September 30, 2010
Stem cells are the building blocks from which replacement cells, everything from blood to bone to brain, grow in early development and throughout life. Researchers consider embryonic stem cells the most useful type for generating replacement tissues, but obtaining them requires the controversial destruction of embryos. Then, in 2006, a Kyoto University team first reported adult skin cells can be "induced" into resembling embryonic stem cells.
That breakthrough relied on viruses infecting cells with four cancer-related genes to spur the transformation. But the new study pulls off the trick with ribonucleic acid (RNA) molecules, normally the workhorses that translate DNA-encoded genes into proteins and perform other housekeeping roles inside cells.
In the journal Cell Stem Cell, a team led by Derrick Rossi of Children's Hospital Boston unveils a cancer-mutation-free method, 40 to 100 times more productive than normal, to create induced stem cells. Induced stem cells are similar to embryonic stem cells in their potential to transform into every type of tissue in the body — but lack the controversy.
"This is very exciting," Rossi says. "We have a new experimental process that can efficiently give us patient cells in clinically useful types."
"RNA, if it works, sounds like a very realistic, promising alternative," says stem cell biologist Gary Stein of the University of Massachusetts Medical School in Worcester, who was not part of the study. Worries about virus contamination and cancer have dogged induced stem cells since their discovery, he notes, along with concerns about their low efficiency rate, with perhaps one cell in 1,000 transforming through the use of viruses.
Treating adult human cells with RNA engineered to overcome immune system defenses reliably creates induced stem cells, the study says. Moreover, the same RNA molecule cued to fire up different genes over three days' time can then be used to turn those induced stem cells into specific types of tissues, such as muscle.
For that reason, "this paper is a major advance in the field of regenerative medicine," says stem cell researcher Douglas Melton of Harvard, who was not part of the study team. Since the isolation of human embryonic stem cells in 1998, researchers have sought ways to turn early stem cells into heart, spine and other tissues needed by transplant patients. The RNA advance means labs can experiment on deriving these tissues in test tubes, he says, speeding progress in the field.