Immune checkpoint blockade (ICB) antibodies against cytotoxic T–lymphocyte–associated protein 4 (CTLA-4) or programmed cell death 1 (PD-1) have demonstrated that reactivating anti-tumor immune responses can lead towards tumor regression1,2, and these ICB antibodies have been approved by the United States Food and Drug Administration (FDA) for the treatment of a broad range of tumors3–7. Here, PDCD1 is linked to neoplasm.