Many cell culture experts will argue that improvements in media and feed have been more responsible than any other factor in raising production titers for therapeutic proteins. While the “nature vs. nurture” argument is far from settled, culture media is at worst the partner of cell-line development in the quest for productivity, safety, and efficacy.
Media selection supports every stage of development and manufacturing, from clone selection to process development, scale-up, and commercial manufacturing. Absent the optimization of cell culture media, meeting biomanufacturing challenges such as scalability, process robustness, time to market, supply chain reliability, and cost of goods becomes impossible.
According to Achim Quandt, cell culture media and consumables business leader at GE Healthcare, scalability, especially for monoclonal antibody production, has improved through platform processes that allow using the same host cell line and culture medium for whole families of products.
“A robust process provides manufacturers with a relatively large design space where product quality remains unaltered. Once validated, platform processes provide huge advantages during scale-up, as wider acceptable ranges for the process parameters can be used.”
One company’s platform may differ significantly from another’s, particularly with respect to media and feed. Yet media manufacturers need to stay ahead of the curve(s). “For media manufacturers, the challenge is to offer a wide portfolio that reflects the needs of the most common cell culture platforms,” notes Pascal Lefebvre, media product manager at Sartorius Stedim Biotech.
Supply chain reliability is a key factor in modern bioprocessing that employs specialized equipment and raw material from a multitude of vendors. “Manufacturers strive for improved control of their supply situation by careful selection of vendors, conducting of supplier audits, and requirements for safety stocks where applicable,” says Quandt.
Cell culture media and media development are significant contributors to cost of goods, but when executed perfectly can greatly shorten time-to-market, Lefebvre notes. “As competition becomes more intense, fast-tracking to the commercial phase becomes critical.”
Related manufacturing issues include process robustness, reproducibility for both upstream and downstream processing, “quick-and-clean” processing, technical and regulatory support, and matching titers for optimal upstream and downstream operations. “You can’t run purification identically for 1 g/L and 6 g/L processes.”
The bioprocessing landscape is not quite settled in terms of culture type: fed-batch (including variants) or perfusion. “We’re seeing hybrid approaches—quasi-continuous processing—employing feeding strategies that do not involve complete media exchanges as you’d see with perfusion,” notes Shawn Smith, senior director, upstream bioprocess technologies at Pall Life Sciences.
The trend toward continuous manufacturing as a cost-saving measure will create additional challenges to media manufacturers and end-users. Right now this is an open-ended area for vendor and customer alike, since broad experience in this manufacturing mode does not yet exist. Top media vendors tell us, however, that they will be prepared when the dust settles.
Media Definition
All the experts interviewed for this article agree that end-users are looking for high-quality media that provides reproducible results and robust yields. As the industry moves toward more chemically defined media products, Stephen W. Brown, Ph.D., CTO at Vivalis, notes that “chemically defined media don’t always provide what you need in terms of yield. That means you have to go back, in some cases, to somewhat more complex media.” That is why poor characterization of media components causes problems.
The adoption of chemically defined media has been slow but steady—a “city on the hill”—for both bioprocessors and media manufacturers. Each step along the way, from serum-based to serum-sparing, serum-free, animal-derived component (ADC)-free, and chemically defined presents new challenges in terms of media optimization and the addition of trace ingredients. Jon Wannlund, R&D director for BD Biosciences, advises companies transitioning between media types to focus on media optimization as early in development as possible.
Paradoxically, as users and vendors alike strive for better definition, uniformity, and simplicity, the process of designing and optimizing cell culture media has taken on greater complexity, demanding a level of formulation sophistication that was hitherto unknown—not to mention a higher level of attention toward media optimization. End-users optimize media by evaluating spent components, then selectively replenishing them through a process Pall’s Smith describes as “an input/output problem that is almost like live biofeedback control, with the bioreactors behaving like a living organism.”
Ken Ludwig, business director, bioprocess at Corning Life Sciences, estimates that approximately 20% of today’s mammalian cell cultures for biotherapeutics are ADC-free, with a slightly lower percentage for vaccine cultures. For vaccines the figure is about 50% serum-free, while therapeutic protein processes are now virtually serum-free, and up to 40% ADC-free. But up to 90% of cultures for cell therapy still employ serum. “They would like to reach the same level of serum-free culture as biotherapy, but the challenges in growing stem cells suggest the transition will take longer.”
The majority of new processes, according to Roberta Morris, cell culture business director at Thermo Fisher Scientific, are attempting to go serum-free, with many attempting the chemically defined route as well. Cell therapy developers try to avoid serum as well, “but this is a very early-stage market that lacks standardization. Everyone is rushing to enter clinical stages. These cells, particularly human embryonic stem cells, are extremely sensitive to culture conditions, including media. But the closer they get to market, the more likely developers will attempt to optimize processes away from serum.”
Stem cell commercialization is further challenged by the fact that subpopulations exist even within distinct lineages, many with their own specific media/feed requirements. “Optimizing these media involves quite a bit of trial and error,” Morris says.
The intrinsic inconsistency of ill-defined media components, along with poor control over culture conditions, is one of the great sources of variability in cell culture, says Suzanne Hector, Ph.D., market development specialist at PromoCell.
“The total absence of human- or animal-derived ingredients, compared with traditional media systems, promotes a more controlled and standardized culture environment with minimal variation, particularly for sensitive cells such as stem cells and immune system cells.”
Defined media enhance culture performance by eliminating the deleterious effects of poorly defined growth supplements. Additionally, the risk of contamination from mammalian pathogens is reliably eliminated, meeting the demands of customers and regulators.