FVIII gene yielded sustained expression in patients with hemophilia A. Similarly, Hu et al. [55] reported the successful preclinical application of SIV-LVs encoding IL2RG for X-linked severe combined immunodeficiency (X-SCID), confirming both efficacy and biosafety. This evidence concerns the gene CD34 and severe combined immunodeficiency.