The circulating pool of functionally competent NK and CD8+ cells predicts the outcome of anti-PD1 treatment in advanced NSCLC

•Immune checkpoint blockade (ICB) has shown unprecedented results in NSCLC.•Immune profiles predictive of ICB efficacy have not been entirely assessed.•Tissue and circulating immune cells were analyzed in nivolumab treated NSCLC.•The pool size of circulating NK and CD8+ cells positively impacts on ICB response.•Cytometric assay of immune effector cells may define patients who benefit from ICB. A prospective investigation of the circulating immune profile in NSCLC patients receiving nivolumab was performed to identify potentially predictive parameters. Flow Cytometry of peripheral blood (PB) CD3+, CD8+, CD4+, NK, Treg and MDSCs was prospectively performed in 31 consecutive advanced NSCLC patients at baseline (T0) and after 2 (T1) and 4 (T2) cycles of bi-weekly nivolumab. Functional molecules (PD-1, CD3ζ, Granzyme B, Perforin), cell proliferation (Ki67) and NK receptors (NKG2 A, NKG2D, NKp30) were also explored. The immunohistochemical evaluation of PD-L1 and TILs was restricted to available tumor biopsies. Tissue and circulating parameters were correlated to clinico-pathological features and treatment outcomes. KRAS mutations, active smoking, COPD and steroid treatment conditioned a different distribution of circulating phenotypes. At baseline, clinical benefit (CB, n = 19) group displayed higher number of phenotypically active NK and PD-1+CD8+ cells (p