Evaluating the PD-1 Axis and Immune Effector Cell Infiltration in Oropharyngeal Squamous Cell Carcinoma

Programmed death-1 (PD-1) inhibitors are approved for the treatment of patients with recurrent and metastatic squamous cell carcinoma of the head and neck (SCCHN). Ongoing and planned randomized phase 3 trials are testing the benefit of combining PD-1/programmed death-ligand 1 (PD-L1) inhibitors with chemoradiation for patients with locoregionally confined SCCHN. Few studies have investigated relationships among potential predictive pathologic biomarkers such as PD-L1, PD-L2, and PD-1 in this population and associations between these markers and clinical characteristics.

We retrospectively reviewed records and pathology from 81 patients with locoregional oropharynx SCCHN treated with curative intent. Samples were analyzed for PD-L1, PD-L2, PD-1, CD8, and CD56 expression using immunohistochemistry. Human papilloma virus (HPV) status was determined by p16-immunohistochemistry and confirmed by in situ hybridization or polymerase chain reaction-based HPV typing. Correlations between HPV status, clinical features, and recurrence status with immune markers in both tumor and tumor-associated stroma were determined. Hazard ratios were estimated via Cox proportional hazards model.

Tumor PD-L1 expression was inversely associated with age (P = .01) and the highest levels of expression (>30% of tumor cells) were observed in HPV-associated tumors. There was a correlation between tumor and stromal PD-L1 expression (P = < .0001). PD-1 and CD8 expression within tumor deposits was associated with HPV status (P = 0.003 and P = .008, respectively) and decreased local recurrence (P = .001 and P < .001, respectively). In addition to the association between tumor and stromal PD-1 (P < .0001), PD-1 was also correlated with tumor PD-L1 expression (P < .001). CD56+ natural killer cell infiltrates correlated with PD-L1 expression.

In patients with untreated oropharyngeal SCCHN, HPV-associated tumors displayed the highest levels of PD-L1 expression and PD-1+ and CD8+ immune cells. Locally recurrent tumors had lower levels of PD-L1, PD-1, and CD-8 positivity. Whereas almost all SCCHN tumors had CD56+ infiltrating natural killer cells, most tumors didn't have PD-L2 expression. These associations may help predict which patients may benefit most from immunotherapeutic approaches.