ADA and T-B+ severe combined immunodeficiency due to gamma chain deficiency: Gene therapy for X-linked SCID (X-SCID) with LV or retroviral SIN vectors has been shown to be successful and to lack the xenotoxicity problems previously observed when using γ-retroviral vectors.38, 39, 40 For ADA-SCID, both retroviral vectors (currently marketed as approved therapy under the name Strimvelis) and LV vectors have shown excellent clinical results that are comparable to HSCT with matched donors.10