Mammalian cell culture is the process of growing cells obtained from mammals in vitro, that is in flasks or bioreactors. It is the technique of growing cells outside their original tissue. Instead, a growth medium is used for the growth process.
Mammalian cells are eukaryotic cells. In this article, you will get an overview of mammalian cell types and how they are categorized by histology scientists.
With this out of the way, we will give you more details what mammalian cell culture is and what it is used for in industry and basic research in cell biology. Finally, we show you how recombinant antibodies are produced in mammalian cell culture.
In general, mammalian cells are eukaryotic cells. That means that each cell itself is much more complex than a bacterial cell. Moreover, since mammals consist of billions of individual cells in many organs and tissues, there is a lot of specialization among mammalian cells.
According to their specialization, mammalian cells are binned into cell types, depending on their localization in the body, their morphology, and their function.
Histology (the science of microscopic anatomy) lists more than 100 distinct types of human cells. Histologic cell types are classified how they originated during early embryonic development:
Cells could also be categorized depending on their main physiological function:
Damage to a sufficient number of cells result in disease states. Therefore, a deep understanding of cell biology and cell types is very important for medicine.
Mammalian cell culture is the technique of growing cells outside of their original tissue but in a growth medium instead.
To maintain cell integrity, the medium contains nutrients, vitamins, amino acids, salts, oxygen and CO2, and growth factors. Some media contain bovine serum, but this comes with the downside of limited reproducibility and potential contaminations.
Today, mammalian cell culture is a key technology in many biotechnological applications and in the medical field. Mammalian cell culture is used for:
A mammalian cell line is a population of mammalian cells that can be grown due to their ongoing cell division. Generally, a normal cell has a limited lifespan and does not divide indefinitely. To generate a cell line, cells must undergo immortalization.
Oftentimes, immortalization processes involve mutations of genes that deregulate the cell cycle or enhance proliferation processes. Natural sources of immortal cell lines are cancerous tissues, from which the first immortal cells originated.
A more specialized approach is the fusion of B cells with myeloma cells to generate immortalized antibody producing hybridoma cells.
In contrast, stem cells have the natural ability to divide indefinitely which is a necessary property for the development of higher life forms, e. g. embryonic stem cells from blastocysts.
A different approach is the culture of primary cells. Normal, mortal cells are removed from a tissue (e. g. via biopsy) and then grown in culture media.
These cells undergo a few cell divisions and then begin to die. This limits their applications but they are more representative of live tissue compared to immortalized cells.
Recombinant antibody expression with mammalian cell culture is a combination of recombinant molecular biology technologies with cell culture of mammalian cells.
It leverages several key advantages of both techniques to arrive at antibody products much superior to traditional technologies.
First, a suitable gene coding for the desired antibody is designed. This abolishes the need for the immunization of animals which comes with the disadvantages of batch to batch variability and even antibodies for highly toxic substances became accessible.
Subsequently, this gene is inserted into a mammalian cell line via a vector. Usually, CHO cells are used for expression due to their superior behaviour in cell culture conditions and high yields of expression. The use of microorganisms is generally ruled out for antibody production, because their expression system is not suitable.
The CHO cell culture is kept under strict control of growth conditions like nutrient, vitamin, mineral and growth factor levels. The cells divide and begin to express the antibodies that the inserted gene codes for.
The importance of the culture medium was highlighted by Austrian scientists in a 2015 peer reviewed publication in Applied Microbiology and Biotechnology1, in which the researchers showed that optimization can lead to seven-fold increases in antibody titers.
Finally, the secreted antibodies are harvested from the cell culture medium and subjected to downstream processes like purification steps to yield the final product.