759. Reduction of HLH-like Manifestations in Murine Model of Munc13-4 Deficiency Following Lentiviral Gene Transfer into Hematopoietic Stem and Progenitor Cells

Abstract

Patients with mutations in UNC13D gene, coding for Munc13-4 protein, suffer from type 3 Familial hemophagocytic lymphohistiocytosis (FHL3), a life-threatening disorder of the immune system which represents 25% of all FHLs. Munc13-4 controls docking of lytic granules before they fused with the plasma membrane in cytotoxic T and NK lymphocytes and it's defect results in defective cytotoxic function of these cells. Hematopoietic stem and progenitor cell (HSPC) transplantation, which is the only curative treatment for FHL3 to date, is partially successful even when a compatible donor is available because of the important inflammatory background of patients. In this context gene therapy could be a promising therapeutic option especially for those patients without any compatible donor. In this study, we took advantages from a murine model of FHL3, the Jinx mice, to investigate the feasibility of HSPC gene therapy for this pathology. Jinx mice do not spontaneously develop clinical features of hemophagocytic lymphohistiocytosis (HLH), but do so when infected with lymphocytic choriomeningitis virus (LCMV). We generated and used a self-inactivated lentiviral vector to complement HSC from Unc13d -/- (Jinx) mice and transplanted them back into the irradiated Jinx recipients. This transplantation led to the complete reconstitution of the immune system at levels comparable to that of control mice. The recipients were then challenged with LCMV. While Jinx mice reconstituted with GFP expressing HSPC developed leukopenia, anemia and body weight loss, characteristic of HLH in this murine model, gene corrected Jinx recipients developed only mild or no HLH manifestations. This reduction in HLH manifestation correlated with a significant reduction of virus titer in the liver and serum level of IFN-g and inflammatory cytokines. All these ameliorations might be explained by the restoration of cytotoxic function of CTLs as demonstrated in an in-vitro degranulation assay. Overall, this study provides data supporting the potential of HSC gene therapy in a FHL immune dysregulation such as UNC13D deficiency.