In the mouse, tumor-infiltrating CD11b+ myeloid cells produce proinflammatory/protumorigenic cytokines (IL-6, IL-23, TNFα) [32–34] but, oddly, also anti-inflammatory cytokines (IL-10, transforming growth factor β [TGFβ]) and molecules with immune-suppressive function (Arg1, peroxynitrite, and indoleamine 2–3 dioxygenase) [8]. The gene discussed is IDO2; the disease is neoplasm.