HPV Vaccine - Mechanism of Action

Mechanism of Action

The HPV vaccines are based on hollow virus-like particles (VLPs) assembled from recombinant HPV coat proteins. The virus possesses circular double stranded DNA and a viral shell that is composed of 72 capsomeres. Every subunit of the virus is composed of two proteins molecules, L1 and L2. The reason why this virus has the capability to affect the skin and the mucous layers is due to its structure. The primary structures expressed in these areas are E1 and E2, these proteins are responsible for the replication of the virus. E1 is a highly conserved protein in the virus, E1 is in charge of the production of viral copies is also involved in every step of replication process. The second component of this process is E2 ensures that non-specific interaction occur while interacting with E1. As a result of these proteins working together is assures that numerous amounts of copies are made within the host cell. The structure of the virus is critical because this influence the infection affinity of the virus. Knowing the structure of the virus allowed for the development of an efficient vaccine, such Gardasil and Cervarix. The vaccines target the two high-risk HPVs, types 16 and 18 that cause the most cervical cancers. Gardasil's proteins are synthesized by the yeast Saccharomyces cerevisiae. Its protein makeup allows it to target four types of HPV. Gardasil contains inactive L1 proteins from four different HPV strains: 6, 11, 16, and 18. Each vaccine dose contains 225 mcg of aluminum, 9.56 mg of sodium chloride, 0.78 mg of L-histidine, 50 mcg of polysorbate 80, 35 mcg of sodium borate, and water. The combination of ingredients totals 0.5 mL. Together, these two HPV types currently cause about 70 percent of all cervical cancer. Gardasil also targets HPV types 6 and 11, which together currently cause about 90 percent of all cases of genital warts.

Gardasil and Cervarix are designed to elicit virus-neutralizing antibody responses that prevent initial infection with the HPV types represented in the vaccine. The vaccines have been shown to offer 100 percent protection against the development of cervical pre-cancers and genital warts caused by the HPV types in the vaccine, with few or no side effects. The protective effects of the vaccine are expected to last a minimum of 4.5 years after the initial vaccination.

While the study period was not long enough for cervical cancer to develop, the prevention of these cervical precancerous lesions (or dysplasias) is believed highly likely to result in the prevention of those cancers.