[Over 100,000 people are on the waitlist for organ replacements with 17 passing away each day](https://www.pennmedicine.org/updates/blogs/transplant-update/2023/april/6-quick-facts-about-organ-donation#:~:text=Did you know that there,an organ to become available.). More innovation is needed around this problem.
Xenotransplantation (animal-to-human transplantation) is slowly reaching more advanced technology readiness. The first successful pig-to-human heart transplantation in 2022 was conducted with therapeutics company, Revivicor. Animal organs for xenotransplantations are genetically modified in multiple places, with genes added from humans and intrinsic genes knocked down to control heart size and mitigate human immune rejection (a main cause of failure/safety issues). Said immune reaction could be circumvented if there was a higher fidelity way of reconstructing human organs.
A potential mode is through blastocyst complementation - which is where whole organs of an animal can be grown in an entirely different animal. For example, scientists have shown that one can grow an entirely mouse pancreas in a rat.
To give more context on this alchemy I want to break down the terminology of blastocyst complementation:
A blastocyst is a mass of cells in early development which would otherwise become a living animal. This blastocyst has stem cells that can grow into any type of cell in the body - heart cells, brain cells, skin cells, etc.
Scientists can take cells from a mouse and cells from a rat and put them together into one blastocyst. The cells from different organisms can work together to (sometimes) grow into a healthy mouse/rat chimera (or hybrid animal). This technique is called "complementation" because the two types of cells complement each other to form a full organism.
In order for the complementation to work, editing/modification of the host animals cells must be completed (e.g. editing out genes of the rat which allow for the development of the pancreas). This deficiency is important in that it allows the cells from the other organism (e.g. mouse) to fill in the embryo development gaps, ideally making a fully new organ. There’s varied success in being able to successfully complement the blastocyst but it has worked in enough cases to merit more investigation (and could change the dire dynamics of organ transplantation.)
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