Optimising canine olfactory ensheathing cell therapy using tissue engineering tools

Abstract

The adult mammalian spinal cord is incapable of significant regeneration following injury. As such, spinal injury is a lifelong debilitating condition which represents a significant burden on healthcare globally. Olfactory ensheathing cells (OECs) have been reported to promote axonal regeneration and improve locomotor function when transplanted into the injured spinal cord. A recent clinical trial demonstrated improved motor function in companion dogs following autologous transplantation of OECs derived from the olfactory mucosa (olfactory mucosal cells; OMCs). Their utility in canine subjects offers considerable promise to human translation, as dogs are highly comparable to human patients in terms of spinal lesion heterogeneity, genetic/environmental variation and management strategies. Moreover, the autologous, minimally invasive derivation of OMCs makes them an attractive cellular therapy for spinal injury in human patients. However, translating this therapy to human patients requires that two key limitations be addressed: (i) incomplete corticospinal tract (CST) regeneration; (ii) cell loss due to mechanical stress and aggregation in injection fluid.

In this regard, this thesis will test the hypothesis that OMCs are amenable to two specific tissue engineering strategies in order to address these barriers to translation: specifically, whether magnetic particles (MPs) in combination with an applied magnetic field can deliver genes encoding therapeutic biomolecules to canine OMCs (cOMCs) in order to enhance their regenerative capabilities in the injured cord. Secondly, whether 3-D hydrogel technology could function as a protective cell delivery system for cOMCs. This is with a view to the eventual development of an implantable hydrogel construct impregnated with genetically engineered OMCs.

In this thesis, it is shown that MPs in combination with an applied magnetic field can mediate safe and efficient delivery of genes encoding a major neurotrophic factor to cOMCs, with a maximum transfection efficiency of 57%. This thesis also reports that cOMC populations can be safely grown in implantable hydrogels, which could be tissue-matched to recipients noninvasively, using a clinically available imaging technique termed ultrasound elastography (USE). The results support the concept of generating a tissue-matched, nano-engineered “plug” of genetically enhanced cOMCs for delivery to sites of spinal cord injury (SCI). Moreover, the use of cells derived from a clinically relevant transplant population indicates a strong translational potential for this approach.