Abstract 1584: MHC-restricted phosphopeptides as broad-based immunotherapeutic targets for cancer
Authors: Angela L. Zarling, Rebecca C. Obeng, Kara L. Cummings, Ashley N. Desch, Ann M. English, Jennifer M. Cottine, Andrew Norris, Louis B. Brill, Donna H. Deacon, Mark Conaway, Jeffrey Shabanowitz, Donald F. Hunt, Craig L. Slingluff, Victor H. Engelhard
Journal: Cancer Research (2012)

Abstract Identification of the antigens (Ags) recognized by CD8+ T cells specific for melanoma and other types of cancer cells has been motivated by the expectation that they will serve as the basis for a therapeutic vaccine or will be useful for the stimulation of more effective CD8+ CTL for adoptive immunotherapy. Few of the currently identified Ags are derived from source proteins directly associated with transformation or metastasis, and many are self-Ags which may be subject to tolerance mechanisms. We have defined a new array of phosphorylated peptides presented by HLA-A1, -A2, -A3, -B7, -B44 and HLA-B27 that are presented on melanomas from multiple patients at &amp;gt;1 copy per cell and derived from source proteins associated with tumorigenesis and metastasis. We evaluated the immunogenicity of several of the HLA-A2-restricted phosphopeptide Ags in an HLA-transgenic murine model system and in vitro human T cell cultures, evaluated the presence of the phosphorylated source protein or display of the phosphorylated epitope on cancers of different histological types, and investigated the ability of phosphopeptide-specific CD8+ T cells to prevent outgrowth of cancer cells in a xenogenic model. Evaluation of metastatic melanoma tissue microarrays and cancer cell lysates demonstrated that the phosphorylated source proteins for β-catenin (Ser33-phosphorylated), Breast cancer anti-estrogen resistance −3 (BCAR3; Thr130-phosphorylated), and Insulin receptor substrate-2 (IRS2; Ser1100-phosphorylated) were broadly expressed in melanomas and other cancers but not normal tissues. In addition, these epitopes can be utilized to elicit phosphopeptide-specific T cells in both murine HLA-A2 transgenic mice in vivo and human in vitro culture. The phospho-β-catenin, phospho-IRS2 and phospho-BCAR3-specific-T cells that were generated differentiate between the phosphorylated and non-modified forms of their respective peptides and recognize the endogenously processed and presented phosphopeptide on the surface of cancer cells. Finally, adoptive transfer of these phosphopeptide-specific T cells slowed outgrowth of melanoma tumors implanted in immunodeficient NOD.SCID.IL2Rα-/- mice. Thus, we have defined a new set of post-translationally modified epitopes derived from source proteins associated with tumorigenesis and metastasis that are immunogenic and capable of slowing tumor outgrowth in a xenograft model. Based on these results, we are currently planning a clinical trial utilizing these HLA-A2-restricted phosphopeptides in melanoma patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1584. doi:1538-7445.AM2012-1584