Scientists at Harvard University have found a way to "reprogramme' adult human cells to an embryonic state. The discovery could provide an alternative to therapeutic cloning, as a way to make embryonic stem cells that are genetically identical to the patient. The researchers fused adult skin cells with embryonic stem cells, producing hybrid cells in which the adult nucleus had returned to an embryonic state. The journal Science will publish their findings. In principle the research could lead to a new way of making stem cells for transplantation into a patient without risk of rejection by the immune system, because they share the same genome. Although embryonic stem cells are used, the technique would not require an early embryo to be created and destroyed for each patient, as with therapeutic cloning.