A Chimeric Toxin Vaccine Protects against Primary and Recurrent Clostridium difficile Infection

Abstract

fThe global emergence of Clostridium difficile infection (CDI) has contributed to the recent surge in severe antibiotic-associated diarrhea and colonic inflammation. C. difficile produces two homologous glucosylating exotoxins, TcdA and TcdB, both of which are pathogenic and require neutralization to prevent disease occurrence. However, because of their large size and complex multifunctional domain structures, it has been a challenge to produce native recombinant toxins that may serve as vaccine candidates. Here, we describe a novel chimeric toxin vaccine that retains major neutralizing epitopes from both toxins and confers complete protection against primary and recurrent CDI in mice. Using a nonpathogenic Bacillus megaterium expression system, we generated glucosyltransferase-deficient holotoxins and demonstrated their loss of toxicity. The atoxic holotoxins induced potent antitoxin neutralizing antibodies showing little cross-immunogenicity or protection between TcdA and TcdB. To facilitate simultaneous protection against both toxins, we generated an active clostridial toxin chimera by switching the receptor binding domain of TcdB with that of TcdA. The toxin chimera was fully cytotoxic and showed potent proinflammatory activities. This toxicity was essentially abolished in a glucosyltransferase-deficient toxin chimera, cTxAB. Parenteral immunization of mice or hamsters with cTxAB induced rapid and potent neutralizing antibodies against both toxins. Complete and long-lasting disease protection was conferred by cTxAB vaccinations against both laboratory and hypervirulent C. difficile strains. Finally, prophylactic cTxAB vaccination prevented spore-induced disease relapse, which constitutes one of the most significant clinical issues in CDI. Thus, the rational design of recombinant chimeric toxins provides a novel approach for protecting individuals at high risk of developing CDI.

A chimeric protein comprising the glucosyltransferase and cysteine proteinase domains of toxin B and the receptor binding domain of toxin A induces protective immunity againstClostridium difficileinfection in mice and hamsters

“…38 The N terminus encompassing the GTD and CPD domains is more conserved between historical and epidemic strains. In our previous study 37 and consistent with others, 35,36 we indicated that the N-terminus of TcdB was able to elicit a protective antibody response. In contrast, the RBD of TcdA has potent adjuvant activity 40 , and has been used as vaccine candidates in several studies.…”

“…We also found that the neutralizing epitopes in TcdB are located in the N terminus 37 in addition to other domains. 32 Moreover, the N terminus of TcdB is more conserved than its RBD.…”

“…35,36 This notion was initially supported by our recent construction of a chimeric recombinant vaccine against TcdA and TcdB, i.e., cTxAB, in which the original RBD of a full-length TcdB was replaced with the corresponding portion of TcdA. 37 cTxAB is protective in animal models. However, the cTxAB protein has a very low yield in B. megaterium, possibly because of the large size of the construct.…”

“…37 Here, we reported the construction of a much simpler immunogen targeting both TcdA and TcdB by fusing the glucosyltransferase and cysteine proteinase domains of TcdB with the receptor binding domain of TcdA. This new construct is stable, and is easy to express and purify in large quantities.…”

Clinical update for the diagnosis and treatment ofClostridium difficileinfection

“…A Phase Ⅱ trial of this vaccine, currently underway in the US, is being conducted to assess primary CDI prevention in 650 at risk adults [225] . Also in development is a chimeric antitoxin vaccine using an endotoxin free expression system from Bacillus metaerium, which was capable of producing neutralizing antitoxins and preventing spore-induced relapse in CDI [226] .…”