Development of novel perfusion chamber to retain nonadherent cells and its use for comparison of human "mobilized" peripheral blood mononuclear cell cultures with and without irradiated bone marrow stroma

Stromalized microreactor supports murine hematopoietic progenitor enrichment

There is an emerging need to process, expand, and even genetically engineer hematopoietic stem and progenitor cells (HSPCs) prior to administration for blood reconstitution therapy. A closed-system and automated solution for ex vivo HSC processing can improve adoption and standardize processing techniques. Here, we report a recirculating flow bioreactor where HSCs are stabilized and enriched for short-term processing by indirect fibroblast feeder coculture. Mouse 3 T3 fibroblasts were seeded on the extraluminal membrane surface of a hollow fiber micro-bioreactor and were found to support HSPC cell number compared to unsupported BMCs. CFSE analysis indicates that 3 T3-support was essential for the enhanced intrinsic cell cycling of HSPCs. This enhanced support was specific to the HSPC population with little to no effect seen with the Lineage^positive and Lineage^negative cells. Together, these data suggest that stromal-seeded hollow fiber micro-reactors represent a platform to screening various conditions that support the expansion and bioprocessing of HSPCs ex vivo.

3D models of the hematopoietic stem cell niche under steady-state and active conditions

Hematopoietic stem cells (HSCs) in the bone marrow are able to differentiate into all types of blood cells and supply the organism each day with billions of fresh cells. They are applied to cure hematological diseases such as leukemia. The clinical need for HSCs is high and there is a demand for being able to control and multiply HSCs in vitro. The hematopoietic system is highly proliferative and thus sensitive to anti-proliferative drugs such as chemotherapeutics. For many of these drugs suppression of the hematopoietic system is the dose-limiting toxicity. Therefore, biomimetic 3D models of the HSC niche that allow to control HSC behavior in vitro and to test drugs in a human setting are relevant for the clinics and pharmacology. Here, we describe a perfused 3D bone marrow analog that allows mimicking the HSC niche under steady-state and activated conditions that favor either HSC maintenance or differentiation, respectively, and allows for drug testing.

Predictions for optimal mitigation of paracrine inhibitory signalling in haemopoietic stem cell cultures

Introduction

Recent studies in the literature have highlighted the critical role played by cell signalling in determining haemopoietic stem cell (HSC) fate within ex vivo culture systems. Stimulatory signals can enhance proliferation and promote differentiation, whilst inhibitory signals can significantly limit culture output.

Methods

Numerical models of various mitigation strategies are presented and applied to determine effectiveness of these strategies toward mitigation of paracrine inhibitory signalling inherent in these culture systems. The strategies assessed include mixing, media-exchange, fed-batch and perfusion.

Results

The models predict that significant spatial concentration gradients exist in typical cell cultures, with important consequences for subsequent cell expansion. Media exchange is shown to be the most effective mitigation strategy, but remains labour intensive and difficult to scale-up for large culture systems. The fed-batch strategy is only effective at very small Peclet number, and its effect is diminished as the cell culture volume grows. Conversely, mixing is effective at high Peclet number, and ineffective at low Peclet number. The models predict that cell expansion in fed-batch cultures becomes independent of increasing dilution rate, consistent with experimental results previously reported in the literature. In contrast, the models predict that increasing the flow rate in perfused cultures will lead to increased cell expansion, indicating the suitability of perfusion for use as an automated, tunable strategy. The effect of initial cell seeding density is also investigated, with the model showing that perfusion outperforms dilution for all densities considered.

Conclusions

The models predict that the impact of inhibitory signalling in HSC cultures can be mitigated against using media manipulation strategies, with the optimal strategy dependent upon the protein diffusion time-scale relative to the media manipulation time-scale. The key messages from this study can be applied to any complex cell culture scenario where cell-cell interactions and paracrine signalling networks impact upon cell fate and cell expansion.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0048-7) contains supplementary material, which is available to authorized users.

Design, characterization and application of a minibioreactor for the culture of human hematopoietic cells under controlled conditions

The in vitro culture of human hematopoietic cells has recently received considerable attention due to its clinical importance. Most studies of the culture and expansion of hematopoietic cells have been performed in static cultures but only very few reports exist on the use of bioreactors where strict control of environmental variables is maintained. In this work, the design, characterization and application of a fully instrumented minibioreactor for the culture of human hematopoietic cells from umbilical cord blood is presented. The system consists of a stirred- tank reactor where cells are maintained in suspension in an homogeneous environment and without the need of a stromal feeding layer. The minibioreactor was coupled to a data acquisition and control system which continuously monitored pH, dissolved oxygen and redox potential. When operated at 75 rpm with a hanging magnetic bar (impeller-to-tank diameter ratio of 0.57), the dead and mixing times were 120 and 80 s, respectively, and the maximum response rate and volumetric oxygen transfer coefficient were 0.8 mM O2 hr-1, and 1.8 hr-1, respectively. Such characteristics allowed a tight control of pH(until day 11) and dissolved oxygen at predetermined set-points, and up to a 7-fold expansion of hematopoietic progenitors was possible in cultures maintained at 20% dissolved oxygen with respect to air saturation. Growth phase and cell concentration could be inferred on- line through determinations of oxygen uptake rate and culture redox potential. Oxygen uptake rate increased during exponential growth phase to a maximum of 40 muM hr-1. Such an increase closely followed the increase in concentration of hematopoietic progenitors. In contrast, culture redox potential decreased during exponential growth phase and then increased during death phase. The designed system permits not only the maintenance of controlled environmental conditions and on-line identification of fundamental culture parameters, but also the application of control strategies for improving expansion of hematopoietic cells.

Scalable stirred-suspension bioreactor culture of human pluripotent stem cells

Advances in stem cell biology have afforded promising results for the generation of various cell types for therapies against devastating diseases. However, a prerequisite for realizing the therapeutic potential of stem cells is the development of bioprocesses for the production of stem cell progeny in quantities that satisfy clinical demands. Recent reports on the expansion and directed differentiation of human embryonic stem cells (hESCs) in scalable stirred-suspension bioreactors (SSBs) demonstrated that large-scale production of therapeutically useful hESC progeny is feasible with current state-of-the-art culture technologies. Stem cells have been cultured in SSBs as aggregates, in microcarrier suspension and after encapsulation. The various modes in which SSBs can be employed for the cultivation of hESCs and human induced pluripotent stem cells (hiPSCs) are described. To that end, this is the first account of hiPSC cultivation in a microcarrier stirred-suspension system. Given that cultured stem cells and their differentiated progeny are the actual products used in tissue engineering and cell therapies, the impact of bioreactor's operating conditions on stem cell self-renewal and commitment should be considered. The effects of variables specific to SSB operation on stem cell physiology are discussed. Finally, major challenges are presented which remain to be addressed before the mainstream use of SSBs for the large-scale culture of hESCs and hiPSCs.

Microfabricated electrospun collagen membranes for 3-D cancer models and drug screening applications

Invasive epithelial tumors form from cells that are released from their natural basement membrane and form 3-D structures that interact with each other and with the microenvironment of the stromal tissues around the tumor, which often contains collagen. Cancer cells, growing as monolayers on tissue culture plastic, do not reflect many of the properties of whole tumors. This shortcoming limits their ability to serve as models for testing of pharmacologically active compounds, including those that are being tested as antineoplastics. This work seeks to create new 3-D cellular materials possessing properties similar to those in native tissues surrounding cancers, specifically electrospun micro- and nanofibrous collagen scaffolds that support tumor growth in 3-D. We hypothesize that a 3-D culture system will provide a better replica of tumor growth in a native environment and, thus, better report the bioactivity of antineoplastic agents. In addition, we optimized conditions and identified physical characteristics that support growth of the highly invasive, prostate cancer bone metastatic cell line C4-2B on these matrices for use in anticancer drug studies. The effects of matrix porosity, fiber diameter, elasticity, and surface roughness on growth of cancer cells were evaluated. Data indicates that while cells attach and grow well on both nano- and microfibrous electrospun membranes, the microfibrous membrane represented a better approximation of the tumor microenvironment. It was also observed that C4-2B nonadherent cells migrated through the depth of two electrospun membranes and formed colonies resembling tumors on day 3. An apoptosis study revealed that cells on electrospun substrates were more resistant to both antineoplastic agents, docetaxel (DOC), and camptothecin (CAM) compared to the cells grown on standard collagen-coated tissue culture polystyrene (TCP). Growth, survival, and apoptosis were measured, as well as the differences in the apoptotic capabilities, of the two above-mentioned compounds compared to known clinical performance. We conclude that 3-D electrospun membranes are amenable to high throughput screening for cancer cell susceptibility and combination killing (Banerjee, S.; Hussain, M.; Wang, Z.; Saliganan, A.; Che, M.; Bonfil, D.; Cher, M.; Sarkar, F.H. Cancer Research, 2007, 67 (8), 3818-26).

Design of well and groove microchannel bioreactors for cell culture

Microfluidic bioreactors have been shown valuable for various cellular applications. The use of micro-wells/grooves bioreactors, in which micro-topographical features are used to protect sensitive cells from the detrimental effects of fluidic shear stress, is a promising approach to culture sensitive cells in these perfusion microsystems. However, such devices exhibit substantially different fluid dynamics and mass transport characteristics compared to conventional planar microchannel reactors. In order to properly design and optimize these systems, fluid and mass transport issues playing a key role in microscale bioreactors should be adequately addressed. The present work is a parametric study of micro-groove/micro-well microchannel bioreactors. Operation conditions and design parameters were theoretically examined via a numerical model. The complex flow pattern obtained at grooves of various depths was studied and the shear protection factor compared to planar microchannels was evaluated. 3D flow simulations were preformed in order to examine the shear protection factor in micro-wells, which were found to have similar attributes as the grooves. The oxygen mass transport problem, which is coupled to the fluid mechanics problem, was solved for various groove geometries and for several cell types, assuming a defined shear stress limitation. It is shown that by optimizing the groove depth, the groove bioreactor may be used to effectively maximize the number of cells cultured within it or to minimize the oxygen gradient existing in such devices. Moreover, for sensitive cells having a high oxygen demand (e.g., hepatocytes) or low endurance to shear (e.g., human embryonic stem cells), results show that the use of grooves is an enabling technology, since under the same physical conditions the cells cannot be cultured for long periods of time in a planar microchannel. In addition to the theoretical model findings, the culture of human foreskin fibroblasts in groove (30 microm depth) and well bioreactors (35 microm depth) was experimentally examined at various flow rates of medium perfusion and compared to cell culture in regular flat microchannels. It was shown that the wells and the grooves enable a one order of magnitude increase in the maximum perfusion rate compared to planar microchannels. Altogether, the study demonstrates that the proper design and use of microgroove/well bioreactors may be highly beneficial for cell culture assays.

Neural Network Analysis of Ex-vivo Expansion of Hematopoietic Stem Cells

The shortage of hematopoietic stem cells (HSCs) greatly limits their widespread clinical applications. Few studies however, investigated the relationship between the cellular expansion and the influencing factors although wide variety results of the ex-vivo expansion of HSCs existed in literature. Here, a back-propagation (BP) neural network model was employed to evaluate the ex-vivo expansions of nuclear cells (NCs), CD34(+) cells, and colony-forming units (CFU-Cs), where the output was the cellular expansion folds and the inputs include inoculated density, cytokines, resources, serum, stroma, culture time, and bioreactor types. Around 124, 86, and 90 samples were used to train the neural network for the expansion evaluations of NCs, CD34(+ )cells, and CFU-Cs, respectively, while 17, 14, and 10 samples were applied to predict respectively. The results show that for the training of network, the interval accuracy of the expansion folds for the different cells is 85.5, 86.1, and 86.7%, respectively, while the truth-value accuracy is still up to 59.7, 50.0, and 62.2%, respectively within a relative error (RE) of +/-20%. For the prediction of network, the interval accuracy can be up to 82.4, 71.4, and 70%, respectively, while the truth-value accuracy is only 29.4, 14.3, and 50.0%, respectively (RE = +/-20%). Moreover, six verification experiments were carried out based on our interval predicted values and the results proved that the five group predicted conditions lead to the correct expansion of the HSCs with the accuracy more than 80%. Considering the complexity of HSC expansion and complicated wide range of the experimental data, such relatively high interval accuracy for training and prediction as well as verification are satisfied. Therefore this nonlinear modeling makes it possible to describe quantitatively the effects of the culture conditions on the HSC expansion and to predict the optimal culture conditions for higher ex-vivo expansion of HSCs.

Microfabricated grooved substrates as platforms for bioartificial liver reactors

An extracorporeal bioartificial liver device has the potential to provide temporary hepatic support for patients with liver failure. Our goal was to optimize the flow environment for the cultured hepatocytes in a flat-plate bioreactor, specifically focusing on oxygen delivery using high medium flow rates while reducing the detrimental effects of the resulting shear stresses. We used photolithographic techniques to fabricate microgrooves onto the underlying glass substrate. The microgrooves, perpendicular to the axial flow direction, protected the hepatocytes from the shear stress induced by the flowing medium. Using finite element analysis, we found that the velocity gradient change near the cell surface (i.e., bottom of the grooves) was smaller than that near the top surface of the flow channel, indicating that the grooves would provide protection to the attached cells from the mechanical effects of the flowing medium. We also determined that the shear stress at the cell surface could be reduced by as much as 30 times (channel height of 100 microm) in the grooved-substrate (0.5 dyn/cm(2)) bioreactor compared to the flat-substrate (15 dyn/cm(2)) bioreactor for a medium flow rate of 4.0 mL/min. Albumin and urea synthesis rates of hepatocytes cocultured with 3T3-J2 fibroblasts remained stable over 5 days of perfusion in the grooved-substrate bioreactor, whereas in the flat-substrate bioreactor they decreased over the same time period. These studies indicate that under "high" flow conditions the microgrooved-substrate in the bioreactor can decrease the detrimental effects of shear stress on the hepatocytes while providing adequate oxygenation, thereby resulting in stable liver-specific function.

Hepatic tissue engineering for adjunct and temporary liver support: critical technologies

The severe donor liver shortage, high cost, and complexity of orthotopic liver transplantation have prompted the search for alternative treatment strategies for end-stage liver disease, which would require less donor material, be cheaper, and less invasive. Hepatic tissue engineering encompasses several approaches to develop adjunct internal liver support methods, such as hepatocyte transplantation and implantable hepatocyte-based devices, as well as temporary extracorporeal liver support techniques, such as bioartificial liver assist devices. Many tissue engineered liver support systems have passed the "proof of principle" test in preclinical and clinical studies; however, they have not yet been found sufficiently reliably effective for routine clinical use. In this review we describe, from an engineering perspective, the progress and remaining challenges that must be resolved in order to develop the next generation of implantable and extracorporeal devices for adjunct or temporary liver assist.

Cultivation of hematopoietic stem and progenitor cells: biochemical engineering aspects

The ex vivo expansion of hematopoietic cells is one of the most challenging fields in cell culture. This is a rapidly growing area of tissue engineering with many potential applications in bone marrow transplantation, transfusion medicine or gene therapy. Over the last few years much progress has been made in understanding hematopoietic differentiation, discovery of cytokines, isolation and identification of cellular subtypes and in the development of a variety of bioreactor concepts. All this has led to a number of (preliminary) clinical trials that gave a hint of the benefits that can be obtained from the use of expanded hematopoietic cells in therapy. Moreover, as we understand the complexity and the regulation of hematopoiesis, it becomes obvious that highly sophisticated cultivation techniques and bioreactor concepts are needed: a new challenge for bioprocess engineering in cell culture.

Ex vivo-expanded hematopoietic cell graft recipients exhibit T cell repertoire diversity similar to that seen after conventional stem cell transplants

The feasibility of using ex vivo-expanded hematopoietic progenitor cells to reconstitute hematopoiesis after high-dose chemotherapy is presently being examined. Early studies have shown that myeloid and erythroid hematopoiesis can be successfully reconstituted after high-dose chemotherapy and ex vivo-expanded hematopoietic cell transplantation. The lymphoid reconstitution, however, has not been addressed previously. In this study, we examined the diversity of the T cell receptor V beta chain (TCRBV) repertoires in 5 breast cancer patients who were transplanted with ex vivo-expanded bone marrow mononuclear cells as the only source of hematopoietic graft. Using the TCRBV third complementarity determining region (CDR3) fingerprinting methodology, it is shown that CD4(+) and CD8(+) T cell subsets after ex vivo-expanded hematopoietic cell graft transplants exhibit TCRBV diversities that are similar in complexity when compared to those seen after conventional autologous peripheral blood stem cell transplants (PBSCT). No apparent difference in the extent of CDR3 diversity was found between ex vivo expanded and conventional autologous PBSCT recipients when the CD4(+) and CD8(+) subsets were further separated into CD45RA(+) "naïve" and CD45RO(+) "memory" subsets. The diversity of the CD45RA(+) naïve subsets was as complex as that of the CD45RO(+) memory subsets. These results indicate that T cell repertoire diversification is not further compromised when ex vivo-expanded hematopoietic cells are used instead of autologous peripheral blood stem cells as the only source of graft.

Ex-vivo expansion of bone marrow progenitor cells for hematopoietic reconstitution following high-dose chemotherapy for breast cancer

The use of hematopoietic growth factors, stromal monolayers, and frequent medium exchange allows the expansion of hematopoietic progenitors ex-vivo. We evaluated the use of ex-vivo expanded progenitor cells for hematopoietic reconstitution following high dose chemotherapy (HDC) in breast cancer patients. Patients with high-risk Stage II or metastatic breast carcinoma underwent bone marrow aspirations using general anesthesia. A total of 675-1125 x 10(6) mononuclear cells (MNC) were seeded for ex-vivo expansion for 12 days in controlled perfusion bioreactors (Aastrom Biosciences, Inc.). The bone marrow cultures, which included the stromal cells collected with the aspirate, were supplemented with erythropoietin, granulocyte-macrophage-colony stimulating factor (GM-CSF)/IL-3 fusion protein (PIXY 321), and flt3 ligand. Stem cell transplant was performed with expanded cells after HDC. A median bone marrow volume of 52.9 mL (range 42-187 mL) was needed to inoculate the bioreactors. Median fold expansion of nucleated cells (NC) and colony forming unit granulocyte-macrophage (CFU-GM) was 4.9 and 9.5, respectively. The median fold expansion of CD34+lin- and long-term culture-initiating culture (LTC-IC) was 0.42 and 0.32, respectively. Five patients were transplanted with ex-vivo expanded NC. Median days to an absolute neutrophil count > 500/microL was 18 (range 15-22). Median days to a platelet count > 20,000/microl was 23 (range 19-39). All patients had sustained engraftment of both neutrophils and platelets. Immune reconstitution was similar to that seen after HDC and conventional stem cell transplantation. We conclude that ex-vivo expansion of progenitor cells from perfusion cultures of small volume bone marrow aspirates, allows hematopoietic reconstitution after HDC.