Humanized Mice for the Evaluation of Francisella tularensis Vaccine Candidates.

Francisella tularensis (FT), a highly infectious pathogen, is considered to be a potential biological weapon owing to the current lack of a human vaccine against it. Tul4 and FopA, both outer membrane proteins of FT, play an important role in the bacterium's immunogenicity. In the present study, we evaluated the immune response of mice-humanized with human CD34+ cells (hu-mice)-to a cocktail of recombinant Tul4 and FopA (rTul4 and rFopA), which were codon-optimized and expressed in Escherichia coli. Not only did the cocktail-immunized hu-mice produce a significant human immunoglobulin response, they also exhibited prolonged survival against an attenuated live vaccine strain as well as human T cells in the spleen. These results suggest that the cocktail of rTul4 and rFopA had successfully induced an immune response in the hu-mice, demonstrating the potential of this mouse model for use in the evaluation of FT vaccine candidates.