Current trends in mesenchymal stem cell application in bone augmentation: a review of the literature

Clinical applications of cell-based approaches in alveolar bone augmentation: a systematic review

BACKGROUND

Cell-based approaches, utilizing adult mesenchymal stem cells (MSCs), are reported to overcome the limitations of conventional bone augmentation procedures.

PURPOSE

The study aims to systematically review the available evidence on the characteristics and clinical effectiveness of cell-based ridge augmentation, socket preservation, and sinus-floor augmentation, compared to current evidence-based methods in human adult patients.

MATERIALS AND METHODS

MEDLINE, EMBASE, and CENTRAL databases were searched for related literature. Both observational and experimental studies reporting outcomes of "tissue engineered" or "cell-based" augmentation in ≥5 adult patients alone, or in comparison with non-cell-based (conventional) augmentation methods, were eligible for inclusion. Primary outcome was histomorphometric analysis of new bone formation. Effectiveness of cell-based augmentation was evaluated based on outcomes of controlled studies.

RESULTS

Twenty-seven eligible studies were identified. Of these, 15 included a control group (8 randomized controlled trials [RCTs]), and were judged to be at a moderate-to-high risk of bias. Most studies reported the combined use of cultured autologous MSCs with an osteoconductive bone substitute (BS) scaffold. Iliac bone marrow and mandibular periosteum were frequently reported sources of MSCs. In vitro culture of MSCs took between 12 days and 1.5 months. A range of autogenous, allogeneic, xenogeneic, and alloplastic scaffolds was identified. Bovine bone mineral scaffold was frequently reported with favorable outcomes, while polylactic-polyglycolic acid copolymer (PLGA) scaffold resulted in graft failure in three studies. The combination of MSCs and BS resulted in outcomes similar to autogenous bone (AB) and BS. Three RCTs and one controlled trial reported significantly greater bone formation in cell-based than conventionally grafted sites after 3 to 8 months.

CONCLUSIONS

Based on limited controlled evidence at a moderate-to-high risk of bias, cell-based approaches are comparable, if not superior, to current evidence-based bone grafting methods, with a significant advantage of avoiding AB harvesting. Future clinical trials should additionally evaluate patient-based outcomes and the time-/cost-effectiveness of these approaches.

Adipose stem cell tissue-engineered construct used to treat large anterior mandibular defect: a case report and review of the clinical application of good manufacturing practice-level adipose stem cells for bone regeneration

PURPOSE

Large mandibular resection defects historically have been treated using autogenous bone grafts and reconstruction plates. However, a major drawback of large autogenous bone grafts is donor-site morbidity.

PATIENTS AND METHODS

This report describes the replacement of a 10-cm anterior mandibular ameloblastoma resection defect, reproducing the original anatomy of the chin, using a tissue-engineered construct consisting of β-tricalcium phosphate (β-TCP) granules, recombinant human bone morphogenetic protein-2 (BMP-2), and Good Manufacturing Practice-level autologous adipose stem cells (ASCs). Unlike prior reports, 1-step in situ bone formation was used without the need for an ectopic bone-formation step. The reconstructed defect was rehabilitated with a dental implant-supported overdenture. An additive manufactured medical skull model was used preoperatively to guide the prebending of patient-specific hardware, including a reconstruction plate and titanium mesh. A subcutaneous adipose tissue sample was harvested from the anterior abdominal wall of the patient before resection and simultaneous reconstruction of the parasymphysis. ASCs were isolated and expanded ex vivo over the next 3 weeks. The cell surface marker expression profile of ASCs was similar to previously reported results and ASCs were analyzed for osteogenic differentiation potential in vitro. The expanded cells were seeded onto a scaffold consisting of β-TCP and BMP-2 and the cell viability was evaluated. The construct was implanted into the parasymphyseal defect.

RESULTS

Ten months after reconstruction, dental implants were inserted into the grafted site, allowing harvesting of bone cores. Histologic examination and in vitro analysis of cell viability and cell surface markers were performed and prosthodontic rehabilitation was completed.

CONCLUSION

ASCs in combination with β-TCP and BMP-2 offer a promising construct for the treatment of large, challenging mandibular defects without the need for ectopic bone formation and allowing rehabilitation with dental implants.

Anti-donor immune responses elicited by allogeneic mesenchymal stem cells: what have we learned so far?

Mesenchymal stem (stromal) cells (MSCs) have potent anti-inflammatory/immunosuppressive properties which underlie much of their therapeutic potential. This fact has led to the widely accepted belief that MSCs from genetically unrelated individuals (allogeneic (allo)-MSCs) can be used therapeutically with equal efficacy to autologous MSCs and without triggering the donor-specific immune responses that are typically associated with allo-transplants. In this article, we critically review available experimental data to determine whether good in vivo evidence exists in support of the 'immune privileged' status of allo-MSCs. We also examine published studies regarding the immunogenicity of allo-MSCs following activation ('licensing') by inflammatory stimuli or following differentiation. Among the identified studies which have addressed in vivo immunogenicity of allo-MSCs, there was substantial variability as regards experimental species, disease model, route of MSC administration, cell dose and stringency of the immunological assays employed. Nonetheless, the majority of these studies has documented specific cellular (T-cell) and humoral (B-cell/antibody) immune responses against donor antigens following administration of non-manipulated, interferon-γ-activated and differentiated allo-MSCs. The consequences of such anti-donor immune responses were also variable and ranged from reduced in vivo survival of allo-MSCs with accelerated rejection of subsequent allogeneic transplants to apparent promotion of donor-specific tolerance. On the basis of these findings and on existing knowledge of allo-antigen recognition from the field of transplant immunology, we propose that the concept of the immune privileged nature of allo-MSCs should be reconsidered and that the range and clinical implications of anti-donor immune responses elicited by allo-MSCs be more precisely studied in human and animal recipients.