All of the body's normal cells experience the effects of aging over time, known as cellular senescence. Repeated divisions cause the cell's DNA to become unstable, and sometimes toxins form. This means that eventually the cells are unable to replicate, or divide, and the cell dies. This is called programmed cell death (PCD), apoptosis or even cellular suicide. It's part of the normal process for many cells, and it varies depending on the type of cell.
While it may sound awful, PCD can be a good thing. It's how fingers and toes are formed in utero (fetuses start out with webbed appendages) and how our immune system kills off cells that are infected by viruses. Too much PCD can cause tissue damage and lead to disease, but so can too little. For example, if cells grow out of control, they can become cancerous.
When grown in a laboratory setting, PCD generally occurs after about 50 cell divisions. But that's what sets HeLa apart. Under the right conditions, HeLa cells form an immortal cell line; they divide indefinitely. Remember that HeLa cells were grown from a tissue sample from Lacks' cervical tumor. Cancerous cells don't experience PCD, and Lacks' particular cells were especially hardy. Just like the cancer grew and spread quickly through Lacks' body, HeLa cells grow and spread quickly in vitro. Nobody knows quite why. Lacks had both the human papillomavirus (HPV) and syphilis, so one theory is that these helped suppress PCD in the cells.
Dr. Gey didn't seek to profit off HeLa, though. After publishing his research, he received requests from other researchers for samples of HeLa, and he was happy to provide them for free. Now HeLa cells are being used all around the world, with more than 60,000 medical journal articles published about their use and at least 11,000 patents related to their use. There are thousands of other cell lines, but HeLa remains the most popular because it is easy to grow, store and ship.
The hardiness and popularity of HeLa has actually led to a problem: contamination. Some researchers even think of the cells as a "weed" -- they are difficult to get rid of and may contaminate as many as 20 percent of other cell lines. The presence of HeLa cells can overwhelm the others and ruin research. Gold contends that mistakes in the handling of HeLa cells have led to costly errors in the medical research community. But let's explore some of the positives of HeLa cells next.