Hancox, L. S. | bioRxiv Science

bioRxiv2025

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.

microbiology↗

bioRxiv2021

Altered cleavage of Caspase-1 in hepatocytes limits control of malaria in the liver

Malaria, caused by Plasmodium parasites, is a devastating disease that kills over half a million people each year1. Plasmodium sporozoites inoculated by mosquitoes into mammalian hosts undergo a clinically silent phase of obligatory development and replication in hepatocytes before initiating the life-threatening blood-stage of malaria2. Thus, understanding the immune responses elicited by Plasmodium infection in the liver is key to controlling clinical malaria and transmission3,4. Here, we show that Plasmodium DNA can be detected by AIM2 (absent in melanoma 2) sensors in the infected hepatocytes, resulting in Caspase-1 activation and pyroptotic cell-death. However, Caspase-1 was observed to undergo only partial cleavage in hepatocytes, limiting pyroptosis, and the maturation of pro-inflammatory cytokines classically associated with Caspase-1 activation. We discovered that the extent of Caspase-1 cleavage in cells is determined by the expression of ASC (apoptosis-associated speck-like protein containing a CARD). ASC expression is inherently low in hepatocytes, and transgenically enhancing it in the hepatocytes induced complete processing of Caspase-1, efficient secretion of pro-inflammatory cytokines, enhanced pyroptotic cell-death, and markedly improved control of malaria infection in the liver. In addition to describing a novel pathway of natural immunity to malaria, our findings uncover a key aspect of liver biology that may have been exploited during evolution by successful hepatotropic pathogens.

immunology↗