Researchers at the Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, are growing hearts containing human cells in pig embryos.
Mouse embryo at 11 days. Image from Adobe Stock.
The pig embryos survived for 21 days, and the hearts had started beating, the researchers announced at the annual meeting of the International Society for Stem Cell Research annual meeting last week.
Human stem cells injected into pig embryos
Animals such as pigs, mice, and cats have been shown to have similar genomes and anatomy to humans. Pigs and mice are most commonly used to develop human-animal chimeras.
In this study, which was profiled in Nature, two genes essential in heart development were removed from generated pig embryos. The research team then introduced reprogrammed human stem cells, which had genes that prevent cell death and bolster cell growth. The scientists transferred these stem cells into the embryos and implanted the embryos into surrogate pigs.
After 21 days, the hearts had grown to the same size as a human heart at that stage, and they were beating, said Lai Liangxue, a developmental biologist at the Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, who led the research.
The embryos did not survive after 21 days, possibly because the human cells disrupted the function of the pig hearts, said Lai.
The human stem cells were tagged with a luminescent biomarker, allowing the researchers to identify them. The fluorescent cells were located in a small section of the heart.
The goal: organ transplants
The long-term goal of creating human-animal chimeras is to develop human organs that can be used for transplants. In order to avoid the immune system attacking the organ, the organs will need to be made entirely of human cells.
This future may not be too far away, and it could help save the lives of those waiting for organs. According to the Health Resources and Services Administration, 103,223 people are on the national transplant waiting list, and an average of 13 people die every day while waiting for an organ. Every eight minutes, another person is added to the waiting list.
Injecting cells into amniotic fluid – another method
Also announced at the International Society for Stem Cell Research meeting, scientists were able to develop mice that have human cells in their organs by injecting human cells into the amniotic fluid of pregnant mice.
Xiling Shen, a biomedical engineer at the University of Texas MD Anderson Cancer
Center in Houston, wanted to find a new method to develop human-animal chimeras that allowed more human cells to survive and enabled researchers to target specific organs. His team allowed the human cells to mature into 3D human-tissue models, organoids, before they were injected. They hoped this method would make the cells more resilient.
The human cells grew and multiplied within the embryo, but only in the organ they belonged to, an important innovation as human stem cells are pluripotent, meaning they can become any organ.
After the mice were born, the researchers found that 10% of them contained about 1% human cells in their intestines, as well as lower proportions of human cells in their livers and brains.
The human cells in the liver were even producing human albumin, a liver protein. The human cells were still present two months after the mice were born, showing their heightened stability.
