Scientists transplant humanoid kidneys into pigs
Chinese scientists have successfully transplanted kidneys containing human cells into pig embryos, the world’s first operation that could one day help tackle the shortage of organ donors.
But the development, described by a study published in the journal Cell Stem Cell on Thursday, raises ethical issues, especially since some human cells have been found in pig brains, experts said.
The researchers from the Guangzhou Institutes of Biomedicine and Health focused on the kidney because it is one of the first organs to develop, and the most common in human medicine.
“Mouse organs were produced in mice, and rat organs were produced in mice, but previous attempts to transplant human organs into pigs were unsuccessful,” lead researcher Liangxu Lai said in a statement.
“Our approach improves incorporation of human cells into recipient tissues and allows us to grow human organs in pigs.”
This is a different approach from recent milestones in the United States, where transgenic pig kidneys, and even hearts, have been transplanted into humans.
The new research “describes pioneering steps in a new approach to bioengineering organs using pigs as incubators for the growth and transplantation of human organs,” said Dusko Ilic, a professor of stem cell sciences at King’s College London who was not involved in the research.
Illich cautioned that there would be many challenges to turning the experiment into a viable solution, but “nevertheless, this attractive strategy deserves further exploration.”
– Gene editing –
The main challenge in creating such hybrids was that pig cells outperform human cells.
To get around the hurdles, the team used gene-editing technology CRISPR to delete two genes essential for kidney formation inside a pig embryo, creating what’s called a “niche”.
Then they added specially prepared human pluripotent stem cells — cells that have the ability to develop into any type of cell — which filled in the space.
Before implanting the embryos into pigs, they grew them in test tubes containing material that fed human and pig cells.
In all, they transferred 1,820 embryos into 13 surrogate mothers. Pregnancies were terminated after 25 and 28 days to assess the success of the experiment.
Five fetuses selected for analysis were found to have had normal kidneys and function for their stage of development, and had begun to develop ureters that would eventually connect them to the bladder.
It contained between 50 and 60 percent of human cells.
“We found that if you create a niche in the pig embryo, human cells will naturally enter these spaces,” said co-author Chen Dai.
“We saw very few human neurons in the brain and spinal cord and we saw no human cells in the genital ridge.”
Preventing the invasion of human cells into reproductive tissues is crucial, because otherwise there would be a risk of creating uncontrolled human-swine hybrids.
Darius Federa, professor of stem cell biology at the University of Reading, said the presence of any human cells in pig brains still raised concerns.
“Although this approach represents a clear milestone and the first successful attempt to grow whole organs containing human cells in pigs, the proportion of human cells in the generated kidneys is still not high enough,” he added.
In the long term, the team wants to improve their technology for use in transplanting human organs, but they admit it’s not ready yet.
An important limitation is that the kidney contains porcine-derived vascular cells, which could cause rejection if transplanted into a human.
However, the scientists plan to go ahead and allow the kidneys to develop longer. They are also working on transplanting other human organs into pigs, such as the heart and pancreas.