Researchers from the University of Edinburgh in Scotland have taken a group of cells from a mouse embryo and grown them into a fully functional thymus, an immune system organ, in an adult mouse.
This is the first time a whole organ has been grown from scratch inside an animal, and the findings, which have been published in Nature Cell Biology, could pave the way for alternatives to organ transplants.
The thymus is an organ that’s found near the heart and produces T-cells, which fight infection and are critical to the immune system.
To grow the organ, the researchers first took fibroblast cells from a mouse embryo, genetically reprogrammed them and triggered their transformation into a type of cell that’s found in the thymus. To do this, they forced the fibroblast cells to express only a single gene, which isn’t normally expressed by fibroblasts. This gene lead to the production of a protein called FOXN1, which triggered the fibroblasts to turn into thymus cells.
These cells were then mixed with some support cells and placed inside mice, where they developed into a complete thymus.
These newly grown thymuses were fully functional, and could even produce T-cells.
Clare Blackburn, a stem cell scientist at the MRC Centre for Regenerative Medicine at the University of Edinburgh who was part of the research team, told James Gallagher, a journalist for BBC News: “This was a complete surprise to us, that we were really being able to generate a fully functional and fully organised organ starting with reprogrammed cells in really a very straightforward way. This is a very exciting advance and it's also very tantalising in terms of the wider field of regenerative medicine."
She explained in a statement to the media: "The ability to grow replacement organs from cells in the lab is one of the 'holy grails' in regenerative medicine. But the size and complexity of lab-grown organs has so far been limited. 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."
However, the thymus is an extremely simple organ, and scientists are still a long way off employing similar techniques in humans. And because the research involved stem cells from an embryo, this process in humans wouldn’t result in a perfect match for the recipient of the organ, meaning there is a chance of it being rejected. The researchers also need to make sure these cells won't grow uncontrollably and pose a cancer risk.
Paolo de Coppi, a regenerative therapy researcher at Great Ormond Street Hospital in London, who wasn't involved in the study, told the BBC: "Research such as this demonstrates that organ engineering could, in the future, be a substitute for transplantation … 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."
But this early research could improve our understanding of the thymus and benefit patients with immune system problems, and it could one day lead to alternatives to organ transplants. The next step is trying to replicate the process with human cells.