Evidence for Efficacy and Safety of Lentiviral Mediated Gene Transfer in T Cells and CD34+ Cells from Wiskott-Aldrich Syndrome Patients.

Wiskott-Aldrich Syndrome (WAS) is an X-linked primary immunodeficiency characterized by eczema, recurrent infections, severe hemorrhages and lymphomas. Transplantation of hematopoietic stem cells from HLA-identical sibling donors is a resolutive treatment, but it is available only for a minority of patients. Therapy based on the transplant of genetically correct autologous stem cells could represent a valid alternative approach. We investigated the efficacy and the safety of WAS gene transfer using HIV-based lentiviral vector encoding for WAS cDNA under the control of an autologous promoter (1.6 kb). T cells obtained from WAS patients showed normal level of WAS expression after lentiviral transduction. Transduced T cells showed a correction in TCR-driven proliferation and IL-2 production. Furthermore, a selective growth advantage of transduced T cells was observed in long-term in vitro cultures. Studies in T cell clones generated from transduced WAS CD4+ T cells revealed that 1–2 vector copies were necessary and sufficient to correct T cells function. CD34+ cells, isolated from mobilized peripheral blood and bone marrow of healthy donors, were transduced using WASP or GFP-encoding lentiviral vectors. Cells were cultured in the presence of different cytokines to investigate if WAS gene transfer could have any effect on short and long-term differentiation (CFU-C, LTC-IC and B/NK assays). Transduction resulted in a comparable number of CFU-C and LTC-IC colonies and normal B and NK cells differentiation with respect to untransduced cells. Furthermore, transduction of CD34+ cells isolated from the bone marrow of a WAS patient was performed under optimized culture conditions. Lentiviral gene transfer led to restoration of WASP expression in differentiated cells with copy number ranging from 1 to 5 copies per cell. In conclusion, our data demonstrate that the WAS promoter/cDNA-containing lentiviral vector can efficiently transduce and restore WASP expression in CD34+ cells and T cells from WAS patients. Experiments in the Rag2−/−/γchain- murine model are ongoing to test the efficacy and safety of the WASP transduced CD34+ cells. Together, our studies provide a preclinical basis for the implementation of a gene therapy trial for WAS patients.