The aging process can be slowed, but it's an inexorable deterioration, as our bodies stop repairing the organs we need to survive. But researchers at the University of Edinburgh have managed to regenerate at least one organ in mice by tweaking a single gene. The team targeted the thymus, an organ responsible for incubating the white blood cells — called T cells — that attack infections. The thymus is crucial in immune system development, but it's also one of the first organs to atrophy in otherwise healthy humans. As a person (or mouse) ages normally, they'll become more and more vulnerable to disease, making something like the flu potentially deadly.

The aging mice in this study, however, saw their atrophied thymuses regenerate, more than doubling in size and increasing production of T cells. Researchers had increased the levels of a protein called FOXN1, which has previously been linked to thymic degeneration, and successfully stimulated cells that helped rebuild the organ. Scientists have previously increased thymus size by castrating animals, but the structure remains "old." By contrast, these mice, they concluded, had thymuses that closely resembled ones that had not yet started to deteriorate. "The exciting thing really is the manner in which it is done," co-author Nick Bredenkamp tells the BBC. "We've targeted a single gene and we've been able to regenerate an entire organ."

The University of Edinburgh news service says it's not yet clear whether the mice saw a concrete improvement in their immune systems, although logically it should be likely. It's also plausible that similar treatments could be applied to humans, partially reversing the aging process or helping people with otherwise suppressed immune systems become less vulnerable to illness. But co-author Clare Blackburn says that more work would need to be carried out, including a search for adverse effects, before the process could be tested on humans. Beyond the potential direct benefits, this breakthrough could also teach us more about how the aging process works in other organs. The study "suggests that organ regeneration in a mammal can be directed by manipulation of a single protein, which is likely to have broad implications for other areas of regenerative biology," says Dr. Rob Buckle, head of regenerative medicine at the University of Edinburgh's Medical Research Council.

The study's results have been published in the journal Development.