PDCD1 and neoplasm: Despite the lack of cross-reactivity with mouse PD-L1, CCX559 demonstrated dose-dependent anti-tumor activity in two mouse models: the MC38-hPD-L1 model, where human PD-L1 on the tumor cells activates PD-1 to suppress anti-tumor responses of the mouse immune system; and the xenograft model, where human PD-L1 on A375 tumors activates PD-1 on hPBMCs to inhibit cytotoxic immune responses.