Deletion of an immune evasion gene, , from a live serovar Typhimurium vaccine improves vaccine responses in aged mice.

Introduction: Non-typhoidal (NTS) generally causes self-limiting gastroenteritis. However, older adults (≥65 years) can experience more severe outcomes from NTS infection. We have previously shown that a live attenuated . Typhimurium vaccine, CVD 1926 (I77 Δ Δ Δ Δ), was immunogenic in adult but not aged mice. Here we describe modification of CVD 1926 through deletion of , a effector responsible for host immune escape, which we hypothesized would increase immunogenicity in aged mice.

Methods: Mel Juso and/or mutuDC cells were infected with . Typhimurium I77, CVD 1926, and their respective mutants, and the MHC-II levels were evaluated. Aged (18-month-old) C57BL/6 mice received two doses of PBS, CVD 1926, or CVD 1926 Δ perorally (10 CFU) and the number of FliC-specific CD4 T cells were determined. Lastly, aged C57BL/6 mice received three doses of PBS, CVD 1926, or CVD 1926 Δ perorally (10 CFU) and then were challenged perorally with wild-type . Typhimurium SL1344 (10 CFU). These animals were also evaluated for antibody responses.

Results: MHC-II induction was higher in cells treated with mutants, compared to their respective parental strains. Compared to PBS-vaccinated mice, CVD 1926 Δ elicited significantly more FliC-specific CD4 T cells in the Peyer's Patches. There were no significant differences in FliC-specific CD4 T cells in the Peyer's patches or spleen of CVD 1926- versus PBS-immunized mice. CVD 1926 and CVD 1926 Δ induced similar serum and fecal anti-core and O polysaccharide antibody titers after three doses. After two immunizations, the proportion of seroconverters for CVD 1926 Δ was 83% (10/12) compared to 42% (5/12) for CVD 1926. Compared to PBS-immunized mice, mice immunized with CVD 1926 Δ had significantly lower . Typhimurium counts in the spleen, cecum, and small intestine upon challenge. In contrast, there were no differences in bacterial loads in the tissues of PBS-vaccinated and CVD 1926-immunized animals.

Conclusion: These data suggest that the deletion enhanced the immunogenicity of our live attenuated . Typhimurium vaccine. Deletion of immune evasion genes could be a potential strategy to improve the immunogenicity of live attenuated vaccines in older adults.