A Combination of Three Fully Human Toxin A- and Toxin B-Specific Monoclonal Antibodies Protects against Challenge with Highly Virulent Epidemic Strains of Clostridium difficile in the Hamster Model

Abstract

C lostridium difficile infection (CDI) is a leading cause of pseudomembranous colitis and diarrhea (C. difficile-associated diarrhea [CDAD]) causally related to a perturbation of the intestinal microbiota due to antibiotic use. Although the transmission of CDI is primarily associated with health care and long-term care facilities, C. difficile is a ubiquitous microorganism that has been found in the environment. There are documented cases of community-acquired CDI; in fact, the community-acquired C. difficile infection rates in the United States have been reported to be 7.7 cases per 100,000 person-years, of which 35% were not associated with antibiotics (1). However, the rates associated with health care and long-term care facilities are much higher, possibly due to the colocalization of a reservoir of the pathogen and a high number of susceptible individuals housed in those environments (2). As the eradication of C. difficile spores is very difficult, spore reservoirs can persist within the health care and long-term care environment for long periods (3-6). In recent years, CDI has increased in severity and incidence, and part of this increase is due to the spread of epidemic antibiotic-resistant strains (7,8). Treatment options remain limited and even appear to be losing efficacy, as evidenced by the continued spread of the epidemic strain and increasing numbers of patients who experience relapses and recurrent disease (9).Clostridial species are normal members of the human gut flora, usually as a small fraction of the microbiome and mostly nontoxigenic species (10). C. difficile pathogenesis in humans is associated with the disruption of the normal enteric flora and colonization with a toxigenic C. difficile strain. This is followed by overgrowth of vegetative cells and production of toxins that damage the cells of the colon through enzymatic activity of a glucosyltransferase, which glucosylates cytoskeletal regulators, such as Ras and Rac (11). Toxigenic C. difficile strains produce at least one of the two major exotoxins, toxin A or toxin B, and most produce both. Only toxigenic strains have been shown to cause intestinal inflammatory and diarrheal disease (12, 13); therefore, toxins A and B are believed to be major virulence factors of CDI, although other lessstudied virulence components of the bacterium can contribute to the disease. For example, the presence of a third toxin known as binary toxin has been associated with a marked increase in disease severity and risk of death. This increase was seen in all strains carrying the gene for the binary toxin, not just the C. difficile NAP1/027 strain associated with recent virulent outbreaks (14), but it remains unclear whether the binary toxin itself causes in-

Gleaning Insights from Fecal Microbiota Transplantation and Probiotic Studies for the Rational Design of Combination Microbial Therapies

“…This hypothesis is supported by data from a study in which a cocktail of monoclonal antibodies directed against TcdA and TcdB was administered intraperitoneally to hamsters prior to C. difficile challenge. This approach was found to protect against GI damage and death from CDI (149,150). The administration of the TcdB-reactive antibody bezlotoxumab in combination with either metronidazole or vancomycin has also been shown to decrease rates of CDI recurrence in humans (151).…”

Immunogenicity and Protection from Receptor-Binding Domains of Toxins as Potential Vaccine Candidates for Clostridium difficile

“…Immunization with recombinant RBDs represents a promising method in vaccine development [22,23]. A number of studies have demonstrated that antibodies induced by RBD-based vaccines can efficiently block the toxicity of bacterial or viral replication in tissue [27]. Several C. difficile vaccine candidates exist worldwide [27][28][29].…”

Pharmacological Targeting of the Host–Pathogen Interaction: Alternatives to Classical Antibiotics to Combat Drug-Resistant Superbugs

“…Obiltoxaximab, a mAb targeting protective antigen (PA), a component of anthrax lethal toxin (LT) and edema toxin (ET) required for toxin entry, prevents dissemination of Bacillus anthracis and reduces mortality in pre- and post-exposure rabbit or cynomolgus macaque models of inhalational anthrax, a foremost biodefense concern [19]. A cocktail of one fully human MAb specific to the receptor binding domain of Clostridium difficile toxin A and two fully human MAbs specific to nonoverlapping regions of the glucosyltransferase domain of C. difficile toxin B reduced severity and duration of diarrhea and mortality upon challenge with highly virulent C. difficile strains [20]. Lastly, an interesting derivation of mAb therapeutics was reported in the treatment of difficult S. aureus infections, where a slow-growing intracellular reservoir of the pathogen is often resistant to antibiotic clearance.…”