Pig-Human Chimera: Making Transplantable Organs Possible?

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Pig-Human Chimera: Making Transplantable Organs Possible?

Modern technology can help save a lot of lives, prevent many injuries and accidents. We are doing a great job of keeping people alive with the help of various medical breakthroughs. Hence, the supply of donor organs is decreasing but the demand for transplants is still growing. Sadly, everyday, there are many people dying while waiting for an organ transplant.

This need led scientists to find ways on how to make organs fit for transplant. For so long, research has been concentrated on human stem cells. Stem cells are "basic cells" in an embryo that can differentiate into different organs of the body. The problem with stem cells grown in petri dishes is that they cannot be made into usable tissues and organs that well. For this reason, scientists need to find another way so that they can grow organs inside the embryo of another species. Thus, a chimera is required.


Two Research Papers on Chimera Possibility

Two researcher papers show that this can be done. One research used human stem cells and implanted them in a pig fetus. Some embryos survived to reach their assigned date of destruction. The date set is for ethical reasons. The embryos that survived had human cells in a pig fetus.

Even though there is a huge gap of evolutionary years between humans and pigs from the last common ancestor, pigs and humans share a good amount of biology. There have also been human-mouse and human-rat chimeras but they were not successful most likely due to the huge difference between humans and rodents.

Jun Wu and his team at the Salk Institute in La Jolla, California tested if a viable embryo can be possible when human stem cells are injected into a pig embryo. The experiment resulted in some viable embryos. However, it was more of a failure than a success even though it worked. Only a small fraction of the cells in the cells of the chimera embryos were human. There were also no reliable patterns that can be observed.

According to Sharon Begley at STAT, the human-pig chimera is more of a failure than a success. The successes only had a few human cells. Wu said that “The overall human contribution was very low, with what we estimate is less than 1 human cell per 100,000 pig cells and no human cells in the chimeras’ brains."

The study attempted a rat-mouse chimera possibility to produce a specific organ or cell type with the use of CRISPR gene editing. In the study, the genes in the rat fetus that is in charge of development were disabled and then replaced with mouse stem cells. This technique was not used in the human-pig chimera experiments.

On the rat-mouse chimera, it is shown that a more focused organ-generating chimera can be possible. It has the possibility to increase growing organs that are viable for transplant patients.

The second paper was about the diabetic mouse that was cured. A rat-mouse chimera was made to grow donor pancreas that eventually cured the diabetic mouse.

In the experiment, it was found out that it was possible to cure diabetes in mice. This was done by growing pancreas cells from mouse stem cells in mouse-rat chimera and then moving these cells into the diabetic mice.

Since the stem cells came from the diabetic mouse, a workaround was done for the immunosuppression issues that happen during organ transplants. Sarah Kaplan from the Washington Post said "Because the transplanted cells were grown from stem cells taken from mice, the animals required just five days of immunosuppressive drugs to keep their bodies from rejecting the new tissue. After that, they were able to live normally with healthy blood glucose levels for over a year — half a lifetime in human terms."


More research

Bruno Reichart at the University of Munich in Germany has led a research on developing a technique where baboons can survive longer than before by using pig hearts. The significant part of the study is figuring out safe heart transplants due to the rise in heart problems.

Christoph Knosalla of the German Heart Center wrote, “Heart failure in the United States is expected to reach more than eight million by 2030, and many of these people will die while waiting for a donor organ.”

The longest a baboon has survived after receiving a pig's heart is 57 days. According to researchers, baboons can last for about six months by modifying heart transplant protocol and using gene editing technology.

There is much to be studied and experimented on when it comes to chimera and growing organs in chimera. Previous studies and trials have shown that it is possible to grow organs that can be fit for transplant with the aid of gene editing technology. However, this can bring up lots of things to debate on with ethics and morality as the major argument.



Ralph Chen

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