Abstract MUC1 is overexpressed in diverse human carcinomas and hematological cancers, and therefore serves as a potential target for immunotherapy. The MUC1 molecule has two distinctive subunits, formed by autocleavage with a SEA domain. The N-terminal (MUC1-N) is the large extracellular domain, and the C-terminal (MUC1-C) has three subunits: a small extracellular domain that is covalently bound to MUC1-N, a single transmembrane domain and a cytoplasmic tail. It has been reported by Kufe et al that the MUC1-C subunit transduces signals that confer growth and survival responses. The MUC1-C cytoplasmic tail located downstream of the SEA domain is sufficient for the induction of anchorage independent growth and tumorigenicity. MUC1-C overexpression is also highly associated with poor prognosis in patients with lung cancer and breast cancer. We and others have previously reported on HLA-A2 binding agonist epitopes to MUC1-N. The objective of this investigation is to identify and characterize HLA-A3 binding cytotoxic T-lymphocyte (CTL) epitopes and agonist epitopes of the MUC1-C subunit. The intention is to add these peptides to vaccines against MUC1 positive carcinomas, as well as using them for monitoring patients’ immune responses in clinical MUC1 vaccine trials. The generation of cellular immune responses to MUC1-C would thus target the portion of MUC1 that is most biologically relevant to the transformation process. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5524. doi:10.1158/1538-7445.AM2011-5524