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Background Barrett’s esophagus (BE) is an established risk factor for the development of high-grade dysplasia (HGD) or esophageal adenocarcinoma (EC). Due to poorly defined clinical predictors of progression, biomarkers of progression risk are in high demand. In order to identify progression risk indicators, we examined the utility of immune cell density and proteomic profiling in biopsy samples from patients with BE.Methods Barrett’s esophagus (BE) paraffin embedded tissue samples (n=58) from patients with non-dysplastic BE undergoing surveillance biopsy were examined. During follow-up, 25 patients were diagnosed with HGD or EC (‘progressors’), while 33 patients did not progress during at least 5 years of surveillance (‘non-progressors’). To analyze immune markers for cell densities, samples were stained for CD3 and CD8 positive lymphocytes, CD68/CD86 co-positive (‘M1- like’) macrophages, and CD68/CD206 co-positive (‘M2-like’) macrophages. Regions of interest (ROI) were selected from the lamina propria of the gastroesophageal junction in the region of BE. Subgroup comparisons of immune cell densities were carried out using the Wilcoxon rank sum test for the progression outcome. Proteomic profiling was assessed using label-free, liquid chromatography-tandem mass spectroscopy (LC-MS/MS), using data-independent acquisition. The raw LC-MS/MS data were searched using Spectronaut against a spectral library generated from 6 progressor and 6 non-progressor samples. Differential protein expression analysis was conducted using Perseus to compare the progressor and non-progressor groups.Results A total of 756 ROIs were examined for non-progressors and 360 ROIs were examined for progressors. The CD3+ lymphocyte density was higher in progressors vs. non-progressors (&xbar;: 4899.9 vs. 2633.9, p=0.02), whereas the CD8+ lymphocyte density was lower (1359 vs 929, p=0.04). M1-like macrophages were significantly elevated in progressors (&xbar; 91.4 vs. 33.8, p<0.001), while M2-like macrophages were decreased (33.3 vs 81.9, p<0.001) ( figure 1). A total of 7,209 proteins were identified across the samples, among which 163 were differentially-expressed based on progression risk (false positive rate<0.05). 4 major GO processes and KEGG pathways were associated with progressors: rRNA processing, Wnt signaling, bacterial invasion of epithelial cells, and G protein-coupled receptor signaling (figure 2).Conclusions Our findings indicate the potential value of immunologic biomarkers in BE surveillance. Specifically, an increase in lamina propria lymphocytes with a relative paucity of CD8+ cells, and a repolarization of macrophages toward M1-like vs. M2-like phenotypes may be early indicators of progression risk in this population.Ethics Approval The investigation was approved by the Allegheny Health Network Institutional Review Board and was conducted in accordance with applicable federal and state laws and regulations. The study followed Good Clinical Practice: Consolidated Guideline established by the International Conference on Harmonization (ICH).Abstract 1206 Figure 1Immunohistochemistry of Barrett’s esophageal tissue. IHC images of non-progressors and progressors with average cell densities of immune cellsAbstract 1206 Figure 2Proteomic analysis of comparing Barrett’s esophagus. Proteomap and enrichment analysis comparing Barrett’s esophagus progressors to non-progressors