- Polyethyleneimine (PEI) is a synthetic cationic polymer that has become a widely used non-viral vector for gene delivery in eukaryotic cells.
- Known for its strong positive charge, PEI can bind negatively charged DNA or RNA molecules to form stable complexes, known as polyplexes, which facilitate the uptake of nucleic acids into cells. Among its forms, branched PEI with a molecular weight of 25 kDa is most commonly used for transfection applications, although linear forms also exist and are sometimes preferred for specific purposes.
- PEI-mediated transfection works primarily through electrostatic interaction. Once PEI binds to DNA, the resulting complexes are internalized by cells through endocytosis. A unique feature of PEI is its “proton sponge effect,” which enables the complexes to escape from endosomes before degradation, thereby increasing the likelihood of successful gene expression. This property contributes significantly to its effectiveness as a transfection reagent, particularly for transient expression systems.
- Due to its cost-effectiveness, ease of use, and scalability, PEI is especially popular in large-scale transient transfection protocols using mammalian suspension cell lines like HEK293 and CHO. It is compatible with serum-free, chemically defined media and can be used in both small-scale lab settings and industrial-scale bioreactors. As such, it has become a key tool in the rapid production of recombinant proteins, monoclonal antibodies, and virus-like particles for research, preclinical studies, and early-stage manufacturing.
- However, the use of PEI is not without limitations. At high concentrations, it can be cytotoxic, and transfection efficiency can vary depending on the cell type and the ratio of DNA to PEI. As a result, empirical optimization is often required for each experimental setup. Despite these challenges, PEI remains a robust and versatile reagent that has transformed the way transient gene expression is carried out in biotechnology and pharmaceutical development.
- Historically, PEI gained prominence in the late 1990s and early 2000s, when researchers sought alternatives to more expensive and complex lipid-based transfection reagents. Its successful adoption in both academic and industrial settings has cemented its role as a mainstay in modern molecular biology, particularly in systems where speed, scalability, and protein yield are critical.
