Porcine heterotopic composite tissue allograft transplantation using a large animal model for preclinical studies

Background: Composite tissue allograft (CTA) transplantation is currently limited by the risks of side effects resulting from long-term high-dose immunosuppression. Therefore, preclinical animal models are essential to help CTA transplantation advance into clinical reality. Evidence has shown that small-animal model (rodents) immunotherapy protocols cannot be directly applied to humans. This study investigated whether a miniature porcine model is reproducible for preclinical studies. Methods: Based on the concept of vascularized skeletal tissue allograft transplantation, limb heterotopic allograft tissue from a mismatched donor miniature pig consisting of the distal femur, knee joint, tibia, fibula, and surrounding muscle with a vascularized skin paddle model supplied by the superficial femoral vessels was transplanted into recipient pigs. Swine viability and rejection signs of the allograft were monitored postoperatively. Histopathological changes in the allograft tissues were examined using hematoxylin and eosin staining if the allo-skin flap was rejected. Results: The recipient pigs were ambulatory immediately following surgery. The flaps showed no visible signs of rejection over the first 4 days of observation. The skin flaps appeared bluish-purple and edematous on postoperative days 5-7, and progressed to tissue necrosis and rejection on postoperative days 8-13. Histological examination revealed marked mononuclear cell infiltration and necrotic changes in the all rejected tissues, especial in the allograft skin tissues (skin > muscle > bone > cartilage). Conclusions: The results showed this the porcine CTA model is reproducible and suitable for preclinical training for human CTA transplantation. Monitoring of the allo-skin flap is a useful strategy to evaluate composite tissue allograft rejection.