Herpes Vaccine HSV529 Shows Favorable Results in Phase 1 Trial

HSV529, a vaccine for herpes simplex virus 2 (HSV2), showed favorable results in a recent phase 1 trial. The study found that the vaccine was safe and elicited antibody and T-cell responses in HSV seronegative adults.

According to details published in the Journal of Infectious Diseases, the randomized, double-blind, placebo-controlled trial included 60 adults ages 18 to 40 years divided into 3 serogroups that received the vaccine or a placebo at 0, 1, and 6 months. In each group, 15 participants received the vaccine, derived from HSV2 strain 186, and 5 received a placebo.

“Prior studies to prevent HSV infection have focused on subunit vaccines with a goal to induce neutralizing antibodies,” the study noted. “HSV2 dl5-29 is a replication-defective HSV2 vaccine that can infect cells and should result in a broader immune response.”

The trial, conducted at the National Institutes of Health Clinical Center, found that 78% of HSV-negative vaccine recipients saw antibody titer increases by 4 times or more after 3 doses of the vaccine. That group saw a 6.1-fold increase in geometric mean titer (GMT) of neutralizing antibody 30 days after the third dose of the vaccine. This compares with a 1.45-fold increase in the GMT 30 days after the third dose of gD2 subunit vaccine in the Herpevac trial.

The subgroups, HSV1^-/HSV2^-, HSVI^+_/HSV2⁺, and HSV1⁺/HSV2^-, saw HSV2-specific CD4⁺ T-cell responses in 36%, 46%, and 27% of participants, respectively, and CD8⁺ T-cell responses in 14%, 8%, and 18%.

“(T)his vaccine may have potential as a prophylactic or a therapeutic vaccine,” the study authors noted. “Modifications of HSV529, such as increasing expression of certain viral proteins, inhibiting expression of viral immune evasion genes, or adding an adjuvant might improve its immunogenicity.”

The vaccinations were well-tolerated, with tenderness or pain at the injection site being the most common adverse effect reported. The most common systemic reactions were headache and malaise. The reactions did not result in refusal of additional doses of the vaccine.

The trial was completed under a clinical trial agreement between the Intramural Research Program of the National Institute of Allergy and Infectious Diseases (NIAID) and Sanofi Pasteur with funding from the National Cancer Institute.

HSV2 affects about 400 million people worldwide and is associated with an increased risk for HIV infection, making it a concern among health officials. The virus also can cause encephalitis or disseminated infection in neonates and severe disease in immunocompromised patients, the study noted.

A recently released study that included more than 1000 participants in South Africa, Uganda, and Zimbabwe found that women using vaginal tenofovir (TFV) gel for pre-exposure prophylaxis (PrEP) saw a reduced risk of HSV-2 and HIV-1 acquisition.

Another study found that patients with HIV and HSV2 coinfection saw an increase in herpes viral shedding when they began antiretroviral treatment, heightening the risk of transmitting the disease.

The HSV529 trial noted that results are pending from a study evaluating whether the vaccine increases immune responses in the skin at the injection site in the form of lesions.