Astellas Pharma Inc. and Vical Incorporated announced that ASP0113, an investigational DNA vaccine being developed for cytomegalovirus (CMV)-seropositive hematopoietic stem cell transplant (HSCT) recipients, did not meet its primary or secondary endpoints in the Phase 3 HELIOS clinical trial. The vaccine was generally well tolerated, with injection-site reactions being the most commonly reported adverse event. The Phase 3 trial was designed to evaluate the efficacy of ASP0113 compared with placebo in CMV-seropositive recipients undergoing an allogeneic stem cell 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 was a 1:1 randomized, double-blind, placebo-controlled study that enrolled a total of 514 CMV seropositive subjects undergoing hematopoietic stem cell transplantation. Randomization was stratified by donor-recipient relatedness and donor CMV serostatus. Subjects were followed for one year post-transplant.