Short Report False and mycoplasma-contaminated leukemia–lymphoma cell lines: time for a reappraisal Hans G. Drexler, Wilhelm G. Dirks, Roderick A.F. MacLeod and Cord C. Uphoff Department of Human and Animal Cell Lines, Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany Leukemia–lymphoma cell lines are important research tools in a variety of fields. To represent adequate model systems it is of utmost importance that cell lines faithfully model the primary tumor material and are not cross-contaminated with unrelated cell material (or contaminated with mycoplasma). As it has been previously reported that cross-contaminated cell lines represent a significant problem, it is of interest to know whether any improvement in the prevalence of such “false cell lines” had occurred since we called the alert in 1999. A retrospective review of our data archives covered 848 cell lines received from 1990 to 2014 from 290 laboratories in 23 countries spanning the spectrum of leukemia–lymphoma entities. Two variables were considered: authenticity and freedom from mycoplasma infection. Regarding provenance, we separately considered primary sources (original investigators having established the cell lines or reference repositories) and secondary sources. The percentages of mycoplasma-contaminated cell lines decreased significantly over the 25-year timespan. Among primary sourced material: mycoplasma-contamination fell from 23% to 0%; among secondary sourced: from 48% to 21%. The corresponding figures for cross-contamination declined from 15% to 6%, while among material obtained from secondary sources prevalence remained remarkably high, throughout the time periods at 14–18%. Taken together, our data indicate that using non-authenticated cell lines from secondary sources carries a risk of about 1:6 for obtaining a false cell line. The use of authentic leukemia–lymphoma cell lines holds important translational value for their model character and the reproducibility of the laboratory data in the clinical arena. Introduction Tumor cell lines are important research tools which over the last decades have contributed significantly to progress knowl- edge in a variety of fields, recently broadly depicting the genomic diversity of cancer and providing valuable insight into their pathobiology. 1,2 However, there are several signifi- cant problems that have plagued this area of research: nota- bly, contamination with mycoplasma or with other cell lines (“false cell lines”), refusal of scientists to provide cell lines upon request, black market (unchecked trafficking of cell lines between labs), excessive bureaucracy and legal issues. In a series of articles we have documented the wide- spread cross-contamination of tumor cell lines in general and in leukemia–lymphoma-derived cell lines in particular. 3,4 Detection of mycoplasma-contamination and authentication of cell lines have markedly changed over the last decades with the introduction of new diagnostic tools, but it is not clear whether this had led to sustained improvements in the prevalence of mycoplasma-positive and false cell lines. The objective of our study was to monitor progress in combating these twin problems of cell culture over several decades. To that end we studied 848 leukemia–lymphoma cell lines received between 1990 and 2014. We chose 1990 as the start date as that was the earliest year for which we had previously banked specimens. Improvements were primarily Key words: authentification, cell lines, leukemia, lymphoma, mycoplasma Additional Supporting Information may be found in the online version of this article. Disclosure: All authors are employees of the Leibniz-Institute DSMZ which is a non-profit research institute owned by the German government. For these studies no research funding had been received. Brief Description Tumor cell lines are essential research tools, but a significant percentage is contaminated with other cell lines and/or mycoplasma. Our study, spanning 25 years of data, documents that the incidence of mycoplasma-contamination decreased significantly over that time-span. Cross-contamination of cell lines remained at an unacceptable high level, particularly among cell lines circulating unchecked between laboratories. Use of authenticated cell lines holds important translational value for their model character and their reproducibility in the clinical area. DOI: 10.1002/ijc.30530 History: Received 23 Sep 2016; Accepted 8 Nov 2016; Online 21 Nov 2016 Correspondence to: Hans G. Drexler, Leibniz-Institute DSMZ-German Collection of Microorganisms and Cell Cultures, Inhoffenstr. 7B, D-38124 Braunschweig, Germany, E-mail: hans.drexler@dsmz.de; Tel: 149 531 2616.160 Tumor Markers and Signatures Int. J. Cancer: 140, 1209–1214 (2017) V C 2016 UICC International Journal of Cancer IJC