"By directly reprogramming cells we've managed to produce an artificial cell type that, when transplanted, can form a fully organised and functional organ. This is an important first step towards the goal of generating a clinically useful artificial thymus in the lab."

The thymus is the central hub of the immune system sending out infection fighting T-cells.

People with a defective thymus lack functioning T-cells and are highly vulnerable to infections. This is especially hazardous for bone marrow transplant patients, who need a working thymus to rebuild their immune systems after surgery.

Around one in 4,000 babies born each year in the UK have a malfunctioning or completely absent thymus, due to rare conditions such as DiGeorge syndrome.

Thymus disorders can be treated with infusions of extra immune cells or transplantation of a new organ soon after birth. However, such approaches are severely limited by a lack of donors and tissue rejection.

The new research, published in the journal Nature Cell Biology, raises the possibility of creating a whole new functioning thymus using cells manufactured in the laboratory.

While fragments of organs, including hearts, livers and even brains, have been grown from stem cells, no one before has succeeded in producing a fully intact organ from cells created outside the body.

Dr Rob Buckle, head of regenerative medicine at the MRC, said: "Growing 'replacement parts' for damaged tissue could remove the need to transplant whole organs from one person to another, which has many drawbacks not least a critical lack of donors.

"This research is an exciting early step towards that goal, and a convincing demonstration of the potential power of direct reprogramming technology, by which once cell type is converted to another. However, much more work will be needed before this process can be reproduced in the lab environment, and in a safe and tightly controlled way suitable for use in humans."

Chris Mason, Professor of Regenerative Medicine at University College London, said: "Using living cells as therapies has the big advantage in that the functionality of cells is many orders of magnitude greater than that of conventional drugs. Nowhere is this level of functionality more needed than in curing disorders of the immune system.

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British scientists create first complete working organ from cells