Second, it has been argued that no remedial action is needed, as the problem will be addressed by new verification techniques. Similarly, it has been argued that the problem is already widely known, that scientists may be expected to implement effective lab protocols and be sufficiently critical about cell lines and their literature. Hence contaminated literature should have faded beyond the time horizon of literature considered relevant for current research and have disappeared from the relevant research record [ 49 ]. However, there is no sign of any ‘fading away’ of the problem. As we demonstrated, both the number of articles using misidentified cell lines, and the number of articles referring to them are still growing. Moreover, as demonstrated in the case studies, scientists show little awareness of the fact that cell lines may be misidentified. The citation analysis of the primary literature shows that articles keep being cited long after misidentifications have been reported, with over 40,000 articles citing contaminated research articles in 2016, including hundreds of citations to primary contaminated literature published decades ago.

First, it has been asserted that, in some cases, the origin or specific characteristics of a cell line might be of little influence on the results of an experiment. Indeed, in some cases all that a researcher needs is ‘a cell line’, independent of type, origin or status. In fact, this argument was already mentioned by Gartler in 1968 to put his findings into perspective [ 10 ]. To be sure, we acknowledge that not all 32,755 articles that we found contain critical errors. However, this is not a valid argument not to label articles that employ misidentified cell lines, for two reasons. To begin with, it is currently up to every individual scientist to judge the status of an article every time they cite or read it, by first checking the ICLAC database of misidentified cell lines to see whether any of the cell lines used in an article are in this database, and subsequently judging the influence that the misidentification may have on the results. This is a cumbersome and unlikely assumption about how researchers cite their literature, given the low levels of awareness indicated in our analysis. In addition, the secondary literature spreads into research fields that do not commonly use cell lines for their research. It is particularly doubtful whether scientists from these fields are aware of the potential issues with research on cell lines and whether they are in the position to make informed decisions about the validity of the claims in research articles based on misidentified cell lines.

Our results seem to present worrying problems for the biomedical sciences. Although the issue of misidentified cell lines has long been known, its effect on the scientific literature has not been properly recognised, let alone properly treated [ 47 , 48 ]. However, various arguments have been presented to suggest that papers based on misidentified cell lines are still valuable and that no remedial action is needed.

Practical measures

Over the past decades thorough attention has been paid to the improvement of authentication testing for cell lines. Authentication of cell lines, and hence the ability to demonstrate cross contamination, became possible by the introduction of genetic markers by Gartler in 1967 [9]. Subsequently, many techniques for cell line authentication were introduced, starting off with inspection of banded marker chromosomes [8], and the visualization of chromosomal pattern and architecture in general [50], subsequently followed by the methods of Human Leukocyte Antigen (HLA) typing [51], enzyme polymorphisms [52] and DNA polymorphisms [53]. More recently, the techniques of ‘DNA fingerprinting’ [54] and the usage of locus-specific probes were introduced. Finally, this led to the now accepted standard method of short tandem repeat profiling [45]. As has been pointed out recently, the techniques for proper cell line authentication are now widely available [55]. However, implementation of these techniques is still falling short for multiple reasons, including time and financial constraints, lack of training and lack of (international) standards [55].

Despite measures to authenticate new and existing cell lines [27], research based on the wrong cells is still present in the literature and in fact continues to be published. Some form of precautionary labelling of contaminated articles seems unavoidable. However, this remedial action should be proportionate and not cause unnecessary damage. For some individual scientists, research departments, or scientific journals, rash measures could turn out to be painful. Indeed, some researchers have authored over a hundred articles in our set of contaminated primary literature. Even though the problem with these articles almost exclusively [56] falls under the heading of ‘honest error’, with no intention to deceive, notifying all those articles as potentially erroneous, or worse: retracting them, would have a disproportionate impact on several scientists’ careers. This would undermine, rather than support, an effective clean-up operation. However, in addition to catching cell line contamination at the source, initiatives to label contaminations ‘downstream’ in the published literature are direly needed. We can make several suggestions.

First, notifications should be posted alongside previously published articles using misidentified cell lines. This could be done in the form of ‘expressions of concern’, which are described as “Neither retractions nor corrections, they alert readers that there may be an issue with a paper, when the full story is not yet clear.” [57] If clear and uncontended, the consequences of the misidentification for the article’s conclusions could be reported, but otherwise the expression of concern could merely state: “Cell line X in this study is known to be misidentified and is actually Y. See Z for more information.” The interpretation of this warning is then entirely up to the expert reader. Such notifications would also serve to preserve as much valuable data as possible: data reported on a misidentified cell line might still be entirely valid, provided the real origin of the cell line is clear. Hence it might be a waste of funds and efforts to automatically dismiss these data. In cases where the use of these cell lines leads to (severely) false conclusions that could have a major impact on future research, articles could be retracted. For recent cases, a system of self-retractions, as proposed by Fanelli [58], could be employed.

Second, to allow for simple future identification of articles using misidentified cell lines, we recommend that authors mention the employed cell lines in easily searchable parts of their article, such as the keywords or abstract. Some journals have already suggested measures in this direction, but implementation seems to be slow [30]. However, some journals have currently installed a system of Research Resource Identifiers (RRIDs), which might assist in tackling the cell line misidentification issues [59]. Alternatively, a system of cross-reference between databases of cell lines and scientific journal publications could be set up. Linking the NCBI databases of ‘BioSamples’ and ‘research articles’ would be a natural candidate for such a system. In similar ways, the Cellosaurus database, the ICLAC database and Research Resource Initiative are already cross-linked.

In addition, better use could be made of paper trails for cell line provenance [60]. A clear and complete overview of the origin of a cell line, as well as the various verification tests, the experiments that it has been part of, and the results that these yielded, would be of great benefit in examining the status and quality of a cell line. In addition, this would allow for easy identification of potentially erroneous research when a cell line is found to be misidentified.

Besides being of use in terms of recognition of erroneous research, the paper trail might also serve other purposes, such as mapping the existing knowledge on a certain cell line (thereby also allowing for simple identification of knowledge gaps) and providing a stage for the publication of negative results of experiments on cell lines. The publication of such results has long been proposed as a way of fostering integrity in research [61].

Nearly half a century after the first concerns about misidentified cell lines, the initiatives to improve authentication need to be complemented by attention to the already contaminated literature. Our analysis shows that the task is sizeable and urgent.