LIKE other fields of endeavour, science has fashions—and one of its most fashionable areas at the moment is the study of stem cells. This is a subject that provokes high passions, particularly when the cells in question are drawn from human embryos. It also encourages the lowest form of scientific behaviour, fabricating data (see article). A tragicomic stem-cell story, however, is probably a first. But a piece of research reported in this week's New England Journal of Medicine by Zhu Jianhong of Fudan University and his colleagues began that way. Its first subject was a woman admitted into Huashan Hospital in Shanghai with a chopstick in her brain. It ended triumphantly, though, with the trial of a treatment that may heal the sort of brain injuries that the woman in question suffered.

Stem cells are the cells responsible for making bodies, and then repairing the natural wear and tear to which they are subject while they are alive. The body-forming cells are the embryonic stem cells that are causing so much political trouble in America because obtaining them involves destroying early-stage embryos known as blastocysts. Some people think that destroying blastocysts is murder.

The repairing sort of cells, though, are uncontroversial, and are turning up in more and more places. Even tissues once believed not to change much after childhood, and thus not to need the renewing ministrations of stem cells, are yielding them. Heart-muscle tissue, for example, has recently been shown to have them.

Another place where they were not, at first, expected to exist is the brain. But they do. And that discovery meant that the unfortunate lady who had had a chopstick thrust through one of her eyes into part of her brain called the inferior prefrontal subcortex (IPS) presented an opportunity. When the utensil was removed, Dr Zhu decided to try culturing the tissue that came out with it, to see whether there were any stem cells there.

Waste not, want not

To his delight, the extracted tissue thrived and grew, and many of the cells in the resulting culture did indeed contain proteins known to be characteristic of neural stem cells. But Dr Zhu wanted to be sure that that was truly what he had.

The defining feature of a stem cell is self-renewal. When such a cell divides, at least one of its daughters is also a stem cell (the other may set off on the route to specialisation that allows stem cells to generate new tissue). The way to test whether a particular cell is a stem cell, therefore, is to grow it individually. A single stem cell will divide continuously and form a spherical colony consisting of its progeny. Other cells will not. Dr Zhu found that about 4% of the cells from his chopstick-injured patient were able to form such colonies, which confirmed his conjecture.

Thus inspired, he started collecting samples from other patients with traumatic open-head injuries (though none with quite such an unusual cause as the first). He has managed to derive neural stem cells from 16 of these patients, out of a total of 22, and believes that success depends on which region of the brain is affected. Cells from the IPS are the best source, so it seems he was lucky in his original patient.

The point of the exercise, though, was to see whether neural stem cells could be obtained reliably, with a view to using them as a treatment. For a suitable dose of stem cells might not only help a damaged piece of tissue to repair itself; it would also, if the cells in question had come from the patient who was being treated, escape attack by his immune system. This idea of self-treatment is one of the reasons adult stem-cell science is so fashionable.

First, Dr Zhu tried it out on mice (the mice in question had had their immune systems turned off, so that they would not reject the transplanted cells). He injected stem cells he had cultured from his patients into mouse brains and found that they successfully differentiated into the various cell types found in the nervous system. Just as importantly, the resulting nerve cells were able to conduct electrical impulses and could form the specialised junctions called synapses, by means of which nerve cells talk to each other.

Having shown that the stem cells worked in healthy mouse brains, Dr Zhu tried them out on injured mouse brains. Another common property of stem cells is to accumulate at sites of injury, where their services are obviously needed. In order to track the movements of the cells, his team attached tiny magnetic particles to them before they transplanted them, and also injected them with a dye. They found that cells implanted into healthy brains stayed put, whereas those implanted into damaged brains moved towards the injured area.

The final animal trial was a safety test using monkeys. It was designed to look for cancer, and for signs that the cells had wandered from the brain to other organs such as the heart and the liver, where they might have caused trouble. No such signs were seen.

So the team moved on to people. They transplanted neural stem cells derived from eight patients with open-head injuries back into the patients who had provided the initial tissue and allowed the cells to migrate to the injury sites. (In one case, they used magnetic particles to follow the process.) Then they asked a separate group of specialists to look both at their experimental patients and at a group of people with similar brain injuries but no transplant. The second research group did not know who had and who had not been treated, so as to make the trial “blind”. Using standard behavioural tests, they concluded that the treated patients had lower disability scores.

As Dr Zhu stresses, this is a mere pilot study, and it is too early to draw strong conclusions. But if subsequent work confirms his finding, what started as an unfortunate piece of serendipity may lead to a valuable new technique for repairing injured brains.