The success of the recent cervical cancer vaccination trial demonstrates the potential of a powerful new weapon in the war against cancer, reports Munizha Ahmad
the cervical cancer vaccine currently being developed by Merck, Sharp and Dohme appears to be years ahead of all other cancer vaccines as the chances of it becoming available within 5-10 years were raised following the recent 100 per cent success of its Phase II trials.
Designed to stimulate the immune system to attack the human papilloma virus (HPV), this is the only preventative cancer vaccine. Investigations have so far focused on HPV 16 - which is linked to over 200,000 cases of cervical cancer worldwide each year - but the aim is to develop a quadrivalent vaccine which will target the four most common types of HPV, including that which causes genital warts.
Hopes have been encouraged by the analysis, two years into an ongoing four-year study of 2,392 American women aged between 16 and 23. The women enrolled were either sexually active or planning to become sexually active in the near future, having had no more than five sexual partners and no history of HPV infection. They were divided into two groups, half of whom received three doses of the vaccine and the other half, three doses of HPV 16-naïve placebo. While no cases of HPV 16 infection have developed in the vaccine recipients, there have been 41 cases - including nine cases of cervical intraepithelial neoplasia (pre-cancer of the cervix) - among the placebo recipients.
As this study continues, Phase III trials, likely to extend over five years, are also due to begin. For this, 6000 women, with similar histories to those in the Phase II trials, will be enrolled in countries across the world, including 250 in Glasgow, London and Nottingham. This stage of the trials will focus on the quadrivalent vaccine and how efficacious it is in treating pre-cancer. Professor David Jenkins of the University of Nottingham, who will be co-ordinating the research in the UK, explains that the trials will be conducted all over the world, from Scandinavia to Latin America: "Although the science is the same across countries, the trials will test the ways in which it might be used in different places." Whether this involves questions of women's access to the vaccine remains to be seen, but this is an issue that will surely need to be considered as the trials extend worldwide. Currently cervical cancer kills around 470,000 women worldwide each year, with 80 per cent of these deaths occurring in the developing world.
One cannot expect things to change overnight, but if the trials are successful and a licence to manufacture and sell the vaccine is obtained, Professor Jenkins is hopeful that major changes will take place over a period of 10-20 years: "The development of a preventative vaccine is enabled by the fact that cervical cancer is caused by a virus. However, because it is preventative, it will not be of use in the treatment of those already infected and so it will take at least 20-30 years before the need for screening is removed." At present, it seems likely that three doses of the vaccine and possibly a booster will be required.
Recent Cancer Vaccine News
A vaccine developed by the Danish company Pharmexa, which could provide an effective treatment for advanced stages of breast cancer, is currently undergoing clinical trials, involving 27 women, in Denmark and the UK. The vaccine targets the HER-2 protein which is overexpressed in many breast cancer patients, using DNA coded with the gene sequence for the protein as well as small amounts of a toxin from the bacterium that causes tetanus. This stimulates the immune system to respond to HER-2 which is also expressed in low levels in normal tissues and not normally recognised by the body as foreign.
Scientists at the Scripps Research Institute, California, are researching a vaccine which targets cells around tumours, rather than tumour cells themselves, thus depriving them of the blood and oxygen they need to grow. The vaccine uses DNA to identify these cells which form blood vessels, but further research needs to be conducted to assess the effect this will have on the body's ability to repair and regrow blood vessels.
Research is underway at the universities of Rochester, Cornell and Tulane to engineer a potato to carry a vaccine against HPV. Recent tests produced an immune response in mice who were fed the potatoes. This and similar projects involving bananas and nasal sprays could provide alternative vaccination methods to needle injections, which would be of benefit in the developing world. However questions of perishability, cooking and the mutual effects of the vaccine and the digestion process need to be closely investigated.
