Great efforts have been made to identify promising antigens and vaccine formulations against schistosomiasis. Among the previously described Schistosoma vaccine candidates, cyclophilins comprise an interesting antigen that could be used for vaccine formulations. Cyclophilin A is the target for the cyclosporine A, a drug with schistosomicide activity, and its orthologue from Schistosoma japonicum induces a protective immune response in mice. Although Schistosoma mansoni cyclophilin A also represents a promising target for anti-schistosome vaccines, its potential to induce protection has not been evaluated. In this study, we characterized the cyclophilin A (SmCyp), initially described as Smp17.7, analyzed its allergenic potential using in vitro functional assays, and evaluated its ability to induce protection in mice when administered as an antigen using different vaccine formulations and strategies. Results indicated that SmCyp could be successfully expressed by mammalian cells and bacteria.The recombinant protein did not promote IgE-reporter system activation in vitro, demonstrating its probable safety for use in vaccine formulations. T and B-cell epitopes were predicted in the SmCyp sequence, with two of them located within the active isomerase site. The most immunogenic antigen, SmCyp (107-121), was then used for immunization protocols. Immunization with the SmCyp gene or protein failed to reduce parasite burden but induced an immune response that modulated the granuloma area. In contrast, immunization with the synthetic peptide SmCyp (107-121) significantly reduced worm burden (48-50%) in comparison to control group, but did not regulate liver pathology. Moreover, the protection observed in mice immunized with the synthetic peptide was associated with the significant production of antibodies against the SmCyp (107-121) epitope. Therefore, in this study, we identified an epitope within the SmCyp sequence that induces a protective immune response against the parasite, thus representing a promising antigen that could be used for vaccine formulation against schistosomiasis.

The helminth Schistosoma mansoni is one of main causes of human schistosomiasis, a health and economic concern in some of the world's poorest countries. Current treatment regimens can lead to serious side effects and are not suitable for breastfeeding mothers. As such, efforts have been undertaken to develop a vaccine to prevent infection. Of these, Sm29 is a promising candidate that has been associated with resistance to infection/reinfection in humans and mice. Its ability to induce resistance to reinfection has also been recently demonstrated using a vaccine formulation containing Freund's adjuvant. However, Freund's adjuvant is unsuitable for use in human vaccines. We therefore evaluated the ability of Sm29 to induce protection against S. mansoni reinfection when formulated with either alum or MPLA as an adjuvant, both approved for human use. Our data demonstrate that, in contrast to Sm29 with MPLA, Sm29 with alum reduced parasite burden after reinfection compared to a control. We next investigated whether the immune response was involved in creating the differences between the protective (Sm29Alum) and non-protective (Sm29MPLA) vaccine formulations. We observed that both formulations induced a similar mixed-profile immune response, however, the Sm29 with alum formulation raised the levels of antibodies against Sm29. This suggests that there is an association between a reduction in worm burden and parasite-specific antibodies. In summary, our data show that Sm29 with an alum adjuvant can successfully protect against S. mansoni reinfection in mice, indicating a potentially effective vaccine formulation that could be applied in humans.

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