This study evaluates the efficacy and safety of three doses of GC1111 in patients with Hunter Syndrome. Participants will be randomized to one of three doses of GC1111 or comparator.

This is a randomized, double-blind, active-controlled, dose-ranging study, where patient will receive one of the three doses of GC1111 (0.5 mg/kg, 1.0 mg/kg, and 1.5 mg/kg) or ELAPRASE 0.5 mg/kg. Approximately 20 patients will be administrated each study drug once every week as an iv infusion for 24 weeks. Efficacy of GC1111 will be evaluated in Six-Minute Walk Test (6MWT), urine Glycosaminoglycans(uGAG), liver and spleen volume, percent predicted Forced Vital Capacity(FVC), and cardiac size and function. Also immunogenicity, Pharmacokinetics(PK) and safety will be evaluated.

Inclusion Criteria:

• Male patients between 5 and 35 years of age
• Informed consent form signed
• Patients diagnosed with hunter syndrome
• Previously untreated with an enzyme replacement therapy

Exclusion Criteria:

• History of tracheostomy, bone marrow transplant, or cord blood transplant
• Treatment with another investigational product within 30 days prior to the start of study drug
• Known hypersensitivity of any of the ingredients of study drug
• Patient with severe hunter syndrome who cannot perform 6MWT
• Female patients