PD-L1 Associates with The Expression of Cancer Cell-Intrinsic PD-1 and p-S6 Proteins and Predicts A Good Prognosis in Nasopharyngeal Carcinoma

Aims: : programmed cell death ligand 1 (PD-L1) is the ligand of programmed death 1 (PD-1), which is a host immunity inhibitory receptor. Expression of PD-L1 in diverse tumor types has been widely discussed, while there is little research about tumor intrinsic-PD-1. P-S6 is an important downstream effector in the PI3K/AKT/mTOR pathway. Our study was focus on investigating PD-L1/PD-1/ p-S6 protein expression and aimed to illustrate their relationship in nasopharyngeal carcinoma (NPC). Methods: : the expression of PD-1, PD-L1 and p-S6 proteins in tissues of NPC, non-cancerous nasopharyngeal epithelia, primary lesions and matching metastases was detected by immunohistochemistry. Results: : PD-1, PD-L1 and p-S6 expression and co-expression of PD-1 and PD-L1 proteins were significantly higher in NPC than in the non-cancerous control tissue, respectively (all P <0.05). Furthermore, there was evidently elevated PD-1 expression and co-expression of PD-1 and PD-L1 in matched metastasis of NPC compared to their primary lesions (all P <0.01). NPC patients with positive expression of PD-L1 showed significantly higher overall survival rate than others ( P =0.035). Multivariate Cox proportional hazard regression analysis confirmed that positive expression of PD-L1 and p-S6 were independent prognostic factors for NPC patients. Conclusions: positive expression of PD-L1 associates with expression of cancer cell-intrinsic PD-1 and p-S6, PD-L1 might serve as a good prognostic biomarker and p-S6 could be a valuable independent poor prognostic biomarker for NPC patients.