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 tarentulae was 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 LACK L. major antigens were synthesized in the pLEXSY-neo 2.1 plasmid and cloned into E. coli strain Top10, and after being linearized with the SwaI enzyme, they were transfected into the genome of L. tarentolae. The L. tarentolae-LACK/KMP11/EGFP in 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, pathogenic L. 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-γ, IL-5, TNF-α, 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 with L. tarentolae-LACK/KMP11/EGFP with 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 of L. tarentolae-LACK/KMP11/EGFP with 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.

[Vaccines against HIV/AIDS]. / Vaccins préventifs anti-VIH/sida.

Some 50 phase I clinical trials of candidate vaccines against HIV/AIDS, 2 phase II trials and 2 phase III trials have been completed since the 1980s, altogether involving more than 16,000 volunteers. Although several neutralization epitopes have been identified on the surface of the virus glycoprotein spikes, the design of an envelope-based HIV vaccine capable of eliciting broadly reactive neutralizing antibodies remains as an elusive goal. A gp120- based vaccine, which was tested in two phase III trials, one in the USA and the other in Thailand, was found to be devoid of protective efficacy. The observation was made in the monkey model, using the simian immunodeficiency virus (SIV), that both virus loads and the clinical evolution of the disease were controlled by the CD8+ T-cell response (CTL) of the animals. This has prompted the development of vaccine candidates capable of inducing HIV-specific T-cell responses. A series of HIV vaccines based on live virus vectors already are in clinical studies, including a live recombinant canarypox virus vaccine (ALVAC), which is in phase III in Thailand, a non-replicative adenovirus type 5 (Ad5) vaccine, which has entered phase II clinical trials in the USA and The Caribbeans, and live recombinant vaccines based on the attenuated vaccinia virus MVA vector, which already have been through several phase I/II studies. These live recombinant vaccines have been evaluated either alone or as booster immunizations after priming with DNA vaccines. A whole array of other vaccines based on live vector vaccines, pseudoviral particles, peptides and other designs, have been tested in nonhuman primate models. So far, using the macaque/SIV model, none of the available vaccine candidates has been able to prevent infection following experimental challenge of the animals, but the vaccinated animals showed significant reduction of viral loads as compared to controls and were able to maintain their CD4+ T-cell count. T-cell stimulating vaccines thus illustrate a new paradigm in vaccinology, that of vaccines which are unable to prevent infection, but can prevent the occurrence of disease or at least slow down its evolution through continuous control of virus replication in the vaccinated host. The efficacy of these vaccines in humans now remains to be established.