Scientists grow human liver inside mouse's head

One of the most promising fields of science is the artificial construction of tissues and organs that can be used for transplantation. After the discovery of stem cells, scientists thought they would be able to make anything and replace damaged tissues and organs in the body. It has proven to be much harder than originally thought, especially the growth of whole organs. To tackle one of the major problems with artificial organs, which is the lack of a blood vessel system providing the nutrients, researchers from Yokohama City University devised an interesting experiment: they tried to grow a human liver inside the head of a mouse.

Purpose
As said, one of the major problems of artificial organ development is the lack of a blood vessel system. A circulatory network is necessary to feed all the cells, and without it, a lab-grown organ can never reach its full size. Because the brain requires a lot of nutrients, it has an extensive network of blood vessels. The Japanese scientists therefore attempted to grow their tissue inside a mouse's head, in order to benefit from its circulatory system. Growing something inside an animal's head may sound weird, but it is actually pretty logical.

Growth
The scientists started off with a bunch of stem cells that were directed to specialize into liver tissue. They also added two other cell types into the mix, of which one normally takes care of the construction of blood vessels. Simple mixing turned the collection of cells into tiny liver tissue, which is quite surprising. The next step comprised of getting the small pieces of tissue inside the brain of a mouse, in order to utilize its vascular system and keep up growth.

Transplantation
Immunocompromised mice were used as recipients for the artificial liver tissue. These animals do not have a functioning immune system, which means the transplanted tissue is not recognized as foreign, leaving it intact and able to grow. After just 48 hours, the scientists noted that blood vessels started to grow inside the tissue, and other measurements revealed the tissue is similar to ordinary human liver.

The liver tissue, lacking a bile duct.

Problems
Not all is well with the artificially constructed liver tissue: some components are still missing, such as a bile duct. Also, the organ needs to increase in size before it becomes usable as a transplant. Therefore it seems that more research is necessary to further optimize artificial organ construction. It is also likely that when the tissue size increases, other problems will arise.

Outlook
Using a mouse's head as a nesting place for artificially constructed organs is curious, but not unreasonable. It enables us to utilize the blood vessel system which we so desperately need. The aforementioned problems show there is much more work to be done, but this proof-of-principle shows we are getting closer to true lab-grown organs that are ready for transplantation. In the end, this could save many lives.