Abstract
Studies in nonhuman primates are indicated in translating research results towards a clinical application, in particular to assess the safety and efficacy of immunosuppressives and cell therapy products. This requires a thorough consideration of animal well-being, i.e., the 3 Rs refinement, reduction, and replacement. A comprehensive refinement approach was initiated
... read more
in the model of transplanting insulin-producing porcine pancreatic islets of Langerhans into diabetic macaques; this model is considered most close to the clinical condition in a diabetic patient. The approach was as follows: Training animals for cooperation with handlers, including handfeeding and drinking; shifting; and limb presentation for examination, injection, or intravenous access for blood sampling and administration of medication, fluids and nutrition. Cooperation with handlers completely eliminated restraint in routine handling, and significantly reduced the stress to the animals as concluded from pathophysiological parameters. Animal cooperation facilitates medical management in chronic (disease) models and allows early detection of adverse events; Implementation of vascular access ports and in-depth evaluation of risk factors for adverse events in relation of the respective procedures. The introduction of novel placements and refinements significantly increased patency, substantially lowered infectious complications, and facilitated cooperation with handling in the familiar homecage. Also, a procedure was developed for access to the portal vein to deliver medication or cell therapy products in the liver, enabling repeated access without the need for multiple major surgeries; Optimization of diabetes induction using the chemotherapeutic streptozotocin, based on careful analysis of adverse events and illustrated by case studies. Also, protocols were developed to recognize adverse events in the earliest stage so that animals could recover from life-threatening adverse events with appropriate medical management; Evaluation of the limitations of the model. Using a well-selected immunosuppressive regimen, islet function and diabetes reversal up to 6 months was achieved. When combined with refinement described above, this period could be extended to meet requirements defined in a consensus statement written by international experts. However, complications were observed such as the absence of weight gain turning in progressive weight loss: this affected the consistency in outcomes and appeared intrinsic to the model and prompted for an in-depth evaluation. Contributing factors were identified and included metabolic incompatibilities (i.e., control of blood glucose) between the species, characteristics of the islet product, and absorption characteristics of immunosuppressive medication. This evaluation included data from other groups that reported long-term outcomes in pig-to-macaque islet transplantation, and the comparison with outcomes in clinical islet transplantation and macaque-to-macaque islet transplantation. These limitations are relevant and give a better positioning of the model when defining studies aimed to translate animal research to a clinical application. This comprehensive approach enabled to capitalize on synergies between various refinement tools, i.e., avoidance of stress and sedation/restraint when using vascular access ports in animals trained for cooperative handling. It is postulated that the increase in refinement leads to a reduction in animal numbers, on the one hand by increasing the scientific quality of outcomes (i.e., limiting confounding by interfering factors), and on the other hand by reduction of non-informative cases.
show less
