Human embryonic kidney 293 cells (HEK 293) are a popular and easy-to-transfect option in cell biology and biotechnology. Transfection efficiencies generally approach 100 percent, and the resulting cultures can be used to produce viral vectors, vaccines, and recombinant proteins. HEK 293 cells are suitable for research purposes and also can be used for scalable production of therapeutics for biopharmaceutical applications. Transient and stable gene expression can be achieved. Some strains of HEK 293 are available that require no adenovirus co-infection, making the system helper virus free. Pre-transformed cells can save time and offer features such as green flourescent protein (GFP), temperature sensitivity, antibiotic resistance, and more. In choosing a product, consider not only your application and the gene you are planning to transfect, but storage and maintenance requirements, as some lines need special care.