Mammalian cells are cells derived from mammals, including humans, and are widely used in biological research, biotechnology, and medicine. Unlike bacterial or yeast cells, mammalian cells are eukaryotic, meaning they have a nucleus and other membrane-bound organelles. They also have more complex cellular structures and signaling pathways, which can make them more challenging to work with but also more relevant for studying human biology and disease.

Mammalian cells are used in various applications, such as:

1. Basic research: Mammalian cells are used to study cellular processes, such as gene expression, signal transduction, cell cycle regulation, and apoptosis. These studies can provide insights into the molecular mechanisms underlying human biology and disease.
2. Disease modeling: Mammalian cells, particularly human cell lines or primary cells, can be used to model diseases in vitro. Researchers can manipulate the cells to express disease-associated genes or create cellular conditions that mimic specific diseases, allowing them to study the disease mechanisms and identify potential therapeutic targets.
3. Drug discovery and development: These cells are used in drug screening, testing the efficacy and safety of potential drug candidates, and studying drug-target interactions. Since mammalian cells closely resemble human cells, they provide a more physiologically relevant model for drug testing than bacteria or yeast.
4. Recombinant protein production: Mammalian cells can be used to produce recombinant proteins, such as therapeutic proteins, antibodies, or enzymes. Mammalian cells are often chosen for this purpose because they can perform complex post-translational modifications, such as glycosylation or disulfide bond formation, which are essential for the proper function of many proteins.
5. Gene therapy and cell therapy: These cells, including stem cells and primary cells, can be genetically modified or manipulated for use in gene therapy or cell therapy applications. For example, T cells can be genetically engineered to express chimeric antigen receptors (CARs) for cancer immunotherapy, or hematopoietic stem cells can be modified to correct genetic mutations in patients with inherited disorders.
6. Vaccine development: They can be used to produce viral antigens or virus-like particles for the development of vaccines. For example, the production of some COVID-19 vaccines relies on mammalian cell lines, such as the human embryonic kidney (HEK) 293 cell line, to produce the spike protein of the SARS-CoV-2 virus.

Working with these cells can be more challenging than working with bacterial or yeast cells due to their complex growth requirements, sensitivity to environmental changes, and the risk of contamination. However, the use of mammalian cells in research and biotechnology has greatly advanced our understanding of human biology and disease and has contributed to the development of numerous therapies and diagnostic tools.