A cytomegalovirus seropositive vaccine for stem-cell transplant recipients did not meet secondary and primary endpoints in recent phase 3 trials, according to a press release from developers Astellas Pharmaceuticals Inc. and Vical Inc.

ASP0113 is an investigational vaccine candidate designed to prevent cytomegalovirus (CMV) disease and associated complications in CMV-seropositive hematopoietic cell transplant recipients. It was initially developed by Vical, which partnered with Astellas for further development and commercialization. ASP0113 received orphan drug designation in the United States and Europe.

The vaccine is meant to treat CMV, a herpes virus that is estimated to infect more than half of all adults in the United States by age 50 years. The virus is more widespread in developing countries.

A healthy immune system typically protects an infected person against CMV disease, but does not prevent or clear latent infection, the companies noted in the release. People whose immune systems are not fully functional are at high risk of CMV reactivation, potentially leading to severe illness or death. Those at greatest risk include hematopoietic cell transplant and solid-organ transplant recipients, as well as infants born to mothers who first become infected during pregnancy, the companies noted.

According to the companies, the vaccine was generally well tolerated, with injection-site reactions being the most commonly reported adverse event.

“We are disappointed that the results did not demonstrate a significant improvement in overall survival and reduction in CMV end-organ disease,” Bernhardt G. Zeiher, president of development at Astellas, said in the release. “We would like to thank the patients and clinicians who participated in this important trial.”

The phase 3 trial enrolled 514 CMV-seropositive patients undergoing an allogeneic stem cell transplant. Patients were followed for 1 year after the transplant. Efficacy was assessed using a primary composite endpoint of overall mortality and CMV end-organ disease through the first year following the transplant, an endpoint which was not met. Secondary endpoints of time to first protocol-defined CMV viremia and time to first use of adjudicated CMV-specific antiviral therapy also were not met.

“The phase 3 trial outcome is disappointing,” Vijay Samant, the CEO of Vical, said in the release. “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.”