A new multi-epitope peptide vaccine induces immune responses and protection against Leishmania infantum in BALB/c mice

Visceral leishmaniasis (VL) is a tropical and subtropical disease which is endemic in more than eighty countries around the world. Leishmania infantum is one of the main causative agents of VL disease. Currently, there is no approved-to-market vaccine for VL therapy. In this study, we evaluated cellular and humoral immune responses induced by our newly designed multi-epitope vaccine in BALB/c mice. Four antigenic proteins, including histone H1, sterol 24-c-methyltransferase (SMT), Leishmania-specific hypothetical protein (LiHy), and Leishmania-specific antigenic protein (LSAP) were chosen for the prediction of potential immunodominant epitopes. Moreover, to enhance vaccine immunogenicity, two toll-like receptors 4 (TLR4) agonists, resuscitation-promoting factors of Mycobacterium tuberculosis (RpfE and RpfB), were employed as the built-in adjuvants. Immunization with the designed multi-epitope vaccine elicited a robust Th1-type immune response, compared to other groups, as shown by increased levels of IL-2, IFN-γ, TNF-α, and IgG2a. Furthermore, a significant decrease was observed in Th-2-type-related cytokines such as IL-4 in immunized mice. The designed construct also induced a significant reduction in parasite load (p < 0.0001), conferring protection against L. infantum challenge. This study could be promising in gaining insight towards the potential of peptide epitope-based vaccines as effective protective approaches against Leishmania species.