Steven Hager, a senior director of technical support, joined the BPI Theater at BIO on 5 June 2019 to describe how Catalent Biologics’s emerging cell-line engineering technologies can aid in developing therapies based on difficult-to-express proteins. Hager presented two case studies to this end, the first involving insertion of a tag into an antibody for conjugation with a toxin to create an antibody–drug conjugate (ADC), and the second showing another antibody with two sites for conjugation on each chain. Using these examples, Hager explored how increasing hygiene insertion efficiency and decreasing selection markers can make the difference in maximizing the production of complex proteins.