An opportunity exists for a next-generation anti-CD22 antibody–drug conjugate (ADC) to address unmet medical needs in the relapsed/refractory NHL population. We describe a site-specifically conjugated antibody–drug conjugate, made using aldehyde tag technology, targeted against CD22 and bearing a noncleavable maytansine payload that is resistant to MDR1-mediated efflux. The construct was efficacious against CD22+ NHL xenografts...Together, the data suggest that this drug has the potential to be used effectively in patients with CD22+ tumors that have developed MDR1-related resistance to prior therapies.