Cellular and molecular characterization of γδ T cells in peripheral blood from patients with metastases from cutaneous and uveal melanoma.

T cells can be divided into two major subtypes based on which chains that make up the T cell receptor (TCR): the conventional αβ T cells and the less common γδ T cells. γδ T cells are attractive targets of cancer immunotherapy due to e.g. their independence from MHC-restricted activation. Despite the successful implementation of immune checkpoint inhibitors for the treatment of metastatic melanoma, not all patients respond favorably to the treatment. In this study we characterized γδ T cells in peripheral blood from patients with cutaneous and uveal melanoma, and from age-matched healthy controls, with ultrasensitive DNA sequencing (SiMSen-Seq) of the δ-chain and flow cytometry to facilitate the introduction of γδ T cell-based treatment strategies. As a general trend, the Vδ1 subpopulation was found to be more abundant in patients labeled as responders versus non-responders. Regarding clonal diversity, although a high oligoclonality was found in each individual and within each group, clonal diversity was lower in patients labeled as responders to treatment. Cutaneous melanoma patients had a larger total number of clonotypes compared to the healthy controls, and did also express higher levels of the receptor NKG2D on the surface of Vδ2 cells. Overall, we could see small differences between cutaneous and uveal melanoma patients and healthy controls in regard to distribution of γδ subpopulations, with high clonal diversities and a mostly private repertoire of the δ receptor among all groups.