Vaccine Therapy in Cancer: Preventive Cancer Vaccines

Previous articles discussed therapeutic cancer vaccines. Now we examine preventive vaccines. Vaccines generally work by introducing a weakened virus to create immunity against it. Preventive cancer vaccines are designed against cancer-causing viruses for this purpose.

Viruses have been known to cause cancer since the early 1900s. According to recent World Health Organization reports, 15 percent of cancers worldwide are virus-related, mostly in underdeveloped and developing countries because vaccination programs are irregular and hygiene requirements unmet. The general term for these viruses is oncovirus .

Oncoviruses infect cells, entering them and taking control to reproduce. Our cells contain DNA controlling basic processes. Viruses insert their genetic information into host DNA. Cells with disrupted genes begin uncontrolled division and proliferation, producing cancer. As we will examine later, some viruses inhibit tumor suppressors, while others add oncogenes (genes stimulating cell growth). Identified cancer-causing viruses and associated cancers are listed below.

-Hepatitis B and C Viruses: Liver cancer

-Human Papilloma Virus (HPV): Cervical and uterine cancer

-Human T-lymhotrophic Virus: Adult T-Cell lymphoma

-Epstein Barr Virus: Burkitt's lymphoma, Hodgking lymphoma, laryngeal cancers

-Kaposis Sarcoma Virus: Muscle cancers

Importantly, these viruses' cancer-causing rates are very low. Studies show an infected person may never develop cancer throughout life.

The most researched viruses with vaccines developed recently are hepatitis viruses and Human Papilloma Virus (HPV). Hepatitis viruses cause chronic hepatitis infection leading to liver cancer. Every year, 750.000 liver cancers are reported, mostly in underdeveloped countries. Hepatitis B has infected 3 percent of the world population and accounts for 90 percent of liver cancers in underdeveloped countries lacking vaccination programs.

Human Papilloma Virus (HPV) is proven to cause cervical cancer; recent studies identify it as the cause of %99. It mainly affects the genital area and is usually sexually transmitted, causing warts or abnormal cell growth. Genital warts are among the most important sexually transmitted infections. Surgery and drugs can treat them, but recurrence occurs in most individuals. How does HPV cause cancer? The answer is loss of genetic control. Let us examine the mechanism;

Cells divide rapidly from life's beginning through adulthood. In adults, division and proliferation occur only to repair injured tissues, and not in all cell types: nerve and muscle cells, for example, cannot renew themselves. The most important gene controlling division is p53. Scientists call it the “guardian of genes.” p53 is a tumor suppressor. When cellular genetic material is damaged, it stops division, prevents damaged genes reaching new cells and initiates repair mechanisms. If unsuccessful, it triggers programmed cell death to eliminate the damaged cell. Thus p53 is critically important. If p53 mutates, uncontrolled growth begins. In % 50 of human cancers, p53 is mutated and inactive. What is the relationship between HPV and p53? HPV infects cells and integrates its genes; resulting viral proteins E6/E7 disable p53, removing cellular control and causing uncontrolled division.

Immunity can be provided by Gardasil and Cervarix, marketed after United States Food and Drug Administration (FDA) approval in 2006. Gardasil is recommended before adolescence and for those who have begun sexual activity. These vaccines do not protect an already infected individual. Gardasil is approved in more than 120 countries. Cervical cancer vaccines are also sold in our country. For detailed HPV vaccine information, click here. Recent studies report reduced cervical cancer incidence in countries implementing vaccination programs.

Remember that these vaccines do not protect an already infected person. Infection risk increases with age and sexual activity. New-generation preventive cancer vaccines do not replace routine checkups, which vaccinated individuals should continue.

To access our article about therapeutic cancer vaccines, click here.