HSC-based gene therapy is gaining traction with a number of clinical trials targeting different conditions (X-SCID, ADA-SCID, ALD, CGD, Fanconi anemia, β-thalassemia) showing encouraging results [2], [3], [6], [27]-[30] and which have implications for curative lifelong treatment. The gene discussed is ADA; the disease is chronic granulomatous disease.