For decades, scientists have tried and failed to develop vaccines for herpes. The evasive nature of the virus makes it notoriously difficult to treat. But in her lab at Yale, Iwasaki has discovered promising clues for an effective vaccination.
Conventional vaccines boost immunity by triggering antibody development. But after vaccinating mice for HSV-2 with conventional vaccines, Iwasaki’s team learned that the animals failed to develop T cells or antibodies in the genital tract. In addition, the virus displays molecules that inactivate antibodies from attacking the virus. The limited access of T cells and antibodies to the viral entry site, and the antibody evasion strategies, likely explain why previous herpes vaccines have failed.
Based on that insight, roughly a decade ago the team developed a vaccine strategy called “prime-and-pull.” Through this mechanism, the researchers used a vaccine to generate T cell immunity in guinea pigs [prime]. Then, they used a cream that can induce chemokines—signaling molecules that can direct immune cells toward an infected site—to attract the T cells into the vaginal tissue [pull].
The strategy was a success—the team found that their vaccine could shut down the reactivation of herpes in infected guinea pigs. But the lack of funding has brought their work to a halt. “We’re looking for partners to be able to take this to humans, and that’s been the bottleneck ever since,” Iwasaki says.
She believes the stigma around sexually transmitted diseases is likely one of the obstacles to getting her vaccine funded. Research shows that the human papillomavirus (HPV) vaccine Gardasil, for example, is dramatically effective in preventing cervical cancer—reducing rates in women by nearly 90 percent. But despite its benefits, convincing parents to vaccinate their children is challenging, experts say.
“We have this fabulous anti-cancer vaccine designed to wipe out cervical cancer. But parents will see that it is ‘an STD vaccine’ and think we’re accusing their son or daughter of being high-risk sexually,” says Sten Vermund, MD, PhD, Anna M.R. Lauder Professor of Public Health. “I tell them that HPV is so ubiquitous and easy to contract that most women will acquire it at some point in their life. It’s not a marker of unsafe sex, but many parents still refuse.”
A herpes vaccine may face similar resistance, making it economically unattractive for the drug industry. “When pharmaceutical companies need to pour millions of dollars into developing a vaccine, if the uptake is going to be low, the profit doesn’t justify the effort,” says Iwasaki. “This makes STD vaccines difficult, even for something so obviously beneficial, safe, and effective as Gardasil.”
As interest in mRNA vaccines grows post-COVID, Moderna and Pfizer have begun working on such a vaccine for herpes. But in a recent talk to the World Health Organization (WHO), Iwasaki warned of the limitations of mRNA vaccines in treating herpes. “If you just make a vaccine without thinking about the mucosal tissue, it’s not going to work,” she said. “Just making an intra-muscular vaccine alone—I think it will be very difficult for such a vaccine to be effective.”