Scientists have successfully genetically engineered Salmonella enterica to deliver an antigen that protects against pneumonia. The method apparently effectively delivers the antigen in the body, does not infect the body with salmonella and does not leave any vaccine cells in the environment.

"If we tried to use live Streptococcus pneumoniae causing pneumonia for a vaccine, we would obviously kill the patient. The benefit of a live vaccine that uses a weakened form of salmonella, is that the salmonella can be taken up through the intestinal lining and stimulate an immune response by using just a portion of the bacteria causing pneumonia that itself is not deadly."

In experiments, the genetically modified Salmonella enterica bacterium colonizes the lymph tissues of the host and manufactures a protein from the S. pneumoniae bacterium, which then triggers a strong antibody response. Unlike most vaccines that are entirely manufactured by a vaccine company, the attenuated recombinant salmonella vaccine after entry into the immunized individual serves as its own factory to produce (manufacture) the protective antigens (proteins) from the S. pneumoniae pathogen. This ability to cause manufacture in the immunized individual dramatically decreases the cost of such vaccines to make them affordable for use in the developing world, Curtiss said.

The research is published in the online version (July 7) of the Proceedings of the National Academy of Sciences.

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