A Vaccine Against Fibroblast Activation Protein Improves Murine Cardiac Fibrosis by Preventing the Accumulation of Myofibroblasts

BACKGROUND: Myofibroblasts are primary cells involved in chronic response-induced cardiac fibrosis. Fibroblast activation protein (FAP) is a relatively specific marker of activated myofibroblasts and a potential target molecule. This study aimed to clarify whether a vaccine targeting FAP could eliminate myofibroblasts in chronic cardiac stress model mice and reduce cardiac fibrosis. METHODS: We coadministered a FAP peptide vaccine with a cytosine-phosphate-guanine (CpG) K3 oligonucleotide adjuvant to male C57/BL6J mice and confirmed an elevation in the anti-FAP antibody titer. After continuous angiotensin II and phenylephrine administration for 28 days, we evaluated the degree of cardiac fibrosis and the number of myofibroblasts in cardiac tissues. RESULTS: We found that cardiac fibrosis was significantly decreased in the FAP-vaccinated mice compared with the angiotensin II and phenylephrine control mice (3.45±1.11% versus 8.62±4.79%; P=4.59×10⁻³) and that the accumulation of FAP-positive cells was also significantly decreased, as indicated by FAP immunohistochemical staining (4077±1746 versus 7327±1741 cells/mm²; FAP vaccine versus angiotensin II and phenylephrine control; P=6.67×10⁻³). No systemic or organ-specific inflammation due to antibody-dependent cell cytotoxicity induced by the FAP vaccine was observed. Although the transient activation of myofibroblasts has an important role in maintaining the structural robustness in the process of tissue repair, the FAP vaccine showed no adverse effects in myocardial infarction and skin injury models. CONCLUSIONS: Our study demonstrates the FAP vaccine can be a therapeutic tool for cardiac fibrosis.