Human(-ish) kidneys grown in pig embryos.

Science News brings home the bacon for humans needing kidney transplants, with news of a Chinese research team that has successfully grown a “humanized” kidney (an organ made mostly of human cells) inside a pig embryo:

Stem cell biologist Liangxue Lai, of the Guangzhou Institutes of Biomedicine and Health in China, and his team spent more than five years refining their methods to enhance the human stem cells’ survivability.

While the pig embryos were still just single cells, the team used the gene-editing tool CRISPR/Cas9 to edit out two genes necessary for kidney development. That created a niche in which the human iPSCs, once injected into the space, could develop into kidney cells. The human stem cells were also tweaked to have especially active genes that dampen apoptosis, or cell death, to keep the cells alive long enough to gain a foothold and begin forming the kidney.

More than 1,800 embryos were then transferred into surrogate sows, of which five were harvested for study within the first 28 days. All five had normal kidneys consistent with their level of development, and the organs contained 50 percent to 60 percent human-derived cells. That’s the highest percentage of human cells yet observed in any organ grown inside a pig, [Kunming University cell biologist Tao] Tan says [as an expert in the field not part of the research project]. Given more time, there’s no indication that the kidneys wouldn’t continue to grow and develop normally, possibly with the human cells increasingly edging out the pig cells, the researchers say.

…[U]ntil researchers can create an organ that is 100 percent human, it’s likely that such transplants will prompt rejection.

In addition, a few iPSCs erroneously differentiated into neural cells in the brains and spinal cords of the embryos. [New York University transport immunologist Massimo] Mangiola [an expert in the field not part of the research project] says that the cells appear to be random, unlike the kidney cells, making him think they’re not likely to result in animals with human brains — which would create an ethical quandary.

To avoid such ethical issues, Lai says that moving forward the team will knock out genes that orchestrate the stem cells’ differentiation into neurons — as well as into germline cells, eggs and sperm, which pass genetic information on to offspring. The team is also pursuing growing other human organ precursors in pigs as well, including the heart and pancreas.

You can read more of the Guangzhou research here, in Stem Cell.