Abstract: The present invention relates to nucleic acids comprising: (a) sequences of a replication competent transmissible gastroenteritis virus (TGEV), which sequences encode a TGEV replicase under the control of expression regulatory sequences so that expression of the replicase in a cell containing the nucleic acid will initiate replication of the nucleic acid and thus increase the number of nucleic acids in the cell; and (b) sequences encoding one or more proteins of a different virus wherein the one or more proteins are capable of associating into a virus-like particle (VLP) that does not contain any infectious nucleic acid. The present invention further relates to vectors, virus particles and host cells comprising these nucleic acids as well as their use for the preparation of vaccines, specifically for the preparation of vaccines.