COUNTLESS research projects around the world into cancer and other major diseases are producing bogus or misleading results because investigators are studying the wrong type of cell.
The mistakes arise when fast-growing “rogue cells” contaminate cell cultures and swamp the correct cells. A team’s work on prostate cancer, for example, might turn out to be worthless because cells researchers thought were prostate cancer cells turn out to be cervical cancer cells.
Although the danger has been known about for decades, most researchers still fail to check the identity of the cells they are working with. And several new types of rogue cell are emerging, 91av has learned.
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Warnings of the potential scale of the problem were issued this week at a conference in Warwick organised by the UK’s Health Protection Agency. Precise figures are hard to come by because researchers are either unaware that they have worked with the wrong cells, or try to cover it up.
“If people have spent three years working on the wrong cells, they are not likely to want to tell people about it,” says David Lewis, manager of the European Collection of Cell Cultures, based at Porton Down in Wiltshire. He will emphasise the importance of getting cells from authenticated sources at this week’s conference.
The best estimates available suggest around a fifth of all experiments in fields such as cancer and microbiology involve the wrong cells. “Various figures between 20 and 40 per cent have been aired,” says Rod MacLeod, head of the genetics laboratory at the DSMZ, the German collection of cell cultures in Braunschweig.
In a study in 1999, MacLeod found that of 252 cancer cell lines, 18 per cent were “impostors”. And newly established cell lines were just as likely to be contaminated as older ones. He blames this on the ease with which cell lines can be contaminated.
The most notorious rogue cells are so-called “HeLa” cells (see “Divide and contaminate”). They rapidly overrun more sluggish colonies. “Just one HeLa cell could survive and proliferate,” MacLeod says. Attempts to purge cell lines contaminated by HeLa cells have waxed and waned since 1967, when the problem first emerged, but now there are new rogue cells to deal with too.
One posing particular problems in cancer research is the T24 line of bladder cancer cells. MacLeod and Hans Drexler, director of the human and animal cell collection at the DSMZ, discovered them last year “posing” as healthy epithelial cells that line organs. They are now popping up all over the place, especially in cultures of other cancer cells. Recently they contaminated prostate cancer cell lines, as Adrie van Bokhoven of the University of Colorado Health Sciences Center in Denver discovered. “Two years after our research, there are still publications that describe it as prostate,” van Bokhoven says.
In a review to be published this November in The Prostate journal, van Bokhoven will highlight the problems posed by another rogue cell, an unusually lively prostate cancer cell line called PC-3. “We reveal that another three ‘unique’ prostate lines were actually PC-3,” he says, adding to others he has already discovered.
Before journals publish a paper van Bokhoven wants editors to insist that researchers provide proof that their cell lines are authentic. “Editors should demand it,” says van Bokhoven, who points out that the DNA fingerprinting tools now available should allow the problem to be eradicated. “There are no more excuses,” he says.
John Masters of University College London, who has struggled for years to highlight the problem, agrees. “I’ve written to journal editors till I’m blue in the face on this, and they do nothing,” he says. This unwillingness to confront the issue has been dubbed “false cell-line denial syndrome” by Drexler, who says that the problem will persist as long as it is swept under the carpet.
Senior figures at the American Type Culture Collection have also tried for years to highlight the problem, says Keith Bostian, of the American Society of Microbiology. The ASM is aware of the problem, he says, and its journals “encourage” authors to deposit cell lines in public collections for authentication.
Yet one survey conducted by the ATCC revealed that two-thirds of journals still fail to cite the source of biological materials. Worse, many of the cultures the ATCC receives for deposit are misidentified or contaminated.
Divide and contaminate
Cell cultures are the workhorses of modern biology, used to study everything from cancer and infectious diseases to the genetic workings of our cells. Whole colonies can be grown in Petri dishes from a single “mother” cell.
But because different cells often look identical, researchers often can’t tell if they are working with the wrong cells. And such mix-ups can happen easily. Sometimes natural mutations result in “genetic drift” away from the original cell. But often the culprit is contamination with fast-growing invaders such as “HeLa” cells, cervical cancer cells that in 1952 became the first human cells to be grown in culture. All it takes is one stray HeLa cell, perhaps in the nutrient medium used to grow cells, and the rogue cells will rapidly overrun a colony.
One cell line called KB, for instance, was supposed come from a mouth tumour. Between 1998 and 2000, it was cited more than 300 times in studies of head and neck cancer. But it turned out to be a HeLa cell line. The same was true of HEp-2, a cell line thought to have originated from a larynx tumour. That was also cited around 300 times.