Serum anti-toxin B antibody correlates with protection from recurrent Clostridium difficile infection (CDI)

Background: Previous studies have demonstrated a correlation between Clostridium difficile anti-toxin A serum antibodies and protection against symptomatic disease and recurrence. Methods: A neutralizing monoclonal antibody to C. difficile toxin A (CDA1) developed by MBL and Medarex, Inc. was studied in a phase II, randomized, double-blind, placebo-controlled trial in patients receiving standard of care treatment for C. difficile infection (CDI). Twenty-nine subjects received a single intravenous infusion of 10 mg/kg CDA1 and 17 subjects received placebo and were evaluated for recurrence of CDI during the 56-day study period. Serum antibodies against C. difficile toxin A and B were measured by ELISA and cytotoxicity assay at various time points before and after infusion. Findings: CDI recurrence occurred in 5 of 29 (17%) in the CDA1 group and 3 of 17 (18%) (p = NS) in the placebo group with a trend toward delay in time to recurrence in the group treated with CDA1. The geometric mean concentration of antibody to an epitope of the receptor-binding domain of toxin B (0.300 and 1.20 μg/ml, respectively; p = 0.02) and geometric mean titer of neutralizing B antibody (8.00 and 100, respectively; p = 0.02) at study day 28 were lower for those subjects with recurrence compared to those who did not recur. In addition, a significantly greater proportion of subjects who recurred were infected with the epidemic BI/NAP1/027 strain compared with those that did not recur (88% vs. 22%; p = 0.002). Finally, in a multiple logistic regression analysis neutralizing anti-toxin B at day 14 (p < 0.001), anti-toxin A at day 28 (p < 0.001) and infection with the BI/NAP1/027 strain at enrollment (p = 0.002) were all predictive of CDI recurrence. Interpretation: In this prospective study, lower concentrations of neutralizing anti-toxin B and anti-toxin A antibody and infection with the BI/NAP1/027 strain of C. difficile were significantly associated with recurrence of CDI. © 2009 Elsevier Ltd.