Immunogenicity of a xenogeneic multi-epitope HER2+ breast cancer DNA vaccine targeting the dendritic cell restricted antigen-uptake receptor DEC205

• Developed a novel highly immunogenic multi-epitope HER2 DNA vaccine. • Designed a novel multi-epitope HER2 protein containing 7T and B-cell epitopes. • Used an antibody fragment (ScFvDEC) to target multi-epitope HER2 to dendritic cells. • Elicited strong antibody response and protective IFN-γ response in murine model. Breast cancer was ranked first in global cancer incidence in 2020, and HER2 overexpression in breast cancer accounts for 20–30% of breast cancer patients. Current therapeutic strategies increase the survival rate, but resistance to them occurs frequently, and there is an urgent need to develop novel treatments such as DNA vaccines which can induce a specific and long-lasting immune response against HER2 antigens. To enhance the immunogenicity of DNA vaccines, dendritic cells (DCs) can be targeted using multi-epitope proteins that provide accurate immune focusing. For this purpose, we generated a DNA vaccine encoding a fusion protein composed of 1) in silico discovered antigenic epitopes of human and rat HER2 proteins (MeHer2) and 2) a single-chain antibody fragment (ScFv) specific for the DC-restricted antigen-uptake receptor DEC205 (ScFvDEC). The xenogeneic multi-epitope DNA vaccine (pMeHer2) encodes three only T-cell epitopes, two only B-cell epitopes, and two T and B cell epitopes, and pScFvDEC-MeHer2 vaccine additionally encodes ScFvDEC introduced at the N terminus of the MeHer2. Then, mouse groups were immunized with pScFvDEC-MeHer2, pMeHer2, pScFvDEC, pEmpty, and PBS to determine the elicited immune response. pScFvDEC-MeHer2 vaccinated mice showed a strong IgG response (P < 0.0001) and pScFvDEC-MeHer2 induced a significant IgG2a increase (P < 0.01). The percentages of both IFN-γ secreting CD4 and CD8 T cells were higher in mice immunized with pScFvDEC-MeHer2 compared with the pMeHer2. pScFvDEC-MeHer2 and pMeHer2 secreted significantly higher levels of extracellular IFN-γ compared with to control groups (P < 0.0001). In addition, the IFN-γ level of the pScFvDEC-MeHer2 vaccine group was approximately two times higher than the pMeHer2 group (P < 0.0001). Overall, this study identified the pScFvDECMeHer2 construct as a potential DNA vaccine candidate, supporting further studies to be conducted on HER2 + animal models.