Zhao and colleagues engineered CAR T cells to secrete IL-10, and tested them in syngeneic and xenograft mouse models of colon cancer, breast cancer, pancreatic cancer and melanoma, where IL-10 secretion promoted both proliferation and effector functions of CAR T cells, leading to complete regression of established solid tumors and metastatic cancers (179). The gene discussed is IL10; the disease is metastatic malignant neoplasm.