The investigational hepatitis B vaccine Heplisav could provide difficult-to-immunize patients with more robust protection than that offered by currently marketed vaccines. Heplisav—jointly developed by Berkeley, California–based Dynavax and partner Merck of Whitehouse Station, New Jersey—was evaluated against London-based GlaxoSmithKline's Engerix-B in a phase 3 trial in patients with end-stage renal disease. The study shows that Heplisav offers 95.1% seroprotection, compared with 81.1% with Engerix-B. The new vaccine combines Dynavax's immunostimulatory sequence (ISS 1018), a short DNA sequence that targets Toll-like receptor 9, with hepatitis B surface antigen. Because Heplisav stimulates the innate immune system, it triggers a robust and rapid antibody response even in patients that respond poorly to existing vaccines using two—rather than three—doses. But the US Food and Drug Administration (FDA) put Heplisav on hold after a single case of Wegener's granulomatosis occurred in this phase 3 trial (Nat. Biotechnol. 26, 484, 2008). The recently released data will form part of the companies' response to the FDA's request for more data. Robin Davison of Edison Investment Research is skeptical of the vaccine's future: “The hepatitis B vaccine market is already well served. Although nonresponders are always a problem, a niche market is a smaller one,' he says.