Anti-CD4 antibody treatment of patients with rheumatoid arthritis: II. Effect of in vivo treatment on in vitro proliferative response of CD4 cells

In treating rheumatoid arthritis (RA) patients with anti-CD4 antibodies (MT151 10 mg/day, 7 d) we observed diminished skin-test response to recall antigens and reduced proliferative response to antigens and mitogens (in vitro) 2-4 h following the injection. To investigate whether this diminished response is due to functional impairment of CD4+ cells, we analyzed the proliferative response of CD4+ cells to various stimuli, in conditions where the CD4 structure was either cross-linked or not. We found that in vivo anti-CD4-antibody-coated cells could be induced to proliferate if the anti-CD4 antibody was cross-linked with an anti-CD3 antibody [BMA030-F(ab')2] added in vitro and per se non-mitogenic. Also, without cross-linking the cell-bound anti-CD4 antibodies, no impairment of the proliferative capacity of CD4-antibody-coated cells could be detected; double fluorescence analyses of phytohaemagglutinin (PHA)- or CD3-stimulated cells showed that a similar proportion of CD4+ cells proliferated before and after anti-CD4-antibody treatment. The diminished proliferation observed following anti-CD4 treatment correlated to the reduced number of CD3+ and CD4+ cells in culture, which suggests that altered cell distribution might be one factor contributing to the impaired immune response.