Phase I/II clinical trials with SIN-lentiviral vectors have been initiated for several PIDs (WAS, ADA-SCID, CGD) as well as for non-PID defects amenable to treatment by gene modified HSCs, including X-linked adrenoleukodystrophy (X-ALD), metachromatic leukodystrophy (MLD) and β-thalassaemia. Here, ADA is linked to severe combined immunodeficiency.