Abstract C220: Characterization of potential immunologic targets found in both mice and man that are expressed in colon adenomas and colorectal cancer.
Authors: Broussard Elizabeth K. , Pritchard David , Lubet Ronald , Disis Mary L. 
Published: June 2012

Abstract
Multiple recent studies have demonstrated that CRC is immunogenic and that host adaptive immunity (especially by CD4+ T cells) may play a role in inhibiting disease relapse or progression. We have shown that overexpressed tumor associated proteins, those that are abundant in the cancer state but expressed at basal levels normal cells, can be immunogenic. The purpose of this study was to identify and characterize genes overexpressed in colorectal adenoma that maintain upregulation in colon carcinoma using publicly available microarray datasets deposited in the Gene Expression Omnibus. Such genes may encode proteins that could be suitable as immunologic targets for a colon cancer vaccine. We identified 5 high quality datasets (GSE 4183, 5206, 8671, 10950, 15960) where human colon adenoma or adenocarcinoma was directly compared to normal colon. Inclusion criteria for the datasets: commercial platforms only (Illumina or Affymetrix), primary tissue, normal colon expression included in the dataset, data generated after 2005, and authors granted access to microarray data. We reanalyzed these datasets and identified 100 genes that were at least 2-fold up-regulated in both adenoma and colorectal carcinoma, relative to normal colon. We hypothesized that genes which were highly conserved across species would potentially have greater biologic relevance, so we identified microarray studies in mouse colon cancer models. We identified 2 studies (GSE 422, 784) in APC Min (Min) mice and performed a similar analysis. We found 93 murine genes that were at least 2-fold up-regulated in gastrointestinal tumors relative to normal colon. Comparison of the human and rodent data sets revealed an overlap of 10 genes. We selected five potential antigens (FOXQ1, PHLDA1, S100A11, TNFRSF11B, TRIP13) for those with ≥90% protein homology between human and mouse. Using a web based algorithm program developed by TVG, we identified peptides that were predicted to be high affinity binders across multiple HLA DR alleles; characteristics we have shown to be associated with native epitopes of self tumor antigens. We selected and synthesized the 17 peptides predicted to be the highest binders, and vaccinated Min mice. Three antigens (FOXQ1 p=.002, S100A11 p=0.001, PHLDA1 p=0.002) demonstrated a statistically significant reduction in tumor count compared to vaccination with adjuvant alone. We evaluated the potential immunogenicity of peptides with IFN-g ELISPOT assays using splenocytes from vaccinated mice. We quantified antigen protein expression in Min tumors. We conclude that there are a limited number of genes up-regulated in adenoma and carcinoma and conserved across disease in mouse and man. In a mouse CRC model, we demonstrated that vaccination with three of these antigens resulted in a significant reduction in tumor development. These may serve as novel immunologic targets to prevent the progression from normal colonic epithelium to adenoma or carcinoma.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C220.