Abstract
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; characteristics we have shown to be associated with native epitopes of self tumor antigens. We selected and synthesized 19 peptides predicted to be the highest binders. We evaluated the potential immunogenicity of peptides with 1. IFN-g ELISPOT assays using PBMC from CRC patients and normal controls and 2. specific IgG antibody response with ELISA using sera from CRC patients and normal controls. We quantitated antigen gene expression using qPCR in cell lines representing microsatellite unstable (MSI), chromosome unstable (CIN) and CpG island methylator phenotype (CIMP) colorectal cancer. 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. Six proteins were positive by ELISA. Seven antigen genes were overexpressed relative to normal colon. 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. there was an overexpression of candidate genes across three different CRC phenotypes, and 4. these antigens may represent novel immunologic targets for CRC.
Citation Information: Cancer Prev Res 2010;3(12 Suppl):A32.
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