(August 1, 1920 – October 4, 1951) A HeLa cell is a cell in an immortal cell line used in scientific research. HeLa cells were used by Jonas Salk to test the first polio vaccine. The cells were propagated by George Otto Gey at St John Hopkins Hospital without Lacks' knowledge or permission. HeLa cells are termed "immortal" in that they can divide an unlimited number of times in a laboratory cell culture plate as long as fundamental cell survival conditions are met. One scientist estimates that the total weight of HeLa cells now exceeds 50 million metric tons.