Research on reprogramming adult cells to make them behave like embryonic stem cells crossed a milestone recently when two Chinese teams succeeded in producing mouse pups using such cells. Ever since induced pluripotent stem (iPS) cells were produced in 2006 by reprogramming adult cells, researchers across the world have been working feverishly to replicate and refine the technique. Though many scientists have succeeded in producing iPS cells, unassailable evidence of their pluripotency — ability of the cells to behave like embryonic stem cells and form all of the 200-odd specialised cells — was lacking. The latest success in producing mouse pups using reprogrammed adult cells has taken research one step closer to proving the pluripotency of iPS cells. One team, headed by Qi Zhous of the Chinese Academy of Science, and the other, led by Shaorong Gao from the National Institute of Biological Sciences in Beijing, were able to produce mouse pups using iPS cells injected into early-stage embryos that can only become the placenta and not develop into animals. While Qi Zhous’ team was able to produce 27 pups, including ‘Tiny,’ using three iPS cell lines, the other team could create only four. If growing to adulthood is considered significant, the pups created by Qi Zhous passed the fundamental test of health — they sired over 200 second-generation pups. More than 100 third-generation pups have also been produced.
Many scientists are turning to iPS cell technique to sidestep the ethical controversy of embryo destruction when somatic cell nuclear transfer (SCNT) technique is used. Also, unlike in the case of SCNT, human eggs are not required when iPS cells are used for making embryos. But this technique is fraught with scientific hurdles. For instance, the Qi Zhous team used retroviral vectors to introduce four genes to reprogramme adult cells. Retroviruses are known to induce cancer in mammals. Though some studies have succeeded in inducing pluripotency without using these viruses, more research remains to be done. Similarly, oncogenes were used for reprogramming adult cells. This again raises the possibility of cancer formation when the pluripotent cells are introduced into an animal. Skin cells are routinely used for making iPS cells. Though available in plenty, turning back their clocks to make them pluripotent is a big challenge. Both the teams had hence used more pliable cells taken from late-stage embryos. This approach will not be useful if the iPS technique is used for patient-matched therapeutic applications. However, the technique is nearing maturity and may pave the way for creating cell lines to study genetic diseases.