ADA and T-B+ severe combined immunodeficiency due to gamma chain deficiency: Currently, the use of self-inactivating lentiviral vectors has shown good promise as a safe and effective platform for HSC gene therapy, as demonstrated in clinical trials for X-linked SCID, adenosine deaminase (ADA)-deficient SCID, Fanconi anemia (FA), CGD and WAS (21–25).