Sensitivity of isoenzyme analysis for the detection of interspecies cell line cross-contamination

The analysis of the gel electrophoresis banding patterns and relative migration distances for the individual isoforms of intracellular enzymes, such as lactate dehydrogenase, purine nucleoside phosphorylase, glucose-6-phosphate dehydrogenase, and malate dehydrogenase, is used routinely in the biopharmaceutical industry for confirmation of cell line species of origin. In the present study, the sensitivity of the technique (AuthentiKit, Innovative Chemistry, Marshfield, MA) for determining interspecies cell line cross-contamination was examined. Extracts were prepared from a CHO-K1 line (AA8, Chinese hamster), MRC-5 (human) cells, and L929 (mouse) cells and from several proportional mixtures of the various binary combinations of cells. The isoenzymes were analyzed according to standard procedures for the technique. Contamination of MRC-5 cells with CHO-K1 or with L929 cells was clearly detectable with each enzyme analyzed. Similarly, the contamination of L929 or CHO-K1 cells with MRC-5 cells was readily apparent with each enzyme. On the other hand, contamination of CHO-K1 cells with L929 cells was only detected with lactate dehydrogenase analysis, and contamination of L929 cells with CHO-K1 cells was not detected with any of the four enzymes examined. For the latter case, the analysis of an additional enzyme (peptidase B) was required. The results indicate that interspecies cross-contamination should be detectable with isoenzyme analysis if the contaminating cells represent at least 10% of the total cell population.