Recently, genetically modified HSCT, termed HSCGT (Hematopoietic Stem Cell - Gene Therapy) has been used successfully to treat metachromatic leukodystrophy patients (MLD) (Biffi et al., 2013; Lorioli and Biffi, 2015) who re-introduced the patients’ own CD34+cells with lentivirus-transfected cells, overexpressing arylsulfatase A (ARSA). The gene discussed is CD34; the disease is metachromatic leukodystrophy.