Programmed Cell Death Ligand 1 Expression in Resected Lung Adenocarcinomas: Association with Immune Microenvironment

Introduction: Programmed cell death ligand 1 (PD-L1) expression on tumor cells can be upregulated via activation of CD8⁺ cytotoxic T lymphocytes (CTLs) or the T helper cell (Th1) pathway, counterbalancing the CTL/Th1 microenvironment. However, PD-L1 expression in association with subtypes of tumor-associated lymphocytes and molecular alterations has not been well characterized in lung adenocarcinomas.

Methods: PD-L1 expression was evaluated in 261 resected lung adenocarcinomas using tissue microarrays and various scoring systems, and was correlated with clinicopathologic/molecular features, including the extent/subtype of tumor-associated lymphocytes (i.e., CD8, T-bet [Th1 transcription factor], and GATA3 [Th2 transcription factor]), and patient outcomes.

Results: PD-L1 expression was present in 129 (49%), 95 (36.5%), and 62 (24%) cases using cutoffs of ≥1%, ≥5%, and ≥50%, respectively, 98 (38%) by H score and 72 (28%) by immune score. PD-L1 expression was associated with abundant CD8⁺ and/or T-bet⁺ tumor-infiltrating lymphocytes and EGFR wild-type, significant smoking history, and aggressive pathologic features. In addition, concurrent PD-L1 expression and abundant CD8⁺ tumor-associated lymphocytes were seen in 25% of KRAS mutants or cases with no alterations by clinical molecular testing as opposed to only 7.4% of EGFR mutants. PD-L1 expression was significantly associated with decreased progression-free and overall survival rates by univariate analysis, but not by multivariate analysis.

Conclusion: PD-L1 expression in resected lung adenocarcinomas is frequently observed in the presence of CTL/Th1 microenvironment, in particular in those with KRAS mutations or no common molecular alterations, suggesting that blockade of the PD-1/PD-L1 axis may be a promising treatment strategy to reinstitute active immune response for at least a subset of such patient populations.