The lack of IL-17A is of particular interest because IL-17A has been proven to be strongly pro-tumourigenic in the DMBA/TPA model24, 25, and also to be a critical cytokine in combination with IL-6 for the inhibition of CD4+ T-cell immunosurveillance and apoptosis, and for the enhanced recruitment of macrophages and neutrophils26, 27, 28, the latter of which are pro-tumourigenic in this and other cancer models33, 34. The gene discussed is IL17A; the disease is cancer.