A comparison between In-111-anti-E-selectin mAb and Tc-99(m)-labelled human non-specific immunoglobulin in radionuclide imaging of rheumatoid arthritis

We have developed and validated a method for imaging inflammation using a monoclonal antibody (1.2B6) against E-selectin, an endothelial-cell 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 the 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 compared with clinical scores of joint involvement. Joint uptake was semiquantitated. 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%, respectively, compared with 69% and 62% for Tc-99(m)-HIG. In-111-1.2B6 also displayed abnormal activity over a number of joints that appeared silent 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 significantly between 4 h and 24 h (mean change: 54+/-40%). This study demonstrates that In-111-1.2B6 scintigraphy is a sensitive method by which to assess RA activity and that targeting is more intense and specific than using Tc-99(m)-HIG. However, the optimum time for In-111-1.2B6 scintigraphy 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)-labelled 1.2B6 for imaging endothelial activation.