The new type of stem cells could be useful for growing personalized replacement tissues, according to a study in Thursday's issue of the journal Nature. But because of their source, their highest promise would apply to only half the world's population: men.
Embryonic stem cells can give rise to virtually any tissue in the body and scientists believe they may offer treatments for diseases like Parkinson's and diabetes and for spinal cord injuries.
The testicular cells avoid the ethical dilemma of embryonic stem cells, which are harvested in a process that destroys the embryos. For that reason, some people, including President George W. Bush, oppose their use for ethical or religious reasons.
"The advantage these cells have in comparison to embryonic stem cells is that there is no ethical problem with these cells and that they are natural," said study lead author Thomas Skutella, a professor at the Center for Regenerative Biology and Medicine in Tuebingen, Germany.
Using testicular cells isn't the only promising method that avoids embryos; there have been impressive experiments in reprogramming ordinary body cells into stem cells by slipping certain genes into them.
The new findings and the reprogrammed cells - which still have technical hurdles - "take some pressure off the stem cell issue," said White House science adviser Jack Marburger.
Earlier studies showed promise using so-called spermatogonial cells from the testes of mice. The new study used cells taken from biopsied tissue from 22 different men undergoing various medical treatments. The men ranged in age from 17 to 81. Researchers found that after a few weeks of growth, the cells could differentiate into various types of cells just like those taken from embryos.
Other scientists hailed the idea as promising, but not a reason to give up on research on embryonic stem cells.
"It's exciting. We could do it for males; that leaves women without as easy a method," said stem cell scientist George Daley of Children's Hospital in Boston and the Harvard Stem Cell Institute. He was not part of the new research.
Embryonic stem cells "have their own place in biology," Daley said.
Skutella said a female equivalent could be in women's egg cells, but Daley said that's unlikely because of the makeup of those cells.
Using the new findings to treat patients could take years. But Daley said the work on the cells from testes can benefit from a decade's worth of research into embryonic cells and advance at a fast pace.
He said the new research showed how similar these testicular cells are to embryonic stem cells; now science needs to see what specific differences exist because those could be important.