CD8A and neoplasm: Because both CyTOF and coculture experiments showed that T cell proliferation was inhibited and that this inhibition could be attributed to immune checkpoint blockade mediated by the PD-1/PD-L1 interaction [61, 62], we next examined the protein levels of PD1 in T cells by co-staining with antibodies against CD8 and PD1 in these tumor tissues.