Vical acknowledged today that it has halted development of its bivalent vaccine candidate for herpes simplex virus type 2 (HSV-2) after it failed a Phase II trial—the company’s second clinical setback this year involving a lead product.

The HSV-2 vaccine missed its primary endpoint in the Phase II study (NCT02837575) of annualized lesion recurrence rate calculated based on those genital recurrences that were both clinically and virologically confirmed during a minimum of nine months of surveillance, Vical said.  

The Phase II study was conducted in 261 healthy HSV-2 seropositive adults ages 18 to 50 years, with a self-reported history of four to nine recurrences per year. Subjects were randomized 2:1 to receive either vaccine or placebo. The vaccine was generally safe and well tolerated, as assessed by an independent safety monitoring board, the company said.

According to Vical, no grade 4 adverse events or serious adverse events were reported related to vaccination.

“The annualized recurrence rate during the trial in the placebo group was far less than what was expected based on their self-reported history. As a result, there was significantly less power to show a vaccine effect in this trial,” Vical president and CEO Vijay Samant said in a statement. “We are extremely disappointed with the outcome, and based upon these results, we will be terminating the HSV-2 program.”

The study protocol requires that patients be followed for 12 months after their last dose. Vical said it will continue to follow the active patients until July.

Shifting Focus to Antifungal, HBV Candidates

The failure of the HSV-2 vaccine program marks Vical’s second clinical setback involving a lead candidate this year. In January, the company ended development of ASP0113—a DNA vaccine being co-developed with Astellas Pharma for cytomegalovirus (CMV)-seropositive hematopoietic stem cell transplant recipients—after it missed its primary and secondary endpoints in the Phase III HELIOS trial.

A week after disclosing the failure of ASP0113 on January 22, Vical ended development of the DNA vaccine candidate and eliminated more than half its staff, shrinking its workforce from 74 to 34 staffers. Vical also said it would shift its clinical development focus to the HSV-2 vaccine as well as VL-2397, its antifungal drug product candidate.

Today Vical said it will focus solely on VL-2397, for which a Phase II trial (NCT03327727) is underway, comparing VL-2397 with standard first-line treatment for invasive aspergillosis in immunocompromised adults.

VL-2397 would be eligible for a Limited Use Indication, assuming a successful outcome of the trial, Vical said.

The company added that it plans to continue the preclinical development of a novel treatment for chronic hepatitis B virus (HBV) infection based on their DNA and lipid-delivery technologies: “The initial aim of our HBV program is to demonstrate proof of concept for inhibiting HBV infection in an in vivo model.”

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