(CNN) – Scientists have created a partially human mouse embryo: 4% to be exact.
The hybrid is what scientists call a human-animal chimera, a single organism made up of two different sets of cells, in this case, a mouse embryo that has mouse cells and human cells.
This human mouse chimera has by far the largest number of human cells ever recorded in an animal, according to the researchers. Their experience suggests that many types of human cells can be generated in mouse embryos, and at a much faster rate than in human embryos.
And this, scientists say, has enormous potential for the treatment of human disease, perhaps even for covid-19.
The results have the potential to treat the disease
These results are important for several reasons, said Jian Feng, Professor of physiology and biophysics at the University of Buffalo, one of the study authors. On the one hand, it shows that it is possible to generate many types of mature human cells in mouse embryos, which could be used to produce cells, tissues or organs to treat diseases.
In this study, the research team injected 10 to 12 human stem cells into developing mouse embryos. In 17 days, these stem cells transformed into millions of mature cells, including human red blood cells and eye cells.
In a human embryo, it would take about eight weeks to generate human red blood cells, and even more to generate human eye cells, said Feng.
“These observations suggest that the mechanism that specifies development time could be changed,” he wrote in an email to CNN. “With this involvement, there will be more spectacular discoveries in the future.”
The team used revolutionary technology
In previous research, scientists had detected only about 0.1% of human cells in mouse embryos.
This is why it is so surprising that these chimeras of human mice have 4% of human cells. And due to the team’s technique of counting cells, Feng said that even that number was an understatement.
The team accomplished this feat by converting human pluripotent stem cells, which can potentially produce any cell or tissue the body needs to repair itself to a previous state.
The conversion of these cells has made them compatible with the internal group of cells within an early-stage mouse embryo, which generates all cells in the body. So when the human cells from the previous step were injected into mouse embryos, they developed much better than they would have done otherwise.
“We thought if we could make human pluripotent stem cells behave like mouse pluripotent stem cells, human cells should mix well with mouse stem cells in a mouse blastocyst,” wrote Feng . “And that’s exactly what we found.”
The team’s experience indicates that “the genetic program integrated in a mouse embryo and the genetic program integrated in human stem cells can cross quite well,” said Feng.
In other words, there is sufficient evolutionary compatibility between mice and humans for mouse embryos to constitute a relatively good environment for culturing human cells.
“Life is a DNA-based software system that harnesses energy to produce information,” wrote Feng. “This experience is like emulating Windows on a Mac.”
Future implications could include organ development
Human-animal chimeras have been the subject of an ethical debate among scientists. Although they can be used to grow human organs for transplants, some scientists claim that there are serious risks that need to be explored.
“The possibilities have many researchers full of emotion. But they also pose serious ethical dilemmas over the moral status of these partially human animals, “wrote Lori Marino, neuroscientist and animal advocate in a Opinion piece 2017 for Stat News.
“Chimera test subjects must be human enough to serve as effective models for health research, but not human enough to benefit from the protection of this research.”
Feng said that his research is still in its infancy and that more studies are needed. But he added that the technology to make human stem cells more compatible with mouse embryos has a number of potential applications.
One, said Feng, is that it can generate better mouse models for studying human diseases, including covid-19. Mice can also be used to develop human immune cells or respiratory cells.
“Such chimeric mice would be very useful in studying covid-19, which seriously affects humans, but hardly affects mice,” said Feng.
“Another example could be malaria, in which the pathogen specifically infects human red blood cells with a mosquito bite. If we can make a mouse with even more human red blood cells, this would be a very good model for studying malaria. “
Future studies could also explore whether this technique could be applied to larger animals, such as pigs, to generate organs for transplantation, said Feng. Although he said that such possibilities are far away, they are promising.
“At the time of the first plane, all of the potential applications only existed in the minds of some people,” said Feng. “If society decided it was a horrible idea to steal, we would lose a lot of wonderful things to everyone. A society that sees the world for what it is, not as it should be, is an efficient society that can move forward. “