http://www.nature.com/news/2009/090723/full/460560a.html
they then created a 'tetraploid' embryo by fusing two cells of an early-stage fertilized embryo. A tetraploid embryo develops a placenta and other cells necessary for development, but not the embryonic cells that would become the body. It is, in essence, a car without a driver.

When implanted into these embryos, the iPS cells began to steer development. The developing embryo was transferred to a surrogate mother, and 20 days later a mouse was born.
......
Rudolf Jaenisch, a cloning expert at the Massachusetts Institute of Technology in Cambridge, had tried to do the same experiment in 2007, but didn't succeed in getting beyond late-stage embryos4. "There were two possible explanations" for his team's failure, he says. "Either iPS cells aren't pluripotent so it was impossible, or we just hadn't tried hard enough. The first would have been more interesting, but I assumed it was the second explanation."

The Chinese team tried harder...

http://www.sjtu.edu.cn/news/shownews.php?id=22199
但是iPS细胞是否真正拥有胚胎干细胞那样的多能性，从而在医疗应用上真正媲美胚胎干细胞呢？当研究人员按照检测胚胎干细胞多能性的方法将iPS细胞注射进正常的小鼠早期胚胎后，在小鼠出生后可以得到部分身体组织由iPS细胞发育而来嵌合体小鼠；但是当应用验证细胞是否具有全能性的方法，将iPS细胞注射进四倍体的小鼠早期胚胎（没有进一步发育能力，仅提供营养环境的胚胎），再种入代孕母鼠体内，观察iPS细胞能否和胚胎干细胞一样发育成活体小鼠时，先前的研究始终未能成功，iPS细胞形成的小鼠胎儿均在怀孕早期至晚期死亡，而这正是验证iPS细胞是否具有全能性的“黄金标准”。