Tetanus toxin fragment C expressed in live Salmonella vaccines enhances antibody responses to its fusion partner Schistosoma haematobium glutathione S-transferase

Tetanus toxoid has been used widely as an adjuvant. The atoxic fragment C from tetanus toxin (TetC) is potently immunogenic when expressed in Salmonella vaccine strains and has been used as a fusion partner for antigens (Ag). However, there has been no formal comparison of the immunomodulatory impact of TetC on its fusion partners. In this study, we have addressed this important issue. The protective 28-kDa glutathione S-transferase (GST) from Schistosoma haematobium (Sh28GST) was expressed either as a fusion to TetC or as the full-length Sh28GST alone in a nonvirulent aroA-attenuated strain of Salmonella enterica serovar Typhimurium. The Sh28GST proteins were soluble and stably expressed in Salmonella, as evaluated by Western blotting with TetC and/or Sh28GST antisera. Mice were immunized orally with a single dose of the live recombinant Salmonella. The constructs were stable in mice but, dramatically, only the strain expressing the TetC-Sh28GST fusion elicited significant antibody (Ab) responses directed against Sh28GST as determined by enzyme-linked immunosorbent assay. An analysis of the isotype profiles showed that these mice also produced anti-Sh28GST immunoglobulin A and GST-neutralizing assays revealed high levels of neutralizing Abs in sera. These are important correlates of protection in schistosomiasis. In addition, stimulation of spleen cells from immunized mice with Sh28GST Ag showed that both strains, expressing Sh28GST alone or the TetC-Sh28GST fusion, were able to stimulate the secretion of Th1-related cytokines (gamma interferon and interleukin 2) to comparable levels. Thus, TetC has modulated the immune responses generated against its fusion partner, Sh28GST, by markedly enhancing the Ab responses elicited. These results have important implications in the rational development of live vaccines.

Development of a nonantibiotic dominant marker for positively selecting expression plasmids in multivalent Salmonella vaccines

We report the novel application of a herbicide-resistance-based dominant marker for the positive selection of expression plasmids in Salmonella serovar vaccines. The beta-lactamase gene of the plasmid pTETnir15, which expresses fragment C of tetanus toxin (TetC), has been replaced with the bar gene marker. The new plasmid pBAT1 can be positively selected in vitro within Salmonella serovars in the presence of the herbicide DL-phosphinothricin. The expression of TetC remains unaltered, and the Salmonella enterica serovar Typhimurium vaccine strain is stable and immunogenic in vivo.

Nefazodone-induced liver failure: report of three cases

BACKGROUND

Liver failure is a rare but devastating result of drug toxicity.

OBJECTIVE

To describe three cases of subfulminant liver failure that were probably caused by nefazodone, a new antidepressant that is a synthetically derived phenylpiperazine.

DESIGN

Case series.

SETTING

Two university medical centers and a children's hospital.

PATIENTS

Three women 16 to 57 years of age.

INTERVENTION

Two patients underwent liver transplantation; the third was listed for transplantation but subsequently improved.

MEASUREMENT

Liver biopsy.

RESULTS

Nefazodone was administered for 14 to 28 weeks before the onset of symptoms. The duration of jaundice before onset of encephalopathy ranged from 4 to 6 weeks. All cases of liver failure had similar histologic appearance, with prominent necrosis in the centrolobular areas (zone 3). One patient had successful liver transplantation, one underwent transplantation but died, and one improved without transplantation. The temporal onset of disease after the start of nefazodone therapy suggested severe hepatocellular injury caused by the drug.

CONCLUSIONS

Because nefazodone seems to cause severe hepatocellular injury in an idiosyncratic manner, routine liver chemistries should be performed before starting nefazodone therapy and patients should be monitored regularly. Therapy should be discontinued if liver enzyme concentrations become abnormal.

Expression and immunogenicity of an Echinococcus granulosus fatty acid-binding protein in live attenuated Salmonella vaccine strains

Fatty acid-binding proteins (FABPs) are candidate molecules for vaccines against several parasitic platyhelminths. A FABP from the cestode Echinococcus granulosus (EgDf1) was expressed in Salmonella vaccine strains as a C-terminal fusion to fragment C of tetanus toxin (TetC) by using expression vector pTECH. The fusion protein was equally expressed in several attenuated vaccine strains derived from bacteria with different genetic backgrounds and different attenuating mutations. Single-dose immunization experiments with the aroA Salmonella typhimurium strain SL3261 carrying the pTECH-EgDf1 construct were conducted with mice, using both the intravenous and the oral routes. Surprisingly, the antibody response to EgDf1 and the antigen-specific cytokine production in spleen cells were stronger in mice immunized orally. Furthermore, immune mouse sera strongly reacted with fixed sections of the worm's larval stage. Analysis of the isotype distribution of the specific anti-EgDf1 antibodies showed similar production of immunoglobulin G1 (IgG1) and IgG2a together with specific IgA antibodies. In addition, stimulation of spleen cells from mice immunized with the different constructs with either Salmonella lysate, TetC, or EgDf1 showed that, together with Th1-related cytokines (gamma interferon and interleukin 2 [IL-2]), significant levels of a Th2 cytokine (IL-5) were produced specifically, indicating a Th2 component to the response to the Salmonella carrier and to the recombinant antigens. Salmonellae expressing the TetC-rEgDfl fusion are currently under evaluation as potential vaccines against E. granulosus.

A Salmonella typhimurium htrA live vaccine expressing multiple copies of a peptide comprising amino acids 8-23 of herpes simplex virus glycoprotein D as a genetic fusion to tetanus toxin fragment C protects mice from herpes simplex virus infection

Multiple tandem copies of an immunogenic epitope comprising amino acids 8-23 of glycoprotein D of herpes simplex virus (HSV) were expressed as C-terminal fusions to tetanus toxin fragment C (TetC) in different Salmonella typhimurium live vaccine strains. Expression of the longer fusions was best in strains harbouring a lesion in htrA, a stress protein gene. SL3261, an aroA strain, did not effectively express the longer fusions. Mice immunised with an S. typhimurium C5 htrA mutant expressing fusions with two or four copies of the peptide made an antibody response to both the peptide and TetC, whereas constructs expressing one copy of the peptide only elicited antibody to TetC. A non-immunogenic octameric fusion underwent rearrangements in vivo resulting in a predominantly monomeric fusion. In contrast, the S. typhimurium SL3261 aroA vaccine expressing the TetC-tetrameric fusion did not elicit antibody to the peptide. Sera from mice immunised with a single dose of the dimer and tetramer fusions in the htrA strain neutralised HSV in vitro, and the mice were protected from HSV infection as measured by a reduction in virus load in the ear pinna. We have previously shown that mice vaccinated with salmonella expressing TetC are protected against tetanus toxin and virulent salmonella challenge. These results suggest that it may be possible to develop a multivalent vaccine against salmonellosis, tetanus and HSV.

Influence of preimmunization with tetanus toxoid on immune responses to tetanus toxin fragment C-guest antigen fusions in a Salmonella vaccine carrier

We have previously described a new system for the delivery of recombinant antigens in live Salmonella vaccines as genetic fusions to the C terminus of fragment C of tetanus toxin (TetC) driven by the anaerobically inducible nirB promoter. It has been reported that preimmunization with tetanus toxoid (TT) can suppress the antibody response to peptides chemically coupled to TT (epitope-specific suppression) in both animals and humans, which could interfere with efficacy of the Salmonella-TetC delivery system. We report that preimmunization of BALB/c mice with TT in alum did not suppress the response to either of two protective antigens of Schistosoma mansoni, the full-length S. mansoni P28 glutathione S-transferase (P28) and a construct consisting of eight tandem copies of the protective peptide comprising amino acids 115 to 131 of P28. The guest antigens were expressed in the aroA Salmonella typhimurium SL3261 vaccine strain as fusions to TetC. Preimmunization with TT 10 weeks before administration of the recombinant salmonellae did not alter the antibody response to the full-length P28, whereas the response to the peptide comprising amino acids 115 to 131 was increased by preimmunization with TT, with the increase seen mainly in the immunoglobulin G1 isotype. The antitetanus response was increased by preimmunization with TT in all groups receiving salmonellae expressing TetC. The results could be important when one is considering the use of the Salmonella-TetC delivery system in populations preimmunized with TT.

The development of oral vaccines against parasitic diseases utilizing live attenuated Salmonella

Genetically defined, live attenuated Salmonella vaccines are proving useful both as oral vaccines against salmonellosis and for the development of multivalent vaccines based on the expression of heterologous antigens in such strains. Several candidate attenuated S. typhi strains are at present being evaluated as new single dose oral typhoid vaccines in human volunteers. The emergence of such a vaccine will facilitate the development of multivalent vaccines for humans. Many antigens from different infectious organisms have been expressed in attenuated Salmonella. A focus of this work has been on developing vaccines against parasitic diseases. This review will summarize the efforts that have been made in this area.

Construction, expression, and immunogenicity of multiple tandem copies of the Schistosoma mansoni peptide 115-131 of the P28 glutathione S-transferase expressed as C-terminal fusions to tetanus toxin fragment C in a live aro-attenuated vaccine strain of Salmonella

Genetic fusions have been constructed between the highly immunogenic but atoxic fragment C of tetanus toxin and a guest peptide, aa115-131, from the protective 28-kDa glutathione S-transferase Ag of Schistosoma mansoni. Fusions have been assembled to express one, two, four, and eight tandem copies of the peptide. The recombinant vectors have been electroporated into the nonvirulent aroA strain of Salmonella typhimurium SL3261. The fusion proteins are soluble and stably expressed in Salmonella as evaluated by Western blotting with fragment C and glutathione S-transferase antisera. Mice have been immunized i.v. with a single dose of the live recombinant salmonellae. The strains are stable in mice and elicit Ab responses directed against fragment C, as determined by enzyme-linked immunosorbent assays. Ab responses were also detected against the guest peptide. The Ab responses improved dramatically toward the aa115-131 peptide with increasing copy number, with the octameric "repitope" fusion displaying the greatest potency. This approach may represent a general strategy for eliciting immune responses against peptides in live bacterial vaccines.

Construction, expression, and immunogenicity of multiple tandem copies of the Schistosoma mansoni peptide 115-131 of the P28 glutathione S-transferase expressed as C-terminal fusions to tetanus toxin fragment C in a live aro-attenuated vaccine strain of Salmonella

Genetic fusions have been constructed between the highly immunogenic but atoxic fragment C of tetanus toxin and a guest peptide, aa115-131, from the protective 28-kDa glutathione S-transferase Ag of Schistosoma mansoni. Fusions have been assembled to express one, two, four, and eight tandem copies of the peptide. The recombinant vectors have been electroporated into the nonvirulent aroA strain of Salmonella typhimurium SL3261. The fusion proteins are soluble and stably expressed in Salmonella as evaluated by Western blotting with fragment C and glutathione S-transferase antisera. Mice have been immunized i.v. with a single dose of the live recombinant salmonellae. The strains are stable in mice and elicit Ab responses directed against fragment C, as determined by enzyme-linked immunosorbent assays. Ab responses were also detected against the guest peptide. The Ab responses improved dramatically toward the aa115-131 peptide with increasing copy number, with the octameric "repitope" fusion displaying the greatest potency. This approach may represent a general strategy for eliciting immune responses against peptides in live bacterial vaccines.

Construction, expression, and immunogenicity of the Schistosoma mansoni P28 glutathione S-transferase as a genetic fusion to tetanus toxin fragment C in a live Aro attenuated vaccine strain of Salmonella

A vector has been constructed to allow genetic fusions of guest antigens via a hinge domain to the C terminus of the highly immunogenic C fragment of tetanus toxin. A fusion has been constructed with the gene encoding the protective 28-kDa glutathione S-transferase (EC 2.5.1.18) from Schistosoma mansoni. The recombinant vector has been electroporated into the nonvirulent Salmonella typhimurium aroA live vaccine strain SL3261. The corresponding chimeric protein is stably expressed in a soluble form in Salmonella as evaluated by Western blotting with fragment C and glutathione S-transferase antisera. Mice immunized intravenously with a single dose of the live recombinant bacteria elicit antibodies to both fragment C and glutathione S-transferase as detected by enzyme-linked immunosorbent assays. Furthermore, all of the mice were solidly protected when challenged with lethal doses of either tetanus toxin or the virulent Salmonella typhimurium strain C5. Mice have also elicited antibodies to fragment C and glutathione S-transferase after oral immunization. It may be that a live trivalent vaccine against typhoid, tetanus, and schistosomiasis is feasible.