Annexon's Tanruprubart Shows Rapid and Durable Improvements in Guillain-Barré Syndrome Phase III Trial
Key Insights
Tanruprubart (search) demonstrated significant functional improvements in Guillain-Barré syndrome (search) patients as early as one week after treatment, with patients 14 times more likely to show improved mobility versus placebo.
The monoclonal antibody targeting C1q protein (search) maintained durable benefits through 26 weeks, with twice as many treated patients achieving full recovery compared to placebo.
If approved, tanruprubart (search) could address a significant unmet need for the estimated 7,000 U.S. and 15,000 EU patients diagnosed with GBS annually, potentially representing a $1 billion market opportunity.
Annexon Biosciences (search)' investigational monoclonal antibody tanruprubart (search) demonstrated rapid and sustained improvements in patients with Guillain-Barré syndrome (search) (GBS), according to Phase III trial results presented at the 2025 Annual Meeting of the American Academy of Neurology and the 2025 Peripheral Nerve Society Annual Meeting.
The Phase III trial enrolled 241 patients with GBS aged 16 years and older who were randomized to receive a single IV infusion of tanruprubart (search) at either 30 mg/kg, 75 mg/kg, or placebo. Data revealed that patients receiving the 30 mg/kg dose were 14 times more likely to show improved mobility, balance, and lower limb function at week 1 compared to placebo. These benefits remained durable through 26 weeks, with twice as many tanruprubart-treated patients achieving full recovery versus placebo.
"These findings indicate that tanruprubart (search) safely allows GBS patients to recover faster and more durably over placebo," noted Jefferies analysts in a Wednesday afternoon investor note.
Significant Quality-of-Life Improvements
The trial also demonstrated significant improvements in quality-of-life measures. Patients in the 30 mg/kg group showed significant improvement on the EQ visual analog scale (EQ-VAS) at week 1 (P = .0089), which remained through week 8 (P = .0391). Using proportional odds regression for the EQ5D-5L domains, researchers documented significant improvements at week 1 in mobility (OR = 5.65; P <.0001), self-care (OR = 9.50; P <.0001), and usual activity (OR = 7.42; P <.0001).
Additionally, patients receiving tanruprubart (search) walked independently a median of 31 days earlier (P = .0211) and spent a median of 28 days less on mechanical ventilation (P = .0356) compared to placebo.
"The data demonstrates tanruprubart (search)'s potential to transform GBS management," said Glenn Morrison, PhD, vice president of clinical development at Annexon Biosciences (search), who presented some of the findings.
Novel Mechanism of Action
Tanruprubart (search) works by targeting and blocking the C1q protein (search) in the peripheral and central nervous system. In GBS, persistent activation of C1q damages nerves throughout the body, leading to acute muscle paralysis and potentially resulting in disability or death if left untreated. By preventing this damage, tanruprubart enables patients to regain muscle strength more quickly.
This mechanism represents a significant advancement over current standard treatments for GBS, which include plasma exchange or intravenous immunoglobulin. These existing approaches aid recovery but do not directly target the disease mechanism.
Real-World Evidence Supports Efficacy
To strengthen its case for tanruprubart (search), Annexon also presented data from a real-world study showing a "rapid increase in muscle strength" compared to current standards of care. The study demonstrated "more complete recovery" with tanruprubart over standard treatments.
These results build on earlier data released in June 2024 from the same Phase III study, which showed that tanruprubart (search) met its primary endpoint of significantly reducing disease-related disability. At week 8, patients on tanruprubart were 2.4 times more likely to be in a better state of health than placebo comparators (OR, 2.4; 95% CI, 1.29-4.50; P = .0058).
Safety Profile
The safety profiles were comparable across treatment groups, with a balanced number of serious adverse events observed. Transient infusion-related reactions occurred in 35.0% of patients treated with tanruprubart (search); however, these did not impact mortality or infection rates.
Market Potential and Regulatory Path
Guillain-Barré syndrome (search) has an estimated annual incidence of 7,000 patients in the U.S. and 15,000 in the EU, representing at least a $1 billion market opportunity for Annexon in these regions alone, according to Jefferies analysts.
The company is currently meeting with the FDA to discuss the regulatory pathway for tanruprubart (search), with a potential approval targeted for mid-2026. If approved, tanruprubart would be the first medication specifically designed to treat GBS, addressing a significant unmet need for patients who currently have no approved therapies that directly target the disease.
GBS is a rare autoimmune disorder with unknown underlying causes. Patients typically rely on immunoglobulin treatments or plasmapheresis to aid in recovery, which can take weeks or years. The rapid onset of benefits seen with tanruprubart (search) could significantly improve outcomes and quality of life for these patients.