For the first time, the team has successfully regenerated a living organ in mice by manipulating DNA.
The organ in question was the thymus, which is located next to the heart and is an integral part of the immune system. In humans, it achieves most of its growth in early life, continuing to then grow slowly until puberty when it slowly begins to shrink for the remainder of a person's life. It's deterioration with age leaves older people with greater susceptibility to infections, such as flu.
Via Ray and Terry's