PD-L1 is a critical mediator of regulatory B cells and T cells in invasive breast cancer.

Regulatory T cells (Tregs), a key mediator in regulating anti-tumor immune suppression, tumor immune escape, metastasis and relapse, are considered an important therapeutic target in immunotherapy of human cancers. In the present investigation, elevated CD19 CD24 CD38 regulatory B cells (Bregs) were observed in PBMCs of invasive carcinoma of breast (IBCa) patients compared with that in patients with fibroadenoma (FIBma) or healthy individuals, and the positive correlation existed between Bregs and CD4 CD25 CD127 Tregs (r = 0.316, P = 0.001). We found that PD-L1 expression was higher on Bregs in IBCa patients compared with patients with FIBma or healthy individuals (P < 0.05, respectively), and that a tight correlation exists between CD19 CD24 CD38 PD-L1 Bregs and CD19 CD24 CD38 Bregs (r = 0.267, P = 0.007), poor TNM phases and up-regulated expression of PD-L1 on Bregs. The pattern of PD-1 expression on CD4 T cells indicated that high level of PD-1 expressed on CD4 CD25 CD127 effector T cells (P < 0.001). More importantly, the presence of PD-L1 on Bregs was positively correlated with Tregs (r = 0.299, P = 0.003), but negatively correlated with PD-1 effector T cells (r = -0.22, P = 0.031). Together, results of the present study indicated that PD-L1 is an important molecule on Bregs, mediated the generation of Tregs in IBCa.