HPV Vaccine

This web page was produced as an assignment for an undergraduate course at Davidson College.

Pap stain of cervical squamous cell carcinoma (200x) National Cancer Institute. 2001. http://visualsonline.cancer.gov/ details.cfm?imageid=2255

Due to the lack of effective treatments for HPV, there is a great focus on preventing infection instead. Like most vaccines, the HPV vaccine exposes the body to viral antigens, which the innate and adaptive systems interpret as an actual infection. One of the results of an infection is the differentiation of B and T cells into long-lived memory cells, which respond more quickly to subsequent infections and produce antibodies that bind the pathogen better. Thus, exposing the body to viral antigens makes its response to an actual viral infection much stronger; in the case of HPV, the body can clear the virus completely and prevent the onset of dysplasia caused by persistent infection (Doeberitz 2006; Jansen & Shaw 2004).

Virus-like particles (VLPs) formed by isolated HPV L1 capsid proteins have shown to be effective and efficient in stimulating innate and adaptive immune systems when administered intramuscularly (Doeberitz 2006; Jansen & Shaw 2004; Stanley 2006). The L1 gene is isolated and inserted into bacteria, which expresses the protein; these proteins then bind together into VLPs, which resemble normal HPV capsids. The immune response raised against the VLPs is systematic, as opposed to the site-specific response against native HPV, but this phenomenon does not seem to affect the efficacy in preventing HPV infection. In fact, the studies so far demonstrate 100% efficacy. Since each strain of HPV has a different L1 protein, the vaccine includes the two types known to cause 70% of cervical cancers, as well as two others that cause anogenital warts: HPV-16, -18, -11 and -2 (Jansen & Shaw 2004).

Worldwide, it is estimated that 1.4 million women suffer from cervical cancer, with 470,000 new cases diagnosed yearly, making it the second-most common cancer in women. Half of these women die from the disease. Regular screening in the form of PAP smears is only 75% successful in detecting pre-cancerous lesions, costing the United States $6 billion dollars annually. Since the availability of screening is reduced in underdeveloped countries, their cervical cancer incidence is four times higher; in these countries, preventing HPV infection from taking hold is more feasible than yearly screening (Doeberitz 2006; Jansen & Shaw 2004).