New research showing that mice cloned from embryonic stem (ES) cells display epigenetic instabilities and alterations in gene expression cannot be extended to cloned human cells without more study. Indeed, the effects of subtle physiological differences in cloned animals and tissues were not explored by the mouse study reported last week in Science. Nevertheless, wide media coverage of the report provided a new opportunity for opponents of therapeutic cloning to cast doubt on the viability of stem cell research for regenerative medicine.

The researchers at the Whitehead Institute compared Northern blot RNA analysis results and methylation patterns of normal neonatal mice to neonatal mice cloned using either nuclear transfer or tetraploid embryo complementation. The latter technique involves injection of a small number of ES cells from a donor into a tetraploid blastocyst such that the embryo is entirely derived from the injected ES cells.