The present invention provides transglutaminase-mediated antibody-drug conjugates with high anti-body-drug ratio (DAR) comprising 1) glutamine-containing tags, endogenous glutamines, and/or endogenous glutamines made reactive by antibody engineering or an engineered transglutaminase (e.g., with altered substrate specifity)； and 2) amine donor agents comprising amine donor units, linkers, and agent moieties, wherein the DAR is at least about 5. The invention also provides methods of making and methods of using such higher drug loaded antibody-drug conjugates.
