Virus-Like Particles Presenting the FGF-2 Protein or Identified Antigenic Peptides Promoted Antitumor Immune Responses in Mice

Background: Fibroblast growth factor (FGF)-2 is overexpressed in various tumor tissues. It affects tumor cell proliferation, invasion and survival, promotes tumor angiogenesis and is tightly involved in the development of systemic and local immunosuppressive tumor mechanisms. Purpose: This study aimed to develop an effective vaccine against FGF-2 and to investigate the effects of anti-FGF-2 immunization on tumor growth and antitumor immune responses. Methods: A set of thirteen synthesized overlapping peptides covering all possible linear B-cell epitopes of murine FGF-2 and a recombinant FGF-2 protein were conjugated to virus-like particles (VLPs) of recombinant hepatitis B core antigen (HBcAg). The VLPs were immunized through a preventive or therapeutic strategy in a TC-1 or 4T1 grafted tumor model. Results: Immunization with FGF-2 peptides or full-length protein-coupled VLPs produced FGF-2-specific antibodies with a high titer. Peptide 12, which is located in the heparin-binding site of FGF-2, or protein-conjugated VLPs presented the most significant effects on the suppression of TC-1 tumor growth. The levels of IFN-γ-expressing splenocytes and serum IFN-γ were significantly elevated; further, the immune effector cells CD8+ IFN-γ+ cytotoxic T lymphocytes (CTLs) and CD4+ IFN-γ+ Th1 cells were significantly increased, whereas the immunosuppressive cells CD4+ CD25+ FOXP3+ Treg cells and Gr-1+ CD11b+ myeloid-derived suppressor cells (MDSCs) were decreased in the immunized mice. In addition, VLP immunization significantly suppressed tumor vascularization and promoted tumor cell apoptosis. In mice bearing 4T1 breast tumor, preventive immunization with FGF-2-conjugated VLPs suppressed tumor growth and lung metastasis, and increased effector cell responses. Conclusion: Active immunization against FGF-2 is a new possible strategy for tumor immunotherapy.