Histological Analysis of Cryopreserved Venous Allografts Used for Liver Transplantation and Hepato‐Biliary‐Pancreatic Surgery

BACKGROUND: Cryopreserved venous allografts, which we pioneered in 1999 for use in living donor liver transplantation and hepato-biliary-pancreatic surgery, are widely used and are believed to preserve vascular architecture with minimal anticoagulation or immunosuppression requirements and patency comparable to autologous grafts. However, in contrast to arterial and heart valve grafts, their detailed histopathological characteristics remain unclear. METHODS: Histopathological and immunohistochemical analyses were performed in 19 non-transplanted and 15 explanted cryopreserved venous allografts. Cell viability was assessed by culture, and tissue chimerism was evaluated using fluorescence in situ hybridization. RESULTS: The normal trilaminar vascular architecture and presence of viable endothelial cells were confirmed in both groups. No findings of immunologic rejection, including medial cell loss, cellular infiltration in the adventitia, or intimal thickening, were observed. Long-term culture demonstrated sustained viability and proliferative capacity of donor cells. In situ hybridization confirmed persistent tissue chimerism with both donor- and recipient-derived cells. CONCLUSIONS: Cryopreserved venous allografts maintained viability and showed no histological evidence of active immunologic rejection after long-term implantation. These findings may help explain the favorable clinical performance and provide foundational insights to improve outcomes of venous reconstruction and the development of novel biologic vascular grafts.