Peptide-based vaccination and induction of CD8+ T-cell responses against tumor antigens in breast cancer.

Tumor-associated antigens (TAAs) have been identified in many malignant tumors. Within these TAAs are peptide sequences that bind major histocompatibility complex (MHC) class I and class II molecules recognized by T cells triggering antigen-specific CD8+ cytotoxic T-cell and CD4+ T-helper cell responses. Efforts to develop vaccines for breast cancer have been underway for more than 20 years, including peptide and whole inactivated tumor cell vaccines as well as antigen-loaded dendritic cell vaccines. The majority of vaccine trials have used peptides, including single-peptide and multiple-peptide formulations using either MHC class I and class II epitopes in oil-based emulsions alone or in combination with an adjuvant, such as granulocyte-macrophage colony-stimulating factor, and Toll-like receptor agonists. Preclinical research in vitro and in animal models has been aimed at improving vaccine efficacy by identifying more immunogenic peptides and combinations of peptides and adjuvants and cytokine adjuvants that induce stronger immune responses and prolong T-cell memory. Clinical studies investigating the therapeutic potential of active immunization using peptide vaccines has found no serious side effects. In this review, we examine TAA peptide-based vaccination regimens showing promise in breast cancer patients that are also being investigated in clinical trials of safety and efficacy. We also discuss the current limitations in the peptide vaccination field and areas for future development.