Basic structure of a mammalian cell. DOI:10.3390/app131810029
Mammalian cells are eukaryotic cells derived from organisms in the mammalian class of animals. They are characterized by their nucleus, which houses the genetic material, and a variety of organelles that enable essential functions like energy production, protein synthesis, and waste management. These cells are widely used in research, biopharmaceutical production, and biotechnology due to their ability to mimic human physiology more closely than prokaryotic or yeast cells.
Mammalian Cell Lines and Their Importance
Mammalian cell lines are established cells that can grow and divide in laboratory conditions, providing a versatile platform for scientific and industrial applications. These cell lines are often derived from tissues of mammals and are grown in culture systems. Although they are more challenging to cultivate compared to simpler cell types like bacterial cells, their ability to replicate the native biological processes of mammals makes them invaluable.
Primary Cells vs. Immortalized Cell Lines
Mammalian cell cultures can be broadly classified into two categories:
Primary cells: These are directly isolated from tissues and retain many of the physiological properties of their tissue of origin. However, they have a limited lifespan and eventually undergo senescence.
Immortalized cell lines: These have undergone genetic modifications or mutations that enable them to proliferate indefinitely. They provide a more consistent and scalable system for research and biopharmaceutical applications.
DOI: 10.3390/ijms241612716
Applications of Mammalian Cells
Recombinant Proteins and Antibodies
Mammalian cells are the preferred system for producing high-quality recombinant proteins and therapeutic antibodies. Their ability to perform native post-translational modifications, such as glycosylation, ensures that the proteins produced are functional and mimic those found in humans. This makes them essential for the production of monoclonal antibodies (mAbs), enzyme replacement therapies, and growth factors used in medical treatments.
The pharmaceutical industry relies heavily on mammalian cells for biologic drug development. Monoclonal antibodies, such as those used in cancer immunotherapy (e.g., pembrolizumab and trastuzumab), must be produced in mammalian cells to ensure proper glycosylation and structural integrity.
Gene Therapy and Vector Production
Mammalian cells are employed to create viral vectors and other delivery systems for gene therapy, providing a platform to study and treat genetic diseases. Cell lines such as HEK293 are commonly used to produce adeno-associated virus (AAV) and lentivirus vectors, which are critical for delivering therapeutic genes in gene therapy applications.
Recent advances in CRISPR/Cas9 gene editing have also leveraged mammalian cells to study gene function and develop targeted therapies for genetic disorders.
Biopharmaceuticals
Clinically important proteins like erythropoietin (EPO), tissue plasminogen activator (tPA), and monoclonal antibodies are commonly produced in mammalian cells. The ability to produce these proteins at scale has led to the widespread availability of biologic therapies for conditions such as anemia, clotting disorders, and autoimmune diseases.
Mammalian expression systems also play a role in the development of biosimilars—biologically equivalent versions of approved biologic drugs that offer cost-effective alternatives for patients.
Scientific Research
Mammalian cell systems are critical tools for understanding gene function, protein expression, and cell physiology. They allow researchers to analyze transcription, translation, and protein processing in a context that closely resembles human biology.
In addition to disease modeling, mammalian cell cultures are essential for toxicology studies, where they are used to assess drug safety and cellular responses to various compounds. The use of 3D cell cultures and organoid models is expanding, providing more physiologically relevant insights into disease mechanisms.
Structural and Functional Protein Studies
Mammalian cells facilitate the production of proteins with correct folding and glycosylation, enabling detailed structural characterization and functional studies. These studies help in understanding enzyme mechanisms, receptor-ligand interactions, and antibody-antigen binding, all of which are critical for drug discovery.
Structural biology techniques, such as cryo-electron microscopy and X-ray crystallography, often rely on mammalian-expressed proteins to determine atomic-level structures.
Production of Viral Antigens
The ability to produce viral proteins, such as prehepatitis B virus surface antigen, supports vaccine development and immunological research. Mammalian cells are commonly used to generate viral antigens for vaccine production, including influenza, SARS-CoV-2, and human papillomavirus (HPV) vaccines.
Illustration of a typical process to develop a mammalian cell line for recombinant protein manufacturing. DOI: 10.3390/ph6050579
Unique Features of Mammalian Cells
Mammalian cells possess several advantages over simpler systems like yeast or bacterial cells. For instance, they can perform post-translational modifications, such as glycosylation, phosphorylation, and sulfation, which are critical for the proper function of many proteins.
Unlike yeast or bacterial systems, mammalian cells can also produce glycoproteins with complex antennary oligosaccharides that closely mimic human glycosylation patterns. This is particularly important for antibody therapeutics, as glycosylation can influence antibody stability, effector functions, and immune system interactions.
Another key advantage of mammalian cells is their ability to secrete properly folded proteins into the culture medium, which simplifies downstream purification processes.
Challenges in Mammalian Cell Systems
Despite their advantages, mammalian cells present several challenges:
Cultivation Requirements: Mammalian cells require specific growth conditions, including defined media, controlled temperature, and CO₂ levels. They are also more sensitive to contamination than bacterial or yeast cultures.
Higher Costs: Culturing mammalian cells is more expensive due to specialized media, bioreactors, and rigorous sterility requirements.
Time-Consuming Processes: Producing recombinant proteins or antibodies in mammalian cells takes longer than in bacterial systems due to slower cell growth and protein production rates.
Limited Genetic Stability: Over multiple passages, some mammalian cell lines can undergo genetic drift, affecting their protein expression consistency.
Chinese hamster ovary (CHO) surface proteins. DOI: 10.1002/bit.27811
Advances in Mammalian Cell-Based Systems
Recent advancements in mammalian cell biotechnology have addressed some of these challenges:
Cell Line Engineering: CRISPR/Cas9 and other genome-editing tools enable precise modifications to optimize protein expression and cell viability.
Scalable Suspension Cultures: Suspension-adapted mammalian cell lines, such as CHO and HEK293 cells, allow for large-scale protein production in bioreactors.
Serum-Free and Chemically Defined Media: Eliminating animal-derived components reduces variability and improves regulatory compliance in biopharmaceutical manufacturing.
Transient vs. Stable Expression Systems: Researchers can choose between transient expression for rapid protein production and stable cell lines for long-term manufacturing needs.
Commonly Used Mammalian Cell Lines
Several mammalian cell lines have emerged as preferred hosts for protein production and research:
Chinese Hamster Ovary (CHO) Cells: Widely used for therapeutic protein production due to their ability to grow in suspension and perform human-like glycosylation. CHO cells are the dominant platform for monoclonal antibody production.
HEK293 Cells: Popular for transient protein expression and viral vector production. HEK293 cells are commonly used in gene therapy and vaccine research.
COS Cells: Ideal for short-term expression studies, particularly in gene verification.
NS0 Myeloma Cells: Commonly used for monoclonal antibody production, especially for hybridoma-based expression systems.
Vero Cells: Used extensively in vaccine production, including for polio and rabies vaccines.
Animal Cell Lines as Expression Platforms in Viral Vaccine Production. DOI: 10.1021/acsomega.3c10484
The choice of cell line depends on factors such as protein yield, post-translational modifications, scalability, and regulatory considerations. As mammalian cell technology advances, new cell lines and expression systems continue to improve productivity and cost-efficiency.
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