Immunological effects of high dose administration of anti-CD4 antibody in rheumatoid arthritis patients

A phase I/II trial of the anti-CD4 monoclonal antibody (mAb) was undertaken in seven rheumatoid arthritis patients in order, (1) to investigate changes in clinical symptoms and possible side effects, and (2) to study the pharmacokinetics and to determine the dose required to achieve saturation of antibody binding sites on blood leucocytes. BL4mAb is a murine IgG2a which binds to the group 2B epitope of the V1 N terminal domain of the CD4 molecule. It inhibits syncitium formation by human immunodeficiency virus-infected cells. BL4 was administered by one hour-long intravenous infusion each day, for 10 days. Doses were steadily increased from 20 mg/d to 40 mg/d in the first three patients (group I) in an attempt to reach a serum antibody residual level sufficient to saturate CD4+ circulating cells. The three other patients (group II) received a dose of 40 mg/d during 10 consecutive days. One patient who presented chills and mild fever during the first BL4 infusion was not included in the analysis. No clinical side effects were observed in the six other BL4-treated patients. Clinical parameters of disease activity were improved within the first 14 days. Clinical improvement was still significant at day 30 in five patients, but at day 60, only the Ritchie index was still below pretreatment levels. Delayed type hypersensitivity reactions decreased in the three patients who exhibited positive reactions before BL4 administration. A transient drop in peripheral blood CD4+ lymphocyte counts occurred during each infusion in the first days of treatment. Pre-infusion CD4+ lymphocyte counts were moderately decreased within the first 8 days, but rose to pretreatment levels 3 days after the last infusion. BL4 residual levels in serum steadily increased to reach 8.0 micrograms/ml in group I and 9.8 micrograms/ml in group II. Saturation of BL4 binding sites was achieved after 2 days of treatment in all patients of group II but in only one of group I. Four out of six patients produced antibodies against the anti-CD4 mAb. Immunization appeared between days 12 and 50. This study shows that saturation of anti-CD4 mAb binding sites can be achieved by infusions of high doses (40 mg/d) of BL4 without clinical side effects. The results would encourage further placebo-controlled trials, since no definite conclusion can be drawn from the present study as regards clinical efficacy.