Abstract 2897: ERBB2 amplicon passenger genes: A novel class of breast cancer antigens
Authors: Plautz Gregory E. , Modi Arun , Wang Li-Xin 
Published: May 2015

Abstract
DNA copy number amplification at the ERBB2 locus on 17q12-21 is a frequent genomic event, present in 10-15% of breast tumors. This gene-dense amplicon contains several genes that are aberrantly overexpressed in ERBB2+ breast cancer. We hypothesized that a subset of amplicon genes with minimal expression in normal tissue could serve as candidates for shared tumor-specific antigens. We eliminated from consideration other amplicon genes with high expression in specific tissues or broad expression in normal tissues due to the potential for autoimmune toxicity. Immunohistochemistry of a breast tumor microarray showed expression of MIEN, GRB7, PGAP3 proteins specifically in ERBB2+ tumor cells but not in stroma or in ERBB2 non-amplified breast tumor samples. We tested several peptide epitopes with predicted high affinity for HLA-A2 (&lt;50 nM) and confirmed that these could stabilize MHC expression on T2 cells. In vitro sensitization of normal donor lymphocytes with the predicted epitopes led to production of IFN-γ. Moreover, Dendritic cells pulsed with lysate from SKBR3 (ERBB2 amplified) but not MCF7 breast cancer cells could sensitize autologous lymphocytes to epitopes from amplicon proteins. This suggests that the natural abundance of the amplicon proteins in ERBB2 positive tumors is sufficient to provide cross-priming. To test whether the amplicon proteins could serve as tumor-rejection antigens we used the murine TM15 breast cancer cell line which has amplification of a syntenic region surrounding the murine Her2/neu gene. Quantitative PCR showed 50-fold overexpression of the amplicon gene pnmt in TM15 cells. Mice vaccinated with recombinant murine or human PNMT protein, but not ovalbumin, rejected challenge with TM15 tumor without any overt toxicity and developed memory against delayed re-challenge.These data indicate that normal host genes which are in immediate proximity to the oncogene ERBB2 are abnormally expressed at high levels in ERBB2+ breast tumor cells. Although the molecular mechanism leading to aberrant expression is unknown, analysis of several breast cancer microarray databases as well as TCGA data also show a very high correlation between ERBB2 overexpression and high expression of these passenger genes so this seems to be a general phenomenon. T lymphocytes normally have tolerance to non-mutated host proteins however tolerance can be reversed with proper sensitization conditions. Antigen overexpression in tumor cells might allow effector T cells to surpass an activation threshold while preserving tolerance for normal tissue. DNA copy number amplification of specific oncogenes is a frequent genomic event in cancer so the general strategy of targeting passenger genes on amplicons may have broader use in cancer immunotherapy.
Citation Format: Gregory E. Plautz, Arun Modi, Li-Xin Wang. ERBB2 amplicon passenger genes: A novel class of breast cancer antigens. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2897. doi:10.1158/1538-7445.AM2014-2897