A novel regulation of PD-1 ligands on mesenchymal stromal cells through MMP-mediated proteolytic cleavage

T cells. We suggest that MMP-dependent cleavage of PD-1 ligands on fibroblasts may limit their immunosuppressive capacity and thus contribute to the exacerbation of inflammation in tissues. In contrast, carcinoma-associated fibroblasts appear PD-1 ligand-depleted through MMP activity that may impair physical deletion of exhausted defective memory T cells through apoptosis and facilitate their regulatory functions. These observations should be considered when using the powerful PD-1/PD-L1 blocking immunotherapies.