Virus production with a newly developed microcarrier system

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

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

Development of 3D Lymph Node Mimetic for Studying Prostate Cancer Metastasis

Lymph node (LN) metastasis causes poor prognosis for patients with prostate cancer (PCa). Although LN-cells and cellular responses play a pivotal role in cancer metastasis, the interplay between LN-cells and PCa cells is undetermined due to the small size and widespread distribution of LNs. To identify factors responsible for LN metastasis, a 3D cell culture biosystem is fabricated to simulate LN responses during metastasis. First, it is determined that LN explants previously exposed to high metastatic PCa release substantially more chemotactic factors to promote metastatic PCa migration than those exposed to low-metastatic PCa. Furthermore, T-lymphocytes are found to produce chemotactic factors in LNs, among which, CXCL12, CCL21, and IL-10 are identified to have the most chemotactic effect. To mimic the LN microenvironment, Cytodex beads are seeded with T cells to produce a LN-mimetic biosystem in both static and flow conditions. As expected, the flow condition permits prolonged cellular responses. Interestingly, when PCa cells with varying metastatic potentials are introduced into the system, it produces PCa-specific chemokines accordingly. These results support that the LN mimetic helps in analyzing the processes underlying metastasized LNs and for testing various treatments to reduce cancer LN metastasis.

Cell confluency analysis on microcarriers by micro-flow imaging

The productivity of cell culture-derived vaccines grown in anchorage-dependent animal cells is limited by bioreactor surface area. One way to increase the available surface area is by growing cells as monolayers on small spheres called microcarriers, which are approximately 100-250 μm in diameter. In order for microcarrier-based cell culture to be a success, it is important to understand the kinetics of cell growth on the microcarriers. Micro-flow imaging (MFI) is a simple and powerful technique that captures images and analyzes samples as they are drawn through a precision flow cell. In addition to providing size distribution and defect frequency data to compare microcarrier lots, MFI was used to generate hundreds of images to determine cell coverage and confluency on microcarriers. Same-day manual classification of these images provided upstream cell culture teams with actionable data that informed in-process decision making (e.g. time of infection). Additionally, an automated cell coverage algorithm was developed to increase the speed and throughput of the analyses.

Serial propagation of mammalian cells on microcarriers

For the large-scale operation of microcarrier culture to be successful, a technically feasible method for sequential inoculation is essential. Using human foreskin fibroblasts, FS-4, we have achieved this by detaching cells viably from microcarriers employing a selection pH trypsinization technique. Cells thus detached are able to reattach to microcarriers and grow normally after subsequent reinoculation into new cultures. However, after reinoculation cells attach to new microcarriers at a higher rate than to used microcarriers on which cells have previously grown. The effect of this differential cell attachment was analyzed and overcome by employing a low inoculum concentration. FS-4 cells could thus be serially propagated on microcarriers and subsequently used for beta-interferon production. This technique has also been applied to the cultivation of a monkey kidney cell line, Vero. We have also shown that Vero cells directly inoculated from a seed microcarrier culture could be used for virus production.

Production of high titre disabled infectious single cycle (DISC) HSV from a microcarrier culture

Disabled Infectious Single Cycle (DISC) HSV-2 has been cultured in the complimentary cell line CR2 to provide high titre bulk material suitable for the purification of the virus as a live viral vaccine. CR2 cells are cultured on the microcarrier Cytodex-1 at 5 g l-1 in small scale (1 l) and larger scale (15 l) reactors. The cells are infected at an MOI of 0.01 pfu cell-1 and the culture harvested 60–72 h later. The infected cells are removed from the microcarriers by the addition of a hypotonic saline and the virus released by low-pressure disruption techniques. Virus titres achieved are compared to the standard roller bottle process. The resulting material is the starting point for the purification of the DISC-HSV virus.

Attachment and growth of anchorage-dependent cells on a novel, charged-surface microcarrier under serum-free conditions

The present study describes a novel microcarrier substrate consisting of a swellable, copolymer of styrene and divinylbenzene, derivatized with trimethylamine. The co-polymer trimethylamine microcarriers support the growth of a number of different cell lines - Madin Darby Bovine Kidney, Madin-Darby Canine Kidney, Vero and Cos-7 - under serum-free conditions, and human diploid fibroblasts in serum-containing medium. Cells attach to the co- polymer trimethylamine microcarriers as rapidly as they attach to other charged-surface microcarriers (faster than they attach to collagen-coated polystyrene microcarriers) and spread rapidly after attachment. All of the cells examined grow to high density on the co- polymer trimethylamine microcarriers. Furthermore, cells are readily released from the surface after exposure to a solution of trypsin/EDTA. In this respect, the co-polymer trimethylamine microcarriers are different from other charged-surface microcarriers. Madin-Darby Bovine Kidney cells grown on this substrate support production of vaccine strain infectious bovine rhinotracheitis virus as readily as on other charged-surface or collagen-coated microcarriers. Thus, the co-polymer trimethylamine microcarriers combine the positive characteristics of the currently available charged-surface and adhesion-peptide coated microcarriers in a single product. The viral vaccine production industry is undergoing considerable change as manufacturers move toward complete, animal product-free culture systems. This novel substrate should find application in the industry, especially in processes which depend on viable cell recovery.

Development of a suspension packaging cell line for production of high titre, serum-resistant murine leukemia virus vectors

To date, only adherent cell lines have been used for the generation of packaging cells for the production of type C retrovirus vectors. The large-scale production of high titre retrovirus vectors could benefit from the development of packaging cells growing in suspension. Here, we describe the ability of two different lymphoid cell lines, one B- and one T-lymphoblastoid cell line (Namalwa and CEM, respectively), to produce MLV-based vectors. Upon transfection with a third generation packaging construct, the virus particle production by Namalwa cells was characterised by low RT-activity, and by CEM cells as high RT activity as previously established adherent packaging cells. An amphotropic packaging cell line (CEMFLYA) was therefore established from CEM cells. Upon introduction of a lacZ vector genome, the novel packaging cell line produced vector particles routinely in the region of 10(7) infectious units/ml. The vectors were helper-free and highly stable in fresh human serum. The potential for scaled up vector production was demonstrated by continuous culture of the new packaging cells for 14 days in a 250 ml spinner flask. These suspension packaging cells should be applicable to large bioreactor systems to bulk produce high titre, complement-resistant retrovirus vectors for gene therapy.

Expression of plasminogen activator and plasminogen activator inhibitor mRNA in human fibroblasts grown on different substrates

mRNA levels for urokinase type plasminogen activator (uPA), tissue type plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1) and plasminogen activator inhibitor-2 (PAI-2) were examined in human diploid (neonatal foreskin) fibroblasts grown in 200-ml microcarrier suspension culture. Four different substrates were used. These included gelatin-coated polystyrene plastic, DEAE-dextran, glass-coated polystyrene plastic and uncoated polystyrene plastic. Our previous studies have shown that culture fluids from diploid fibroblasts grown on DEAE-dextran contained higher levels of plasminogen-dependent fibrinolytic activity than culture fluids from the same cells grown on other substrates. The increased plasminogen activator activity was due largely to elevated amounts of tPA (In Vitro Cell. Develop. Biol. 22: 575-582, 1986). The present study shows that there is a corresponding elevation of tPA mRNA in diploid fibroblasts cultured on DEAE-dextran relative to the other substrates. There does not appear to be any difference in uPA mRNA or in mRNA for PAI-1 or PAI-2 produced by the same cells on the four substrates. These data suggest that the influence of the substrate on plasminogen activator production is mediated at the genetic level.

Use of recombinant and synthetic peptides as attachment factors for cells on microcarriers

Polystyrene culture dishes and polystyrene microcarriers were coated with Pronectin-F and poly-L-lysine (polylysine), either alone or in combination. Pronectin-F is a recombinant peptide containing repeats of the RGD cell-attachment sequence from fibronectin. Polylysine is a polymer of L-lysine. Pronectin-F supported attachment of Madin-Darby Canine Kidney (MDCK) cells at concentrations as low as 0.025 micrograms/cm2 of surface area. The cells rapidly spread after attachment. Polylysine at concentrations of 0.05-0.5 micrograms/cm2 also supported cell attachment but cells did not rapidly spread after attachment to this substrate. Higher concentrations of polylysine could not be used because of toxicity. When the two peptides were used in conjunction, MDCK cells attached and spread at lower peptide concentrations than they did when either substrate was used alone. These findings suggest that recombinant Pronectin-F alone or in conjunction with a cationic polymer could be a useful replacement for materials such as gelatin or collagen which are currently used as microcarrier surfaces.

Evaluation of a microcarrier process for large-scale cultivation of attenuated hepatitis A

Microcarrier culture was investigated for the propagation of attenuated hepatitis A vaccine in the anchorage-dependent human fibroblast cell line, MRC-5. Cells were cultivated at 37 degrees C for one to two weeks, while virus accumulation was performed at 32 degrees C over 21 to 28 days. The major development focus for the microcarrier process was the difference between the cell and virus growth phases. Virus antigen yields, growth kinetics, and cell layer/bead morphology were each examined and compared for both the microcarrier and stationary T-flask cultures. Overall, cell densities of 4-5 x 10(6) cells/ml at 5-10 milligrams beads were readily attained and could be maintained in the absence of infection at either 37 degrees C or 32 degrees C. Upon virus inoculation, however, substantial cell density decreases were observed as well as 2.5 to 10-fold lower per cell and per unit surface area antigen yields as compared to stationary cultures. The advantages as well as the problems presented by the microcarrier approach will be discussed.

High density microcarrier culture with a new device which allows oxygenation and perfusion of microcarrier cultures

A novel system useful for aeration and cell retention in continuous perfused microcarrier cultures is described. The system is based on a vibrating cage that separates cells and microcarriers from the oxygenation chamber and allows gas bubble free oxygen transfer. In the cultivation of monkey kidney cells (VERO) on gelatin coated microcarriers, using different concentrations (5, 10 and 15 g Cytodex 3/liter) cell densities up to 10(7) cells per ml were obtained. The described system is scaleable.

The effect of substrate on the production of infectious virus by cells in culture

Herpes simplex virus type I (HSV-1), infectious bovine rhinotracheitis virus (IBR) and turkey herpesvirus were examined for growth in cells cultured on three different substrates. The substrates were glass, DEAE-dextran and collagen gel. With two of the viruses, HSV-1 and IBR, there were no apparent differences in production as a function of substrate. In contrast, the amount of the turkey herpesvirus which was recovered varied greatly with the substrate. Titers were highest on glass, followed by DEAE-dextran and then collagen gel. Our previous studies have indicated that the substrate on which anchorage-dependent cells are grown in vitro has an affect on a number of biological and biochemical properties. The present study indicates that the production of commercially important biologicals can be affected by the substrate.

Proteolytic enzymes and arachidonic acid metabolites produced by MRC-5 cells on various microcarrier substrates

Human diploid fibroblasts were cultured on microcarriers made from DEAE-dextran, denatured collagen, DEAE-dextran linked to denatured collagen, and glass. Cells grown on these four substrates were examined for the production of proteolytic enzymes and arachidonic acid metabolites. Culture fluids from cells grown on the DEAE-dextran microcarriers contained the highest amounts of proteolytic enzyme activity. Both plasminogen-independent and plasminogen-dependent fibrinolytic activities were present and the plasminogen-dependent activity seemed to result from the presence of both urokinase and tissue plasminogen activator. Culture fluid from the cells grown on the glass microcarriers contained the least amount of protease activity, and nearly all of the plasminogen-activator activity seemed to be of the urokinase type. Protease activity in the culture fluids of cells grown on the other two substrates were intermediate. With regard to arachidonic acid metabolites, cells grown on the DEAE-dextran microcarriers produced the highest amounts of cyclooxygenase products but very low levels of lipoxygenase metabolites. Cells grown on the other three substrates produced comparable amounts of various cyclooxygenase products (lower than that produced by cells on the DEAE-dextran substrate). Cells grown on the glass microcarriers also produced detectable amounts of two lipoxygenase metabolites--leukotriene B4 and leukotriene C4. Inasmuch as both proteolytic enzymes and arachidonic acid metabolites regulate basic cell properties, the differential amounts of these metabolites observed in the culture fluids on the various substrates may contribute to the biological differences that exist on these substrates.

Substrate-dependent differences in growth and biological properties of fibroblasts and epithelial cells grown in microcarrier culture

Normal diploid human fibroblasts and first passage monkey kidney epithelial cells were examined for growth and metabolic activity on microcarriers made from glass and on microcarriers made from DEAE-dextran. The cells grew to a higher density (cells cm2 of surface area) on the glass microcarriers made from glass and on microcarriers made from DEAE-dextran. The cells grew to a higher density (cells/cm2 of surface area) on the glass microcarriers than they did on the DEAE-dextran microcarriers and morphological differences were observed between the cells growing on the two substrates. On the DEAE-dextran microcarriers, the cells were much more resistant to protease-mediated detachment than were the cells on the glass microcarriers. In these respects, the cells grown on the glass microcarriers were similar to cells grown in conventional monolayer culture. Interestingly, the cells grown on the DEAE-dextran microcarriers expressed higher levels of proteolytic enzyme activity than the cells grown on the glass microcarriers. Substrate-dependent differences in prostaglandin production also occurred--both in unstimulated cells and in cells stimulated with 12-0-tetradecanoyl phorbol acetate. The unstimulated cells on the glass microcarriers produced slightly higher levels of three different prostaglandins than did the cells on the DEAE-dextran microcarriers. However, after stimulation the levels were much higher in the DEAE-dextran microcarrier cultures than in the glass microcarrier cultures. In contrast to these results, there was no significant, substrate-dependent difference in the production of infectious herpes simplex virus. Taken together, these findings suggest that when commercially-useful cells such as normal fibroblasts and epithelial cells are grown in large quantities on microcarriers, the nature of the substrate may have a profound effect on the growth and physiology of the cells. They also suggest that when microcarriers are used, unexpected results based on preliminary work in conventional monolayer culture may be obtained.

A microcarrier cell culture system for large scale production of hepatitis A virus

Hepatitis A virus (HAV) was isolated from human faeces using a fetal rhesus monkey kidney cell line (Frhk-4). Infectious medium from passage 12 was used to inoculate a large (5000 cm2) microcarrier cell culture maintained in suspension. The microcarriers used were swollen, collagen-coated dextran beads on which it was easy to propagate Frhk-4 cells. Intra- and extra-cellular virus levels were assayed and compared with conventional cultures in 25 cm2 plastic flasks. The results show that virus production per cell was similar in both systems. The number of cells per area unit in confluent cultures was initially lower in the microcarrier culture but subsequently increased. Two to three weeks post inoculation the virus yield per area unit in the microcarrier system was half of that of the conventional culture. The lower cell density per area unit in the microcarrier system was compensated by the large growth area that could be maintained in a single vessel and the total production of virus was substantial. Weekly harvests of medium with HAV antigen titres around 10(-2) contained antigenic material sufficient for several thousands of anti-HAV IgM tests. Propagation of HAV in microcarrier cell cultures thus seems a safe and simple way to produce large amounts of HAV.

Selection of mitotic Chinese hamster ovary cells from microcarriers. Cell cycle-dependent induction of mutation by 5-bromo-2'-deoxyuridine and ethyl methanesulfonate

Large quantities of mitotic cells may be collected by mitotic detachment from a population of Chinese hamster ovary cells growing on positively charged dextran microcarriers in suspension culture. Exponentially growing cells are treated for 2.5 h with colcemid and mitotic cells are detached from the microcarriers by increasing the stirring speed. A yield of 4-6% of the total population is obtained and, of the cells collected, 85-95% are arrested in metaphase. Using this means to synchronize cells we have determined the cell cycle dependence of the toxic and mutagenic effects of 5-bromo-2'-deoxyuridine (BUdR) and ethyl methanesulfonate (EMS). Mutation was measured at two independent loci: resistance to 6-thioguanine and resistance to ouabain. Both mutagens were more toxic during S phase as compared to G1 or G2 or mitosis. BUdR induced significant mutation only during S phase. The maximum induction of 6-thioguanine resistance was observed in cultures treated 10 h after plating of mitotic cells (2 h into S phase), while the maximum induction of ouabain resistance was observed in cultures treated 10-12 h after plating of mitotic cells (2-4 h into S phase). EMS induced significant mutation at all points in the cell cycle. Mutation induction reached a minimum during S phase but the magnitude of difference between any two points in the cell cycle was found to be less than two-fold.

Growth of anchorage dependent mammalian cells on glycine-derivatized polystyrene in suspension culture

Glycine-derivatized polystyrene beads were prepared and used as microcarriers to grow normal cells of human embryonic kidney, rhesus monkey kidney, an human foreskin fibroblasts in suspension cultures. Growth of the cells on polystyrene beads derivatized with other amino acids, peptides, and carboxylic acids also was investigated.

Cell growth optimization in microcarrier culture

Three monkey kidney cell lines and primary chicken embryo cells were grown in microcarrier culture. The carrier support was DEAE-Sephandex gel beads at low anion exchange capacity prepared according to a protocol developed at the Massachusetts Institute of Technology. The growth rate of the cells and the final cell density in microcarrier culture was dependent on the concentration of the beads in culture and on the size of the initial cell inoculum. A bead concentration of 1.0 to 2.0 mg of beads/ml of tissue culture medium and a cell inoculum of 20,000 cells/cm2 of bead surface appeared to be optimal. The efficiency of the microcarrier culture system was compared to that of stationary and roller bottle cultures. Stationary flasks gave cell densities about twofold higher than maximal densities in roller bottles and about threefold and twofold higher than cell densities in microcarrier culture at a bead concentration of 2.5 and 1.0 mg/ml, respectively. In terms of cell yield per milliliter of tissue culture medium, the microcarrier culture was superior to roller bottle and stationary cultures. An advantage of the microcarrier culture system is its suitability for scale up into large volume production units.

Examination of parameters affecting human interferon production with microcarrier-grown fibroblast cells

Various parameters were examined for their effects on interferon production with human fibroblast cells (FS-4) grown on microcarriers, using a superinduction procedure. Optimal concentrations of cycloheximide and actinomycin D during induction were 10 micrograms/ml, respectively. Cells required 5 to 6 h of exposure to cycloheximide and at least 2 h of exposure to actinomycin D to achieve maximum yields. FS-4 cells were found to grow well at low serum concentrations (2.5 and 5%) and actually produced higher yields of interferon than cells grown at higher serum concentration (10 and 20%). Kinetics of interferon production at various temperatures revealed that significantly higher yields could be obtained at 34 degrees C than at either 37 or 30 degrees C. Priming cells for 16 h with 50 U of interferon per ml resulted in consistently higher yields of interferon. By modifying the superinduction procedure in accordance with the above findings, it is now possible to consistently obtain interferon yields of greater than 20,000 international units per 10(6) cells.

Feasibility studies of oncornavirus production in microcarrier cultures

Studies conducted with virus-infected monolayer cell cultures have demonstrated the feasibility of producing several tumor-associated viruses in microcarrier (mc) cultures (Sephadex G50 beads treated with DEAE-chloride). The efficiency of cell adherence to mc varied with the cell type, the pH of the growth medium, and the stirring force applied to keep the mc in suspension. Most cells attached firmly to the mc and could not be removed easily with routine trypsinization procedures. Techniques using Enzar-T and Pronase were effective in detaching cells from mc in 10 to 15 min while retaining 95% cell viability. After detachment, Ficoll gradients were used for rapid and complete separation of viable cell suspensions from the mc. Retrovirus production in large volumes of mc cultures was investigated with periodic harvesting of growth fluids. Physical, biochemical, and biological properties of the Mason-Pfizer monkey virus and the RD114 virus recovered from the mc cultures were identical to those produced in conventional cultures. The utilization of mc has several applications in research and short-term cultures, but the as-yet-unsolved technical problems met were found to be serious limitations when attempting mass cell culturing on a long-term basis.

Growth of Fish Cell Lines on Microcarriers

Microcarrier beads were evaluated as substrates for the propagation of five anchorage-dependent fish cell lines. Growth of rainbow trout gonad (RTG-2) and Atlantic salmon cells was limited on microcarriers maintained in suspension. However, stationary microcarriers were suitable substrates for the growth of RTG-2, AS, Chinook salmon embryo (CHSE-214), and fathead minnow cells. Cell yields ranged from 2 × 10 6 to 2.9 × 10 6 cells per ml, representing 7- to 10-fold increases over the initial cell concentrations. The yield of new RTG-2 cells per unit volume of growth medium was 2.8 times greater in microcarrier cultures than in standard monolayer cultures. Northern pike cells failed to grow on microcarriers. Yields of infectious pancreatic necrosis virus propagated in microcarrier cultures of RTG-2 cells were more than twice the yields in standard monolayer cultures. The greater economy of microcarrier cultures in terms of growth vessel and medium requirements holds great promise for the large-scale production of anchorage-dependent fish cell cultures and fish viruses.

Production of cells and viruses in a new multiple-tube tissue culture propagator

A novel method for large-scale culture of anchorage-dependent cells is described. Culture vessels were constructed by using roller bottles and Pyrex tubing. Parallel glass tubes, equally spaced by silicone rings and inserted into the roller bottles, provided an increased culture area. The roller bottles were fitted with a second opening for medium recirculation. Culture vessels of 1,000-, 4,000-, 8,000- and 16,000-cm2 growth area were constructed to propagate Vero, BS-C-1, primary chicken embryo, and IMH-P cells. These cultured cells were used to efficiently produce several viruses: rubella virus, measles virus, poliovirus, cytomegalovirus, and herpesvirus of turkey.

Human interferon production with diploid fibroblast cells grown on microcarriers

A variety of diploid human fibroblast lines have been successfully grown to high densities (greater than 10(6) cell/ml) on recently developed microcarriers. Interferon induction using poly I.poly C and a superinduction procedure resulted in yields greater than 10,000 units/ml with one cell line. A direct comparison of microcarrier cultures to roller bottle cultures showed equivalent interferon yields on a per cell basis and some apparent differences relating to optimum inducer concentrations and kinetics of interferon accumulation.