Other gene therapies are being investigated for treatment of X-linked SCID, hyper IgM syndrome, chronic granulomatous disease, and X-linked agammaglobulinemia. T-cell gene therapy (CAR-T) is also being studied to correct T cell-intrinsic defects in IPEX syndrome, hyper IgM syndrome, X-linked lymphoproliferative disease, Munc 13 - 4 deficiency, and perforin deficiency (4).