Tuesday June 1 2010
The vaccine was tested on a small number of mice
Clinical trials of a breast cancer vaccine “could begin within the next two years”, according to The Guardian.
The news comes after mouse testing of a new vaccine that prompts the immune system to attack cells possessing a protein called alpha-lactalbumin, which is found in most breast cancer cells. Tests on cancer-prone mice showed that, while six mice receiving the vaccine did not develop breast tumours by the age of 10 months, six mice receiving a sham vaccine all developed tumours. The alpha-lactalbumin protein is also found in the breast tissue of women currently lactating (producing milk). This means that any human vaccine targeting the protein would not be appropriate for women who are likely to become pregnant in the future.
This research is at an early stage, and it is likely that more animal research will be needed before the vaccine could be considered for testing in humans. This research will take time, and it is not clear whether the two-year timescale for human testing is realistic. While awaiting the results, women can reduce their chances of developing breast cancer by limiting their consumption of alcohol, maintaining a healthy weight and taking regular exercise.
Where did the story come from?
The study was carried out by researchers from the Cleveland Clinic and Cleveland State University, and funded by the US National Institutes of Health. The study was published in the peer-reviewed journal Nature Medicine.
BBC News, The Guardian, The Times and the Daily Mirror reported on this research. BBC News, The Guardian and The Times all report that this study was in mice, however, the Daily Mirror does not. The Times covers the limitations of the study well, and highlights the fact that the study was in mice in its headline: “The breast cancer vaccine is great news – for mice”. The Guardian suggests that the vaccine could be tested in humans “within the next two years”, while the Mirror says tests could begin “as early as next year”. It is not clear how these timescales have been arrived at, or whether they are realistic.
What kind of research was this?
This was animal research aimed at developing a breast cancer vaccine. A vaccine primes the immune system to attack a specific target. It does this by presenting the immune system with a molecule from that target, such as a cancer, so that the body can ‘recognise’ the target and mount a response against it quickly if it encounters it again. For their potential breast cancer vaccine, the researchers selected a protein called alpha-lactalbumin (a-lactalbumin) as the molecule to be targeted. This protein is produced at high levels in most human breast cancers, as well as in breast tissue that is producing milk.
Using an a-lactalbumin vaccine to prevent breast cancer is a new approach, and testing it in animals is an important first step in determining whether this approach might work. If the vaccine looks effective and safe in animals, then it may go on to be tested in humans. However, there is a possibility that the vaccine may not prove effective or safe enough for testing in humans. If the vaccine does reach human testing, researchers will then need to prove that it is safe in humans and that it can reduce the risk of breast cancer, before it could be made commercially available. Such testing could take many years.
What did the research involve?
The researchers first assessed the immune response that occurred when mice were vaccinated with a-lactalbumin. They found that mice did mount an immune response against this protein, and that this caused inflammation of breast tissue in lactating mice but not in non-lactating mice (a-lactalbumin is found in breast tissue that is producing milk).
They then tested the effect of the a-lactalbumin vaccine in a strain of mice that have a high risk (a 50% chance) of spontaneously developing breast tumours by the age of 205 days. They immunised a total of 12 of these mice with either a-lactalbumin vaccine or a control solution at eight weeks of age and monitored them to see how many developed breast tumours.
The researchers also assessed the effects of the a-lactalbumin vaccine or control injections on normal mice injected with breast tumour cells. Injections of either a-lactalbumin vaccine or a control vaccination containing no a-lactalbumin were given either 13 days before, or 5, 13 or 21 days after the mice were injected with the tumour cells. The researchers looked at the tumours in these mice to determine whether the immune system appeared to be attacking them. The researchers also looked at how cancer-prone mice with aggressive breast tumours were affected by an injection of a-lactalbumin vaccine or a control vaccination containing no a-lactalbumin given at six weeks of age.
Each individual experiment compared up to eight mice treated with the a-lactalbumin vaccination and eight control mice.
What were the basic results?
The researchers found that none of the six breast-cancer-prone mice immunised with a-lactalbumin vaccine developed detectable breast tumours by the age of 10 months. However, all six of the breast-cancer-prone mice given the control injection did develop breast tumours by this age.
The researchers also found that the a-lactalbumin vaccine given either 5 or 13 days after, or 13 days before injection with breast tumour cells reduced the growth of tumours in the mice. The tumours of mice injected with a-lactalbumin vaccine had been infiltrated by immune system cells. Injection of the mice with a-lactalbumin vaccine 21 days after the tumour cell injection did not reduce the growth of tumours.
Giving cancer-prone mice with pre-existing aggressive breast tumours injections of a-lactalbumin vaccine at the age of six weeks also reduced the growth of these tumours.
In normal, non-lactating mice, an injection of a-lactalbumin vaccine did not lead to inflammation of the normal breast tissue, as the a-lactalbumin protein is only produced in breast tissue that is producing milk. In normal, lactating mice, injection of a-lactalbumin vaccine caused the immune system to attack the milk-producing breast tissue.
How did the researchers interpret the results?
The researchers concluded that “a-lactalbumin vaccination may provide safe and effective protection against the development of breast cancer for women in their post-child-bearing, premenopausal years, when lactation is readily avoidable and risk for developing breast cancer is high”.
This study has shown that a-lactalbumin vaccination can reduce the risk of developing breast tumours and slow the growth of existing breast tumours in cancer-prone mice or mice injected with breast-tumour cells. The experiments also suggest that vaccination with a-lactalbumin does not affect normal breast tissue in mice not producing milk, which is an advantage from a safety perspective. The fact that the vaccine did cause the immune system to respond to lactating breast tissue means that (should this type of vaccination ever reach human testing) it would probably be appropriate only for women unlikely or unable to become pregnant.
It is worth bearing in mind that this is early research in a small number of mice, and much further research will be needed to determine whether this a-lactalbumin vaccination might be safe to try in humans. A spokesperson for the charity Breakthrough Breast Cancer has added that women can reduce their risk of breast cancer by limiting alcohol consumption, maintaining a healthy weight and taking regular exercise.