Expression of recombinant fusion proteins in attenuated bacteria

The invention provides a DNA molecule comprising a promoter sequence operably linked to a DNA sequence encoding first and second proteins linked by a hinge region wherein in that the promoter sequence can be one having activity which is induced in response to a change in the surrounding environment and the first protein can be Tetanus toxin C fragment or one or more epitopes thereof. The invention also provides intermediate molecules having a promoter operably linked to a DNA sequence encoding a first antigenic sequence and a hinge region, and at or adjacent the 3′-end thereof one or more restriction sites for the introduction of a second anti-genic sequence. In addition, the invention provides replicable expression vectors containing the DNA fusion proteins expressed therefrom, bacterial transformed with the vectors and the use of the bacteria, in vaccines.