Development of an immune-related gene signature applying Ridge method for improving immunotherapy responses and clinical outcomes in lung adenocarcinoma

Background Lung adenocarcinoma (LUAD) is a major cause of cancer mortality. Considering the critical role of tumor infiltrating lymphocytes in effective immunotherapy, this study was designed to screen molecular markers related to tumor infiltrating cells in LUAD, aiming to improve immunotherapy response during LUAD therapy. Methods The ConsensusClusterPlus method was used for clustering immune molecular subtypes of LUAD. Immune cell infiltration and immunotherapeutic potential in each subtype was evaluated employing single-sample gene set enrichment analysis (ssGSEA), Tumor Immune Dysfunction and Exclusion (TIDE), and Immunophenoscore (IPS). Immune-related co-expression modules were classified by weighted gene co-expression network analysis (WGCNA) analysis. The sequencing data of immune-related genes were comprehensively analyzed by introducing a new computational framework and 10 machine learning algorithms (a total of 101 combinations) to determine the prognostic genes, which were further combined to develop an immune prognostic signature (IMMPS) using the stepCox and Ridge methods. The expression of the signature genes was validated by quantitative real-time PCR (qRT-PCR). Results Samples from The Cancer Genome Atlas dataset (TCGA-LUAD) were divided into two subtypes (immunosuppressive subgroup C1 and immune-activated subgroup C2); notably, the C2 subgroup was more likely to benefit from immunotherapy (p < 0.05). An IMMPS developed based on seven immune infiltrating cell-related genes (SEMA7A, EFHD2, CHST11, SLC24A4, MAL, JCHAIN, and SCARF1) could accurately predict the overall survival of LUAD in five LUAD cohorts, with an average C-index higher than 0.69. LUAD patients with a low IMMPS value had a higher immune cell infiltration (p < 0.05). In addition, the IMMPS exhibited better prediction performance in comparison to 154 published gene signatures, suggesting that the IMMPS was an independent prognostic risk factor for evaluating the overall survival of LUAD patients. Since BTNL9 was the most relevant immune checkpoint gene, in vitro experiment showed that the expression of the seven key genes (SEMA7A, EFHD2, CHST11, SLC24A4, MAL, JCHAIN, and SCARF1) in LUAD cell lines was consistent with that in normal lung epithelial cells after inhibiting BTNL9 expression (p < 0.05). Conclusions Our results contributed to a better understanding of immunological characteristics of LUAD. The IMMPS could serve as a promising tool for improving the clinical outcome of patients suffering from LUAD.