Staphylococcus aureus Infection of Mice Expands a Population of Memory γδ T Cells That Are Protective against Subsequent Infection

The development of vaccines against Staphylococcus aureus has consistently failed in clinical trials, likely due to inefficient induction of cellular immunity. T cell-derived IL-17 is one of the few known correlates of antistaphylococcoal immunity, conferring protection against S. aureus infections through its ability to promote phagocytic cell effector functions. A comprehensive understanding of the discrete T cell subsets critical for site-specific IL-17-mediated bacterial clearance will therefore be necessary to inform the development of vaccines that efficiently target cellular immunity. In this study, we have identified a population of CD44+ CD27- memory γδ T cells, expanded upon infection of C57BL/6 mice with S. aureus, which produce high levels of IL-17 and mediate enhanced bacterial clearance upon reinfection with the bacterium. These cells are comprised largely of the Vγ4+ subset and accumulate at the site of infection subsequent to an initial Vγ1.1+ and Vγ2+ T cell response. Moreover, these Vγ4+ T cells are retained in the peritoneum and draining mediastinal lymph nodes for a prolonged period following bacterial clearance. In contrast to its critical requirement for γδ T cell activation during the primary infection, IL-1 signaling was dispensable for activation and expansion of memory γδ T cells upon re-exposure to S. aureus. Our findings demonstrate that a γδ T cell memory response can be induced upon exposure to S. aureus, in a fashion analogous to that associated with classical αβ T cells, and suggest that induction of IL-17-expressing γδ T cells may be an important property of a protective vaccine against S. aureus.