Vaccination to prevent VIrusassociated cancer

One approach which has been successful in using the immune system to prevent cancer is vaccination against tumor viruses. A chronic infection with hepatitis B virus increases one’s risk of getting liver cancer about 200-fold, and roughly 20% of long-term, hepatitis B carriers eventually develop this disease. Moreover, hepatitis B virus ranks as one of the most infectious of all viruses: transfer of a fraction of a drop of blood is sufficient to spread the virus from one human to another. Fortunately, vaccines that protect against infection by hepatitis B virus have been available, and the current vaccine is administered not only to healthcare professionals, who routinely come into contact with blood and blood products, but also to children. This subunit vaccine gives the immune system a “preview” of a real hepatitis B infection, allowing ample time for memory B cells and the antibodies they produce to be mobilized. Then, if infection does occur, the prepared immune system can quickly eradicate the virus, effectively preventing hepatitis B-associated liver cancer.

Infection with certain “oncogenic” types of human papilloma virus (HPV) can increase the risk of cervical cancer. These viruses are spread by sexual contact, and there are now so many women infected with this virus that cervical carcinoma has become the second most common cancer in women worldwide, resulting in about 250 000 deaths per year. Although there are about a dozen, slightly different types of HPV that are associated with cervical cancer, two types, HPV-16 and HPV-18, are implicated in about 70% of all cervical cancer cases. Recently, two pharmaceutical companies, Merck and GSK, have pioneered vaccines that are effective in preventing infection by both types of HPV. These are subunit vaccines made from viral coat proteins. In addition, the Merck vaccine includes coat proteins from two other HPV types, HPV-6 and HPV-11, which are not associated with cervical cancer, but which do cause genital warts in both men and women. Their thinking in including these two “extras” is that preventing genital warts might encourage boys and men to be vaccinated, since they might otherwise be reluctant to be vaccinated to prevent a disease (cervical cancer) they cannot get.

Although the Merck and GSK vaccines will be very helpful in decreasing the number of deaths from cervical cancer, a vaccine that would protect against the five HPV types that are most commonly associated with cervical carcinoma could prevent hundreds of thousands of deaths from cancer each year worldwide – providing that most sexually active young women could be vaccinated. Unfortunately, many of the cases of cervical cancer occur in underdeveloped parts of the world, where immunization via injection is problematic.

Although vaccination against infection by cancerassociated viruses is the current star in the effort to enlist the immune system in the battle against cancer, many new approaches are in various stages of testing. We all can hope that these experiments will be successful – because, as it stands now, about one out of every three of us will get cancer during our lifetime.

Дата добавления: 2015-06-04