US researchers have found a way to dramatically increase the harvest of stem cells from adult tissue.

美国研究人员发现了从成年人体组织中显著增加干细胞收获数量的方法。

The research was done using fibroblast skin cells

It is a practical step forward in techniques to produce large numbers of stem cells without using embryos¹（晶胚）.

Using three drug-like chemicals, the team made the procedure 200 times more efficient and twice as fast, the Nature Methods journal reported.

It is hoped stem cells could one day be widely used to repair damaged tissue in diseases and after injuries.

Much of the work on stem cells has focused on those taken from embryos as they have an unlimited² capacity to become any of the 220 types of cell in the human body - a so-called pluripotent（多能的） state.

But this has proven controversial and some campaigners have objected to their use on the grounds that it is unethical to destroy embryos in the name of science.

The creation of stem cells from human adult skin cells was first reported in 2007 by Japanese and US researchers, opening the way for new sources of stem cells.

It was done by using viruses to insert four genes³ into the cells which prompt the switching on and off of other genes and cause the cells to revert⁴ to（回复，归还） stem cells.

But the process took weeks and the success rate was only about one in 10,000 cells.

Better and faster

The latest research builds on that process by adding specific chemicals to improve the process.

The Scripps Research Institute team had already boosted the number of cells created with two compounds initiating⁵（开始） a naturally occurring process that moves the cell nearer to a stem-cell like state.

But they have now discovered that by adding thiazovivin, a small molecule⁶（分子） involved in cell survival, they doubled that to get 200 times the number of transformed cells.

The final process also took two weeks compared with a month needed for the original.

Study leader Professor Sheng Ding said they had manipulated a "fundamental" process in the cell.

"Both in terms of speed and efficiency, we achieved major improvements over conventional conditions," he said.

"This is the first example in human cells of how reprogramming speed can be accelerated.

"I believe that the field will quickly adopt this method, accelerating research significantly."

Dr Keisuke Kaji, a stem cell researcher at the Medical Research Council Centre for Regenerative Medicine in Edinburgh said the technique was a "great advance" in cell reprogramming technology.

He added it had already been shown in mouse cells but this was the first time in human cells.

"I am interested in how widely this drug can have positive effect, for example, if it helps to generate induced pluripotent stem cells from old people's cells which are usually more difficult to reprogram and if it can improve the efficiency in non-viral reprogramming strategies."