This study aimed to identify Tumor Associated Antigens (TAA)s by Immunoaffinity purification of MHC peptides and LCMS analysis, verifying their immunogenicity and testing their tumor control potential in a highly aggressive preclinical model of triple-negative breast cancer in mice. Among the MHC peptides thus identified, an Endogenous Retroviral (ERV) peptide was also found, and this peptide, as well as several other peptides from TAAs, were shown to possess tumor control potential in a cancer vaccine setting in mice, by restricting tumor growth compared to controls.