It’s a very common and unfortunate reality, even with today’s medical technology — many people still die while waiting for organ transplants, while people who get new organs from donors may occasionally encounter setbacks, due to the organs being rejected. And while it might not be the most conventional solution around, researchers have developed sheep embryos with human cells, which could potentially hit two birds with one stone and address the issues mentioned above.
According to a report from The Guardian, the human-sheep “chimeras” were created by the same team that had, in 2017, introduced human cells into pig embryos. At that time, it was hoped that the technique could lead to actual human organs being grown, but with no other group of scientists having stepped up to continue where last year’s project left off, the researchers have just come up with something similar, this time involving sheep embryos.
Compared to the human-pig chimeras from last year, where only about one out of every 100,000 cells were human, the percentage of human cells is substantially higher this time around, though still extremely low in the grander scheme of things. According to researcher Dr. Pablo Ross from the University of California-Davis, about one in 10,000 cells in the new human-sheep chimeras are human cells.
Speaking at the American Association for the Advancement of Science conference in Austin, Texas, project lead and Stanford University professor of genetics Dr. Hiro Nakauchi explained that his team had previously had success creating a mouse pancreas in rats, then transplanting the new organ into a diabetic mouse. This procedure proved to be successful, as the mouse was “almost completely” cured following the transplant.
For the new project, the researchers have been using genome editing to create pig and sheep embryos that do not have a pancreas, The Guardian wrote. At the moment, the researchers believe that the technique still needs to be refined, but they remain hopeful that the introduction of human cells into the sheep and pig embryos will allow the missing pancreas to grow over time.
If everything goes as planned and the researchers are able to grow human pancreas and other organs inside the animal embryos, this could lead to two things. As noted by The Guardian, this could benefit people waiting for an organ transplant by giving them more options. But since it might also be possible to edit the organs and use a recipient’s own cells to ensure that the organs are compatible with the patient’s immune system, the new technique could reduce, or even eliminate the chance of an organ being rejected.
“Even today the best matched organs, except if they come from identical twins, don’t last very long because with time the immune system continuously is attacking them,” Ross explained.
Compared to pig embryos, sheep embryos have multiple advantages that could potentially make them better choices for experimentation. According to Ross, only four of these embryos need to be transferred to a recipient, a much lower figure than the requirement of 50 embryos for human-pig chimeras. Sheep embryos can also be produced by in vitro fertilization (IVF) without much difficulty. Furthermore, the heart, lungs, and other sheep organs are of a similar size to their human equivalents.
Pigs, on the other hand, have some advantages as well, such as speed of growth and the option to simultaneously produce more offspring, thereby allowing researchers to use fewer pigs when conducting their chimera experiments.
The new project isn’t without its share of challenges. Aside from the ethical concerns of whether human-sheep chimeras could eventually “think” as people do, there’s also the possibility of viruses from the host animals infecting human cells, thus resulting in what could be a “very fast” rejection, as opined by Francis Crick Institute stem cell biology head Robin Lovell-Badge, who was not involved in the study. Additionally, about one percent of the chimeras’ cells need to be human for the researchers to have them develop for 70 days as planned. Currently, they are only allowed to let the embryos develop for 28 days, as pointed out by The Guardian.
Despite the challenges the sheep embryo project might face, the researchers remain optimistic that their experiments will ultimately see human organs growing inside the embryos of animals, though it might take some time before this happens.
“It could take five years or it could take 10 years but I think eventually we will be able to do this,” Nakauchi predicted.
According to the Daily Mail, approximately 76,000 U.S. residents and 6,500 U.K. residents are on organ transplant lists each year, and some patients have to wait as many as five years before they make it to the top spot. Out of these thousands of patients, about 32 individuals per day die without ever receiving an organ transplant.