This is a Phase 1, multi-center, double-blind, randomized, placebo-controlled, dose-escalation study in subjects with relapsing Multiple Sclerosis (MS). The primary outcome will be the safety and tolerability of a single dose of rHIgM22 in relapsing MS subjects.

Inclusion Criteria:

• Males or females (18-70 years of age; < 104 kg)
• Capable of giving informed consent
• Meet diagnostic criteria for MS, as defined by revised (2010) McDonald criteria
• Present with a clinical acute relapse defined as a new or worsening neurological symptoms attributable to MS preceded by a stable or improving neurological state of at least 30 days, not associated with fever or infection, lasting at least 24 hours and accompanied by an objective physical (neurological) exam finding as confirmed by the Investigator
• Has at least one new, identifiable, measurable and active lesion on MRI (Gd+) meeting the criteria of the imaging charter.

Exclusion Criteria:

• Certain specified co-morbidities (including pregnancy)
• Taking certain proscribed medications
• A medical regimen that has changed in the month prior to screening
• Inability to undergo requisite MRI evaluations
• Drug or alcohol abuse
• Any other reason for which, in the opinion of the Investigator, the subject should not participate in the study.