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.本發明係關於使用經遺傳修飾之條件式複製缺陷型細胞巨大病毒(CMV)誘導對CMV之免疫反應的方法。本發明方法可用於治療及/或預防原發性CMV感染、因潛伏CMV再活化所致之感染,及先前曾遭遇之不同株CMV之再感染(super-infection)。本發明亦關於複製缺陷型CMV,其已經重組改變以允許外部控制病毒複製。本發明亦涵蓋包含該複製缺陷型CMV之組合物。