806. Immunologic Improvement after Gene Therapy in 3 Preadolescents with X-Linked Severe Combined Immunodeficiency (XSCID)
Authors: Javier Chinen, Joie Davis, Suk-See de Ravin, Gilda Linton, Amy Hsu, B. Nora Naumann, Effie Nomicos, Christopher Silvin, Narda Theobald-Whiting, Jean Ulrick, Harry Malech, Jennifer Puck
Journal: Molecular Therapy (2006)

XSCID results from mutations in the IL2RG gene encoding the common gamma chain (γc) shared by several cytokine receptors. Gene therapy as primary treatment for XSCID infants can restore immunity, but 2 teenagers with XSCID did not benefit from gene transfer to autologous bone marrow CD34+ cells. We used retrovirally transduced autologous peripheral mobilized CD34+ cells to treat 3 XSCID preadolescents 10-14 years old with immunodeficiency despite haploidentical bone marrow transplants (BMT). After 6-24 m we found selective gene marking of T cells in all 3 patients, with variable evidence of immunologic improvement. Prior to gene therapy, they had growth failure, frequent infections, diarrhea, T lymphocytopenia, and poor T, NK and B cell function. Each received 30-40 million cells/kg transduced ex vivo with GALV-MFGS-γc. Patient 1 (P1) had a poly-A addition signal mutation allowing residual γc function and had rejected 4 BMTs. At 24 m post gene therapy P1 had provirus detected by quantitative PCR in 4.3% of T cells and 0.1% of both B and myeloid cells. In P2 proviral marking at 18 m was 110% (or average copy number of 1.1), 5% and 0.1% in T, B and myeloid cells, respectively. P3 at 6 m had 22% marking in T cells, with low levels in other leukocyte lineages. CD4+ T cell counts in all patients have increased, but remain below the normal range. P1 has experienced improvement in well-being and resolution of lifelong diarrhea, abdominal distention and rashes; he has not had infections except for an otitis externa 12 m after treatment. A 0.5 cm submandibular nodule consistent with a lymph node arose 6 m post gene therapy and has not changed. After gene therapy P2 has had less frequent diarrhea and respiratory infections. At 6 m post treatment his T cells developed normal proliferative responses to mitogens and Candida antigen. At 12 m, P2 acquired detectable CD4+CD45RA+ T cells and T cell receptor excision circles, indicating new thymic output; donor chimerism assay showed autologous T cell expansion from 49% before gene therapy to 87% at 12 m and beyond. P3 has also reported improved well-being, exercise tolerance and appetite at 6 m; he has had increases in T cell number and proliferative responses to mitogens. Analysis of retroviral insertion sites in P1 and P3 consistently showed polyclonality. T cells of P2 had an oligoclonal pattern by LAM-PCR, but linker-mediated PCR yielded a wide variety of insertions. Furthermore, both Vβ TCR usage and spectratyping showed increasing diversity after gene therapy. Proviral insertions near LMO2, implicated in European XSCID leukemia cases, have not been identified. Our preliminary results suggest that gene therapy may benefit some XSCID patients who have failed previous BMT treatment. Prior production of allogeneic T cells in P2 may have helped to preserve his thymic function. Further follow-up will establish long-term safety, efficacy and indications for XSCID gene therapy in preadolescent subjects with XSCID.