Serum-free products reduce cell-culture challenges and open new opportunities
Cell-culture tools are continuously being refined, especially media. In the early 1980s, I worked in a cell-culture lab where we made our own media from chick-embryo extract, horse serum and a collection of other concoctions. This sounds like witchcraft more than science, even though we didn’t add eye of newt or toe of frog. Many modern biologists take a different tack, using completely defined media made from a precise chemical recipe, such as serum-free culture media. This approach provides an array of benefits and few challenges.
Traditional media, which many tissue culture scientists still use, can contain up to 20% fetal bovine serum (FBS). “This FBS provides the cells with growth factors, insulin, hormones and other specialized nutrients found in the bloodstream,” says Vishal G. Warke, director of R&D for cell culture and immunology at Himedia Laboratories (Mumbai, India). “The FBS is therefore quite rich and it can be used to grow any and every cell line.” Serum-free media needs additives, which often depend on the cells that will be grown, but may include proteins, such as albumin, or chemicals, such as zinc, as well as chemical versions of some of the components in FBS, which “drives up the costs to a considerable extent,” says Warke.
“Serum-free culture media is considered to be more defined than traditional media,” says Jennifer Crean, senior product development manager at Thermo Fisher Scientific (Waltham, Mass.), “but that’s a very loose term.” Each product will need to be examined to see just how defined it is.
Most of all, serum-free culture media reduces variability, which can be a significant problem with serum-supplemented media. The addition of serum can make media different from one season to another. “Just as an example,” says Warke, “cattle that are fed hay in sheds in the winter, and cattle that grass-feed in the open in the summer can have varying concentrations of cryoglobulins and other proteins in their blood.” He adds, “This eventually impacts serum, as one can get variable levels of cryoprecipitates on freezing and thawing.”
These issues are avoided with serum-free media. “By adding more defined components and knowing what’s in them,” says Sandra Kuligowski, senior product development manager at Thermo Fisher Scientific, “you should expect more consistent results.”
Less variation also simplifies some applications. “On the regulatory side, it is possible to better characterize and analyze individual raw materials used for the production of complex mixtures of 50–80 components as [a] typical example for a formulation,” says Jörg von Hagen, R&D director of the Biopharm Material & Technologies (BM&T) Franchise at Merck KGaA’s Millipore division (Darmstadt, Germany). “This reduces the risk of batch-to-batch variability.”
Serum-free culture also reduces some risks. “Serum-supplemented media can have safety risks, like viral contamination from the animal,” says Kuligowski. “Then, it’s hard to trace the contamination to the donor animal.”
As von Hagen explains, “The risk of viral contamination is lower by avoiding the usage of animal-derived components, which were regarded as likely source[s] of contamination in several large-scale biomanufacturing processes reported independently by several drug manufacturers.”
Use of chemically defined media can also prevent some disease-based problems. As Warke says, they are “free of antibodies to different infections that the animal may have suffered.”
Clinical applications can also benefit from serum-free media. In 2015 in Clinical & Translational Immunology, researchers from the QIMR Berghofer Medical Research Institute in Australia and Thermo Fisher Scientific stated, “One of the key components in manufacturing of T-cell therapies is human serum (HS) or fetal bovine serum (FBS), which can potentially expose immunotherapy recipient (sic) to adventitious infectious pathogens and are thus considered as non-cGMP compliant for adoptive therapy.” So these researchers developed a system that used serum-free media, reporting that it was “highly efficient in expanding both polyclonal and virus-specific T-cells directed against both dominant and subdominant antigens.” They also noted that it cost about the same as the traditional approach.
The cost of serum-free culture can be higher, but it can lead to economic benefits. “There [are] additional time and costs of prequalifying lots for different applications, such as T-cells, with serum-supplemented media, so prequalified serum-free media, such as CTS Immune Cell SR, can be more cost-effective overall,” says Kuligowski.
Another benefit is chemically defined versions are readily available. That means that biologists don’t need to make method changes, which can be costly and require a fair amount of time.
Labs can save time in other ways with the right media. Thermo Fisher Scientific designed the new Essential 8 Flex as media for pluripotent stem cells. “Usually, you have to come in every day to care for these cells in culture, but this is designed for weekend-free culture,” says Crean.
In fact, making serum-free media for specific cells can save money. “In certain applications where the scientist works with a particular cell type, not all nutrients of the FBS are needed and serum-free media can be created for that particular cell type or associated cell types, in order to reduce the costs of the serum-free media,” Warke explains. So Himedia Laboratories developed serum-free media for many cell lines, including Chinese hamster ovary (CHO), baby hamster kidney (BHK) 21 and Madin-Darby canine kidney (MDCK) cells. The company even makes serum-free media for some insect cell lines.
Other suppliers offer serum-free media for very specific cells. Irvine Scientific (Santa Ana, Calif.) makes it for hybridoma cells, which can be used to produce monoclonal antibodies. It also makes serum-free media for MDCK cells and others. GE Healthcare Life Sciences HyClone Laboratories (South Logan, Utah) offers HyClone CCM5 CHO media, which the company website describes as “a serum-free media that supports the growth of anchoragedependent CHO cells.”
Serum-free media make cell culture more precise and repeatable. (Image courtesy of Himedia Laboratories.)
In high-volume situations, the media can matter even more. “With a fully chemically defined cell culture media platform,” says von Hagen, “we are able to apply a single-feed strategy by using chemically modified tyrosine and cysteine sources to produce cell culture feeds at neutral pH.” He says that this eliminates the “additional caustic feed at a pH above 11.0, to achieve the solubility of the required concentrations of these amino acids.” He adds, “This simplifies the feed batch process and is thus an additional benefit to reduce the risks in GMP large-scale manufacturing.”
If a lab wants to switch from serum-supplemented media to serum-free, some adjustments will probably be required. “You’d usually need to make some tweaks,” Crean says. “Serum can cover lots of sins in your culture system.”
Cell attachment could even become an issue when making the switch. “Serum can have an attachment factor in it,” Crean says. “So you might need to add one to serum-free media.”
Biologists will not always need to change methods to make a media switch. Still, says Warke, “Cells in some cases need to be acclimatized to the serum-free media by a gradual transition from traditional media in a step-by-step approach, wherein one reduces the traditional media and FBS and increases the serum-free media amount.”
Some cells come ready for serum-free conditions. As von Hagen explains, “Nontransformed cell lines are these days available already adapted to chemically defined media by various cell banks like ATCC or ECACC.”
In many applications, the benefits of transitioning to serum-free media can overshadow the minor challenges, and the growing list of serum-free media options and acclimated cell lines makes it easier than ever.
Mike May is a freelance writer and editor living in Ohio. He can be reached at [email protected].