Role of cytolytic ZEB2+ memory CD4+ T cells in protection against liver stage malaria

Abstract Malaria remains a major human parasitic disease with over half a million deaths and 247 million cases every year. The WHO approved vaccines, RTS,S/AS01 (MosquirixTM) and R21/Matrix-M target the major Plasmodium falciparum (Pf) pre-erythrocytic stage circumsporozoite protein (CSP) antigen (Ag). They have limited efficacy and fall short of the global Malaria Vaccine Technology Roadmap goal of developing a 75%- effective vaccine. The mechanisms underlying both vaccines are poorly understood. There was only very limited analysis of the cellular responses associated with RTS,S/AS01 vaccination, partially due to the lack of sufficiently powerful high dimensional flow cytometry analyses at the time of the study. In contrast to protection afforded by vaccines, natural immunity provides long lived, robust protection from severe disease and death and infection is associated with minimal to no clinical symptoms. Thus, there is a pressing need to understand the cellular immune determinants associated with clinical immunity, to inform second generation vaccines. To gain insights into clinical immunity, we conducted a prospective study in a malaria endemic region in Malawi, with clinically immune and clinically susceptible individuals, using high dimensional flow cytometry phenotyping and single cell transcriptomic. We discovered in the blood of Pf-infected patients, a population of clonally expanded memory CD4+ T cells that express a robust cytolytic signature and reacted to the Pf-derived CSP Ag that is also the target of RTS,S/AS01 and R21 vaccines. We hypothesize that CSP-specific cytolytic memory CD4+ T cells could represent important mediators of natural and vaccine-induced immunity against malaria by limiting sporozoite and liver stage pre-erythrocytic infection. Here we propose to use murine models of radiation arrested sporozoites (RAS) immunization and sporozoite mosquito infection to explore the kinetics, differentiation requirements, functions and protective capacity of CSP-specific cytolytic CD4+ T cells during malaria.