The Surprising Upside of Herpes
Herpesviruses get a bad rap. Their poor reputation isn't entirely undeserved. Widely maligned for causing cold sores, mononucleosis, shingles, chickenpox, and the overly stigmatized genital herpes, the eight herpesviruses that infect humans can't really bemoan their sinister status. One in five adults in the U.S. is infected with genital herpes, typically caused by herpes simplex type 2.
Herpesviruses are also some of nature's most notorious squatters. When their infectious antics are halted by the immune system, they linger on within their human hosts in a latent phase, often for life. Their rent-free stay is almost always innocuous, but the little blighters sometimes flare up at opportunistic moments when the immune system is taxed by illness or bodily stress. One herpesvirus, the cold sore-causing herpes simplex type 1, may slightly increase the risk for Alzheimer's disease. Roughly two-thirds of Americans aged 12-70 have had an active cold sore infection, and likely still host the latent phase of the virus.
Herpesviruses do have a few upsides, however. Scientists have long wondered whether their prolonged stay inside their hosts imparts any beneficial effects on the hosts themselves, and a couple studies hint that it does! Back in 2007, a team from Washington University School of Medicine in St Louis infected young mice with a herpesvirus similar to the strain that causes mononucleosis in humans. After the mice beat back their initial infections, the invading viruses entered their latent stage. The team then infected the mice with pathogens that cause encephalitis, meningitis, and plague. Turned out, the mice with herpes showed more resistance to the bacteria than mice without the infection!
Mouse studies are useful, but they don't always translate to humans. Last year, however, a study revealed that a type of herpesvirus called cytomegalovirus (CMV), which infects 50 to 80 percent of all 40-year-olds, enhances the immune response to the influenza virus. Critically, the researchers behind the study achieved the same results in both mice and humans.
Scientists are now doing more than just analyzing the effects of a latent herpes infection; they're actively enlisting the virus in the fight against cancer. Last summer, an international team announced that they engineered the herpesvirus that causes cold sores to instead attack cancer cells. The therapy, called T-VEC, worked wonders in a phase III clinical trial involving 436 patients afflicted with late stage melanoma.
“Patients given T-VEC at an early stage survived about 20 months longer than patients given a different type of treatment," University of Louisville cancer researcher Jason Chesney reported. "For some, the therapy has lengthened their survival by years. ”
In T-VEC, the modified herpesviruses cannot replicate in normal cells, but they gleefully infect and destroy cancer cells. What's more, they release antigens that enable the immune system to target cancer cells.
Mere months after the success of T-VEC was announced, the FDA approved the therapy for primetime use. Melanoma patients can now turn to the herpesvirus for some small glimmer of hope in their fight against cancer.
The scientists behind T-VEC are hopeful that their herpesvirus can be further modified to attack all sorts of cancer cells. What a fascinating turn of fate: that such a maligned virus can transform from pariah to potential savior!