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Reconsidering pluripotency tests: Do we still need teratoma assays?

In 2010 the set Foundation organized an international workshop on the use of the mouse teratoma assay in stem cell research. The mouse teratoma assay is considered to be the gold standard for the assessment of pluripotency in human embryonic stem cells and iPS cells.

For the testing of pluripotency these cells are injected into immunodeficient mice. If the cells are pluripotent, a teratoma might grow, which is a tumor containing cell types from all three germ layers. This has to be confirmed by histological examination.

There are several reasons to question this method:

  • The growth of often several tumors up to 2 cm in diameter as well as the use of immunodeficient mice itself have to be considered as moderately severe to severe animal experiments.
  • Despite its status as gold standard the teratoma assay is far from being standardized in any way. There is no common approach, e.g. about the number of injected cells, the mouse strains used or the injection site. Additionally the discrimination between teratomas and other tumor types should be performed by specialists with histopathological training, which most often is not the case. 
  • For most tasks in stem cell research other methods to confirm pluripotency are faster, better suited and/or sufficient. Many scientists prefer these other techniques. Though, when it comes to publication of their results, they often need to add the teratoma assay, else their publication would not be accepted.

During the workshop all available methods (e.g. formation of embryonic bodies, specific biomarkers, chicken egg model) were critically discussed regarding their feasibility, their results, and their area of application.

The outcome of this workshop has now been published in “Stem Cell Research (2013) 11, 552-562”. The free pdf can be downloaded at


or  here.