Harnessing the body's own immune system could be an effective weapon in the battle against tumours, writes CLAIRE O'CONNELL
NEWS OF a prototype breast cancer “vaccine” caused something of a stir in the media recently, with flurries of reports on how researchers at the Cleveland Clinic have come up with a jab that could prime the body to recognise and destroy breast cancer cells.
The approach centres on a naturally occurring protein called alpha- lactalbumin, which crops up in many breast cancers.
By using a vaccine to introduce the protein to the immune system, the body should be able to recognise it at a later date if needed and mount a defence against it.
At the moment, it seems to work well in a pre-clinical model: if a mouse that is susceptible to developing tumours gets a single dose of this vaccine, its risk of developing breast cancer is cut.
The findings, published in Nature Medicine, could eventually form the basis of a human vaccine that women could get if they are particularly at risk of breast cancer, or at a point where they are no longer likely to become pregnant and breastfeed (when alpha-lactalbumin also arises naturally as part of milk production).
“If it works in humans the way it works in mice, this will be monumental. We could eliminate breast cancer,” said researcher Dr Vincent Tuohy in a release from the clinic.
Vaccines that have already been approved for liver and cervical cancer recruit the immune system to fight off viruses associated with the diseases, but the breast cancer vaccine targets the cancer cells themselves.
It’s a promising step, and more generally it highlights how scientists are working out the links between cancer and the immune response. Several drug companies are now developing and testing potential immune-based therapies to help manage and treat cancer.
It’s not a new idea – as far back as the 18th century insightful physicians were spotting that an infection (which stimulates the immune system) could be linked with tumour regression.
More recently, researchers in Cork have noted that patients who have a strong immune response to a tumour tend to have a better outcome, according to Dr Declan Soden, general manager at the Cork Cancer Research Centre (CCRC).
‘By the time a tumour presents, you are guaranteed to have millions of cancer cells circulating in the bloodstream, and where the immune system is fighting the tumour those patients have a good life expectancy,” he says.
If the body’s own defences are zapping those circulating cancer cells, they are less likely to be able to cause trouble by seeding new tumours elsewhere in the body, he explains. “So you get this correlation between the presence of the immune response and long-term survival, or a lower risk of recurrence.”
But why doesn’t our immune system just kill off tumours in the first place as a matter of course?
Cancerous growths can engineer a local “radar blackout”, so the immune system won’t pick them up, explains Soden. “The tumour stimulates a certain type of cell that suppresses the local response, so it becomes a no-go zone for the immune system.”
Removing this blanket of protection can require some trickery, and CCRC researchers have been working on an approach that injects immune-stimulating “cytokines” directly into tumour tissue, explains Soden.
The idea is that you lift the local radar blackout and instead put up a flare that highlights to the immune system that these cancer cells need to be destroyed, he describes. “So you would use gene therapy to take that suppressive blanket away from the tumour while putting in another gene to recruit the immune response and draw the immune cells in.”
Researchers at the University College Cork centre are also looking at another, more specific way of getting a patient’s immune system to weigh in on campaigns against cancer cells.
Just as the Cleveland Clinic scientists came up with a way of flagging breast cancer cells to the immune system, the Cork researchers have developed a DNA-vaccine that targets prostate-specific antigen (PSA), a biochemical found in prostate cells.
If a patient has had his prostate removed because of a tumour, getting this vaccine would prime his immune system to recognise and kill off any prostate cancer cells remaining in the body.
That would help to prevent recurrence of the disease, explains Soden.
“It’s similar to the breast-cancer vaccine approach taken by the Cleveland researchers and our prostate vaccine would be at the same level in that we have proven it pre-clinically, it has been peer reviewed and published as showing the potential.”
He believes such immune or vaccine-based cancer treatments could be in the clinic within five to 10 years, but he cautions that the approach is not a silver bullet for a complex disease.
“There’s no miracle cure, you have to look for the best fit.”
“By the time a tumour presents, you are guaranteed to have millions of cancer cells circulating in the bloodstream, and where the immune system is fighting the tumour, those patients have a good life expectancy
PROVENGE: EXPENSIVE BUT PROMISING
In April, the Food and Drug Administration in the US approved an immune-therapy drug called Provenge after trials in people with advanced prostate cancer that had spread beyond the prostate gland showed that it extended patient survival time by a median of 4.1 months.
The drug works by stimulating the patient's own immune system and is designed to induce an immune response against the cancer.
But it doesn't come cheap. The cost of a single infusion has been reported as $31,000 (about €26,500), so a course of three infusions would amount to $93,000 (almost €77,000).
– CLAIRE O'CONNELL