Identification of contaminated cells impacts decades of research

In biomedical research, one key system used to model disease and test treatments are ‘immortalised’ cell lines. These are cultures of cells, taken from a patient sample or an organ biopsy, and grown in a petri dish. Under the correct conditions they continually divide and do not die, meaning many dishes can be prepared and widely used. The most famous of these lines are the HeLa cells, which are cervical cancer cells and have been cultured since 1951. Their incredible ability to divide and survive, however, may also be their biggest weakness.

A recent study in PLOS One, authored by SPJM Horbach and W Halffman, examines the potential contamination of these cell lines by other cells, leading to invalid results. They used the research database ‘Web of Science’, and looked for scientific articles based on any of the known misidentified cell lines as listed by the International Cell Line Authentication Committee’s (ICLAC) Register of Misidentified Cell Lines.

The study identifies 451 cell lines that have been contaminated or mislabelled, dating back decades. The knock-on impact into further studies is estimated to affect 33,000 papers.

If a researcher starts a cell line, there is a lag phase where the starting cells must establish and begin dividing. This process involves several steps to immortalise the cell.

At this early stage, however, contamination can occur from insufficient cleanliness, leading to cells from a neighbouring dish also being transferred, to take one example. If these contaminating cells are already immortalised, they will begin dividing immediately and out-compete the desired cells. If steps are not taken to accurately determine the cell type in the petri dish, the researcher may begin to test this cell culture under the impression that it is, for example, mouse lung cells, when instead it is HeLa cells. For some experiments, the difference in result gained from using the wrong cells may be negligible, but in others the entire experimental conclusion may be wrong.

Horbach and Halffman’s study highlights that cancer studies are most impacted by incorrect lines, as cell culture is a frequently used model system. Because different forms of cancer can exhibit varied behaviours and responses to treatment, it is vital to have the correct cells. In one paper, two types of prostate cancer cells were compared against each other to determine their response to certain conditions, but it was later found that the two cultures contained the same cell line.

A major challenge comes from how to deal with the published data once a misidentified cell line is discovered, and how rigorous the measures are in place to find contaminated lines. The study suggests using genetic testing to confirm that the immortal cell line is correct before beginning research, but researchers pushed to publish data may not have time to fully test their lines, especially if it comes from a historic line that has been used for years.

Private companies that sell cell cultures for researchers’ use may not admit contamination to prevent reputation damage and financial loss. The study recommends that journals issue notices when errors are found, to make it more visible that published research may not be reproducible.

The source and lineage of these cell lines should also be made more transparent, so that it is clear when cell types have been properly confirmed. In any case, small errors in establishing cell lines may have had far-reaching effects into the whole field, with the ghost of HeLa contaminating thousands of findings.

Image: National Cancer Institute via Linda Bartlett

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