A scientific team from the Guangzhou Institute of Biomedicine and Health (China) has succeeded in developing pig embryos whose kidneys contain a combination of human and pig cells. The long-term goal is Improving this technology for transplantation of the human organs.
The study was published today in the journal cell stem cellhas as one of its main authors the Spanish researcher Miguel A EstebanExpert in reprogramming pig cells.
This is the first time a solid humanized organ has been cultured within another species. Similar methods have been used in previous studies to generate human tissue such as blood or skeletal muscle in pigs.
The researchers decided to focus on the kidneys because they are one of the first organs to develop and they are also the most commonly transplanted in human medicine.
Our method aims to create human organs in pigs using cells from a specific patient. This would avoid the risk of immune rejection
Esteban told SINC that he and his team have been working on this project for five years. Unlike xenotransplantation, which uses genetically engineered animal organs, this method aims to “create human organs in pigs using cells from a specific patient.” This would avoid that Risks of immune rejection that they are doing xenotransplantation at the moment,” he emphasizes.
So far, “organs from mice have been grown in female mice, but previous attempts to grow human organs in pigs have been unsuccessful,” he notes. Liangxue Lai, union leader. “Our technology improves that Integration of human cells into recipient tissue and it allows us to grow human organs in pigs,” he points out.
The researchers acknowledge that integrating human stem cells into pig embryos is a major challenge “because pig cells are more numerous than human cells and both have different physiological needs.”
A niche in the pig embryo
To solve this problem, the team first created a niche in the pig embryo so that human cells do not have to compete with those of the pig. “We use CRISPR-Cas9 to genetically manipulate the unicellular embryo so that it lacks two genes necessary for kidney development,” Esteban explains.
Later the authors changed human pluripotent stem cells — those that have the potential to transform into any type of cell — to make them more prone to integration and less prone to self-destruct, temporarily disabling their apoptosis (programmed cell death). They then turned them into so-called cells naive or “naïve”, which resemble the first human embryonic cells, are grown in a special medium.
Then, before implanting the developing embryos into the sows, they reared the chimeras under improved conditions to feed them unique nutrients and signals for both human and pig cells as both species tend to have different needs.
Total implanted 1,820 embryos in 13 sows. On day 25 or 28, they terminated the pregnancy and extracted the embryos to see if the chimeras had managed to produce humanized kidneys.
The scientists collected five chimeric embryos to analyze them – two 25 days and three 28 days after implantation – and confirmed that this was the case structurally normal kidneys for their development phase and consisted of between 50 and 60% human cells.
By 25–28 days, the kidneys were in the mesonephros stage (the second stage of kidney development) and had formed tubules and cell buds that eventually became ureters connecting the kidney to the bladder.
The team also looked at whether the human cells contributed to other tissues in the embryos, which would raise ethical concerns. In this sense, Esteban notes that they “found very few human cells in other tissues and that these were mainly located in the kidneys”.
“Ethical implications could arise especially if the cells were numerous or in impaired lineages such as the neural and germ cells, and especially if these pigs were born,” explains Esteban.
“Anyway,” he adds, we are very careful and advance everything step by step to avoid surprises. One of our solutions is to genetically engineer human cells so that they cannot produce these fixed lineages in the pig embryo,” he explains.
Next up: heart and pancreas
Having improved conditions for growing humanized kidneys in human-pig chimeras, the team now wants to make headway Kidneys develop longer. He is also working to create other human organs such as the heart and pancreas in pigs.
When asked what phase these other projects are at, the Spanish researcher replies: “We have not yet prolonged the gestation of pig embryos with human kidneys, we are investigating how to do it efficiently and safely.” But our studies to create other human organs – at an early stage of embryonic development – in pig embryos are well advanced.”
The long-term goal is to improve this technology for human organ transplantation, but the researchers concede that the work will be complex and could take many years.
“Since organs aren’t made up of a single cell line, we would probably have to design pigs in a much more complex way to have an organ where everything is human, and that’s quite a challenge.” additional challenges‘ Esteban advances.
Our studies of creating other human organs – at an early stage of development – in pig embryos are well advanced.
Specifically, he adds: “We would have to do that.” Modifications of other genes in pigsbut I think it is possible and we have an extraordinary platform for genetically engineering these animals.”
Meanwhile, “our method provides a window for study human development“For example, we can track and manipulate the human cells we inject to study disease and cell lineage formation,” Esteban points out.
The Spanish researcher points out that both he and his colleagues are aware “that these organs will still be years away from being available in clinical practice and that there are a number of molecular obstacles to be solved.” “However, after this first major breakthrough, we are excited about the next steps that can be taken.”
Jiaowei Wang et al. “Generation of a humanized porcine mesonephros from induced pluripotent stem cells by embryo complementation”. cell stem cell2023