How useful are 3-month repeat-dose toxicology studies for the development of T cell engagers for oncology indications?

Development of T cell engagers (TCEs) for oncology indications is regulated mainly by ICH S6 and S9. Investigational new drug applications are usually supported by a 1-month toxicology study in a relevant animal species. Before the start of registrational clinical trials, a longer-duration toxicology study, typically 3 months, is performed in the same species to support marketing. As longer-term studies with human-specific biologics in animal species can be hampered by development of anti-drug antibodies and TCEs are quick-acting molecules, we analyzed the value of 3-month toxicology studies for some of our TCEs. We present data from 1- and, where applicable, 3-month toxicology studies for 4 TCE programs and describe our interactions with regulatory agencies. In none of the cases did the 3-month studies reveal new information to influence further the respective clinical development plans. Considering 3Rs (Replacement, Reduction and Refinement) in pharmaceutical development, we highlight that 3-month studies with TCEs don't always offer additional safety insights. Therefore, alternative strategies should be evaluated and conduct of 3-month studies carefully considered in the light of 3Rs and discussed case-by-case with health authorities.