1. Serum uric acid control during month 6 [6 months]
   The percentage of patients who achieve and maintain reduction in serum uric acid (sUA) < 6 mg/dL for at least 80% of the time during month 6 in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo

1. Reduction of mean serum uric acid [6 months]
   To assess changes in mean serum uric acid in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
2. Percent reduction of mean serum uric acid [6 months]
   To assess percent changes in mean serum uric acid in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
3. SF-36 [6 months]
   To assess change in Patient Reported Outcomes (PROs) including assessments of: patients' quality of life (QoL) (SF-36) in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
4. Tophus burden [6 months]
   To assess change in tophus burden by photographic area assessment in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
5. Serum uric acid control in patients with tophi [6 months]
   To assess change in the percentage of patients with tophi at baseline who achieve and maintain reduction in serum uric acid (sUA) < 6 mg/dL for at least 80% of the time during month 6 in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
6. Tender and Swollen Joint Counts [6 months]
   To assess changes in number of tender and swollen joints in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
7. HAQ-DI [6 months]
   To assess change in Patient Reported Outcomes (PROs) including assessments of: activity limitation (HAQ-DI) in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo
8. Gout Flare Incidence [6 months]
   To assess changes in gout flare incidence in patients with gout refractory to conventional treatment treated with two different dose levels of SEL-212 compared to placebo

• Chronic Gout

Drug: SEL-212 low-dose

IV infusion of SEL-212 low-dose every 28 days for a total of up to 12 infusions

Experimental: SEL-212 low-dose
SEL-212 low-dose Drug: SEL-037 (0.2 mg/kg) SEL-037, PEGylated uric acid specific enzyme (uricase) Other Names: Pegadricase, pegsiticase Drug: SEL-110.36 (0.1 mg/kg) SEL-110.36, ImmTOR

• Drug: SEL-212 low-dose

Experimental: SEL-212 high-dose
SEL-212 high-dose Drug: SEL-037 (0.2 mg/kg) SEL-037, PEGylated uric acid specific enzyme (uricase) Other Names: Pegadricase, pegsiticase Drug: SEL-110.36 (0.15 mg/kg) SEL-110.36, ImmTOR

• Drug: SEL-212 high-dose

Placebo Comparator: Placebo
Normal saline

• Other: Normal Saline

Inclusion Criteria:

• Has negative results of an FDA Emergency Use Authorized COVID-19 molecular assay for detection of SARS-CoV-2 RNA from a nasal or oropharyngeal specimen;
• History of symptomatic gout defined as:
• ≥ 3 gout flares within 18 months of Screening or
• Presence of ≥ 1 gout 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 nonchildbearing potential is defined as:
• a. > 6 weeks after hysterectomy with or without surgical bilateral salpingooperhectony or b. Post-menopausal (> 24 months of natural amenorrhea or in the absence of >24 months of amenorrhea, one documented confirmatory FSH measurement)
• Has chronic refractory gout defined as having failed to normalize sUA and whose signs and symptoms are inadequately controlled with any of the xanthine oxidase inhibitors, or for whom these drugs are contraindicated for the patient;
• Has at the Screening Visit SUA ≥ 7 mg/dL
• Negative serology for HIV-1/-2 and negative antigen to hepatitis B and negative antibodies to hepatitis C;

Exclusion Criteria:

• Has a history of anaphylaxis, severe allergic reactions, or severe atopy;
• Has a history of any allergy to pegylated products, including, but not limited to pegloticase (Krystexxa®), peginterferon alfa-2a (Pegasys®), peginterferon alfa-2b (PegIntron®), pegfilgrastim (Neulasta®), pegaptanib (Macugen®), pegaspargase (Oncaspar®), pegademase (Adagen®), peg-epoetin beta (Mircera®), pegvisomant (Somavert®) certolizumab pegol (Cimzia®), naloxegol (Movantik®), peginesatide (Omontys®), and doxorubicin liposome (Doxil®);
• Is taking and cannot discontinue known major CYP3A4/P-gp inhibitors or major CYP3A4/P-gp inducers at least 14 days before dosing. Patients must remain off these medications for the duration of the study, including natural products such as St. John's Wort or grapefruit juice.
• Is taking drugs known to interact with rapamycin (sirolimus - Rapamune®) such as cyclosporine, diltiazem, erythromycin, ketoconazole, posaconazole, voriconazole, itraconazole, rifampin, verapamil unless they are stopped 14 days prior to dosing and will not be used/prescribed during the trial.
• Had major surgery within 3 months of initial screening.
• Had a gout flare during Screening that was resolved for less than 1 week prior to first treatment with study drug (exclusive of chronic synovitis/arthritis) unless the patient has a history of inter-flare intervals of < 1 week.
• Has uncontrolled diabetes at Screening with HbA1c ≥ 8.5%;
• Has fasting Screening glucose > 240 mg/dL;
• Has fasting Screening triglyceride > 500 mg/dL;
• Has fasting Screening low-density lipoprotein (LDL) > 200 mg/dL;
• Has glucose-6-phosphate dehydrogenase (G6PD) deficiency;
• Has uncontrolled hypertension defined as blood pressure > 170/100 mmHg at Screening and 1 week prior to dosing
• Individual laboratory values which are exclusionary
• White blood cell count (WBC) < 3.0 x109/L
• Serum aspartate aminotransferase (AST) or alanine amino transferase (ALT) > 3x upper limit of normal (ULN) in the absence of known active liver disease
• Estimated glomerular filtration rate (eGFR) < 30 mL/min/1.73 m2
• Urine albumin creatinine ratio (UACR) > 30 mg/g
• Hemoglobin (Hgb) < 9 g/dL
• Serum phosphate < 2.0 mg/dL
• Is receiving ongoing treatment for arrhythmia, including placement of an implantable defibrillator, unless considered stable and on active treatment;
• Has evidence of unstable cardiovascular disease or unstable cerebrovascular vascular disease. This includes patients who have had a cardiac/vascular event(s) in the last 3 months including heart attack, stroke or vascular bypass surgery or patients who are deemed, by their physician or PI, to have active cardiovascular, cerebrovascular or peripheral vascular symptoms/disease inadequately controlled by medication;
• Has congestive heart failure, New York Heart Association Class III or IV;
• Unless clinically stable and/or appropriately treated, electrocardiogram (ECG) with evidence of clinically significant arrhythmia or other abnormalities that, in the opinion of the investigator, are consistent with significant underlying cardiac disease;
• History of significant hematological disorders within 5 years or autoimmune disorders, and/or patient is currently immunosuppressed or immunocompromised;
• Prior exposure to any experimental or marketed uricase (e.g., rasburicase (Elitek, Fasturtec), pegloticase (Krystexxa®®), pegadricase (SEL 037))
• Patient has received a live vaccine in the previous 6 months.
• Patient is planning to receive any live vaccine during the study.
• History of malignancy within the last 5 years other than basal skin cancer;
• Patients with a documented history of moderate or severe alcohol or substance use disorder within the 12 months prior to randomization.
• History of or evidence of clinically severe interstitial lung disease
• Immunocompromised state, regardless of etiology

Studies a U.S. FDA-regulated Drug Product: Yes

Studies a U.S. FDA-regulated Device Product: No

Product Manufactured in and Exported from the U.S.: Not Provided