CTLA4 and neoplasm: CTP reduces the levels of PD-1, PD-L1, and CTLA4 in ApcMin/+ mice, which have been confirmed to regulate the immune reactivity of tumor cells (Sansom, 2000; de Vries et al., 2016), and antibodies against PD-1 and PD-L1 have been successfully used for tumor therapy (Sunshine and Taube, 2015).