Researchers have successfully regenerated an elderly organ into a "youthful state" for the first time in history.

As people age the thymus (which produces T-cells and is responsible for immune responses) shrinks, leaving them more susceptible to infections, the BBC reported. By the age of 70 the thymus is about one-tenth of the size it would have been in youth.

"This has a lot of impacts later in life, when the functionality of the immune system decreases with age and you become more vulnerable to infection and less responsive to vaccines," researcher Doctor Nick Bredenkamp, told the BBC.

A research team was able to rejuvenate a rodent's thymus by manipulating the DNA. The regenerated thymus proved to be very similar to what would be seen in a young mouse, an MRC Centre for Regenerative Medicine at the University of Edinburgh news release reported.

The organ started producing more T-cells, which work to fight off infection. Further research will be required in order to determine if the mice with regenerated organs actually had strengthened immune systems.

"By targeting a single protein, we have been able to almost completely reverse age-related shrinking of the thymus. Our results suggest that targeting the same pathway in humans may improve thymus function and therefore boost immunity in elderly patients, or those with a suppressed immune system. However, before we test this in humans we need to carry out more work to make sure the process can be tightly controlled," Professor Clare Blackburn from the MRC Centre for Regenerative Medicine, at the University of Edinburgh, who led the research, said in the news release.

The team targeted a protein called FOXN1, which works to control how thymus genes that are switched on. The researchers used genetically modified mice that were programed to have increased levels of this protein.

The researchers were able to "instruct immature cells in the thymus" to rebuild the organ.

"One of the key goals in regenerative medicine is harnessing the body's own repair mechanisms and manipulating these in a controlled way to treat disease. This interesting 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," Doctor Rob Buckle, Head of Regenerative Medicine at the MRC, said in the news release.