CD274 and neoplasm: Tumor-derived MDSCs activate the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/nuclear factor kappa B (NF-κB) signaling pathway in PD-1- PD-L1+ Bregs via the PD-1/PD-L1 axis, which mediates their immunosuppressive function [62].