A recombinant non-pathogenic Leishmania vaccine expressing human immunodeficiency virus 1 (HIV-1) Gag elicits cell-mediated immunity in mice and decreases HIV-1 replication in human tonsillar tissue following exposure to HIV-1 infection.

Live-vector human immunodeficiency virus (HIV) vaccines are an integral part of a number of HIV vaccine regimens currently under evaluation that have yielded promising results in pre-clinical testing. In this report, a non-pathogenic protozoan parasitic vector, Leishmania tarentolae, which shares common target cells with HIV-1, was used to express full-length HIV-1 Gag protein. Immunization of BALB/c mice with recombinant L. tarentolae led to the expansion of HIV-1 Gag-specific T cells and stimulated CD8(+) T cells to produce gamma interferon in response to specific viral Gag epitopes. A booster immunization with recombinant L. tarentolae elicited effector memory HIV-1 Gag-specific CD4(+) T lymphocytes and increased antibody titres against HIV-1 Gag. Most importantly, immunization of human tonsillar tissue cultured ex vivo with Gag-expressing L. tarentolae vaccine vector elicited a 75% decrease in virus replication following exposure of the immunized tonsils to HIV-1 infection. These results demonstrated that recombinant L. tarentolae is capable of eliciting effective immune responses in mice and human systems, respectively, and suggest that this novel non-pathogenic recombinant vaccine vector shows excellent promise as a vaccination strategy against HIV-1.