Reduced immune responses after vaccination with a recombinant herpes simplex virus type 1 vector in the presence of antiviral immunity

1 Institute for Immunology, Ludwig Maximilians University Munich, Goethestrasse 31, 80336 Munich, Germany 2 University Claude-Bernard Lyon 1, Centre de Genetique Moleculaire et Cellulaire, Lyon, France 3 University of Ferrara, Department of Experimental and Diagnostic Medicine, Ferrara, Italy Correspondence Thomas Brocker tbrocker{at}med.uni-muenchen.de Due to the continuous need for new vaccines, viral vaccine vectors have become increasingly attractive. In particular, herpes simplex virus type 1 (HSV-1)-based vectors offer many advantages, such as broad cellular tropism, large DNA-packaging capacity and the induction of pro-inflammatory responses. However, despite promising results obtained with HSV-1-derived vectors, the question of whether pre-existing virus-specific host immunity affects vaccine efficacy remains controversial. For this reason, the influence of pre-existing HSV-1-specific immunity on the immune response induced with a replication-defective, recombinant HSV-1 vaccine was investigated in vivo . It was shown that humoral as well as cellular immune responses against a model antigen encoded by the vaccine were strongly diminished in HSV-1-seropositive mice. This inhibition could be observed in mice infected with wild-type HSV-1 or with a replication-defective vector. Although these data clearly indicate that pre-existing antiviral host immunity impairs the efficacy of HSV-1-derived vaccine vectors, they also show that vaccination under these constraints might still be feasible. Present address: The Scripps Research Institute, Division of Virology, Department of Neuropharmacology, La Jolla, CA, USA.