AbstractObjective. To study the effect of chimeric anti‐CD4 monoclonal antibody (MAb) therapy on synovial inflammation, in order to interpret the clinical experience with anti‐CD4 treatment.Methods. The immunohistologic features of synovial biopsy specimens before and 4 weeks after anti‐CD4 MAb (cM‐T412) therapy were studied in patients with rheumatoid arthritis. The patients received intravenous doses of either placebo (n = 1) or 10 mg (n = 4), 25 mg (n = 2), or 50 mg (n = 1) of cM‐T412 daily for 5 consecutive days.Results. Although the patients did not experience clinical improvement, significant decreases in the number of circulating CD4+ cells, the degree of synovial inflammatory infiltration, and the mean scores for expression of adhesion molecules were found in the 7 patients 4 weeks after receiving cM‐T412. The scores for infiltration with CD4+ and other inflammatory cells were particularly reduced following treatment with either 25 mg or 50 mg cM‐T412. Cytokines, such as interleukin‐1β and tumor necrosis factor α, could still be detected in the synovial tissue after treatment.Conclusion. The decline in the numbers of inflammatory cells and adhesion molecules in synovial tissue after CD4+ cell depletion supports the view that CD4+ T cells orchestrate local cellular infiltration. The lack of clinical effect of anti‐CD4 therapy might be explained by an insufficient decrease in the number of synovial CD4+ cells and by the persistence of cytokines. Determination of whether more adequate dosing would lead to a clinical improvement must
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