65. Long-Term Effects of Hematopoietic Stem Cell Gene Therapy in the Murine Model of Wiskott-Aldrich Syndrome: Persistence of Functional Correction of T Cells and Lack of Malignant Trasformation

Wiskott-Aldrich syndrome (WAS) is a severe X-linked immunodeficiency characterized by recurrent infections, thrombocytopenia, eczema and increased risk of autoimmune disorders and lymphomas. Hematopoietic stem cell (HSC) transplantation from HLA-identical sibling donors is a resolutive treatment, but it is available only for a minority of patients. Transplantation of genetically corrected autologous HSC could represent an alternative treatment, potentially applicable to all patients. In a murine model of WAS (WAS|[minus]|/|[minus]|), we recently demonstrated correction of the T cell defect 4 months after lentiviral vector-mediated gene therapy [Dupr|[eacute]|, Marangoni, et al. Hum Gene Ther. 2006, 17]. The aim of the present study was to investigate the long-term efficacy and safety of our gene therapy approach in WAS|[minus]|/|[minus]| mice

IL-3 or IL-7 Increases ex Vivo Gene Transfer Efficiency in ADA-SCID BM CD34 + Cells while Maintaining in Vivo Lymphoid Potential

To improve maintenance and gene transfer of human lymphoid progenitors for clinical use in gene therapy of adenosine deaminase (ADA)-deficient SCID we investigated several gene transfer protocols using various stem cell-enriched sources. The lymphoid differentiation potential was measured by an in vitro clonal assay for B/NK cells and in the in vivo SCID-hu mouse model. Ex vivo culture with the cytokines TPO, FLT3-ligand, and SCF (T/F/S) plus IL-3 or IL-7 substantially increased the yield of transduced bone marrow (BM) CD34+ cells purified from ADA-SCID patients or healthy donors, compared to T/F/S alone. Moreover, the use of IL-3 or IL-7 significantly improved the maintenance of in vitro B cell progenitors from ADA-SCID BM cells and allowed the efficient transduction of B and NK cell progenitors. Under these optimized conditions transduced CD34+ cells were efficiently engrafted into SCID-hu mice and gave rise to B and T cell progeny, demonstrating the maintenance of in vivo lymphoid reconstitution capacity. The protocol based on the T/F/S + IL-3 combination was included in a gene therapy clinical trial for ADA-SCID, resulting in long-term engraftment of stem/progenitor cells. Remarkably, gene-corrected BM CD34+ cells obtained from one patient 4 and 11 months after gene therapy were capable of repopulating the lymphoid compartment of SCID-hu hosts