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Abstract: Patients with mutations in the UNC13D gene (coding for Munc13-4 protein) suffer from familial hemophagocytic lymphohistiocytosis type 3 (FHL3), a life-threatening immune and hyperinflammatory disorder. The only curative treatment is allogeneic hematopoietic stem cell (HSC) transplantation, although the posttreatment survival rate is not satisfactory. Here, we demonstrate the curative potential of UNC13D gene correction of HSCs in a murine model of FHL3. We generated a self-inactivating lentiviral vector, used it to complement HSCs from Unc13d-deficient (Jinx) mice, and transplanted the cells back into the irradiated Jinx recipients. This procedure led to complete reconstitution of the immune system (ie, to wild-type levels). The recipients were then challenged with lymphocytic choriomeningitis virus to induce hemophagocytic lymphohistiocytosis (HLH)–like manifestations. All the clinical and biological signs of HLH were significantly reduced in mice having undergone HSC UNC13D gene correction than in nontreated animals. This beneficial effect was evidenced by the correction of blood cytopenia, body weight gain, normalization of the body temperature, decreased serum interferon-γ level, recovery of liver damage, and decreased viral load. These improvements can be explained by the restoration of the CD8+ T lymphocytes' cytotoxic function (as demonstrated here in an in vitro degranulation assay). Overall, our results demonstrate the efficacy of HSC gene therapy in an FHL-like setting of immune dysregulation.