title: CD20 antigen imaging with ¹²⁴I-rituximab PET/CT in patients with rheumatoid arthritis.
abstract: BACKGROUND
  Visualization of the CD20-antigen expression could provide a tool to localize sites of inflammation and could be of additive value in the diagnosis, and subsequently, in the treatment follow-up of patients with rheumatoid arthritis. In this study, an anti-CD20 monoclonal antibody, rituximab (Mabthera®), was radiolabeled with ¹²⁴Iodine. We report the first results of I¹²⁴-rituximab PET/CT in patients with rheumatoid arthritis.
  
  
  METHODS
  Eligible patients received 50 MBq ¹²⁴I-rituximab. Wholebody PET/CT imaging was performed at 10 min, 24 h, 48 h and 72-96 h post injection. Images were evaluated primarily on a visual basis and were correlated with disease activity as determined by physical examination and clinical measures.
  
  
  RESULTS
  Joints with visually detectable targeting of ¹²⁴I-rituximab were observed in 4 out of 5 evaluable patients. Only the images at 24 h and later showed accumulation in joints, indicating that the visualized signal represented active targeting of rituximab to the CD20 antigen. Several images showed CD20 positive B-cell infiltration in joints which were clinically normal, while a few clinically diagnosed arthritis localizations were not visualized. This discrepancy suggests that infiltration of CD20 positive B-cells in synovium is a phenomenon that is at least partially independent of clinical inflammation. The level of uptake in joints was generally low, representing less than 0.5% of the injected dose.
  
  
  CONCLUSIONS
  We have shown the feasibility of CD20 antigen imaging using ¹²⁴I-rituximab in patients with rheumatoid arthritis. Further research is needed to elucidate the clinical significance of demonstrated B-cell infiltration in rheumatic joints.
authors.affiliation: Department of Pharmacy & Pharmacology, The Netherlands Cancer Institute / Slotervaart Hospital, Amsterdam, The Netherlands. Ly.Tran@slz.nl
authors.forename: L
authors.initials: L
authors.lastname: Tran
authors.forename: A D R
authors.initials: AD
authors.lastname: Huitema
authors.forename: M H
authors.initials: MH
authors.lastname: van Rijswijk
authors.forename: H J
authors.initials: HJ
authors.lastname: Dinant
authors.forename: J W
authors.initials: JW
authors.lastname: Baars
authors.forename: J H
authors.initials: JH
authors.lastname: Beijnen
authors.forename: W V
authors.initials: WV
authors.lastname: Vogel
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology / Q000493:pharmacokinetics*; D058846:Antibodies, Monoclonal, Murine-Derived / Q000276:immunology / Q000493:pharmacokinetics*; D018951:Antigens, CD20 / Q000096:biosynthesis / Q000276:immunology; D018501:Antirheumatic Agents / Q000276:immunology / Q000493:pharmacokinetics*; D001172:Arthritis, Rheumatoid / Q000175:diagnosis / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000009:adverse effects; D007553:Isotope Labeling / Q000379:methods; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D000069283:Rituximab; D013583:Synovial Membrane / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D013961:Thyroid Gland / Q000187:drug effects; D014018:Tissue Distribution; D016896:Treatment Outcome; D051598:Whole Body Imaging
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D018501:Antirheumatic Agents; D007457:Iodine Radioisotopes; D000069283:Rituximab