HEK-293T cells are a human cell line derived from embryonic kidney cells. They are widely used in biological research and biotechnology due to their ability to grow rapidly and efficiently produce proteins. The "T" in HEK-293T indicates that these cells have been modified to express the SV40 large T antigen, which allows for enhanced replication of certain plasmids. These cells are particularly valuable for gene expression studies, vaccine development, and the production of recombinant proteins. Their ease of transfection makes them a popular choice for researchers working with DNA and RNA technologies.