Treatment of Individuals with Guillain-Barré Syndrome Using a Monoclonal Antibody Therapy Shown to be Safe and Effective

ANX005 (Annexon Biosciences, San Francisco, CA), a monoclonal antibody designed to inhibit the C1q protein complex, significantly improved functional outcomes for people with Guillain-Barré syndrome (GBS), according to the results of a phase 3 multicenter study (NCT04701164) presented at the 2025 American Academy of Neurology Annual Meeting. The trial found that a single 30 mg/kg intravenous infusion of ANX005 was associated with rapid and sustained clinical improvement compared to placebo, potentially offering a new therapeutic approach for individuals with GBS.

The study included 242 people with a diagnosis of GBS aged ≥16 years who had GBS disability scores (GBS-DS) of 3 to 5 points. Participants were randomized 1:1:1 to receive either a single intravenous (IV) infusion of ANX005 at 30 or 75 mg/kg or placebo, without concurrent IV immunoglobulin (IVIg) or plasma exchange treatments. Participants were stratified by muscle strength and time from weakness onset to infusion. The primary endpoint at 8 weeks was improvement in state of health as measured by a trichotomy of the GBS-DS scale, which collapsed the scale into 3 categories: good state of health (GBS-DS, 0 to 1), disabled (GBS-DS, 2 to 3), or severely disabled/death (GBS-DS, 4 to 6).

• Participants who received ANX005 30 mg/kg met the primary endpoint, showing a 2.4-fold higher likelihood of improved health at 8 weeks compared to placebo (odds ratio [OR], 2.4; 95% CI 1.29 to 4.50; P=.0058), with improved function seen as early as week 1 (OR, 7.2; 95% CI 3.07 to 16.96; P<.001).
• ANX005 75 mg/kg did not meet the primary endpoint—participants treated with this dose level did not show improved state of health on the GBS-DS trichotomy relative to placebo.
• 2.5-times more participants who received ANX005 returned to normal health by week 8 compared with placebo (OR, 4.1; 95% CI, 1.422 to 12.04; P=.0092).
• Participants treated with ANX005 had a median 28 fewer days on mechanical ventilation (P=.0356) and walked independently a median of 31 days earlier (P=.0211) than those who received placebo.
• While 35% of ANX005-treated patients experienced transient infusion-related reactions, safety profiles were generally comparable across groups with no impact on mortality or infection rates.

Source: Kroon H-A, Islam Z, Collins P, et al. Efficacy and safety of targeted immunotherapy with ANX005 in treating Guillain-Barré syndrome: a phase 3 multicenter study. Presented at: American Academy of Neurology Annual Meeting; April 5–9, 2025; San Diego, CA.