The established method for screening cell lines for pluripotency involves introducing stem cells into an animal model, usually mice, to observe if teratomas develop. Teratomas are encapsulated tumors that contain tissue from all three germ layers. The mice are usually immunodeficient, meaning their immune system is modified in some way, usually through a genetic mutation. The presence of teratomas in the mice confirms that the cell lines are pluripotent.
This method is referred to as the teratoma assay. In order for it to be useful, researchers need to prepare vials containing stem cells for testing. About 1,000,000 cells are required for each sample. Many laboratories require the sample to be tested for pathogens before being sent for the teratoma assay. Some labs will conduct a pathogen test at an additional cost. Usually, detailed information about the cell line needs to be provided to the lab, including method of genetic modification. Once the lab receives the samples, they will prepare enough cell lines for several injections. The cells are introduced into several mice either subcutaneously or intramuscularly. The progression of teratomas is monitored for six to eight weeks. Afterward, the lab creates a report outlining the results.
