Immunogenicity and potential protection of DNA vaccine of Leishmania martiniquensis against Leishmania infection in mice

In Thailand, Leishmania martiniquensis is the predominant species causing cutaneous and visceral leishmaniasis. Its incidence has been increasing among immunocompetent and immunocompromised hosts. We developed a prototype DNA vaccine using a partial consensus sequence of the cysteine protease B (cpb) gene derived from L. martiniquensis from Thai patients. Methodology: The laboratory inbred strain of albino BALB/c mice were immunized intramuscularly three times at 2-week intervals (weeks 0, 2, and 4) with cpb plasmid DNA (pcDNA_cpb) with or without the adjuvant, monoolein (pcDNA_cpb-MO). Mice were challenged at week 6 with L. martiniquensis promastigotes. Sera were analysed for IgG1, IgG2a, interferon gamma and interleukin 10 (IFN-γ and IL-10, respectively) levels at weeks 0, 4, and 9. Additionally, livers and spleens were also analysed for parasite burden using immunohistochemistry and real-time polymerase chain (qPCR) assays. Results: Three weeks after promastigote challenge, vaccinated mice showed significantly increased levels of IgG2a and IFN-γ while IL-10 level was significantly reduced when compared with those in the control group (p < 0.01). Parasite burden in the livers and spleens of vaccinated mice significantly decreased. In addition, a significant increase in mature granuloma formation in the livers when compared with those of the control group (p < 0.05) was found, indicating increased T-helper cells (Th1)-induced inflammation and destruction of amastigotes. Monoolein produced a booster effect to enhance the mouse Th1 protective immunity. Conclusions: The prototype DNA vaccine could induce a Th1 immune response that conferred potential protection to the L. martiniquensis promastigote challenge in BALB/c mice.