370. Potent In Vivo Inhibition of HIV-1 Infection in Thy/Liv-SCID-Hu Mice after In Vivo Treatment with a Combination of SV40-Derived Vectors Targeting CCR5 Expression

Abstract

The efficacy of gene therapy using constructs that downregulate the expression of CCR5, the cellular coreceptor necessary for infection by the majority of primary HIV-1 isolates, to protect cells from in vivo HIV-1 infection was examined using an SV40 virus-vector gene delivery system that efficiently tranduces human leukocytes combined with an HIV-1-infectible thy/liv-SCID-hu mouse model. Three different SV40-derived vectors expressing a single chain antibody, (2C7), a ribozyme (VcKA1), or a small interfering RNA (siRNA) duplex (RNAi5) specific for CCR5 were used. After the SV40 vectors were injected into the human thymic grafts of thy/liv-SCID-hu mice, the thymic implants were challenged by injection with HIV-1 JR-CSF. Two weeks later, the number of HIV-1-infected thymocytes in the thymic grafts was determined by limiting dilution coculture to quantify HIV-1 infection in the human thymic grafts. The data combined from three separate experiments performed according to this protocol demonstrated that the number of HIV-1-infected thymocytes in the thymic grafts of thy/liv-SCID-hu mice (n = 10 mice) injected with the combination of SV(2C7), SV(VcKA1), and SV(RNAi5), 81 ± 18 TCID/106 thymocytes, was significantly lower (p = 0.000011) than that of the thymic grafts of thy/liv-SCID-hu mice (n = 10 mice) injected with the control rSV40 vector, SV(HBS), 2,375 ± 382 TCID/106 thymocytes. HIV-1 infection of the human thymic implants was inhibited more effectively by treatment with the combination of the three vectors than by treatment with SV(2C7) or SV(RNAi5) alone. Analysis of thymocytes for populations single or double positive for CD4 and CD8 indicated that thymopoiesis in the human thymic graft was not affected by transduction with the SV(2C7), SV(VcKA1), and SV(RNAi5) vectors. Thus, these findings demonstrate the in vivo efficacy of HIV-1-specific gene therapy delivered by SV40-based vectors targeting expression of CCR5.