Key developments in battling sexually transmitted viruses include a new version of the HPV vaccine that protects against nine strains, and continued progress against HSV, says an expert.
Maui – Despite a broadening of the protection offered by the human papillomavirus (HPV) vaccine, uptake remains relatively sluggish, an expert says. Meanwhile, development of therapeutic vaccines for the herpes simplex virus (HSV) continues.
The quadrivalent HPV vaccine approved in 2006 protects against two non-oncogenic strains and two oncogenic strains that account for approximately 70% of HPV-related cancers, says Stephen K. Tyring, M.D., Ph.D., clinical professor of dermatology, microbiology/molecular genetics, and internal medicine at the University of Texas Health Science Center, and medical director of the Center for Clinical Studies in Houston, Texas.
Now that a new HPV vaccine approved in December 2014 (Gardasil 9, Merck) protects against an additional five oncogenic strains, "We have protection against more than 90% of the cancer-causing viruses. That's a big step forward. It's going to be even more effective at preventing the vast majority of cervical, oral, external genital, and anal cancers." The new vaccine also can prevent most of the highly aggressive skin cancers that HPV can cause in immunocompromised patients, including organ transplant recipients, Dr. Tyring says.
Like the quadrivalent HPV vaccine, the nine-valent vaccine requires intramuscular injections at months zero, two, and six. Unlike a live or killed vaccine, adds Dr. Tyring, the new vaccine contains purely recombinant glycoproteins. "That means there is absolutely no chance it can cause infection."
Since the first HPV vaccines became available in 2006, says Dr. Tyring, uptake has been slow among girls – and even slower among boys, for whom the vaccine earned approval in 2009. "It takes a while to build compliance to a vaccine that prevents a disease that doesn't have immediate consequences, like measles."
Herpes simplex virus (HSV)
In HSV, says Dr. Tyring, vaccines under development are truly therapeutic, not preventative. "Three different pharmaceutical companies have made molecular copies of HSV proteins that we are giving patients with recurrent genital herpes to boost their immunity." These projects include:
Other products in development target the virus' helicase-primase complex, he says, which allows them to work against viral strains that are resistant to traditional therapies on the market.1
"In other words, acyclovir, valacyclovir, and famciclovir all have the same problem with resistance in certain viruses that have mutations or deficiencies of an important enzyme, thymidine kinase." However, he says that helicase-primase inhibitors including pritelivir (AiCuris) block an earlier stage of viral replication. "That's important for our immunocompromised patients, so we will have something that will benefit them on the market someday if they develop resistance." Pritelivir already has demonstrated efficacy and safety in this population, he says.
Additionally, a clinical trial reported by Dr. Tyring last year showed pritelivir to be significantly better than valacyclovir in reducing viral shedding and outbreaks among HSV-2-infected patients with genital herpes.2
Dr. Tyring has been a clinical investigator for Genocea, Agenus, Vical, AiCuris and Astellas (amenamevir).
For more info:
1. Tyring S, Wald A, Zadeikis N, Dhadda S, Takenouchi K, Rorig R. ASP2151 for the treatment of genital herpes: a randomized, double-blind, placebo- and valacyclovir-controlled, dose-finding study. J Infect Dis. 2012;205(7):1100-10.
2. Wald A, Corey L, Timmler B, et al. Helicase-primase inhibitor pritelivir for HSV-2 infection. N Engl J Med. 2014;370(3):201-10.