Identification of discrepancy between CTLA4 expression and CTLA4 activation in gastric cancer

Objective: Recently, immune checkpoints blockers showed higher anti-tumor activity for advanced gastric cancer (GC). The purpose of the study is to find out predictive biomarkers related to anti-cytotoxic lymphocyte antigen 4 (CTLA4) therapy. Materials and methods: Datasets of gene expression omnibus (GEO), the cancer genome atlas (TCGA), and gene set enrichment analysis (GESA) were extracted. Differential expression of CTLA4 between cancer tissues and normal mucosa, enrichment of WT (wild type) vs. CTLA4_KO (knockout) upregulated gene set and clinical significance were analyzed. The expression of CTLA4, CD3, and granzyme A (GZMA) were validated on 30 cases of Chinese GC. Microsatellite instability (MSI) marker MLH1 and Epstein-Barr virus (EBV) marker EBER were examined on 30 cases of Chinese GC by immunohistochemistry and in situ hybridization. Results: CTLA4 was upregulated in GC tissue relative to normal mucosa in datasets of GSE27342 (fold change = 1.586, p < .001) and GSE63089 (fold change = 1.365, p < .001). Increased CTLA4 expression was positively related to CTLA4 activation. EBV-associated GC (EBVaGC) and microsatellite instability GC (MSIGC) disclosed higher CTLA4 levels than other GCs. Genomic stability GC (GSGC) also showed higher enrichment score of CTLA4 activation. CTLA4 activation resulted in shorter overall survival in GC. The expression level of CTLA4 was well correlated to expression levels of GZMA (R = 0.701, p < .001) and CD3 (R = 0.750, p < .001). Conclusions: Based on bioinformatics analysis, GSGC should be worth noticed as a potential GC subtypes responsive to anti-CTLA4 treatment.