"Your business is bad," says the doctor.. "Your liver is no good at all.". After that, he takes the stem cells of your bone marrow and inserts them into the fetus of a sheep that is still in the womb. When a sheep is born, its liver consists mainly of your own cells - this organ is ready to be transplanted to you.
Before the appearance of this method of growing organs for many years, but the first step in this direction has already been made. A group of scientists led by Ismail Zanjani from the University of Nevada has achieved amazing results on this field.
Scientists hope that one day chimeras (the body or part of it, consisting of genetically dissimilar tissues. - Prim. red. ), which they create, will be able to provide cells that are genetically identical to the patient's cells, to repair damaged organs, and possibly whole organs. Of course, the immune rejection of some animal cells can not be ruled out, but this is not an insurmountable problem, says Alan Flake of the Children's Hospital of Philadelphia.
Growth Factors.
Such a technique could greatly help researchers dealing with the problem of growing tissues and organs for transplantation, since it is able to give significant amounts of any cells and tissues without having to worry about suitable nutrient media and growth factors.
The growth of human cells to the required condition will be taken care of by the animal's own development program. "We can use the scheme of development and growth of the fetus," Zanjani said..
Also, this technique will allow physicians to obtain immunosupplemented cells without the need to grow a human embryo by therapeutic cloning. Human cells can be separated from animal cells if modern cells for cell sorting are modified.
Provided that this method really allows to receive normal human cells, these cells will not be rejected, whereas any cells of the animal that have penetrated into the body are destroyed by the human immune system.
Needless to say, the idea of ??using semi-human semi-animals as living factories for the production of cells and organs puts a lot of ethical and security issues on the agenda. To begin with at least that there is a risk of human transmission of animal diseases. And, besides, does the sheep with human cells remain in the brain just a sheep?.
Stem cells.
Zanjani's initial goal was to determine whether it is possible to treat unborn children with genetic defects by introducing healthy stem cells into the fetus. This remains his main goal, but, carrying out experiments on animals, he realized that this method can also be used to grow "humanized" organs.
The first hint of this possibility was given by Flake's study, conducted a few years ago. Flake showed that if the stem cells extracted from the human bone marrow enter the sheep into the fetus, then these human cells become part of the heart, skin, muscular and fat tissue of the sheep. However, the number of human cells in these tissues was extremely small. Now the Zanjani group managed to achieve an amazing increase in the content of human cells in separate organs of the sheep. According to the information presented by scientists at the conference that took place this month, in some cases, human cells account for 7 to 15% of all sheep cells.
Human cells should be introduced into the fetus of the animal approximately in the middle of the gestation period - before the immune system of the fetus has learned to recognize its own and foreign cells so that rejection does not arise, but after the basic anatomical features. This ensures that the animals appearing in the world will look like normal sheep, and not as strange hybrids like those that result from the crossing of sheep and goat embryos.
Functional parts of organs.
In some cases, human liver cells introduced into the sheep fruit form the functional, fully human parts of the liver, says Graca Almeida-Porada, another member of the team of scientists from Nevada. These parts can be transplanted entirely as auxiliary organs.
Moreover, human blood albumin, a blood protein that produces the liver, has been found in the blood of animals injected with human stem cells.
The results of similar experiments related to the heart will be published in early 2004. "The type of stem cells we use generates a large number of cells in the heart tissue," as long as that's all Zanjani is prepared to tell about these experiments.
If he is right, then this will be a serious breakthrough, as he will open the door for creating embryonic cardiac cells for conventional therapy. For example, cardiac embryonic cardiomyocyte cells have already proven effective in treating heart disease in mice and rats. However, there is one big obstacle: at the moment, the only source of human embryonic cardiac cells is the human fetus.
According to Robert Cloner, an expert on heart disease at the University of Southern California in Los Angeles, Zanjani's approach addresses this ethical issue.
Place and time.
According to Zanjani, using his method, it will be possible to grow a wide range of various tissues, for example insulin-producing cells, for the treatment of diabetes. He hopes that he will be able to further increase the proportional content of human cells in the organs of experimental animals.
Now scientists are trying to establish a subpopulation of stem cells, which are most effective for the formation of a particular organ. According to scientists, the time and place of the introduction of stem cells into the fetus of an animal.
However, all members of the Nevada team emphasize that before the implementation of their method is still far away - perhaps decades will pass before it is tested on a person. First you need to make sure that the human cells obtained in this way are really functional. In recent experiments, it was found that when administered, some stem cells are mixed with others, rather than forming normal heart or liver cells.
The key problem, of course, is the mixing of human cells and sheep cells.
Mixing itself is not a catastrophe, but one should study what consequences this can generate.
Zanjani is optimistic about this issue, emphasizing that sheep with human cells would simply die if, in the course of experiments, nonfunctional mixed cells would appear in their bodies.
In the United Kingdom and Canada, many protest the transplantation of organs grown in animals. The opponents of this method are concerned about the fact that animal DNA can bring new diseases to humans.
Medicus. En.
Keywords:.