Toward implementing virtual control groups in nonclinical safety studies.

Historical data from control groups in animal toxicity studies are currently mainly used for comparative purposes to assess validity and robustness of study results. Due to the highly controlled environment in which the studies are performed and the homogeneity of the animal collectives it has been proposed to use the historical data to build so-called virtual control groups, which could partly or entirely replace the concurrent control group. This would constitute a substantial contribution to the reduction of animal use in safety studies. Before the concept can be implemented, the prerequisites regarding data collection, curation, and statistical evaluation together with a validation strategy need to be identified to avoid any impairment of the study outcome and subsequent consequences for human risk assessment. To further assess and develop the concept of virtual control groups, the transatlantic think tank for toxicology (t4) sponsored a workshop with stakeholders from the phar­maceutical and chemical industry, academia, FDA, contract research organizations (CROs), and non-governmental organizations in Washington, which took place in March 2023. This report sum­marizes the current efforts of a European initiative to share, collect, and curate animal control data in a centralized database and the first approaches to identify optimal matching criteria between virtual controls and the treatment arms of a study as well as first reflections about strategies for a qualifi­cation procedure and potential pitfalls of the concept.