Regeneration across cold preserved peripheral nerve allografts

Abstract

The feasibility of peripheral nerve allograft pretreatment utilizing cold storage (5 degrees C in the University of Wisconsin Cold Storage Solution) or freeze-thawing to prevent rejection was investigated. Regeneration across cold-stored (3 or 5 weeks) or freeze-thawed (FT), 3.0-cm sciatic nerve allografts were compared to fresh auto- and allografts in an inbred rat model. At 16-week post-engraftment, only FT allografts appeared similar to autografts on gross inspection; FT grafts were neither shrunken nor adherent to the surrounding tissue as seen in the other allograft groups. Qualitatively, the pattern of regeneration in the graft segments of the fresh allograft and to a lesser extent of pretreated allografts was inferior to that of autografts as evidenced by a disruption in the perineurium, more extrafascicular axons, smaller and fewer myelinated axons, increased intrafascicular collagen deposition, and the persistence of perineurial cell compartmentation and perivascular infiltrates. Distal to these grafts, the regeneration became more homogenous between groups, although areas of ongoing Wallerian degeneration, new regeneration as well as compartmentation, were more prevalent in fresh and pretreated allografts. Although the number of myelinated fibres was equivalent to autografts, the fibre diameters, the number of large diameter fibres, and the G-ratio were significantly decreased in the allograft groups, which, in part, accounted for the significant decrease in conduction velocity in the 3-week stored and fresh allograft, and the slight decrease in the 5-week stored and FT allograft groups. There was a small return in the Sciatic Function Index towards normal, but no consistent differences between groups were found. Prolonged cold storage and freeze-thawing of nerve allografts resulted in regeneration that was better than fresh allografts, but inferior to autografts. With the concomitant use of host immunosuppression or other immunotherapies, these storage techniques can provide a means of transporting nerve allografts between medical centres and for converting urgent into elective procedures.

Peripheral nerve and neuromuscular allotransplantation: Current status

“…18 Storage of nerve grafts in University of Wisconsin solution has been extensively studied. [19][20][21] Progressive duration of storage will decrease rejection but viable Schwann cells will be lost. An optimal period of storage is 7 days at 5°C.…”

Nerve regeneration across cryopreserved allografts from cadaveric donors: a novel approach for peripheral nerve reconstruction

“…Autologous nerve grafting is considered the gold standard for repair of nerve gaps, acting as a scaffold and providing viable Schwann cells that produce neurotrophic factors for axonal regeneration. 10,11,20 Synthetic or viable biological nerve conduits represent an interesting area of research, but their use is limited to short nerve gaps and small nerve injuries (approximately 2 cm in length). Recently, allografts from human cadavers have attracted renewed interest.…”

“…This cold preservation method may provide an almost unlimited supply of graft material to be used in peripheral nerve reconstruction and enables long-term storage of the grafts. 10,13,20 The roles of tissue processing and cryopreservation in immunogenicity have been a matter of debate: several studies in animals have demonstrated that cryopreservation and controlled freezing decrease the immune response and risk of graft rejection in recipients, preserve Schwann cell viability, and maintain the nerve basal lamina. These techniques have been also shown to decrease the expression of Class II HLAs (human leukocyte antigens) and intercellular adhesion molecule-1, which are essential for immunological recognition of foreign tissues, and this decreased expression supports axonal regeneration across short peripheral nerve gaps.…”

“…These techniques have been also shown to decrease the expression of Class II HLAs (human leukocyte antigens) and intercellular adhesion molecule-1, which are essential for immunological recognition of foreign tissues, and this decreased expression supports axonal regeneration across short peripheral nerve gaps. 1,9,10,13,20 Other authors have failed to demonstrate axonal elongation after cryopreservation of longsegment allografts (8 cm in length). 26 The freeze-thawing process seems to leave perineurial and endoneurial connective tissues intact, effectively preventing infiltration by host lymphocytes as has been observed in fresh allografts and allowing nerve regeneration similar to that observed for autografts, as assessed by qualitative histology.…”

The effects of cold preservation and subimmunosuppressive doses of FK506 on axonal regeneration in murine peripheral nerve isografts

“…Cold preservation in University of Wisconsin solution decreases the antigencity of a nerve allograft in part via the down-regulation of intercellular adhesion molecules (15,(28)(29)(30)(31)(32). In fact, subimmunosuppressive doses of FK506 that are ineffective in stimulating nerve regeneration in a standard nerve allograft stimulate nerve regeneration in nerve allografts that have been pretreated with cold preservation (15).…”