PDCD1 and neoplasm: Interestingly, combined treatment with CTLA-4 mAbs (Ipilimumab) and PD-1 (nivolumab) mAbs can kill tumor cells to the greatest extent and delay the occurrence and development of tumors, including metastatic melanoma, metastatic renal cell carcinoma, colorectal cancer with MSI-H and MMR aberrations (123–125).