GM-CSF+ Tc17 cells mediate vaccine-immunity, but not immunopathology, against lethal fungal pneumonia under CD4+ T-cell lymphopenia

Abstract Although opportunistic fungal infections are rising at alarming rates in immunocompromised individuals, there is no licensed vaccine available nor the clear understanding of the protective host responses. In a mouse model of fungal vaccine-immunity in CD4+ T-cell lymphopenia, we have previously shown that vaccine-induced IL-17A producing CD8+ T (Tc17) cells are necessary for controlling lethal fungal pneumonia. However, we found a significant number of Tc17 cells that co-expressed GM-CSF (>50%), but their role has been implicated as ‘pathogenic’ in autoimmune disorders. In this study, using state-of-the-art approaches, we found that GM-CSF +Tc17 cells are essential for vaccine-immunity against lethal fungal pneumonia without precipitating an adverse immunopathology. Induction of GM-CSF+Tc17 cells, following vaccination, required signaling from cytokines, IL-1 and IL-23, that promoted differentiation and proliferation of effectors. However, memory homeostasis of GM-CSF+Tc17 cells was mostly independent of IL-23. Following the lethal challenge by the pulmonary route, IL-23 was required for the GM-CSF+Tc17 cells responses, but not for their re-differentiation, and was necessary to mitigate the immunopathology of the lungs. Collectively, GM-CSF+Tc17 cells are required for vaccine-mediated immunity against lethal fungal pneumonia.