This study is a multi center, open-label, study of ANX005 in combination with IVIg in subjects diagnosed with GBS.

The study will enroll approximately 12 subjects into one cohort, with subjects receiving 75 mg/kg of ANX005, a dose shown to be safe and well-tolerated as monotherapy and that provides a meaningful level of exposure to be tested in combination with IVIg. Dosing of IVIg will be administered as is the current standard of care (0.4 g/kg/day x 5 days) and ANX005 will be administered concurrently, beginning on Day 1 or 2 of the treatment period. Subjects will be followed for 6 months after treatment for observation and evaluation.

Inclusion Criteria:

• Diagnosis of GBS according to the National Institute of Neurological Disorders and Stroke Diagnostic Criteria for Guillain Barré Syndrome
• Onset of GBS-related weakness ≤14 days prior to infusion
• GBS-DS score of 3, 4, or 5

Exclusion Criteria:

• Clinically significant findings that may interfere with the conduct of the study or the interpretation of the data
• Be at risk of suicide or self-harm
• Received previous treatment with plasma exchange for GBS
• Any diagnosis of a variant of GBS
• Have a history of anaphylaxis or severe systemic response to immunoglobulin
• Documented, clinically significant, pre-existing polyneuropathy from another cause
• Clinically significant intercurrent illness, medical condition, or medical history
• History of chronic use of steroid or immunosuppressant medication
• Active alcohol, drug, or substance abuse
• Females who are pregnant, breast feeding, or unable or unwilling to use highly effective methods of contraception throughout the study