Immunogenic composition

A recombinant bacteriophage comprising

• a phage genome polynucleotide including a deletion of at least one gene encoding a bacteriophage structural protein;
• a gene encoding a heterologous antigen protein(s) without an appropriate leader sequence, wherein the expression of the heterologous antigen protein is driven by a strong promoter, and
• a killing gene encoding a protein that kills a host bacterium, wherein the expression of the killer gene is driven by a weak promoter,
• wherein the recombinant bacteriophage is incapable of carrying out a lysogenic cycle by deletion of a portion of the phage genome polynucleotide that encodes an enzyme required for the lysogenic cycle,
• wherein the recombinant bacteriophage is adapted to bind to a host bacterium and insert the phage genome polynucleotide into said host bacterium;
• wherein following entry of the recombinant bacteriophage into a host bacterium, expression of the heterologous antigen protein is driven by the strong promoter,
• wherein the heterologous antigen is released from the host bacterium and the heterologous antigen protein(s) is not expressed as part of a phage coat/capsid protein;
• wherein the heterologous antigen protein, after expression is released into the cytoplasm of a bacterium infected by the bacteriophage due to the absence of the appropriate leader sequence.