Kidneys with human cells grown in pig embryos

Humanised kidneys have been grown from human stem cells, transplanted into pig embryos, for the first time.

Scientists in China created a chimeric embryo, containing both human and pig cells, that developed early-stage, humanised kidneys when grown in pigs. The chimeric embryo was made by transplanting human stem cells into a pig embryo, which was then carried by a surrogate pig.

'Rat organs have been produced in mice, and mouse organs have been produced in rats, but previous attempts to grow human organs in pigs have not succeeded,' senior author Dr Liangxue Lai, from the Guangzhou Institutes of Biomedicine and Health, said. 'Our approach improves the integration of human cells into recipient tissues and allows us to grow human organs in pigs.'

The research, published in Cell Stem Cell used single-cell pig embryos lacking two genes required for kidney development. This provided a niche environment for human stem cells to cultivate and develop into a humanised kidney without being outcompeted by pig cells. Pigs were selected due to similar embryonic development and organ sizes to humans.

Due to ethical considerations, the gestation of the chimeric embryos was terminated at day 25 to 28, once the kidney had formed, but the brain of the embryo had not. This eliminated the possibility of a chimeric human-pig brain from developing from human stem cells.

Kidneys remain one of the most frequently required organs for transplantation due to lack of human donors. As the blood vessels in these kidneys were composed of pig cells, the humanised kidneys developed within this research could not be used for transplantation. This is due to transplant rejection exhibited by human recipients receiving transplanted organs containing pig cells. This highlights the limitations associated with this technique currently.

'The paper describes pioneering steps in a new approach to organ bioengineering using pigs as incubators for growing and cultivating human organs,' said Professor Dusko Ilic, a stem cell scientist at King's College London, who was not involved in the research. 'As the authors admitted, there are plenty of challenges. Will this approach prove to be the ultimate solution? Only time holds the answer.'