The importance of large animal models in transplantation.

Animal models have been extensively used in transplantation research. However, animal experimentation is contentious and subject to legal and ethical restrictions. Most experiments are carried out on rodents, but crucial prerequisites for the development of safe pre-clinical protocols in biomedical research are needed through suitable large animal models. In transplantation particularly, large animal models have developed dramatically. This article provides an overview of the large animal models commonly used to evaluate organ transplant experiments and analyzes the specificity of several models in various situations such as induction of allospecific tolerance and xenotransplantation. The key determination that remains be addressed is the most appropriate species and strains to model human immune and physiological systems. Because of their phylogenetic and physiologic similarities to man, non-human primates play an increasingly important role in pre-clinical testing. Nevertheless, a number of studies have shown the pig to be a reliable large animal model for transplantation research, and the availability of genetically defined or modified pigs establishes a stronger position for pigs as a large animal model.