A COMPARISON BETWEEN IN-111-ANTI-E-SELECTIN MAB AND TC-99(M)-LABELED HUMAN NONSPECIFIC IMMUNOGLOBULIN IN RADIONUCLIDE IMAGING OF RHEUMATOID-ARTHRITIS

We have developed and validated a method for imaging inflammation usin g a monoclonal antibody (1.2B6) against E-selectin, an endothelial-cel l specific adhesion molecule. This study was undertaken to compare In- 111-1.2B6 with Tc-99(m)-labelled non-specific IgG (Tc-99(m)-HIG) in th e detection of synovitis in II patients with rheumatoid arthritis (RA) . Imaging was performed 4 h and 20-24 h post-injection (pi) of 555 MBq Tc-99(m)-HIG and 15 MBq In-111-1.2B6. Scintigraphic results were comp ared with clinical scores of joint involvement. Joint uptake was semiq uantitated. The scintigraphic appearances with both tracers correlated well, although In-111-1.2B6 at 24 h showed the highest detection rate . Taking joint tenderness or swelling as evidence of clinical activity , the sensitivity of In-111-1.2B6 at 4 h and 24 h was 69% and 82%, res pectively, compared with 69% and 62% for Tc-99(m)-HIG. In-111-1.2B6 al so displayed abnormal activity over a number of joints that appeared s ilent on clinical examination. Joint-to-soft tissue ratios were higher for In-111-1.2B6 at 24 h (4.0+/-1.9; p<0.0001 us all) than at 4 h (2. 4+/-1.4) or than for Tc-99(m)-HIG at 4 h and 24 h (1.6+/-0.5 and 2.3+/ -0.7, respectively). Net In-111 counts over joints increased significa ntly between 4 h and 24 h (mean change: 54+/-40%). This study demonstr ates that In-111-1.2B6 scintigraphy is a sensitive method by which to assess RA activity and that targeting is more intense and specific tha n using Tc-99(m)-HIG. However, the optimum time for In-111-1.2B6 scint igraphy is 24 h whereas good results are already obtained with Tc-99(m )-HIG at 4 h pi. Current efforts are directed at developing Tc-99(m)-l abelled 1.2B6 for imaging endothelial activation.