Neointimal hyperplasia, transplant rejection and thus immunogenicity of allografts are possible reasons for poorer patency rates in cryopreserved venous allografts for peripheral bypass surgery in comparison with autologous venous grafts. To expand the limited knowledge from human allografts, we histologically investigated allogeneic and autologous venous grafts in arterial location. Specimens of allogeneic and autologous venous graft stenosis, harvested 6 months after bypass implantation, were immunohistochemically characterized. Examination of the lesions showed a uniform morphological pattern. A continuous endothelial layer, tissue fibrosis and a thickened neointima with monocytes and dedifferentiated vascular smooth muscle cells were seen in both conduits with very low cell turnover and the absence of acute and chronic inflammation. Neoangiogenesis with CD34-positive endothelium was abundant in the vessel media. The morphological patterns of allogeneic and autologous neointima formation are similar. Consequently, neointimal hyperplasia in venous grafts may reflect a uniform physiological host response of non-immunological factors with the reasons for poorer clinical outcome of cryopreserved allografts yet to be elucidated.

Introduction: Cryopreserved venous allografts are considered as possible alternative to autologous venous grafts in peripheral bypass surgery. Neointima formation is responsible for poorer patency. For a better understanding of this process we investigated allogeneic and autologous venous grafts in arterial position by histologic means. Materials and Methods: Allogeneic and autologous venous graft stenosis were examined by Ki67, CD31, CD34, CD3, CD20, vWF, CD68, actin, vimentin and desmin. Results: The morphological Examination of autologous and cryopreserved allogeneic grafts appears very uniform. Dedifferentiated vascular smooth muscle cells are the main cellular effector in both grafts. Neoangiogenesis is abundant in the vessel media whereas immunologic infiltrates are largely absent. Conclusion: The uniform morphological appearance of allogeneic and autologous neointimal hyperplasia suggests an overreaction in venous grafts in response to non-immunological factors as reason for poorer clinical outcome of cryopreserved allografts.