Live Oral Salmonella enterica Serovar Typhi Vaccines Ty21a and CVD 909 Induce Opsonophagocytic Functional Antibodies in Humans That Cross-React withS. Paratyphi A andS. Paratyphi B

Abstract

ABSTRACTLive oralSalmonella entericaserovar Typhi vaccine Ty21a induces specific antibodies that cross-react againstSalmonella entericaserovar Paratyphi A andSalmonella entericaserovar Paratyphi B, although their functional role in clearance remains unknown. We utilized anin vitroassay with THP-1 macrophages to compare the phagocytosis and survival ofSalmonellaopsonized with heat-inactivated human sera obtained before and after vaccination with Ty21a or a live oralS. Typhi vaccine, CVD 909. Opsonization with postvaccination sera predominantly increased the phagocytosis ofS. Typhi relative to the corresponding prevaccination sera, and increases were also observed withS. Paratyphi A andS. Paratyphi B, albeit of lower magnitudes. Relative to prevaccination sera, opsonization with the postvaccination sera reduced the survival inside macrophages ofS. Typhi but not ofS. Paratyphi A orS. Paratyphi B. Higher anti-S. Typhi O antigen (lipopolysaccharide [LPS]) IgG, but not IgA, antibody titers correlated significantly with postvaccination increases in opsonophagocytosis. No differences were observed between immunization with four doses of Ty21a or one dose of CVD 909. Ty21a and CVD 909 induced cross-reactive functional antibodies, predominantly againstS. Typhi. IgG anti-LPS antibodies may be important in phagocytic clearance of these organisms. Therefore, measurement of functional antibodies might be important in assessing the immunogenicity of a new generation of typhoid and paratyphoid A vaccines. (The CVD 909 study has been registered at ClinicalTrials.gov under registration no. NCT00326443.)