Continuing advances in a fast-growing field, biologists reported a purely-chemical recipe for growing normal skin cells into human embryonic stem cell lookalikes.

Called “induced pluripotent” stem cells, researchers hope to see whether these lookalikes can grow into all organ tissues like embryonic stem cells, making them candidates for transplant medicine treatments in the future.

Reported in the journal Cell Stem Cell, the team headed by Kwang-Soo Kim of Harvard Medical School describes a method for treating skin cells with proteins produced by four cancer genes that trigger the transformation into induced pluripotent cells, a change first demonstrated in 2006.

“This is the first safe method for producing (induced pluripotent cells),” says study co-author Robert Lanza of Advanced Cell Technology in Worcester, Mass. Previous methods involved inserting the cancer genes into the skin cells, and then removing them by various methods. In the study, the researchers bound their proteins to cell-penetrating molecules, treated skin cells with them for 16 hours, and then grew them for six days over a number of cycles. The process produced two colonies, or lines, of induced pluripotent stem cells that continue to grow today, and contain the same gene markers as embryonic stem cells.

“The work represents another important milestone, however, challenges remain,” says University of Wisconsin stem cell biologist James Thomson., by e-mail. “The most important criteria for choosing a particular reprogramming approach will be whether one can derive an (induced pluripotent stem) cell line from an easily obtained clinical sample consistently, and whether the resulting (induced pluripotent) cell line has a normal genetic and epigenetic (gene activation) status. It is not yet clear what approach, or combination of approaches, will most consistently meet these criteria.”

One limitation of the study’s protein approach is its low efficiency, about 100 times less likely to produce cell lines than the already very-inefficient genetic engineering approaches. Marius Wernig of Stanford University, for example, says, “it is also clear that the method described is far from being robust and there is a lot more to do until this approach will become really applicable in a reproducible manner.”

However Lanza says that purified forms of the proteins applied to skin cells will raise the processes’ efficiency. “We are moving ahead to see how these cells differentiate into (organ) tissues,” Lanza says. “So far they are doing so beautifully.”