Abstract PR-9: Characterization of colon cancer associated antigens which would be key therapeutic targets in the prevention of disease relapse or progression.
Authors: Broussard Elizabeth K. 
Published: June 2012

Colon cancer (CRC) is an immunogenic tumor and adaptive immunity may play a role in inhibiting disease relapse. A vaccine to boost cellular immunity in CRC patients could prevent disease recurrence, but there have been few defined immunogenic proteins identified as vaccine candidates. TVG has shown that overexpressed tumor associated proteins, abundant in the cancer state but expressed at basal levels in normal cells, can be immunogenic. We hypothesized that ideal candidate antigens would be ones already validated as prognostic markers in multivariate analysis. We performed a directed literature review using search words e.g. colon cancer, prognosis, biomarker, multivariate analysis. We selected a panel of eight proteins based on (1) incidence of expression, (2) independent predictor of poor prognosis, (3) independent predictor of early disease recurrence, and (4) known biologic function in CRC pathogenesis. 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. We selected and synthesized 19 peptides predicted to be the highest binders. We evaluated the potential immunogenicity of peptides with IFN-g ELISPOT assays using PBMC from CRC patients and normal controls. The eight proteins are: CDC25B, COX-2, EBAG9, EGFR, Fascin-1, IGF-1R, PRL-3 and VCP. Two of the eight proteins had already been shown to be human tumor antigens. For all candidate antigens there was a greater IFN-g response in CRC patients than in controls; for three proteins, this difference reached statistical significance. We then evaluated the efficacy of vaccination in reducing tumor formation in a mouse model of carcinogen induced CRC. FVB mice were vaccinated with PBS alone, adjuvant alone, or adjuvant plus peptide vaccine. Seven days after final immunization, mice were treated with AOM for 6 weeks, and all mice sacrificed at 25 weeks of age. Four antigens (COX-2 p&lt;.0001, CDC25B p&lt;.0002, and EGFR p=.01, Fascin-1 p=.05) demonstrated a statistically significant reduction in the development of colon tumors 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 AOM tumors. We conclude that: 1. biologically relevant CRC associated proteins can be identified that are associated with prognosis, 2. epitopes predicted to bind multiple DR alleles, derived from candidate antigens, elicit T cell responses greater in CRC patients than in normal controls, 3. vaccination with peptides derived from four antigens resulted in a statistically significant reduction in the development of colon tumors in a mouse model, and 4. these antigens may represent novel immunologic targets for CRC.

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 PR-9.