Early clinical studies of IL-2 fusion toxin in patients with severe rheumatoid arthritis and recent onset insulin-dependent diabetes mellitus.

DAB486IL-2 is the first of a new class of targeted biologicals called fusion toxins. This agent is an interleukin-2 receptor (IL-2R)-targeted cytotoxin which kills activated IL-2R-expressing lymphocytes at 10(-10) M concentrations. Since activated lymphocytes are thought to play a role in many autoimmune conditions, DAB486IL-2 has been evaluated in patients with severe rheumatoid arthritis and recent onset autoimmune insulin-dependent diabetes mellitus. Initial safety, pharmacokinetics and evidence of IL-2R specific cytotoxicity were obtained in patients with IL-2 receptor expressing malignancies; these studies served as a basis for the initiation of an open label phase I/II evaluation of DAB486IL-2 in patients with severe, methotrexate refractory rheumatoid arthritis. This pilot study provided preliminary evidence of acceptable safety at doses which induced meaningful (> 25%) or substantial (> 50%) improvement in 9 of 18 patients who received a mid (130 kU/kg/d) or a high (260 kU/kg/d) dose daily for 5 to 7 days. The most frequent adverse effects were transient hepatic transminase elevation and fever. Although some patients noted a transient increase in joint pain, onset of improvement occurred within 7 to 14 days of initiation of DAB486IL-2. Because of these results, a two-center, double-blind, placebo-controlled trial was conducted from December 1991 to December 1992. Forty-five patients with active severe RA unresponsive to at least 2 DMARDS were randomized to placebo or DAB486IL-2 following a 3 to 4 week washout/run-in period to establish a stable baseline (< 40% fluctuation in swollen and painful, tender joint counts).(ABSTRACT TRUNCATED AT 250 WORDS)