Best practices in cell culture: an overview.

This overview describes a series of articles to provide an unmet need for information on best practices in animal cell culture. The target audience primarily consists of entry-level scientists with minimal experience in cell culture. It also include scientists, journalists, and educators with some experience in cell culture, but in need of a refresher in best practices. The articles will be published in this journal over a six-month period and will emphasize best practices in: (1) media selection; (2) use and evaluation of animal serum as a component of cell culture medium; (3) receipt of new cells into the laboratory; (4) naming cell lines; (5) authenticating cell line identity; (6) detecting and mitigating risk of cell culture contamination; (7) cryopreservation and thawing of cells; and (8) storing and shipping viable cells.

Exposure to Bovine Leukemia Virus Is Associated with Breast Cancer: A Case-Control Study.

BACKGROUND: Age, reproductive history, hormones, genetics, and lifestyle are known risk factors for breast cancer, but the agents that initiate cellular changes from normal to malignant are not understood. We previously detected bovine leukemia virus (BLV), a common oncogenic virus of cattle, in the breast epithelium of humans. The objective of this study was to determine whether the presence of BLV DNA in human mammary epithelium is associated with breast cancer. METHODS: This was a case-control study of archival formalin fixed paraffin embedded breast tissues from 239 donors, received 2002-2008 from the Cooperative Human Tissue Network. Case definition as breast cancer versus normal (women with no history of breast cancer) was established through medical records and examination of tissues by an anatomical pathologist. Breast exposure to BLV was determined by in situ-PCR detection of a biomarker, BLV DNA, localized within mammary epithelium. RESULTS: The frequency of BLV DNA in mammary epithelium from women with breast cancer (59%) was significantly higher than in normal controls (29%) (multiply- adjusted odds ratio = 3.07, confidence interval = 1.66-5.69, p = .0004, attributable risk = 37%). In women with premalignant breast changes the frequency of BLV DNA was intermediate (38%) between that of women with breast cancer and normal controls (p for trend < .001). CONCLUSIONS: Among the specimens in this study, the presence of amplified BLV DNA was significantly associated with breast cancer. The odds ratio magnitude was comparable to those of well-established breast cancer risk factors related to reproductive history, hormones, and lifestyle and was exceeded only by risk factors related to genetics (familial breast cancer), high dose ionizing radiation, and age. These findings have the potential for primary and secondary prevention of breast cancer.

Bovine leukemia virus DNA in human breast tissue.

Bovine leukemia virus (BLV), a deltaretrovirus, causes B-cell leukemia/lymphoma in cattle and is prevalent in herds globally. A previous finding of antibodies against BLV in humans led us to examine the possibility of human infection with BLV. We focused on breast tissue because, in cattle, BLV DNA and protein have been found to be more abundant in mammary epithelium than in lymphocytes. In human breast tissue specimens, we identified BLV DNA by using nested liquid-phase PCR and DNA sequencing. Variations from the bovine reference sequence were infrequent and limited to base substitutions. In situ PCR and immunohistochemical testing localized BLV to the secretory epithelium of the breast. Our finding of BLV in human tissues indicates a risk for the acquisition and proliferation of this virus in humans. Further research is needed to determine whether BLV may play a direct role in human disease.

Are viruses associated with human breast cancer? Scrutinizing the molecular evidence.

The three viruses most studied as possible causes of human breast cancer are mouse mammary tumor virus-like sequences (MMTV-LS), Epstein-Barr virus (EBV), and oncogenic (high risk) types of human papilloma virus (HPV). The first step in fulfilling traditional criteria for inferring that a cancer is caused by a virus is to demonstrate the virus in the affected tissue. Molecular techniques, compared to host antibody assessment and immunohistochemistry, are the most definitive in establishing viral presence. Results of 85 original molecular research investigations to detect one or more of the three viruses have been extremely divergent with no consensus reached. We evaluated the methodology of these studies for the following: type of molecular assay, DNA/RNA quality control, positive and negative assay controls, type of fixation, genome targets, methods for preventing and detecting molecular contamination, pathology of specimens processed, sample size, and proportion of specimens positive for the viral genome region targeted. Only seven of the studies convincingly demonstrated the presence of an oncogenic virus biomarker (EBV: 4/30 studies (13%); HPV 3/29 studies (10%), whereas 25 convincingly demonstrated absence of the virus studied (MMTV-LS: 4/25 (16%); EBV: 15/30 (50%); 6/29 (21%). The remainder of the studies suffered shortcomings, which, in our opinion, prevented a definitive conclusion. Only one of the studies compared frequency of the virus in breast tissue of breast cancer patients versus appropriate normal control subjects with no history of breast cancer. None of the studies were designed as epidemiologic studies to determine if the presence of the virus was significantly associated with breast cancer. Based on our evaluation, the data in the publications reviewed here remain preliminary, and do not justify a conclusion that MMTV-LS, HPV, or EBV are causally associated with breast cancer. However, they form a valuable basis for redirecting future studies.

Presence of epithelial cells in nipple aspirate fluid is associated with subsequent breast cancer: a 25-year prospective study.

Fluid and epithelial cells obtained from the breasts of non-pregnant, non-lactating women by nipple aspiration, can be used for early diagnosis of breast neoplasms. However, since nipple aspirate fluid (NAF) with cells is obtainable from less than half of women sampled, the question arises: Is this method capable of targeting the women most likely to develop breast cancer? We approached this question with a 25-year prospective study to determine if subjects yielding NAF with or without epithelial cells were more likely to develop breast cancer during the follow-up period than subjects from whom no NAF or epithelial cells were obtained. Logistic regression analysis was used to determine relative risk (RR) with 95% confidence intervals (CI). The follow-up cohort of 972 was representative of the eligible cohort of 1605 for factors related to breast cancer risk and nipple aspiration outcome, and representative of the general population for breast cancer risk. After a mean follow-up period of 25 years, women with epithelial cells in NAF were significantly more likely to develop breast cancer (RR=1.92; CI=1.22-3.01; p

Cell line cross-contamination: how aware are Mammalian cell culturists of the problem and how to monitor it?

HeLa was the first human cell line established (1952) and became one of the most frequently used lines because of its hardiness and rapid growth rate. During the next two decades, the development of other human cell lines mushroomed. One reason for this became apparent during the 1970s, when it was demonstrated that many of these cell lines had been overgrown and replaced by fast-growing HeLa cells inadvertently introduced into the original cultures. Although the discovery of these "HeLa contaminants" prompted immediate alarm, how aware are cell culturists today of the threat of cell line cross-contamination? To answer this question, we performed a literature search and conducted a survey of 483 mammalian cell culturists to determine how many were using HeLa contaminants without being aware of their true identity and how many were not using available means to ensure correct identity. Survey respondents included scientists, staff, and graduate students in 48 countries. HeLa cells were used by 32% and HeLa contaminants by 9% of survey respondents. Most were also using other cell lines; yet, only about a third of respondents were testing their lines for cell identity. Of all the cell lines used, 35% had been obtained from another laboratory instead of from a repository, thus increasing the risk of false identity. Over 220 publications were found in the PubMed database (1969-2004) in which HeLa contaminants were used as a model for the tissue type of the original cell line. Overall, the results of this study indicate a lack of vigilance in cell acquisition and identity testing. Some researchers are still using HeLa contaminants without apparent awareness of their true identity. The consequences of cell line cross-contamination can be spurious scientific conclusions; its prevention can save time, resources, and scientific reputations.

Humans have antibodies reactive with Bovine leukemia virus.

Bovine leukemia virus (BLV) is an oncogenic retrovirus that commonly infects cattle and causes B cell leukosis in 1-5% of infected cattle. BLV-infected cells are present in marketed beef and dairy products. In the decade after the discovery of BLV in 1969, studies using agar gel immunodiffusion and complement fixation assays failed to find antibodies to BLV in human sera. This led to the prevailing opinion that exposure of humans to BLV and/or the potential for infection are not significant and therefore the virus is not a public health hazard. We reexamined this issue using more sensitive immunological techniques available today. Using immunoblotting to test the sera of 257 humans for antibodies of four isotypes (IgG1, IgM, IgA, and IgG4) to the BLV capsid antigen (p24), we detected at least one antibody isotype reactive with BLV in 74% of the human sera tested. The specificity of the reactivity was strongly suggested by competition studies and by ruling out cross-reacting antibodies to other chronic human viruses. Our results suggest that antibodies reactive with the BLV capsid antigen may serve as a biomarker for exposure to BLV and this exposure may be widespread. The results do not necessarily mean that humans are actually infected with BLV; the antibodies could be a response to heat-denatured BLV antigens consumed in food. They do, however, suggest that further studies in this area could be important.

Relative sensitivity and specificity of agar gel immunodiffusion, enzyme immunosorbent assay, and immunoblotting for detection of anti-bovine leukemia virus antibodies in cattle.

Three serologic methods for the detection of antibodies to bovine leukemia virus (BLV) were compared using the sera of 140 dairy cows. A widely used commercial agarose immunodiffusion screening assay and a commercial antibody capture enzyme immunosorbent assay were compared for sensitivity and specificity with immunoblotting as the standard. The immunoblot utilized the same antigen preparations that were provided in the commercial kits. The agarose immunodiffusion and the enzyme immunosorbent assay were comparable in the number of positive animals detected. However, the commercial screening kits failed to detect 39% (agarose immunodiffusion) and 35% (immunosorbent assay), respectively, of the animals determined serologically positive by immunoblot. These findings corroborate those of some other groups and emphasize the need for more sensitive tests to identify BLV positive cattle for culling or separation in order to create BLV-free herds.