PDCD1 and neoplasm: CircRNA-002178 could enhance PDL1 expression via sponging miR-34a in lung adenocarcinoma (LUAD) cells and also be delivered into T cells through tumor-secreted exosomes to promote PD1 expression via sequestering miR-28-5p, thereby inducing CD8 + T cell depletion and inhibiting their anti-tumor activity [29].