Mesenchymal stem cell concentration and bone repair: potential pitfalls from bench to bedside.
BACKGROUND
Mesenchymal stem cells are multipotent and have the ability to differentiate into bone. We conducted a preclinical trial comparing the osteogenic potential of human bone marrow aspirate with that of mesenchymal stem cell-enriched bone marrow aspirate (both mixed with demineralized bone matrix) in a critical-sized rat femoral defect model.


METHODS
The buffy coat was extracted from human bone marrow aspirate to obtain mesenchymal stem cell-enriched bone marrow aspirate. Fifty-nine athymic rats, each with a 6-mm femoral defect, were divided into six treatment groups: defect only (Group I), demineralized bone matrix and saline solution (Group II), demineralized bone matrix and bone marrow aspirate (Group III), demineralized bone matrix and mesenchymal stem cell-enriched bone marrow aspirate (Group IV), demineralized bone matrix and recombinant human bone morphogenetic protein-2 (rhBMP-2) (Group V [positive control]), and absorbable collagen sponge and rhBMP-2 (Group VI [positive control]). All animals were killed at twelve weeks for radiographic, micro-computed tomography, histomorphometric, and histologic analysis.


RESULTS
There was wide variability in the mesenchymal stem cell concentrations obtained from the human donors. All ten defects healed in the positive control groups (Groups V and VI). Only one defect healed in each experimental group (Groups II, III, and IV) (i.e., three of forty-four defects healed). There was no significant difference among the radiographic scores of Groups II, III, and IV (p = 0.59), and the score for each of those groups was significantly higher than that for Group I (p <or= 0.005) and significantly lower than those for Groups V and VI (p <or= 0.001). The bone volume and mineral density did not differ among Groups III, IV, and V (p = 0.53). The percent total bone volume and percent normal bone volume in Group VI were significantly higher than those values in Groups I, III, and IV (p < 0.0001) and those in Group II (p = 0.048). In Groups II through V, the cortical bone was more dense than the lace-like bone in Group VI.


CONCLUSIONS
Neither bone marrow aspirate nor mesenchymal stem cell-enriched bone marrow aspirate mixed with demineralized bone matrix resulted in reliable healing of critical-sized bone defects. It is possible that a greater number of mesenchymal stem cells or an enhanced osteoinductive signal is required for adequate bone-healing. Mesenchymal stem cell and/or carrier variability may also contribute to differences in bone formation.
David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA 90095, USA.
Anna V
AV
Cuomo
Mandeep
M
Virk
Frank
F
Petrigliano
Elise F
EF
Morgan
Jay R
JR
Lieberman
D000818:Animals; D015519:Bone Density; D016026:Bone Marrow Transplantation; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D005269:Femur / Q000000981:diagnostic imaging; D006801:Humans; D045164:Mesenchymal Stem Cell Transplantation; D009929:Organ Size; D010012:Osteogenesis / Q000502:physiology; D011859:Radiography; D051381:Rats; D011923:Rats, Nude; D011994:Recombinant Proteins / Q000494:pharmacology; D023822:Tissue Engineering; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014184:Transplantation, Homologous
D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C499469:recombinant human bone morphogenetic protein-2