Jefferies analysts predict Annexon’s tanruprubart could be approved by mid-2026.
Annexon’s investigational antibody tanruprubart can improve functional outcomes in patients with Guillain-Barré syndrome as early as one week into treatment, according to a Phase III readout on Wednesday.
In a Wednesday afternoon note to investors, Jefferies analysts said these findings indicate that tanruprubart “safely allows [Guillain-Barré syndrome (GBS)] patients to recover faster and more durably over placebo.” Annexon is meeting with the FDA to discuss the regulatory pathway for tanruprubart, building up to a potential approval in mid-2026, as per Jefferies.
Jefferies estimates an annual incidence of 7,000 GBS patients in the U.S. and 15,000 in the EU, which opens up at least a $1 billion opportunity for Annexon in those two regions alone.
The Phase III data, presented at the 2025 Annual Meeting of the American Academy of Neurology, demonstrated that patients on tanruprubart were 14 times more likely to show improved mobility, balance and lower limb function at week 1 versus placebo. Tanruprubart likewise boosted motor ability and eased limitations in upper and lower limb activity at this time point, as per Annexon’s Wednesday release.
These treatment benefits were durable through 26 weeks, at which point there were twice as many tanruprubart-treated patients who fully recovered as compared with placebo.
Wednesday’s findings build on prior evidence establishing tanruprubart as a potential treatment for GBS. In June 2024, Annexon released early data from the same Phase III study, showing that tanruprubart 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.
Functional outcomes at the time were likewise better with tanruprubart, with patients being able to walk and going off ventilation roughly a month earlier than placebo counterparts.
To beef up its case for tanruprubart, Annexon also announced on Wednesday that a real-world study of the drug likewise showed a “rapid increase in muscle strength” versus current standards of care in GBS, comprising plasma exchange or intravenous immunoglobulin. Tanruprubart also elicited “more complete recovery” over standard care.
Tanruprubart is a monoclonal antibody that works by targeting and blocking the C1q protein in the peripheral and central nervous system. In GBS, the persistent activation of C1q damages nerves throughout the body, in turn leading to acute muscle paralysis and, if left unchecked, can result in disability and death. Tanruprubart’s mechanism allows it to prevent this damage, enabling patients to regain their muscle strength.
The underlying cause of GBS is unknown and there are currently no approved medications that directly treat the disease. Patients instead rely on immunoglobulin treatments or plasmapheresis to aid in recovery, which can take weeks or years.
