Oral administration of a recombinant attenuated Yersinia pseudotuberculosis strain elicits protective immunity against plague

A Yersinia pseudotuberculosis PB1+ (Yptb PB1+) mutant strain combined with chromosome insertion of the caf1R-caf1A-caf1M-caf1 operon and deletions of yopJ and yopK, χ10068 [pYV-ω2 (δyopJ315 δyopK108) δlacZ044::caf1R-caf1M-caf1A-caf1] was constructed. Results indicated that gene insertion and deletion did not affect the growth rate of χ10068 compared to wild-type Yptb cultured at 26°C. In addition, the F1 antigen in χ10068 was synthesized and secreted on the surface of bacteria at 37°C (mammalian body temperature), not at ambient culture temperature (26°C). Immunization with χ10068 primed antibody responses and specific T-cell responses to F1 and YpL (Y. pestis whole cell lysate). Oral immunization with a single dose of χ10068 provided 70% protection against a subcutaneous (s.c.) challenge with ~2.6×10⁵ LD₅₀ of Y. pestis KIM6+ (pCD1Ap) (KIM6+Ap) and 90% protection against an intranasal (i.n.) challenge with ~500 LD₅₀ of KIM6+Ap in mice. Our results suggest that χ10068 can be used as an effective precursor to make a safe vaccine to prevent plague in humans and to eliminate plague circulation among humans and animals.