The brain is protected from circulating agents in the bloodstream by the stringent blood-brain barrier (BBB). While blocking entry of pathogenic microorganisms, this barrier also limits access to the brain by research tools and therapeutics. Viviana Gradinaru studies how molecules cross the BBB in order to engineer gene delivery vectors that can access the brain from the bloodstream. By understanding the mechanisms that allow passage through the BBB, Gradinaru’s team may gain therapeutic access to specific regions and cell types throughout the brain. The research may also help prevent infections from emerging pathogens that evolve to breach the BBB.