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 impact on clinical outcome in Non Small Cell Lung Cancer (NSCLC), an extended analysis of PD-L1 and Tumor Infiltrating Lymphocytes (TILs) was performed. Experimental Design Samples from resected adenocarcinoma (ADC 42) and squamous cell carcinoma (SCC 58) and from 26 advanced diseases (13 ADC, 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 was immunohistochemically assessed. Results PD-L1 levels inversely correlated with N involvement although did not show a statistical significant prognostic value in resected patients. The incidence and phenotype of TILs differed in SCC vs 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 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 CD8pos 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.
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