Wednesday November 14 2007
Research takes a long time to reach humans
It may be possible to produce a cancer vaccine from the body’s own tumour cells, reported The Independent. The technique “involves the use of ultra-violet light to trigger the vaccine in a process known as photodynamic therapy (PDT)”, the newspaper said. The technique was tested in mice and was shown to produce a “personalised vaccine” in which drugs were triggered when they reach their targets, without causing “toxic reactions in other parts of the body”, it said.
The story is based on research into a potential area of cancer treatment. However, this is only a small preliminary study into a certain skin cancer in mice. Whether such a vaccine could have a role in the treatment of this type of skin cancer, or any other cancer, in humans is a long way off.
Where did the story come from?
The research was carried out by Dr Mladen Korbelik and colleagues of the Department of Cancer Imaging, British Columbia Cancer Agency, Vancouver. The study was funded by a research grant from the Canadian Institute of Health and it was published in the peer-reviewed British Journal of Cancer.
What kind of scientific study was this?
This was a laboratory study in mice investigating the theory that tumour cells treated by photodynamic therapy (PDT) can be used as a vaccine against cancer of the same type. PDT works by using ultraviolet light in combination with a light sensitive drug (a photosensitising agent) to destroy cancer cells. The drug enters the target cancer cells, but it is only activated when it is exposed to the correct type of light.
The researchers took tumour cells from mice with a particular form of skin cancer (squamous cell carcinoma). Some of these cells were then placed under the skin of other mice to generate tumours. The remaining cells were mixed with a photosensitising agent and exposed to ultraviolet light (PDT), and then to X-ray. These cells were then injected around the tumour site of the mice. A separate group of control mice were injected with cells that had been exposed to X-ray only, with no PDT, and another group of control mice had inactive saline solution injected instead.
The researchers looked to see what happened to the tumours in these three groups of mice. If the mouse’s tumour shrunk until it could no longer be felt under the skin, and there was no recurrence of the tumour within 90 days, the mice were considered to be “cured”.
The researchers then looked whether the mice whose tumours were “cured” by the PDT vaccine would then be resistant to forming new tumours by re-injecting them with tumour cells and watching for tumour growth. In order to investigate the immune responses involved, the researchers cut out the tumours three days following the injections, and weighed them, treated them with particular antibodies, and examined them in the laboratory for the presence of these immune cells.
What were the results of the study?
The researchers found that the average size of both PDT-vaccinated and control tumours increased over time, but the tumours treated with the PDT vaccines were, on average, smaller than the tumours which were injected with X-ray treated cells or a saline injection only (control tumours). There was no difference in the size of the control tumours between the two groups.
They found that mice whose tumours were cured by the PDT vaccine were resistant to developing the same cancer again if they were re-injected with tumour cells. They found that tumours that were treated with the PDT vaccine contained large numbers of specific immune cells (T lymphocytes) that are thought to be attacking the tumour. Mice with a good response to the PDT vaccine had more of these immune cells in their tumours than mice that had a poor response to the vaccine, and these mice, in turn, had more of these cells than the control tumours.
What interpretations did the researchers draw from these results?
The researchers conclude that they found increased numbers of body cells involved in the immune response to destroy cancer cells in tumours that had been primed with the PDT vaccine than when not. They say that their research “opens attractive prospects for employing PDT vaccines tailored for individual patients targeting … the patient’s tumour”.
What does the NHS Knowledge Service make of this study?
This is very interesting research into another potential area of cancer treatment. However, human use of this technique is a long way off. Currently this research has been carried out in mice only and, as with all animal studies, it is difficult to extrapolate these findings to humans.
The research has only looked at one type of skin cancer in mice. Light therapies in different forms have often been used in the treatment of skin conditions, and we do not even know whether the same effects would be seen in tumours in other locations of the mouse body. It is also worth noting that the vaccine had varying levels of success in different mice. Much further research would be needed into this subject before we would be ready to think about developing possible treatments for trial in a human population.
Sir Muir Gray adds...
All medical treatment can do harm as well as good; usually the more powerful the treatment, the greater the risk. Cancer treatment is now much more powerful but it can have adverse effects on cells that are not affected by cancer. The holy grail for cancer treatment is to deliver these powerful treatments only to the cancer cells, or make them active only in the affected cells by “switching on” the active chemical.