A multi-antigen chimeric PvCSP-MSP119 vaccine induces robust humoral responses against distinct stages of Plasmodium vivax.

Plasmodium vivax is the leading cause of malaria outside Africa, highlighting the need for an effective vaccine. However, the development of vaccines against this parasite remains challenging because of its complex life cycle and antigenic diversity. In this study, we evaluated vaccine formulations targeting both the pre-erythrocytic and erythrocytic stages of P. vivax using either individual antigens or a novel chimeric protein. The chimeric construct combined the C-terminal region and variant repeat domains of the P. vivax circumsporozoite protein (PvCSP) with the 19-kDa C-terminal fragment of merozoite surface protein 1 (PvMSP119). Structural predictions indicated that the PvCSP region was predominantly disordered, whereas the PvMSP119 domain displayed a more ordered conformation, supporting the preservation of key antigenic features within the fusion protein. We also evaluated recombinant replication-defective adenoviral vectors expressing PvCSP (AdC68-PvCSP) or PvMSP119 (AdHu5-PvMSP119). Homologous (protein/protein/protein) and heterologous (protein/adenovirus or adenovirus/protein) prime-boost regimens were assessed in C57BL/6 mice. Homologous immunization with either the chimeric protein or coadministered antigens induced robust IgG responses against PvCSP and PvMSP119, although anti-PvMSP119 titers were lower in mice receiving the chimeric construct. Among heterologous strategies, protein priming followed by adenoviral boosting elicited the highest IgG titers against both antigens. The chimeric protein consistently induced elevated IgG1/IgG2c ratios under both homologous and heterologous regimens. Furthermore, the frequency of antigen-specific antibody-secreting cells in the bone marrow closely paralleled the observed humoral responses. Collectively, these findings demonstrate that the PvCSP-MSP119 chimeric protein is highly immunogenic and capable of inducing immune responses against distinct stages of the P. vivax life cycle, supporting its further development as a multistage malaria vaccine candidate.