Genetic Immunization with Glycoprotein 63 cDNA Results in a Helper T Cell Type 1 Immune Response and Protection in a Murine Model of Leishmaniasis

Abstract

Genetic immunization is a promising gene therapy approach for the prevention and treatment of infectious disease. Plasmid DNA expressing genes of pathogens is directly introduced into host cells and specific cell-mediated and/or humoral immune responses are elicited against the encoded protein. Leishmaniasis is a significant world-wide health problem for which no vaccine exists. In susceptible animals, such as BALB/c mice, protection from leishmaniasis requires induction of a Th1 immune response. In this study, cell-mediated immunity to Leishmania major (L. major) was induced by injecting BALB/c mice intradermally with plasmid DNA expressing the conserved L. major cell surface glycoprotein gp63 (gp63-pcDNA-3). CD4 T lymphocytes from gp63-pcDNA-3-immunized mice proliferated and produced IFN-γ (but not IL-4) when stimulated in vitro with freeze-thawed parasites, consistent with a Th1 immune response. In contrast, lymphocyte proliferation in animals immunized with freeze–thawed parasites was associated with IL-4 (but not IFN-γ) production, suggesting a nonprotective Th2 response. Challenge studies revealed that gp63-pcDNA-3 vaccination protected 30% of susceptible mice (21 of 70) from Leishmania infection while neither gp63 protein (0 of 20) nor freeze–thawed parasite vaccines (0 of 50) were efficacious. Dendritic cells derived from skin of gp63-pcDNA-3-injected mice also immunized naive recipients and protected them from leishmaniasis. We conclude that gp63-pcDNA-3 genetic vaccination results in a CD4-dependent Th1 immune response that correlates with protection from disease, and suggest that skin-derived dendritic cells are involved in priming this response. Genetic immunization is a potentially important therapeutic application of gene therapy that directly introduces and expresses genes in the skin. Skin is readily accessible and dendritic cells residing in the skin are potent antigen-presenting cells. We show that genetic immunization can effectively vaccinate recipients against infectious organisms, such as Leishmania, for which no effective vaccine currently exists. In this study, DNA vaccines expressing a Leishmania protein (gp63) induced a specific Th1 immune response against Leishmania lysate and protected susceptible mice from challenge with live parasites. Furthermore, dendritic cells derived from the skin of DNA-vaccinated animals were able to immunize and protect naive recipient mice from Leishmania. Because it is simple and effective, genetic immunization may become an increasingly common application of gene therapy.