Therapeutic breast cancer vaccines: a new strategy for early-stage disease

Treatment of breast cancer in the adjuvant setting has changed rapidly over the last few years. In addition to improvements in chemotherapy, radiation, hormone manipulation, and surgery, immunotherapy has emerged as an effective adjunct for the treatment of breast cancer. Passive immunotherapeutic agents such as trastuzumab have been widely adopted as the standard of care for HER-2/neu overexpressing breast cancer. Vaccine therapy in the metastatic setting has yet to demonstrate clinical significance in a phase III testing. This may be due to the enhanced immunosuppressive effects demonstrated in the tumor microenvironment. Lack of co-stimulatory molecules, activation of the cytotoxic T-lymphocyte antigen-4 (CTLA-4), increased T regulatory cells as well as soluble immunosuppressive factors produced by the tumor contribute to the ineffectiveness of vaccine therapy. Based on these observations, there has been a shift towards treating patients with minimal residual disease and a high risk of relapse. In this adjuvant setting, immune mechanisms of tumor evasion are less formidable, and the use of vaccine therapy in these patients may offer a higher chance of clinical benefit. There are several different vaccine approaches, including the use of cell-based vaccines (autologous, allogeneic, or dendritic cell-based), tumor-associated peptide or protein vaccines, DNA vaccines, heat shock proteins, and recombinant technology using viral or bacterial vectors to enhance immunogenicity of vaccine preparations. This review summarizes principles involving vaccine formulation and antigen selection, followed by a brief synopsis of therapeutic vaccines given in the metastatic setting and possible reasons for their lack of efficacy. The current literature regarding vaccine development for the treatment of breast cancer in the adjuvant setting is also reviewed.