Researchers led by Liangxue Lai from China’s Guangzhou Institute of Biomedical and Health Research recently extended the amount of time human stem cells can survive in animal embryos. The research team is working on a five-year project to grow human organs that can be transplanted into patients without waiting for a donor. So far, no scientist has been able to grow an organ containing 100% human cells inside an animal embryo.
Because pigs are similar to humans in terms of physiology and embryonic development, Lai’s team injected human stem cells into pig embryos. They inactivated a gene in the pig embryo that allows the pig to develop its own organs, allowing human stem cells to replace the pig cells while the organ grows.
The research team also treated the embryos with a small amount of an antibiotic called doxycycline. This makes it possible to control which genes in stem cells are activated. They explained that the antibiotic activated genes in the stem cells that helped them withstand the stress of being injected into the embryo, increasing their chances of developing into complete organs.
Lai hypothesized that if human stem cells were implanted into pig embryos, they would develop and regenerate over time to form organs compatible with humans. Lai’s team used this method to transplant kidneys because they are some of the most frequently transplanted organs around the world and are some of the first organs formed by a human fetus during development. trying to grow it.
Scientists collected about 2,000 pig embryos and implanted them into 13 surrogate pigs. After about 20 days, the embryo began to develop kidneys. Once the kidneys were fully grown, the scientists terminated each pig’s pregnancy and removed the embryos to see how many human stem cells they contained.
They removed some of the embryos after 25 days of development and others after 28 days. They adjusted the timing of removal to reduce the risk of embryos experiencing extensive cell death. This process is Degeneration. The scientists explained that the risk of the cells degenerating is highest after about 30 days, so they removed the embryos just before that.
Despite precautions, few embryos survived. The researchers were able to recover just nine embryos from the surrogate mothers, six of which were collected after 25 days and three after 28 days. They found that four of the embryos taken after 25 days had already begun to develop cell death and developmental defects, and only five survived further testing.
The researchers used a genetic fingerprinting method called polymerase chain reaction, or PCR for short, tests whether each surviving embryo has a gene sequence found in human cells. They found that all five embryos contained human genetic sequences. They ran PCR a second time, looking for a specific type of DNA sequence that is present in all human cells. mitochondrial dna. They used this method to determine which parts of the developing kidney were made up of human and pig cells.
If the researchers found human cells in the embryos, they stained them to see if the cells were starting to form organs other than the kidneys. The researchers explained that they did not want the human cells to grow into other parts of the animal fetus, such as its heart or central nervous system.
Scientists found that all five pig embryos developed kidneys and that 50-60% of the cells were of human origin. The researchers suggested that this meant the cells could have grown into a full human kidney after a longer gestation period. However, it was also discovered that none of the kidneys grown during the experiment were compatible with humans. Additionally, human cells were detected in the fetus’s liver, heart, and central nervous system.
Scientists have concluded that it is possible to grow human kidney cells in pig embryos, but some questions remain. For example, it is not yet known why the embryonic cells died early, and whether cell degeneration can be avoided in future experiments or is an unavoidable risk. They also don’t know how to prevent human cells from growing organs other than the kidneys, but they suggested that this could be prevented by inactivating other genes in the stem cells. In any case, Lai’s team proposed that similar techniques could one day be used to grow human-compatible kidneys and other organs for transplantation.
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Source: sciworthy.com
