Selective imaging of chronic cardiac rejection using a human antibody specific to the alternatively spliced EDA domain of fibronectin

Background Chronic cardiac rejection is intimately associated with cardiac allograft vasculopathy and fibrosis, both causing severe complications that cannot be reversed. Thus, there is an urgent need for early diagnosis and for development of therapeutic agents. Chronic rejection is accompanied by the dramatic upregulation of EDA⁺ fibronectin (EDA⁺ Fn), which is virtually undetectable in the normal healthy adult. Methods In this study, we evaluated the potential of the monoclonal antibody F8, specific to that molecule, to selectively accumulate in chronically rejected allografts. Results A syngeneic immunocompetent heterotopic rat heart transplantation model was used to induce chronic rejection within 70 days. The F8 antibody or an antibody of irrelevant specificity, labeled with the dye DY-682, was administered and near-infrared fluorescence (NIRF) imaging was performed. Targeting performance was assessed by macroscopic organ imaging and fluorescence microscopy. A selective accumulation of the F8 antibody (but not of the negative control antibody) was observed by NIRF imaging in cardiac allografts. The antibody localized to diseased blood vessels as well as to fibrotic regions, where the cognate antigen is abundantly expressed. Conclusions This is the first example of antibody-mediated imaging of chronic cardiac rejection. The findings pave the way to immuno-positron emission tomography (immuno-PET) imaging of this clinical condition in patients using the human F8 antibody labeled with a suitable radionuclide (e.g., iodine-124). Furthermore, it would be conceivable to use the F8 antibody as a delivery vehicle to assess experimentally whether a bioactive payload (e.g., drug or cytokine) may be able to reduce disease progression.