Mammalian expression systems are invaluable tools for the production of a wide range of complex recombinant proteins, including antibodies, due to the ability of mammalian cells to promote correct post-translational modifications and folding.
When it comes to expressing proteins in mammalian cells, there are two main alternatives: transient or stable production. Both methods have advantages and disadvantages, and the choice between transient expression and stable expression systems will depend on your program’s nature, scale, and timing.
Transient expression systems are ideal for quickly achieving early developmental milestones. In contrast, stable expression creates a route toward long-term manufacturing and regulatory compliance. Abzena supports clients in balancing the two options – identifying the most efficient route from gene to protein for every therapeutic.
What Is Transient Expression?
Transient expression involves the temporary introduction of genetic material into the host cells. There is no permanent integration into the host genome, and so no selection is required. Consequently, it is the faster of the two approaches, allowing researchers to generate recombinant proteins in days rather than weeks. It’s an ideal choice for early research, small-scale screening, or the generation of material for initial analytical or structural needs.
- Speed: Proteins can be produced within a few days of transfection.
- Flexibility: Excellent for evaluating multiple constructs or formats in parallel, or for examining, for example, the effect of different chain ratios for a complex bispecific.
- Scale: Best suited to small-scale production (milligram to gram quantities).
- Cost: Transients are generally more cost-effective than stables
Transient expression systems are particularly beneficial when evaluating multiple candidates or on an accelerated discovery timeline. However, since no gene integration occurs, production cells are short-lived, making this approach unsuitable for long-term manufacturing.
At Abzena, we offer a range of rapid transient production systems, including ExpiCHO™, enabling clients to test design concepts quickly before committing to more extensive cell line development.
What is Stable Expression?
By contrast, stable expression integrates the gene of interest into the host genome resulting in a permanent change to the host that is maintained as a cell divides. This allows for continuous, reproducible protein production.
Stable expression takes longer to establish – typically three to four weeks – but it’s critical to obtaining the consistent yields and quality that is necessary for preclinical and clinical manufacturing. While it requires greater upfront investment, long term it supports regulatory submissions and supply for clinical and commercial stages.
Key benefits include:
- Long-term, reproducible expression suitable for GMP manufacturing.
- Stable, well-characterized cell lines that meet regulatory expectations.
- Ability to scale from development to commercial production.
- Larger scale production.
Developers will typically create a stable cell line from a lead candidate sequence identified during the preceding discovery and developability campaign. The process involves transfection, clone selection, and rigorous testing for titre and product quality as well as genetic and phenotypic stability. At Abzena we utilize a platform approach to efficiently generate a stable cell line, which consists of initial generation of stable pools from which high expressing clones are identified, using state of the art technology, underpinned by best-in-class bioassay and analytical characterization.
They Work Together: Transients, Stables and the Combined Approach
In most programs, transient vs stable systems are not an either/or approach but are complementary to each other.
Transients are often the workhorse of early R&D, rapidly providing material to support R&D activities. After generating preliminary data via transient expression, researchers then move to stable systems for consistent, large-scale production.
One increasingly common approach is that, rather than progressing straight to a clone, an alternative is to use stable pools. Here, the stably transfected pool comprises a heterogeneous population of cells, all transfected with the same construct but have not yet progressed through clonal isolation. Stable pools act as an intermediate step before full clone selection. Although they form a mixed population, expression remains consistent enough over the short term to generate material and explore molecule performance ahead of establishing a clonal cell line. The products obtained from pools typically show similar product quality as from the ultimate clonal cell line meaning they are a valuable tool, with the key advantage being that stable pools can be generated in as little as three weeks, so significantly reducing the timeframe.
Stable pools can also provide much larger quantities than transient expression allowing developers to rapidly explore certain aspects of molecule performance that would have otherwise been challenging due to their material heavy requirements.
Once you are ready to progress the molecule, a high expressing clone is established by single cell cloning from the stable pool, leading to the generation of a research cell bank (RCB) and eventual transition to a GMP-compliant master cell bank.
Bridging together early development and manufacturing potential combines parts of both processes to reduce overall project risk.
Creating Stable Cell Lines: The Abzena Advantage
When it comes to creating stable cell lines, reliability and reproducibility are a must. Our scientists ensure every detail at every stage of the process for the creation of stable cell lines is considered, from vector design and clone selection through to bank creation and long-term storage down the line.
This process includes:
- Host cell and vector optimization for optimal productivity.
- Productivity screening across multiple clones.
- Comprehensive characterization and stability testing.
- Creation of a master cell bank and working cell bank under GMP conditions.
With extensive experience creating and generating stable cell lines for a variety of clients across industries, Abzena scientists bring flexibility to ensure accelerated biologics development.
Stable vs. Transient Expression FAQs
What Is the Main Difference Between Transient and Stable Expression?
Transient expression is used for short-term, rapid protein production, while stable expression integrates the gene into the genome for long-term, consistent yields.
When Should I Transition from Transient to Stable Expression?
Most projects transition to stable expression once a lead candidate is confirmed and larger quantities or regulatory submissions are required. Stable pools often serve as the bridge between the two.
How Long Does It Take to Create a Stable Cell Line?
Timelines vary but stable line creation takes in the region of 10-12 weeks from transfection to a clonal cell line based on productivity screening and derived complexity.
Can Complex Proteins Be Expressed?
Yes. Transients are ideal for exploring how best to express complex proteins. Take for example, bispecifics. These sometimes can have two, three or even four chains and transients are ideal to start exploring what vector ratios may lead to the best product. Learnings from the transient setup can then be transferred across to the stable transfections.
What Are Double Stable Cell Lines?
Double stable cell lines express two genes of interest simultaneously, ideal for multi-component products such as bispecific antibodies or fusion proteins.
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