Malaria antigens are presented to CD8 T cells via the non-classical HLA-E

Abstract

Abstract CD8 T cells have long been known to target infected hepatocytes during the intracellular liver stages of Plasmodium—the causative agent of malaria. Current T cell vaccine strategies are limited by the inability to obtain sufficient amounts of Plasmodium-infected hepatocytes to identify peptides presented on MHC-I (“immunopeptidomics”). Recently, we demonstrated that the blood stages of Plasmodium vivax are also susceptible to CD8 T cell killing and performed immunopeptidomics on Pv-infected reticulocytes. Peptides mapped to proteins conserved across Plasmodium spp. and were common across volunteers. Furthermore, ~50% of the peptides detected are not predicted to bind classical HLA-I molecules and thus could be presented by non-classical HLA. In support of this, blocking HLA-E during in vitro stimulation of PBMCs with a pool of newly-identified peptides substantially reduced the CD8 T cell response. Mechanistic studies conducted in the rhesus macaque/P. cynomolgi malaria model demonstrated that CD8 T cell killing of infected reticulocytes is conserved in this model as are CD8 responses to the newly identified peptides. In vitrostimulation assays showed that CD8 T cell responses to at least 3 of 9 peptides tested are completely restricted to MHC-E. This is supported by in vitro binding assays showing peptide binding to HLA-E. In summary, we demonstrate for the first time that malaria infection induces HLA/MHC-E-restricted CD8 T cell responses to newly identified peptides that are conserved across host and parasite species. Given the extreme conservation of MHC-E, these results pave the way to explore a universal, species-transcending vaccine for malaria based on MHC-E presentation of novel antigens.