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Human embryonic stem cells (hESCs) are derived from the inner cell mass of 3-to 5-day-old blastocysts. 1-5 hESCs are characterized by a high nucleus-to-cytoplasm ratio, prominent nucleoli, and distinct colony morphology. 6 Recently, pluripotent stem cells that are similar to ESCs were derived from an adult somatic cell by the “forced” expression of certain pluripotency genes, 7-11 such as Oct3/4, Sox2, c-Myc, and klf-4, or their proteins12 and microRNAs. 13 These cells are known as induced pluripotent stem cells (iPSCs). iPSCs are believed to be similar to ESCs in many respects, including the expression of certain stem cell genes and proteins, chromatin methylation patterns, doubling time, embryoid body formation, teratoma formation, viable chimera formation, potency, and differentiability. However, the full extent of their similarities to ESCs is still under investigation. 7, 10 hESCs and human iPSCs have …