Henrietta Lacks died of cervical cancer in 1951, but cells taken from her tumour have lived on to the present day as the HeLa immortal cell line. The mutated cancerous cells can divide an unlimited number of times. Of course, normal cells don't do that, which is why we age and die, and also why we aren't all dead from cancer. Fascinating and deeply ironic at the same time, no?
"HeLa cells have an active version of telomerase during cell division, which prevents the incremental shortening of telomeres that is implicated in aging and eventual cell death. In this way the cells circumvent the Hayflick Limit, which is the limited number of cell divisions that most normal cells can later undergo before becoming senescent." (Senescence being aging)
Apparently about 20 tons of Henrietta's cancer cells have been grown to be used in the testing of various things.