A whole functional organ has been grown from scratch inside an animal for the first time by researchers in Scotland.
A group of cells when transplanted into mice developed into a thymus an integral part of the human immune system.
The findings, published in Nature Cell Biology, could pave the way to alternatives to organ transplantation.
Experts said the research was promising, but still years away from human therapies.
The thymus is found near the heart and produces a component of the immune system, called T-cells, which fight against infection.
Patients who need a bone marrow transplant and children who are born without a functioning thymus could all benefit.
Ways of boosting the thymus could also help elderly people. The organ shrinks with age and leads to a weaker immune system.
However, there are a number of obstacles to overcome before this research moves from animal studies to hospital therapies.
The current technique uses embryos. This means the developing thymus would not be a tissue match for the patient.
The field of regenerative medicine has developed rapidly.
There are already patients with lab-grown blood vessels, windpipes and bladders. These have been made by “seeding” a patient’s cells into a scaffold which is then implanted.
“It remains to be seen whether, in the long term, cells generated using direct reprogramming will be able to maintain their specialised form and avoid problems such as tumour formation.”