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Nerve allotransplantation (allo- means "other" in Greek) is the transplantation of a nerve to a receiver from a donor of the same species. For example, nerve tissue is transplanted from one person to another. Allotransplantation is a commonly used type of transplantation of which nerve repair is one specific aspect. The transplant is called an allograft, allogeneic transplant, or homograft〔http://www.axogeninc.com/docs/AXG_9010_Avance_Tech_Guide.pdf〕 Currently the only FDA approved nerve allograft is the Avance graft of AxoGen. == Nerve Allograft == A nerve allograft is used for the reconstruction of peripheral nerve discontiuities in order to support the axonal regeneration across a nerve gap caused by any injury. It is human nerve tissue, processed to remove cellular and noncellular factors such as cells, fat, blood, axonal debris and chondroitin sulfate proteoglycans while preserving the three-dimensional scaffold and basal lamina tubular structure of the nerve. This means the nerve allograft only consists of extracellular matrix (ECM), which is sterile and decullularized.〔 There are three types of nerves; * Sensory nerves, which carry sensory information from peripheral organs, for example the skin, to the central nervous system. Sensory fibers are, amongst other things, responsible for sensation, proprioception and the sense of movement. * Motor nerves, which carry the information from the central nervous system to peripheral organs, especially the muscles. Signals cause either relaxation and contraction of muscles, thereby enabling movement. * Mixed nerves, which contain both sensory and motor fibers. In a trauma or surgical resection, a nerve can be damaged, which is called a nerve defect. This defect needs to be repaired in order to regain full or partial sensory and motor function. Peripheral nerve injury is a major clinical problem and can result in neuropathic pain. Which is pain arising as a direct consequence of a lesion or disease affecting the somatosensory system. Damaged nerve fibers continuously excite electric pulses, inducing pain or abnormal sensation dysesthesia. It has been shown that in allograft surgeries, post-operative neuropathic pain was present in some patients, but only if they suffered from this condition pre-operatively.〔Yates D (2013) Processed nerve allograft for trigeminal nerve repair: safety and effectiveness in sensory nerve reconstruction. J of Oral and Maxillofac Surg. 71 (9), 14 – 15〕 Patients without neuropathic pain before their surgery did not complain about neuropathic pain afterwards.〔 Hence, allograft treatment does not seem to be a risk factor for this specific problem. Golden standard therapy for transected nerves is an end-to-end repair of the nerve, also known as primary nerve repair. With a certain amount of tension on the nerve due to the injury, the blood flow to the nerve decreases, which can eventually lead to ischemia and nerve damage. The gap between the nerve ends could then, for example be bridged by a nerve that is harvested from a less critical area from the same patient. The piece of nerve used in this case is called an autograft autotransplantation.〔Siemionow M. (2007) Nerve allograft transplantation: a review. J of reconstr microsurg. 23 (8), 511 - 520〕〔Mackinnon S.E., Doolabh VB, Novak CB, Trulock EP (2001) Clinical outcome following nerve allograft transplantation. Plast Reconstr Surg. 107. 1419–1429〕〔Cho M.S. (2012) Functional Outcome Following Nerve Repair in the Upper Extremity Using Processed Nerve Allograft. J Hand Surg. 37 (11), 2340 - 2349〕〔Lundborg G. Nerve injury and repair: regeneration, reconstruction and cortical remodeling. 2nd ed. Philadelphia: Elsevier, 2005.〕〔IJpma FF, Nicolai JP, Meek MF. Sural nerve donor-site morbidity: thirty-four years of follow-up. Ann Plast Surg 2006;57:391–395.〕 A commonly used nerve for autotransplantation is the sural nerve in the upper leg. Unfortunately, this treatment does have some disadvantages. First, there is a risk of donor site morbidity and functional loss. Secondly, patients have an increased risk of symptomatic neuroma formation. Thirdly, a longer anaesthesia time is needed because of the additional surgical site for the donor nerve. Lastly, higher costs also due to the extra surgical site. Despite these downsides, reducing the function of the affected area is beyond the risks committed with harvest of the donor nerve.〔〔〔Brooks D.N. (2012) Processed nerve allografts for peripheral nerve reconstruction: a multicenter study of utilization and outcomes in sensory, mixed and motor nerve reconstructions. Microsurgery. 32 (1), 1 - 14〕 In case of insufficient amount of autologous nerve tissue or the inability to attach both nerve ends securely and tension free, these two options are not possible. Another option to bridge the gap is nerve allotransplantation. Nerve allografts are prepared from donated human nerve tissue. An allograft contains many of the beneficial characteristics of nerve autograft, such as three-dimensional microstructural scaffolding and protein components inherent to nerve tissue.〔 One of the adverse effects of nerve allotransplantation is the immunogenic response Tissue from another human being is used to restore the defect, which can induce an immunogenic response. An immune response against an allograft or xenograft is called Transplant rejection. To prevent this rejection, new immunosuppressive techniques are performed on the graft, before it is transplanted into the receiver. The donated nerve tissue is disinfected, by selectively removing cellular components and debris to cleave growth inhibitors and then terminally sterilized.〔 These procedures make the immunogenic response insignificant. Since a couple of decades processed nerve allografts has been used to restore nerve continuity. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nerve allograft」の詳細全文を読む スポンサード リンク
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