A Study to Compare the Efficacy of SEL-212 to KRYSTEXXA® in Gout Participants Refractory to Conventional Therapy

This is a randomized, parallel-arm, multicenter study to compare the safety and efficacy profiles of SEL-212 and KRYSTEXXA®. Participants will be randomized 1:1 to receive treatment with SEL-212 [a combination of pegadricase (SEL-037) and ImmTOR (SEL-110)] or KRYSTEXXA® for 6 months.

Study participants in the SEL-212 arm will receive study drug every 28 days for a total of up to 6 infusions of SEL-212. Study participants in the KRYSTEXXA® arm will receive study drug according to the manufacturer's prescribing information, i.e., every 14 days for a total of up to 12 infusions of KRYSTEXXA®.

Efficacy assessments, as measured by SUA levels, will be conducted at intervals that are appropriate to determine treatment effect differences. Safety will be monitored throughout the study.

Key Inclusion Criteria:

• History of symptomatic gout defined as:

• ≥ 3 gout flares within 18 months of Screening or
• Presence of ≥ 1 tophus or
• Current diagnosis of gouty arthritis
• At the Screening Visit: male age 21 - 80 years, inclusive, or female of non-childbearing potential age 21-80 years, inclusive, where non-childbearing potential is defined as:

• > 6 weeks after hysterectomy with or without surgical bilateral salpingooperhectony or
• Post-menopausal (> 24 months of natural amenorrhea)
• Has at the Screening Visit SUA ≥ 7 mg/dL, with chronic refractory gout defined as having failed to normalize SUA and whose signs and symptoms are inadequately controlled with xanthine oxidase inhibitors at the medically appropriate dose or for whom these drugs are contraindicated;
• Willing to provide written informed consent prior to the conduct of any study specific procedures;
• Understands and is willing and able to comply with study requirements, including the schedule of follow-up visits

Key Exclusion Criteria:

• Prior exposure to any experimental or marketed uricase (e.g., pegloticase [Krystexxa®], pegadricase [SEL-037], rasburicase [Elitek, Fasturtec]);
• History of anaphylaxis or severe allergic reactions to medications;
• History of any allergy to pegylated products
• Drugs known to interact with Rapamune cannot be used during the trial;
• Uncontrolled diabetes;
• Glucose-6-phosphate dehydrogenase (G6PD) deficiency;
• Uncontrolled hypertension;
• Participants whose arrhythmia is unstable on current treatment;
• History of coronary artery disease, including myocardial infarction or unstable angina, within the last 6 months;
• Congestive heart failure;
• History of hematological disorders within 1 year or autoimmune disorders, is immunosuppressed or immunocompromised;
• Has received an inactivated vaccine in the previous 3 months or has received a live virus vaccine in the previous 6 months;
• Is planning to receive any vaccination or live virus vaccination during the study;