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Cancer vaccine: what's next?

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http://www.hindu.com/seta/2005/05/12/st ... 011600.htm

Cancer vaccine: what's next?


"Vaccines can only be used to prevent cancers which are caused by a virus" Richard Sullivan

MENTION VACCINES and most people — if they're not too busy wincing at the thought of a sharp needle plunging into their upper arm — will think of an injection that prevents an illness such as flu, rubella or measles. Drop the C-word into conversation and talk automatically turns to chemotherapy, radiation or surgery.

Effective in trials

This could be about to change with the news that a vaccine against cervical cancer is on the way. The jab, which targets the virus that is the main cause of cervical cancer, has proved so effective in trials that it is expected to be licensed for use in the UK within five years.

Experts estimate that it will be another two decades before the vaccine eliminates the need for cervical screening, but are optimistic that it could eventually substantially reduce the incidence of the disease.

It is an exciting prospect, but one which raises an important question: are we on the cusp of a new age for cancer treatment, in which preventative vaccines will become commonplace?

Emphatically not, according to Richard Sullivan of the UK charity Cancer Research. "Vaccines can only be used to prevent those cancers which are caused by a virus, and there are a limited number of these," he says.

Infection falls greatly

These are: those 70 per cent of cervical cancers caused by the human papillomavirus (HPV); liver cancers brought on by hepatitis B; the Aids-related cancer Kaposi's sarcoma; and Burkitt's lymphoma, which is triggered by the glandular fever virus.

The cervical cancer vaccine — to be marketed by GlaxoSmithKline as Ceravix and Merck as Gardasil — protects against four types of HPV. In clinical tests, infections in those patients with the four HPV types fell by 90 per cent compared with the control group.

The HPV virus is mainly passed on during sexual intercourse, which is why doctors believe it would be most effective to vaccinate young girls aged between 10 and 13 before they have had any sexual experience.

Most sexually active women have the virus at some time in their lives, but for most women, most of the time the virus is knocked out by their immune system without them even being aware that they have been affected. So while it's likely that girls will be rolling up their sleeves to be administered cancer-thwarting jabs in the near future, the boys won't be joining them for injections to ward off prostate cancer, or other non-viral cancers.

Nevertheless, vaccines could well have an exciting role to play in cancer treatment, but as a therapeutic, not a preventive, measure. Scientists around the world are exploring such vaccines in a variety of cancers: melanoma, prostate, colon, renal, breast, non-Hodgkin's lymphoma, non-small-cell lung and ovarian are just some of the ones being targeted.

Though these are still very much in the experimental stage, experts are increasingly excited about the possible effect they could have on cancer recovery rates. These therapeutic vaccines work by stimulating a response from the human immune system to help seek out and destroy cancer cells in people already diagnosed with the disease.

Kick-starting defences

Essentially, they attempt to make the body's defence mechanism recognise there is something wrong, and to kick-start it into action to destroy the dangerous cells.

Put simply, it's a question of priming the immune system in people known to be at risk (that is, those who have already been diagnosed with cancer)by injecting them with a substance that gives their body the ability to mark, and then deal with, invading malignant cells when they turn up again in the body's system.

Mary Collins, professor of immunology at University College London, has been involved in various trials of melanoma vaccines. She believes therapeutic vaccines will turn out to be particularly good at warding off recurrent skin cancers.

"This is because with melanoma it's very easy to predict the likelihood of the disease coming back with a secondary tumour," she says. "If a primary tumour is more than a certain depth, you can say with reasonable certainty that it will return."

There are two different ways of administering therapeutic vaccines, according to Professor Angus Dalgleish, professor of oncology at St. George's Hospital in London.

"There are those in which tumour antigens are injected alone, in the form of cells; or dendritic cell vaccines (named after the special class of immune cells that initiate the immune response), which collect the patient's own stem cells, isolating the dendritic cells, incubating them to make a vaccine, then returning them to the patient to `supercharge' their blood to fight the cancer."

Understanding rationale

Perhaps surprisingly, experts do not believe that cancer patients will have a psychological problem with being reinjected with the disease that has infected their body. Professor Mary Collins says that in her experience, "patients already suffering from cancer can understand the rationale and are surprisingly keen to take part in experimental trials."

It is important to bear in mind, though, that immunotherapy will never replace traditional therapies, stresses Margaret Stanley, professor in epithelial biology at Cambridge University, England.

"There is absolutely never going to be just one treatment for cancer," she says. "Tumours can evade the immune system in many different ways, so it would be a case of using the vaccine in conjunction with chemotherapy, radiotherapy or surgery. We have to consider all possibilities." Dalgleish concurs.

Works only for some

"Vaccines are not a one-size-fits-all approach," he says. "They do not work for everyone. In our research on therapeutic vaccines for prostate cancer, we've noticed, for example, that they seem to work best in fit, healthy people with good diets."

One thing is for sure: there is a lot more research to be done before these vaccines will be licensed and available on the open market.

"The whole field is being taken really seriously now that there's increasing evidence to show that the vaccines can induce some kind of positive response to improve survival rates," reckons Dalgleish. But he goes on to add a note of caution: "To get it right, there's a long way to go."

- Guardian Newspapers Limited 2005

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