Research progress on the intrinsic non-immune function of PD-L1 in tumors (Review)

Programmed death ligand 1 (PD-L1) is widely expressed in human tumors. It is widely known for its immunosuppressive function as it can help tumor cells evade T cell immune killing through the PD-1/PD-L1 signal. A number of clinical trials have proved that the destruction of the combination of PD-1 and PD-L1 by antibodies could significantly affect patients with advanced cancer. However, a number of patients with cancer still cannot benefit from PD-1/PD-L1 blocking therapy. The main reason is that PD-L1 also has some intrinsic regulatory functions to promote the progression of tumors. PD-L1 Protein contains an intrinsic domain that could link to other signal pathways, but the mechanism has not yet been fully revealed. The present review mainly discussed the non-immune checkpoint functions of PD-L1, such as its role in regulating cell proliferation, cell metabolism, drug resistance and maintaining epithelial-mesenchymal transition and stemness.