Immunological response of using emulsifying elongation factor 1 alpha of Plasmodium falciparum-based vaccines in complete Freund's adjuvant

Most studies of malarial vaccines focused on increasing immunity against target molecules on the surface of Plasmodium spp. parasites. While the surface antigens are variable among all Plasmodium spp., intracellular antigens are highly conserved, and thus, intracellular targets must be studied as vaccine candidates. However, there is a scarcity of intracellular vaccine candidates in Plasmodium parasites. In this study, immune responses induced by complete Freund's Adjuvant (CFA) emulsified with an elongation factor-1 alpha of P. falciparum (PfEF-1α) was analyzed as a Plasmodium spp. conserved vaccine candidate. In vivo vaccine efficacy, antibody production, and ex vivo T-cell cytokine assays were analyzed to validate the potential of PfEF-1α at CFA-based formulation in a rodent model. Immunoinformatics was employed to predict potential vaccine epitope candidates, and a novel peptide candidate was validated by ex vivo T-cell study. The survival rate of the rPfEF-1α plus CFA-immunized group was increased by 50% and among the survived mice, half proportion of mice was not patent at all while all BSA plus CFA showed the patency. Upon co-culturing of T cells with dendritic cells, PfEF-1α-specific ex vivo T-cell assay revealed CD4⁺IFN-γ⁺ secretion as the dominant immune response, followed by CD8⁺IFN-γ⁺ and CD4⁺IL-4⁺ subsets. Immunization with rPfEF-1-α plus CFA elicited robust humoral immunity, demonstrating a 16-fold higher antigen-specific IgG endpoint titer compared to the BSA plus CFA-immunized group. IgG1 and IgG2c titers in rPfEF-1α plus CFA-immunized mice were highly elevated over BSA plus CFA-immunized group. Furthermore, the PfEF-1α epitope (410-FAIRDMRQTI-419), identified through in silico prediction and validated, induced IFN-γ secretion in ex vivo C57BL/6 T-cell study. These results demonstrate PfEF-1α's capacity to drive protective T-cell responses and antibody production with CFA adjuvant. Our findings suggest the use of intracellular antigen for development of malaria vaccine targets.