The present invention is related to a viral particle released after infection of mammalian cells by human cytomegalovirus (HCMV), wherein a) the particle is surrounded by a lipid membrane in which viral glycoproteins are embedded, b) the particle contains neither viral DNA nor capsids and c) the particle contains a fusion protein comprising one or more parts of the T-cell antigen pp65 and at least one heterologous peptide, and wherein the at least one heterologous peptide is inserted at amino acid position W175 or A534 of the amino acid sequence of the T-cell antigen pp65.
