Pre-clinical And Preliminary Clinical Studies Of Chemically Extracted Acellular Nerve Allograft

Our previous studies showed that chemical extraction could remove Schwann cells and myelinated sheath in the peripheral nerves of big mammalian animals, reduce the immonogenicity of nerve allografts, and therefore decrease the immune rejection after allotransplantation. Acellular nerve allograft by chemical extraction supported nerve regeneration of 5cm segment sciatic nerve defect in dogs. Our present studies were undertaken to investigate the immune response of allogeneic nerve grafts in rats, observe the effects of repair of long-length nerve loss in dogs and in primates, examine the biological safety of acellular nerve allografts chemically extracted from human peripheral nerves. Peripheral nerves of inbred SD rats were harvested and made acellular by chemical extraction. Acellular and fresh allogeneic nerve grafts from SD rats were transplanted into subcutaneous tissue of inbred Wistar rats.The humoral immune response was evaluated via measuring the levels of antibody specific to nerve antigen at 2, 4, 8, and 12 weeks after transplantation. Cell-mediated immune response was assessed with the scales of infiltration of T lymphocyte and its subgroups. Immunological experiments showed low immune response in chemically extracted acellular nerve allografts, because the number of CD3, CD4 and CD8 positive lymphocytes infiltration was far lower than that in the control group of fresh nerve allografts. Studies on repair of long-length nerve defect suggested that 8cm segment acellular nerve allografts may be the longest distance for supporting nerve regeneration with good function The number of regenerated axons across the nerve allograft and motorend-plates in the reinnervated muscles in 8cm group were far more than those in 10cm group. Study on preservation showed that freeze-drying did not affect Schwann cell basal lamina or laminin distribution in the acellular nerves and 5cm segment freeze-dried acellular nerve allografts had good nerve regeneration in the repair of nerve defect in dogs. Experiments in primates showed that chemically acellular nerve allotransplantation could repair 5cm gap of median nerves in the arm. Examinations of biological safety demonstrated that human acellular nerve by chemical extraction had good safety according to the national criteria. Six patients repaired nerve defect with chemically extracted acellular nerve allograft had satisfying results in the preliminary clinical application.