The first successful attempt of gene therapy using autologous HSCT was performed using gamma retroviral vectors (RVs) in X-linked severe combined immunodeficiency (SCID-X1) and adenosine deaminase deficiency (ADA-SCID) (Bordignon et al., 1995; Cavazzana-Calvo et al., 2000). The gene discussed is ADA; the disease is hyperinsulinemic hypoglycemia, familial, 4.