Purpose: The success of immune checkpoint inhibitors strengthens the notion that tumor growth and regression are immune regulated. To determine whether distinct tissue immune microenvironments differentially affect clinical outcome in non-small cell lung cancer (NSCLC), an extended analysis of PD-L1 and tumor-infiltrating lymphocytes (TIL) was performed.Experimental Design: Samples from resected adenocarcinoma (ADC 42), squamous cell carcinoma (SCC 58), and 26 advanced diseases (13 ADC and 13 SCC) treated with nivolumab were analyzed. PD-L1 expression and the incidence of CD3, CD8, CD4, PD-1, CD57, FOXP3, CD25, and Granzyme B TILs were immunohistochemically assessed.Results: PD-L1 levels inversely correlated with N involvement, although they did not show a statistically significant prognostic value in resected patients. The incidence and phenotype of TILs differed in SCC versus ADC, in which EGFR and KRAS mutations conditioned a different frequency and tissue localization of lymphocytes. NSCLC resected patients with high CD8^pos lymphocytes lacking PD-1 inhibitory receptor had a longer overall survival (OS: HR = 2.268; 95% CI, 1.056-4.871, P = 0.03). PD-1-to-CD8 ratio resulted in a prognostic factor both on univariate (HR = 1.952; 95% CI, 1.34-3.12, P = 0.001) and multivariate (HR = 1.943; 95% CI, 1.38-2.86, P = 0.009) analysis. Moreover, low PD-1 incidence among CD8^pos cells was a distinctive feature of nivolumab-treated patients, showing clinical benefit with a prolonged progression-free survival (PFS: HR = 4.51; 95% CI, 1.45-13.94, P = 0.004).Conclusions: In the presence of intrinsic variability in PD-L1 expression, the reservoir of PD-1-negative effector T lymphocytes provides an immune-privileged microenvironment with a positive impact on survival of patients with resected disease and response to immunotherapy in advanced NSCLC. Clin Cancer Res; 24(2); 407-19. ©2017 AACR.

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