Two research teams inserted stem cells in embryos of pig and developed pancreas of mice in rats
This week, biologists reported two significant advances that approach the realms of science fiction to the real world: it is possible to replace the defective organs or sick a patient by others derived from their own cells and then cultivate them in a host animal.
The idea is to develop stem cells derived from the skin of a patient; then, from them to grow the new organ is desired in an animal of large size -such as a pig, for example-, and finally transplanting the organ to the patient without fear that it will be rejected.
The pigs where they would grow human organs would be what are known as chimeras. That is to say, animals generated from two genomes: the animal and the human. To achieve these copies, would be implemented by the stem cells of a patient in an embryo pig in its first stage of gestation.
The team of biologists at the Salk Institute, led by Jun Wu and Juan Carlos Izpisua Belmonte, demonstrated for the first time that human stem cells can contribute to the formation of tissues of a pig.
Another group headed by Tomoyuqui Yamaguchi and Hideyuki Sato, University of Tokyo, and by Hiromitsu Nakauchi, Stanford, already managed to reverse diabetes in mice by implantarles glands pancreatic composed of mouse cells grown in a rat. The team’s report of the Salk Institute was published yesterday in the journal Cell, while the team Tokyo-Stanford appeared the day before yesterday in the journal Nature.”In principle, this is a very promising”, says Rudolf Jaenisch, a specialist in stem cells at the Whitehead Institute, Massachusetts.
although you will still need to overcome many technical barriers and ethical, the research is advancing at the pace of the desperate need for organs for transplant.
The team of Izpisua Belmonte demonstrated that human stem cells themselves survive in embryos of pig, and they help to form organs, although not efficiently. “The human cell does not contribute much. In the brain we observe almost no, or no contribution”, says his colleague Wu. “And that’s good, because we can guide the human cell to the organ that we want.”
Both Izpisua Belmonte as Nakauchi say that it takes a lot so that they can be grown successfully human organs in animals like pigs.
Humanization
The creation of chimeric animals, in particular, that contain human stem cells, it is an idea controversial, because the test samples can be “humanized” in a way unwanted. For example that is incorporating human stem cells into the brain of a pig and confer on certain attributes of the man.
In 2005, senator Sam Brownsback introduced a law imposing a fine of a million dollars to create or lucrara with a chimera that had human cells in your brain or reproductive tissue. The draft law fell into oblivion, but in 2015, the National Institute of Health of Usa (NIH, for its acronym in English) declared the suspension of the use of public funds to insert human cells into animal embryos.
last August, the NIH proposed to lift the ban, but with the condition that the requests for funds to make the procedures go through the filter of a committee of experts.
The insertion of human stem cells in early embryos of monkeys was banned since 2009.
The interest of the biologists for the chimeras is driven by the moderate success achieved in forcing the growth of tissues medically usable from stem cells in vitro. In 1998 he succeeded the first time human stem cells multi-purpose derived from human embryos, and in 2007 it achieved the same from cells common of an adult human. After each one of these developments, it potentiated the hope of using them for therapeutic purposes, exposing them in vitro to the natural sequence of chemical reactions in a living embryo lead to the formation of a heart, a brain, lungs and other organs.
however, no one knows exactly what sequence of chemicals is needed to generate each type of tissue or organ. Perhaps, that is why the in vitro experiments with stem cells are not yet at the height of the expectations. Some biologists believe that it would be better not to cultivate stem cells in vitro, but in a developing embryo, where they would be exposed to the natural sequence of chemicals that induce each type of organ.
Both the team Izpisua Belmonte as Nakauchi opted for the strategy of directing the cells of the human donor to the generation of specific organs in species as receptors. It is an approach desirable, both for medical reasons as ethical. Nakauchi managed to switch off the gene master builder of the pancreas in rats, so that when the early embryo of that animal is to insert the stem cells of a mouse, you do not have more remedy than to develop a mouse pancreas.
The next step is to repeat the tests in pigs that produce organs more similar to human-sized.
A procedure surrounded by controversy
although it would solve two of the pressing problems of the donation of organs for transplantation (immune rejection and the chronic lack), the project of develop in animals, they have ahead a long path full of technical difficulties, and surrounded by ethical controversies. Some of this is reflecting the prohibitions in force for this type of experiments in several countries. It will be necessary to find procedures that ensure that the human cells are directed to tissues that they want to replace and to increase the proportion of animal cells is sufficiently low as to avoid the rejection. For now, these experiments are just a proof of concept that shows the feasibility of combining tissues from two species, but whose validity will have to be corroborated to the extent that other teams replicate this experience.
Translation by Jaime Arrambide
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