Astellas Pharma and US-based biopharmaceutical firm Vical have reported unsuccessful top-line results from the Phase III HELIOS clinical trial of ASP0113 vaccine in cytomegalovirus (CMV) seropositive haematopoietic stem cell transplant (HSCT) recipients.
ASP0113 is an investigational bivalent DNA vaccine candidate being developed for the prevention of CMV infection and related complications in these recipients.
Made using a poloxamer-based delivery system, the vaccine candidate encodes CMV phosphoprotein 65 and glycoprotein B antigens for stimulation of cellular and humoral immune responses.
While ASP0113 was found to be well-tolerated during the trial, it did not meet the primary and secondary endpoints in 514 subjects undergoing an allogeneic stem cell transplant.
Astellas Pharma Development president Bernhardt Zeiher said: "We are disappointed that the results did not demonstrate a significant improvement in overall survival and reduction in CMV end-organ disease."
The randomised, double-blind, placebo-controlled Phase III trial was designed to compare the efficacy of ASP0113 with placebo. It evaluated overall mortality and CMV end-organ disease through the first year after the transplant as the primary composite endpoint.
Secondary endpoints of the trial included time to first protocol-defined CMV viremia and to that of the first adjudicated CMV-specific antiviral therapy use.
Vical CEO Vijay Samant said: "Astellas and Vical employees, the investigators and study site personnel did an outstanding job conducting this study, but unfortunately, the vaccine was unable to provide protection against all-cause mortality in this very difficult-to-treat patient population."
Vical initially developed the ASP0113 vaccine and later collaborated with Astellas for further development and commercialisation.