Early antibody–drug conjugates (left) were mouse monoclonal antibodies linked covalently to anticancer drugs such as doxorubicin, vinblastine, and methotrexate, and had several limitations. Technological advances have enabled design of antibody–drug conjugates that comprise humanised antibodies (right), which are less immunogenic than earlier antibody–drug conjugates, with several favourable pharmacokinetic properties. IC50=concentration needed to achieve 50% inhibition. DM1=emtansine. DM4=ravtansine. MMAE=monomethyl auristatin E. MMAF=monomethyl auristatin F.