Femke Mathot

7 Motor results of MSC-seeded nerve allografts 111 INTRODUCTION Peripheral nerve defects not amendable to direct end-to-end neurorrhaphy require reconstruction with interposition nerve graft which could be accomplished with autograft, allograft or synthetic bioabsorbable conduits, each with their benefits and controversies. 1-3 Decellularized nerve allografts have been proposed as an ideal alternative to overcome donor site morbidity and limited supply of autografts. 1, 4-7 Improvement of outcomes of decellularized allografts by addition of host derived mesenchymal stem cells (MSCs) has been proposed to overcome the limitations of decellularized allograft nerves by producing trophic factors resulting in a favorable micro-environment for tissue regeneration. 8-14 MSCs are hypothesized to not only stimulate tissue regeneration, but potentially form extracellular matrix components, enhance angiogenesis, inhibit scar formation and control immune responses. 15 Adipose derived MSCs are easily accessible and proliferate faster than bone marrow derived MSCs, while having a similar effect on nerve regeneration and are thus ideal for translation to clinical use. 16-18 In comparison to undifferentiated MSCs, MSCs differentiated into Schwann cell-like cells express neurotrophic and angiogenic genes to a greater extent than undifferentiated MSCs in vitro. 16, 19-21 Several in vivo studies using different MSC-delivery strategies did not demonstrate clear differences between the outcomes of undifferentiated and differentiated MSCs. 22, 23 Others reported that differentiated MSCs led to longer regenerating axon distance in vivo 19, 21, 24, 25 , without resulting in improved functional outcomes. 21 The differentiation process of MSCs requires additional preparation time and expensive differentiation factors, which should be considered in translating bench work to clinical application. 16 Recent studies have reported a non-traumatic strategy to adhere undifferentiated and differentiatedMSCs to the surface of decellularized allografts, leading to a 29-day in vivo survival of seeded MSCs. 26-28 The adherence of MSCs to the decellularized allograft has demonstrated an interaction between MSCs and the extracellularly matrix leading to enhanced expression of neurotrophic, angiogenic, extracellular matrix and regulatory cell cycle genes in the first three (differentiated MSCs) to seven (undifferentiated MSCs) days after seeding in vitro, implying a direct effect of differentiated MSCs after implementation while undifferentiated MSCs require time to interact with the environment. 14 A comparative study focusing on functional outcomes can elucidate the effect of different cells and their different effective phases on motor nerve regeneration. The purpose of this study was to determine the effect of dynamically seeding undifferentiated and differentiated MSCs onto decellularized nerve allografts 7 with respect to functional and histologic outcomes in a rat sciatic nerve defect model. METHODS Experimental design After IACUC institutional review committee and our Institutional Review Board approval