University College London London UK J.Masters{at}ucl.ac.uk
Dear Editor
I would like to direct your interest and that of your readers to the increasing and frequently neglected problem concerning the contamination of cell lines with cells derived from another species or individual. Cross-contamination can happen in any tissue culture laboratory as a result of defective technique or mislabelling, when two cell lines get mixed (1). The faster growing cell line rapidly and completely displaces the slower growing cell line. There is no evidence for mixed parentage or somatic cell hybridization in the cultures that result from cross-contaminationthey are composed exclusively of the faster growing cells. Sometimes the mistake is spotted and no harm is done, but often the error goes unnoticed and years of work can be wasted.
False cell lines are widely distributed in cancer research laboratories and cell banks worldwide, and their use is increasing. Estimates from national testing services indicate that up to 36% of cell lines were incorrectly designated (2). The German cell bank reported that of the cell lines submitted to them, nearly 20% were derived from a different species or individual to that claimed (3). The problem arises from cross-contamination and the continued use of cross-contaminated cell lines under false descriptions.
Many of the problems relate to HeLa cells, the first human cancer cell line to be established. HeLa cells were derived from a glandular cancer of the cervix. Some cross-contaminated cell lines continue to be sold with misleading descriptions. When buying a cell line, it is important to be aware that cell lines may masquerade as being derived from heart (Girardi heart), epidermoid cancer (KB), liver (Chang, liver), eye (WKD) and amnion (WISH), despite the fact that these are all the cervical cancer cell line HeLa. Similarly, ECV304 and EJ are cross-contaminants of the T24 bladder cancer cell line. Some publications in high impact journals such as Cancer Research describe KB cells as oral epidermoid cancer cells, despite the fact that they are cervical cancer cells. It is apparent that many referees and editors are ignorant of the problems associated with false cell lines.
Many tests are available for identifying cross-contamination (e.g. isozyme typing, HLA typing, karyotyping, DNA fingerprinting), but these tests are difficult to reproduce between laboratories. A simple and cheap test that is reproducible between laboratories is needed to identify cross-contamination. Short tandem repeat (STR) profiling of DNA is used by the forensic service for identifying crime suspects and for paternity issues. In brief, the sizes of 710 loci are calculated to within 1 bp to provide a unique series of numbers, equivalent to a bar code or credit card number. STR profiling was applied to 251 human cell lines, and shown to provide an international reference standard that could be applied to human cell lines (4).
STR profiling is cheap and reliable. Laboratories that cannot undertake STR profiling can obtain such profiles by sending a cell pellet or DNA to commercial suppliers such as the Laboratory of the Government Chemist (LGC). The service is cheap, costing less than $200 for each sample, a tiny fraction of the costs of the experiments within a publication. The simplest means to prevent the continued use of false descriptions in publications is for the editors of journals to require that all cell lines published in their journals should be STR profiled during the course of the study. I would appreciate if this journal and its editors took a lead in bringing STR profiling to the attention of their readers and reviewers and to initiate procedures to prevent publications with cell lines that have not been authenticated.
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