Protective immune responses induced by the immunization of mice with a recombinant bacteriophage displaying an epitope of the human respiratory syncytial virus.

We investigated whether a recombinant bacteriophage displaying a disease-specific protective epitope could be experimentally used as a vaccine to confer protection of immunized animals against infection. We genetically engineered a recombinant phage, fd, displaying at its surface a chimeric pIII coat protein fused to the previously identified protective epitope 173-187 from the glycoprotein G of the human respiratory syncytial virus (RSV). A selected recombinant fd phage elicited a strong immune response in mice, inducing a high level of circulating RSV-specific antibodies. Mice immunized with the recombinant phage acquired a complete resistance to RSV infection as evidenced by the lack of detectable virus particles in their lungs following intranasal challenge with live RSV. In contrast, a high level of virus particles was found in the lungs of either animals immunized with the wild-type fd phage or nonimmunized mice. To our knowledge, this is the first study to report the ability of a phage presenting an immunogenic peptide to prevent infection of immunized animals by a pathogen. This finding should facilitate the identification of pathogen-specific protective epitopes selected from random phage peptide libraries, as it is simpler and less expensive than the conventional method of synthesis and coupling of phage-specific peptide ligand sequences for immunization.