T helper type 17 cells contribute to anti‐tumour immunity and promote the recruitment of T helper type 1 cells to the tumour

Summary T helper type 17 ( T h17) lymphocytes are found in high frequency in tumour‐burdened animals and cancer patients. These lymphocytes, characterized by the production of interleukin‐17 and other pro‐inflammatory cytokines, have a well‐defined role in the development of inflammatory and autoimmune pathologies; however, their function in tumour immunity is less clear. We explored possible opposing anti‐tumour and tumour‐promoting functions of T h17 cells by evaluating tumour growth and the ability to promote tumour infiltration of myeloid‐derived suppressor cells ( MDSC ), regulatory T cells and CD 4 +  interferon‐γ + cells in a retinoic acid‐like orphan receptor γt ( ROR γt) ‐deficient mouse model. A reduced percentage of T h17 cells in the tumour microenvironment in ROR γt‐deficient mice led to enhanced tumour growth, that could be reverted by adoptive transfer of T h17 cells. Differences in tumour growth were not associated with changes in the accumulation or suppressive function of MDSC and regulatory T cells but were related to a decrease in the proportion of CD 4 + T cells in the tumour. Our results suggest that T h17 cells do not affect the recruitment of immunosuppressive populations but favour the recruitment of effector T h1 cells to the tumour, thereby promoting anti‐tumour responses.