Bone marrow‐derived mesenchymal stem cells inhibit CD8+ T cell immune responses via PD‐1/PD‐L1 pathway in multiple myeloma

Summary High expression of the inhibitory receptor programmed cell death ligand 1 (PD‐L1) on tumor cells and tumor stromal cells have been found to play a key role in tumor immune evasion in several human malignancies. However, the expression of PD‐L1 on bone marrow mesenchymal stem cells (BMSCs) and whether the programmed cell death 1 (PD‐1)/PD‐L1 signal pathway is involved in the BMSCs versus T cell immune response in multiple myeloma (MM) remains poorly defined. In this study, we explored the expression of PD‐L1 on BMSCs from newly diagnosed MM (NDMM) patients and the role of PD‐1/PD‐L1 pathway in BMSC‐mediated regulation of CD8+ T cells. The data showed that the expression of PD‐L1 on BMSCs in NDMM patients was significantly increased compared to that in normal controls (NC) (18·81 ± 1·61 versus 2·78± 0·70%; P