In a CT26 subcutaneous mouse tumor model, CpG-A slightly inhibited tumor growth but had no synergistic antitumor effect with the anti-PD-1 antibody; low doses of CpG-B significantly inhibited tumor growth and had a synergistic antitumor effect with the anti-PD-1 antibody; and CpG-C combined with the anti-PD-1 antibody inhibited tumor growth more rapidly and effectively than CpG-B because CpG-B significantly upregulated PD-L1 expression on multiple host immune cells, thereby promoting tumor immune escape [132]. Here, PDCD1 is linked to neoplasm.