• Takeo Nomi, Masayuki Sho, Takahiro Akahori, Kaoru Hamada, Atsushi Kubo, Hiromichi Kanehiro, Shinji Nakamura, Koji Enomoto, Hideo Yagita, Miyuki Azuma, and Yoshiyuki Nakajima.
• Department of Surgery, Second Department of Internal Medicine, First Department of Internal Medicine, Nara Medical University, Nara, Japan.
• Clin Cancer Res. 2007 Apr 1; 13 (7): 2151-7.

PurposeThe programmed death-1 ligand/programmed death-1 (PD-L/PD-1) pathway has been recently suggested to play a pivotal role in the immune evasion of tumors from host immune system. In this study, we tried to reveal the clinical importance and therapeutic potential of the PD-L/PD-1 pathway in pancreatic cancer, which is one of the most aggressive and intractable malignant tumors.Experimental DesignWe used immunohistochemistry to investigate PD-L expression in 51 patients with pancreatic cancer who underwent surgery and explored the therapeutic efficacy of blocking the PD-L1/PD-1 pathway in murine pancreatic cancer in vivo.ResultsPD-L1-positive patients had a significantly poorer prognosis than the PD-L1-negative patients, whereas there was no significant correlation of tumor PD-L2 expression with patient survival. PD-L1 expression was inversely correlated with tumor-infiltrating T lymphocytes, particularly CD8(+) T cells. These clinical data have suggested that the PD-L1/PD-1 pathway may be a critical regulator in human pancreatic cancer. Monoclonal antibodies against PD-L1 or PD-1 induced a substantial antitumor effect on murine pancreatic cancer in vivo. PD-L1 blockade promoted CD8(+) T-cell infiltration into the tumor and induced local immune activation. Furthermore, the combination of anti-PD-L1 monoclonal antibody and gemcitabine exhibited a significant synergistic effect on murine pancreatic cancer and resulted in complete response without overt toxicity.ConclusionOur data suggest for the first time that PD-L1 status may be a new predictor of prognosis for patients with pancreatic cancer and provide the rationale for developing a novel therapy of targeting the PD-L/PD-1 pathway against this fatal disease.

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