3D culture of murine hematopoietic cells with spatial development of stromal cells in nonwoven fabrics

Bone-marrow mimicking biomaterial niches for studying hematopoietic stem and progenitor cells

This review discusses the considerations and approaches that have been employed for designing biomaterial based cultures for replicating the hematopoietic stem and progenitor cell niche.

Novel porous scaffolds of pH responsive chitosan/carrageenan-based polyelectrolyte complexes for tissue engineering

Polyelectrolyte complexes (PECs) represent promising materials for drug delivery and tissue engineering applications. These substances are obtained in aqueous medium without the need for crosslinking agents. PECs can be produced through the combination of oppositely charged medical grade polymers, which include the stimuli responsive ones. In this work, three-dimensional porous scaffolds were produced through the lyophilization of pH sensitive PECs made of chitosan (CS) and carrageenan (CRG). CS:CRG molar ratios of 1:1 (CSCRG1), 2:1 (CSCRG2), and 3:1 (CSCRG3) were used. The chemical compositions of the PECs, as well as their influence in the final structure of the scaffolds were meticulously studied. In addition, the pH responsiveness of the PECs in a range including the physiological pH values of 7.4 (simulating normal physiological conditions) and 4.5 (simulating inflammatory response) was assessed. Results showed that the PECs produced were stable at pH values of 7.4 and under but dissolved as the pH increased to nonphysiological values of 9 and 11. However, after dissolution, the PEC could be reprecipitated by decreasing the pH to values close to 4.5. The scaffolds obtained presented large and interconnected pores, being equally sensitive to changes in the pH. CSCRG1 scaffolds appeared to have higher hydrophilicity and therefore higher water absorption capacity. The increase in the CS:CRG molar ratios improved the scaffold mechanical properties, with CSCRG3 presenting the higher compressive modulus under wet conditions. Overall, the PEC scaffolds appear promising for tissue engineering related applications that require the use of pH responsive materials stable at physiological conditions.

Large-scale in-vitro expansion of RBCs from hematopoietic stem cells

The quest for RBCs in transfusion medicine has prompted scientists to explore the large-scale expansion of human RBCs from various sources. The successful production of RBCs in the laboratory depends on the selection of potential cell source, optimized culture, bio-physiological parameters, clinically applicable culture media that yields a scalable, contamination-free, non-reactive, non-tumorogenic, stable and functional end product. The expansion protocol considering the in vivo factors involved in homeostasis can generate a cost-effective and readily available cell source for transfusion. This review paper discusses several approaches used to expand RBCs from various sources of stem cells.

Micromarrows--three-dimensional coculture of hematopoietic stem cells and mesenchymal stromal cells

Hematopoietic stem cell (HSC) transplant is a well established curative therapy for some hematological malignancies. However, achieving adequate supply of HSC from some donor tissues can limit both its application and ultimate efficacy. The theory that this limitation could be overcome by expanding the HSC population before transplantation has motivated numerous laboratories to develop ex vivo expansion processes. Pioneering work in this field utilized stromal cells as support cells in cocultures with HSC to mimic the HSC niche. We hypothesized that through translation of this classic coculture system to a three-dimensional (3D) structure we could better replicate the niche environment and in turn enhance HSC expansion. Herein we describe a novel high-throughput 3D coculture system where murine-derived HSC can be cocultured with mesenchymal stem/stromal cells (MSC) in 3D microaggregates--which we term "micromarrows." Micromarrows were formed using surface modified microwells and their ability to support HSC expansion was compared to classic two-dimensional (2D) cocultures. While both 2D and 3D systems provide only a modest total cell expansion in the minimally supplemented medium, the micromarrow system supported the expansion of approximately twice as many HSC candidates as the 2D controls. Histology revealed that at day 7, the majority of bound hematopoietic cells reside in the outer layers of the aggregate. Quantitative polymerase chain reaction demonstrates that MSC maintained in 3D aggregates express significantly higher levels of key hematopoietic niche factors relative to their 2D equivalents. Thus, we propose that the micromarrow platform represents a promising first step toward a high-throughput HSC 3D coculture system that may enable in vitro HSC niche recapitulation and subsequent extensive in vitro HSC self-renewal.

Effects of mixed feeder cells on the expansion of CD34⁺ cells

Synergistic effects of mesenchymal stem cells (MSCs) isolated from bone marrow (BM), umbilical cord blood (UCB) and periosteum, and fibroblasts as mixed feeder cells (MFCs) on the expansion of hematopoietic progenitor cells (HPCs) were investigated in serum- and exogenous cytokine-free conditions. Enriched CD34(+) cells were cultured for 2weeks over the cell lines alone, individually, or selected combinations of them. When the cells were cultured over MFCs, the maximum increase in expansion of total nucleated cells and CD34(+)/CD38(-) cells was 157.3- and 128.6-fold, respectively. Furthermore, hematopoietic cytokine such as IL-6 and chemokines (e.g., IL-8, growth related oncogene (GRO), GRO-alpha, matrix metalloproteinase (MMP)-1, and MMP-3) were significantly increased in mixed feeder cells. Based on these results, MFCs can be more efficient for the ex vivo expansion of HPCs. These results strongly suggest that MFCs are more suitable for HPCs mass production.

In vitro reconstruction of a three-dimensional mouse hematopoietic microenvironment in the pore of polyurethane foam

Hematopoietic stem cells exist in specific niches in the bone marrow, and generate either more stem cells or differentiated hematopoietic progeny. In such microenvironments, cell-cell and cell-matrix interactions are as important as soluble factors such as cytokines. To provide a similar environment for in vitro studies, a three-dimensional culture technique is necessary. In this manuscript, we report the development of a three-dimensional culture system for murine bone marrow mononuclear cells (mBMMNCs) using polyurethane foam (PUF) as a scaffold. The mBMMNCs were inoculated into two kinds of PUF disks with different surface properties, and cultured without exogenous growth factors. After seeding the inside of the PUF pores with mBMMNCs, PUF disks were capable of supporting adherent cell growth and continuous cell production for up to 90 days. On days 21-24, most nonadherent cells were CD45 positive, and some of the cells were of the erythroid type. From comparisons of the cell growth in each PUF material, the mBMMNC culture in PUF-W1 produced more cells than the PUF-R4 culture. However, the mBMMNC culture in PUF-W1 had no advantages over PUF-R4 with regard to the maintenance of immature hematopoietic cells. The results of scanning electron microscopy and colony-forming assays confirmed the value of the different three dimensional cultures.

Marrow stromal fibroblastic cell cultivation in vitro on decellularized bone marrow extracellular matrix

The in vitro biocompatibility of decellularized bone marrow extracellular matrix was evaluated. Following a freeze-thaw cycle, sectioned discs of fresh frozen rat metaphyseal bone were sequentially incubated in solutions of hypertonic, then hypotonic Ringer's solution, followed by deoxycholic acid, then DNAase I. The adequacy of decellularization of marrow stroma was examined by light microscopy. Marrow stromal fibroblastic cells were harvested by dispersion of rat long bone marrow, followed by concentration by discontinuous Ficoll-Paque gradient centrifugation. The fibroblastic cells were expanded by in vitro cultivation, and second passage cells were cryopreserved until needed. Cryopreserved marrow stromal cells were applied dropwise to sections of decellularized bone marrow extracellular matrix, and cultured in BJGb medium with 20% fetal bovine serum for ten days. Mature cultures were formalin fixed, decalcified, and embedded in paraffin. Light microscopy of hematoxylin and eosin stained sections showed individual spindle cells invading the upper portion of the decellularized extracellular matrix, and also a monolayer of spindle cells on the upper surfaces of exposed trabecular and cortical bone. This experiment showed that decellularized marrow extracellular matrix is a biocompatible three dimensional in vitro substrate for marrow stromal fibroblastic cells.

In vitro analog of human bone marrow from 3D scaffolds with biomimetic inverted colloidal crystal geometry

In vitro replicas of bone marrow can potentially provide a continuous source of blood cells for transplantation and serve as a laboratory model to examine human immune system dysfunctions and drug toxicology. Here we report the development of an in vitro artificial bone marrow based on a 3D scaffold with inverted colloidal crystal (ICC) geometry mimicking the structural topology of actual bone marrow matrix. To facilitate adhesion of cells, scaffolds were coated with a layer of transparent nanocomposite. After seeding with hematopoietic stem cells (HSCs), ICC scaffolds were capable of supporting expansion of CD34+ HSCs with B-lymphocyte differentiation. Three-dimensional organization was shown to be critical for production of B cells and antigen-specific antibodies. Functionality of bone marrow constructs was confirmed by implantation of matrices containing human CD34+ cells onto the backs of severe combined immunodeficiency (SCID) mice with subsequent generation of human immune cells.

An adaptable hydrogel array format for 3-dimensional cell culture and analysis

Hydrogels have been commonly used as model systems for 3-dimensional (3-D) cell biology, as they have material properties that resemble natural extracellular matrices (ECMs), and their cell-interactive properties can be readily adapted in order to address a particular hypothesis. Natural and synthetic hydrogels have been used to gain fundamental insights into virtually all aspects of cell behavior, including cell adhesion, migration, and differentiated function. However, cell responses to complex 3-D environments are difficult to adequately explore due to the large number of variables that must be controlled simultaneously. Here we describe an adaptable, automated approach for 3-D cell culture within hydrogel arrays. Our initial results demonstrate that the hydrogel network chemistry (both natural and synthetic), cell type, cell density, cell adhesion ligand density, and degradability within each array spot can be systematically varied to screen for environments that promote cell viability in a 3-D context. In a test-bed application we then demonstrate that a hydrogel array format can be used to identify environments that promote viability of HL-1 cardiomyocytes, a cell line that has not been cultured previously in 3-D hydrogel matrices. Results demonstrate that the fibronectin-derived cell adhesion ligand RGDSP improves HL-1 viability in a dose-dependent manner, and that the effect of RGDSP is particularly pronounced in degrading hydrogel arrays. Importantly, in the presence of 70mum RGDSP, HL-1 cardiomyocyte viability does not decrease even after 7 days of culture in PEG hydrogels. Taken together, our results indicate that the adaptable, array-based format developed in this study may be useful as an enhanced throughput platform for 3-D culture of a variety of cell types.

The effect of three-dimensional matrix-embedding of endothelial cells on the humoral and cellular immune response

The endothelium is a unique immunologic target. The first host-donor reaction in any cell, tissue or organ transplant occurs at the blood-tissue interface, the endothelium. When endothelial cells are themselves the primary component of the implant a second set of immunologic reactions arises. Injections of free endothelial cell implants elicit a profound major histocompatibility complex (MHC) II dominated immune response with significant sensitivity, cascade enhancement and immune memory. Endothelial cells embedded within three-dimensional matrices retain all the biosecretory capacity of quiescent endothelial cells. Perivascular implants of such cells are the most potent inhibitor of intimal hyperplasia and thrombosis following controlled vascular injury, but without any immune reactivity. Allo- and even xenogeneic endothelial cells evoke no significant humoral or cellular immune response in immunocompetent hosts when embedded within matrices. Moreover, endothelial implants are immunomodulatory, reducing the extent of the memory response to previous free cell implants. Attenuated immunogenicity results in muted activation of adaptive and innate immune cells. These findings point toward a pivotal role of matrix-cell-interconnectivity for the cellular immune phenotype and might therefore assist in the design of extracellular matrix components for successful tissue engineering.

Matrix adherence of endothelial cells attenuates immune reactivity: induction of hyporesponsiveness in allo‐ and xenogeneic models

Endothelial integrity regulates vascular tone, luminal patency, and the immune reactivity to tissue grafts. Endothelial dysfunction is the first marker and site of disease initiation and severity. It has long been known that endothelial biochemical function is density dependent, and we have recently shown that endothelial immunobiology is anchorage dependent. Matrix-embedded endothelial cells (EC) establish a controlled anchorage state and are not only immune protected but also induce a system immune protective state. We now define this aspect of vascular and immune biology in detail. The in vitro immune response of allogeneic splenocytes (proliferation, lytic activity, and cytokine expression) on exposure to aortic EC was significantly reduced if EC were embedded within three-dimensional collagen matrices (3D-EC; P<0.005) to an even greater extent than EC that had reached confluence as monolayers on tissue culture plates (EC-TCPS). Splenocyte reactivity was enhanced with repeated exposure to EC-TCPS but minimally if preexposed to 3D-EC (P<0.002). 3D-EC induced significantly greater differentiation of splenocytes into CD4+ CD25+ Foxp3+ regulatory T cells than EC-TCPS (P<0.02). The reduced response to 3D-EC and potential protective effect to subsequent exposure were confirmed in vivo. Repeated exposure of immune-competent mice to injections of xenogeneic EC-TCPS induced vigorous host immunity. In contrast, prior implantation of 3D-EC induced hyporesponsiveness toward subsequent injection of EC-TCPS with reduced humoral response, decreased lytic activity, and lower frequency of effector splenocytes (P<0.001). EC interaction with its matrix determines phenotype, viability, and biosecretory potential. We now show that this microenvironmental interaction also influences endothelial-mediated activation of allo- and xenogeneic immune cells. 3D matrix-embedding limits the ability of EC to initiate adaptive immunity, and initial exposure to 3D-EC confers hyporesponsiveness to subsequent exposure to immunogeneic EC. These effects transcended the traditional control that confluence imposes on EC and reflects perhaps even higher order control. Our findings might offer novel insights to endothelial-mediated diseases and potential cell-based therapies.

Influence of scaffold physical properties and stromal cell coculture on hematopoietic differentiation of mouse embryonic stem cells

Recent studies have suggested that three-dimensional (3D) biomaterial-based scaffolds and dynamic culture conditions could provide significant enhancement in the differentiation efficiency of embryonic stem cells (ESCs). Here we report that scaffold physical properties, like pore size, polymer concentration and compression modulus as well as specific culture conditions, e.g. cell seeding density and coculture with stromal cells can significantly influence hematopoietic differentiation of ESCs. PLLA scaffolds of various polymer concentrations (7.5%, 10% and 20% w/v) and pore size distributions (<150 microm, 150-425 microm, >425 microm) were fabricated using a standard solvent casting-salt leaching method. Mouse R1 ESCs were allowed to differentiate on these scaffolds either alone or in coculture with OP9 cells, a bone-marrow derived murine stromal cell line. Following one week of culture, cells were detached and analyzed using flow cytometry to evaluate the frequency of hematopoietic progenitor cells (HPC). Our results indicate that decreasing scaffold pore size increases hematopoietic differentiation of ESCs. In addition, increasing polymer concentration which resulted in increased scaffold compression modulus also provided significantly enhanced hematopoiesis. Furthermore, higher cell seeding densities as well as coculture with marrow-derived stromal cells increased HPC generation. Collectively, these results indicate that physical and mechanical properties of the 3D microenvironment as well as cell-cell and cell-stromal interactions might play a significant role in ESC differentiation and therefore warrants further investigation to elucidate the molecular mechanisms.

Proliferation and differentiation of human embryonic germ cell derivatives in bioactive polymeric fibrous scaffold

Human embryonic germ cell derivatives, a heterogeneous population of uncommitted embryoid body derived (EBD) cells, were studied in a bioactive three-dimensional (3D) fibrous culture. Their proliferation, morphology, gene expression and differentiation were investigated to gain insights on development of 3D bioactive scaffold for pluripotent stem cells. The expansion of the EBD cells in 3D environment was significantly higher than their two-dimensional controls after 21 days. No apparent differentiation of the EBD cells cultured in the 3D environment, as indicated by histology and gene expression profile analysis, was evident. Extracellular matrix production was weak in the long-term 3D culture, and the EBD cells maintained their multilineage gene expressions for the period studied. When nerve growth factor (NGF) was surface-immobilized on the fibrous scaffold via chemically-modified Pluronic, the EBD cells cultured in this scaffold showed evidence of entering the neural pathway. An upregulation of tyrosine hydroxylase mRNA expression was observed when EBD cells were cultured in the NGF-immobilized fibrous scaffold, as demonstrated by real-time PCR and immunofluorescence staining. The study suggests the value of such fibrous 3D culture in manipulating stem cell proliferation/differentiation and as a model for developing a bioactive scaffold.

Engineering a mimicry of bone marrow tissue ex vivo

Hematopoietic stem cells reside in specific niches in the bone marrow and give rise to either more stem cells or maturing hematopoietic progeny depending on the signals provided in the bone marrow microenvironment. This microenvironment is comprised of cellular components as well as soluble constituents called cytokines. The use of cytokines alone for the ex vivo expansion of stem cells in flat, two-dimensional culture flasks, dishes or bags is inadequate and, given the three-dimensionality of the in vivo bone marrow microenvironment, inappropriate. Three-dimensional culture conditions can therefore provide an ex vivo mimicry of bone marrow, recapitulate the desired niche, and provide a suitable environment for stem cell expansion and differentiation. Choice of scaffold, manipulation and reproducibility of the scaffold properties and directed structuring of the niche, by choosing pore size and porosity may inform the resident stem cells of their fate in a directed fashion. The use of bioreactors for cultivation of hematopoietic cells will allow for culture control, optimization, standardization, scale-up, and a "hands-off" operation making the end-product dependable, predictable and free of contaminants, and therefore suitable for human use and therapeutic applications.

A cultural renaissance: in vitro cell biology embraces three-dimensional context

Increasingly, researchers are recognizing the limitations of two-dimensional (2-D), monolayer cell culture and embracing more realistic three-dimensional (3-D) cell culture systems. Currently, 3-D culture techniques are being employed by neuroscientists to grow cells from the central nervous system. From this work, it has become clear that 3-D cell culture offers a more realistic milieu in which the functional properties of neurons can be observed and manipulated in a manner that is not possible in vivo. The implications of this technical renaissance in cell culture for both clinical and basic neuroscience are significant and far-reaching.

Cell processing engineering for ex-vivo expansion of hematopoietic cells

The cell processing engineering for ex vivo expansion of hematopoietic cells is reviewed. All hematopoietic cells of different lineages and/or at various stages of differentiation are derived from the same precursor, pluripotent hematopoietic stem cells. Bone marrow stromal cells promote and regulate the self-renewal, commitment, differentiation, and proliferation of stem cells and progenitors through their secreted extracellular matrices and cytokine environment in the hematopoietic microenvironment. Although stroma-mediated hematopoiesis has been studied in vitro using the Dexter culture system in tissue culture flasks, hematopoiesis in the Dexter culture system is almost limited to a granulocyte lineage and the system could not expand primitive cells. The addition of large amounts of cytokines to the culture of hematopoietic cells enabled their expansion, but is too expensive. Some clonal stromal cell lines have been established from the Dexter culture of murine bone marrow cells in order to simplify and stimulate the ex vivo expansion of hematopoietic cells. In order to solve the problem regarding the usage of exogeneic stromal cell lines, a novel membrane-separated coculture system, in which stromal cells adhere onto the lower surface of a porous membrane and hematopoietic cells are incubated on the upper surface of the membrane, was proposed. In order to mimic the contact between stromal and hematopoietic cells in vivo in the bone marrow, several types of three-dimensional (3-D) culture of hematopoietic cells were developed. The 3-D coculture of hematopoietic cells with spatial development of stromal cells in nonwoven fabrics enabled the expansion of progenitors without cytokine addition. Progenitors in cord blood mononucleated cells were also successfully expanded without the addition in the 3-D coculture with primary human bone marrow stromal cells in 3-D. Heparin addition to the 3-D coculture and coating the nonwoven fabrics with N-(O-beta-(6-O-sulfogalactopyranosyl)-6-oxyhexyl)-3,5-bis(dodecyloxy)-benzamide further increased the number of progenitors.