An allograft generated from adult stem cells and their secreted products efficiently fuses vertebrae in immunocompromised athymic rats and inhibits local immune responses

Abstract

BACKGROUND CONTEXT Spine pain and the disability associated with it are epidemic in the United States. According to the National Center for Health Statistics, more than 650,000 spinal fusion surgeries are performed annually in the United States, and yet there is a failure rate of 15%–40% when standard methods employing current commercial bone substitutes are used. Autologous bone graft is the gold standard in terms of fusion success, but the morbidity associated with the procedure and the limitations in the availability of sufficient material have limited its use in the majority of cases. A freely available and immunologically compatible bone mimetic with the properties of live tissue is likely to substantially improve the outcome of spine fusion procedures without the disadvantages of autologous bone graft. PURPOSE This study aimed to compare a live human bone tissue analog with autologous bone grafting in an immunocompromised rat model of posterolateral fusion. DESIGN/SETTING This is an in vitro and in vivo preclinical study of a novel human stem cell–derived construct for efficacy in posterolateral lumbar spine fusion. METHODS Osteogenically enhanced human mesenchymal stem cells (OEhMSCs) were generated by exposure to conditions that activate the early stages of osteogenesis. Immunologic characteristics of OEhMSCs were evaluated in vitro. The secreted extracellular matrix from OEhMSCs was deposited on a clinical-grade gelatin sponge, resulting in bioconditioned gelatin sponge (BGS). Bioconditioned gelatin sponge was used alone, with live OEhMSCs (BGS+OEhMSCs), or with whole human bone marrow (BGS+hBM). Efficacy for spine fusion was determined by an institutionally approved animal model using 53 nude rats. RESULTS Bioconditioned gelatin sponge with live OEhMSCs did not cause cytotoxicity when incubated with immunologically mismatched lymphocytes, and OEhMSCs inhibited lymphocyte expansion in mixed lymphocyte assays. Bioconditioned gelatin sponge with live OEhMSC and BGS+hBM constructs induced profound bone growth at fusion sites in vivo, with a comparable rate of fusion with syngeneic bone graft (negative [0 of 10], BGS alone [0 of 10], bone graft [7 of 10], BGS+OEhMSC [10 of 15], and BGS+hBM [8 of 8]). CONCLUSIONS Collectively, these studies demonstrate that BGS+OEhMSC constructs possess low immunogenicity and drive vertebral fusion with efficiency matching syngeneic bone graft in rodents. We also demonstrate that BGS serves as a promising scaffold for spine fusion when combined with hBM.

Rapid Osteogenic Enhancement of Stem Cells in Human Bone Marrow Using a Glycogen-Synthease-Kinase-3-Beta Inhibitor Improves Osteogenic Efficacy In Vitro and In Vivo

“…A). In a previous study, we demonstrated that the ECM scaffold exhibits no inherent healing capacity without supplementation with an appropriate cell source . When compared with untreated hBM, VRE‐BIO treated hBM did not affect fusion frequency (5/5 fused in each case) or the volume of the fusion masses (Fig.…”

“…For this purpose, hBM was subjected to VRE‐BIO for 1 hour with 800 nM BIO because these conditions resulted in the most robust upregulation of osteogenic parameters tested. The hBM was then combined with a radiolucent scaffold we developed consisting of porcine gelatin foam with hMSC‐derived extracellular matrix and positioned over decorticated the posterolateral processes of the L4‐L6 vertebrae followed by an 8 week (period of healing ) (Fig. A).…”

“…The 800‐nM concentration was chosen because it was well tolerated by the cells and resulted in robust effects on the osteogenic parameters tested. The hBM was washed in PBS followed by mixing with a previously described scaffold generated from the gelatin foam coated with extracellular matrix derived from cultured hMSCs . Controls received no BIO but were treated in exactly the same way.…”

“…Ten 6‐week‐old (approximately 135 g) female athymic nude rats (Hsd:RH‐Foxn rnu ) ( n = 5 per group) were acquired from Harlan Laboratories (Indianapolis, IN). A bilateral intertransverse process fusion at L5‐L6 was performed on them as previously described , but with some modifications .…”

“…In most cases, it was impossible to distinguish the new bone from the mature transverse processes because outgrowths were completely contiguous with original bone. We therefore used previously described methods that compared total volumes of fused vertebrae . For histomorphometric analysis of fusion beds, specimens were scanned at 18 μm/pixel resolution with image smoothing and ring artifact compensation set to maximum.…”