U.S. medical researchers say the cloning of human embryos is still their best hope for developing effective treatments for diseases.

Researchers pursue stem cell technologies

Those opposed to using embryonic stem cells, including President George Bush and some religious leaders, say a new technique for genetically "reprogramming" ordinary adult skin tissue into stem cells could eliminate the need for using human embryos.

At Harvard University, where about 750 lead medical scientists work in 119 laboratories, researchers worry the new technology may never offer help for humans, The Boston Globe reported Monday.

So-called induced pluripotent stem cells, or IPS, made by the skin-cell process may never be safe for humans, some researchers say, the newspaper reported.

"For doing basic research on human cells, IPS as a method has won -- it's huge," said Dr. George Daley, a stem cell researcher at Children's Hospital Boston. "But for the ultimate goal of getting cells into a patient, it's a lot less clear. These cells may never be useful for direct therapy."