Harvard researchers have retracted a far-reaching claim they made in January that the aging of stem cells might be reversible.

The retraction was published in Thursday’s issue of Nature and is signed by the senior author, Amy J. Wagers, and two others. They say that serious concerns, which they did not specify, have undermined their confidence in the original report.

A fourth author, Shane R. Mayack, maintained that the results were still valid and refused to sign the retraction. All four scientists are affiliated with Harvard University and the Joslin Diabetes Center, a Harvard affiliate.

The original article, published by Nature in January, asserted that there was a rejuvenating factor in the blood of young mice that could reverse symptoms of aging in the blood-forming stem cells of elderly mice. The therapeutic use of such a factor would be “to extend the youthful function of the aging blood system,” Dr. Wagers and her colleagues wrote.