Introduction

Transient production refers to the temporary expression of recombinant proteins within host cells without stable integration of the target gene into the host genome. This approach allows for rapid, scalable protein production and is widely used in research, diagnostics, and therapeutic development. Compared to stable production systems, transient expression offers faster turnaround times, greater flexibility, and reduced development costs.

Mechanisms of Transient Production

• Gene Delivery
  The target gene is introduced into host cells using plasmid DNA or viral vectors. Common delivery methods include:
  • Chemical transfection: Using polyethyleneimine (PEI) or calcium phosphate.
  • Electroporation: Applying electrical pulses to create temporary pores in the cell membrane.
  • Viral transduction: Using adenoviruses or baculoviruses for efficient gene delivery.
• Transient Gene Expression
  • Once inside the host cell, the plasmid remains episomal (extrachromosomal) and does not integrate into the genome. This allows the host’s transcription machinery to rapidly transcribe the gene of interest.
  • Strong promoters, such as the cytomegalovirus (CMV) promoter, drive high levels of gene expression within days of transfection.
• Protein Synthesis and Secretion
  • The host cell’s ribosomes translate the mRNA into protein, which is then folded.
  • Secreted proteins are transported to the extracellular space, simplifying downstream purification. Intracellular proteins remain within the cytoplasm or other organelles.
• Limited Duration of Expression
  • As cells divide, the plasmid is gradually diluted and lost, leading to a decline in protein expression over time. Typically, high expression levels are maintained for 3–7 days, depending on the cell line and culture conditions.

Host Systems for Transient Production

• Mammalian Cells
  • Chinese Hamster Ovary (CHO) cells: Used for rapid production of therapeutic proteins, including monoclonal antibodies.
  • Human Embryonic Kidney (HEK293) cells: Preferred for producing proteins with human-like post-translational modifications.
• Insect Cells
  • Sf9 and Sf21 cells: Transfected with baculovirus vectors for high-yield protein production, particularly for structural biology studies.
• Plant Systems
  • Nicotiana benthamiana: Used in agroinfiltration methods for the rapid production of biopharmaceuticals such as monoclonal antibodies and vaccines.

Applications of Transient Production

• Research: Quickly produces recombinant proteins for structural studies, enzyme assays, and molecular biology experiments. For example, proteins produced in HEK293 cells are commonly used in crystallography and surface plasmon resonance (SPR) assays.
• Therapeutic Development: Enables rapid prototyping and testing of monoclonal antibodies, vaccines, and therapeutic enzymes.Such as trastuzumab (Herceptin®).
• Diagnostics: Produces antigens and antibodies for diagnostic assays, such as ELISA kits, such as ELISA kits for detecting infectious diseases like COVID-19 and hepatitis B.
• Vaccine Production: Used for the rapid development of protein-based vaccines, including COVID-19 vaccines （Covifenz） produced in Nicotiana benthamiana.

Challenges and Limitations

• Transient Nature of Expression: Expression declines as plasmids are lost during cell division, limiting the duration of production.
• Scale-Up Limitations: Scaling transient production to large bioreactors is challenging due to variability in transfection efficiency and plasmid stability.
• Cost of Plasmid DNA: Large quantities of high-quality plasmid DNA are required, increasing production costs.
• Host Cell Viability: Some transfection methods, such as electroporation, can reduce cell viability, impacting overall protein yield.
• Post-Translational Modifications (PTMs): Not all host systems provide human-like PTMs, which may limit the functionality of certain therapeutic proteins.

GenScript Services and Products

• Gene Synthesis and Codon Optimization : Enhances expression efficiency in E. coli and mammalian systems.
• Mammalian Expression Platforms: TurboCHO™ Recombinant Antibody Expression - Ship in 5 Business Days | GenScript: TurboCHO™ High Throughput Antibody Production of purified antibodies.
• Protein Purification Products: Affinity chromatography and size-exclusion chromatography provide high-purity proteins.

Conclusion

Transient production is a versatile and efficient method for generating recombinant proteins, offering rapid expression without the need for stable cell lines. This approach is essential for research, diagnostic applications, and the rapid development of biopharmaceuticals. While its transient nature and scalability pose challenges, service providers like GenScript offer comprehensive solutions, from gene synthesis to large-scale transient protein production, accelerating innovation and enabling advancements in both science and industry.