Inducing immunity to liver stage malaria through endogenous tissue resident memory cells

Abstract

Tissue-resident memory CD8 T (TRM) cells provide effective tissue surveillance and can respond rapidly to infection due to their strategic location. Within the liver, TRM cells can induce effective protection against liver-stage Plasmodium infection. Recently, members from our group identified a highly immunogenic peptide (named Pb-1) within the putative 60S ribosomal protein L6 of P. berghei ANKA. Experiments conducted and presented in this thesis aimed to assess the suitability of Pb-1 for the induction of endogenous liver TRM cells that confer sterilizing protection in B6 mice. To this end, a series of different immunisation strategies targeting the Pb 1 epitope were implemented and specific CD8 T cell responses were assessed. Results revealed that the number of naïve specific CD8 T cell precursors for the Pb-1 epitope was very large. Substantial expansion and formation of specific liver TRM cells was achieved by two different immunisation strategies: i) Single injection with Clec9A mAb plus adjuvant and ii) Prime-and-trap, both targeting the Pb-1 epitope. While mice vaccinated with Clec9A mAb developed partial protection, almost all mice vaccinated with prime-and-trap targeting Pb-1 were sterily protected against liver-stage challenge. <br /> Inflammation favours the formation TRM cells and adjuvants can affect their numbers. Accordingly, a second focus of this thesis sought to investigate how to enhance liver TRM cell formation by using TLR and RIG-I-like receptors agonists as adjuvants. For this, 8 different agonists were assessed for the generation of liver TRM cells induced by Clec9A targeted immunisation with the Pb-1 epitope. Data from this screen showed that CpG-based adjuvants were most effective at inducing the formation of TRM cells in the livers of vaccinated mice and that the transfection reagent DOTAP enhanced this effect. Based on this understanding, we then investigated the potential of CpG and its encapsulation in DOTAP to improve TRM cell generation by other vaccination strategies. Surprisingly, these studies revealed that CpG-based adjuvants did not improve liver TRM cell generation by vaccination with radiation-attenuated sporozoites. The basis for this outcome is discussed. <br /> Altogether, these findings provide insights into elements that favour the generation of protective liver TRM cells; information that can be used for the design of TRM cell-based subunit vaccines against Plasmodium infection.