“IMMORTAL CELL populations derived from a variety of human and animal tissues were reported to occur spontaneously in dozens of laboratories in the twenty year period from the early 1940’s to the early l960’s. These cell populations, now numbering in the hundreds, are best known by the prototype cell lines HeLa (derived from a human cervical carcinoma in 1952) and L cells (derived from mouse mesenchyme in 1943). They continue to flourish in cell culture laboratories throughout the world to this day.” The source of some legal controversy for HeLa cells.
http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html