In mice bearing tumors and cancer patients, the production of immune suppressive cytokines such as interleukin (IL)-10 and transforming growth factor (TGF)-β is accelerated, and immune regulatory cells such as regulatory T (Treg) cells and IL-10-producing type I Treg (Tr1) cells are highly infiltrated in tumor microenvironment. The gene discussed is IL10; the disease is neoplasm.