Stem cells: the human is not model suitable

José Masdeu. Director of the Dept. of Neurology. University Clinic of Navarra. Pamplona.
Published in Diario Medico, November 28, 2001.
(http://www.diariomedico.com/edicion/noticia/0,2458,80997,00.html).

New strategies to treat neurodegenerative diseases are always welcome news. On the other hand, all readers want a healthy realism, especially from medical professionals who are so accustomed to suffering from hyperbole about new therapies.

This is now the case with regard to the role of cell transplants as a panacea for curing various types of neurodegenerative disorders. In the latest chapter of the saga, a Massachusetts company has claimed to have succeeded in cloning human embryos in order to provide cells to replace those that have degenerated in the brain or other organs.

However, the so-called cloned embryos died before they had eight cells, and no stem cells were produced. Researchers from other laboratories, such as George Seidel, a cloning expert at Colorado State University, and Danish cloning scientist area, Steen Willadsen, call the experiment "a complete failure". But even if the researchers had succeeded in cloning a human embryo, this experiment subject leaves out two fundamental facts.

First of all, it is unethical to destroy one human life, in any state of development or with any quality of life, in order to cure another. Secondly, and this is what I am going to concentrate on, experimentation with human embryonic cells is not going to give us the core topic of whether stem cells are going to have any role in the treatment of neurodegenerative diseases.

Before we can use stem cells to attempt to treat human diseases, we need to know the factors that regulate their reproduction, cause their differentiation into the desired cell subject (e.g., dopaminergic cells for Parkinson's disease) and allow them to establish physiological connections with other cells so that their growth and activity can be regulated accordingly. Without having this knowledge, the use of human cells to treat disease is dangerous, as evidenced by the essay transplantation of human fetal cells into patients with Parkinson's disease.

Safety margin

The results of this experiment were disastrous, causing quite a few patients to have uncontrollable movements, who in several cases needed artificial feeding in order to survive in a state incomparably worse than before the treatment. Before trying new therapies in humans we must have a margin of safety that they will help them.

According to a simplistic way of thinking, if we are going to treat humans, let's experiment with human cells. However, humans are not the right model for this subject experimentation for many reasons, including the following:

1. The behavior of human cells cannot be studied with the depth, speed and certainty that genetically modified animals (especially knock-out and transgenic mice) can provide.

2. For obvious ethical and practical reasons of subject , the behavior of stem cells transplanted into an adult of the same species cannot be studied in humans. Transplantation of human cells into experimental animals complicates the topic, because the behavior of the transplanted cells is modified by the immune system of the recipient, altering precisely the factors of proliferation, differentiation and recognition under study.

3. Furthermore, given the genetic kinship between humans and primates, it is very likely that the stem cell behavior of these species is similar for many body tissues, including cells of the nervous system that constitute the substantia nigra, which is similar in structure and function in primates and humans.

There are many other experimental animal models, such as planarians, that are providing important information for one day achieving cell regeneration in humans.

Let's not waste resources and ink on dead ends.