This invention relates to non-integrating, non-replicating retroviral vectors that cause an immune response in an animal host when administered to the host. The vectors transduce cells in the host, where they produce virus-like particles (VLPs), which stimulate an additional immune response in the host when they are released from the cells. The vectors are non-integrating, non-replicating retroviral vectors comprising long terminal repeats, a packaging sequence, and a heterologous promoter operably linked to one or more polynucleotide sequences that together encode the structural proteins of a virus. Methods of making and using the vectors are also disclosed.
