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How Scientists Grew a New Organ Inside a Mouse's Body

The future of regenerative medicine now includes organs that can self-assemble inside of you.

For the first time ever, a fully-functioning organ—the thymus—has been grown from scratch, inside of a living mouse. The research was conducted by the University of Edinburgh's Centre for Regenerative Medicine, and could eventually lead to less-invasive organ replacement in humans. The team's results were published on Sunday in Nature Cell Biology.

"The replacement thymus appears to be very similar to the normal thymus," lead author Clare Blackburn told me. "It has normal organization, most of the genes that we expect to be expressed are expressed, and all of the types of cell we would look for in a normal thymus are there [and] are organized correctly in relation to each other."

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Most importantly, the replacement thymus was able to carry out its central function normally: producing T-cells, the immune system's disease-fighting vigilantes. Without normal T-cell production, the body is much more vulnerable to infection and illness.

Blackburn's team created the beginnings of their replacement thymus in the lab, by "reprogramming" fibroblasts from a mouse embryo into thymic epithelial cells (TECs). Fibroblasts are the most common type of cell in connective tissue, but as the researchers discovered, they will forget their original identity if they are forced to express the Foxn1 gene.

"We use a technique that allows us to re-aggregate cells in the lab to make clumps of cells containing the reprogrammed cells," Blackburn explained. "This re-aggregate is what we transfer into the mouse."

"At the stage at which we transplant, the cells have been reprogrammed, but they have not formed a complete, organized thymus," she continued. "We analyzed the mice three or four weeks after the transplant, and by then it had become an organized thymus."

Clare Blackburn explains her team's research. Video: Medical Research Centre/YouTube.

The team conducted their experiment on mice that were born without a thymus, as well as mice with normal organs. "In both cases, a functioning thymus was formed," she said. "Because the mice with no thymus had no pre-existing T-cells, we knew that the T-cells that developed in those mice after the transplant came from the transplanted thymus."

The study presents a promising strategy for a number of different thymic defects. For example, one in 4,000 babies is born with DiGeorge Syndrome, which is characterized by a missing or malfunctioning thymus. Transplanting reprogrammed cells into these individuals would equip patients with a normal immune system. This procedure could also be useful for augmenting our immune systems as we get older, given that the thymus begins to deteriorate with age.

"The next step for us is see if we can replicate these findings using human cells," Blackburn said. "We're also starting to work with tissue engineers to start to work out how to make a thymus for transplant at the size that we would need for patients."

The notion of an organ self-assembling inside a patient's body reads more like Neill Blomkamp plot device than a genuinely achievable medical procedure. But it's far from the only win that regenerative medicine has racked up recently. Researchers have also been able to keep modified pig hearts alive and viable inside a baboon's body for a full year, and laboratory-grown vaginas have been transplanted into women born without them.

So while there is plenty of dystopian news circulating in other fields, regenerative medicine is poised to deliver advances that could radically improve life expectancy and quality in the coming decades.