Wednesday, December 23, 2009

What cell line is this anyway?

By Dr. Ray Nims

For about as long as scientists have been using cell cultures in biomedical research, there have been cases of cell line misidentification. This has been especially true for continuous cell lines, with the increased probability over time of mislabeling or cross-contamination. The primary cross-contaminant historically has been HeLa, a human cervical carcinoma cell which, given the opportunity, could outgrow most other cells in culture. More recently, the use of feeder cells for the propagation of human stem cells, and the use of xenografting for the propagation of human tumor cells, has provided additional opportunities for cell line cross-contamination and misidentification.

In the past, confirmation of cell line species of origin has been the main approach for authenticating cell lines. This was done initially by karyotyping or by immunological techniques, but more recently it has been done through the technique of isoenzyme analysis. An example of an isoenzyme analysis is shown below for Peptidase B and Aspartate Aminotransferase.  These agarose gels show a positive control, a negative control (this is the band that does not line up with the others), the test article and a standard extract.  These gels confirmed the identity of the test article as mouse derived, as expected. 

Isoenzyme analysis has the advantage that it is rapid, not very technically demanding, and may be used not only to confirm species of origin but also to detect the presence of a cross-contaminating cell if the latter is present in the culture at 10% or greater (Nims et al., Sensitivity of Isoenzyme Analysis for the Detection of Interspecies Cell Line Cross-Contamination. In Vitro Cell. Dev. Biol.-Animal 34:35-39, 1998). In fact, isoenzyme analysis is currently the primary method employed within the biopharmaceutical industry for cell line authentication in satisfaction of 1993 Points to Consider and ICH Q5D guidance.

Recent advances in molecular diagnostic techniques have made possible the authentication of human cell lines to the individual level. DNA fingerprinting technologies have matured to the point that some of them, especially single nucleotide polymorphism (SNP) typing and single tandem repeat (STR) profiling, are now considered to be viable options for standardizing human cell authentication (see ATCC SDO newsletter article, page 5. For both human and animal cells, DNA fingerprinting provides a means of determining authenticity to the individual level. However, the primary drawback is that the fingerprinting techniques as routinely performed will be less or not at all useful for detecting interspecies cocultivations or cross-contaminations. For this purpose, it may be necessary to retain isoenzyme analysis as part of the authentication armament even when the molecular technologies become the definitive authentication practices for human and animal cell lines.

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