Streamlining the generation of an osteogenic graft by 3D culture of unprocessed bone marrow on ceramic scaffolds

A relativity concept in mesenchymal stromal cell manufacturing

Mesenchymal stromal cells (MSCs) are being experimentally tested in several biological systems and clinical settings with the aim of verifying possible therapeutic effects for a variety of indications. MSCs are also known to be heterogeneous populations, with phenotypic and functional features that depend heavily on the individual donor, the harvest site, and the culture conditions. In the context of this multidimensional complexity, a recurrent question is whether it is feasible to produce MSC batches as "standard" therapeutics, possibly within scalable manufacturing systems. Here, we provide a short overview of the literature on different culture methods for MSCs, including those employing innovative technologies, and of some typically assessed functional features (e.g., growth, senescence, genomic stability, clonogenicity, etc.). We then offer our perspective of a roadmap on how to identify and refine manufacturing systems for MSCs intended for specific clinical indications. We submit that the vision of producing MSCs according to a unique standard, although commercially attractive, cannot yet be scientifically substantiated. Instead, efforts should be concentrated on standardizing methods for characterization of MSCs generated by different groups, possibly covering a vast gamut of functionalities. Such assessments, combined with hypotheses on the therapeutic mode of action and associated clinical data, should ultimately allow definition of in-process controls and measurable release criteria for MSC manufacturing. These will have to be validated as predictive of potency in suitable pre-clinical models and of therapeutic efficacy in patients.

Synergistic enhancement of ectopic bone formation by supplementation of freshly isolated marrow cells with purified MSC in collagen-chitosan hydrogel microbeads

PURPOSE

Bone marrow-derived mesenchymal stem cells (MSC) can differentiate osteogenic lineages, but their tissue regeneration ability is inconsistent. The bone marrow mononuclear cell (BMMC) fraction of adult bone marrow contains a variety of progenitor cells that may potentiate tissue regeneration. This study examined the utility of BMMC, both alone and in combination with purified MSC, as a cell source for bone regeneration.

METHODS

Fresh BMMC, culture-expanded MSC, and a combination of BMMC and MSC were encapsulated in collagen-chitosan hydrogel microbeads for pre-culture and minimally invasive delivery. Microbeads were cultured in growth medium for 3 days, and then in either growth or osteogenic medium for 17 days prior to subcutaneous injection in the rat dorsum.

RESULTS

MSC remained viable in microbeads over 17 days in pre-culture, while some of the BMMC fraction were nonviable. After 5 weeks of implantation, microCT and histology showed that supplementation of BMMC with MSC produced a strong synergistic effect on the volume of ectopic bone formation, compared to either cell source alone. Microbeads containing only fresh BMMC or only cultured MSC maintained in osteogenic medium resulted in more bone formation than their counterparts cultured in growth medium. Histological staining showed evidence of residual microbead matrix in undifferentiated samples and indications of more advanced tissue remodeling in differentiated samples.

CONCLUSIONS

These data suggest that components of the BMMC fraction can act synergistically with predifferentiated MSC to potentiate ectopic bone formation. The microbead system may have utility in delivering desired cell populations in bone regeneration applications.

Direct comparison of current cell-based and cell-free approaches towards the repair of craniofacial bone defects - A preclinical study

For craniofacial bone defect repair, several alternatives to bone graft (BG) exist, including the combination of biphasic calcium phosphate (BCP) biomaterials with total bone marrow (TBM) and bone marrow-derived mesenchymal stromal cells (MSCs), or the use of growth factors like recombinant human bone morphogenic protein-2 (RhBMP-2) and various scaffolds. Therefore, clinicians might be unsure as to which approach will offer their patients the most benefit. Here, we aimed to compare different clinically relevant bone tissue engineering methods in an "all-in-one" study in rat calvarial defects. TBM, and MSCs committed or not, and cultured in two- or three-dimensions were mixed with BCP and implanted in bilateral parietal bone defects in rats. RhBMP-2 and BG were used as positive controls. After 7 weeks, significant de novo bone formation was observed in rhBMP-2 and BG groups, and in a lesser amount, when BCP biomaterials were mixed with TBM or committed MSCs cultured in three-dimensions. Due to the efficacy and safety of the TBM/BCP combination approach, we recommend this one-step procedure for further clinical investigation.

STATEMENT OF SIGNIFICANCE

For craniofacial repair, total bone marrow (BM) and BM mesenchymal stem cell (MSC)-based regenerative medicine have shown to be promising in alternative to bone grafting (BG). Therefore, clinicians might be unsure as to which approach will offer the most benefit. Here, BM and MSCs committed or not were mixed with calcium phosphate ceramics (CaP) and implanted in bone defects in rats. RhBMP-2 and BG were used as positive controls. After 7 weeks, significant bone formation was observed in rhBMP-2 and BG groups, and when CaP were mixed with BM or committed MSCs. Since the BM-based procedure does not require bone harvest or cell culture, but provides de novo bone formation, we recommend consideration of this strategy for craniofacial applications.

Three-dimensional culture and characterization of mononuclear cells from human bone marrow

BACKGROUND AIMS

The diverse phenotypic changes and clinical and economic disadvantages associated with the monolayer expansion of bone marrow-derived mesenchymal stromal cells (MSCs) have focused attention on the development of one-step intraoperative cells therapies and homing strategies. The mononuclear cell fraction of bone marrow, inclusive of discrete stem cell populations, is not well characterized, and we currently lack suitable cell culture systems in which to culture and investigate the behavior of these cells.

METHODS

Human bone marrow-derived mononuclear cells were cultured within fibrin for 2 weeks with or without fibroblast growth factor-2 supplementation. DNA content and cell viability of enzymatically retrieved cells were determined at days 7 and 14. Cell surface marker profiling and cell cycle analysis were performed by means of multi-color flow cytometry and a 5-ethynyl-2'-deoxyuridine incorporation assay, respectively.

RESULTS

Total mononuclear cell fractions, isolated from whole human bone marrow, was successfully cultured in fibrin gels for up to 14 days under static conditions. Discrete niche cell populations including MSCs, pericytes and hematopoietic stem cells were maintained in relative quiescence for 7 days in proportions similar to that in freshly isolated cells. Colony-forming unit efficiency of enzymatically retrieved MSCs was significantly higher at day 14 compared to day 0; and in accordance with previously published works, it was fibroblast growth factor-2-dependant.

CONCLUSIONS

Fibrin gels provide a simple, novel system in which to culture and study the complete fraction of bone marrow-derived mononuclear cells and may support the development of improved bone marrow cell-based therapies.

Stem cell engineered bone with calcium-phosphate coated porous titanium scaffold or silicon hydroxyapatite granules for revision total joint arthroplasty

Aseptic loosening in total joint replacements (TJRs) is mainly caused by osteolysis which leads to a reduction of the bone stock necessary for implant fixation in revision TJRs. Our aim was to develop bone tissue-engineered constructs based on scaffolds of clinical relevance in revision TJRs to reconstitute the bone stock at revision operations by using a perfusion bioreactor system (PBRS). The hypothesis was that a PBRS will enhance mesenchymal stem cells (MSCs) proliferation and osteogenic differentiation and will provide an even distribution of MSCs throughout the scaffolds when compared to static cultures. A PBRS was designed and implemented. Scaffolds, silicon substituted hydroxyapatite granules and calcium-phosphate coated porous TiAl6V4 cylinders, were seeded with MSCs and cultured either in static conditions or in the PBRS at 0.75 mL/min. Statistically significant increased cell proliferation and alkaline phosphatase activity was found in samples cultured in the PBRS. Histology revealed a more even cell distribution in the perfused constructs. SEM showed that cells arranged in sheets. Long cytoplasmic processes attached the cells to the scaffolds. We conclude that a novel tissue engineering approach to address the issue of poor bone stock at revision operations is feasible by using a PBRS.

Comparison of uncultured marrow mononuclear cells and culture-expanded mesenchymal stem cells in 3D collagen-chitosan microbeads for orthopedic tissue engineering

Stem cell-based therapies have shown promise in enhancing repair of bone and cartilage. Marrow-derived mesenchymal stem cells (MSC) are typically expanded in vitro to increase cell number, but this process is lengthy, costly, and there is a risk of contamination and altered cellular properties. Potential advantages of using fresh uncultured bone marrow mononuclear cells (BMMC) include heterotypic cell and paracrine interactions between MSC and other marrow-derived cells including hematopoietic, endothelial, and other progenitor cells. In the present study, we compared the osteogenic and chondrogenic potential of freshly isolated BMMC to that of cultured-expanded MSC, when encapsulated in three-dimensional (3D) collagen-chitosan microbeads. The effect of low and high oxygen tension on cell function and differentiation into orthopedic lineages was also examined. Freshly isolated rat BMMC (25 × 10(6) cells/mL, containing an estimated 5 × 10(4) MSC/mL) or purified and culture-expanded rat bone marrow-derived MSC (2 × 10(5) cells/mL) were added to a 65-35 wt% collagen-chitosan hydrogel mixture and fabricated into 3D microbeads by emulsification and thermal gelation. Microbeads were cultured in control MSC growth media in either 20% O2 (normoxia) or 5% O2 (hypoxia) for an initial 3 days, and then in control, osteogenic, or chondrogenic media for an additional 21 days. Microbead preparations were evaluated for viability, total DNA content, calcium deposition, and osteocalcin and sulfated glycosaminoglycan expression, and they were examined histologically. Hypoxia enhanced initial progenitor cell survival in fresh BMMC-microbeads, but it did not enhance osteogenic potential. Fresh uncultured BMMC-microbeads showed a similar degree of osteogenesis as culture-expanded MSC-microbeads, even though they initially contained only 1/10th the number of MSC. Chondrogenic differentiation was not strongly supported in any of the microbead formulations. This study demonstrates the microbead-based approach to culturing and delivering cells for tissue regeneration, and suggests that fresh BMMC may be an alternative to using culture-expanded MSC for bone tissue engineering.

Materiomics: an -omics approach to biomaterials research

The past fifty years have seen a surge in the use of materials for clinical application, but in order to understand and exploit their full potential, the scientific complexity at both sides of the interface--the material on the one hand and the living organism on the other hand--needs to be considered. Technologies such as combinatorial chemistry, recombinant DNA as well as computational multi-scale methods can generate libraries with a very large number of material properties whereas on the other side, the body will respond to them depending on the biological context. Typically, biological systems are investigated using both holistic and reductionist approaches such as whole genome expression profiling, systems biology and high throughput genetic or compound screening, as already seen, for example, in pharmacology and genetics. The field of biomaterials research is only beginning to develop and adopt these approaches, an effort which we refer to as "materiomics". In this review, we describe the current status of the field, and its past and future impact on the biomedical sciences. We outline how materiomics sets the stage for a transformative change in the approach to biomaterials research to enable the design of tailored and functional materials for a variety of properties in fields as diverse as tissue engineering, disease diagnosis and de novo materials design, by combining powerful computational modelling and screening with advanced experimental techniques.