Transplantation of encapsulated autologous olfactory ensheathing cell populations expressing chondroitinase for spinal cord injury: A safety and feasibility study in companion dogs

Abstract

Spinal cord injury (SCI) can cause irreversible paralysis, with no regenerative treatment clinically available. Dogs with natural SCI present an established model and can facilitate translation of experimental findings in rodents to people. We conducted a prospective, single arm clinical safety study in companion dogs with chronic SCI to characterize the feasibility of intraspinal transplantation of hydrogel-encapsulated autologous mucosal olfactory ensheathing cell (mOEC) populations expressing chondroitinase ABC (chABC). mOECs and chABC are both promising therapies for SCI, and mOECs expressing chABC drive greater voluntary motor recovery than mOECs alone after SCI in rats. Canine mOECs encapsulated in collagen hydrogel can be matched in stiffness to canine SCI. Four dogs with complete and chronic loss of function caudal to a thoraco-lumbar lesion were recruited. After baseline measures, olfactory mucosal biopsy was performed and autologous mOECs cultured and transduced to express chABC, then hydrogel-encapsulated and percutaneously injected into the spinal cord. Dogs were monitored for 6 months with repeat clinical examinations, spinal MRI, kinematic gait and von Frey assessment. No adverse effects or significant changes on neurological examination were detected. MRI revealed large and variable lesions, with no spinal cord compression or ischemia visible after hydrogel transplantation. Owners reported increased pelvic-limb reflexes with one dog able to take 2-3 unsupported steps, but gait-scoring and kinematic analysis showed no significant improvements. This novel combination approach to regeneration after SCI is therefore feasible and safe in paraplegic dogs in a clinical setting. A randomised-controlled trial in this translational model is proposed to test efficacy.

Keywords: canine translational model; cell therapy / transplantation; chondroitinase ABC; hydrogel encapsulation; neurology; neuroscience; olfactory ensheathing cells; spinal cord injury; spontaneous animal model.

FIGURE 1

Characterization of transplanted cell population. Cell population was characterized by immunofluorescence. Example images showing p75+ (mOECs, red) and fibronectin+ (fibroblasts, green) cells, with all nuclei (DAPI, blue), for each case are shown (a). Total number of cells transplanted and the proportion of each cell type (% shown in black text) is displayed in (b). Transplanted cells were transduced to express chABC. chABC activity in vitro was determined by Morgan Elson Assay (c) with no significant difference in chABC activity seen between cases

FIGURE 2

MR imaging. Example T2W sagittal images from each case are shown ((a); numbers indicate case). White bracket highlights extent and variability of T2 hyperintensity and abnormal spinal cord parenchyma. White arrow heads in case 2 mark area of spinal cord hemorrhage. Lesion volume was calculated by ROI volume measures on transverse T2W BAL TGRAD images and resulting volume renders of lesion morphology in each case are presented here viewed from left lateral (b). For each case, lesions were quantified pre‐transplant, immediately after transplant, and 2–3 months after transplant and measurements of lesion volume (c), lesion length (d) and lenght of MSCC (e) are graphed. MSCC: maximal spinal cord compromise

FIGURE 3

Functional testing: von Frey threshold responses and gait analysis. A von Frey aesthesiometer was used to determine pressure at which hindlimb withdrawal ((a). N.B. case 2 had flaccid paralysis and was therefore excluded from this analysis) or cutaneous trunci reflex (b) were triggered, and pressure at which the animal could feel and respond to stimulus at the skin overlying the lesion site (c). N.B. Case 3 was not able to return at 2 months due to the UK COVID‐19 lockdown. There were significant differences between cases in all measures, and significant differences between time‐points for hindlimb withdrawal and lesion sensation. There was no significant difference between baseline and final time‐point for hindlimb withdrawal, but lesion sensation threshold increased significantly between baseline and 6 months in case 1 and 2 (c). Two video‐based gait scores (d, e) showed no statistically significant change in gait over time. Kinematic gait analysis assessed fore‐hind limb coordination (f) and lateral stability (g), with no significant change over time seen