Abstract 6122: Different characteristics of tumor immune microenvironment between LUSC and LUAD

Abstract

Abstract Background: Patients with lung squamous cell carcinoma (LUSC) have higher tumor mutation burden (TMB) and PD-L1 expression than those with lung adenocarcinoma (LUAD). Several studies showed that tumor immune microenvironment (TIME), mainly the tumor-infiltrating immune cells, may affect the efficacy of immunotherapy. However, the comparison of tumor immune microenvironment between LUAD and LUSC is little known. Methods: 14 patients with LUSC and 21 patients with LUAD were enrolled in the retrospective analysis of multiple immunofluorescence staining to assess the number of immune cells. Genomic profiling of DNA was performed on formalin-fixed paraffin-embedded tumor samples from 3752 LUAD and 459 LUSC patients by NGS with 733 cancer-related genes panel. TMB is defined as the total counts of single nucleotide variants and indels in the exon region. Results: Overall, as the most abundant tumor-infiltrating immune cells in both groups, CD3+ cells are more in LUAD [median (number/mm2 in LUSC vs in LUAD): 312 vs 918, p = 0.02]. However, there were no significant differences in CD8+ T cells (median: 48 vs 36, p = 0.74), indicating higher infiltration of T lymphocytes rather than cytotoxic T lymphocytes (CTLs) in LUAD than that in LUSC. Unlike in tumor, LUAD patients had both more T lymphocytes (p < 0.001) and CTLs (p < 0.01) in stroma. Besides, LUSC was correlated with fewer M2 tumor-associated macrophages (TAMs) and PD-1+ immune cells (p < 0.001; p = 0.02), while no significant differences were found in tumor-infiltrating FOXP3+ cells (p = 0.41) and B lymphocytes (p = 0.61). In addition, natural killer cells were the fewest among the tumor-infiltrating lymphocytes detected in both groups (median: 2 vs 13). Similar to the previous studies, TMB level was higher in LUSC (median: 8.94 vs 3.36, p < 0.0001). Although LUSC patients had a larger proportion of positive PD-L1 expression (45% vs 30.5%, p < 0.0001) and strong PD-L1 expression in tumor cells (20.9% vs 10.7%, p < 0.0001), the number of CTLs and TAMs expressing PD-L1 is significantly lower than that in LUAD ( p = 0.04; p = 0.0001). Conclusion: LUAD had more immune invasion, while LUSC was related to higher TMB and PD-L1 expression. It suggested that the mechanisms affecting the benefits of immunotherapy may be different. The immune microenvironment of tumor and stroma should be considered simultaneously to explore the mechanism of immunotherapy and the respective thresholds should be selected according to the types of immune cells. Citation Format: Na Li, Mengna Hu, Ding Zhang, Xiaoyu Ji. Different characteristics of tumor immune microenvironment between LUSC and LUAD [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6122.