Researchers announced Saturday a major breakthrough towards growing tailor-made human organs for transplant, according to the Guardian. University of California Davis researcher Pablo Ross, said, at a meeting of the American Association for the Advancement of Science, that his team had successfully introduced human stem cells into sheep embryos.
Last year, Ross and his colleagues announced another breakthrough, with human cells transferred to pig embryos. Roughly one in 100,000 of those cells were human cells. Now, with the sheep embryos, the researchers increased this ratio to one in 10,000 cells.
Ross’s team has also found success using genome editing techniques to yield pig and sheep embryos that do not develop a pancreas. This is a key step in the process towards allowing human cells to develop the missing organ.
The ratio, however, may still be too low. Ross says that for human organs to develop, roughly 1 percent of the embryo’s cells would need to be human. However, the new development is a significant step in that direction.
Furthermore, the use of sheep, rather than pig embryos, holds certain advantages. Fewer sheep embryos are necessary for each experiment, since fewer need to be transplanted into each adult. In pigs, 50 embryos are normally transplanted into a single recipient, according to Ross. In addition, some sheep organs, including the heart and lungs, have a close resemblance to human organs.
The experiments have also been held back to some degree by ethical concerns. The embryos were only allowed to develop for 28 days. The team would need permission from institutional review boards to allow the embryos to develop for 70 days, which the team says would allow for more convincing results as to the real feasibility of developing the organs. There are a range of concerns, including whether the cells could lead to sheep developing human traits affecting their mind. Ross says that he shares these concerns.
“Let’s say that if our results indicate that the human cells all go to the brain of the animal, then we may never carry this forward,” he noted.
In the US, the National Institutes of Health has moratorium on providing funding for research of this nature, but is currently considering replacing the moratorium with a review process.