Soluble PD-1 and PD-L1: predictive and prognostic significance in cancer

// Xinxin Zhu 1 and Jinghe Lang 1 1 Department of Obstetrics and Gynecology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China Correspondence to: Jinghe Lang, email: langjh@hotmail.com , doctorlangjh@163.com Keywords: soluble, PD-1, PD-L1, tumor immunity, biomarker Received: April 25, 2017      Accepted: May 22, 2017      Published: May 31, 2017 ABSTRACT The membrane-bound molecules programmed death 1 (PD-1) and its ligand PD-L1 (PD-1/PD-L1) belong to the immune checkpoint pathway. PD-1 pathway downregulates effector T cells in immune response, thereby causing immune suppression. Recent studies have revealed that membrane-bound PD-1 and PD-L1 also have soluble forms. These soluble forms increase the complexity and diversity of the composition and function of the PD-1/PD-L1 signaling pathway. However, the exact roles of these molecules remain unknown. The objective of this systematic review was to elucidate the biological significance of soluble PD-1/PD-L1 in human cancers and evaluate whether they are potential diagnostic, therapeutic, or prognostic biomarkers. We expect to provide new clues for future research on soluble PD-1/PD-L1 pathway in human malignant tumors.