PDCD1 and cancer: For examples, tumor necrosis factor superfamily member 9 (TNFSF9), programmed cell death-1 (PDCD1) and cytotoxic T-lymphocyte-associated protein-4 (CTLA4) are the common immune checkpoint markers in tumor immunotherapy and have been maturely applied in treatments of many kinds of cancers, including kidney carcinoma[32] and malignant uveal melanoma[33].