Effectiveness of anti-folate receptor β antibody conjugated with truncated Pseudomonas exotoxin in the targeting of rheumatoid arthritis synovial macrophages

Objective. To define the distribution of folate receptor beta (FR beta)-expressing cells in various tissues, including rheumatoid arthritis (RA) synovial tissues, and to verify the effects of an immunotoxin composed of an anti-FR beta monoclonal antibody (mAb) and truncated Pseudomonas exotoxin A (PEA) on apoptosis and tumor necrosis factor alpha (TNF alpha) production by adherent synovial mononuclear cells from RA patients. Methods. Anti-FRO mAb were produced by immunizing mice with FR beta-transfected murine pre-B cells. The distribution of the FR beta antigen was examined by immunohistochemical analysis using anti-FR beta mAb and macrophage-specific anti-CD163 mAb. Anti-FR beta mAb was chemically crosslinked with truncated PEA. FR beta-expressing macrophages were produced by the transfection of adenovirus vector containing the FR beta gene. Apoptotic cells were detected by staining with propidium iodide. TNF alpha was measured by enzyme-linked immunosorbent assay. Results. FR beta-expressing cells were not present in peripheral blood leukocytes and their activated cells. In all of the tissues examined, most FR beta-expressing cells were CD163+. The immunotoxin significantly induced the apoptosis of FR beta-transfected macrophages and adherent RA synovial mononuclear cells and inhibited TNF alpha production by adherent RA synovial mononuclear cells. Conclusion. We demonstrated the limited distribution of FR beta-expressing cells in various tissues. The immunotoxin targeting FR beta-expressing cells will provide a therapeutic tool for rheumatoid synovitis.