Reconsidering pluripotency tests: Do we still need teratomas?

The production of teratomas in immunodeficient mice is regarded as the "gold standard" assay for pluripotency. This assay has been used to demonstrate the pluripotency of embryonic stemcells, induced pluripotent stem cells (iPSC) and other pluripotent cells. However, the teratoma assay raises two main issues concerning animal welfare: (i) the inoculation of animals with potentially malignant tumors, and (ii) the breeding of genetically deficient experimental animals. Both of these issues are associated with suffering of the animals. To explore pluripotency testing in the context of the 3Rs, the German Foundation for the Promotion of Alternatives to Animal Testing (Stiftung zur Förderung von Ersatz- und Ergänzungsmethoden zur Einschränkungvon Tierversuchen, set) organized an expert workshop in December 2010. This presentation will demonstrate the results of this workshop. Several alternatives to the mouse teratoma assay were discussed, including the directed differentiation of ES and iPS cells into organotypic cells, expression of pluripotency-associated markers such as TRA-1-60, DNMT3B, REX1 that correlate well with the teratoma forming potential of ES and iPS cells, epigenomic footprints, such as DNA methylation, and histone modifications. Each of these assays is capable of addressing one or several aspects of pluripotency. It is imperative that more research be performed in order to standardize such alternative tests. Simple, robust, reliable, standardised tests need to be developed to facilitate the testing of pluripotency of new and existing cell lines.