mRNA vaccination overcomes hemozoin-mediated impairment of whole parasite vaccine efficacy for malaria
Malaria is a persistent global public health threat. Immunization with Radiation Attenuated Sporozoites (RAS) drives efficient CD8+ T cell dependent sterilizing immunity to malaria in humans. However, this protection is compromised in individuals living in malaria endemic regions and the mechanism(s) of the vaccine failure remain incompletely understood. In this study, we develop a murine model of Plasmodium infection where prior blood-stage exposure compromises RAS-induced CD8+ T cell responses and subsequent protection. We further identify the persisting malarial pigment hemozoin as a mediator of impaired CD8+ T cell responses. Mechanistically, we link this defect to impaired antigen uptake by dendritic cells, leading to reduced T cell activation. Importantly, we designed a lipid nanoparticle-encapsulated mRNA vaccine that encodes a string of Plasmodium CD8+ T cell epitopes and found that this vaccine overcomes the T cell defect and restores protection in Plasmodium exposed mice. Moreover, a combined RAS+mRNA vaccine regimen enhances liver resident memory T cells and protection even in malaria experienced hosts. These findings support the identification of hemozoin as a long-lived obstacle to vaccine efficacy in malaria endemic areas and provide a rational framework for designing malaria vaccines that are effective in endemic settings.