March 15, 2018 (Vol. 38, No. 6)
Sandeep Kumar Ph.D. Director Cell Applications
Formulations Adapt to Specific Cell Types to Support Diverse Applications
In the last few decades, mammalian cell culture has become an indispensable research tool for cellular and molecular biologists, providing useful and practical in vitro model systems for investigating normal cell physiology, biological processes, and disease mechanisms. Every day, scientists and researchers around the world are using cell culture as a tool for basic and translational research, the screening of compounds for drug development, and biologics manufacturing.
Whether they use primary cells, cell lines, or tissue explants, cell culture models are integral to scientific and preclinical research workflows, and they continue to facilitate scientific breakthroughs in human cell biology.
One Size Does Not Fit All
A cell culture medium must do more than simply support cell survival and proliferation. It must also support whatever cellular functions may be of interest. For example, it may need to promote cellular activities that demonstrate physiological relevance or productive potential.
Both cell culture medium type and quality could directly impact a research and development effort. It is essential, then, that designers and developers of cell culture assays select appropriate cell culture media, that is, media that are suitable for whatever applications are envisioned. Cells of any given type are unique, which means that they have specific conditions that must be satisfied if they are to remain sociable and happy in their culture environment. Accordingly, it is imperative to match an individual cell type with a culture medium that is specifically designed and optimized to support optimal growth and vital cell functions.
Cell culture media development and optimization is a complex process, involving fine tuning of all components to their optimal concentrations to increase cell viability, promote robust growth, and maintain phenotype. In media optimization, different formulations are designed, developed, and tested for individual cell types.
Several essential components and supplements in media formulation (such as growth factors, vitamins, hormones, trace elements, and other micronutrients) are individually optimized based on different growth requirements of specific cell types.1 For example, human umbilical vein endothelial cells grow best in specific culture conditions, whereas cardiac cells require different basal media and growth supplements.
In addition, different media formulations are required for supporting different processes. For example, growth media formulation is required for the differentiation of one cell type to another. Media optimization requires consideration of several important factors such as ingredient types, concentration of individual components, cell type, cGMP manufacturing requirements, and quality control processes.
Typically, several rounds of initial testing, optimization, and preliminary analysis are required before an optimal media formulation can be selected for a specific cell type. Moreover, additional factors play crucial roles in selecting the right culture media for large-scale research and development needs. In the context of custom media optimization, these factors include reasonable costs, consistent quality attributes, reliable supplies, and realistic timelines. Incidentally, the FDA enforces cGMP regulations and guidelines to ensure proper design and monitoring of manufacturing processes and facilities to ensure the manufacturing of high-quality cell culture media products.
Chemically Defined Media and Xeno-Free Media
Advances in cell culture technology in recent years have relied heavily on cell culture media. The need for serum substitutes and serum-free media formulations tailored to the specific cell type and process is continuously growing due to risk of contaminants from animal-derived components, high lot-to-lot variation of bovine serum, and poor cell culture performance.
In today’s life sciences research marketplace, multiple options are available for cell culture media without the use of human or animal-derived components, including growth factors, hormones, or other compounds for preclinical research and development. In addition to providing batch consistency for a small- or large-scale project, chemically defined media are often more affordable and cost-effective than standard culture media or serum-based products.
Cell growth media can be classified as serum-based or serum-free, chemically defined, or xeno-free. Typically, media for research and biotechnology applications are serum-free with individually added nutrients to ensure consistent batch-to-batch performance, to reduce experimental variability, and to support greater data reproducibility.
As a result of media optimization, new options are available for media that are free of human or animal-derived organic products, growth factors, hormones, or other components. These options are relevant to serum replacement, where recombinant proteins and highly characterized components (defined chemically and by concentration) provide nutrients and promote cell functions such as proliferation and attachment.
For example, when the growth characteristics of human dermal fibroblasts, keratinocytes, and mesenchymal stem cells in serum containing defined (serum-free) or xeno-free media are compared, it is demonstrated that chemically defined or xeno-free media perform equally well or better than standard growth media (Figure 1).
Typically, animal-free recombinant proteins, growth factors, and other components required for media formulations are produced using non-mammalian manufacturing system and processes, allowing researchers to select accordingly for their cell culture needs, serum-free applications, and in vitro preclinical studies. Serum-free and xeno-free culture media formulations using highly characterized components (defined chemically) help reduce or eliminate altogether any risks of contaminating growth factors, viruses, prions, and animal-derived ingredients.
iPSC and Stem Cell Media
Shinya Yamanaka, M.D., Ph.D., is the Nobel Prize–winning scientist who pioneered induced pluripotent stem cell (iPSC) technology a decade ago. In 2006, he and his colleagues first reported that four critical transcription factors under defined culture conditions could reprogram a somatic cell into pluripotent stem cells. Since then, it has been shown that human induced pluripotent stem cells (hiPSCs) have the ability to self-renew and differentiate into different cell types, making these cells a valuable tool for human disease modeling, drug screening, and regenerative medicine and cell transplantation therapies.
Although the basic biochemical techniques for stem cell reprogramming are now established and are becoming increasingly standardized, both small molecule or transcription factor–driven approaches and bioengineering technologies for differentiating iPSCs into specific cell types are still evolving.
Research and development efforts that improved the ability of defined medium formulations to keep pluripotent stem cells in the undifferentiated state set the stage for subsequent advances—the development of techniques that initiate desired differentiation in vitro toward specific cell types of interest. Now, researchers have the ability to direct iPSCs to differentiate into various specialized and functional cell types including neurons, cardiomyocytes, hepatocytes, and hematopoietic cells using cell-specific differentiation media.
So far, several small molecules have been identified that are involved in maintaining the self-renewal potential of stem cells and their ability to induce lineage differentiation.2 Furthermore, research and development approaches focused on screening and characterization of small molecules in the defined culture media that target specific signaling modulators or pathways, epigenetic mechanisms, and other critical cellular processes could provide new biological insights and ways for manipulating stem cell fate and function in vitro.
There is immense therapeutic potential for iPSC technology. Further improvements in reprogramming techniques will ultimately advance stem cell biology and accelerate the development of safe regenerative medicine–based therapies for human diseases.
Cell culture technology is advancing rapidly, as demonstrated by the transition from 2D to 3D cultures, the rise of human tissue bioprinting, and the ever-greater specificity of stem cell differentiation. To ensure that these movements don’t stall, however, the designers and developers of cell culture media formulations must attend to specific cell types and applications. Cell culture technology is posed for expansive growth in the coming years as the fields of regenerative medicine, tissue engineering, cellular therapy, and gene therapy progress. Cell culture media play a critical role in driving new discoveries and technological breakthroughs such as iPSCs, 3D cellular models, and tissue bioengineering, and new formulations are continuing to advance scientific research and drug discovery efforts for combating human disease.
1. Davis JM, Ed. 1994. Basic Cell Culture: A Practical Approach. Oxford University Press. Oxford.
2. Hirschi KK, Li S, Roy K. 2014. Induced pluripotent stem cells for regenerative medicine. Annu. Rev. Biomed. Eng. 16: 277–294.