Identification Of Novel Immune Checkpoint Biomarkers For Survival Prediction In Lung Adenocarcinoma

Objective Lung cancer is the leading cause of cancer death among both sexes globally.Immune checkpoint(ICP)plays a profound role in tumor biology.Characterization of ICP biomarkers and identification of novel prognostic signature is of values for risk-stratification,survival prediction,and therapy management of patients with lung adenocarcinoma(LUAD).This research sought to identify novel prognostic ICP biomarkers for LUAD patients.Methods RNA sequencing data of LUAD from the Cancer Genome Atlas(TCGA)database and microarray data from the Gene Expression Omnibus(GEO)database were downloaded.The prognostic value of 16 immune checkpoint genes(ICGs)was discovered from the TCGA dataset and further validated in the GEO dataset using the Kaplan-Meier and multivariate Cox analyses.Pearson correlation coefficients were used for correlations of expression of ICGs with five markers of tumor-infiltrating immune cells,as well as a Thl/IFNγ gene signature.Finally,gene set enrichment analysis evaluation(GSEA)was used to explore the potential molecular mechanisms of two immune checkpoint genes with prognostic value in lung adenocarcinoma,and the correlation between these two immune checkpoint genes and tumor immunoinfiltrating cells(TIICs)was also analyzed.Results Low expression levels of CD276,PVR,as well as the combination of high CD226 expression and low NECTIN2 expression(CD226+/NECTIN2-)were associated with favorable overall survival(OS).After adjusting known risk factors for survival,in the TCGA cohort,LUAD patients with low CD276,PVR and CD226+/NECTIN2-expression had a 35%,36%and 67%decreased risk for death respectively,compared to those with high CD276(hazard ratio[HR]0.65,P=0.041),PVR(HR 0.64,P=0.028)and CD226-/NECTIN2+expression(HR 0.33,P=0.004).These associations were validated using independent GEO datasets.In addition,immune-resistance subsets of infiltrating leukocytes were in correlation with ICG expression.CD226,CTLA4,and TIGIT were positively correlated with majorities of the 84 genes in the Th1/IFNγ gene expression signature.Furthermore,CD276 was associated with more established tumor immune signaling pathways than PVR,and might play a more significant role in the regulation of the immune microenvironment in lung adenocarcinoma.Conclusion This study identified and validated several novel immune checkpoint biomarkers for predicting prognosis of LUAD patients based on the TCGA and GEO databases.Low expression levels of CD276 or CD226+/NECTIN2-expression was associated with favorable overall survival,both of them were identified as independent prognostic factors.Low expression levels of PVR was also associated with favorable overall survival but not served as independent prognostic factor.In addition,immune-resistance subsets of infiltrating leukocytes were in correlation with ICG expression.Compared with PVR,CD276 was associated with more established tumor immune signaling pathways and might play a more significant role in the regulation of the immune microenvironment in LUAD.