Although mAbs targeting either PD-1 or PD-L1 have showed certain anti-tumor efficacy in cancer patients (Hamanishi et al., 2016), current mAb agents have many intrinsic limitations such as expensive production, still poor therapeutic responses (only approximately 20% of patients with a durable response) (Yang et al., 2016), and considerable individual differences as well as immunotherapy-induced improper immune-related responses (Fishman et al., 2019). Here, PDCD1 is linked to cancer.