The blood-brain barrier blocks the entry of antibodies into the brain. This limits the potential use of antibody therapeutics to treat brain diseases, such as brain tumors. Elsewhere in the body, more than 100 United States Food and Drug Administration-approved therapeutic antibodies are used by medical teams to treat cancers and autoimmune, infectious and metabolic diseases. Now researchers report that the site-directed addition of an FDA-approved, biodegradable polymer at the hinge and near hinge regions of the therapeutic antibody trastuzumab effectively facilitated the brain delivery of this human monoclonal IgG1 antibody.