Construction of a single-chain interleukin-12-expressing retroviral vector and its application in cytokine gene therapy against experimental coccidioidomycosis

T-cell-mediated immunity is an important determinant in protection against primary infection with Coccidioides immitis, a dimorphic fungal pathogen that causes the disease coccidioidomycosis. To determine if interleukin-12 (IL-12) gene therapy could potentiate host response against C. immitis, we constructed a single-chain cDNA encoding the p40 and p35 subunits linked by a polylinker and, using a retroviral vector, transfected J774 macrophages with the construct. The transduced J774 cells expressed IL-12 in vitro, with a mean concentration of 28,440 pg from 10⁶ cells in 48 h as measured by an IL-12 (p75)-specific enzyme-linked immunosorbent assay. The secreted IL-12 was biologically active, as judged by its ability to induce the production of gamma interferon (IFN-γ) by spleen cells from BALB/c mice. Treatment of the highly susceptible BALB/c mouse strain with the IL-12- transduced J774 cells inhibited C. immitis growth in tissues from mice challenged by a pulmonary route, as evidenced by 1.37-, 2.59-, and 1.22-log reductions in the number of CFU in the lungs, spleens, and livers, respectively, compared to the fungal load in mice given vector-transduced J774 cells. The protective effect of IL-12 gene therapy was accompanied by increased levels of IFN-γ in the lungs and sera of mice treated with IL-12- transduced J774 cells and the constitutive production of IFN-γ by their spleen cells cultured in vitro. These results suggest that IL-12 gene therapy could be used as adjunct therapy for coccidioidomycosis.