PDCD1 and metastatic neoplasm: A fraction of CTLs in the CD8+ T cell subtype expressed high levels of PD1, CTLA4, and TIGIT inhibitory receptors in both primary and metastatic tumor samples, and their interacting ligand transcripts such as PDCDILG2 and CD80 were overexpressed in a small fraction of CD4+T cells, CAFs, and malignant cell subpopulations (Figure 4C).