Endogenous IL-17 contributes to reduced tumor growth and metastasis.

It has been reported that ectopically expressed interleukin-17 (IL-17) in tumor cells suppresses tumor progression through enhanced antitumor immunity in immune competent mice or promote tumor progression through an increase in inflammatory angiogenesis in immune-deficient mice. The role of endogenous IL-17 in tumor immunity remains undefined. Here we showed that tumor growth and lung metastasis were enhanced in IL-17-deficient mice, associated with decreased interferon-gamma(+) natural killer cells and tumor specific interferon-gamma(+) T cells in the tumor draining lymph nodes and tumors. Together with the published data showing that in vitro transforming growth factor-beta and IL-6-polarized Th17 cells induce tumor regression, our work supports the notion that endogenous IL-17 or/and Th17 cells may play a protective role in tumor immunity.