An Open-label, Multicenter, Phase 4 Study to Assess the Effects of a Prophylactic Immune Tolerizing Regimen in MPS II Treatment-Naïve Patients Planned to Receive ELAPRASE Who Are at Risk of Developing Persistent Neutralizing Antibodies
The main aim of this study is to evaluate the ability of a prophylactic immune tolerizing regimen (ITR) to prevent or reduce the development of high titer anti-idursulfase antibodies in treatment-naïve participants with Hunter syndrome. In this open label, single arm study, all participants will receive ELAPRASE treatment and a prophylactic ITR. Participants will be treated with ELAPRASE for up to 104 weeks. The prophylactic ITR will start 1 day prior to the start of ELAPRASE. The prophylactic ITR will consist of a 5-week cycle of: Rituximab (intravenously \[IV\], weekly for 4 weeks); Methotrexate (oral, 3 times per week for 5 weeks) and intravenous immunoglobulin (IVIG) (IV, every 4 weeks of the cycle). Following the completion of 1 cycle, an assessment will be made at Month 6, 12, and 18 regarding the need for administering another 5-week cycle of the ITR. Participants will be in the study for approximately 112 weeks (including 6 weeks for screening, up to 104 weeks for treatment, and 2 weeks for follow-up).
• Participant is male.
• Participant is ELAPRASE-naïve at study entry.
• Participant must have a documented diagnosis of MPS II. The following combination will be accepted as diagnostic of MPS II:
‣ Participant has a deficiency in iduronate-2-sulfatase (I2S) enzyme activity of less than or equal to (\<=) 10 percent (%) of the lower limit of the normal range as measured in plasma, fibroblasts, or leukocytes (based on the reference laboratory's normal range). The participant has a normal enzyme activity level of at least 1 other sulfatase as measured in plasma, fibroblasts, or leukocytes (based on the reference laboratory's normal range).
⁃ Participant has a documented mutation in the IDS gene; additionally, participants must have a severe mutation (example, large deletion or complex gene rearrangement), which is predicted to lead to development of a persistent anti-idursulfase antibody response.
• Participant will be less than (\<) 6 years of age at enrollment.
• Participant has a negative test result for serum anti-idursulfase antibodies.