We read with great interest the excellent review by Maherali and Hochedlinger (2008) that recommends standards for characterization of pluripotent stem cell lines, especially the many new lines being generated using factor-based reprogramming techniques (induced pluripotent stem cells, or iPSCs). Of note was the suggestion that iPSCs should be assessed for “functional differentiation through the highest-stringency test acceptable.” For murine iPSCs, this means germline transmission following blastocyst chimerism, and for human iPSCs this means assessment of teratoma pathology.
