Assessment of Bezlotoxumab Immunogenicity.

Bezlotoxumab is a fully human monoclonal antibody that binds and neutralizes Clostridium difficile toxin B. This analysis investigated the potential of bezlotoxumab to induce immunogenicity in healthy phase 1 trial participants and in phase 2/3 trial participants receiving oral antibacterial therapy for primary or recurrent C difficile infection. Immunogenicity to bezlotoxumab was evaluated following a single intravenous dose (≤20 mg/kg) or 2 consecutive doses (10 mg/kg) given 84 days apart in healthy participants across 3 phase 1 trials (Protocol MK-3415A-004, N = 30; Protocol CA-GCDX-05-01, N = 54; Protocol MK-3415A-006, N = 12) and following a single 10 mg/kg dose in 1 phase 2 trial (Protocol CA-GCDX-06-02, ClinicalTrials.gov identifier: NCT00350298; N = 97) and 2 phase 3 trials (Protocols MK-3415A-001 and MK-3415A-002, ClinicalTrials.gov identifiers: NCT01241552 and NCT01513239; N = 1414). No treatment-emergent antidrug antibodies were observed following single or repeated dosing of bezlotoxumab. No phase 1 participants and only 1 phase 2 participant tested positive before bezlotoxumab exposure (non-treatment-emergent positive). Nine participants tested non-treatment-emergent positive in phase 3 trials, 1 of whom was neutralizing antibody-positive. Overall, the immunogenicity potential of bezlotoxumab is considered to be low.