According to ICLAC (International Cell Line Authentication Committee) terms of reference, a cell line is considered to be misidentified if its DNA profile (genotype) is no longer consistent with the donor from whom it was first established. Such a cell line is described as a misidentified or false cell line .
To know if a cell line is authentic or misidentified, it is consequently important to look at its genotype and not its behavior (phenotype). Indeed, the cell line’s phenotype can vary with the passage number and/or the culture conditions. Misidentification can be due to several causes.
Whatever the problem, depending on the moment it occurs, a distinction is made between “false cell line” and “misidentified cell line”. If it happens early, during cell line establishment, no original material has been retained, and the cell line will be considered a false cell line. If it happens late, after the cell line has been established and distributed, the original material still exists. Only some stocks are therefore false and these will be defined as misidentified cells.
Misidentified cell lines can be generated by a large variety of labeling errors or they can be the result of cross-contamination. The term cross-contamination refers to the introduction of foreign material into a cell culture.
Cross-contamination occurs when that foreign material consists of cells from another culture. Cross-contamination initially results in a mixed culture, containing cells from the original culture and the contaminant. If the contaminant divides more rapidly, it will overgrow and replace the original cells within the culture.
The first immortal cell line was established in culture in 1951. It was derived from cancerous cervical tissue. This cell line called HeLa was widely distributed and passed on from one laboratory to another. In the late 1960s, the first data on cross-contamination of human cell lines with HeLa cells were published [2,3]. A decade later, the first inter-species cross-contamination of cell lines was described . Cell line cross-contamination and misidentification is a continuing problem. The latest version of the database maintained by ICLAC (version 7.2, released in October 2014) lists 438 false cell lines and 37 additional misidentified cell lines. The most common contaminant continues to be HeLa (24%). Based on those recent figures, it has been estimated that between 15% and 20% of human cell lines are in reality not derived from the claimed source.
Cross-contamination is not always the reason for an altered genotype of a cell line. Cells in culture can also change over time without any external contamination. Cell line genetics may be altered by chromosomal duplications, deletions or rearrangements, mutations and epigenetic changes . Genomic rearrangements can also result from many types of stresses such as contamination with bacteria, mycoplasma or exposure to drugs .
Whatever the research purpose, the use of misidentified cells always leads to the same consequences: unreliable results, loss of time, loss of money, and on top of that a tarnished reputation. When a cell line is used as a model of an organ or tissue, all results generated from the misidentified cells become questionable. In basic research, important progress may be halted in its tracks by using the wrong source material. As a result, more and more journals are now strongly recommending cell line authentication prior to publication, and some are even making it a pre-requisite for being published . In June 2015, the NIH revised instructions for funding. Those new rules have been in effect since January 2016 and clearly specify that: “The quality of the resources used to conduct research is critical to the ability to reproduce the results. NIH expects that key biological and/or chemical resources will be regularly authenticated to ensure their identity and validity for use in the proposed studies.”
The first step is becoming aware of the problem. Even if the cell authentication problem has existed for decades, the majority of researchers continues to ignore the subject or is not overly concerned. An online survey conducted in 2015 by the Global Biological Standards Institute (GBSI) revealed that 52% of respondents never perform cell authentication. Among reasons reported for bypassing this control, 24% indicated that they don’t see the necessity and 22% admitted that they were not aware of this issue .
Establishing Good Cell Culture Practice in your lab and eliminating practices that could introduce misidentification and cross-contamination are the key to reliable cell-based research.
ICLAC is an independent, global committee founded in 2012. ICLAC members have extensive expertise in cell line authentication testing. They act in a voluntary capacity and meet every 2-3 months by teleconference. The two major missions of ICLAC are the following:
Goal 1: Make Cell Line Misidentification More Visible
ICLAC members have developed a database of misidentified cell lines. This database is accessible for the scientific community and is regularly updated. The ICLAC list of misidentified cell lines can be found on the ICLAC website.
Goal 2: Promote Authentication Testing
ICLAC also focusses on scientific community education. On their website, documents (guidelines, checklists, protocols, etc.) are available to help scientists learn about the topic of cell identification and to facilitate the integration of authentication within good cell culture practices. The group also offers assistance to researchers wishing to authenticate cell lines. Finally, ICLAC members closely interact with journals and funding bodies to encourage mandatory authentication testing.
2. Gartler (1967) Genetic markers as tracers in cell culture. Natl Cancer Inst Monogr. 26:167-95.
3. Gartler (1968) Apparent HeLa cell contamination of human heteroploid cell lines. Nature. 217:750-751.
4. Nelson-Rees and Flandermeyer (1977). Inter- and intraspecies contamination of human breast tumor cells HBC and BrCa5 and other cell cultures. Science. 195(4284):1343-4.
5. Lorsch et al. (2014) Cell Biology. Fixing problems with cell lines. Science. 346(6216):1452-3.
6. Marx (2014) Cell-line authentication demystified. Nature Methods. 11: 483-488.
9. Freedman et al. (2015) The culture of cell culture practices and authentication - Results from a 2015 survey. BioTechniques. 59:189-192.