Anti-PD-L1 peptide improves survival in sepsis

Background Sepsis remains a leading cause of death in most intensive care units. Many deaths in sepsis are due to nosocomial infections in patients who have entered the immunosuppressive phase of the disorder. One cause of immunosuppression in sepsis is T-cell exhaustion mediated by programmed cell death-1 (PD-1) interaction with its ligand (PD-L1). Studies demonstrated that blocking the interaction of PD-1 with PD-L1 with knockout mice or inhibitory antibodies reversed T-cell dysfunction and improved sepsis survival. This study assessed the efficacy of a novel short-acting peptide (compound 8) that inhibits PD-1:PD-L1 signaling in a clinically relevant second-hit fungal sepsis model. Methods Mice underwent cecal ligation and puncture to induce peritonitis. Three days later, mice received intravenous injection of Candida albicans. Forty-eight hours after Candida infection, mice were treated with compound 8 or inactive peptide. The effect of Candida infection on expression of coinhibitory molecules, PD-1, and PD-L1 were quantitated by flow cytometry on CD4⁺ cells, CD8⁺ cells, natural killer (NK) cells, and natural killer T-cells (NKT). The effect of compound 8 on survival was also examined. Results Four days after fungal infection, PD-1 and PD-L1 expressions were markedly increased on CD4⁺, NK, and NKT cells in septic versus sham-operated mice (%PD-1 on CD4⁺, 11.9% versus 2.8%; and %PD-L1 on NKT, 14.8% versus 0.5%). Compared with control, compound 8 caused a 2-fold increase in survival from 30% to 60%, P < 0.05. Conclusions Compound 8 significantly improved survival in a clinically relevant immunosuppressive model of sepsis. These results support immunoadjuvant therapy targeting T-cell exhaustion in this lethal disease.