NEW YORK Scientists at two universities - the University of California at San Francisco and Harvard - will try to develop embryonic stem cells from the adult cells of patients suffering from certain diseases.
 
Their purpose in creating the cell lines, which require making an early human embryo, is to study how the diseases develop, and to see if replacement cells can be generated to repair the patient's own degenerating tissues. But the field, despite its much emphasized promise, faces many serious uncertainties.
 
"Clinical applications may be a decade or more away," said George Daley, a Harvard expert on blood diseases.
 
Harvard announced its plans Tuesday at a news conference; the University of California at San Francisco did so less conspicuously a month ago, resuming a program abandoned in 2001. Both universities, having received required approvals, will at first obtain the human eggs needed for cloning from fertility clinics, starting with eggs deemed too low quality to produce a successful pregnancy. Both programs are privately financed because federal support for human stem cell research is available only for cell lines made before Aug. 9, 2001.
 
Advanced Cell Technology in Worcester, Massachusetts, also has a human nuclear transfer program "well under way," said Robert Lanza, the company's vice president, but has run into problems in recruiting egg donors. Under guidelines issued by the National Academy of Sciences, which are voluntary but widely observed, donors may not be paid anything beyond expenses.
 
The new efforts, if successful, would accomplish what the disgraced South Korean scientist Hwang Woo Suk claimed he had achieved in articles published in the journal Science in 2004 and 2005. Both papers turned out to be based on forged data. But the flaws remained undetected by scientists involved in the cloning field, raising doubts about the rigor and expertise with which the work in the new field was being conducted. The problems came to light only after a whistle-blower in Hwang's lab contacted the media.
 
The University of California at San Francisco said last month that one of its researchers, Renee Reijo Pera, would start the cloning procedure, which involves transferring the nucleus of an adult cell into an unfertilized egg whose own nucleus has been removed.
 
A composite egg of this kind should develop in glassware into an early embryo, or blastocyst, from which embryonic stem cells could be isolated. There is no evident reason why this should not work in people as it has already done in several animal species, yet so far no one has succeeded. Hwang used no less than 2,000 fresh eggs donated by a healthy woman but failed to accomplish anything useful.
 
Reijo Pera will switch to using donated eggs if those rejected by fertility clinics do not work, a university spokeswoman said. Harvard researchers said Tuesday that they, too, would seek to derive eggs from healthy donors in the future.
 
Lanza, of Advanced Cell Technology, said that freshly harvested human eggs were "much better" for nuclear transfer experiments but that a six-month effort by his company to recruit egg donors "appears to be a losing effort." Many women had come forward, saying they would donate their eggs for research without compensation but, after seeing the battery of tests required, "most of the donors change their mind," Lanza said. 
 
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