γδ T cells in cancer: a small population of lymphocytes with big implications.

γδ T cells are a small population of mostly tissue-resident lymphocytes, with both innate and adaptive properties. These unique features make them particularly attractive candidates for the development of new cellular therapy targeted against tumor development. Nevertheless, γδ T cells may play dual roles in cancer, promoting cancer development on the one hand, while participating in antitumor immunity on the other hand. In mice, γδ T-cell subsets preferentially produce IL-17 or IFN-γ. While antitumor functions of murine γδ T cells can be attributed to IFN-γ+ γδ T cells, recent studies have implicated IL-17+ γδ T cells in tumor growth and metastasis. However, in humans, IL-17-producing γδ T cells are rare and most studies have attributed a protective role to γδ T cells against cancer. In this review, we will present the current knowledge and most recent findings on γδ T-cell functions in mouse models of tumor development and human cancers. We will also discuss their potential as cellular immunotherapy against cancer.