Vaccination with Plasmid DNA Encoding TSA/LmSTI1 Leishmanial Fusion Proteins Confers Protection againstLeishmania majorInfection in Susceptible BALB/c Mice

Abstract

We have recently shown that a cocktail containing two leishmanial recombinant antigens (LmSTI1 and TSA) and interleukin-12 (IL-12) as an adjuvant induces solid protection in both a murine and a nonhuman primate model of cutaneous leishmaniasis. However, because IL-12 is difficult to prepare, is expensive, and does not have the stability required for a vaccine product, we have investigated the possibility of using DNA as an alternative means of inducing protective immunity. Here, we present evidence that the antigens TSA and LmSTI1 delivered in a plasmid DNA format either as single genes or in a tandem digene construct induce equally solid protection against Leishmania major infection in susceptible BALB/c mice. Immunization of mice with either TSA DNA or LmSTI1 DNA induced specific CD4؉ -T-cell responses of the Th1 phenotype without a requirement for specific adjuvant. CD8 responses, as measured by cytotoxic-T-lymphocyte activity, were generated after immunization with TSA DNA but not LmSTI1 DNA. Interestingly, vaccination of mice with TSA DNA consistently induced protection to a much greater extent than LmSTI1 DNA, thus supporting the notion that CD8 responses might be an important accessory arm of the immune response for acquired resistance against leishmaniasis. Moreover, the protection induced by DNA immunization was specific for infection with Leishmania, i.e., the immunization had no effect on the course of infection of the mice challenged with an unrelated intracellular pathogen such as Mycobacterium tuberculosis. Conversely, immunization of BALB/c mice with a plasmid DNA that is protective against challenge with M. tuberculosis had no effect on the course of infection of these mice with L. major. Together, these results indicate that the protection observed with the leishmanial DNA is mediated by acquired specific immune response rather than by the activation of nonspecific innate immune mechanisms. In addition, a plasmid DNA containing a fusion construct of the two genes was also tested. Similarly to the plasmids encoding individual proteins, the fusion construct induced both specific immune responses to the individual antigens and protection against challenge with L. major. These results confirm previous observations about the possibility of DNA immunization against leishmaniasis and lend support to the idea of using a single polygenic plasmid DNA construct to achieve polyspecific immune responses to several distinct parasite antigens.

Cross-Protective Efficacy of a ProphylacticLeishmania donovaniDNA Vaccine against Visceral and Cutaneous Murine Leishmaniasis

“…These observations also confirm that DNA vaccines may have a greater potential than protein vaccines to protect against Leishmania, an observation that has been repeatedly made in vaccines studies comparing various recombinant and DNA vaccines (16,21,30,(53)(54)(55)(56)(57). Furthermore, even in the case of successfully protective recombinant vaccines against cutaneous leishmaniasis, their plasmid DNA counterparts have the additional advantage of being more stable and easier to prepare (9).…”

“…Interestingly, these antigens used as DNA vaccines induced a stronger cellular immune response and a better protection than their recombinant counterparts (19,20,45,55,56,58), suggesting that DNA vaccines may be more effective for controlling Leishmania infection. Indeed, DNA vaccines have been shown to induce a preferentially Th1 immune response, which is necessary for the elimination of intracellular parasites (9,19,52).…”

Assessment of Protection Induced by DNA and Live Vaccine Encoding Leishmania MHC Class I Restricted Epitopes against L. major Challenge in Balb/c Mice Model

“…Furthermore, Campos-Neto et al proved that vaccination with a plasmid DNA encoding both TSA and LmSTI-1 fusion proteins confers protection against Leishmania major high dose challenge in Balb/c mice. This effect was attributed to CD8 + T-cells' stimulation by TSA protein [39]. Also a cocktail of 4 plasmids encoding L. infantum histone proteins cross protected against high dose L. major challenge in Balb/c mice with both CD4 + and CD8 + T-cells as contributors [40].…”

Immunogenicity in dogs of three recombinant antigens (TSA, LeIF and LmSTI1) potential vaccine candidates for canine visceral leishmaniasis

“…Here, we began the evaluation of a mixture of the recombinant antigens TSA, LmSTI1 and LeIF as candidate vaccine for VL. These antigens have been successfully shown to induce an excellent protection against cutaneous leishmaniasis in the murine and non-human primate models [9,30,41] and currently are been tested in Phase I/II human vaccine clinical trials. Because these antigens are highly conserved among the Leishmania species and are expressed in both the amastigote and the promastigote forms of the parasites [39,40,46], they could be useful as a component of a panLeishmania vaccine [20].…”

“…Three highly conserved antigens among the Leishmania genus, TSA, LmSTI1 and LeIF, have been shown to induce excellent protection in both the murine and non-human primate models of the human disease [8,41]. Moreover, vaccination with plasmid DNA encoding these antigens conferred protection against L. major infection in BALB/c [9,30,31]. A single recombinant polyprotein comprising the sequences of all three recombinant proteins has been produced and tested in BALB/c mice against L. major infection formulated with MPL-SE ® (Monophosphoryl Lipid A plus squalene) and the results showed excellent protective immunity against the challenge with virulent parasites [41].…”