Rat VCA Heterotopic Hindlimb Model of Rejection and Vasculopathy in the Presence of Maintenance Immunosuppression

Abstract

IntroductionVascularized composite allograft (VCA) is an emerging medical field that has advanced rapidly over the past two decades, following advances in microsurgery and immunosuppressive therapy. Since VCA is a relatively new field, our knowledge regarding long term outcomes and potential complications is limited. Although VCA is regarded as a success in improvement of quality of life for patients with severe facial or hand injuries, we are far from understanding the biological processes involved in graft acceptance. While acute rejection episodes respond well to standard immunosuppression, chronic rejection and especially vasculopathy remains an unsolved problem. Two hand recipients in our clinical program have suffered graft loss due to ischemic vasculopathy. Frequently there are no clinical signs to suggest that vasculopathy is advancing, making diagnosis and treatment even more complex. The purpose of this study was to develop an adaptable rat model of VCA which, with carefully titrated immunosuppression, mimics acute rejection, chronic rejection, and vasculopathy as seen in a clinical setting.MethodsBrown Norway and Lewis rats were used as VCA donor and recipients, respectively. Heterotopic vascularized osteomyocutaneous flap composed of disarticulated fibula and tibia, including its related muscles and dorsal skin were transplanted in the recipient groin area. The pedicle was anastomosed to the recipient femoral artery and vein. All VCA recipients were treated with full dose Tacrolimus for the first 11 post operative days. Following that, the recipient animals were divided into three groups, in which each group treated with different immunosuppressive protocol to induce acute rejection, chronic rejection and vasculopathy. Each group was followed for clinical and histopathological signs of rejection.ResultsThe acute rejection group presented clinical signs after 2 weeks and included skin erythema, atrophy, fur loss and de‐epithelization. Histopathology revealed lack of adnexa, epidermal necrosis, mononuclear cell infiltration, and massive perivascular infiltration. The chronic rejection group presented gradual fur loss, atrophy and shrinkage. Histopathology revealed lack of adnexa, epidermal necrosis and mononuclear cell infiltration as well as capillary thrombosis and intimal hyperplasia in small and large arteries. In the vasculopathy group no clinical sign of rejection was observed, and histopathology as well did not show any sign of rejection in the skin. The vasculature however revealed intimal hyperplasia of large and small arteries.ConclusionThis model allows induction of acute and chronic rejection as well as vasculopathy, and this is supported by clear clinical and histopathological results. This model is applicable for mechanistic studies of chronic rejection and vasculopathy, as well as testing potential therapies to prevent their development.Support or Funding InformationDoD grant W81XWH‐13‐2‐0057This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.