Background
Protein therapeutics directed toward CD20 antigen on B lymphocytes have been demonstrated to be highly effective in the treatment of rheumatoid arthritis (RA) [1–3]. Small modular immunopharmaceutical drugs are single-chain polypeptides that are smaller than antibodies. TRU-015 is a CD20-directed small modular immunopharmaceutical drug candidate that effectively depletes B lymphocytes in cynomolgus monkeys in a dose-dependent manner, and improves survival in mouse xenograft tumor models [4, 5].