Although adeno-associated virus (AAV) vector-mediated gene therapy has shown promise in animal models, humans can develop AAV-specific neutralizing antibodies that block gene transfer. Mingozzi et al. showed that the addition of an empty viral capsid to the vector formulation could adsorb these antibodies to increase the efficacy of transduction in mouse and primate models. Moreover, an immunologically inert capsid that did not bind to target cells could still adsorb antibodies. Doses of empty capsids — based on a patient's anti-AAV titres — might increase the efficacy of gene transfer in humans.