Expression of PD-1 and Its Ligands, PD-L1 and PD-L2, in Smokers and Never Smokers with KRAS-Mutant Lung Cancer

Introduction: Clinical responses to immune checkpoint blockade by anti-programmed cell death protein-1 (PD-1)/PD-L1 monoclonal antibodies in non-small-cell lung cancer (NSCLC) are associated with PD-L1 expression and smoking status. We aimed to determine the expression profile of PD-1 and its ligands, PD-L1 and PD-L2, in both smokers and never smokers patients with KRAS-mutant NSCLC. Methods: We retrospectively analyzed the clinical and molecular characteristics of 114 KRAS-mutant NSCLC patients (84 smokers and 30 never smokers) and their clinical tumor samples for the expression of PD-1, PD-L1, and PD-L2 by immunohistochemistry (IHC). We used murine monoclonal antibodies anti-PD-L1 (clone 9A11) and anti-PD-L2 (clone 9E5) to examine for tumor cell expression (0, negative; 1, weak; 2, moderate; 3, intense) and anti-PD-1 (clone EH33) for tumor-infiltrating lymphocytes. Results: PD-L1 expression was detected in 27 of 114 patients (24%; 95% confidence interval [CI], 16-33%) and associated with smoking status (current smokers, 44%; former smokers, 20%; never smokers, 13%; p = 0.03). Higher intensity of PD-L1 expression (IHC-2+/IHC-3+) was more frequently observed in smokers and associated with more pack-years. PD-L2 was positive in 54 of 114 patients (47%; 95% CI, 38-57%) and not related to smoking status. PD-1-positive tumor-infiltrating lymphocytes were present in 77 of 114 tumor specimens tested (68%; 95% CI, 59-77%) including 21 of 27 samples with PD-L1 expression and 39 of 54 samples with PD-L2-positive expression. We found that PD-L1 expression fades with the age of the specimens used for analyses decreasing beyond 3 years (p = 0.016). Conclusions: The expression of PD-1 and its ligands PD-L1 and PD-L2 is heterogeneous within KRAS-mutant NSCLC and suggests an inducible expression of PD-L1 by smoking.