Expression and immunogenicity of human immunodeficiency virus type 1 Gag expressed by a replication-competent rhabdovirus-based vaccine vector

A replication-competent rhabdovirus-based vector expressing human immunodef iciency virus type 1 (HIV-1) Gag protein was characterized on human cell li nes and analyzed for the induction of a cellular immune response in mice. W e previously described a rabies virus (RV) vaccine strain-based vector expr essing HIV-1 gp160. The recombinant RV was able to induce strong humoral an d cellular immune responses against the HIV-1 envelope protein in mice (M. J. Schnell et al., Proc. Natl. Acad. Sci. USA 97:3544-3549, 2000; J. P. McG ettigan et al., J. Virol. 75:4430-4434, 2001). Recent research suggests tha t the HIV-1 Gag protein is another important target for cell-mediated host immune defense. Here we show that HIV-1 Gag can efficiently be expressed by RV on both human and nonhuman cell lines. Infection of HeLa cells with rec ombinant RV expressing HIV-1 Gag resulted in efficient expression of HIV-1 precursor protein p55 as indicated by both immunostaining and Western blott ing. Moreover, HIV-1 p24 antigen capture enzyme-linked immunosorbent assay and electron microscopy showed efficient release of HIV-1 virus-like partic les in addition to bullet-shaped RV particles in the supernatants of the in fected cells. To initially screen the immunogenicity of this new vaccine ve ctor, BALB/c mice received a single vaccination with the recombinant RV exp ressing HIV-1 Gag. Immunized mice developed a vigorous CDS' cytotoxic T-lym phocyte response against HIV-1 Gag. In addition, 26.8% of CD8(+) T cells fr om mice immunized with RV expressing HIV-1 Gag produced gamma interferon af ter challenge with a recombinant vaccinia virus expressing HIV-1 Gag. These results further confirm and extend the potency of RV-based vectors as a po tential HIV-1 vaccine.