Scalable GMP compliant suspension culture system for human ES cells

Suspension bioreactors are an attractive alternative to static culture of human embryonic stem cells (hESCs) for the generation of clinically relevant cell numbers in a controlled system. In this study, we have developed a scalable suspension culture system using serum-free defined media with spinner flasks for hESC expansion as cell aggregates. With optimized cell seeding density and splitting interval, we demonstrate prolonged passaging and expansion of several hESC lines with overall expansion, yield, viability and maintenance of pluripotency equivalent to adherent culture. Human ESCs maintained in suspension as aggregates can be passaged at least 20 times to achieve over 1×10(13) fold calculated expansion with high undifferentiation rate and normal karyotype. Furthermore, the aggregates are able to differentiate to cardiomyocytes in a directed fashion. Finally, we show that the cells can be cryopreserved in serum-free medium and thawed into adherent or suspension cultures to continue passaging and expansion. We have successfully used this method under cGMP or cGMP-equivalent conditions to generate cell banks of several hESC lines. Taken together, our suspension culture system provides a powerful approach for scale-up expansion of hESCs under defined and serum-free conditions for clinical and research applications.     

Abelson virus-infected cells can exhibit restricted in vitro growth and low oncogenic potential.

We have designed a method for growing bone marrow cells infected with Abelson murine leukemia virus which permits examination of target cell growth early after infection. This culture system increases the efficiency of target cell growth by favoring rapid growth of a mixed population of adherent cells in the primary culture. The nonadherent Abelson virus-infected cell populations expressed pre-B-cell differentiation markers characteristic of Abelson virus-transformed cells (mu-heavy chains of immunoglobulin M and terminal deoxynucleotidyltransferase). Early after infection, these cell populations exhibited restricted in vitro and in vivo growth properties which differed from those of an established Abelson virus-transformed cell line, 2M3. These included a marked dependency upon the adherent cell layer for growth and viability, a lower efficiency of agar colony formation, and a lower capacity for tumor production in syngeneic animals. Growth of the early populations could be maintained in the absence of the adherent cell layer by using conditioned medium from long-term adherent cell cultures established in the absence of viral infection. After passage of the populations for several weeks, the in vitro growth properties gradually shifted toward that of the 2M3 cell line. Twelve-week-old populations grew independently of the adherent cell layer and showed an increased efficiency of agar colony formation. These data indicate that many lymphoid target cells exhibit an intermediate transformed phenotype when infected with Abelson virus. Growth of these cells in culture is mediated via a synergistic interaction between intracellular expression of the viral transforming gene and an exogenous growth-promoting activity which can be provided by cultures of adherent bone marrow cells.     

Cell adhesion promotes Ebola virus envelope glycoprotein-mediated binding and infection

Ebola virus infects a wide variety of adherent cell types, while nonadherent cells are found to be refractory. To explore this correlation, we compared the ability of pairs of related adherent and nonadherent cells to bind a recombinant Ebola virus receptor binding domain (EboV RBD) and to be infected with Ebola virus glycoprotein (GP)-pseudotyped particles. Both human 293F and THP-1 cells can be propagated as adherent or nonadherent cultures, and in both cases adherent cells were found to be significantly more susceptible to both EboV RBD binding and GP-pseudotyped virus infection than their nonadherent counterparts. Furthermore, with 293F cells the acquisition of EboV RBD binding paralleled cell spreading and did not require new mRNA or protein synthesis.     

A novel time resolved fluorometric assay of anoikis using Europium-labelled Annexin V in cultured adherent cells

Background: Adherent cells undergo apoptosis when detached from their home ground, a process called anoikis (homelessness).Methods: We developed a new and sensitive method to analyse apoptosis and anoikis of adherent cell types using a time resolved fluorometric assay with Europium-labelled Annexin V. Anoikis was induced with tumor necrosis factor- /cycloheximide and three cell fractions of the cell cultures were prepared and analysed. Fraction 1 consisted of adherent cells, analysed while growing on their support (without detachment by trypsinisation). Fraction 2 contained detached cells due to anoikis (floating cells) and fraction 3 contained apoptotic bodies. Both fractions 2 and 3 were present in the culture medium and were isolated by differential centrifugation.Results: TNF- treatment of three different types of adherent cell cultures induced a significant increase of the amount of floating cells (anoikis) and apoptotic bodies compared to control cell cultures. Also in the adherent cell fractions a small amount of apoptosis was observed.Conclusions: The novel time resolved assay provides the ability to analyse the cell death cascade in adherent cell cultures of the same sample at the same time in a sensitive and reproducible way.     

Altered biochemical properties of mitochondria in mouse mammary epithelial cells during primary culture.

A liquid culture system is described whereby proliferation of haemopoietic stem cells (CFU-S), production of granulocyte precursor cells (CFU-C), and extensive granulopoiesis can be maintained in vetro for several months. Such cultures consist of adherent and non-adherent populations of cells. The adherent population contains phagocytic mononuclear cells, "epithelial" cells, and "giant fat" cells. The latter appear to be particularly important for stem cell maintenance and furthermore there is a strong tendency for maturing granulocytes to selectively cluster in and around areas of "giant fat" cell aggregations. By "feeding" the cultures at weekly intervals, between 10 to 15 "population doublings" of functionally normal CFU-S regularly occurs. Increased "population doublings" may be obtained by feeding twice weekly. The cultures show initially extensive granulopoiesis followed, in a majority of cases, by an accumulation of blast cells. Eventually both blast cells and granulocytes decline and the cultures contain predominantly phagocytic mononuclear cells. Culturing at 33 degrees C leads to the development of a more profuse growth of adherent cells and these cultures show better maintenance of stem cells and increased cell density. When tested for colony stimulating activity (CSA) the cultures were uniformly negative. Addition of exogenous CSA caused a rapid decline in stem cells, reduced granulopoiesis and an accumulation of phagocytic mononuclear cells.     

Further studies on generation of macrophages in in vitro cultures of mouse spleen cells and its inhibition by the capsular polysaccharide of Klebsiella pneumoniae.

Although the number of macrophages detected in cultures of mouse spleen cells at the start of the culture was very small, it markedly increased during further incubation. Macrophages were generated not only from the glass-adherent cell fraction of spleen cells, but also from the nonadherent cell fraction obtained after removal of adherent cells either by incubating in glass petri dishes or by passing through a glass bead column. The generation of macrophages from the nonadherent cell fraction occurred even when it was separated as late as 48 hr after the start of the culture. The phagocytic activity of macrophages newly generated from the nonadherent cell fraction was relatively weak, but it was activated during further incubation. Based on these results, the maturation process of macrophages can be divided into at least the following four stages; glass-nonadherent nonphagocytic precursor cells, glass-adherent nonphagocytic precursor cells, immature macrophages with low phagocytic activity, and mature macrophages with full phagocytic activity. The addition of the capsular polysaccharide of Klebsiella pneumoniae (CPS-K) to cultures of spleen cells markedly suppressed the generation of macrophages. The suppressive effect of CPS-K depended on its dosage, and the minimum concentration of CPS-K showing a definite effect was 0.05 μg/ml. CPS-K inhibited further generation of macrophages in either the nonadherent or adherent cell fraction at any time after the start of the culture. The suppressive effect of CPS-K on the generation of macrophages could not be reversed by simple washing of spleen cells which had been kept in contact with CPS-K for 3 hr. There was no evidence which showed that CPS-K exhibited direct cytotoxic effects on spleen cells in the culture.     

In vitro differentiation of B lymphocytes from primitive hemopoietic precursors present in long-term bone marrow cultures

B lymphocytes are not produced in the Dexter long-term bone marrow cultures, but a primitive B cell precursor is present. The findings presented in this study demonstrate that this precursor can be induced to produce B lymphocytes by transferring the cultures to the Whitlock conditions for the long-term growth of B cells in vitro. Two weeks after the transfer of cultures maintained at 33 degrees C in medium supplemented with horse serum and steroids to low concentrations of fetal calf serum at 37 degrees C, marked effects can be observed. The pattern of cell growth changes from one in which the hemopoietic cells are clustered in tight foci containing several hundred cells to smaller ones in which the cells are not as densely packed. Fat cells in the adherent layer disappear and the supporting stroma becomes more uniform in appearance. This change in the culture format is accompanied by a decrease in the number of nonadherent cells and a shift from myelopoiesis to lymphopoiesis. The numbers of granulocyte-macrophage progenitors decline weekly after the change in culture conditions and are not detected by the third week. B cell colony-forming units appear by 3 wk. Cells that express the 14.8 cell surface antigen are induced by 1 wk after the change in culture conditions, followed by the appearance of surface IgM-bearing cells 2 wk later. This shift to lymphopoiesis can be confirmed morphologically. Granulocytes and macrophages disappear from the cultures by 4 wk, at which time almost all of the cells have a characteristic lymphocyte morphology. Upon switching these cultures back to the original Dexter conditions, only low levels of transient myelopoiesis can be reinitiated.     

A cGMP-applicable Expansion Method for Aggregates of Human Neural Stem and Progenitor Cells Derived From Pluripotent Stem Cells or Fetal Brain Tissue

A cell expansion technique to amass large numbers of cells from a single specimen for research experiments and clinical trials would greatly benefit the stem cell community. Many current expansion methods are laborious and costly, and those involving complete dissociation may cause several stem and progenitor cell types to undergo differentiation or early senescence. To overcome these problems, we have developed an automated mechanical passaging method referred to as “chopping” that is simple and inexpensive. This technique avoids chemical or enzymatic dissociation into single cells and instead allows for the large-scale expansion of suspended, spheroid cultures that maintain constant cell/cell contact. The chopping method has primarily been used for fetal brain-derived neural progenitor cells or neurospheres, and has recently been published for use with neural stem cells derived from embryonic and induced pluripotent stem cells. The procedure involves seeding neurospheres onto a tissue culture Petri dish and subsequently passing a sharp, sterile blade through the cells effectively automating the tedious process of manually mechanically dissociating each sphere. Suspending cells in culture provides a favorable surface area-to-volume ratio; as over 500,000 cells can be grown within a single neurosphere of less than 0.5 mm in diameter. In one T175 flask, over 50 million cells can grow in suspension cultures compared to only 15 million in adherent cultures. Importantly, the chopping procedure has been used under current good manufacturing practice (cGMP), permitting mass quantity production of clinical-grade cell products.     

Evaluation of the "Cellscreen" system for proliferation studies on liver progenitor cells

Proliferation studies on mammalian cells have been disadvantaged by the limited availability of non-invasive assays as the majority of approaches are based on chemical treatment, sampling or staining of cells removed from culture. In this study, we utilised the Cellscreen system (Innovatis AG, Bielefeld, Germany), a non-invasive automated technique for measuring proliferation of adherent and suspension cells over time. We have evaluated the ability of the Cellscreen system to monitor and quantify growth of adherent liver progenitor cells over time and tested several applications, (i) serum reduction or (ii) treatment with a cytokine. Our results demonstrate that the Cellscreen system reproducibly documents pro- and anti-proliferative effects of cytokines and growth factors and quantifies changes by providing cell-doubling times for control and test cultures. However, we found that for the conversion of cell density values into absolute cell numbers different conversion factors, which better suit the individual growth phases, need to be established. Collectively, these findings reveal that the Cellscreen system is applicable for the determination of cell proliferation of adherent and suspension cells in response to a variety of (growth) factors. It minimises operator participation and thus enables more rapid and larger screens and, being non-invasive, permits multiple assays on the same culture of cells. Hence, this technique proves superior to the common proliferation assays opening up new dimensions of proliferation studies in cell biology.     

Development of a bone marrow culture for maintenance and growth of normal human B cell precursors.

The absence of long term bone marrow cultures for studying the growth and differentiation of human B cell precursors (BCP) has placed restrictions on the ability to analyze the early stages of human B cell ontogeny. We now describe a bone marrow-derived adherent cell microenvironment that maintains human BCP for several weeks in vitro. The adherent cells are maintained in a serum-free tissue culture medium, and consist of a predominant population of CD10+ fibroblast-like cells and a minor population of CD10+/nonspecific esterase+ macrophages. Adherent cell cultures seeded with fresh or cryopreserved fetal bone marrow, or purified CD10+/surface IgM- cells, provide a supportive microenvironment for lymphoid cells with a predominant phenotype of CD10+/CD19+/HLA-DR+/surface IgM-. Supplementation of the adherent cell cultures with human IL-7 induces active growth of BCP during the first 14 to 21 days of culture. However, the expansion of these cells does not continue past 21 days, and the cultures undergo a steady decline in BCP. Analysis of adherent cell conditioned medium revealed the presence of an unidentified soluble factor (or factors) that acts in concert with IL-7 to promote the growth of CD10+/surface IgM- cells. This culture system will be useful in elucidating the patterns of gene expression and growth factor requirements that characterize normal human B cell ontogeny, and perturbations of normal B cell ontogeny that lead to immunodeficiency and leukemia.     

Stable expression of recombinant human coagulation factor XIII in protein-free suspension culture of Chinese hamster ovary cells

The recombinant a and bsubunits for human coagulation factor XIII were transfected into Chinese hamster ovary (CHO) cells. CHO cells were amplified and selected with methotrexate in adherent cultures containing serum, and CHO 1-62 cells were later selected in protein-free medium. To develop a recombinant factor XIII production process in a suspension culture, we have investigated the growth characteristics of CHO cells and the maintenance of factor XIII expression in the culture medium. Suspension adaptation of CHO cells was performed in protein-free medium, GC-CHO-PI, by two methods, such as serum weaning and direct switching from serum containing media to protein-free media. Although the growth of CHO cells in suspension culture was affected initially by serum depletion, cell specific productivity of factor XIII showed only minor changes by the direct switching to protein-free medium during a suspension culture. As for the long-term stability of factor XIII, CHO 1-62 cells showed a stable expression of factor XIII in protein-free condition for 1000 h. These results indicate that the CHO 1-62cells can be adapted to express recombinant human factor XIII in a stable maimer in suspension culture using a protein-free medium. Our results demonstrate that enhanced cell growth in a continuous manner is achievable for factor XIII production in a protein-free medium when a perfusion bioreactor culture system with a spin filter is employed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pluronic Enhances the Robustness and Reduces the Cell Attachment of Mammalian Cells

The addition of the non-ionic surfactant, Pluronic F-68, to serum-free CHO cultures causes multi-functional effects that enhance cell yield in agitated cultures and reduce cell adhesion in stationary cultures. Three independent CHO cell lines were subjected to high liquid shear in assay systems that either included or excluded a liquid-gas interface. In the absence of Pluronic, there was a loss in cell viability in either assay system, although there was an intrinsic variability in sensitivity of the cell lines to shear damage. Supplementation with Pluronic prevented loss of cell viability, indicating protection in either a gas sparged or bubble-free environment. However, we found no evidence of long-term protection of cells once Pluronic was removed. Pluronic was capable of repairing trypsin-damaged cells as evidenced by enhanced growth, reduced membrane porosity, and improved robustness under liquid shear. The proportion of adherent cells was reduced to a minimal level by the presence of Pluronic although its effect was rapidly reversible with a high proportion (70%) of adherent cells observed within a few culture passages of its removal. The observed effects of Pluronic on these cultures are compatible with a mechanism in which the polymer forms a protective layer on the cell membrane, which has a significantly lower hydrophobicity.     

One Mouse,Two Cultures: Isolation and Culture of Adult Neural Stem Cells from the Two Neurogenic Zones of Individual Mice

The neurosphere assay and the adherent monolayer culture system are valuable tools to determine the potential (proliferation or differentiation) of adult neural stem cells in vitro. These assays can be used to compare the precursor potential of cells isolated from genetically different or differentially treated animals to determine the effects of exogenous factors on neural precursor cell proliferation and differentiation and to generate neural precursor cell lines that can be assayed over continuous passages. The neurosphere assay is traditionally used for the post-hoc identification of stem cells, primarily due to the lack of definitive markers with which they can be isolated from primary tissue and has the major advantage of giving a quick estimate of precursor cell numbers in brain tissue derived from individual animals. Adherent monolayer cultures, in contrast, are not traditionally used to compare proliferation between individual animals, as each culture is generally initiated from the combined tissue of between 5-8 animals. However, they have the major advantage that, unlike neurospheres, they consist of a mostly homogeneous population of precursor cells and are useful for following the differentiation process in single cells. Here, we describe, in detail, the generation of neurosphere cultures and, for the first time, adherent cultures from individual animals. This has many important implications including paired analysis of proliferation and/or differentiation potential in both the subventricular zone (SVZ) and dentate gyrus (DG) of treated or genetically different mouse lines, as well as a significant reduction in animal usage.     

狗骨髓长期培养的贴壁层细胞及条件培养液对粒系祖细胞的影响

本文报告狗骨髓长期培养的初步研究结果。采用马血清与狗血清混合加入培养体系中,可建立起比较稳定的贴壁细胞层,可以维持19周以上。但是,这种贴壁层不能有效地维持造血干细胞的增殖与分化,上清液中血细胞与GM-CFU_C的数目,在第二次接种骨髓后2—3周即迅速下降。狗骨髓培养的条件液中存在着抑制GM-CFU_C生长的物质,但它对小鼠骨髓GM-CFU_C和CFU-S无影响。如以贴壁细胞作为底层,用双层琼脂平皿培养法与正常狗骨髓共同培养,发现贴壁细胞不仅没有抑制反而有加强CSF刺激GM-CFU_C生长的作用。因此对狗骨髓长期培养体系不能长期支持造血干细胞生长和繁殖的可能原因尚须作进一步探索。     

Roots1

ABSTRACT Many unicellular eukaryotic organisms possess complex fiber systems that organize and anchor the flagellar basal apparatus in the cell [20, 24]. In 1978 we first published the observation that one of these fiber systems, the striated flagellar root of the quadriflagellate green alga Tetraselmis subcordiformis (=Platymonas subcordiformis), is a contractile organelle [31]. We subsequently found that striated flagellar roots are composed, in part, of the Ca²⁺-binding protein centrin [30]. Since that time, centrin has been found to be a ubiquitous component of the flagellar basal apparatus, basal bodies and centrioles, and centrosomes and mitotic spindle poles of eukaryotic cells (for general reviews see [28, 34]). While we have learned a great deal about centrin from other organisms, our earliest success in understanding the biology of centrin was in large part due to the extraordinary extent to which Tetraselmis cells have elaborated their centrin-based organelles. In this paper, I will return attention to several unanswered questions concerning Tetraselmis striated flagellar root behavior and I will suggest several new directions that students may wish to pursue in order to tease fresh insights from this fascinating organism.     

Filamentous growth ofPseudomonas aeruginosa

Summary The growth of two strains ofPseudomonas aeruginosa in stirred batch cultures was monitored by optical density, DNA concentration, and acridine orange direct cell count measurements. Growth of adherent bacteria in pure culture was also observed on suspended glass discs by light and scanning electron microscopy. Strain MUCOID produced significant numbers of filamentous cells in broth culture and in the adherent population, while strain PAO 381 did not produce elongated cells. Filamentous growth of MUCOID could be prevented by the addition of 5 × 10^–2 M Mg²⁺. However, the addition of 0.66 mM EDTA caused an increased proportion of the population (>50%) of MUCOID cells to become filamentous in broth culture. The results are discussed and related to theories regarding bacterial plasticity, and filamentation of normally bacillary cells.     

Development and proliferation of Trypanosoma musculi in the presence of adherent splenic cells

The development and proliferation of Trypanosoma musculi parasites were studied in vitro in the presence of adherent splenic cells. The parasites grew and proliferated only when attached by their flagellar tips to adherent splenic cells. Analyses of excretory-secretory products of the adherent cells-parasites did not indicate any detectable soluble growth factor that might be responsible for the growth of these trypanosomes. During the proliferation, the kinetoplast migrated toward the nucleus, and once in the vicinity of the nucleus, nuclear division was triggered. The nucleus and kinetoplast divided at the same time Trypanosoma musculi parasites started dividing from their flagellar ends, and daughter cells were formed within 48 hr. In the absence of adherent splenic cells in vitro, the parasites were transformed into round nonviable forms.     

Cellular characteristics of head and neck cancer stem cells in type IV collagen-coated adherent cultures

Although head and neck squamous carcinoma cancer stem cells (HNSC-CSCs) can be enriched in serum-free suspension cultures, it is difficult to stably expand HNSC-CSC lines in suspension due to spontaneous apoptosis and differentiation. Here, we investigated whether HNSC-CSCs can be expanded without loss of stem cell properties by adherent culture methods. Cell culture plates were coated with type IV collagen, laminin, or fibronectin. We examined cancer stem cell traits of adherent HNSC-CSCs grown on these plates using immunocytochemistry for stem cell marker expression and analyses of chemo-resistance and xenograft tumorigenicity. We also assessed the growth rate, apoptosis rate, and gene transduction efficiency of adherent and suspended HNSC-CSCs. HNSC-CSCs grew much faster on type IV collagen-coated plates than in suspension. Adherent HNSC-CSCs expressed putative stem cell markers (OCT4 and CD44) and were chemo-resistant to various cytotoxic drugs (cisplatin, fluorouracil, paclitaxel, and docetaxel). Adherent HNSC-CSCs at the limiting dilution (1000 cells) produced tumors in nude mice. Adherent HNSC-CSCs also showed less spontaneous apoptotic cell death and were more competent to lentiviral transduction than suspended HNSC-CSCs. In conclusion, compared to suspension cultures, adherence on type IV collagen-coated culture plates provides better experimental conditions for HNSC-CSC expansion, which should facilitate various refined cellular studies.     

In Vitro Analysis of Breast Cancer Cell Line Tumourspheres and Primary Human Breast Epithelia Mammospheres Demonstrates Inter- and Intrasphere Heterogeneity

Mammosphere and breast tumoursphere culture have gained popularity as in vitro assays for propagating and analysing normal and cancer stem cells. Whether the spheres derived from different sources or parent cultures themselves are indeed single entities enriched in stem/progenitor cells compared to other culture formats has not been fully determined. We surveyed sphere-forming capacity across 26 breast cell lines, immunophenotyped spheres from six luminal- and basal-like lines by immunohistochemistry and flow cytometry and compared clonogenicity between sphere, adherent and matrigel culture formats using in vitro functional assays. Analyses revealed morphological and molecular intra- and inter-sphere heterogeneity, consistent with adherent parental cell line phenotypes. Flow cytometry showed sphere culture does not universally enrich for markers previously associated with stem cell phenotypes, although we found some cell-line specific changes between sphere and adherent formats. Sphere-forming efficiency was significantly lower than adherent or matrigel clonogenicity and constant over serial passage. Surprisingly, self-renewal capacity of sphere-derived cells was similar/lower than other culture formats. We observed significant correlation between long-term-proliferating-cell symmetric division rates in sphere and adherent cultures, suggesting functional overlap between the compartments sustaining them. Experiments with normal primary human mammary epithelia, including sorted luminal (MUC1⁺) and basal/myoepithelial (CD10⁺) cells revealed distinct luminal-like, basal-like and mesenchymal entities amongst primary mammospheres. Morphological and colony-forming-cell assay data suggested mammosphere culture may enrich for a luminal progenitor phenotype, or induce reversion/relaxation of the basal/mesenchymal in vitro selection occurring with adherent culture. Overall, cell line tumourspheres and primary mammospheres are not homogenous entities enriched for stem cells, suggesting a more cautious approach to interpreting data from these assays and careful consideration of its limitations. Sphere culture may represent an alternative 3-dimensional culture system which rather than universally ‘enriching’ for stem cells, has utility as one of a suite of functional assays that provide a read-out of progenitor activity.     

THE FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF CARTERIA1,2

The fine structure of the flagellar apparatus of 5 species of the green quadriflagellate alga Carteria is described. The 5 species can be morphologically separated into 2 groups on the bases of cell shape and ultrastructure of the pyrenoid and flagellar apparatus. Group I cells are spherical, possess many pyrenoid thylakoids, and retain a flagellar apparatus similar to that of Chlamydomonas reinhardi. The flagellar bases are oriented at approximately 90° to one another, have distal and proximal fibers, and are associated with 4 cruciately arranged microtubule bands. Cells of group II are ellipsoid, possess few pyrenoid thylakoids, and show a complex system of microtubule bands and sigmoid-shaped, electron dense rods which extend between opposite pairs of basal bodies. The basal bodies of group II cells are directed inward in a circular pattern rather than outward as in group I cells. Unlike Chlamydomonas, the distal fiber of the Carteria species is nonstriated. The proximal fiber is striated, and both distal and proximal fibers are composed of 60–80 Å diameter microfibrils.