Allogeneic mesenchymal progenitor cells for posterolateral lumbar spine fusion in sheep.
BACKGROUND
Osteoconductive porous ceramic bone graft materials supplemented with mesenchymal precursor cells (MPC) derived from autologous bone marrow aspirates have been shown to stimulate successful interbody and posterolateral spine fusion in preclinical models. Recent advances in immunomagnetic cell sorting have enabled purification and isolation of pluripotent stem cells from marrow aspirates and have expanded stem cell technology to allogeneic cell sources. Allogeneic MPC technology combined with appropriate synthetic biomaterial carriers could provide both the osteogenic and osteoconductive components needed for successful posterolateral spine fusion without the need for autologous bone harvest or expensive recombinant protein technology.


OBJECTIVE
To determine the safety and efficacy of a hydroxyapatite:tricalcium phosphate graft material supplemented with allogeneic mesenchymal precursor cells in posterolateral lumbar spine fusion using an ovine model.


METHODS
Skeletally mature ewes underwent single-level instrumented posterolateral lumbar spine fusion using either autograft (AG), hydroxyapatite:tricalcium phosphate carrier (CP), or CP supplemented with allogeneic mesenchymal progenitor cells (MPCs). Three doses of MPCs were evaluated: 25 × 10⁶ cells (low dose, LD), 75 × 10⁶ cells (mid dose, MD), and 225 × 10⁶ cell (high dose, HD). Animals survived for either 4 or 9 months.


METHODS
Plain radiographs were acquired and scored for bridging bone at regular intervals during healing to monitor fusion development. Hematology, coagulation, and serum chemistry were monitored at regular intervals throughout the study to monitor animal health. After necropsy, computed tomography, high-resolution radiography, biomechanical testing, organ pathology, bone histopathology, and bone histomorphometry were conducted to monitor the safety and ascertain the efficacy of MPC treatment.


RESULTS
MPC treatment in this spine fusion model resulted in no observed adverse systemic or local tissue responses. Radiographically, fusion scores for MPC-treated animals were uniformly higher compared with those treated with carrier alone (CP) after 3 months and continued the same trend throughout 9 month of healing. Quantitative computed tomography confirmed better connectivity of the fusion for MPC treatment groups compared with CP. Biomechanical analyses were not able to differentiate between treatment groups. Histomorphometry results confirmed radiographic and quantitative computed tomography results; cell-supplemented treatment groups and autograft had equivalent amounts of bone within the fusion mass and less bony fusion tissue was found within the fusion mass in specimens from the CP treatment group. No conclusive effects of cell dose of fusion efficacy were noted.


CONCLUSIONS
Adult allogeneic mesenchymal precursor cells delivered via a hydroxyapatite:tricalcium phosphate carrier were both safe and efficacious in this ovine spine fusion model. Results from this preclinical study support that allogeneic mesenchymal precursor cells produced fusion efficacy similar to that achieved using iliac crest autograft, thereby providing a safe and viable option to achieve successful posterolateral spine fusion.
BioSolutions Consulting LLC, 3416 Henderson Cir, Santa Rosa, CA 95403, USA. Electronic address: donna.wheeler@biosoln.com.
Donna L
DL
Wheeler
Hospital for Special Surgery, Department of Orthopaedics, 535 E 70th St, New York, NY 10021, USA.
Joseph M
JM
Lane
Colorado State University, College of Veterinary Medicine, Department of Clinical Sciences, 300 W Drake Rd, Fort Collins, CO 80525, USA.
Howard B
HB
Seim
Colorado State University, College of Engineering, Department of Mechanical Engineering, Campus Delivery 1374, Fort Collins, CO 80525, USA.
Christian M
CM
Puttlitz
Columbia University, College of Physicians and Surgeons, 630 W 168th St., New York, NY 10032, USA; Mesoblast Limited, 505 Fifth Ave., Level 3, New York, NY 10036, USA.
Silviu
S
Itescu
Colorado State University, College of Veterinary Medicine, Department of Clinical Sciences, 300 W Drake Rd, Fort Collins, CO 80525, USA.
A Simon
AS
Turner
D000818:Animals; D001696:Biomechanical Phenomena; D016025:Bone Transplantation / Q000379:methods*; D002130:Calcium Phosphates; D002516:Ceramics; D017886:Durapatite; D005260:Female; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation / Q000379:methods*; D023421:Models, Animal; D011859:Radiography; D012756:Sheep; D013123:Spinal Fusion / Q000379:methods*; D014182:Transplantation, Autologous
D002130:Calcium Phosphates; D017886:Durapatite; C018392:tricalcium phosphate
Biomechanics; Bone graft substitute; Computed tomography; Histology; Mesenchymal stem cells; Ovine posterolateral lumbar spine fusion