Repeated infection in humans drives the clonal expansion of an adaptive γδ T cell repertoire.

Repeated infections drive the development of clinical immunity to malaria in humans; however, the immunological mechanisms that underpin this response are only partially understood. We investigated the impact of repeated infections on human γδ T cells in the context of natural infection in Malian children and adults, as well as serial controlled human malaria infection (CHMI) of U.S. adults, some of whom became clinically immune to malaria. In contrast to the predominant Vδ2 T cell population in malaria-naïve Australian individuals, clonally expanded cytotoxic Vδ1 T cells were enriched in the γδ T cell compartment of Malian subjects. Malaria-naïve U.S. adults exposed to four sequential CHMIs defined the precise impact of on the γδ T cell repertoire. Specifically, innate-like Vδ2 T cells exhibited an initial robust polyclonal response to infection that was not sustained with repeated infections, whereas Vδ1 T cells increased in frequency with repeated infections. Moreover, repeated infection drove waves of clonal selection in the Vδ1 T cell receptor repertoire that coincided with the differentiation of Vδ1 T cells into cytotoxic Vδ1 T cells. Vδ1 T cells of malaria-exposed Malian and U.S. individuals were licensed for reactivity to parasites in vitro. Together, our study indicates that repeated infection drives the clonal expansion of an adaptive γδ T cell repertoire and establishes a role for Vδ1 T cells in the human immune response to malaria.