Vaccination with the Leishmania infantum acidic, ribosomal P0 protein plus CpG oligodeoxynucleotides induces protection against cutaneous leishmaniasis in C57BL/6 mice but does not prevent progressive disease BALB/c mice

We have examined the efficacy of the administration in mice of a molecularly defined vaccine based on the Leishmania infantum acidic ribosomal protein PO (rLiP0). Two different challenge models of murine cutaneous leishmaniasis were used: (i) subcutaneous inoculation of L. major parasites in susceptible BALB/c mice (a model widely used for vaccination analysis) and (ii) the intradermal inoculation of a low infective dose in resistant C57BL/6 mice (a model that more accurately reproduces the L. major infection in natural reservoirs and in human hosts). First, we demonstrated that C57BL/6 mice vaccinated with LiP0-DNA or LiP0 protein plus CpG oligodeoxynucleotides (ODN) were protected against the development of dermal pathology and showed a reduction in the parasite load. This protection was associated with production of gamma interferon (IFN-gamma) in the dermal site. Secondly, we showed that immunization with rLiP0 plus CpG ODN is able to induce only partial protection in BALB/c, since these mice finally developed a progressive disease. Further, we demonstrated that LiP0 vaccination induces a Th1 immunological response in both strains of mice. In both cases, the antibodies against LiP0 were predominantly of the immunoglobulin G2a isotype, which was correlated with an rLiP0-stimulated production of IFN-gamma in draining lymph nodes. Finally, we demonstrated that LiP0 vaccination does not prevent the Th2 response induced by L. major infection in BALB/c mice. Taken together, these data indicate that the BALB/c model of cutaneous leishmaniasis may undervalue the potential efficacy of some vaccines based on defined proteins, making C57BL/6 a suitable alternative model to test vaccine candidates.