Novel Clostridium difficile Anti-Toxin (TcdA and TcdB) Humanized Monoclonal Antibodies Demonstrate In Vitro Neutralization across a Broad Spectrum of Clinical Strains and In Vivo Potency in a Hamster Spore Challenge Model

Abstract

Clostridium difficile (C. difficile) infection (CDI) is the main cause of nosocomial antibiotic-associated colitis and increased incidence of community-associated diarrhea in industrialized countries. At present, the primary treatment of CDI is antibiotic administration, which is effective but often associated with recurrence, especially in the elderly. Pathogenic strains produce enterotoxin, toxin A (TcdA), and cytotoxin, toxin B (TcdB), which are necessary for C. difficile induced diarrhea and gut pathological changes. Administration of anti-toxin antibodies provides an alternative approach to treat CDI, and has shown promising results in preclinical and clinical studies. In the current study, several humanized anti-TcdA and anti-TcdB monoclonal antibodies were generated and their protective potency was characterized in a hamster infection model. The humanized anti-TcdA (CANmAbA4) and anti-TcdB (CANmAbB4 and CANmAbB1) antibodies showed broad spectrum in vitro neutralization of toxins from clinical strains and neutralization in a mouse toxin challenge model. Moreover, co-administration of humanized antibodies (CANmAbA4 and CANmAbB4 cocktail) provided a high level of protection in a dose dependent manner (85% versus 57% survival at day 22 for 50 mg/kg and 20 mg/kg doses, respectively) in a hamster gastrointestinal infection (GI) model. This study describes the protective effects conferred by novel neutralizing anti-toxin monoclonal antibodies against C. difficile toxins and their potential as therapeutic agents in treating CDI.

Clostridioides difficile Biology: Sporulation, Germination, and Corresponding Therapies for C. difficile Infection

“…To meet this challenge, non-antibiotic and immune-based therapies against CDI have been developed, such as anti-toxins, vaccines, fecal microbiota transplant (FMT), and anti-germination-based compounds (Gerding et al, 2008 ; Howerton et al, 2013 ; Kociolek and Gerding, 2016 ). Many anti-toxins and vaccines for CDI have been developed in the past two decades (Cox et al, 2013 ; Monteiro et al, 2013 ; Mathur et al, 2014 ; Zhao et al, 2014 ; Wang Y. K. et al, 2015 ; Yang et al, 2015 ; Qiu et al, 2016 ). Though these treatments can effectively decrease the morbidity and mortality of CDI, most of the anti-toxins and vaccines cannot suppress C. difficile colonization and kill C. difficile spores.…”

A neutralizing antibody that blocks delivery of the enzymatic cargo of Clostridium difficile toxin TcdB into host cells

“…Given that some of the reported TcdB receptors bind outside of the CROPS domain (8 -10), there is a potential that neutralizing antibodies against other toxin domains could provide comparable or enhanced efficacy. A survey of other anti-toxin antibodies reveals that the GTD-containing N-terminal portion of TcdB can also present neutralizing epitopes (20,(25)(26)(27)(28). This led us to characterize the mechanism of TcdB neutralization by the humanized monoclonal antibody PA41, which targets the N-terminal region of the toxin.…”

Adaptive immune response to Clostridium difficile infection: A perspective for prevention and therapy

“…Hamster model [43] anti-toxin antibody frequency in the "healthy controls" selected for the various studies, which would also skew results. Because of these discrepancies, the ability of naturally occurring anti-TcdA and anti-TcdB to convincingly predict CDI acquisition, illness, and recurrence remains uncertain.…”

“…The authors tested these mAbs using nine different toxinproducing strains and found that they demonstrated extensive neutralization of all toxins. Moreover, mAbs CANmAbA4 and CANmAbB4 increased survivability in NAP1/BI infected hamster models [43]. …”