Bacteriophage (phage) display has been widely used in attempts to create novel vaccines but the oral route of administration has been little explored. A useful tool for display in T-even phages is small outer capsid protein (SOC), a non-essential capsid protein which is present at a high copy number. Salmonella enterica causes typhoid fever in humans following infection by the oral route and is thus an ideal target for oral vaccination. Homologous recombination with plasmids was used to display the middle segments of the flagellin proteins FliC (H1 antigen) and FljB (H2 antigen) attached to the SOC N-terminal of T2 phage to give two recombinant phages, T2FliCm and T2FljBm which were orally administered to mice. 19 BALB/c mice were administered twice over 14 days with either purified recombinant FliCm and FljBm protein or 1010-1011PFU of T2FliCm and T2FljBm with or without 109 CFU of Escherichia coli BE. Feces were sampled over ten weeks and examined for phage by plaque assay and for the presence of mucosal IgA by ELISA. Relatively few phages were detected relative to the amount administered (up to 8.21x103PFU/g faeces) and none were detected 5 days after initial administration. The administration of a large number of phages appeared to cause no clinical symptoms. The IgA concentration in feces peaked around four weeks after the second administration and had subsided after eight weeks. The highest relative titres were observed in the protein group (0.37% for anti-FliCm and 0.22% for anti-FljBm) and the mouse group which received no E. coli (0.33% and 0.35%) despite the theoretical amount of protein contained in a phage dose being 85-500 times lower than the protein dose administered. As phage is known to stimulate the immune system, it is possible that the phage itself acts as an adjuvant to enhance the immunogenic properties of the displayed proteins. We conclude that phage may be valuable as a vector for oral vaccines.
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