349. Partial Correction of IL-12 Receptor beta-1 (IL-12Rb1) Deficiency in Mice upon Transplantation of Retrovirally Transduced Hematopoietic Stem Cells

Patients carrying genetic defects in the IL-12 signaling pathway (IL-12 p40 or IL-12Rb1) show defective immunity against intracellular pathogens, resulting in increased vulnerability to weakly pathogenic strains of Mycobacteria and Salmonella. Despite early diagnosis and treatment with antibiotics and IFN-g, IL12Rb1-deficient patients can still succumb to complications of serious infections. Reversion of patients' susceptibility by corrective gene transfer could be beneficial by preventing the infectious episodes. We showed that gene transfer of IL-12Rb1 chain in PHA-activated T cells blasts of IL-12Rb1 deficient patients through retroviral-mediated transduction restored the expression of the receptor chain and reconstituted IL-12 signaling, as demonstrated by STAT4 phosphorylation and IFN-g production._In addition, to test the feasibility and safety of retroviral-mediated gene correction in vivo, we established a murine model of gene therapy in IL-12Rb1-deficient mice. Treated mice did not show adverse effects upon gene therapy. Transplantation of gene-corrected hematopoietic stem cells resulted in IL-12Rb1 expression in PBMCs, thymocytes and SP cells of IL-12Rb1 KO mice. In addition, splenocytes isolated from gene-corrected IL-12Rb1 KO mice acquired the ability to respond to IL-12, as demonstrated by the production of IFN-g, which is completely impaired in IL-12Rb1 KO mice. However, restoration of IL-12Rb1 membrane expression as well as the production of IFN-g in response to IL-12 where significantly lower than those detected in wild type control mice. Interestingly, we couldn't detect in the periphery of gene corrected mice the presence of cells expressing high levels of IL-12Rb1 chain, comparable to those detected in their thymuses. These data indicate the possibility of a selective elimination of potentially dangerous IL-12Rb1 high expressing cells in the periphery that prevented the achievement of a complete correction of gene therapy treated mice. In addition, production of IFN-g upon challenge with LPS from Salmonella enteriditis provided in vivo evidence of partial correction of IL-12 signaling pathway in IL-12Rb1 KO mice after gene therapy. We are performing experiments of infections with intracellular pathogens, such as Mycobacterium tuberculosis, to establish if the degree of gene correction reached in our experimental model is sufficient to overcome their immunodeficiency