Single-cell analysis uncovers differential regulation of lung γδ T cell subsets by the co-inhibitory molecules, PD-1 and TIM-3

IL-17A-producing {gamma}{delta} T cells within the lung consist of both V{gamma}6+ tissue-resident cells and V{gamma}4+ circulating cells that play important roles in homeostasis, inflammation, infection, tumor progression and metastasis. How these {gamma}{delta} T cell subsets are regulated in the lung environment during homeostasis and cancer remains poorly understood. Using single-cell RNA sequencing and flow cytometry, we show that lung V{gamma}6+ cells express a repertoire of cell surface molecules distinctive from V{gamma}4+ cells, including PD-1 and ICOS. We found that PD-1 functions as a co-inhibitory molecule on V{gamma}6+ cells to reduce IL-17A production, whereas manipulation of ICOS signaling fails to affect IL-17A in V{gamma}6+ cells. In a mammary tumor model, ICOS and PD-1 expression on lung V{gamma}6+ cells remained stable. However, V{gamma}6+ and V{gamma}4+ cells within the lung pre-metastatic niche increased expression of IL-17A, IL-17F, amphiregulin (AREG) and TIM-3 in response to tumor-derived IL-1{beta} and IL-23, where the upregulation of TIM-3 was specific to V{gamma}4+ cells. Inhibition of either PD-1 or TIM-3 in mammary tumor-bearing mice further increased IL-17A by V{gamma}6+ and V{gamma}4+ cells, indicating that both PD-1 and TIM-3 function as negative regulators of IL-17A-producing {gamma}{delta} T cell subsets. Together, these data demonstrate how lung {gamma}{delta} T cell subsets are differentially controlled by co-inhibitory molecules in steady-state and cancer.