An independent laboratory has been able to reprogram differentiated human skin cells to an embryonic-like state using the method originally reported by Shinya Yamanaka of Kyoto University, in Japan1,2. Also, late last year, two other laboratories announced their success in reprogramming differentiated human cells via slightly different methods3,4. The latest work, by Kathrin Plath of the University of California, Los Angeles, indicates that current technique is broadly feasible and introduces a potentially easier method to pluck reprogrammed cells from culture5.

Notably, all the groups that have reported success with this method have experience working with embryonic stem (ES) cells. At least two have produced human ES cells, and the genes that must be introduced to reprogram cells were identified through research done with ES cells.

Plath's team used cultured skin cells originally collected from circumcisions. She infected the cells with retroviruses carrying the four genes originally identified in reprogramming work. After about two weeks the researchers began to see colonies proliferating. They looked clearly different from the cultured skin cells, but they did not go on to become induced pluripotent cells, and analysis showed that they had not taken in copies of all four genes. Colonies of cells destined to become reprogrammed lines showed up about 21 days after infection; they clustered together as human ES cells do, and they also displayed a variety of cell-surface markers characteristic of ES cells. A week later, Plath and researchers hand-selected colonies that stained positive for one particular cell-surface marker. All cells analyzed from these colonies contained copies of all four genes.

Of the 30 colonies isolated, cells from 7 of them were closely analyzed. As expected, all of these cells were expressing endogenous genes associated with pluripotency, and the viral genes were silenced. Though the cells express markers of the three main types of tissues forming the body, the team has not yet tested the functionality of the cells by differentiating them into teratomas or other cell types.