Anti-HER2/neu IgG3–(IL-2) and anti-HER2/neu IgG3–(GM-CSF) promote HER2/neu processing and presentation by dendritic cells: Implications in immunotherapy and vaccination strategies

HER2/neu, a transmembrane glycoprotein overexpressed in several types of human cancers, is a potential target for active immunotherapy. However, this protein and especially its extracellular domain (ECDHER2), is weakly immunogenic and is poorly processed by dendritic cells (DCs). Previously, we showed that anti-HER2/neu IgG3–(IL-2) and anti-HER2/neu IgG3–(GM-CSF) fusion proteins can enhance the immunogenicity of ECDHER2 in mice, and that the non-covalent physical association between each antibody fusion proteins and ECDHER2 was critical to elicit optimal protective immunity against HER2/neu expressing tumors. We now use the professional antigen-presenting DCs to investigate the effect of the antibody fusion protein binding to ECDHER2 on its trafficking and presentation. We found that when the extracellular domain of HER2/neu fused to ovalbumin (OVA–ECDHER2) is bound by HER2/neu-specific antibody–(IL-2) or antibody–(GM-CSF) fusion proteins, the bound antigen is more efficiently processed by murine bone-marrow-derived dendritic cells (BMDCs) and presented to OVA-specific T-cells than the unbound OVA–ECDHER2. We also found that ECDHER2 bound by anti-HER2/neu IgG3–(IL-2) is very efficiently internalized and that the internalized ECDHER2 is not retained in the early endosomal compartments but traffics to the antigen-processing compartments. These results are consistent with our earlier in vivo studies and suggest that both antibody–(IL-2) and antibody–(GM-CSF) fusion proteins can be used to enhance the immune response to poorly immunogenic antigens including tumor-associated antigens (TAAs).