Immune Response to Plant Viral Nanoparticle Tobacco Mosaic Virus as a Breast Cancer Vaccine Platform

Introduction: A major goal of current efforts directed towards developing a vaccine involves determining how to elicit durable titers of potent broadly-neutralizing antibodies. The hypothesis we ultimately wish to address is if a highly-ordered multivalent display of epitopes will facilitate the above goal. Specifically, we are interested in developing vaccine approaches to treat patients with HER2+ breast cancer. Passive immunotherapy using trastuzumab has been shown to be promising. Active immunotherapy, i.e. vaccines, has the potential to reduce undesired side effects resulting from repeated administration of the drug. Traditional vaccine platforms used to generate multivalent antigens yield variable inter-epitope spacing and geometry. With these methods, the best that can be accomplished is a pre-determined average spacing. Conversely, creating a deterministic epitope array, in which inter-epitope spacing and geometry are more uniform, is a major challenge. To address this challenge, we turned toward a bio-inspired approach, specifically the plant virus tobacco mosaic virus (TMV). TMV is a 300 by 18 nm rod-like, helical structure composed of 2130 identical coat proteins. We are assessing it as a platform for deterministic multivalent epitope display of HER2 antigens. In order to use TMV as a platform for the multivalent presentation and delivery of the HER2 antigens, it is imperative to understand and thoroughly characterize the immunogenicity of TMV in vivo.

Methods: Immunogenic characterization of TMV involved immunizing C57BL/6J mice with TMV using subcutaneous and intraperitoneal administrations. Solid-phase ELISA assays were subsequently employed to evaluate the antigen-specific serum antibody titer, relative to IgG, IgM and IgA responses. Immunohistochemistry characterization of spleen and liver tissue and lymph node sections from immunized mice was also performed to understand the trafficking of TMV and the relevant stimulation of various immune cells in these tissues.

Results: ELISA preliminary results indicate no immunogenicity of TMV in eliciting an IgA response, minimal IgG response, and a substantial IgM response. These results are consistent with a thymus-independent (TI) immune response, however further experimentation is needed. Immunohistochemistry analysis of mouse spleen sections, post booster immunization, demonstrates B cell interaction with TMV, in addition to macrophage clustering near TMV, in the white pulp section of the spleen.

Conclusions: Preliminary data indicate that TMV induces a TI response. However, further experimentation includes immunizing C57BL/6J mice with a higher dose of TMV, over longer periods of time to get a fuller picture of the immunogenicity of TMV in mice. We plan to subsequently evaluate the immunogenicity of HER2 antigens expressed on the surface of TMV, in comparison with free antigens and contemporary vaccination platforms.