Cytolytic memory CD4+ T cell clonotypes are expanded during Plasmodium falciparum infection

Abstract

Plasmodium falciparum (Pf) malaria causes high rates of morbidity and mortality and lacks a sufficiently effective vaccine. Clinical immunity develops in residents of malaria endemic regions which confers reduced clinical symptoms during infection and protection against severe disease. We hypothesized that understanding the immune mechanisms of clinical immunity could inform vaccine design to improve efficacy. We compared the peripheral blood cellular and humoral immune responses during a mild episode of Pf malaria infection. Participants were classified as either clinically susceptible or clinically protected, based on the number of recurrent clinical infections over an 18-month longitudinal study in a malaria endemic region in Malawi. Susceptible participants had three or more recurrent clinical episodes while clinically immune individuals had one or none. Protected participants exhibited higher plasma immunoglobulin G (IgG) breadth and titers against Pf antigens, and greater antibody (Ab)-dependent Pf opsonization compared to susceptible participants. Using high dimensional mass cytometry (CyTOF), spectral flow cytometry and single-cell transcriptomic analyses, we identified expanded memory CD4+ T cell clones sharing identical T cell receptor clonotypes in the blood of protected participants during malaria infection. These cells express a strong cytolytic T helper 1 effector program with transcripts encoding granzymes (A, B, H, M), granulysin, NKG7 and the Zeb2 master transcriptional regulator of terminally differentiated effector T cells. Memory CD4+ T cells expressing Zeb2+ were CD39hiTIGIThi and expressed multiple chemotactic and checkpoint inhibitory receptors, although the cellular levels of several of these receptors were reduced in protected compared to susceptible individuals. We propose that clonally expanded Zeb2+ cytolytic memory CD4+ Th1 cells could represent essential contributors to clinical immunity against Pf malaria. One Sentence SummaryA population of cytolytic memory CD4+ T cells is clonally expanded in patients with Plasmodium falciparum malaria and has reduced chemotactic and inhibitory receptor expression in patients with naturally acquired clinical malaria immunity.