Expi293 cells are a specialized, human-derived cell line used extensively in biotechnology and pharmaceutical research. They serve as microscopic factories for producing large quantities of specific proteins and viral vectors. Developed for rapid and high-yield production, these cells are a go-to tool for researchers needing to generate biological materials for study, diagnostics, and the early stages of therapeutic development.
Origin and Defining Characteristics
Expi293 cells are derived from the well-established Human Embryonic Kidney 293 (HEK293) cell line. The parent HEK293 line was created in 1973 by introducing sheared adenovirus 5 DNA into cultured human embryonic kidney cells. This process immortalized the cells, allowing them to divide indefinitely in a laboratory setting. The “293” designation came from the researcher’s method of numbering experiments, with this specific cell clone originating from the 293rd experiment.
The primary engineered feature of Expi293 cells is their adaptation for high-density suspension culture. Unlike traditional adherent cells that must grow attached to a surface, suspension cells float freely in a liquid culture medium. This characteristic is advantageous for scaling up production, as it allows for growing vast numbers of cells in large bioreactors without the surface area limitations of flasks or plates.
A second defining characteristic is their human origin, which is important for producing complex human proteins. When proteins are made, they often undergo chemical modifications known as post-translational modifications. One common type, glycosylation, involves the attachment of sugar chains. Because Expi293 cells are human, they perform these modifications in a way that closely resembles how they occur naturally in the human body, which is important for the protein’s proper folding and function.
The Complete Expression System
Expi293 cells are rarely used in isolation; they are a central component of an integrated platform called the Expi293 Expression System. It consists of three core, optimized components that function in concert to achieve high protein yields.
The first component is the Expi293F cells themselves, which have been selected for their ability to grow to very high densities and their high efficiency in taking up foreign DNA. The second part is the specialized Expi293 Expression Medium, a chemically defined, serum-free liquid that provides the nutrients needed for high-level protein production. Because it is chemically defined and free of animal-derived components, it ensures high reproducibility between experiments.
The final component is a transfection reagent called ExpiFectamine. Transfection is the process of introducing a piece of DNA—containing the genetic instructions for making a specific protein—into the cells. ExpiFectamine is a lipid-based chemical that surrounds the DNA, forming tiny complexes that can fuse with the cell membrane to deliver the DNA. This reagent is optimized to work with high-density Expi293F cells, ensuring that a large percentage of cells receive the DNA and begin producing the target protein.
Core Applications in Biotechnology
One of its primary uses is for recombinant protein production. Researchers can instruct the cells to produce large amounts of a specific protein they wish to study, for instance, to analyze its three-dimensional structure or to develop it into a diagnostic test component. For example, during the COVID-19 pandemic, Expi293 cells were used to produce antigens from the SARS-CoV-2 virus for use in serological assays and research.
Another major application is in the rapid production of antibodies. Antibodies are proteins used by the immune system, and their unique binding capabilities make them valuable tools in research and as potential therapeutics. Using the Expi293 system, scientists can generate significant quantities of a specific antibody in just a week. This allows for rapid screening of different antibody candidates to find the most effective ones for further development.
The system is also employed for the generation of viral vectors. Viral vectors are modified, harmless viruses that are used to deliver genetic material into cells, a technique in gene therapy research and vaccine development. The Expi293 system can be used to produce these vectors in sufficient quantities for preclinical studies.
Comparison with Other Expression Platforms
Compared with standard adherent HEK293 cells, the primary advantage of Expi293 cells is scalability. Growing adherent cells requires a large surface area, which is cumbersome for large-scale production. In contrast, Expi293 cells grow in suspension, making it easy to scale production in large-volume bioreactors.
A more frequent comparison is made with Chinese Hamster Ovary (CHO) cells, which are the industry workhorse for manufacturing approved therapeutic proteins. The primary advantage of the Expi293 system over stable CHO cell lines is speed. Generating a stable, high-producing CHO cell line can take months, while the transient expression process with Expi293 cells can produce high yields of protein in about a week. This makes Expi293 ideal for rapid research and development phases.
However, the choice between them also depends on post-translational modifications. While Expi293 cells produce proteins with human-like glycosylation, CHO cells produce proteins with hamster-specific patterns. For many approved therapeutics produced on a massive industrial scale, the consistent glycosylation from stable CHO cell lines is preferred. Therefore, Expi293 is used for quick, early-stage development and research, while CHO cells remain the standard for large-scale commercial manufacturing.