Vaccination is one of the most cost-effective public health interventions and is largely responsible for reduction of under 5 mortality rates across the world.
We are all familiar with the vaccines given as a part of the Expanded Program on Immunization. However our knowledge regarding Cancer Vaccines needs to be updated. Many would wonder as to How could there be a vaccine against Cancer.
There are two categories of Cancer Vaccines available:
- Preventive Cancer Vaccines
- Therapeutic Cancer Vaccines
Preventive Cancer Vaccines:
Human Papilloma Virus Vaccine (HPV): HPV is a DNA virus, transmitted mostly by sexual contact. Over 200 serotypes of HPV have been discovered, of which 15-20 are oncogenic. Presence of Oncogenic HPV – DNA has been demonstrated in 99.7% of all cervical cancer cases. In India the most common prevalent genotypes are HPV 16 and HPV 18. Chronic HPV infection can cause various types of cancers including head and neck cancer, cervical cancer, vulval cancer, penile cancer. The HPV vaccine reduces the burden of such cancers.
Presently two types of HPV vaccine are available in the market.
a. 9 valent HPV vaccine- 6,11,16,18,31,33,45,52 and 58 strains of HPV vaccine, The vaccine is recommended for females aged between 9-26 years, and males 9-14 years, for girls between 9-14 years two dose series – 0.5 ml to be given intra muscularly six months apart.
a.2 For females aged between 15-26 years- three doses, 0.5 ml each to be given intra muscularly at 0-, 2- and 6-months interval.
a.3 For males: the dose schedule is two doses – 0.5 ml intra muscular six months apart.
b. 4 valent vaccine- 6,11,16,18 strains of vaccine, for girls aged between 9-14 years two doses 0.5 ml intramuscular six months apart, for boys aged between 9-14 years 2 doses 0.5ml intramuscular six months apart. For females aged between 14-45 years three dozes, 0.5 ml intramuscular at 0,2 and 6 months.
Hepatitis B vaccine:
The younger the age at which an individual contracts the Hepatitis B virus higher the chances of developing Hepato Cellular Carcinoma.
Recommended schedule: Three Doses of 0.5 ml each at 0,1,6 months (for children aged between 0-18 years), for people above 18 years three doses 1 ml each at 0,1,6 months.
Therapeutic Cancer Vaccines:
These are type of vaccine which work by training your body to protect itself against its own damaged or abnormal cells, including cancer cells.
Therapeutic cancer vaccines expose the immune system to molecules called antigens, that are associated with a specific type of cancer. These vaccines enable the immune system to recognize and destroy the cancer cells carrying the same antigen. Therapeutic cancer vaccines consist of specific antigens combined with another immune system trigger called an adjuvant.
Therapeutic cancer vaccines can:
- Stop a tumour from growing or spreading.
- Destroy cancer cells still in the body after treatments like surgery or radiation therapy.
- Keep cancer from coming back after treatment.
What are the challenges for therapeutic cancer vaccines?
- Cancer cells produce molecules that suppress the immune response. Even if a vaccine can switch on immune cells, those immune cells may not be able to enter the tumour area. And if they do enter, they may be immediately shut down.
- Cancer cells start out as normal cells and don’t look as if they would threaten the immune cells. This makes it harder for the immune system to detect what to attack.
- It can be hard to find antigens that are cancer-specific. If the antigen exists on both normal and abnormal cells, the vaccine will attack the normal cells too. This causes unwanted side effects.
- The tumour may be too big. Large tumours have more immune-suppressive cells, which can negate the power of the immune cells triggered to attack them. Because of this, vaccines may be used in combination with other treatments.
- Some people have weakened immune systems. Older people and many others — especially people with cancer — might not be able to respond well enough to a vaccine. Even if the immune cells receive the vaccine’s signal, they cannot mount a strong enough attack.
Approved Therapeutic Cancer Vaccines
Several therapeutic cancer vaccines have been approved by the U.S. Food and Drug Administration (FDA) and are already in use for different cancers:
- Prostate Cancer Vaccine
Sipuleucel (Provenge) is used for the treatment of people whose cancer has metastasised. Provenge is created by removing some immune cells, exposing them to a molecule from prostate cancer cells, and then infusing them back into the body. It has been shown to extend survival in people with metastatic prostate cancer.
- Bladder Cancer Vaccines
- Bacillus Calmette Guerrin is used to treat early-stage bladder cancers. It is made from inactivated tuberculosis bacteria (Mycobacterium Bovis strain). The reconstituted BCG vaccine is instilled into the bladder.
- Nadofaragene is approved for treatment of early-stage bladder cancers that have progressed despite BCG therapy. It consists of an engineered, weakened virus that activates an immune response in the bladder. Like BCG, it is delivered into the bladder through a catheter.
- Melanoma Vaccine
- T-Vec is an oncolytic virus-based vaccine (see below) that is used to treat advanced melanoma that cannot be completely removed with surgery. It is made of a virus that has been genetically modified to promote an anticancer immune response. The vaccine is injected intralesional into lesions.
There are some other vaccines which are in the pipeline hoping to provide a cure for various cancers.
Sources:
- IAP textbook of Vaccinology
- Memorial Sloan Kettering Cancer Center
