CD20-directed therapy is well established in oncology, and was recently demonstrated to be highly effective in the treatment of rheumatoid arthritis (RA) [1]. Small modular immunopharmaceutical drugs are smaller than antibodies yet are capable of utilizing effector functions of antibody-dependent cellular cytotoxicity, complement-mediated cytotoxicity and apoptotic signaling. TRU-015 is a small modular immunopharmaceutical drug candidate that is specific for CD20. TRU-015 has been demonstrated to effectively deplete B lymphocytes in cynomolgus monkeys in a dose-dependent manner, and to improve survival in mouse xenograft tumor models [2, 3].

This phase 1 dose escalation study was performed to evaluate the safety, pharmacokinetics and pharmacodynamics of TRU-015 in subjects with RA.

Thirty-seven RA subjects receiving a stable background of methotrexate were enrolled in eight dosage groups (single dosages of TRU-015 of 0.015, 0.05, 0.15, 0.5, 1.5, 5, or 15 mg/kg, or two doses of 15 mg/kg given 1 week apart (30 mg/kg)). Safety was assessed at baseline, during infusion and at prespecified intervals after infusion by clinical (adverse events, physical examination, vital signs) and laboratory parameters. Serum samples were collected for pharmacokinetic analysis. Pharmacodynamic response was measured using B-cell counts (CD19⁺ cells by flow cytometry) at prespecified timepoints. Subjects were evaluated for a minimum of 4 weeks and until B-cell recovery.

TRU-015, a novel CD20-directed therapy, was generally well tolerated and resulted in dose-dependent B-lymphocyte depletion. Following intravenous infusion, pharmacokinetic properties of TRU-015 (area under the curve, maximum concentration of drug) were approximately dose proportional. Further evaluation of TRU-015 is warranted for the treatment of RA, and other autoimmune diseases.