Fast and fierce versus slow and smooth: Heterogeneity in immune responses to Plasmodium in the controlled human malaria infection model

Abstract

Controlled human malaria infection (CHMI) is an established model in clinical malaria research. Upon exposure to Plasmodium falciparum parasites, malaria-naive volunteers differ in dynamics and composition of their immune profiles and subsequent capacity to generate protective immunity. CHMI volunteers are either inflammatory responders who have prominent cellular IFN-γ production primarily driven by adaptive T cells, or tempered responders who skew toward antibody-mediated humoral immunity. When exposed to consecutive CHMIs under antimalarial chemoprophylaxis, individuals who can control parasitemia after a single immunization (fast responders) are more likely to be protected against a subsequent challenge infection. Fast responders tend to be inflammatory responders who can rapidly induce long-lived IFN-γ+ T cell responses. Slow responders or even non-responders can also be protected, but via a more diverse range of responses that take a longer time to reach full protective efficacy, in part due to their tempered phenotype. The latter group can be identified at baseline before CHMI by higher expression of inhibitory ligands CTLA-4 and TIM-3 on CD4+ T cells. Delineating heterogeneity in human immune responses to P. falciparum will facilitate rational design and strategy towards effective malaria vaccines.