Considering the elimination of immunosuppressive CD8+ T cells in the TME as an example (Topalian et al., 2016), antibodies that can block cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death-1 (PD-1) have been marketed and have achieved remarkable results in the treatment of melanoma (Eroglu et al., 2015), lymphoma (Robert et al., 2015), Merkel cell carcinoma (Engels, 2019), and other tumors. Here, PDCD1 is linked to Merkel cell skin cancer.