The present invention relates to methods of inducing an immune response to cytomegalovirus (CMV) using a genetically modified CMV that is conditionally replication defective. The methods of the invention can be used to treat and/or prevent primary CMV infection, infection due to reactivation of a latent CMV and a super-infection of a different strain of CMV that had been previously encountered. The present invention also relates to a replication defective CMV which has been recombinantly altered to allow for external control of viral replication. Compositions comprising the replication defective CMV are also encompassed by the present invention.
