For example, the patients with adenosine deaminase deficiency [46], Wiskott–Aldrich syndrome (WAS) [47] and X-linked severe combined immunodeficiency [48,49] were successfully treated in clinical trials by transplantation of autologous CD34+ cells retrovirally or lentivirally transduced with the wild-type gene. Here, CD34 is linked to Wiskott-Aldrich syndrome.