The most famous cell culture line to date. These are cells taken from the cervix of one Henrietta Lacks, who in 1951 was operated on for cervical cancer.
Prior to this, scientists had been unable to grow human cells in a culture medium for more than 50 generations. Whilst Henrietta ultimately died of her cancer eight months after the operation, her cells have lived on, still surviving in laboratories today.
The surprising bit is that the combined biomass of all the HeLa cell cultures in the world is probably much bigger and more massive than Henrietta could ever be. HeLa cells have somehow acquired cellular immortality, in that the normal mechanisms of programmed cell death after a certain number of divisions have somehow been switched off in her cells.
HeLa cells are apparently so aggressive in growth that a slight contamination by these cells can result in their overwhelming other cultures. There are stories floating around of how some labs had thought they had found new human cell lines, only to find out later that they had inadvertently grown more HeLa cells. Similar stories arose from scientists growing various human tissue samples (other cancers for example) in the laboratory.
I think this quote explains it better:
Within a few years the problem had reached unbelievable proportions. In 1966 the geneticist Stanley Gartler compared 17 cultures of various human cell types, obtained from a number of different laboratories, against a known HeLa strain. He found that all 17 were HeLa cells. In 1968 the American Type Culture Collection, the premiere cell bank in the United States, set up specifically to maintain pedigreed cell lines of unquestioned authenticity and to supply such to researchers all over the world, tested all its lines of human cells. Of these 34 cell lines, 24 proved to be HeLa. In 1972, in an important scientific exchange program connected with Nixon's "War on Cancer," Russian scientists supplied American scientists with six tissue cultures taken from six cancer patients from six different locations in the Soviet Union. All six turned out to be HeLa.
One woman died, her cells live on. Is this a form of immortality?
sources:
http://www.uow.edu.au/arts/sts/bmartin/dissent/documents/AIDS/Pascal91.html
http://www.libfind.unl.edu/wglider/biofacts/hela.html
http://www.lrb.co.uk/v22/n08/enri2208.htm (I like this one) | 
