[Correlation between Immune Microenvironment Features and EGFR Mutation Status 
in Lung Adenocarcinoma]

The morbidity and mortality rates of lung cancer remain high worldwide, and lung adenocarcinoma is one of the most important tissue subtypes of lung cancer. Epidermal growth factor receptor (EGFR) mutation is an important driver gene mutation for lung adenocarcinoma. In recent years, immune checkpoint inhibitors (ICIs), such as programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) inhibitors, have achieved remarkable efficacy in some lung cancer patients. Patients with EGFR mutations enjoyed limited benefits from immunotherapy according to recent studies. This study aimed to explore the relationship between EGFR mutation status and the spatial distribution as well as infiltration number of various immune cells in patients with EGFR mutant lung adenocarcinoma.

This study included 62 lung adenocarcinoma patients who underwent surgery. Through multi-point sampling of surgically removed tumor tissues in different areas, 223 tumor tissue samples were finally obtained. We aquired EGFR mutations status including variant allele frequency (VAF) and mutation subtype in each tumor tissue by genetic test. Afterwards, hematoxylin-eosin (HE) staining, immunohistochemical staining and multiplex fluorescence immunohistochemistry staining have been performed, therefore the infiltration of various immune cells and the distribution of tertiary lymphoid structure (TLS) in tumor tissues were obtained by calculating the immunohistochemical score.

Compared with EGFR wild-type patients, patients with EGFR-mutant lung adenocarcinoma had more infiltration of CD68+ macrophages and major histocompatibility complex (MHC) class II antigen-presenting cells and higher spatial distribution heterogeneity of MHC class II antigen presenting cells in tumor tissues, while CD56+ natural killer cells and CD8+ T cells had lower infiltration. Tumor tissues with higher EGFR VAF were associated with lower cell infiltration such as CD3+ T cells, CD20+ B cells, CD56+ natural killer cells, CD68+ macrophages, CD8+ T cells, and only CD3+ T cells showed a lower spatial distribution heterogeneity. For the two common subtypes of EGFR mutations in Chinese population, tumor tissues with EGFR exon 19 deletion mutations have lower immune cell infiltration but higher spatial distribution heterogeneity of CD3+ T cells, CD56+ natural killer cells, CD68+ macrophages, and CD8+ T cells than that in EGFR exon 21 L858R mutant tumor tissues. Prognostic analysis found that patients with EGFR mutations with high degree of CD3+ T cells, CD20+ B cell infiltration and larger numbers of TLS formation and high spatial distribution heterogeneity of CD8+ T cell had longer disease-free survival.

EGFR-mutated lung adenocarcinoma had a unique "non-inflammatory" tumor microenvironment with low infiltration of immune cells, and there was also heterogeneity in the tumor microenvironment among the tumors with different mutation subtypes and mutation abundance. These differences were not only reflected in the number but also the spatial distribution of immune cell infiltration. Hence, further studies on the immune microenvironment of EGFR-mutant lung adenocarcinoma were of great significance for improving the efficacy of immunotherapy in EGFR-mutant lung adenocarcinoma patients in the future.