Increased acceptance of western lifestyle in developing world has led to overburdening of non-communicable chronic diseases of which cancer grabs the major share. Add to this, the lack of extensive treatment options and resistance to chemotherapy, this has become a notorious concern. Deaths commonly occur due to lung, prostrate, cervical, uterus, stomach, and breast cancers, most of which are caused through infectious diseases. Infections account for 25% cancers in developing countries while in western countries the rate is much lower (10%). Cancer can be dealt by implementing preventive strategies. However, early recognition and optimal treatment of cancer in affected patients have greater possibilities of being cured. Since the invent of cancer vaccines, a dramatic change has been expected in cancer treatment and prevention.
In the year 2020, 15 million people may be affected by cancer worldwide and 12 million deaths can be expected.
Cancer vaccines are biological response modifiers, i.e., they harness the power of the patient’s own defense mechanism to fight against infections and disease. The merits of cancer vaccines are:
- They mediate immune response irrespective of drug resistance.
- Immune attack is specific to tumor cells thus reducing side effects.
- The immune system restores an effective immunologic memory to target cancer threats in future.
Cancer vaccines are of two types:
Therapeutic cancer vaccines
They treat cancer patients by directing the immune system to specifically target and kill cancer cells, further delaying or blocking cancer cell growth and thus preventing relapse (come back of cancer). Till date, the US Food and Drug Administration (FDA) has approved only one vaccine, i.e. Sipuleucel-T, used to treat metastatic prostate cancer. The immune system can target two types of cancer antigens (a protein or any molecule that activates immune response) — tumor specific antigens (TSA) which are dutifully expressed on cancer cells, but are rare and tumor associated antigens (TAA) which are expressed on both the tumor and host cells and are common in cancer patients.
Sipuleucel-T is customised to each patient. Peripheral blood mononuclear cells (PBMCs) taken from the patient’s blood are cultured with a protein, prostatic acid phosphatase (PAP), which is a TAA expressed in prostate cancer patients. A type of white blood cell in PBMC, i.e., dendritic cells, take up the PAP antigen and help the killer T cells to identify them. Finally, the activated killer T cells multiply. The culture of activated ready to kill T cells is then injected back into the patient. Three treatments, 2 weeks apart, with each treatment involving the above procedure is advised.
Preventive cancer vaccines
These vaccines are intended to prevent cancer in healthy people. The US FDA has approved two vaccines under this section.
- Gardasil targets four subsets of human papilloma virus (HPV) — 6, 11, 16, and 18 thereby protecting females from HPV infection. HPV 16 and 18 are the prime cause for 70% of cervical cancer cases and other cancers (vaginal, vulvar, anal, oral) too. The vaccine is a mixture of the subsets of non-infectious HPV-like particles that stimulate antibody response upon injection. Gardasil is used in females between the age group 9-26 years to prevent cervical cancer and other cancers caused by HPV.
- HBV vaccine — Chronic hepatitis B virus (HBV) infection is the major cause of liver cancer worldwide. HBV vaccine is now included in the vaccination programs in children. Given in three doses, the vaccine is truly effective in preventing HBV infection.
