Tumor PD-L1 status and CD8⁺ tumor-infiltrating T cells: markers of improved prognosis in oropharyngeal cancer

Introduction: The aim of this study was to evaluate the expression of PD-L1 in oropharyngeal squamous cell carcinoma. Its relation with clinicopathological variables, tumor infiltrating lymphocytes and survival was also determined.

Results: Positive PD-L1 status for the SP142 clone related with improved overall survival in oropharyngeal squamous cell carcinoma. Tumors heavily infiltrated by tumor infiltrating lymphocytes were also linked with better outcome, and this as well for the total number of tumor infiltrating lymphocytes as for the CD3⁺ and CD8⁺ T cell count. A Cox proportional hazard model proved that solely infiltrating CD8⁺ T cells exhibit a positive effect on overall survival (hazard ratio = 0.31 [0.14-0.70]; P = 0.0050).

Materials and methods: Formalin-fixed, paraffin-embedded tissue from oropharyngeal tumors of 99 patients was immunohistochemically stained for PD-L1 (SP142 and 22C3 clones), CD3, CD8 and FoxP3. Expression of PD-L1, CD3, CD8, FoxP3 and HPV status were correlated with clinicopathological variables. Overall survival was determined by a log-rank (Mantel-Cox) test whereas the Cox proportional hazard model was used for multivariate analysis.

Conclusions: Our results demonstrate that CD8⁺ T lymphocytes constitute an independent prognostic marker in patients diagnosed with oropharyngeal squamous cell carcinoma. PD-L1 positivity for SP142, but not for 22C3, also tends to have a positive effect on survival in oropharyngeal squamous cell carcinoma.