Targeting of the non-mutated tumor antigen HER2/neu to mature dendritic cells induces an integrated immune response that protects against breast cancer in mice

INTRODUCTION: Given their relative simplicity of manufacture and ability to be injected repeatedly, vaccines in a protein format are attractive for breast and other cancers. However, soluble human epidermal growth factor receptor (HER2)/neu protein as a vaccine has not been immunogenic. When protein is directly targeted to antigen uptake receptors, such as DEC205 (DEC), efficient processing and presentation of antigen take place. The aim of this study was to determine the immunogenicity of a HER2 protein vaccine that directly targets to DEC(+ )dendritic cells (DCs) in a mouse breast cancer model. METHODS: We genetically engineered the HER2 extracellular domain into a monoclonal antibody specific for DEC (DEC-HER2). Mice of various genetic backgrounds were immunized with DEC-HER2 in combination with DC maturation stimuli (poly IC ± CD40 Ab). Vaccine-induced T cell immunity was determined by analyzing the ability of CD4(+)/CD8(+ )T cell to produce interferon (IFN)-gamma and proliferate upon antigen rechallenge. Sera were assessed for the presence of antigen specific antibody (Ab). For vaccine efficacy, FVB/N mice were immunized with DEC-HER2 in combination with poly IC and protection against neu-expressing mammary tumors was assessed. Protection mechanisms and tumor-specific T cell responses were also evaluated. RESULTS: We demonstrate that DEC-HER2 fusion mAb, but not Ctrl Ig-HER2, elicits strong, broad and multifunctional CD4(+ )T cell immunity, CD8(+ )T cell responses, and humoral immunity specific for HER2 antigen. Cross-reactivity to rat neu protein was also observed. Importantly, mice xeno-primed with DEC-HER2 were protected from a neu-expressing mammary tumor challenge. Both CD4(+ )and CD8(+ )T cells mediated the tumor protection. Robust anti-tumor T cell immunity was detected in tumor protected mice. CONCLUSIONS: Immunization of mice with HER2 protein vaccine targeting DEC(+ )DCs in vivo induced high levels of T- and B-cell immunity. Non-targeted HER2 protein was poorly immunogenic for CD4(+ )and CD8(+ )T cells. This vaccination approach provided long-term survival benefit for mice challenged with neu-expressing tumor following as little as 2.7 μg of HER2 protein incorporated in the vaccine. Vaccine-induced CD4(+ )and CD8(+ )T cells were both essential for tumor protection. This immunization strategy demonstrates great potential towards the development of vaccines for breast cancer patients.