Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N7/00—Viruses; Bacteriophages; Compositions thereof; Preparation or purification thereof
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M25/00—Means for supporting, enclosing or fixing the microorganisms, e.g. immunocoatings
  • C12M25/14—Scaffolds; Matrices
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12M—APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS
  • C12M47/00—Means for after-treatment of the produced biomass or of the fermentation or metabolic products, e.g. storage of biomass
  • C12M47/10—Separation or concentration of fermentation products
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
  • C12N2770/00—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA ssRNA viruses positive-sense
  • C12N2770/00011—Details
  • C12N2770/24011—Flaviviridae
  • C12N2770/24111—Flavivirus, e.g. yellow fever virus, dengue, JEV
  • C12N2770/24151—Methods of production or purification of viral material

Definitions

• Cell culturing is an essential step in manufacturing biological products such as, for example, nucleic acids, viruses for use in vaccines, antibodies, and proteins, for example, interferons.
• biological products such as, for example, nucleic acids, viruses for use in vaccines, antibodies, and proteins, for example, interferons.
• Anchorage-dependent cells such as certain animal cells, need to attach to a surface in order to grow and divide.
• microcarriers provide the large surface area needed for growing anchorage-dependent cells. Van Wezel, in 1967, described the use of microcarriers, small beads or particles approximately 0.2 mm in diameter, for growing such cells. Using gentle agitation, the microcarriers to which the cells will attach are suspended in a liquid culture medium within a bioreactor.
• the process may begin with the addition of cells (the inoculum) to the liquid culture medium in which the microcarriers are suspended.
• the culture medium contains the nutrients essential for metabolism and growth of the cells. Conditions of temperature, pH, and oxygen concentration are controlled to promote cell growth and division in order to increase cell density and confluence.
• Continuous or Perfusion Mode In a continuous or perfusion mode, nutrients are continuously added to the system, and product is harvested throughout the culture period. With the continuous mode, the on-going difficulty in obtaining sufficiently high product titers is well recognized. In addition to the low titer issue, there is a need to concentrate product of the continuous mode. These problems have a direct impact on production time and cost, and make the continuous mode less feasible at least for vaccine production.
• Batch Mode In a batch mode, all nutrients are added at the beginning and products are not removed until the end of the batch. Waste products accumulate during the run, and nutrients are used up, making the batch process inefficient for many applications.
• a fed-batch mode is similar to the batch mode in that products are removed only at the end of the run, but differs in that nutrients are added at multiple intervals during the process. Most virus-producing, microcarrier cultures are carried out, post infection, in a fed-batch process. In the fed-batch mode, there is also an increase in waste products and other contaminants, such as host cell protein and host cell DNA, and dead cells falling off of the microcarriers.
• the inventors of the present subject matter have now discovered a new method of harvest and re-feed for culturing, post infection, virus-producing cells on a scaffold such as a microcarrier, a method that significantly increases product titer while reducing the concentration of contaminants in the culture.
• the disclosed “semi-harvest and re-feed method, also referred to herein as the “drain down and re-feed method,” and the “harvest and re-feed method,” is also applicable to the culturing of other product-secreting cells on a scaffold, for example a microcarrier, to harvest diverse products, such as antibodies, proteins, hormones, peptides and growth factors.
• An example of a protein product is an interferon.
• the invention inter alia, includes the following, alone or in combination.
• the present invention relates to a method of increasing product yield per culture in a population of product-secreting cells bound to a scaffold at least partially immersed in an original volume of a culture medium in a bioreactor, the method comprising: semi-harvesting product by removing from the bioreactor a first portion of the original volume of the culture medium with a first-secreted product concentration from the bioreactor while leaving the scaffold with the bound population of product-secreting cells in the bioreactor; re-feeding the bound population of product-secreting cells by adding to the bioreactor an amount of a fresh culture medium sufficient to increase the volume of the culture medium in the bioreactor to approximately the original volume of the culture medium; agitating the culture medium in the bioreactor under sufficient conditions and for a sufficient time period to allow the bound population of product-secreting cells to grow and to release a second-secreted product concentration into the culture medium; and harvesting product by removing from the bioreactor at least a portion of the culture medium with the second-secreted product concentration
• the present invention relates to a method for increasing virus yield per culture in a population of virus-infected cells bound to a microcarrier suspended in an original volume of a culture medium in a bioreactor, the method comprising: semi-harvesting virus by removing from the bioreactor a first portion of the original volume of the culture medium with a first-shed virus while leaving the microcarrier with the bound population of virus-infected cells and a remaining volume of the culture medium in the bioreactor; re-feeding the bound population of virus-infected cells by adding to the bioreactor an amount of a fresh culture medium sufficient to increase the remaining volume of the culture medium in the bioreactor to approximately the original volume of the culture medium; agitating the culture medium and the microcarrier with the bound population of virus-infected cells under sufficient conditions and for a sufficient time period to allow the virus to continue to infect the bound population of virus-infected cells and to allow the bound population of virus-infected cells to release a second-shed virus into the culture medium
• Another embodiment of the invention is a method of increasing virus yield per culture in cells growing on a conditioned microcarrier in a bioreactor, the method comprising: transferring a plurality of seed cells into the bioreactor containing the conditioned microcarrier and an original volume of a culture medium, to form in the bioreactor a mixture comprising the seed cells, the culture medium, and the microcarrier; agitating the mixture in the bioreactor at a sufficient rate of agitation and for a sufficient time to allow the seed cells to bind to the microcarrier; cultivating the seed cells bound to the microcarrier under sufficient conditions and for a sufficient time period for the seed cells to form a bound cell population that is from about 35 percent to about 95 percent confluent on the microcarrier; removing from the bioreactor from about 30 percent to about 88 percent of the original volume of the culture medium in the bioreactor, while leaving the microcarrier with the bound cell population in the bioreactor, to form a first reduced volume of culture medium; infecting the bound cell population with a
• the invention also relates to a method of increasing virus yield per culture in cells growing on a conditioned microcarrier in a bioreactor, the method comprising: transferring a plurality of seed cells into the bioreactor containing a microcarrier and an original volume of a culture medium; cultivating the seed cells to bind to the microcarrier and form a bound cell population that is from about 35 percent to about 95 percent confluent on the microcarrier; removing from the bioreactor from about 30 percent to about 88 percent of the original volume of the culture medium in the bioreactor, while leaving the microcarrier with the bound cell population in the bioreactor, to form a first reduced volume of culture medium; infecting the bound cell population with a virus, which can optionally be a flavivirus; adding fresh culture medium to the bioreactor to maintain the bound cell population; culturing the bound cell population for a sufficient time period to allow the infected, bound cell population to release a shed virus concentration into the culture medium in the bioreactor; and harvesting virus by removing from
• methods of increasing virus yield per culture in cells growing in a bioreactor comprising the steps of: transferring a plurality of seed cells into the bioreactor containing a support substrate, such as conditioned microcarriers, and an original volume of a culture medium, to form in the bioreactor a mixture comprising the seed cells, the culture medium, and the substrate; and cultivating the seed cells bound to the substrate under sufficient conditions and for a sufficient time period for the seed cells to form a bound cell population that is optionally from about 35 percent to about 95 percent confluent on the substrate.
• a support substrate such as conditioned microcarriers, and an original volume of a culture medium
• a bound cell population is formed, from about 30 percent to about 88 percent of the original volume of the culture medium in the bioreactor is removed, while leaving the substrate with the bound cell population in the bioreactor, to form a first reduced volume of culture medium; infecting the bound cell population with a virus; allowing the virus to adsorb to the bound cell population and to infect the bound cell population.
• Fresh culture medium can then be added to the bioreactor and the bound cell population is cultured under sufficient conditions and for a sufficient time period to allow the virus to infect the bound cell population and to allow the infected, bound cell population to release a virus into the culture medium.
• the virus can then be harvested by the above-described drain down and re-feed method or any other known harvesting techniques.
• the present disclosure relates to the production of cells on microcarriers or other structures for cell attachment, the microcarriers suspended in bioreactors, including, for example, spinner flasks, bench top bioreactors, and larger non-disposable and disposable bioreactors.
• the inventors of the present subject matter have now discovered a new method of culturing anchorage-dependent cells on a scaffold, a method that addresses the potential problem of metabolite depletion and waste product build-up and which provides increased product titer within a given time period as compared to the amount of product titer achieved within the same time period using the fed-batch process.
• suspension cultures are maintained in serum free media.
• the disclosed method provides for a supply of specific nutrients, growth factors, lipids, amino acids, vitamins, salts, and trace metals by increasing their relative concentration during culture to an optimal level, and removing contaminants, thus improving not only the cell growth rates, but also culture density, specific productivity and/or specific product quality and concentration.
• An embodiment of the invention provides a “drain-down” or “semi-harvest and re-feed” step that significantly reduces the concentration of metabolic waste products and cellular byproducts such as host cell protein and host cell DNA.
• Host cell protein and host cell DNA are contaminants that interfere with production of a virus for use in a vaccine, for example.
• the drain-down step can remove a large portion of the contaminated culture medium, and the re-feed step replenishes the nutrient-depleted, contaminated culture medium by adding fresh medium.
• the invention provides for the use of a harvest or semi-harvest and re-feed of an infected attachment culture, including, but not limited to virus-producing microcarrier cultures, in order to increase virus titer, for example.
• the invention provides for increasing product yield per culture in a population of product-secreting cells bound to a scaffold.
• Disclosed herein is a method for sterilely removing a volume of the conditioned culture medium, for example, the removal of about seventy-five percent (75%) of the culture medium, while retaining in the bioreactor the total cell population bound to a microcarrier. This semi-harvest is followed by replacement with an equal volume of fresh culture medium. The culturing process is allowed to continue.
• “semi-harvest” and “harvest” have substantially the same meaning and are sometimes used interchangeably. “Semi-harvest” is often used to denote a step in which the culture medium is drained down, for example, using a sieve, to collect the virus that was shed into the culture medium during an early phase of the culturing process. “Harvest” is generally used herein to denote the final drain-down of the culture medium to collect the virus shed during a later phase of the culturing process. The final harvest is typically done when the cytopathic effect (CPE) is from about 60 percent to about 90 percent, or at about 80 percent. As the terms are used herein, a “liter” is denoted by “L” and a milliliter or cubic centimeter is denoted by “ml”.
• One embodiment of the present invention relates to a method of increasing product yield per culture in a population of product-secreting cells bound to a scaffold immersed in a culture medium in a bioreactor.
• the scaffold can optionally be a microcarrier, such as microcarrier beads.
• the method includes: semi-harvesting the product by removing a first portion of the culture medium which includes a first-secreted product concentration, while leaving the scaffold with the bound population of product-secreting cells behind in the bioreactor; then re-feeding the bound population of product-secreting cells by adding fresh culture medium in an amount sufficient to increase the volume of the culture medium to approximately the original volume of the culture medium.
• the culture medium in the bioreactor is agitated under sufficient conditions and for a sufficient time period to allow the bound population of product-secreting cells to grow and to release a second-secreted product concentration into the culture medium.
• the product is harvested by removing from the bioreactor at least a portion of the culture medium with the second-secreted product concentration from the bioreactor while leaving the scaffold with the bound population of product-secreting cells in the bioreactor.
• Another embodiment of the present invention is a method for increasing virus yield per culture in a population of virus-infected cells bound to a microcarrier suspended in an original volume of a culture medium in a bioreactor.
• This embodiment of the method includes: semi-harvesting virus by removing a first portion of the original volume of the culture medium with a first-shed virus while leaving the microcarrier with the bound population of virus-infected cells and a remaining volume of the culture medium in the bioreactor; then re-feeding the bound population of virus-infected cells by adding to the bioreactor an amount of a fresh culture medium sufficient to increase the remaining volume of the culture medium in the bioreactor to approximately the original volume of the culture medium; then agitating the culture medium and the microcarrier with the bound population of virus-infected cells under sufficient conditions and for a sufficient time period to allow the virus to continue to infect the bound population of virus-infected cells and to allow the infected, bound population of virus-infected cells to release a second-shed virus into
• in yet another embodiment is a method of increasing virus yield per culture in cells growing on a conditioned microcarrier in a bioreactor, the method including: transferring a plurality of seed cells into the bioreactor containing the conditioned microcarrier and an original volume of a culture medium.
• the bioreactor at this point contains a mixture comprising the seed cells, the culture medium, and the microcarrier.
• the mixture in the bioreactor is agitated at a sufficient rate and for a sufficient time to allow the seed cells to bind to the microcarrier.
• the bound seed cells are cultivated under sufficient conditions and for a sufficient time period for the seed cells to form a bound cell population that is from about 35 percent to about 95 percent confluent on the microcarrier.
• a drain-down or semi-harvest is performed, thereby removing from the bioreactor from about 30 percent to about 88 percent of the original volume of the culture medium in the bioreactor, while leaving the microcarrier with the bound cell population in the bioreactor.
• the bound cell population is infected with a virus, which is allowed to adsorb to the bound cell population and to infect the bound cell population.
• the bound cell population including the virus adsorbed thereto is re-fed with fresh medium, by adding first amount of a fresh culture medium sufficient to increase the first reduced volume of the culture medium in the bioreactor to approximately the original volume of the culture medium.
• the culture medium and the microcarrier with the bound cell population is agitated under sufficient conditions and for a sufficient time period to allow the virus to infect the bound cell population and to allow the infected, bound cell population to release a first-shed virus into the culture medium.
• the virus is then semi-harvested by removing from the bioreactor a portion of the culture medium with the first-shed virus, the portion of the culture medium removed equal to from about 50 percent to about 90 percent of the original volume of the culture medium, while leaving the microcarrier with the infected, bound cell population, and a second reduced volume of the culture medium in the bioreactor. Then the bound cell population is re-fed by adding a second amount of a fresh culture medium sufficient to increase the second reduced volume of the culture medium in the bioreactor to approximately the original volume of the culture medium.
• Agitating the culture medium and the microcarrier with the bound cell population is continued under sufficient conditions and for a sufficient time period to allow the virus to continue to infect the bound cell population and to allow the infected, bound cell population to release a second-shed virus into the culture medium in the bioreactor. Finally, the virus is harvested by removing the culture medium with the second-shed virus while leaving the microcarrier with the infected, bound cell population in the bioreactor.
• the semi-harvesting of the virus may comprise removing about 75 percent of the culture medium with the first-shed virus from the bioreactor.
• the bioreactor may be, for example, a disposable or a non-disposable bioreactor having a volume of from about 25 liters to about 200 liters.
• bioreactor is chosen from a bench-top bioreactor and a spinner flask.
• the cells cultured are VERO cells.
• virus as used herein is intended to cover not only complete infectious viral particles but also any other secreted products that can be used to immunize a subject, including for example, attenuated viruses, genetically engineering viruses that are defective, e.g., in their envelope, nucleocapsid, or genome, viral fragments and any other viral derivatives suitable for use in vaccines or screening assays.
• the virus is a Flavivirus.
• Flaviviruses include: St. Louis encephalitis, Japanese encephalitis, tick-borne encephalitis viruses, dengue virus, Kyasanur Forest disease virus, and Yellow Fever virus.
• SUMMARY Using a 10 L New Brunswick (NBS) benchtop bioreactor operating at 8 L culture volume with 5 g/L microcarriers, we prepared HYPERFLASK® (CORNING®, Corning N.Y.) seed cultures and the benchtop bioreactor; performed infection, semi-harvest and re-feed on the bioreactor.
• NBS New Brunswick
• HYPERFLASK® CORNING®, Corning N.Y.
• Example 1 test run of the disclosed drain-down and re-feed method as performed in a 10 Liter bench top bioreactor are shown in the Table below.
• the Table shows the viral count in plaque forming units (PFU) at Time zero at 2.50E+02, and reaching a peak of 1.15E+08 at 48 hours, then decreasing to 1.01E+07 at 96 hours. The best time to harvest would have been at the peak titer, reached at 48 hours.
• PFU plaque forming units
• the microcarriers In subsequent cultures utilising the disclosed method, we typically seeded the microcarriers at from about 4E+05 VC/ml to about 6E+05 VC/ml. We then typically infected at about 48 hours post-seed, when the cells are about 85 percent (85%) confluent. Infection may also be done when the bound cell population is from about 35 percent to about 95 percent confluent on the microcarrier. In one embodiment of the invention, at infection, the concentration of cells is greater than or equal to about 7E5 VC/ml.
• the VERO host cell protein and DNA are also shown in the Table.

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• 2010
  • 2010-07-23 CA CA2769003A patent/CA2769003C/fr active Active
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