According to an article in BMC Molecular and Cell Biology, transfection can be achieved via several basic methods:
1. Physical Transfection
Physical transfection methods deliver DNA or RNA into the cytoplasm or cell nucleus via physical disruption of the cellular membranes. Examples of physical transfection include biolistic particle delivery (also known as the gene gun method), direct microinjection, electroporation, and laser-mediated transfection.
Physical methods can have very high transfection efficacy but can be damaging to cells and even trigger significant cell death. In addition, most physical transfection methods require specialized equipment, and many have a low throughput.
2. Chemical Transfection
Chemical transfection methods rely on carrier molecules that encapsulate or otherwise bring the DNA or RNA into the cell. These carrier molecules include cationic lipid-based carriers, calcium phosphate, and cationic polymers.
Some chemical transfection methods, like calcium phosphate transfection, are inexpensive but have lower efficacy and a higher risk of damaging cells. These are best used with hardy, non-primary cell lines. Others, like cationic lipid carriers, are known for their high transfection efficacy and applicability to many cell types, but they can be more costly and may require more complex and optimized procedures.
3. Viral Transduction
Sometimes considered "biological transfection", viral-mediated transfer of genetic material—transduction—utilizes genetically engineered viruses such as adenoviruses, adeno-associated viruses or retroviruses to introduce DNA or RNA into cells. These viral vectors are typically produced by the other transfection methods.
Viral transduction is often preferred for its high efficiency and ability to achieve stable gene delivery. It may succeed with cells that do not yield easily to other transfection methods, although it is more technically challenging. Use of viral vectors carries risk of cellular immune response, potential mutation in host cells, and biosafety concerns, as well.
Stable and Transient Transfection Techniques
The nucleic acids inserted into cells during transfection can exist in either a stable or transient form. Physical, chemical, and biological transfection methods can each be used to achieve stable or transient transfection.
Transient transfection: With transient transfection, intersected nucleic materials (e.g., (e.g., plasmids, oligonucleotides, messenger RNA) do not merge with the host cell genome and will persist only for a limited time. Transient transfection is often simpler to achieve, but its use is limited to short-term procedures, such as gene silencing experiments or small-scale protein production. Physical and chemical transfection methods are typically used for transient transfection but can be optimized to provide stable transfection in certain cases.
Stable transfection: If you need to generate cells that will retain the inserted genetic material even after replication, choose a stable transfection technique in which the inserted genes either integrate into the cell genome or are carried on a persistent episomal vector. The genetic material of interest often carries a selection marker, such as an antibiotic resistance, to facilitate the identification and enrichment of stably transfected cells. Achieving stable transfection tends to be more time-consuming, particularly if using physical or chemical methods of DNA transfer. For this reason, biological methods, such as viral transduction, are often preferred because lentiviral or other retroviral vectors can efficiently integrate genetic material into the host genome, ensuring long-term expression.