Critical attributes of human early mesenchymal stromal cell-laden microcarrier constructs for improved chondrogenic differentiation

Cellular In Vitro Responses Induced by Human Mesenchymal Stem/Stromal Cell-Derived Extracellular Vesicles Obtained from Suspension Culture

Mesenchymal stem/stromal cells (MSCs) and their extracellular vesicles (MSC-EVs) have been described to have important roles in tissue regeneration, including tissue repair, control of inflammation, enhancing angiogenesis, and regulating extracellular matrix remodeling. MSC-EVs have many advantages for use in regeneration therapies such as facility for dosage, histocompatibility, and low immunogenicity, thus possessing a lower possibility of rejection. In this work, we address the potential activity of MSC-EVs isolated from adipose-derived MSCs (ADMSC-EVs) cultured on cross-linked dextran microcarriers, applied to test the scalability and reproducibility of EV production. Isolated ADMSC-EVs were added into cultured human dermal fibroblasts (NHDF-1), keratinocytes (HaCat), endothelial cells (HUVEC), and THP-1 cell-derived macrophages to evaluate cellular responses (i.e., cell proliferation, cell migration, angiogenesis induction, and macrophage phenotype-switching). ADMSC viability and phenotype were assessed during cell culture and isolated ADMSC-EVs were monitored by nanotracking particle analysis, electron microscopy, and immunophenotyping. We observed an enhancement of HaCat proliferation; NHDF-1 and HaCat migration; endothelial tube formation on HUVEC; and the expression of inflammatory cytokines in THP-1-derived macrophages. The increased expression of TGF-β and IL-1β was observed in M1 macrophages treated with higher doses of ADMSC-EVs. Hence, EVs from microcarrier-cultivated ADMSCs are shown to modulate cell behavior, being able to induce skin tissue related cells to migrate and proliferate as well as stimulate angiogenesis and cause balance between pro- and anti-inflammatory responses in macrophages. Based on these findings, we suggest that the isolation of EVs from ADMSC suspension cultures makes it possible to induce in vitro cellular responses of interest and obtain sufficient particle numbers for the development of in vivo concept tests for tissue regeneration studies.

Culturing and Scaling up Stem Cells of Dental Pulp Origin Using Microcarriers

Ectomesenchymal stem cells derived from the dental pulp are of neural crest origin, and as such are promising sources for cell therapy and tissue engineering. For safe upscaling of these cells, microcarrier-based culturing under dynamic conditions is a promising technology. We tested the suitability of two microcarriers, non-porous Cytodex 1 and porous Cytopore 2, for culturing well characterized dental pulp stem cells (DPSCs) using a shake flask system. Human DPSCs were cultured on these microcarriers in 96-well plates, and further expanded in shake flasks for upscaling experiments. Cell viability was measured using the alamarBlue assay, while cell morphology was observed by conventional and two-photon microscopies. Glucose consumption of cells was detected by the glucose oxidase/Clark-electrode method. DPSCs adhered to and grew well on both microcarrier surfaces and were also found in the pores of the Cytopore 2. Cells grown in tissue culture plates (static, non-shaking conditions) yielded 7 × 105 cells/well. In shake flasks, static preincubation promoted cell adhesion to the microcarriers. Under dynamic culture conditions (shaking) 3 × 107 cells were obtained in shake flasks. The DPSCs exhausted their glucose supply from the medium by day seven even with partial batch-feeding. In conclusion, both non-porous and porous microcarriers are suitable for upscaling ectomesenchymal DPSCs under dynamic culture conditions.

Polysaccharides on gelatin-based hydrogels differently affect chondrogenic differentiation of human mesenchymal stromal cells

Selection of feasible hybrid-hydrogels for best chondrogenic differentiation of human mesenchymal stromal cells (hMSCs) represents an important challenge in cartilage regeneration. In this study, three-dimensional hybrid hydrogels obtained by chemical crosslinking of poly (ethylene glycol) diglycidyl ether (PEGDGE), gelatin (G) without or with chitosan (Ch) or dextran (Dx) polysaccharides were developed. The hydrogels, namely G-PEG, G-PEG-Ch and G-PEG-Dx, were prepared with an innovative, versatile and cell-friendly technique that involves two preparation steps specifically chosen to increase the degree of crosslinking and the physical-mechanical stability of the product: a first homogeneous phase reaction followed by directional freezing, freeze-drying and post-curing. Chondrogenic differentiation of human bone marrow mesenchymal stromal cells (hBM-MSC) was tested on these hydrogels to ascertain whether the presence of different polysaccharides could favor the formation of the native cartilage structure. We demonstrated that the hydrogels exhibited an open pore porous morphology with high interconnectivity and the incorporation of Ch and Dx into the G-PEG common backbone determined a slightly reduced stiffness compared to that of G-PEG hydrogels. We demonstrated that G-PEG-Dx showed a significant increase of its anisotropic characteristic and G-PEG-Ch exhibited higher and faster stress relaxation behavior than the other hydrogels. These characteristics were associated to absence of chondrogenic differentiation on G-PEG-Dx scaffold and good chondrogenic differentiation on G-PEG and G-PEG-Ch. Furthermore, G-PEG-Ch induced the minor collagen proteins and the formation of collagen fibrils with a diameter like native cartilage. This study demonstrated that both anisotropic and stress relaxation characteristics of the hybrid hydrogels were important features directly influencing the chondrogenic differentiation potentiality of hBM-MSC.

Three dimensional microcarrier system in mesenchymal stem cell culture: a systematic review

Stem cell-based regenerative medicine is a promising approach for tissue reconstruction. However, a large number of cells are needed in a typical clinical study, where conventional monolayer cultures might pose a limitation for scale-up. The purpose of this review was to systematically assess the application of microcarriers in Mesenchymal Stem Cell cultures. A comprehensive search was conducted in Medline via Ebscohost, Pubmed, and Scopus, and relevant studies published between 2015 and 2019 were selected. The literature search identified 53 related studies, but only 14 articles met the inclusion criteria. These include 7 utilised commercially available microcarriers, while the rest were formulated based on different surface characteristics, all of which are discussed in this review. Current applications of microcarriers were focused on MSC expansion and induction of MSCs into different lineages. These studies demonstrated that MSCs could proliferate in a microcarrier culture system in-fold compared to monolayer cultures, and the culture system could simulate a three-dimensional environment which induces cell differentiation. However, detailed studies are still required before this system were to be adapted into the scale of GMP manufacturing.

Biological Considerations in Scaling Up Therapeutic Cell Manufacturing

Cell therapeutics - using cells as living drugs - have made advances in many areas of medicine. One of the most clinically studied cell-based therapy products is mesenchymal stromal cells (MSCs), which have shown promising results in promoting tissue regeneration and modulating inflammation. However, MSC therapy requires large numbers of cells, the generation of which is not feasible via conventional planar tissue culture methods. Scale-up manufacturing methods (e.g., propagation on microcarriers in stirred-tank bioreactors), however, are not specifically tailored for MSC expansion. These processes may, in principle, alter the cell secretome, a vital component underlying the immunosuppressive properties and clinical effectiveness of MSCs. This review outlines our current understanding of MSC properties and immunomodulatory function, expansion in commercial manufacturing systems, and gaps in our knowledge that need to be addressed for effective up-scaling commercialization of MSC therapy.

Dispersible and Dissolvable Porous Microcarrier Tablets Enable Efficient Large-Scale Human Mesenchymal Stem Cell Expansion

Human mesenchymal stem cells (hMSCs) have wide applications in regenerative medicine but their clinical translation is largely hindered by limited production capacity of current cell expansion regime. This study utilizes a novel dispersible and dissolvable porous microcarrier tablet, 3D TableTrix™, in stirred bioreactor to demonstrate a scalable expansion protocol for industrial manufacturing of hMSCs. The 3D TableTrix is a ready-to-use tablet that disperses into 10s of 1000s porous microcarriers upon contact with culture media, eliminating the need to prepare microcarriers before cell seeding, hence simplifying operation process. We demonstrate over 500 times expansion of adipose-derived hMSCs using serum-free culture medium in 11 days with bead-to-bead transfer for a partial scale-up from laboratory-scale spinner flasks to a 1-L bioreactor system. A final yield of 1.05 ± 0.11 × 10⁹ hMSCs was achieved, and yield of over 3 × 10⁹ with an overall expansion factor of 1530 could theoretically be realized with full scale-up. Cells were harvested by dissolving microcarriers with 98.6% ± 0.1% recovery rate. Cells retained their immunophenotypic characteristics, trilineage differentiation potential, and genome stability with low indications of senescence phenotype. This study illuminates the potential of industrializing clinical-grade hMSC production using 3D TableTrix microcarrier tablets and stirred tank bioreactors. Impact statement The 3D TableTrix™ is a newly available microcarrier ingeniously designed as dispersible and dissolvable porous microcarrier tablets for human mesenchymal stem cell (hMSC) expansion. This eliminates the need of tedious preparation work usually required for microcarriers and its dissolvable nature allows for high cell recovery rate of 98.6% ± 0.1%. Over 500 times expansion of adipose-derived mesenchymal stem cells in serum-free culture media using a 1-L bioreactor system demonstrates its tremendous potential for industrial production of hMSCs.

Enhancing survival, engraftment, and osteogenic potential of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are promising candidates for bone regeneration therapies due to their plasticity and easiness of sourcing. MSC-based treatments are generally considered a safe procedure, however, the long-term results obtained up to now are far from satisfactory. The main causes of these therapeutic limitations are inefficient homing, engraftment, and osteogenic differentiation. Many studies have proposed modifications to improve MSC engraftment and osteogenic differentiation of the transplanted cells. Several strategies are aimed to improve cell resistance to the hostile microenvironment found in the recipient tissue and increase cell survival after transplantation. These strategies could range from a simple modification of the culture conditions, known as cell-preconditioning, to the genetic modification of the cells to avoid cellular senescence. Many efforts have also been done in order to enhance the osteogenic potential of the transplanted cells and induce bone formation, mainly by the use of bioactive or biomimetic scaffolds, although alternative approaches will also be discussed. This review aims to summarize several of the most recent approaches, providing an up-to-date view of the main developments in MSC-based regenerative techniques.

Improved expansion of equine cord blood derived mesenchymal stromal cells by using microcarriers in stirred suspension bioreactors

Equine mesenchymal stromal cells (MSCs) are increasingly investigated for their clinical therapeutic utility. Such cell-based treatments can require cell numbers in the millions or billions, with conventional expansion methods using static T-flasks typically inefficient in achieving these cell numbers. Equine cord blood-derived MSCs (eCB-MSCs), are promising cell candidates owing to their capacity for chondrogenic differentiation and immunomodulation. Expansion of eCB-MSCs in stirred suspension bioreactors with microcarriers as an attachment surface has the potential to generate clinically relevant numbers of cells while decreasing cost, time and labour requirements and increasing reproducibility and yield when compared to static expansion. As eCB-MSCs have not yet been expanded in stirred suspension bioreactors, a robust protocol was required to expand these cells using this method. This study outlines the development of an expansion bioprocess, detailing the inoculation phase, expansion phase, and harvesting phase, followed by phenotypic and trilineage differentiation characterization of two eCB-MSC donors. The process achieved maximum cell densities up to 75,000 cells/cm2 corresponding to 40 million cells in a 100 mL bioreactor, with a harvesting efficiency of up to 80%, corresponding to a yield of 32 million cells from a 100 mL bioreactor. When compared to cells grown in static T-flasks, bioreactor-expanded eCB-MSC cultures did not change in surface marker expression or trilineage differentiation capacity. This indicates that the bioreactor expansion process yields large quantities of eCB-MSCs with similar characteristics to conventionally grown eCB-MSCs.

Fabrication and in vitro evaluation of a packed-bed bioreactor based on an optimum two-stage culture strategy

A packed-bed (PB) bioreactor for bioartificial liver (BAL) was fabricated based on an optimum two-stage culture strategy and evaluated in vitro in this research. Human induced hepatocytes (hiHeps) were first expanded using Cytodex 3 microcarriers and the choice of microcarrier concentration and fetal bovine serum (FBS) content was optimized. Then, the cells expanded under the optimum expansion condition were perfused into a perfusion system containing Fibra-Cel (FC) disks to fabricate a PB bioreactor. Operating parameters including flow rate and seeding density for perfusion culture were optimized, respectively. Results indicated that during suspension culture, rapid cell proliferation and favorable amino acid metabolism were achieved at 3 mg/mL microcarriers combined with 1% FBS. While for the perfusion culture, the most effective flow rate and seeding density were 2 mL/min and 1 × 10⁶ cells/mL, respectively. Under this optimum perfusion condition, hiHeps showed good proliferation ability, high viability, homogeneous distribution, high metabolism activities and efficient albumin secretion as well as high liver-specific genes expression. Therefore, the two-stage culture strategy based on operating parameters optimization provides a new method for the development of PB bioreactors.

Fabrication of Innovative Silk/Alginate Microcarriers for Mesenchymal Stem Cell Delivery and Tissue Regeneration

The aim of this study was to exploit silk fibroin’s properties to develop innovative composite microcarriers for mesenchymal stem cell (MSCs) adhesion and proliferation. Alginate microcarriers were prepared, added to silk fibroin solution, and then treated with ethanol to induce silk conformational transition. Microcarriers were characterized for size distribution, coating stability and homogeneity. Finally, in vitro cytocompatibility and suitability as delivery systems for MSCs were investigated. Results indicated that our manufacturing process is consistent and reproducible: silk/alginate microcarriers were stable, with spherical geometry, about 400 μm in average diameter, and fibroin homogeneously coated the surface. MSCs were able to adhere rapidly onto the microcarrier surface and to cover the surface of the microcarrier within three days of culture; moreover, on this innovative 3D culture system, stem cells preserved their metabolic activity and their multi-lineage differentiation potential. In conclusion, silk/alginate microcarriers represent a suitable support for MSCs culture and expansion. Since it is able to preserve MSCs multipotency, the developed 3D system can be intended for cell delivery, for advanced therapy and regenerative medicine applications.