Immune marker profiling and PD-L1, PD-L2 expression mechanisms across non-small cell lung cancer mutations.

Abstract

9076 Background: PD-1/PD-L1 axis inhibitors have been proven effective, especially in patients expressing Programmed Death Ligand 1 (PD-L1). Their clinical efficacy in patients with epidermal growth factor receptor (EGFR) activating mutations is still unclear, while KRAS mutations seem to be associated with high response rates. In this study we investigated the expression of PD-L1, PD-L2 and Tumor Infiltrating Lymphocyte (TIL) status as a function of mutation status in Non-Small Cell Lung Cancer (NSCLC). Methods: We used the AQUA method of quantitative fluorescence (QIF) to compare PD-L1 and PD-L2 expression and to characterize TILs populations and their activation status in over 150 NSCLC patient tumors with known mutation status. EGFR activation was assessed in situ using the proximity ligation assay (PLA) for EGFR and GRB2 and T cell activation was assessed using a novel multiplexed QIF assay including CD3, Granzyme B and Ki67. Results: PD-L1 tumor and stroma expression was significantly lower in EGFR mutant compared to KRAS mutant (p = 0.009) and EGFR/KRAS Wild Type (p < 0.0001) tumors, while they had a higher frequency of PD-L2 expression. Conversely, KRAS mutants had significantly lower PD-L2 tumor and stroma expression but they were also more inflamed with higher CD4+, CD8+ and CD20+ TILs. Subgroup analysis of patients by their TILs activation status revealed that EGFR mutants had a very high frequency of inactive TILs even though lymphocytes were present in the tumor microenvironment. In contrast, in KRAS mutants, when TILs were present, they were almost always active. Finally, we find that PLA-defined activated EGFR correlated with increased PD-L1 expression in EGFR mutants but not in EGFR WT, while TIL activation was associated with higher PD-L1 in EGFR/KRAS WT. Conclusions: Our findings are consistent with the unique biology of EGFR mutant tumors. The high frequency of inactive TILs could explain the low immune therapy response rates in this patient group. Similarly, in this group, the reason PD-L1 expression fails to predict response may be due to expression as a result of constitutive oncogenic signaling rather than immune signaling, which would be associated with high PD-L1 levels and TILs activation.