Engineering a human bone marrow model: a case study on ex vivo erythropoiesis

Challenges and innovations in hematopoietic stem cell transplantation: exploring bone marrow niches and new model systems

Hematopoietic stem cell transplantation (HSCT) remains an indispensable therapeutic strategy for various hematological diseases. This review discusses the pivotal role of bone marrow (BM) niches in influencing the efficacy of HSCT and evaluates the current animal models, emphasizing their limitations and the need for alternative models. Traditional animal models, mainly murine xenograft, have provided significant insights, but due to species-specific differences, are often constrained from accurately mimicking human physiological responses. These limitations highlight the importance of developing alternative models that can more realistically replicate human hematopoiesis. Emerging models that include BM organoids and BM-on-a-chip microfluidic systems promise enhanced understanding of HSCT dynamics. These models aim to provide more accurate simulations of the human BM microenvironment, potentially leading to improved preclinical assessments and therapeutic outcomes. This review highlights the complexities of the BM niche, discusses the limitations of current models, and suggests directions for future research using advanced model systems. [BMB Reports 2024; 57(8): 352-362].

Clinical Application of Three-Dimensional Printing of Polycaprolactone/Beta-Tricalcium Phosphate Implants for Cranial Reconstruction

Polycaprolactone (PCL) implants are a biodegradable polymeric material with appropriate mechanical strength and durability for use in cranioplasty. They can be manufactured as patient- customized implants using a three-dimensional (3D) printer. Herein, the authors aimed to share our experience in cranioplasty of patients with deformed and asymmetric skulls using PCL/beta- tricalcium phosphate (ß-TCP) implants.

Seven patients underwent cranioplasty using patient-specific PCL/ß-TCP implants. Cranial computed tomography images were converted to a 3D model and mirrored to design a patient-specific implant. Based on the 3D simulation, an implant was 3D printed using PCL/ß-TCP. A 6-month follow-up was conducted with periodic visits and computed tomography scans. Symmetry after surgery and complications were evaluated.

Postoperatively, the soft tissue volumes increased to 15.8 ± 17.2 cm³ and 14.9 ± 15.7 cm³ at 2 weeks and 6 months of follow-up, respectively. The volume change from 2 weeks to 6 months was —4.4 ± 2.5%. Six patients achieved complete symmetry after cranioplasty, whereas 1 patient noticed partial symmetry. The symmetry remained unchanged at 6 months of follow-up. Upon palpation to assess smoothness, 6 patients exhibited a smooth edge interface, whereas 1 patient had a slightly irregular edge.

Based on these findings, 3D-printed PCL/ß-TCP implants are an excellent material for cranioplasty, and a favorable cosmetic outcome can be achieved. Specifically, these novel PCL/ß-TCP implants have good biocompatibility and mechanical strength without any postoperative foreign body reaction.

Graphene Oxide promotes embryonic stem cell differentiation to haematopoietic lineage

Pluripotent stem cells represent a promising source of differentiated tissue-specific stem and multipotent progenitor cells for regenerative medicine and drug testing. The realisation of this potential relies on the establishment of robust and reproducible protocols of differentiation. Several reports have highlighted the importance of biomaterials in assisting directed differentiation. Graphene oxide (GO) is a novel material that has attracted increasing interest in the field of biomedicine. In this study, we demonstrate that GO coated substrates significantly enhance the differentiation of mouse embryonic stem (ES) cells to both primitive and definitive haematopoietic cells. GO does not affect cell proliferation or survival of differentiated cells but rather enhances the transition of haemangioblasts to haemogenic endothelial cells, a key step during haematopoietic specification. Importantly, GO also improves, in addition to murine, human ES cell differentiation to blood cells. Taken together, our study reveals a positive role for GO in haematopoietic differentiation and suggests that further functionalization of GO could represent a valid strategy for the generation of large numbers of functional blood cells. Producing these cells would accelerate haematopoietic drug toxicity testing and treatment of patients with blood disorders or malignancies.

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.

Development and molecular characterization of polymeric micro-nanofibrous scaffold of a defined 3-D niche for in vitro chemosensitivity analysis against acute myeloid leukemia cells

Standard in vitro drug testing employs 2-D tissue culture plate systems to test anti-leukemic drugs against cell adhesion-mediated drug-resistant leukemic cells that harbor in 3-D bone marrow microenvironments. This drawback necessitates the fabrication of 3-D scaffolds that have cell adhesion-mediated drug-resistant properties similar to in vivo niches. We therefore aimed at exploiting the known property of polyurethane (PU)/poly-l-lactic acid (PLLA) in forming a micro-nanofibrous structure to fabricate unique, not presented before, as far as we are aware, 3-D micro-nanofibrous scaffold composites using a thermally induced phase separation technique. Among the different combinations of PU/PLLA composites generated, the unique PU/PLLA 60:40 composite displayed micro-nanofibrous morphology similar to decellularized bone marrow with increased protein and fibronectin adsorption. Culturing of acute myeloid leukemia (AML) KG1a cells in FN-coated PU/PLLA 60:40 shows increased cell adhesion and cell adhesion-mediated drug resistance to the drugs cytarabine and daunorubicin without changing the original CD34⁺/CD38⁻/CD33⁻ phenotype for 168 hours compared to fibronectin tissue culture plate systems. Molecularly, as seen in vivo, increased chemoresistance is associated with the upregulation of anti-apoptotic Bcl2 and the cell cycle regulatory protein p27^Kip1 leading to cell growth arrest. Abrogation of Bcl2 activity by the Bcl2-specific inhibitor ABT 737 led to cell death in the presence of both cytarabine and daunorubicin, demonstrating that the cell adhesion-mediated drug resistance induced by Bcl2 and p27^Kip1 in the scaffold was similar to that seen in vivo. These results thus show the utility of a platform technology, wherein drug testing can be performed before administering to patients without the necessity for stromal cells.

Large-scale production of red blood cells from stem cells: what are the technical challenges ahead?

Blood-transfusion centers regularly face the challenge of donor blood shortages, especially for rare blood groups. The possibility of producing universal red blood cells from stem cells industrially has become a possible alternative since the successful injection of blood generated in vitro into a human being in 2011. Although there remains many biological and regulatory issues concerning the efficacy and safety of this new product, the major challenge today for future clinical applications is switching from the current limited 2-dimensional production techniques to large-scale 3-dimensional bioreactors. In addition to requiring technological breakthroughs, the whole process also has to become at least five-fold more cost-efficient to match the current prices of high-quality blood products. The current review sums up the main biological advances of the past decade, outlines the key biotechnological challenges for the large-scale cost-effective production of red blood cells, proposes solutions based on strategies used in the bioindustry and presents the state-of-the-art of large-scale blood production.

Stem cell bioengineering strategies to widen the therapeutic applications of haematopoietic stem/progenitor cells from umbilical cord blood

Umbilical cord blood (UCB) transplantation has observed a significant increase in recent years, due to the unique features of UCB haematopoietic stem/progenitor cells (HSCs) for the treatment of blood-related disorders. However, the low cell numbers available per UCB unit significantly impairs the widespread use of this source for transplantation of adult patients, resulting in graft failure, delayed engraftment and delayed immune reconstitution. In order to overcome this issue, distinct approaches are now being considered in clinical trials, such as double-UCB transplantation, intrabone injection or ex vivo expansion. In this article the authors review the current state of the art, future trends and challenges on the ex vivo expansion of UCB HSCs, focusing on culture parameters affecting the yield and quality of the expanded HSC grafts: novel HSC selection schemes prior to cell culture, cytokine/growth factor cocktails, the impact of biochemical factors (e.g. O2 ) or the addition of supportive cells, e.g. mesenchymal stem/stromal cell (MSC)-based feeder layers) were addressed. Importantly, a critical challenge in cellular therapy is still the scalability, reproducibility and control of the expansion process, in order to meet the clinical requirements for therapeutic applications. Efficient design of bioreactor systems and operation modes are now the focus of many bioengineers, integrating the increasing 'know-how' on HSC biology and physiology, while complying with the GMP standards for the production of cellular products, i.e. through the use of commercially available, highly controlled, disposable technologies.

Two-dimensional polymer-based cultures expand cord blood-derived hematopoietic stem cells and support engraftment of NSG mice

Currently, ex vivo expansion of hematopoietic stem cells (HSC) is still insufficient. Traditional approaches for HSC expansion include the use of stromal cultures, growth factors, and/or bioreactors. Biomaterial-based strategies provide new perspectives. We focus on identifying promising two-dimensional (2D) polymer candidates for HSC expansion. After a 7-day culture period with cytokine supplementation, 2D fibrin, poly(D,L-lactic-co-glycolic acid; Resomer® RG503), and Poly(ɛ-caprolactone; PCL) substrates supported expansion of cord blood (CB)-derived CD34⁺ cells ex vivo. Fibrin cultures achieved the highest proliferation rates (>8700-fold increase of total nuclear cells, p<0.001), high total colony-forming units (3.6-fold increase, p<0.001), and highest engraftment in NSG mice (7.69-fold more donor cells compared with tissue culture polysterene, p<0.001). In addition, the presence of multiple human hematopoietic lineages such as myeloid (CD13⁺), erythroid (GypC⁺), and lymphoid (CD20⁺/CD56⁺) in murine transplant recipients confirmed the multilineage engraftment potential of fibrin-based cultures. Filopodia development in fibrin-expanded cells was a further indicator for superior cell adhesion capacities. We propose application of fibrin, Resomer® RG503, and PCL for future strategies of CB-CD34⁺ cell expansion. Suitable polymers for HSC expansion might also be appropriate for future drug discovery applications or for studies aimed to develop hematological therapies.

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.

Cord blood-hematopoietic stem cell expansion in 3D fibrin scaffolds with stromal support

Expansion of multipotent, undifferentiated and proliferating cord blood (CB)-hematopoietic stem cells (HSC) in vitro is limited and insufficient. Bone marrow (BM) engineering in vitro allows mimicking the main components of the hematopoietic niche compared to conventional expansion strategies. In this study, four different 3D biomaterial scaffolds (PCL, PLGA, fibrin and collagen) were tested for freshly isolated cord blood (CB)-CD34(+) cell expansion in presence of (i) efficient exogenous cytokine supplementation and (ii) umbilical cord (UC)-mesenchymal stem cells (MSC). Cell morphology, growth and proliferation were analyzed in vitro as well as multi-organ engraftment and multilineage differentiation in a murine transplantation model. All scaffolds, except 3D PLGA meshes, supported CB-CD34(+) cell expansion, which was additionally stimulated by UC-MSC support. CB-CD34(+) cells cultured on human-derived 3D fibrin scaffolds with UC-MSC support i) reached the highest overall growth (5 × 10(8)-fold expansion of total nuclear cells after fourteen days and 3 × 10(7)-fold expansion of CD34(+) cells after seven days, p < 0.001), ii) maintained a more primitive immunophenotype for more cell divisions, iii) exhibited superior morphological, migratory and adhesive properties, and iv) showed the significantly highest numbers of engraftment and multilineage differentiation (CD45, CD34, CD13, CD3 and CD19) in BM, spleen and peripheral blood in long-term transplanted NSG mice compared to the other 3D biomaterial scaffolds. Thus, the 3D fibrin scaffold based BM-mimicry strategy reveals optimal requirements for translation into clinical protocols for CB expansion and transplantation.

Mandibular reconstruction in the rabbit using beta-tricalcium phosphate (β-TCP) scaffolding and recombinant bone morphogenetic protein 7 (rhBMP-7) - histological, radiographic and mechanical evaluations

This investigation assesses the histological, radiographic and mechanical properties of regenerated bone in a unilateral critical-size osteoperiosteal mandibular continuity defect in the rabbit model, following the application of beta-tricalcium phosphate (β-TCP) scaffolding and recombinant human bone morphogenetic protein 7 (rhBMP-7). The study was carried out on nine cases; in six cases the critical-size defect was filled with rhBMP-7 in the β-TCP scaffolding, and in three cases the β-TCP was used alone. The cases were sacrificed 3 months post-operatively. Histologically the overall mean of the percentage of regenerated bone volume in the cases that received rhBMP-7 was 29.41% ± 6.25%, which was considerably greater than the 6.35% ± 3.08% in the cases treated with β-TCP alone. Mechanical testing of the cases treated with rhBMP-7 gave failure moments (55 mNm-2.040 Nm) that were consistently greater than those treated with β-TCP alone (0 mNm-48 mNm). In some cases the mechanical properties of the regenerated bone were comparable to those of untreated bone. RhBMP-7 in prefabricated β-TCP scaffolding appeared, radiographically and histologically, to be an effective method for bone regeneration in mandibular critical-size defects in the rabbit model. This points towards possible future clinical applications.

Three-dimensional culture of mouse bone marrow cells on stroma formed within a porous scaffold: influence of scaffold shape and cryopreservation of the stromal layer on expansion of haematopoietic progenitor cells

This study's primary goal was to develop an effective ex vivo expansion method for haematopoietic cells. 3D culture of mouse bone marrow cells was performed in porous scaffolds using a sheet or cube shape. Bone marrow cells were cultured on bone marrow-derived stromal layers formed within the scaffolds and the effect of scaffold shape on the expansion of haematopoietic cells was examined. In some experiments, stromal layers within cubic scaffolds were frozen and then used to culture bone marrow cells after thawing. Results show that after comparison, total cell density and expansion of haematopoietic cells were greater in cultures using the cubic scaffold, suggesting that it was superior to the sheet-like scaffold for expanding haematopoietic cells. When cryopreserved stroma was used, it effectively supported the expansion of haematopoietic cells, and a greater expansion of haematopoietic cells [(erythroid and haematopoietic progenitor cells (HPCs)] was achieved than in cultures with stromal cells that had not been cryopreserved. Expansion of cells using cryopreserved stroma had several other advantages such as a shorter culture period than the conventional method, a stable supply of stromal cells, and ease of handling and scaling up. As a result, this is an attractive method for ex vivo expansion of haematopoietic stem cells (HSCs) and HPCs for clinical use.

Development of a fixed bed bioreactor for the expansion of human hematopoietic progenitor cells

The ex vivo expansion of hematopoietic progenitor cells is of great interest for a variety of clinical applications, e.g. bone marrow transplantation or gene therapy. Therefore it is of general interest to develop a culture system, able to mimic the in vivo hematopoesis, which is a prerequisite for long-term hematopoietic culture. Our approach was to modify a continuously perfused bioreactor for cultivation and expansion of human hematopoietic stem cells. Therefore we immobilized stromal cells (human primary stromal cells or the murine cell line M2-10B4) in porous glass carriers in a fixed bed reactor and cocultivated human hematopoietic progenitor cells for several weeks. After inoculation of mononuclear cells derived from umbilical cord blood or peripheral blood stem cells both adherent and non adherent cells were harvested and analyzed by flow cytometry and short-term colony assays. During cultivation there was a permanent production of progenitor cells and mature blood cells derived from the immobilized cells in the carriers. We could demonstrate the immobilization of hematopoietic progenitor cells of the myeloid system detectable in short-term colony assays. Additionally we could observe the expansion of very early progenitor cells (CFU-GEMM) up to 4.2-fold and later progenitor cells (CFU-GM and BFU-E) up to 7-fold and 1.8-fold, respectively.

Stem cell cultivation in bioreactors

Cell-based therapies have generated great interest in the scientific and medical communities, and stem cells in particular are very appealing for regenerative medicine, drug screening and other biomedical applications. These unspecialized cells have unlimited self-renewal capacity and the remarkable ability to produce mature cells with specialized functions, such as blood cells, nerve cells or cardiac muscle. However, the actual number of cells that can be obtained from available donors is very low. One possible solution for the generation of relevant numbers of cells for several applications is to scale-up the culture of these cells in vitro. This review describes recent developments in the cultivation of stem cells in bioreactors, particularly considerations regarding critical culture parameters, possible bioreactor configurations, and integration of novel technologies in the bioprocess development stage. We expect that this review will provide updated and detailed information focusing on the systematic production of stem cell products in compliance with regulatory guidelines, while using robust and cost-effective approaches.

Three-dimensional culture of mouse bone marrow cells within a porous polymer scaffold: effects of oxygen concentration and stromal layer on expansion of haematopoietic progenitor cells

To establish an ex vivo expansion method of haematopoietic progenitor cells (HPCs) and erythroid cells, three-dimensional (3D) cultures of mouse bone marrow cells were performed, employing a porous polyvinyl formal (PVF) resin as a scaffold. In these cultures, the effects of oxygen concentration and co-cultures with stromal cells on the expansion of HPCs and erythroid cells were investigated. When bone marrow cells were cultured under 3D conditions, HPCs and erythroid cells expanded without supplementation of exogenous cytokines, irrespective of the presence of stromal cells. On the contrary, slight expansion of HPCs or erythroid cells was observed in monolayer cultures as controls, indicating that the 3D cultures using the PVF scaffold were far better in expanding HPCs and erythroid cells than the monolayer cultures. Under hypoxic conditions, bone marrow stromal cells allowed for a 3D culture of erythroid cells and HPCs at higher cell densities compared to cultures without stromal cells, and the duration of the expansion of HPCs and erythroid cells after initiating the 3D co-cultures was prolonged. The number of these cells increased throughout the culture period up to 3 weeks under hypoxic conditions, although the number decreased after 2 weeks under normoxic conditions. In conclusion, the 3D co-culture method of haematopoietic cells with stromal cells under hypoxic conditions was confirmed to be effective in expanding HPCs and erythroid cells, and this method seemed to be useful for developing an ex vivo expansion method for haematopoietic cells.

Long-term immunologically competent human peripheral lymphoid tissue cultures in a 3D bioreactor

Peripheral lymphoid organs (PLOs), the primary sites of development of adaptive immune responses, display a complex structural organization reflecting separation of cellular subsets (e.g., T and B lymphocytes) and functional compartments which is critical for immune function. The generation of in vitro culture systems capable of recapitulating salient features of PLOs for experimental, biotechnological, and clinical applications would be highly desirable, but has been hampered so far by the complexity of these systems. We have previously developed a three-dimensional bioreactor system for long-term, functional culture of human bone marrow cells on macroporous microspheres in a packed-bed bioreactor with frequent medium change. Here we adapt the same system for culture of human primary cells from PLOs (tonsil) in the absence of specific exogenous growth factors or activators. Cells in this system displayed higher viability over several weeks, and maintain population diversity and cell surface markers largely comparable to primary cells. Light microscopy showed cells organizing in large diverse clusters within the scaffold pores and presence of B cell-enriched areas. Strikingly, these cultures generated a significant number of antibody-producing B cells when challenged with a panel of diverse antigens, as expected from a lymphoid tissue. Thus the three-dimensional tonsil bioreactor culture system may serve as a useful model of PLOs by recapitulating their structural organization and function ex vivo.

Response kinetics of radiation-induced micronucleated reticulocytes in human bone marrow culture

The frequency of micronucleated reticulocytes (MN-RETs) in the bone marrow or peripheral blood is a sensitive indicator of cytogenetic damage. While the kinetics of MN-RET induction in rodent models following irradiation has been investigated and reported, information about MN-RET induction of human bone marrow after radiation exposure is sparse. In this report, we describe a human long-term bone marrow culture (LTBMC), established in three-dimensional (3D) bioreactors, which sustains long-term erythropoiesis. Using this system, we measured the kinetics of human bone marrow red blood cell (RBC) and reticulocyte (RET) production, as well as the kinetics of human MN-RET induction following radiation exposure up to 6Gy. Human bone marrow established in the 3D bioreactor demonstrated an average percentage of RBCs among total viable cells peaking at 21% on day 21. The average percentage of RETs among total viable cells reached a maximum of 11% on day 14, and remained above 5% by day 28, suggesting that terminal erythroid differentiation was still active. Time- and dose-dependent induction of MN-RET by gamma radiation was observed in the human 3D LTBMC, with peak values occurring at approximately 3 days following 1Gy irradiation. A trend towards delayed peak to 3-5 days post-radiation was observed with radiation doses ≥2Gy. Our data reveal valuable information on the kinetics of radiation-induced MN-RET of human bone marrow cultured in the 3D bioreactor, a synthetic bioculture system, and suggest that this model may serve as a promising tool for studying MN-RET formation in human bone marrow, thereby providing opportunities to study bone marrow genotoxicity testing, mitigating agent effects, and other conditions that are not ordinarily feasible to experimental manipulation in vivo.

Maintenance and expansion of hematopoietic stem/progenitor cells in biomimetic osteoblast niche

In this study, we employed bio-derived bone scaffold and composited with the marrow mesenchymal stem cell induced into osteoblast to replicate a "biomimetic niche." The CD34(+) cells or mononuclear cells (MNC) from umbilical cord blood were cultured for 2-5 weeks in the biomimetic niche (3D system) was compared with conventional two dimensional cultures (2D system) without adding cytokine supplement. After 2 weeks in culture, the CD34(+) cells from umbilical cord blood in the 3D system increased 3.3-4.8 folds when compared with the initial CD34(+) cells. CD34(+)/CD38(-) cells accounted for 82-90% of CD34(+) cells. After 5 weeks, CD34(+)/CD38(-) cells in the 3D system increased when compared with initial (1.3 ± 0.3 × 10(3) vs. 1.0 ± 0.5 × 10(4), p < 0.05), but were decreased in the 2D system (1.3 ± 0.3 × 10(3) vs. 2.5 ± 0.7 × 10(2), p < 0.05). The CFU progenitors were produced more in the 3D system than in the 2D system (4.6-9.3 folds vs. 1.0-1.5 folds) after 2 weeks in culture, and the colony distribution in the 3D system manifested higher percentage of BFU-E and CFU-GEMM, but in the 2D system was mainly CFU-GM. The LTC-ICs in the 3D system showed 5.2-7.2 folds increase over input at 2 weeks in culture, and maintain the immaturation of hematopoietic progenitor cells (HPCs) over 5 weeks. In conclusion, this new 3D hematopoietic progenitor cell culture system is the first to utilize natural cancellous bone as scaffold with osteoblasts as supporting cells; it is mimicry of natural bone marrow HSC niche. Our primary work has demonstrated it could maintain and expand HSC/HPC in vitro.

In vitro human bone marrow analog: clinical potential

Bone marrow is the primary site of hematopoiesis in adult humans. Bone marrow can be cultured in vitro but few simple culture systems fully support hematopoiesis beyond a few months. Human bone marrow analogs are long-term in vitro cultures of marrow stromal and hematopoietic stem cells that can be used to produce cells and products normally harvested from human donors. Bone marrow analog systems should exhibit confluence of the stromal cell populations, persistence of hematopoietic progenitor cells, presence of active regions of hematopoiesis and capacity to produce mature cell types for extended periods of time. Although we are still years away from realizing clinical application of products formed by artificial bone marrow analogs, the process of transitioning this research tool from bench to bedside should be fairly straightforward. The most obvious application of artificial marrow would be for production of autologous hematopoietic CD34(+) stem cells as a stem cell therapy for individuals experiencing bone marrow failure due to disease or injury. Another logical application is for 'blood farming', a process for large-scale in vitro production of red blood cells, white blood cells or platelets, for transfusion or treatment. Other possibilities include production of nonhematopoietic stem cells such as osteogenic stromal cells, osteoblasts and rare pluripotent stem cells. Bone marrow analogs also have great potential as ex vivo human test systems and could play a critical role in drug discovery, drug development and toxicity testing in the future.

Gamma-radiation induces micronucleated reticulocytes in 3D bone marrow bioreactors in vitro

Radiation injury to the bone marrow is potentially lethal due to the potent DNA-damaging effects on cells of the hematopoietic system, including bone marrow stem cell, progenitor, and the precursor cell populations. Investigation of radiation genotoxic effects on bone marrow progenitor/precursor cells has been challenged by the lack of optimal in vitro surrogate organ culture systems, and the overall difficulty to sustain lineage-specific proliferation and differentiation of hematopoiesis in vitro. We report the investigation of radiation genotoxic effects in bone marrow cultures of C57Bl/6 mice established in 3D bioreactors, which sustain long-term bone marrow cultures. For these studies, genotoxicity is measured by the induction of micronucleated reticulocytes (MN-RETs). The kinetics and dose-response relationship of MN-RET induction in response to gamma-radiation of bioreactor-maintained bone marrow cultures are presented. Our data showed that 3D long-term bone marrow cultures had sustained erythropoiesis capable of generating reticulocytes up to 8 weeks. The peak time-interval of viable cell output and percentage of reticulocytes increased steadily and reached the initial peak between the 14th and 21st days after inoculations. This was followed by a rebound or staying relatively constant until week 8. The percentage of MN-RET reached the maximum between 24 h and 32 h post 1 Gy gamma-ray. There was a near linear MN-RET induction by gamma-radiation from 0 Gy to 1.0 Gy, followed by an attenuated increase to 1.5-2.0 Gy. The MN-RET response showed a downtrend beyond 2 Gy. Our data suggest that bone marrow culture in the 3D bioreactor may be a useful organ culture system for the investigation of radiation genotoxic effect in vitro.

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.

Prolonged continuous in vitro human platelet production using three-dimensional scaffolds

OBJECTIVE

Methods producing human platelets using growth on plastic, on feeder layers, or in suspension have been described. We hypothesized that growth of hematopoietic progenitors in a three-dimensional (3D) scaffold would enhance platelet production sans feeder layer.

MATERIALS AND METHODS

We grew CD34 positively selected human cord blood cells in surgical-grade woven polyester fabric or purpose-built hydrogel scaffolds using a cocktail of cytokines.

RESULTS

We found production of functional platelets over 10 days with two-dimensional (2D), 24 days with 3D scaffolds in wells, and more than 32 days in a single-pass 3D perfusion bioreactor system. Platelet numbers produced daily were higher in 3D than 2D, and much higher in the 3D perfusion bioreactor system. Platelet output increased in hydrogel scaffolds coated with thrombopoietin and/or fibronectin, although this effect was largely obviated with markedly increased production caused by changes in added cytokines. In response to thrombin, the platelets produced aggregated and displayed increased surface CD62 and CD63.

CONCLUSION

Use of 3D scaffolds, especially in a bioreactor-maintained milieu, may allow construction of devices for clinical platelet production without cellular feeder layers.

Co-culture of umbilical cord blood CD34+ cells with human mesenchymal stem cells

Insufficient numbers of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) sometimes limit allogenic transplantation of umbilical cord blood (UCB). Ex vivo expansion may overcome this limitation. Mesenchymal stem cells (MSCs), as non-hematopoietic, well-characterized skeletal and connective-tissue progenitor cells within the bone marrow stroma, have been investigated as support cells for the culture of HSCs/HPCs. MSCs are attractive for the rich environmental signals that they provide and for immunological compatibility in transplantation. Thus far, HSC/MSC co-cultures have mainly been performed in 2-dimensional (2D) configuration. We postulate that a 3-dimensional (3D) culture environment that resembles the natural in vivo hematopoietic compartment might be more conducive for regulating HSC expansion. In this study, we compared the co-culture of HSCs and MSCs in 2D and 3D configurations. The results demonstrated the benefit of MSC inclusion in HSC expansion ex vivo. Direct contact between MSCs and HSCs in 3D cultures led to statistically significantly higher expansion of cord blood CD34+ cells than in 2D cultures (891- versus 545-fold increase in total cells, 96- versus 48-fold increase of CD34+ cells, and 230- versus 150-fold increase in colony-forming cell assay [CFC]). Engraftment assays in non-obese diabetic/severe combined immunodeficiency mice also indicated a high success rate of hematopoiesis reconstruction with these expanded cells.

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.

Culture systems for pluripotent stem cells

Pluripotent stem cells have the capacity to self renew and to differentiate to cells of the three somatic germ layers that comprise an organism. Embryonic stem cells are the most studied pluripotent stem cells. Pluripotent stem cells have also been derived from adult tissues. Both embryonic and adult stem cells represent valuable sources of cells for applications in cell therapy, drug screening and tissue engineering. While expanding stem cells in culture, it is critical to maintain their self-renewal and differentiation capacity. In generating particular cell types for specific applications, it is important to direct their differentiation to the desired lineage. Challenges in expansion of undifferentiated stem cells for clinical applications include the removal of feeder layers and non-defined components in the culture medium. Our limited basic knowledge on the requirements for maintaining pluripotency of adult pluripotent stem cells and the lack of appropriate markers associated with pluripotency hinders the progress toward their wide spread application. In vitro differentiation of stem cells usually produces a mixed population of different cell lineages with the desired cell type present only at a small proportion. Use of growth factors that promote differentiation, expansion or survival of specific cell types is key in controlling the differentiation towards specific cell lineages. A variety of bioreactors for cell cultivation exist and can be readily adapted for stem cell cultivation and differentiation. They provide a well-controlled environment for studying the process of stem cell propagation and differentiation. Their wide use will facilitate the development of processes for stem cell application.

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.

Role of nutrient supply on cell growth in bioreactor design for tissue engineering of hematopoietic cells

In the present study, a dynamic mathematical model for the growth of granulocyte progenitor cells in the hematopoietic process is developed based on the principles of diffusion and chemical reaction. This model simulates granulocyte progenitor cell growth and oxygen consumption in a three-dimensional (3-D) perfusion bioreactor. Material balances on cells are coupled to the nutrient balances in 3-D matrices to determine the effects of transport limitations on cell growth. The method of volume averaging is used to formulate the material balances for the cells and the nutrients in the porous matrix containing the cells. All model parameters are obtained from the literature. The maximum cell volume fraction reached when oxygen is depleted in the cell layer at 15 days and is nearly 0.63, corresponding to a cell density of 2.25 x 10(8) cells/mL. The substrate inhibition kinetics for cell growth lead to complex effects with respect to the roles of oxygen concentration and supply by convection and diffusion on cell growth. Variation in the height of the liquid layer above the cell matrix where nutrient supply is introduced affected the relative and absolute amounts of oxygen supply by hydrodynamic flow and by diffusion across a gas permeable FEP membrane. Mass transfer restrictions of the FEP membrane are considerable, and the supply of oxygen by convection is essential to achieve higher levels of cell growth. A maximum growth rate occurs at a specific flow rate. For flow rates higher than this optimal, the high oxygen concentration led to growth inhibition and for lower flow rates growth limitations occur due to insufficient oxygen supply. Because of the nonlinear effects of the autocatalytic substrate inhibition growth kinetics coupled to the convective transport, the rate of growth at this optimal flow rate is higher than that in a corresponding well-mixed reactor where oxygen concentration is set at the maximum indicated by the inhibitory kinetics.

Hematopoietic stem cells: from the bone to the bioreactor

The ex vivo expansion of human hematopoietic stem cells is a rapidly developing area with a broad range of biomedical applications. The mechanisms of renewal, differentiation and plasticity of stem cells are currently under intense investigation. However, the complexity of hematopoiesis, the heterogeneity of the culture population and the complex interplay between the culture parameters that significantly influence the proliferation and differentiation of hematopoietic cells have impaired the translation of small scale results to the highly demanded large-scale applications. The better understanding of these mechanisms is providing the basis for more rational approaches to the ex vivo expansion of hematopoietic stem cells. Efforts are now being made to establish a rational design of bioreactor systems, allowing the modeling and control of large-scale production of stem cells and the study of their proliferation and differentiation, under conditions as similar as possible to those in vivo.

Cloning, characterization and chromosome mapping of the human SMAP1 gene

Stromal membrane associated protein (smap-1) is a new murine cell surface molecule on the stromal cells. The murine smap-1 protein is induced in stromal cells by the contact with erythroid cells, which suggests that this protein may be involved in the haematopoietic progenitor cells to stromal cells interactions. Here we report the structure, map location and expression analysis of the human SMAP1 gene, which cover approximately 100 kb on chromosome 6 between D6S455 and D6S1673 markers. This gene is composed of 11 exons and encodes a 468-amino-acid protein, which shows an 86% of homology with the murine smap-1 protein. The expression of smap-1 in erythropoietic organs as well as the correlation with the erythropoietic activity of the haematopoietic organs suggest that smap-1 is induced in stromal cells by the contact with erythroid cells, defining smap-1 as a key molecule that induced an erythropoietic microenvironment in haematopoietic organs. The high sequence conservation between murine and human SMAP1, as well as its expression in bone marrow, strongly suggest conserved functions of this protein in both organisms. Recently, a constitutional translocation t(6;10)(q13;q22) has been described in a patient with severe aplastic anaemia. SMAP1 gene localizes to 6q13 and is probably implicated in erythropoiesis, therefore it remains as an interesting candidate gene.

Effect of growth factors on ex vivo bone marrow cell expansion using three-dimensional matrix support

To develop a culture system for bone marrow (BM) cell expansion, we examined the effect of growth factors (GFs) on the proliferation and differentiation of BM cells cultured in three-dimensional (3D) scaffolds of porous polyvinyl formal (PVF) resin. Murine BM cells were cultured for 2 weeks in the PVF resin or in culture dishes as a control, in the presence or absence of 4 GFs (erythropoietin, stem cell factor, interleukin [IL]-3, and IL-6). These GFs remarkably stimulated cell proliferation both in PVF and dish cultures. In addition, the PVF cultures showed enhanced cell proliferation in comparison with the corresponding dish cultures. Moreover, PVF cultures with GFs revealed the highest number of colony-forming units and the highest percentage of hematopoietic progenitor cells (HPCs) among all the cultures examined. Therefore, this 3D PVF culture system with GFs is considered as a potential alternative method for the ex vivo expansion of HPCs.

Human cord cell hematopoiesis in three-dimensional nonwoven fibrous matrices: in vitro simulation of the marrow microenvironment

Current hematopoietic culture systems mainly utilize two-dimensional devices with limited ability to promote self-renewal of early progenitors. In vivo-like three-dimensional (3-D) culture environments might be conducive to regulating stem cell proliferation and differentiation similar to in vivo hematopoiesis. The few 3-D cultures reported in the literature either produced few progenitors or provided little information about microenvironment. In this study, we constructed a 3-D hematopoietic microenvironment composed of nonwoven matrix and human cord blood (CB) cells to simulate the marrow microenvironment and expand cord progenitors. Nonwoven polyethylene terephthalate (PET) fabric with defined microstructure was used as the 3-D scaffold and the PET surface was modified by hydrolysis to improve cell adhesion. Different cell organizations were formed in a 3-D matrix in a developmental manner, from individual cells and cells bridging between fibers to large cell aggregates. Both stromal and hematopoietic cells were distributed spatially within the scaffold. Compared to two-dimensional (2-D) CD34(+) cell culture, 3-D culture produced 30-100% higher total cells and progenitors without exogenous cytokines. With thrombopoietin and flt-3/flk-2 ligand, it supported two- to three-fold higher total cell number (62.1- vs. 24.6-fold), CD34(+) cell number (6.8- vs. 2.8-fold) and colony-forming unit (CFU) number for 7-9 weeks (n = 6), indicating a hematopoiesis pathway that promoted progenitor production. Culture in 3-D nonwoven matrices enhanced cell-cell and cell-matrix interactions and allowed 3-D distribution of stromal and hematopoietic cells. The formation of cell aggregates and higher progenitor content indicated that the spatial microenvironment in 3-D culture played an important role in promoting hematopoiesis. This 3-D culture system can be used as an in vitro model to study stem cell or progenitor behavior, and to achieve sustained progenitor expansion.

A cDNA from human bone marrow encoding a protein exhibiting homology to the ATP1gamma1/PLM/MAT8 family of transmembrane proteins

A cDNA clone, IWU-1, was cloned from human bone marrow. Its putative open reading frame encoded a protein of 115 amino acids with a calculated molecular mass of 12.9 kDa. The deduced amino acid sequence exhibited high homology (>68%) to members of the ATP1gamma1/PLM/MAT8 family of single transmembrane proteins, primarily in the region containing the putative transmembrane domain. The sequence at the amino-terminal side exhibited high homology (>61%) to the cytoplasmic region of the angiotensin II type 1 receptors.

New type of matrix support for bone marrow cell cultures: in vitro culture and in vivo transplantation experiments

A new type of bone marrow cell culture system was developed by using a highly porous substrate matrix, i.e., porous polyvinyl formal (PVF) resin. Murine bone marrow (BM) cells were cultured without the use of exogenous growth factors in a three-dimensional matrix support made of collagen coated porous PVF resin. To examine the optimal conditions for highest stromal cell density, short-term and long-term in vitro culture experiments using PVF were performed. In the short-term culture experiments, it was found that cubes of PVF (10 x 10 x 2 mm and 130 microm in pore size) coated with type I collagen with a seeding density of 2x10(7) BM cells offered the most appropriate culture conditions. In the long-term cultures, BM cells in PVF maintained their viability for up to 6 weeks. In another series of re-inoculation experiments, freshly isolated BM cells were inoculated onto the already developed stromal layer. In this study, a higher cell density of the stromal layer was obtained in the PVF culture compared with those in the control dish culture. Based upon the results of in vitro experiments, in vivo transplantation studies were also performed. Histologic examinations of the subcutaneously transplanted PVF with stroma revealed host derived hematopoiesis inside the PVF matrix. Moreover, survival of approximately 15% of the transplanted BM cells that were cultured in PVF were confirmed in X-ray irradiated recipients. From these results, it is suggested that PVF resin is a promising three-dimensional substrate for BM cell culture and that it can maintain hematopoietic stem cells or progenitor cells after transplantation.

Extended culture of multipotent hematopoietic progenitors without cytokine augmentation in a novel three-dimensional device

The ability to culture multipotent hematopoietic progenitor cells for extended periods is of practical importance to both clinical and research efforts involving these cells. Conventional techniques for the extended culture of hematopoietic progenitor cells (HPCs) have proven largely ineffective in sustaining these cells and preserving their multipotency over protracted periods. To overcome barriers to extended HPC culture, numerous alternative approaches, including cytokine augmentation and co-culture with bone marrow stroma, have been explored to enhance HPC maintenance but have generally yielded mixed results. The present study examined the ability of a novel, three-dimensional, tantalum-coated porous biomaterial (TCPB) to support HPC maintenance and multipotency in long-term cultures to which no exogenous cytokines have been added. As a follow-up to previously published short-term HPC cultures in TCPB, we examined the maintenance, phenotype and multipotency of HPCs cultured for up to 6 weeks in the TCPB matrix compared to control systems, including fibronectin-coated plastic, bone marrow stroma cocultures and other three-dimensional materials. These studies indicated that TCPB supports the maintenance of immature progenitors for up to 6 weeks in the absence of supplemented cytokines. Further, the results demonstrate that the TCPB matrix facilitates and enhances HPC maintenance and leads to a 1.5-fold expansion of HPC numbers following 1 week in culture and a 6.7-fold increase in colony-forming ability following 6 weeks in culture in the absence of exogenous cytokines. Under the same conditions, control systems were less able to support progenitor viability and multipotency. These findings point to new approaches that may improve the in vitro preservation of progenitors and may have important implications in clinical areas such as progenitor expansion, bone marrow transplantation and gene therapy.