293T cells are a type of human embryonic kidney cell line that is commonly used in laboratory research. They are derived from the original 293 cell line, which was created in the early 1970s. The "T" in 293T refers to the introduction of the SV40 large T antigen, which allows these cells to replicate SV40 vectors and produce large amounts of proteins. These cells are particularly useful for gene expression studies and the production of recombinant proteins. Their ability to grow rapidly and support high levels of transfection makes them a popular choice for researchers working with plasmids and viral vectors.