Multiparameter approach in the identification of cross-contaminated leukemia cell lines

The costs of using unauthenticated, over-passaged cell lines: how much more data do we need?

Increasing data demonstrate that cellular cross-contamination, misidentified cell lines, and the use of cultures at high-passage levels contribute to the generation of erroneous and misleading results as well as wasted research funds. Contamination of cell lines by other lines has been recognized and documented back to the 1950s. Based on submissions to major cell repositories in the last decade, it is estimated that between 18% and 36% of cell lines may be contaminated or misidentified. More recently, problems surrounding practices of over-subculturing cells are being identified. As a result of selective pressures and genetic drift, cell lines, when kept in culture too long, exhibit reduced or altered key functions and often no longer represent reliable models of their original source material. A review of papers showing significant experimental variances between low- and high-passage cell culture numbers, as well as contaminated lines, makes a strong case for using verified, tested cell lines at low- or defined passage numbers. In the absence of cell culture guidelines, mandates from the National Institutes of Health (NIH) and other funding agencies or journal requirements, it becomes the responsibility of the scientific community to perform due diligence to ensure the integrity of cell cultures used in research.

Malignant hematopoietic cell lines: in vitro models for the study of erythroleukemia

A panel of leukemia cell lines has been assembled over the last 30 years representing a spectrum of erythroid cells arrested at various stages of differentiation. The oldest cell line is K-562 which is one of the most prolific in use. Most cell lines have been established from acute myeloid leukemia M6 or chronic myeloid leukemia in blast crisis and generally express immunoprofiles typically seen in immature erythroid cells. Several cell lines are constitutively growth factor-dependent, responding proliferatively to a variety of cytokines. The predominant cytogenetic abnormalities are the t(9;22)(q34;q11) found exclusively in CML-derived cell lines, and rearrangements of chromosomes 5 and 7 which occur in all disease subtypes. Ph+ve cell lines consistently displayed structural and numerical changes associated with disease evolution, including +8, -17/17p-/i(17q), and +19. It is striking that many cell lines though committed to either the erythroid or megakaryocytic lineage tend to co-express features of the other lineage, consistent with the concept of a common erythroid-megakaryocytic progenitor. Several cell lines may be induced to differentiate along the erythroid, megakaryocytic or monocytic pathway by treatment with pharmacological or physiological reagents. Notable functional features include expression of various globin chains or the complete hemoglobins as erythroid attributes. Taken together, this class of cell lines is relatively well characterized and affords useful model systems for immature erythroid cells.

False leukemia-lymphoma cell lines: an update on over 500 cell lines

Human leukemia-lymphoma (LL) cell lines represent an extremely important resource for research in a variety of fields and disciplines. As the cell lines are used as in vitro model systems in lieu of primary cell material, it is crucial that the cells in the culture flasks faithfully correspond to the purported objects of study. Obviously, proper authentication of cell line derivation and precise characterization are indispensable requirements to use as model systems. A number of studies has shown an unacceptable level of LL cell lines to be false. We present here the results of authenticating a comprehensively large sample (n = 550) of LL cell lines mainly by DNA fingerprinting and cytogenetic evaluation. Surprisingly, near-identical incidences (ca 15%) of false cell lines were observed among cell lines obtained directly from original investigators (59/395: 14.9%) and from secondary sources (23/155: 14.8%) implying that most cross-contamination is perpetrated by originators, presumably during establishment. By comparing our data with those published, we were further able to subclassify the false cell lines as (1) virtual: cross-contaminated with and unretrievably overgrown by other cell lines during initiation, never enjoying independent existence; (2) misidentified: cross-contaminated subsequent to establishment so that an original prototype may still exist; or (3) misclassified: unwittingly established from an unintended (often normal) cell type. Prolific classic leukemia cell lines were found to account for the majority of cross-contaminations, eg CCRF-CEM, HL-60, JURKAT, K-562 and U-937. We discuss the impact of cross-contaminations on scientific research, the reluctance of scientists to address the problem, and consider possible solutions. These findings provide a rationale for mandating the procurement of reputably sourced LL cell lines and their regular authentication thereafter.

Continuous hematopoietic cell lines as model systems for leukemia-lymphoma research

Along with other improvements, the advent of continuous human leukemia-lymphoma (LL) cell lines as a rich resource of abundant, accessible and manipulable living cells has contributed significantly to a better understanding of the pathophysiology of hematopoietic tumors. The first LL cell lines, Burkitt's lymphoma-derived lines, were established in 1963. Since then, more than 1000 cell lines have been described, although not all of them in full detail. The major advantages of continuous cell lines is the unlimited supply and worldwide availability of identical cell material, and the infinite viable storability in liquid nitrogen. LL cell lines are characterized generally by monoclonal origin and differentiation arrest, sustained proliferation in vitro under preservation of most cellular features, and specific genetic alterations. The most practical classification of LL cell lines assigns them to one of the physiologically occurring cell lineages, based on their immunophenotype, genotype and functional features. Truly malignant cell lines must be discerned from Epstein-Barr virus (EBV)-immortalized normal cells, using various distinguishing parameters. However, the picture is not quite so straightforward, as some types of LL cell lines are indeed EBV+, and some EBV+ normal cell lines carry also genetic aberrations and may mimic malignancy-associated features. Apart from EBV and human T-cell leukemia virus in some lines, the majority of wild-type LL cell lines are virus-negative. The efficiency of cell line establishment is rather low and the deliberate establishment of new LL cell lines remains by and large an unpredictable random process. Difficulties in establishing continuous cell lines may be caused by the inappropriate selection of nutrients and growth factors for these cells. Clearly, a generally suitable microenvironment for hematopoietic cells, either malignant or normal, cannot yet be created in vitro. The characterization and publication of new LL cell lines should provide important and informative core data, attesting to their scientific significance. Large percentages of LL cell lines are contaminated with mycoplasma (about 30%) or are cross-contaminated with other cell lines (about 15-20%). Solutions to these problems are sensitive detection, effective elimination and rigorous prevention of mycoplasma infection, and proper, regular authentication of cell lines. The underlying cause, however, appears to be negligent cell culture practice. The willingness of investigators to make their LL cell lines available to others is all too often limited. There is a need in the scientific community for clean and authenticated high-quality LL cell lines to which every scientist has access. These are offered by various institutionalized public cell line banks. It has been argued that LL cell lines are genetically unstable (both cytogenetically and molecular genetically). For instance, cell lines are supposed to acquire numerical and structural chromosomal alterations and various types of mutations (e.g. point mutations) in vitro. We present evidence that while nearly 100% of all LL cell lines indeed carry genetic alterations, these alterations appear to be stable rather than unstable. As an example of the practical utility of LL cell lines, the recent advances in studies of classical and molecular cytogenetics, which in large part were made possible by cell lines, are highlighted. A list of the most useful, robust and publicly available reference cell lines that may be used for a variety of experimental purposes is proposed. Clearly, by opening new avenues for investigation, studies of LL cell lines have provided seminal insights into the biology of hematopoietic neoplasia. Over a period of nearly four decades, these initially rather exotic cell cultures, known only to a few specialists, have become ubiquitous powerful research tools that are available to every investigator.

Malignant hematopoietic cell lines: in vitro models for the study of natural killer cell leukemia-lymphoma

Malignancies involving natural killer (NK) cells are rare disorders. The complexity of NK cell-involving disorders has only recently been appreciated. Modern classifications discern immature (precursor) from mature NK cell leukemias-lymphomas. Continuous NK leukemia-lymphoma cell lines represent important model systems to study these neoplasms. While there are a number of putative NK cell lines which are, however, either not characterized, not immortalized, non-malignant, non-NK, or plain false cell lines, six bona fide malignant NK cell lines have been established and are sufficiently well characterized: HANK1, KHYG-1, NK-92, NKL, NK-YS and YT. Except for YT which was derived from a not further defined acute lymphoblastic lymphoma, these cell lines were established from patients with various NK cell malignancies. Five of the six cell lines are constitutively interleukin-2-dependent. Their immunoprofile is remarkably similar: CD1-, CD2+, surface CD3 (but cytoplasmic CD3epsilon+), CD4-, CD5-, CD7+, CD8-, CD16-, CD56+, CD57-, TCRalphabeta-, TCRgammadelta-, negative for B cell and myelomonocytic markers. The immunoglobulin heavy chain and T cell receptor genes are all in germline configuration. All six lines show complex chromosomal alterations, with both numerical and structural aberrations, attesting to their malignant and monoclonal nature. Functionally, these cells which contain azurophilic granules in their cytoplasm are nearly universally positive in NK activity assays. Three of five cell lines are Epstein-Barr virus-positive (type II latency). The composite data on these six cell lines allow for the operational definition of a typical malignant NK cell line profile. NK leukemia-lymphoma cell lines will prove invaluable for studies of normal and malignant NK cell biology.

Widespread intraspecies cross-contamination of human tumor cell lines arising at source

We present a panoptic survey of cell line cross-contamination (CLCC) among original stocks of human cell lines, investigated using molecular genetic methods. The survey comprised 252 consecutive human cell lines, almost exclusively tumor-derived, submitted by their originators to the DSMZ and 5 additional cell repositories (CRs), using a combination of DNA profiling (4-locus minisatellite and multilocus microsatellite probes) and molecular cytogenetics, exploiting an interactive database (http://www.dsmz.de/). Widespread high levels of cross-contaminants (CCs) were uncovered, affecting 45 cell lines (18%) supplied by 27 of 93 originators (29%). Unlike previous reports, most CCs (42/45) occurred intraspecies, a discrepancy attributable to improved detection of the more insidious intraspecies CCs afforded by molecular methods. The most prolific CCs were classic tumor cell lines, the numbers of CCs they caused being as follows: HeLa (n = 11), T-24 (n = 4), SK-HEP-1 (n = 4), U-937 (n = 4) and HT-29 (n = 3). All 5 supposed instances of spontaneous immortalization of normal cells were spurious, due to CLCC, including ECV304, the most cited human endothelial cell line. Although high, our figure for CCs at the source sets a lower limit only as (i) many older tumor cell lines were unavailable for comparison and (ii) circulating cell lines are often obtained indirectly, rather than via originators or CRs. The misidentified cell lines reported here have already been unwittingly used in several hundreds of potentially misleading reports, including use as inappropriate tumor models and subclones masquerading as independent replicates. We believe these findings indicate a grave and chronic problem demanding radical measures, to include extra controls over cell line authentication, provenance and availability.

Cell cross-contamination in cell cultures: the silent and neglected danger

Cell cross-contamination in cell cultures is a common problem during cell culturing and use. Contamination invalidates research results, compromises the comparison of results between laboratories, reduces reproducibility required in industrial production of cell lines, and may lead to unusable therapeutic products. The problem can be solved by increasing the awareness of its seriousness and by introducing regular quality control of cell cross-contamination in every laboratory where cells are grown and used.

Isoenzyme analysis as a rapid method for the examination of the species identity of cell cultures

One of the major problems in cell culturing is the misidentification or cross-contamination of authentic continuous cell lines. We applied a rapid and efficient isoelectric focusing (IEF) technique for the routine analysis to detect interspecies contamination of cell cultures and for the identification of unknown animal cell lines. The method is based on the isoelectric separation of a specific set of intracellular enzymes which can be used to distinguish between cell lines of human, murine, or other mammalian origin. By means of preformed agarose gels, standardized conditions and equipment, this technique is especially applicable for routine work and allows the analysis of a large number of unknown samples with reproducible results. One hundred seventy-seven cell lines which have been sent to the Department of Human and Animal Cell Cultures at the DSM (Deutsche Sammlung von Mikroorganismen and Zellkulturen) were analyzed for species authentication; only three cell lines were found not to be of the presumed species. Our study strongly emphasizes standardized IEF as an efficient and rapid method for routinely monitoring the authenticity of cell lines.