Overexpression Of Programmed Death Ligand 1 In Dendritic Cells Inhibits Allogeneic Lymphocyte Activation In Mice

Background. Co-stimulatory molecules are pivotal for T cell activation. It is increasingly recognized that programmed death ligand 1 (PD-L1) is a novel costimulatory molecule, which raises the question as to whether PD-L1 regulates T cell responses. This study aimed to investigate the inhibitory effects of PD-L1 on T cell activation.Materials and Methods. We constructed a transgenic vector containing the complete PD-L1 gene, which interacts with the inhibitory receptor PD-1 in T cell-mediated immune activation. Donor dendritic cells (DCs) derived from C57BL/6 mice were transfected with PD-L1 and mixed with allogeneic, recipient T cells from BALB/c mice. The T cell activation was determined by the MTT assay and T cell proliferation was determined using carboxyfluoroscein succinimidyl ester (CFSE)-labeling following in vitro mixed leukocyte reactions.Results. The expression of PD-L1 protein in PD-L1-transfected DCs was 47.97% +/- 1.06%, compared with 4.66% +/- 0.76% and 5.30% +/- 0.60% in blank and negative controls, respectively (P < 0.05). PD-L1 protein was effectively expressed in DCs. Furthermore, in DCs stably transfected with PD-L1, T cell activation was significantly suppressed and T cell proliferation rate was decreased by 35% compared with untransfected DCs (P < 0.05).Conclusion. PD-L1 delivers an immunoinhibitory signal, suppressing T cell activation. Overexpression of PD-L1 signaling induces tolerance, which presents a promising immunotherapeutic approach for long-term graft acceptance. (C) 2012 Elsevier Inc. All rights reserved.