Protection of mice against Chlamydophila abortus infection with a bacteriophage-mediated DNA vaccine expressing the major outer membrane protein.

A bacteriophage-delivered DNA vaccine against Chlamydophila abortus was constructed by cloning a eukaryotic cassette containing the ompA gene (which expresses the Major Outer Membrane Protein) into a bacteriophage lambda vector. Four groups, each of 20 BALB/c mice were inoculated separately with the phage vaccine, a conventional DNA vaccine based on the same ompA expression cassette, a live attenuated vaccine (strain 1B) or the empty phage vector. The phage and DNA vaccines and empty phage vector were administered intramuscularly on days 0, 14 and 28; the attenuated vaccine was given once on day 0. Half the animals in each group were challenged on day 42 by intraperitoneal injection of live C. abortus and sacrificed on day 49. Phage-vaccinated mice developed moderate antibody levels against C. abortus and yielded higher levels of IFN-γ and IL-2 compared with the attenuated live vaccine group. Clearance of chlamydiae from spleens was significantly better in the attenuated vaccine group compared with the phage vaccine group, while both groups were significantly superior to the DNA vaccine and control groups (p<0.01). Although levels of protection in the mouse model were lower in phage-vaccinated animals, than in 1B vaccinated animals, phage vaccines offer several other advantages, such as easier handling and safety, potentially cheaper production and no chance of reversion to virulence. Although these are preliminary results in a model system, it is possible that with further optimisation immunization with phage vaccines may provide a novel way to improve protection against C. abortus infection and trials in large animals are currently being initiated.