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

gamma delta 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, gamma delta 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, gamma delta T-cell subsets preferentially produce IL-17 or IFN-gamma. While antitumor functions of murine gamma delta T cells can be attributed to IFN-gamma(+) gamma delta T cells, recent studies have implicated IL-17(+) gamma delta T cells in tumor growth and metastasis. However, in humans, IL-17-producing gamma delta T cells are rare and most studies have attributed a protective role to gamma delta T cells against cancer. In this review, we will present the current knowledge and most recent findings on gamma delta T-cell functions in mouse models of tumor development and human cancers. We will also discuss their potential as cellular immunotherapy against cancer.