A Chimeric Protein-based Malaria Vaccine Candidate Induces Robust T Cell Responses Against Plasmodium Vivax MSP1

The most widespread Plasmodium species, Plasmodium vivax, poses a significant public health threat. An effective vaccine is needed to reduce global malaria burden. Of the erythrocytic stage vaccine candidates, the 19 kDa fragment of the P. vivax Merozoite Surface Protein 1 (PvMSP1) is one of the most promising. Our group has previously defined several promiscuous T helper epitopes within the PvMSP1 protein, with features that allow them to bind multiple MHC class II alleles. We describe here a P. vivax recombinant modular chimera based on MSP1 (PvRMC-MSP1) that includes defined T cell epitopes genetically fused to PvMSP1. This vaccine candidate preserved structural elements of the native PvMSP1 and elicited cytophilic antibody responses, and CD4+ and CD8+ T cells capable of recognizing PvMSP1. Although CD8+ T cells that recognize blood stage antigens have been reported to control blood infection, CD8+ T cell responses induced by P. falciparum or P. vivax vaccine candidates based on MSP1 have not been reported. To our knowledge, this is the first time a protein based subunit vaccine has been able to induce CD8+ T cell against PvMSP1. The PvRMC-MSP1 protein was also recognized by naturally acquired antibodies from individuals living in malaria endemic areas with an antibody profile associated with protection from infection. These features make PvRMC-MSP1 a promising vaccine candidate.