Where can I get tissue for transplantation?
Surgeons have long learned to transplant human organs. This requires donor material from a healthy person. Some organs, such as a kidney, can be donated to a patient and the patient is alive, but a donor heart can only be taken from a deceased person. That is why donor material received from people is always insufficient, and it is impossible to greatly increase its supply.
There are two alternatives to this. The tissues of some animals can take root in the human body; For example, heart valves for humans can be made from pig biomaterial. Recently, American doctors managed to transplant a whole pig heart into a person, and the operation was successful at first glance. A few months later the patient died, but not due to tissue rejection. showed investigation.
In addition, living tissue can be printed layer by layer using a 3D printer that can work with cells. So to doctors successful Create relatively simple “sections” of the body, such as neurons, but the moment when it will be possible to print a working liver or lung is still far away.
The ideal solution would be for animals to have human organs. At first glance, this seems impossible: any organ in the body develops according to a genetic program, and if an animal has human DNA in its cells, it is a human. However, in living nature there are many chimeras – organisms with tissues from genetically different cells. Chimeras can also be interspecies, so growing human tissue in another animal is hypothetically possible.
Human kidneys in pig’s body
Experts from Guangzhou Institute of Biomedicine and Health can produces chimeric embryos containing a combination of human and pig cells. The kidneys are “humanized” in the embryo because the kidneys are one of the first to develop and are also the most popular organ for transplantation. The task was challenging because human and pig cells require different conditions to develop.
To start, biologists edited the embryo’s genome and turned off two genes within it to prevent its own kidneys from developing. This created an empty space in the body where foreign tissue could develop. The study authors then transformed the human stem cells into embryonic cell-like cells and inserted them into a pig embryo at the blastocyst stage (the first stage of fetal development). At this stage, embryos look like a round collection of cells that have not yet attached to the uterine wall. The resulting embryos were grown for a period of time in a special nutrient medium suitable for both human and pig cells before being transferred to surrogate pig mothers.
A total of 1,820 embryos were transplanted into 13 surrogate pig mothers. After 25-28 days, the pregnancy was terminated and the resulting embryos were removed for analysis. In five chimeric organisms, the authors found kidneys with normal structure for this stage of pregnancy; these formed tubules and cell primordia that later became ureters. 50-60% of these kidneys were human cells.
Why didn’t all pigs become humans?
Cell transplantation took place at the blastocyst stage, when organ rudiments are not even present. This has also raised some ethical concerns: Can a fetus develop human nerves or brains?
Because the cell injection was done blindly, the concentration of human cells in the kidney area occurred only because there was free space there.
“We found that if you create a niche in a pig embryo, human cells will naturally fall into that niche. We found very few human nerve cells in the fetal brain and spinal cord and no human cells in the genital area. This suggests that human pluripotent stem cells do not differentiate into sex cells,” said one of the study’s authors which is Zhen Dai.
Now that they’ve proven it’s possible to create such chimeras, the authors want to give the embryos a chance to develop over a long period of time, as well as “humanize” their hearts or pancreas. The ultimate goal of this work is to provide doctors with an infinite supply of human organs for transplantation (in terms of genes), but so far scientists are only at the very beginning of the journey.
For example, a niche was created only for one group of cells, that is, future buds. The vessels in these kidneys remained porous, which will contribute to organ rejection during transplantation. To transform kidneys into fully human ones, chimeras must be produced in a much more complex manner. The authors estimate that it will take many years to obtain actual human organs from an animal’s body.