Her name was Henrietta Lacks, but scientists know her as HeLa. She was a poor Southern tobacco farmer whose cancer cells - taken without her knowledge - became one of the most important tools in medicine. The first 'immortal' human tissue grown in culture, HeLa cells were vital for developing the polio vaccine; uncovered secrets of cancer, viruses, and the effects of the atom bomb; helped lead to important advances like in vitro fertilization, cloning, and gene mapping. Henrietta herself remains virtually unknown, buried in an unmarked grave.