Introduction: Vascularized Composite Allotransplantation (VCA) can restore both form and function, improving the quality of life for patients who have suffered significant injuries leading to large tissue defects. Vasculopathy is a major feature of chronic VCA rejection. Although no definitive treatment currently exists for vasculopathy, early diagnosis and modification of immunosuppressive therapy may halt or slow the progression of this process. We here describe a VCA model in swine used to assess minimally invasive biomarkers of rejection. Non-invasive approaches that accurately detect early signs of vasculopathy in the skin and deeper tissues could lead to effective management strategies that prevent VCA graft rejection.
Method: Six allogeneic and two autologous VCAs were performed using Sinclair donors and Yucatan recipients. Immunosuppression therapy was not used in this cohort. Using an ultrabright porphyrin molecular oxygen sensor known as a Clickaphor, skin temperature and tissue oxygenation were measured transcutaneously, every 24 hours until euthanasia. Donor-specific antibodies (DSAs) were measured by flow cytometry. Daily punch biopsies were performed for histological analysis and results were correlated with physical exams, transcutaneous readings, and CBC data.
Results: Histological rejection was evident in the allogeneic VCA biopsies by POD2-4, including increased inflammation surrounding the superficial vascular plexus in the dermis (Banff grade 1), that progressed to junctional inflammation, intraepidermal inflammation, and piecemeal necrosis (grades 2-3). By POD4-6 vascular congestion with arterial, epidermal and diffuse dermal necrosis were present (grade 4). Daily CBC analysis revealed spikes in the WBC and granulocyte counts for each pig between POD5 and 6, correlating with histological and visual signs of rejection. Most allografts were completely rejected and no longer viable by POD7. In contrast, histological analysis of the autografts showed only mild dermal edema beginning on POD3 and resolving by POD7. The autografts were completely healed and well-integrated with the surrounding tissue by POD14. Transcutaneous temperature readings correlated well with allograft rejection and DSAs were detected in the recipients as early as POD6 and levels continued to rise post-operatively.
Conclusion: This study illustrates the rapid onset and progression of histological rejection in allogeneic VCA grafts. The correlation between changes in graft temperatures and clinical and histological indicators of rejection offers a non-invasive and readily accessible method to monitor the health and viability of allografts. This study underscores the ability of temperature monitoring to identify when adverse reactions, such as vasculopathy, are occurring so that measures can be taken to prevent acute and chronic graft rejection.