Depletion of synovial macrophages in rheumatoid arthritis by an anti-FcγRI-calicheamicin immunoconjugate
- 1Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht, Utrecht, PO Box 85500, 3508 GA, The Netherlands
- 2Immunotherapy Laboratory, Department of Immunology, University Medical Centre Utrecht, PO Box 85500, 3508 GA, The Netherlands
- 3Genmab, Utrecht, The Netherlands
- Correspondence to:
Dr J A G van Roon
Department of Rheumatology and Clinical Immunology, University Medical Centre Utrecht, F02.127, Utrecht, PO Box 85500, 3508 GA, The Netherlands;
- Accepted 9 October 2004
- Published Online First 11 November 2004
Background: Monocytes/macrophages have an important and versatile role in joint inflammation and destruction in rheumatoid arthritis (RA).
Objective: To determine the efficiency of monocyte/macrophage elimination by a new drug conjugated antibody (CD64-calicheamicin (CD64-CaMi)) directed to the high affinity receptor for IgG (FcγRI).
Methods: Mononuclear cells from peripheral blood and synovial fluid of patients with RA were cultured in the presence of CD64-CaMi. Cell death of monocytes/macrophages was measured by analysis of phenotypic changes (light scatter patterns, CD14 expression, and FcγRI expression) and nuclear DNA fragmentation. The selectivity of CD64-CaMi was checked by using FcγRI deficient and FcγRI transfected cell lines. In addition, the indirect effect of CD64-CaMi-induced macrophage cell death on arthritogenic T(h1) cell activity was determined.
Results: Inflammatory macrophages from RA synovial fluid, expressing increased FcγRI levels, were efficiently killed by CD64-CaMi through induction of DNA fragmentation. CD64-CaMi-induced cell death of monocytes/macrophages from peripheral blood of patients with RA proved less efficient. Induction of synovial macrophage death by CD64-CaMi was accompanied by efficient inhibition of proinflammatory T(h1) cytokine production.
Conclusion: Together, the presented data suggest that elimination of macrophages through a new FcγRI directed CD64-CaMi is feasible. Because monocytes from peripheral blood are also eliminated by this immunoconjugate, additional experimental studies should validate its potential for local (intra-articular) application in the treatment of RA.
- CaMi, calicheamicin
- FSC, forward scatter
- IFNγ, interferon γ
- MC, mononuclear cells
- MFI, mean fluorescence intensity
- PB, peripheral blood
- PBS, phosphate buffered saline
- PI, propidium iodide
- RA, rheumatoid arthritis
- RTA, ricin toxin A
- SSC, side scatter
- SF, synovial fluid
- TNFα, tumour necrosis factor α