Clostridium perfringens beta toxin DNA prime-protein boost elicits enhanced protective immune response in mice

Toxicity and Efficacy Evaluation of Soluble Recombinant Ricin Vaccine

BACKGROUND

Ricin, a toxin extracted from the seeds of Ricinus communis, is classified as a ribosome-inactivating protein. The A-subunit of ricin shows RNA N-glycosidase activity that cleaves ribosomal RNA (rRNA) and exhibits toxicity by inhibiting protein synthesis and inducing vascular leak syndrome.

METHODS

In this study, we created a truncated version of the previously developed R51 ricin vaccine (RTA 1-194 D75C Y80C) through in silico analysis.

RESULTS

The resulting R51-3 vaccine showed a more-than-six-fold increase in soluble protein expression when compared to R51, with over 85% solubility. In a pilot toxicity test, no toxicity was observed in hematological and biochemical parameters in BALB/c mice and New Zealand white rabbits following five repeated administrations of R51-3. Furthermore, R51-3 successfully protected mice and rabbits from a 20 × LD50 ricin challenge after three intramuscular injections spaced 2 weeks apart. Similarly, monkeys that received three injections of R51-3 survived a 60 µg/kg ricin challenge.

CONCLUSIONS

These findings support R51-3 as a promising candidate antigen for ricin vaccine development.

Clostridium perfringens type C necrotic enteritis in pigs: diagnosis, pathogenesis, and prevention

Clostridium perfringens type C causes severe and lethal necrotic enteritis (NE) in newborn piglets. NE is diagnosed through a combination of pathology and bacteriologic investigations. The hallmark lesion of NE is deep, segmental mucosal necrosis with marked hemorrhage of the small intestine. C. perfringens can be isolated from intestinal samples in acute cases but it is more challenging to identify pathogenic strains in subacute-to-chronic cases. Toxinotyping or genotyping is required to differentiate C. perfringens type C from commensal type A strains. Recent research has extended our knowledge about the pathogenesis of the disease, although important aspects remain to be determined. The pathogenesis involves rapid overgrowth of C. perfringens type C in the small intestine, inhibition of beta-toxin (CPB) degradation by trypsin inhibitors in the colostrum of sows, and most likely initial damage to the small intestinal epithelial barrier. CPB itself acts primarily on vascular endothelial cells in the mucosa and can also inhibit platelet function. Prevention of the disease is achieved by immunization of pregnant sows with C. perfringens type C toxoid vaccines, combined with proper sanitation on farms. For the implementation of prevention strategies, it is important to differentiate between disease-free and pathogen-free status of a herd. The latter is more challenging to maintain, given that C. perfringens type C can persist for a long time in the environment and in the intestinal tract of adult animals and thus can be distributed via clinically and bacteriologically inapparent carrier animals.

Vaccination against Clostridium perfringens type C enteritis in pigs: a field study using an adapted vaccination scheme

Background

Clostridium perfringens type C induced necrotizing enteritis (NE) causes high mortality in newborn piglets. Immunization programs employing commercially available vaccines are used to prevent disease. Sows are vaccinated during every gestation period and piglets take up antibodies from the colostrum. Antibodies against the major clostridial toxin beta-toxin (CPB) are considered essential for protective immunity. Because the pathogen can persist for several years on farms, continuous vaccination is essential to protect pig herds from the re-occurrence of NE.

Results

In two field trials using commercially available vaccines we monitored neutralizing anti-CPB antibodies in pigs after vaccination. The first trial compared antibody titers in primiparous (gilts) and multiparous sows and their piglets after vaccination. A proportion of gilts and their piglets’ showed no or low antibody titers. All multiparous sows developed significantly higher serum and colostrum antibody titers after a booster vaccination shortly before their next farrowing. These colostral antibody titer highly correlated with the serum antibody titer of their piglets after consumption of colostrum. In a second field trial, we adapted the vaccination schemes using 3 instead of 2 initial vaccinations before the first farrowing of gilts. This significantly increased serum and colostrum antibody titers in gilts and serum antibody titers in piglets.

Conclusion

We demonstrate that despite following recommended vaccination protocols, a proportion of gilts might not sufficiently seroconvert to provide efficient passive immunity to their offsprings. A simple adaptation of the vaccination scheme can however improve passive protection of piglets from NE.

Vaccination against Clostridium difficile by Use of an Attenuated Salmonella enterica Serovar Typhimurium Vector (YS1646) Protects Mice from Lethal Challenge

Clostridium difficile disease is mediated primarily by toxins A and B (TcdA and TcdB, respectively). The receptor binding domains (RBD) of TcdA and TcdB are immunogenic, and anti-RBD antibodies are protective. Since these toxins act locally, an optimal C. difficile vaccine would generate both systemic and mucosal responses. We have repurposed an attenuated Salmonella enterica serovar Typhimurium strain (YS1646) to produce such a vaccine. Plasmid-based candidates expressing either the TcdA or TcdB RBD were screened. Different vaccine routes and schedules were tested to achieve detectable serum and mucosal antibody titers in C57BL/6J mice. When given in a multimodality schedule over 1 week (intramuscularly and orally [p.o.] on day 0 and p.o. on days 2 and 4), several candidates provided 100% protection against lethal challenge. Substantial protection (82%) was achieved with combined p.o. TcdA and TcdB vaccination alone (days 0, 2, and 4). These data demonstrate the potential of the YS1646-based vaccines for C. difficile and strongly support their further development.

Application of an Endothelial Cell Culture Assay for the Detection of Neutralizing Anti-Clostridium Perfringens Beta-Toxin Antibodies in a Porcine Vaccination Trial

BACKGROUND

Beta-toxin (CPB) is the major virulence factor of Clostridium perfringens type C, causing hemorrhagic enteritis in newborn pigs but also other animals and humans. Vaccines containing inactivated CPB are known to induce protective antibody titers in sow colostrum and neutralization of the CPB activity is thought to be essential for protective immunity in newborn piglets. However, no method is available to quantify the neutralizing effect of vaccine-induced antibody titers in pigs. (2) Methods: We developed a novel assay for the quantification of neutralizing anti-CPB antibodies. Sera and colostrum of sows immunized with a commercial C. perfringens type A and C vaccine was used to determine neutralizing effects on CPB induced cytotoxicity in endothelial cells. Antibody titers of sows and their piglets were determined and compared to results obtained by an ELISA. (3) Results: Vaccinated sows developed neutralizing antibodies against CPB in serum and colostrum. Multiparous sows developed higher serum and colostrum antibody titers after booster vaccinations than uniparous sows. The antibody titers of sows and those of their piglets correlated highly. Piglets from vaccinated sows were protected against intraperitoneal challenge with C. perfringens type C supernatant. (4) Conclusions: The test based on primary porcine endothelial cells quantifies neutralizing antibody activity in serum and colostrum of vaccinated sows and could be used to reduce and refine animal experimentation during vaccine development.