Lentiviral Gene Therapy With Low Dose Busulfan For Infants With X-Scid Results In The Development Of A Functional Normal Immune System: Interim Results Of An Ongoing Phase I/Ii Clinical Study

Early clinical studies of gene therapy for patients with X-linked Severe Combined Immunodeficiency (XSCID) only restored T cell immunity and carried a significant risk of iatrogenic leukemia. We developed a new gene therapy approach that utilizes a safety-modified lentiviral (LV) vector together with reduced exposure busulfan conditioning for newly diagnosed infants with XSCID (NCT01512888). Of the first enrolled 8 patients, 7 demonstrated robust reconstitution of T-, NK-, and B-cells with a median follow up of 16.4 months (range: 6.7 to 24.9 months; Mamcarz et al, N Engl J Med, 2019). Here we provide an update on our clinical study, which now includes 3 more patients (n=11 total), 8 months additional median follow-up (23.6 months; range: 1.5 to 33.9 months), more extensive analysis of T and B cell functional recovery, and detailed vector integration site studies.