Characterization of PD-L1 expression and immune cell infiltration in nasopharyngeal cancer

Abstract Objectives Locally recurrent or metastatic nasopharyngeal cancer (NPC) remains an important challenge, with more effective and durable therapeutic options needed. Cancer immunotherapy, and in particular therapies that target the PD-L1/PD-1 immune checkpoint pathway, may provide new options to treat NPC patients. This study evaluated PD-L1 and CD8 expression levels and the respective associations with clinical and histopathological characteristics of patients with NPC. Materials and methods Diagnostic tumour biopsies were obtained before radical radiotherapy with or without chemotherapy from 161 patients with NPC. These biopsies were analysed for PD-L1 expression levels on tumour cells (TC) and tumour-infiltrating immune cells (IC), and for CD8 T-cell infiltration. Results were correlated with baseline characteristics and clinical outcomes with standard-of-care treatment regimens. Additionally, pre- and post-treatment–paired tumour samples were analysed (n = 146). Results 75% of tumours expressed PD-L1 on IC and 24% on TC. Baseline clinical characteristics of stage, sex and age did not correlate with PD-L1 expression. Additionally, overall survival and progression-free survival of standard-of-care treatment did not correlate with baseline PD-L1 expression. CD8 levels did correlate with clinical outcomes; however, results were confounded by other baseline characteristics. After treatment, PD-L1 expression dropped a median of 1.5% on IC and a median of 2.75% on TC. Median CD8 expression dropped 1.9%. Conclusions Majority of NPC biopsy samples demonstrated PD-L1 expression on ⩾1% of IC, with fewer expressing PD-L1 on TC. In contrast to previous smaller studies, no prognostic value was observed for PD-L1 expression levels in patients with NPC.