Immune checkpoint blockades, including anti-CTLA4 antibody (ipilimumab), anti-PD-1 antibodies (pembrolizumab and nivolumab), and anti-PD-L1 antibodies (atezolizumab and durvalumab), have showed remarkable and durable responses across multiple cancer types and received FDA approval [21, 26, 30, 31]. Here, PDCD1 is linked to cancer.