A New Vaccination Method Based on Phage NgoΦ6 and Its Phagemid Derivatives

Phagemid particles based on the Neisseria gonorrhoeae filamentous phage NgoΦ6 were used as a vaccine delivery system. We demonstrate that the host proteins incorporated into/associated with these particles can be encoded by chromosomal genes of the host bacterium or from plasmids able to replicate as an autonomous entity in the phagemid host. Phagemid particles were prepared from three types of cells, namely, Salmonella enterica ser. Typhimurium [pBSKS::Φ6fm(ST)] containing phagemid genome as an autonomous plasmid, Haemophilus influenzae Rd containing phagemid [pBSKS::Φ6fm(Hin)] integrated into the chromosome, and S. enterica ser. Typhimurium [pMPMT6::Φ6fm(ST)] containing an additional plasmid, pE1 HCV, encoding the Hepatitis C virus envelope glycoprotein E1. Approximately 200 μg of purified phage particles was used to immunize rabbits. The phagemid particles prepared from these three strains all elicited a large amount of IgG antibodies that were able to recognize bacterial host cells and proteins, as determined by ELISA and FACS analysis. The amount of specific anti-S. enterica ser. Typhimurium, anti-H. influenzae, and anti-E1 HCV antibodies elicited by vaccination was 170 μg/ml for anti-Salmonella, 80 μg/ml for anti-H. influenzae, and 65 μg/ml for anti-E1 HCV. Taken in toto, these data suggest that classical phage display methods have underestimated the potential for filamentous phage as a novel immunogen delivery system.