Patent Application
20240287431
This disclosure generally relates to cell culture substrates in fixed bed configurations, as well as systems and methods for manufacturing such cell culture substrates. In particular, the present disclosure relates to fixed-bed cell culturing substrates in a rolled configuration with defined zones of controlled and variable porosity, as well as bioreactor systems incorporating such substrates, and methods of manufacturing cell culture substrate.
In the bioprocessing industry, large-scale cultivation of cells is performed for purposes of the production of hormones, enzymes, antibodies, vaccines, and cell therapies. Cell and gene therapy markets are growing rapidly, with promising treatments moving into clinical trials and quickly toward commercialization. However, one cell therapy dose can require billions of cells or trillions of viruses. As such, being able to provide a large quantity of cell products in a short amount of time is critical for clinical success.
A significant portion of the cells used in bioprocessing are anchorage dependent, meaning the cells need a surface to adhere to for growth and functioning. Traditionally, the culturing of adherent cells is performed on two-dimensional (2D) cell-adherent surfaces incorporated in one of a number of vessel formats, such as T-flasks, petri dishes, cell factories, cell stack vessels, roller bottles, and HYPERStack® vessels. These approaches can have significant drawbacks, including the difficulty in achieving cellular density high enough to make it feasible for large scale production of therapies or cells.
Alternative methods have been suggested to increase volumetric density of cultured cells. These include microcarrier cultures performed in stir tanks. In this approach, cells that are attached to the surface of microcarriers are subject to constant shear stress, resulting in a significant impact on proliferation and culture performance. Another example of a high-density cell culture system is a hollow fiber bioreactor, in which cells may form large three-dimensional aggregates as they proliferate in the interspatial fiber space. However, the cells growth and performance are significantly inhibited by the lack nutrients. To mitigate this problem, these bioreactors are made small and are not suitable for large scale manufacturing
Another example of a high-density culture system for anchorage dependent cells is a packed-bed bioreactor system. In this this type of bioreactor, a cell substrate is used to provide a surface for the attachment of adherent cells. Medium is perfused along the surface or through the semi-porous substrate to provide nutrients and oxygen needed for the cell growth. For example, packed bed bioreactor systems that contain a packed bed of support or matrix systems to entrap the cells have been previously disclosed U.S. Pat. Nos. 4,833,083; 5,501,971; and 5,510,262. Packed bed matrices usually are made of porous particles as substrates or non-woven microfibers of polymer. Such bioreactors function as recirculation flow-through bioreactors. One of the significant issues with such bioreactors is the non-uniformity of cell distribution inside the packed bed. For example, the packed bed functions as depth filter with cells predominantly trapped at the inlet regions, resulting in a gradient of cell distribution during the inoculation step. In addition, due to random fiber packaging, flow resistance and cell trapping efficiency of cross sections of the packed bed are not uniform. For example, medium flows fast though the regions with low cell packing density and flows slowly through the regions where resistance is higher due to higher number of entrapped cells. This creates a channeling effect where nutrients and oxygen are delivered more efficiently to regions with lower volumetric cells densities and regions with higher cell densities are being maintained in suboptimal culture conditions.
Another significant drawback of packed bed systems disclosed in a prior art is the inability to efficiently harvest intact viable cells at the end of culture process. Harvesting of cells is important if the end product is cells, or if the bioreactor is being used as part of a “seed train,” where a cell population is grown in one vessel and then transferred to another vessel for further population growth. U.S. Pat. No. 9,273,278 discloses a bioreactor design to improve the efficiency of cell recovery from the packed bed during cells harvesting step. It is based on loosening the packed bed matrix and agitation or stirring of packed bed particles to allow porous matrices to collide and thus detach the cells. However, this approach is laborious and may cause significant cells damage, thus reducing overall cell viability.
An example of a packed-bed bioreactor currently on the market is the iCellis® by produced by Pall Corporation. The iCellis uses small strips of cell substrate material consisting of randomly oriented fibers in a non-woven arrangement. These strips are packed into a vessel to create a packed bed. However, as with similar solutions on the market, there are drawbacks to this type of packed-bed substrate. Specifically, non-uniform packing of the substrate strips creates visible channels within the packed bed, leading to preferential and non-uniform media flow and nutrient distribution through the packed bed. Studies of the iCellis® have noted a “systemic inhomogeneous distribution of cells, with their number increasing from top to bottom of fixed bed,” as well as a “nutrient gradient . . . leading to restricted cell growth and production,” all of which lead to the “unequal distribution of cells [that] may impair transfection efficiency.” (Rational plasmid design and bioprocess optimization to enhance recombinant adeno-associated virus (AAV) productivity in mammalian cells. Biotechnol. J. 2016, 11, 290-297). Studies have noted that agitation of the packed bed may improve dispersion, but would have other drawbacks (i.e., “necessary agitation for better dispersion during inoculation and transfection would induce increased shear stress, in turn leading to reduced cell viability.” Id.). Another study noted of the iCellis® that the uneven distribution of cells makes monitoring of the cell population using biomass sensors difficult (“ . . . if the cells are unevenly distributed, the biomass signal from the cells on the top carriers may not show the general view of the entire bioreactor.” Process Development of Adenoviral Vector Production in Fixed Bed Bioreactor: From Bench to Commercial Scale. Human Gene Therapy, Vol. 26, No. 8, 2015).
In addition, because of the random arrangement of fibers in the substrate strips and the variation in packing of strips between one packed bed and another of the iCellis®, it can be difficult for customers to predict cell culture performance, since the substrate varies between cultures. Furthermore, the packed substrate of the iCellis® makes efficiently harvesting cells very difficult or impossible, as it is believed that cells are entrapped by the packed bed.
While manufacturing of viral vectors for early-phase clinical trials is possible with existing platforms, there is a need for a platform that can produce high-quality product in greater numbers in order to reach late-stage commercial manufacturing scale. As discussed above, existing cell culture platforms rely on adherent cell substrates of random and uncontrolled structure or porosity, resulting in nonuniform and even unpredictable substrate structure and performance due to random packing, channeling effects, cell entrapment, etc. Regardless of whether the packed bed substrate matrix is uniform or random, there can nonetheless be difficulties in controlling fluid flow as desired through the packed bed, which leads to difficulties in various aspects of cell culture, including uniform cell seeding, cell growth distribution, cell culture media flow uniformity, and harvesting capability.
There is a need for packed-bed cell culture matrices, systems, and methods that enable culturing of cells in a high-density format, with uniform cell distribution, easily attainable and increased harvesting yields, and controllable packed-bed porosity for improved seeding, culturing, and/or harvesting performance.
According to an embodiment of this disclosure, a packed-bed bioreactor system for culturing cells is provided. The system includes: a cell culture vessel comprising an inlet, an outlet, and at least one interior reservoir fluidly connected to and disposed in a fluid pathway between the inlet and the outlet; a cell culture matrix disposed in the reservoir in a wound configuration around a winding axis extending in a direction from the inlet to the outlet, the cell culture matrix comprising a structurally defined substrate comprising a substrate material defining a plurality of pores, the substrate material being configured for adhering cells thereto; and a plurality of permeability zones in the cell culture matrix, each of the plurality of permeability zones comprising an opening in the substrate, the opening being larger than a diameter of any of the plurality of pores, wherein the substrate comprises a length extending in a direction tangential to the winding axis and wherein the plurality of permeability zones comprises a variable periodicity along a length of the substrate in the wound configuration. As used herein, “periodicity” refers to the frequency of occurrence, and “variable periodicity” refers to a change in the frequency of the occurrence over a distance or length of the substrate. For example, the plurality of permeability zones having a variable periodicity along a length of the substrate refers to the frequency of permeability zones changing along a length of the substrate, or the density of permeability zones in terms of number of permeability zones per unit length of the substrate changing along the length of the substrate. An increasing periodicity refers to the permeability zones increasing in frequency over a distance, while a decreasing periodicity refers to the permeability zones decreasing in frequency over a distance.
According to additional embodiments of this disclosure, a fixed-bed cell culture matrix for culturing adherent-based cells is provided. The cell culture matrix includes a structurally defined substrate comprising a substrate material defining a plurality of pores, the substrate material being configured for adhering cells thereto, and the substrate material being arranged in a wound configuration; and a plurality of permeability zones in the cell culture matrix, each of the plurality of permeability zones comprising an opening in the substrate, the opening being larger than a diameter of any of the plurality of pores, wherein the substrate material is wound about a winding axis, and the substrate comprises a length extending in a direction tangential to the winding axis.
Additional aspects of the present disclosure will be set forth, in part, in the detailed description, figures and any claims which follow, and in part will be derived from the detailed description, or can be learned by practice of the disclosure. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure as disclosed.
Various embodiments of the disclosure will be described in detail with reference to drawings, if any. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not limiting and merely set forth some of the many possible embodiments of the claimed invention.
Embodiments of this disclosure packed-bed cell culture substrates, as well as cell culture or bioreactor systems incorporating such packed-bed substrates, and methods of culturing cells using such packed-bed substrates and bioreactor systems.
In conventional large-scale cell culture bioreactors, different types of packed bed bioreactors have been used. Usually these packed beds contain porous substrates or matrices to retain adherent or suspension cells, and to support growth and proliferation. Packed-bed matrices provide high surface area to volume ratios, so cell density can be higher than in the other systems. However, the packed bed often functions as a depth filter, where cells are physically trapped or entangled in fibers of the matrix. Thus, because of linear flow of the cell inoculum through the packed bed, cells are subject to heterogeneous distribution inside the packed bed, leading to variations in cell density through the depth or width of the packed bed. For example, cell density may be higher at the inlet region of a bioreactor and significantly lower nearer to the outlet of the bioreactor. This non-uniform distribution of the cells inside of the packed bed significantly hinders scalability and predictability of such bioreactors in bioprocess manufacturing, and can even lead to reduced efficiency in terms of growth of cells or viral vector production per unit surface area or volume of the packed bed.
Another problem encountered in packed-bed bioreactors disclosed in prior art is the channeling effect. Due to random nature of packed nonwoven fibers, the local fiber density at any given cross section of the packed bed is not uniform. Medium flows quickly in the regions with low fiber density (high bed permeability) and much slower in the regions of high fiber density (lower bed permeability). The resulting non-uniform media perfusion across the packed bed creates the channeling effect, which manifests itself as significant nutrient and metabolite gradients that negatively impact overall cell culture and bioreactor performance. Cells located in the regions of low media perfusion will starve and very often die from the lack of nutrients or metabolite poisoning. Cell harvesting is yet another problem encountered when bioreactors packed with non-woven fibrous scaffolds are used. Due to the packed bed functioning as a depth filter, cells that are released at the end of the cell culture process are entrapped inside the packed bed, and cell recovery is very low. This significantly limits utilization of such bioreactors in bioprocesses where live cells are the products. Thus, the non-uniformity leads to areas with different exposure to flow and shear, effectively reducing the usable cell culture area, causing non-uniform culture, and interfering with transfection efficiency and cell release.
To address these and other problems of existing cell culture solutions, embodiments of the present disclosure provide cell growth substrates, packed-bed matrices of such substrates, and/or packed-bed systems using such substrates that enable efficient and high-yield cell culturing for anchorage-dependent cells and production of cell products (e.g., proteins, antibodies, viral particles). Embodiments include a porous cell-culture matrix made from an ordered and regular array of porous substrate material that enables uniform cell seeding and media/nutrient perfusion, as well as efficient cell harvesting. Embodiments also enable scalable cell-culture solutions with substrates and bioreactors capable of seeding and growing cells and/or harvesting cell products from a process development scale to a full production size scale, without sacrificing the uniform performance of the embodiments. For example, in some embodiments, a bioreactor can be easily scaled from process development scale to product scale with comparable viral genome per unit surface area of substrate (VG/cm2) across the production scale. The harvestability and scalability of the embodiments herein enable their use in efficient seed trains for growing cell populations at multiple scales on the same cell substrate. In addition, the embodiments herein provide a cell culture matrix having a high surface area that, in combination with the other features described, enables a high yield cell culture solution. In some embodiments, for example, the cell culture substrate and/or bioreactors discussed herein can produce 1016 to 1018 viral genomes (VG) per batch. Embodiments also include packed-bed cell culture matrices with controlled zonal porosity and defined virtual channels through the packed bed as a way to control the overall performance of the packed bed in terms of fluid flow through the cell culture matrix. This ability to form zones in the packed bed with different porosity will improve, for example, cell seeding uniformity, media perfusion uniformity, cell culture and growth uniformity, and cell harvest.
In one embodiment, a matrix is provided with a structurally defined surface area for adherent cells to attach and proliferate that has good mechanical strength and forms a highly uniform multiplicity of interconnected fluidic networks when assembled in a packed bed or other bioreactor. As used herein, “structurally defined” means that a substrate or matrix having a defined and ordered structure as opposed to a random and disordered structure. Non-woven substrates are considered random and/or disordered, for example. In a structurally defined matrix or substrate, the porosity, fiber size and orientation, and even orientation of separate pieces of substrate material can be designed and controlled.
In particular embodiments, a mechanically stable, non-degradable woven mesh can be used as the substrate to support adherent cell production. The cell culture matrix disclosed herein supports attachment and proliferation of anchorage dependent cells in a high volumetric density format. Uniform cell seeding of such a matrix is achievable, as well as efficient harvesting of cells or other products of the bioreactor. In addition, the embodiments of this disclosure support cell culturing to provide uniform cell distribution during the inoculation step and achieve a confluent monolayer or multilayer of adherent cells on the disclosed matrix, and can avoid formation of large and/or uncontrollable 3D cellular aggregates with limited nutrient diffusion and increased metabolite concentrations. Thus, the matrix eliminates diffusional limitations during operation of the bioreactor. In addition, the matrix enables easy and efficient cell harvest from the bioreactor. The structurally defined matrix of one or more embodiments enables complete cell recovery and consistent cell harvesting from the packed bed of the bioreactor.
According to some embodiments, a method of cell culturing is also provided using bioreactors with the matrix for bioprocessing production of therapeutic proteins, antibodies, viral vaccines, or viral vectors.
In contrast to existing cell culture substrates used in cell culture bioreactors (i.e., non-woven substrates of randomly ordered fibers), embodiments of this disclosure include a structurally defined cell culture substrate having a defined and ordered structure. The defined and order structure allows for consistent and predictable cell culture results. In addition, the substrate has an open porous structure that prevents cell entrapment and enables uniform flow through the packed bed. This construction enables improved cell seeding, nutrient delivery, cell growth, and cell harvesting. According to one or more particular embodiments, the matrix is formed with a substrate material having a thin, sheet-like construction having first and second sides separated by a relatively small thickness, such that the thickness of the sheet is small relative to the width and/or length of the first and second sides of the substrate. In addition, a plurality of holes or openings are formed through the thickness of the substrate. The substrate material between the openings is of a size and geometry that allows cells to adhere to the surface of the substrate material as if it were approximately a two-dimensional (2D) surface, while also allowing adequate fluid flow around the substrate material and through the openings. In some embodiments, the substrate is a polymer-based material, and can be formed as a molded polymer sheet; a polymer sheet with openings punched through the thickness; a number of filaments that are fused into a mesh-like layer; a 3D-printed substrate; or a plurality of filaments that are woven into a mesh layer. The physical structure of the matrix has a high surface-to-volume ratio for culturing anchorage dependent cells. According to various embodiments, the matrix can be arranged or packed in a bioreactor in certain ways discussed here for uniform cell seeding and growth, uniform media perfusion, and efficient cell harvest.
Embodiments of this disclosure can achieve viral vector platforms of a practical size that can produce viral genomes on the scale of greater than about 1014 viral genomes per batch, greater than about 1015 viral genomes per batch, greater than about 1016 viral genomes per batch, greater than about 1017 viral genomes per batch, or up to or greater than about g 1016 viral genomes per batch. In some embodiments, production is about 1015 to about 1018 or more viral genomes per batch. For example, in some embodiments, the viral genome yield can be about 1015 to about 1016 viral genomes or batch, or about 1016 to about 1019 viral genomes per batch, or about 1016-1018 viral genomes per batch, or about 1017 to about 1019 viral genomes per batch, or about 1018 to about 1019 viral genomes per batch, or about 1018 or more viral genomes per batch.
In addition, the embodiments disclosed herein enable not only cell attachment and growth to a cell culture substrate, but also the viable harvest of cultured cells. The inability to harvest viable cells is a significant drawback in current platforms, and it leads to difficulty in building and sustaining a sufficient number of cells for production capacity. According to an aspect of embodiments of this disclosure, it is possible to harvest viable cells from the cell culture substrate, including between 80% to 100% viable, or about 85% to about 99% viable, or about 90% to about 99% viable. For example, of the cells that are harvested, at least 80% are viable, at least 85% are viable, at least 90% are viable, at least 91% are viable, at least 92% are viable, at least 93% are viable, at least 94% are viable, at least 95% are viable, at least 96% are viable, at least 97% are viable, at least 98% are viable, or at least 99% are viable. Cells may be released from the cell culture substrate using, for example, trypsin, TrypLE, or Accutase.
In
A given fiber of the plurality of fibers 102 has a thickness t1, and a given fiber of the plurality of fibers 104 has a thickness t2. In the case of fibers of round cross-section, as shown in
In one or more embodiments, a fiber may have a diameter in a range of about 50 μm to about 1000 μm; about 100 μm to about 750 μm; about 125 μm to about 600 μm; about 150 μm to about 500 μm; about 200 μm to about 400 μm; about 200 μm to about 300 μm; or about 150 μm to about 300 μm. On a microscale level, due to the scale of the fiber compared to the cells (e.g., the fiber diameters being larger than the cells), the surface of monofilament fiber is presented as an approximation of a 2D surface for adherent cells to attach and proliferate. Fibers can be woven into a mesh with openings ranging from about 100 μm×100 μm to about 1000 μm×1000 μm. In some embodiments, the opening may have a diameter of about 50 μm to about 1000 μm; about 100 μm to about 750 μm; about 125 μm to about 600 μm; about 150 μm to about 500 μm; about 200 μm to about 400 μm; or about 200 μm to about 300 μm. These ranges of the filament diameters and opening diameters are examples of some embodiments, but are not intended to limit the possible feature sizes of the mesh according to all embodiments. The combination of fiber diameter and opening diameter is chosen to provide efficient and uniform fluid flow through the substrate when, for example, the cell culture matrix comprises a number of adjacent mesh layers (e.g., a stack of individual layers or a rolled mesh layer).
Factors such as the fiber diameter, opening diameter, and weave type/pattern will determine the surface area available for cell attachment and growth. In addition, when the cell culture matrix includes a stack, roll, or other arrangement of overlapping substrate, the packing density of the cell culture matrix will impact the surface area of the packed bed matrix. Packing density can vary with the packing thickness of the substrate material (e.g., the space needed for a layer of the substrate). For example, if a stack of cell culture matrix has a certain height, each layer of the stack can be said to have a packing thickness determined by dividing the total height of the stack by the number of layers in the stack. The packing thickness will vary based on fiber diameter and weave, but can also vary based the alignment of adjacent layers in the stack. For instance, due to the three-dimensional nature of a woven layer, there is a certain amount of interlocking or overlapping that adjacent layers can accommodate based on their alignment with one another. In a first alignment, the adjacent layers can be tightly nestled together, but in a second alignment, the adjacent layers can have zero overlap, such as when the lower-most point of the upper layer is in direct contact with the upper-most point of the lower layer. It may be desirable for certain applications to provide a cell culture matrix with a lower density packing of layers (e.g., when higher permeability is a priority) or a higher density of packing (e.g., when maximizing substrate surface area is a priority). According to one or more embodiments, the packing thickness can be from about 50 μm to about 1000 μm; about 100 μm to about 750 μm; about 125 μm to about 600 μm; about 150 μm to about 500 μm; about 200 μm to about 400 μm; about 200 μm to about 300 μm.
The above structural factors can determine the surface area of a cell culture matrix, whether of a single layer of cell culture substrate or of a cell culture matrix having multiple layers of substrate). For example, in a particular embodiment, a single layer of woven mesh substrate having a circular shape and diameter of 6 cm can have an effective surface area of about 68 cm2. The “effective surface area,” as used herein, is the total surface area of fibers in a portion of substrate material that is available for cell attachment and growth. Unless stated otherwise, references to “surface area” refer to this effective surface area. According to one or more embodiments, a single woven mesh substrate layer with a diameter of 6 cm may have an effective surface area of about 50 cm2 to about 90 cm2; about 53 cm2 to about 81 cm2; about 68 cm2; about 75 cm2; or about 81 cm2. These ranges of effective surface area are provided for example only, and some embodiments may have different effective surface areas. The cell culture matrix can also be characterized in terms of porosity, as discussed in the Examples herein.
The substrate mesh can be fabricated from monofilament or multifilament fibers of polymeric materials compatible in cell culture applications, including, for example, polystyrene, polyethylene terephthalate, polycarbonate, polyvinylpyrrolidone, polybutadiene, polyvinylchloride, polyethylene oxide, polypyrroles, and polypropylene oxide. Mesh substrates may have a different patterns or weaves, including, for example knitted, warp-knitted, or woven (e.g., plain weave, twilled weave, dutch weave, five needle weave).
The surface chemistry of the mesh filaments may need to be modified to provide desired cell adhesion properties. Such modifications can be made through the chemical treatment of the polymer material of the mesh or by grafting cell adhesion molecules to the filament surface. Alternatively, meshes can be coated with thin layer of biocompatible hydrogels that demonstrate cell adherence properties, including, for example, collagen or Matrigel®. Alternatively, surfaces of filament fibers of the mesh can be rendered with cell adhesive properties through the treatment processes with various types of plasmas, process gases, and/or chemicals known in the industry. In one or more embodiments, however, the mesh is capable of providing an efficient cell growth surface without surface treatment.
As shown by the above table, the three-dimensional quality of the meshes provides increased surface area for cell attachment and proliferation compared to a planar 2D surface of comparable size. This increased surface area aids in the scalable performance achieved by embodiments of this disclosure. For process development and process validation studies, small-scale bioreactors are often required to save on reagent cost and increase experimental throughput. Embodiments of this disclosure are applicable to such small-scale studies, but can be scaled-up to industrial or production scale, as well. For example, if 100 layers of Mesh C in the form of 2.2 cm diameter circles are packed into a cylindrical packed bed with a 2.2 cm internal diameter, the total surface area available for cells to attach and proliferate is equal to about 935 cm2. To scale such bioreactor ten times, one could use a similar setup of a cylindrical packed bed with 7 cm internal diameter and 100 layers of the same mesh. In such a case, the total surface area would be equal 9,350 cm2. In some embodiments, the available surface area is about 99,000 cm2/L or more. Because of the plug-type perfusion flow in a packed bed, the same flow rate expressed in ml/min/cm2 of cross-sectioned packed bed surface area can be used in smaller-scale and larger-scale versions of the bioreactor. A larger surface area allows for higher seeding density and higher cell growth density. According to one or more embodiments, the cell culture substrate described herein has demonstrated cell seeding densities of up to 22,000 cells/cm2 or more. For reference, the Corning HyperFlask® has a seeding density on the order of 20,000 cells/cm2 on a two-dimensional surface.
Another advantage of the higher surface areas and higher cell seeding or growing densities is that the cost of the embodiments disclosed herein can be the same or less than competing solutions. Specifically, the cost per cellular product (e.g., per cell or per viral genome) can be equal to or less than other packed-bed bioreactors.
In a further embodiment of the present disclosure discussed below, a woven mesh substrate can be packed in a cylindrical roll format within the bioreactor (see
where L is the total length of mesh required to pack the bioreactor (i.e., H in
By using a structurally defined cell culture matrix of sufficient rigidity, high-flow-resistance uniformity across the matrix or packed bed is achieved. According to various embodiments, the matrix can be deployed in monolayer or multilayer formats. This flexibility eliminates diffusional limitations and provides uniform delivery of nutrients and oxygen to cells attached to the matrix. In addition, the open matrix lacks any cell entrapment regions in the packed bed configuration, allowing for complete cell harvest with high viability at the end of culturing. The matrix also delivers packaging uniformity for the packed bed, and enables direct scalability from process development units to large-scale industrial bioprocessing unit. The ability to directly harvest cells from the packed bed eliminates the need of resuspending a matrix in a stirred or mechanically shaken vessel, which would add complexity and can inflict harmful shear stresses on the cells. Further, the high packing density of the cell culture matrix yields high bioprocess productivity in volumes manageable at the industrial scale.
As discussed herein, the cell culture substrate can be used within a bioreactor vessel, according to one or more embodiments. For example, the substrate can be used in a packed bed bioreactor configuration, or in other configurations within a three-dimensional culture chamber. However, embodiments are not limited to a three-dimensional culture space, and it is contemplated that the substrate can be used in what may be considered a two-dimensional culture surface configuration, where the one or more layers of the substrate lay flat, such as within a flat-bottomed culture dish, to provide a culture substrate for cells. Due to contamination concerns, the vessel can be a single-use vessel that can be disposed of after use.
A cell culture system is provided, according to one or more embodiments, in which the cell culture matrix is used within a culture chamber of a bioreactor vessel.
In one or more embodiments, flow resistance and volumetric density of the packed bed can be controlled by interleaving substrate layers of different geometries. In particular, mesh size and geometry (e.g., fiber diameter, opening diameter, and/or opening geometry) define the fluid flow resistance in packed bed format. By interlaying meshes of different sizes and geometries, flow resistance can be controlled or varied in one or more specific portions of the bioreactor. This can enable better uniformity of liquid perfusion in the packed bed. For example, 10 layers of Mesh A (Table 1) followed by 10 layers of Mesh B (Table 1) and followed by 10 layers of Mesh C (Table 1) can be stacked to achieve a desired packed bed characteristic. As another example, the packed bed may start with 10 layers of Mesh B, followed by 50 layers of Mesh C, followed by 10 layers of Mesh B. Such repetition pattern may continue until the full bioreactor is packed with mesh. These are examples only, and used for illustrative purposes without intending to be limiting on the possible combinations. Indeed, various combinations of meshes of different sizes are possible to obtain different profiles of volumetric density of cells growth surface and flow resistance. For example, a packed bed column with zones of varying volumetric cells densities (e.g., a series of zones creating a pattern of low/high/low/high, etc. densities) can be assembled by interleaving meshes of different sizes. As discussed below, zones of variable porosity can also be provided by creating channels through all or part of the packed bed.
In
As discussed above, packed-bed cell culture matrices such as those shown in
As used herein, “permeability zone” is defined as a portion of a cell culture matrix where the cell culture substrate is altered to increase permeability or porosity of the matrix in a defined area relative to a portion of the cell culture matrix containing only unaltered cell culture substrate. The cell culture matrix is considered “altered” when the otherwise regular defined and ordered structure of the cell culture substrate is interrupted to increase permeability or porosity in the altered location relative to the unaltered location. Such alternation can be achieved by removal of portions of the substrate material (e.g., by cutting out substrate material; gaps molded into the substrate material; controlled dissolution of portions of a dissolvable substrate; or vacancies left in a substrate material made by any other method, including 3D printing). Although the term “altered” may imply temporality wherein the substrate material undergoes a change from its original form, it should be understood that, within the context of this disclosure, “altered” can mean any variation of the defined and regular structure of the cell culture substrate, whether that variation is created when the substrate material itself is created or that variation is achieved by changing the substrate material after the substrate material is already created. In other words, the alteration results in an opening in the substrate material or matrix that is larger than an average pore size of the structurally defined cell culture substrate of the matrix. An “unaltered” area of cell culture substrate should be understood to mean any portion of a cell culture substrate having the defined and ordered structure of the structurally defined substrate, without any alterations or interruptions of that structure. Due to the permeability zone being the result of altered portions of cell culture substrate, permeability zones are differentiated from local variations in permeability due to non-uniform or randomly packed substrates in existing packed-bed systems discussed above.
As used herein, a “virtual channel” is defined as a fluid flow pathway through the matrix that has higher local permeability than a portion of the matrix containing only unaltered cell culture substrate. Such channels are described as “virtual” because they channels are not physically constrained (e.g., by walls or tubing), but rather exist within the cell culture matrix, which has an open porous structure. Thus, there is not necessarily any barrier separating a virtual channel from the remainder of the cell culture matrix. A virtual channel may be considered to extend in a horizontal (i.e., perpendicular to a bulk flow direction of media through the cell culture matrix or bioreactor) cross-section of the matrix, or it may be considered to extend longitudinally (i.e., parallel to the bulk flow direction) through part of or the entirety of the packed-bed matrix.
“Permeability zones” and “virtual channels” as used herein can contain areas of both altered and unaltered substrate material. For example, embodiments of this disclosure include multi-layered packed-bed cell culture matrices having stacked layers of cell culture substrate. A permeability zone or virtual channel can be created in the stacked layers by removing substrate material from a vertical section of the packed-bed, and all or only a portion of the layers in the vertical section may have material removed to increase permeability. For example, even if only a fraction of the layers in the vertical section have material removed, the permeability through that vertical section can be higher than through another vertical section of the matrix containing only unaltered substrate layers.
According to embodiments of this disclosure, the permeability zones will exhibit higher permeability relative to the other portions of the cell culture matrix. As discussed above, the permeability zones can contain one or more openings in the cell culture matrix that results in a higher than normal permeability in those zones. The permeability zones can extend along the extent of the height h of the cell culture matrix, but this does not necessarily mean that the entirety of the zones are open and unobstructed. Rather, the permeability zones may include only one or select areas where portions of the cell culture matrix have an opening for increased permeability. However, the permeability zones can still be considered to extend along the extent of the height h because any reduction in flow resistance within those zones can result in increased permeability within the zones, along the flow direction F.
The use of defined permeability zones to control permeability in a packed-bed cell culture matrix can have many uses. For example, depending on the type or stage of cell culture, it may desirable to achieve a particular permeability profile. One use of the permeability zones is to compensate for non-uniform flow properties of a bioreactor system. That is, where a bioreactor system inherently has non-uniform flow of media or fluid, permeability zones in the packed bed can be used to compensate for that non-uniformity and can result in a composite flow profile that is more uniform.
In some embodiments, the opening of the virtual channel can have a width of from about 200 μm to about 3000 μm, from about 300 μm to about 2500 μm, from about 400 μm to about 2000 μm, from about 500 μm to about 1500 μm, from about 600 μm to about 1800 μm, from about 1000 μm to about 2000 μm, from about 1000 μm to about 1800 μm, or from about 1300 μm to about 1400 μm. Also, as discussed above, the shape of the virtual channels can vary a great deal, and so too can the dimension of the opening.
The media from the media 506 conditioning vessel 504 is delivered to the bioreactor 502 via an inlet 508, which may also include an injection port for cell inoculum to seed and begin culturing of cells. The bioreactor vessel 502 may also include on or more outlets 510 through which the cell culture media 506 exits the vessel 502. In addition, cells or cell products may be output through the outlet 510. To analyze the contents of the outflow from the bioreactor 502, one or more sensors 512 may be provided in the line. In some embodiments, the system 500 includes a flow control unit 514 for controlling the flow into the bioreactor 502. For example, the flow control unit 514 may receive a signal from the one or more sensors 512 (e.g., an O2 sensor) and, based on the signal, adjust the flow into the bioreactor 502 by sending a signal to a pump 516 (e.g., peristaltic pump) upstream of the inlet 508 to the bioreactor 502. Thus, based on one or a combination of factors measured by the sensors 512, the pump 516 can control the flow into the bioreactor 502 to obtain the desired cell culturing conditions.
The media perfusion rate is controlled by the signal processing unit 514 that collects and compares sensors signals from media conditioning vessel 504 and sensors located at the packed bed bioreactor outlet 510. Because of the pack flow nature of media perfusion through the packed bed bioreactor 502, nutrients, pH and oxygen gradients are developed along the packed bed. The perfusion flow rate of the bioreactor can be automatically controlled by the flow control unit 514 operably connected to the peristaltic pump 516, according to the flow chart in
One or more embodiments of this disclosure offer a cell inoculation step that is different from conventional methods. In conventional methods, a pack bed with a conventional matrix is filled with culture media and concentrated inoculum is injected into the media circulation loop. The cell suspension is pumped through the bioreactor at increased flow rate to reduce nonuniformity of cell seeding via capture on the conventional packed bed matrix. In such conventional methods, the pumping of cells in the circulation loop at an elevated flow rate continues for perhaps several hours until the majority of the cells are captured in packed bed bioreactor. However, because of the nonuniform deep bed filtration nature of conventional packed bed bioreactors, cells are distributed nonuniformly inside the packed bed with the higher cell density at the inlet region of the bioreactor and lower cell density at the outlet region of the bioreactor.
In contrast, according to embodiments of the present disclosure, cell inoculum of equal volume to the void volume of the culture chamber in the bioreactor is directly injected into the packed bed through a cell inoculum injection port at the inlet 508 of the bioreactor 502 (
The cell culture matrix can be arranged in multiple configurations within the culture chamber depending on the desired system. For example, in one or more embodiments, the system includes one or more layers of the substrate with a width extending across the width of a defined cell culture space in the culture chamber. Multiple layers of the substrate may be stacked in this way to a predetermined height. As discussed above, the substrate layers may be arranged such that the first and second sides of one or more layers are perpendicular to a bulk flow direction of culture media through the defined culture space within the culture chamber, or the first and second sides of one or more layers may be parallel to the bulk flow direction. In one or more embodiments, the cell culture matrix includes one or more substrate layers at a first orientation with respect to the bulk flow, and one or more other layers at a second orientation that is different from the first orientation. For example, various layers may have first and second sides that are parallel or perpendicular to the bulk flow direction, or at some angle in between.
In one or more embodiments, the cell culture system includes a plurality of discrete pieces of the cell culture substrate in a packed bed configuration, where the length and or width of the pieces of substrate are small relative to the culture chamber. As used herein, the pieces of substrate are considered to have a length and/or width that is small relative to the culture chamber when the length and/or width of the piece of substrate is about 50% or less of the length and/or width of the culture space. Thus, the cell culture system may include a plurality of pieces of substrate packed into the culture space in a desired arrangement. The arrangement of substrate pieces may be random or semi-random, or may have a predetermined order or alignment, such as the pieces being oriented in a substantially similar orientation (e.g., horizontal, vertical, or at an angle between 0° and 90° relative to the bulk flow direction).
The “defined culture space,” as used herein, refers to a space within the culture chamber occupied by the cell culture matrix and in which cell seeding and/or culturing is to occur. The defined culture space can fill approximately the entirety of the culture chamber, or may occupy a portion of the space within the culture chamber. As used herein, the “bulk flow direction” is defined as a direction of bulk mass flow of fluid or culture media through or over the cell culture matrix during the culturing of cells, and/or during the inflow or outflow of culture media to the culture chamber.
In one or more embodiments, the cell culture matrix is secured within the culture chamber by a fixing mechanism. The fixing mechanism may secure a portion of the cell culture matrix to a wall of the culture chamber that surrounds the matrix, or to a chamber wall at one end of the culture chamber. In some embodiments, the fixing mechanism adheres a portion of the cell culture matrix to a member running through the culture chamber, such as member running parallel to the longitudinal axis of the culture chamber, or to a member running perpendicular to the longitudinal axis. However, in one or more other embodiments, the cell culture matrix may be contained within the culture chamber without being fixedly attached to the wall of the chamber or bioreactor vessel. For example, the matrix may be contained by the boundaries of the culture chamber or other structural members within the chamber such that the matrix is held within a predetermined area of the bioreactor vessel without the matrix being fixedly secured to those boundaries or structural members.
One aspect of some embodiments provides a bioreactor vessel in a roller bottle configuration. The culture chamber is capable of containing a cell culture matrix and substrate according to one or more of the embodiments described in this disclosure. In the roller bottle configuration, the bioreactor vessel may be operably attached to a means for moving the bioreactor vessel about a central longitudinal axis of the vessel. For example, the bioreactor vessel may be rotated about the central longitudinal axis. The rotation may be continuous (e.g., continuing in one direction) or discontinuous (e.g., an intermittent rotation in a single direction or alternating directions, or oscillating in back and forth rotational directions). In operation, the rotation of the bioreactor vessel causes movement of cells and/or fluid within the chamber. This movement can be considered relative with respect to the walls of the chamber. For example, as the bioreactor vessel rotates about its central longitudinal axis, gravity may cause the fluid, culture media, and/or unadhered cells to remain toward a lower portion of the chamber. However, in one or more embodiments, the cell culture matrix is essentially fixed with respect to the vessel, and thus rotates with the vessel. In one or more other embodiments, the cell culture matrix can be unattached and free to move to a desired degree relative to the vessel as the vessel rotates. The cells may adhere to the cell culture matrix, while the movement of the vessel allows the cells to receive exposure to both the cell culture media or liquid, and to oxygen or other gases within the culture chamber.
By using a cell culture matrix according to embodiments of this disclosure, such as a matrix including a woven or mesh substrate, the roller bottle vessel is provided with an increased surface area available for adherent cells to attach, proliferate, and function. In particular, using a substrate of a woven mesh of monofilament polymer material within the roller bottle, the surface area may increase by of about 2.4 to about 4.8 times, or to about 10 times that of a standard roller bottle. As discussed herein, each monofilament strand of the mesh substrate is capable of presenting itself as 2D surface for adherent cells to attach. In addition, multiple layers of mesh can we arranged in roller bottle, resulting in increases of total available surface area ranging from about 2 to 20 times that of a standard roller bottle. Thus, existing roller bottle facilities and processing, including cell seeding, media exchange, and cell harvesting, can be modified by the addition of the improved cell culture matrix disclosed herein, with minimal impact on existing operation infrastructure and processing steps.
The bioreactor vessel optionally includes one or more outlets capable of being attached to inlet and/or outlet means. Through the one or more outlets, liquid, media, or cells can be supplied to or removed from the chamber. A single port in the vessel may act as both the inlet and outlet, or multiple ports may be provided for dedicated inlets and outlets.
The packed bed cell culture matrix of one or more embodiments can consist of the woven cell culture mesh substrate without any other form of cell culture substrate disposed in or interspersed with the cell culture matrix. That is, the woven cell culture mesh substrate of embodiments of this disclosure are effective cell culture substrates without requiring the type of irregular, non-woven substrates used in existing solution. This enables cell culture systems of simplified design and construction, while providing a high-density cell culture substrate with the other advantages discussed herein related to flow uniformity, harvestability, etc.
As discussed herein, the cell culture substrates and bioreactor systems provided offer numerous advantages. For example, the embodiments of this disclosure can support the production of any of a number of viral vectors, such as AAV (all serotypes) and lentivirus, and can be applied toward in vivo and ex vivo gene therapy applications. The uniform cell seeding and distribution maximizes viral vector yield per vessel, and the designs enable harvesting of viable cells, which can be useful for seed trains consisting of multiple expansion periods using the same platform. In addition, the embodiments herein are scalable from process development scale to production scale, which ultimately saves development time and cost. The methods and systems disclosed herein also allow for automation and control of the cell culture process to maximize vector yield and improve reproducibility. Finally, the number of vessels needed to reach production-level scales of viral vectors (e.g., 1016 to 1018 AAV VG per batch) can be greatly reduced compared to other cell culture solutions.
Embodiments are not limited to the vessel rotation about a central longitudinal axis. For example, the vessel may rotate about an axis that is not centrally located with respect to the vessel. In addition, the axis of rotation may be a horizonal or vertical axis.
The following is a description of various aspects of implementations of the disclosed subject matter. Each aspect may include one or more of the various features, characteristics, or advantages of the disclosed subject matter. The implementations are intended to illustrate a few aspects of the disclosed subject matter and should not be considered a comprehensive or exhaustive description of all possible implementations.
“Wholly synthetic” or “fully synthetic” refers to a cell culture article, such as a microcarrier or surface of a culture vessel, that is composed entirely of synthetic source materials and is devoid of any animal derived or animal sourced materials. The disclosed wholly synthetic cell culture article eliminates the risk of xenogeneic contamination.
“Include,” “includes,” or like terms means encompassing but not limited to, that is, inclusive and not exclusive.
“Users” refers to those who use the systems, methods, articles, or kits disclosed herein, and include those who are culturing cells for harvesting of cells or cell products, or those who are using cells or cell products cultured and/or harvested according to embodiments herein.
“About” modifying, for example, the quantity of an ingredient in a composition, concentrations, volumes, process temperature, process time, yields, flow rates, pressures, viscosities, and like values, and ranges thereof, or a dimension of a component, and like values, and ranges thereof, employed in describing the embodiments of the disclosure, refers to variation in the numerical quantity that can occur, for example: through typical measuring and handling procedures used for preparing materials, compositions, composites, concentrates, component parts, articles of manufacture, or use formulations; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of starting materials or ingredients used to carry out the methods; and like considerations. The term “about” also encompasses amounts that differ due to aging of a composition or formulation with a particular initial concentration or mixture, and amounts that differ due to mixing or processing a composition or formulation with a particular initial concentration or mixture.
“Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.
The indefinite article “a” or “an” and its corresponding definite article “the” as used herein means at least one, or one or more, unless specified otherwise.
Abbreviations, which are well known to one of ordinary skill in the art, may be used (e.g., “h” or “hrs” for hour or hours, “g” or “gm” for gram(s), “mL” for milliliters, and “rt” for room temperature, “nm” for nanometers, and like abbreviations).
Specific and preferred values disclosed for components, ingredients, additives, dimensions, conditions, and like aspects, and ranges thereof, are for illustration only; they do not exclude other defined values or other values within defined ranges. The systems, kits, and methods of the disclosure can include any value or any combination of the values, specific values, more specific values, and preferred values described herein, including explicit or implicit intermediate values and ranges.
Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that any particular order be inferred.
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the disclosed embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the embodiments may occur to persons skilled in the art, the disclosed embodiments should be construed to include everything within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 63/448,907 filed on Feb. 28, 2023, the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63448907 | Feb 2023 | US |
