Evaluation of a new live recombinant vaccine against cutaneous leishmaniasis in BALB/c mice

Background: Leishmaniasis is a serious health problem in some parts of the world. In spite of the many known leishmaniasis control measures, the disease has continued to increase in endemic areas, and no effective vaccine has been discovered. Methods: In this study,Leishmania tarentulaewas used as a living factory for the production of two LACK and KMP11 immunogenic antigens in the mice body, and safety profiles were investigated. The sequences of the KMP11 and LACKL. majorantigens were synthesized in the pLEXSY-neo 2.1 plasmid and cloned intoE. colistrain Top10, and after being linearized with theSwaIenzyme, they were transfected into the genome ofL. tarentolae. TheL. tarentolae-LACK/KMP11/EGFPin the stationary phase with CpG ODN as an adjuvant was used for vaccination in BALB/c mice. Vaccination was performed into the left footpad. Three weeks later, the booster was injected in the same manner. To examine the effectiveness of the injected vaccine, pathogenicL. major(MRHO/IR/75/ER) was injected into the right footpad of all mice three weeks following the booster vaccination. In order to assess humoral immunity, the levels of IgG1, and IgG2a antibodies before and 6 weeks after the challenge were studied in the groups. In addition, in order to investigate cellular immunity in the groups, the study measured IFN-gamma, IL-5, TNF-alpha, IL-6 and IL-17 cytokines before, 3 weeks and 8 weeks after the challenge, and also the parasite load in the lymph node with real-time PCR. Results: The lowest level of the parasitic load was observed in the G1 group (mice vaccinated withL. tarentolae-LACK/KMP11/EGFPwith CpG) in comparison with other groups (L. tarentolae-LACK/KMP11/EGFP +non-CpG (G2);L. tarentolae-EGFP + CpG (G3, control);L. tarentolae-EGFP + non-CpG (G4, control); and mice injected with PBS (G5, control). Moreover, the evaluation of immune response showed a delayed-type hypersensitivity towards Th1. Conclusions: According to the results of this study, the live recombinant vaccine ofL. tarentolae-LACK/KMP11/EGFPwith the CpG adjuvant reduced the parasitic load and footpad induration in infected mice. The long-term effects of this vaccine can be evaluated in volunteers as a clinical trial in future planning.