Usually, we think of vaccines as preventative, a shot we get to prevent the flu or some childhood disease like measles or mumps. But there are vaccines for other purposes, such as the ones studied by researchers from the Netherlands.
A report published in Current Opinion in Virology by researchers at Leiden University Medical Center and ISA Pharmaceuticals describes human papillomavirus vaccines (HPV) that can activate an immune response to kill the virus already present in the body, one that's causing precancerous changes to cells.
About 90% of HPV infections are controlled within two years because healthy people mount immune responses to the virus. Dendritic cells of the immune system are attracted to and pick up the viral proteins, digest them, and present pieces of them to T cells. Those T cells are called to the infection where they release interferons, interleukins, and tumor necrosis factors to kill the virus.
If this response is too weak or too late, increased HPV protein production can suppress the immune response and allow the infection to progress to cause precancerous lesions and, ultimately, cancer.
Therapeutic vaccines made against the HPV proteins—called E6 and E7—in early infections trigger a strong T-cell response against those proteins and can be used to treat patients at the premalignant stage. After immunization, the vaccines stimulate T cells in patients' lymph nodes, then the T cells leave and travel to the precancerous lesions to decrease them.
The study authors summarized findings of four different types of vaccines that were tested for their capacity to treat HPV-associated highly abnormal (i.e., signaling an increased risk of squamous cervical cancer) cervical lesions.
Results of two studies showed that lesions were decreased 50%, compared to 30% without a vaccine in one study, and lesions regressed in seven out of nine patients in another study. The studies showed that vaccines that resulted in a strong T cell response had the best clinical outcome.
Right now, there are about 20 different clinical trials underway testing HPV vaccines in precancerous and cancerous lesions of different types. These vaccines have the potential to help the body's immune system regain control and stop HPV infections that are destined to become cancer.
We talk about how HPV is a sexually transmitted disease—passed by vaginal, anal, or oral sex—that can cause genital warts or cervical cancer. But we don't talk about how 79 million Americans are infected with HPV right now. Or that, despite a preventative vaccine, about 14 million more people will be infected each year.
The infection is so common that an estimated 80% of sexually active people will get it during their lifetime.
The virus causes a significant number, about 5%, of all cancers. Of the 14 different HPV types found in cervical cancer, HPV16 and 18 are the most common. HPV16 is the predominant type in all other HPV-induced cancers, such as cancers of the back of the throat, including the base of the tongue and tonsils in men.
The HPV vaccine, introduced in 2006, had the potential to change those statistics. Two shots, six to 12 months apart, are recommended for kids ages 11 or 12—and it looks like it's working. HPV prevalence has decreased over 50% in 14–19 year old female teenagers.
But with so many people already infected, it will be some time before the infection numbers drop in older people—and those are the people being diagnosed with cancer.
That's why the report from the Netherlands researchers is so encouraging. To have a vaccine that might actually help the 10% of 79 million people who have a persistent HPV infection before it becomes cancer is a game-changer. And to those 8 million people, it could be a lifesaver.