A strategy for peripheral nerve allografting: Immunosuppression versus chimeric nerve grafting

Hogg, Fiona Jacqueline (2002) A strategy for peripheral nerve allografting: Immunosuppression versus chimeric nerve grafting. MD thesis, University of Glasgow.

Abstract

Chimera: (Biology) An organism consisting of at least two genetically different kinds of tissue as a result of mutation, grafting, etc. Collins English Dictionary This thesis has set out to investigate the regenerative potential of peripheral nerve allografting in a rodent model. In particular, the strategy of reconstructing a nerve defect using a novel chimeric graft of mixed antigenicity (Sandwich graft) was explored as an alternative to autografting or immunosuppression. Peripheral nerve injury produces significant individual and community morbidity. Despite technical and surgical advances, even the results from urgent repair of single modality nerves are sub-optimal. This situation is compounded when nerve structure is lost and a bridging conduit is required to reconstruct the defect. While many organic and inorganic materials have been investigated, autografting remains the mainstay of current clinical practice. However, suitable autografts are in limited supply and associated with donor site morbidity. Like autografts, peripheral nerve allografts (PNAG) possess all the features required of an ideal nerve conduit, especially Schwann cells. Studies with acellular conduits have shown the addition of Schwann cells is advantageous to regeneration. However, immunological rejection of antigenic Schwann cells within nerve allografts renders the graft acellular, inhibiting regeneration. Immunosuppression preserves allogenic Schwann cells and results in regeneration equivalent to autografts. But immunosuppressants are associated with serious side effects such that their use in peripheral nerve injuries is deemed unethical. Temporary immunosuppression has been proposed as a solution to this problem until the non-antigenic host axon regeneration is established. However this has produced conflicting results although an axonopathic process following drug withdrawal is acknowledged. The aims of this project were firstly to assess the regenerative potential of non- immunosuppressed PNAGs. The hypothesis being that rejection would produce acellular grafts as donor Schwann cells were destroyed. Host Schwann cells are known to repopulate acellular conduits from adjacent nerve ends. By using a chimeric Sandwich graft, the second aim of the project was to assess whether augmenting host Schwann cell graft repopulation could improve axonal regeneration and reduce immunosuppressant requirements. A clinically reproducible chimeric construct of a nerve allograft with an intervening segment of autologous nerve (a Sandwich graft) was used to bridge a standard traumatic nerve gap within the experimental groups. Comparisons were made between simple and sandwich grafts composed of autologous, isogeneic and allogenic nerves split into immunosuppressed and non-immunosuppressed limbs, incompatible rat strains were employed using Cyclosporin (CyA) as the sole immunosuppressant. Qualitative and quantitative analyses of immunohistochemical and conventional histological specimens, along with measurement of Gastrocnemius muscle mass, were used to assess the outcome of nerve regeneration. Analyses were undertaken within the early and late regeneration periods of 21 days and 32 weeks respectively. Immunohistochemistry and conventional histological techniques were employed, along with measurements of muscle mass recovery to indicate target organ reinnervation. Cyclosporin (CyA) was the sole immunosuppressants used. Non-immunosuppressed PNAGs were shown to support less early axonal regeneration than their immunosuppressed counterparts and non-allogenic controls. This was associated with a reduction in Schwann cells and increased inflammation indicating rejection. However, the pattern of regeneration followed that of the other groups and improved with time. Sandwich allografting was associated with improved axonal regeneration, increased Schwann cells and less inflammation suggesting reduced antigenicity of the sandwich construct. The increased neurorrhaphies compared to simple grafts did not appear deleterious. Long-term myelinated nerve counts and target organ reinnervation produced similar results from all experimental groups regardless of immunosuppression. This work validates the use of a chimeric sandwich graft within this model. The addition of a depot of host Schwann cells within an allograft without immunosuppression produces similar regeneration to non-allogenic grafts and reduces the early delay period associated with rejection. Further analysis of the formulations of CyA used indicated that although oily and parenteral CyA did adequately immunosuppress the allografts, the results from parenteral CyA were marginally better. Also, CyA use did contribute to model morbidity and mortality within these experiments.

• Item Type: Thesis (MD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Dr. Giorgio Terenghi.
• Keywords: Immunology.
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Supervisor, not known
• Date of Award: 2002
• Depositing User: Enlighten Team
• Unique ID: glathesis:2002-71270
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 10 May 2019 10:49
• Last Modified: 07 Jun 2021 10:48
• URI: https://theses.gla.ac.uk/id/eprint/71270