But even if scientists had enough eggs to perfect the nuclear transfer process, there’s no telling at this point whether the technique will prove to be the best way to regenerate tissues to treat disease. So far, the only two human stem cell trials that have been approved by the Food and Drug Administration involve embryonic stem cells obtained from excess IVF embryos. Although these cells are not immunologically matched to patients who are receiving them, as cells generated with nuclear transfer would be, they may still help treat the spinal cord injury and eye diseases for which they are being tested.
Another stem-cell technique that involves neither eggs nor embryos, but requires only skin cells that can be reverted back to an embryonic state, also holds promise as a source for patient-specific stem cells. But studies of these so-called induced pluripotent stem (iPS) cells have shown that while they are stem cells, they are genetically distinct from embryonic stem cells, and those differences may bar them from safe use in patients.
The new findings, however, may help to improve the iPS process and, in turn, the prospects of stem-cell therapy, Daley says. “Understanding how eggs reprogram may allow us to make iPS cells even better,” he says.
Daley, who co-directs a project at the Harvard Stem Cell Institute to establish a bank of iPS cell lines from patients with various diseases, believes that iPS cells may be the more efficient way to generate patient-specific stem cells. But he notes that advances in any area of stem-cell research have wide-ranging benefits for the field as a whole. “This study is not about taking us a step closer to therapy,” he says of the Nature paper. “Instead, the immediate value is this: we can now compare the fidelity of reprogramming by nuclear transfer against the [iPS] method. We need to compare and contrast the two different strategies to determine which gets us closest to the gold standard of embryonic stem cells.”
In other words, as research progresses, scientists can continue to compare the therapeutic viability of stem cells created in various ways — a pursuit that ultimately brings the potential for treatment within closer reach. “The long-term goal of all of this research is to derive cells for therapeutic purposes,” Egli says.