Researchers in Oregon have successfully used cloning technology to develop human embryos and grow stem cells from them.
The ultimate goal of the technique is to create cells that could be perfect matches for patient-specific transplants.
The scientific team, from Oregon Health & Science University, used a human egg cell and parts of a human skin cell to grow a very early human embryo and then nurtured cells from the elemental ball of cells into beating heart cells and skin cells.
The process, according to a study published in the journal Cell, may eventually help treat a range of diseases, from Parkinson's to rare inherited conditions.
The researchers said in the study that the embryonic cells they developed almost certainly could not grow into living human babies or even start a pregnancy - the cells are very different from so-called adult stem cells, such as those taken from bone marrow.
Adult stem cells cannot be cultivated to cells of other tissue types and blood cells cannot be used to make brain cells, for instance.
"These stem cells are kind of very early un-programmed cells but they have the capacity to become any other cell type," said Shoukhrat Mitalipov, who led the research.
Dr. George Daley, a stem cell expert at Harvard Medical School, called it a "beautiful piece of work."
Nonetheless, harvesting the cells for research introduces a number of ethical questions the research team admits they haven't fully resolved yet.
When human embryonic stem cells were first discovered in 1998, scientists soon started dreaming of using cloning technology to help people grow their own organ and tissue transplants and to use them to study disease.
Such stem cells would be perfect genetic matches for pasture, which would mean no longer having to take dangerous immune-suppressing drugs after an o transplant.
But over the two-and-a-half decades since that initial find, no lab has been able to do the work easily --- as it's a much harder task to clone a human cell than that of a sheep, frog or mouse.
A federal court only recently ruled in the past year that government funds may be used in the research.
Other research groups have learned how to manipulate ordinary skin cells into re-modeling themselves into different tissues. But again, the technique isn't easy, nor is it straightforward.
O. Carter Snead, a bioethicist and professor of law at the University of Notre Dame, called news about the cloned cells sad.
"The use and destruction of living human beings - at any stage of biological development - for scientific research is a terrible injustice. Human cloning for biomedical research is a particularly aggravated form of this harm," Snead said in a statement.