Scientific and Regulatory Policy Committee Points to Consider: Proposal and Recommendations to Reduce Euthanasia of Control Nonhuman Primates in Nonclinical Toxicity Studies.

Nonhuman primates (NHPs) have been and remain a highly valuable animal model with an essential role in translational research and pharmaceutical drug development. Based on current regulatory guidelines, the nonclinical safety of novel therapeutics should be evaluated in relevant nonclinical species, which commonly includes NHPs for biotherapeutics. Given the practical and ethical limitations on availability and/or use of NHPs and in line with the widely accepted guiding "3Rs" (replace, reduce, and refine) principles, many approaches have been considered to optimize toxicity study designs to meaningfully reduce the number of NHPs used. Standard general toxicity studies usually include four groups of equal size, including one group of vehicle control animals. Here, we describe an approach to achieve an overall significant reduction in control animal use, while also resolving many of the issues that may limit application of fully virtual control animals. We propose in Good Laboratory Practice (GLP)-compliant toxicity studies to maintain concurrent control group animals for the in-life phase of the studies, but to limit euthanasia to a subset of control animals. The nonterminated control animals can then be returned to the facility colony for reuse in subsequent studies. The proposed study design could lead to a 15% to 20% reduction in NHP usage. The scientific, logistical, and animal welfare considerations associated with such an approach and suggested solutions are discussed in detail.