Immunogenicity and protective effects of recombinant attenuated Salmonella enterica Serovar Typhimurium vaccine strains encoding a non toxic Stx2 (Stx2ÄAB) form

ROJAS RLG; BENTANCOR L; GÓMEZ PADP; SBROGIO-ALMEIDA ME; MASSIS LM; FERREIRA RCC; PALERMO MS; FERREIRA LCS

Buenos Aires

Simposio; 7th International Symposium on Shiga -Toxin (Verocytotoxin)- Producing Eschericchia coli (VTEC2009); 2009

Asociación Argentina de Microbiología

Shiga-like toxins  (Stx) have a crucial role on in the pathogenesis of enterohemorrhagic Escherichia coli (EHEC) leading to the hemolytic-uremic syndrome (HUS), characterized by hemolytic anemia, thrombocytopenia, and renal failure.  No effective therapeutic/prophylactic measures are presently available and efficient vaccines are eagerly required. In an effort to develop a candidate vaccine against HUS, we designed a strategy based on recombinant attenuated Salmonella Typhimurium vaccine strains encoding a mutated Stx2 composed of the B subunit plus the A2 subunit (Stx2ÄAB). The gene encoding the mutated toxoid was cloned in pGEM-T vector (pCVT2) under the control of the native promoter and the recombinant plasmid was introduced into two attenuated aroA S. Typhimurium strains differing in flagellin expression, the structural flagellar subunit. Both strains expressed the target antigen both in the intracellular compartment and as a secreted protein. pCVT2 was stable under non-selective conditions in both tested strains either under in vitro or in vivo conditions. Mice immunized with the Salmonella vaccine strains elicited enhanced serum Stx-specific IgG responses, including both IgG1 and IgG2a subclass antibodies, but low Stx-specific fecal IgA responses. Higher anti-Stx IgG responses were achieved in mice immunized with the flagellated Salmonella vaccine strain. Serum samples harvested from mice immunized with the Salmonella strains showed in vitro and ex vivo Stx2 neutralization activity. In addition, 25% of mice vaccinated with the flagellated Salmonella vaccine strain were protected to lethal challenges with Stx2. Collectively these results indicate that Stx2ÄAB-expressing recombinant Salmonella vaccine strains represent promising candidates in the search of effective anti-HUS therapeutic/prophylactic alternatives. Financial Support:  Fapesp and Capes/SECYT.