Study of Pegloticase in Participants With Uncontrolled Gout Who Have Had a Kidney Transplant

- Willing and able to give informed consent; - Willing and able to comply with the prescribed treatment protocol and evaluations for the duration of the study; - Adult men or women ≥ 18 years of age; - Is a recipient of a de novo kidney from a living or deceased donor and is >1 year post transplant prior to screening; - Is on a stable standard of care immunosuppression therapy for at least 3 months prior to screening; - Kidney allograft is functional at entry, based on an estimated glomerular filtration rate (eGFR) ≥ 15 mL/min/1.73m²; - Women of childbearing potential have a negative screening serum pregnancy test and will be required to use a medically approved form of birth control during their participation in the study; - Uncontrolled gout, defined as: a. Hyperuricemia during screening as documented by sUA ≥ 7 mg/dL during Screening and prior to entry into the Treatment Period (Note: the sUA may be repeated up to 3 times during the Screening Period to confirm eligibility), and b. Inability to maintain sUA <6 mg/dL on other urate-lowering therapy or intolerable side effects or contraindicated with conventional urate-lowering therapy, and c. At least 1 of the following: i. Evidence of tophaceous deposits; ii. Recurrent gout flares defined as 2 or more flares in the 12 months prior to Screening; iii. Presence of chronic gouty arthritis; - Able to tolerate low-dose prednisone (< 10 mg/day) as part of the required standard gout flare prophylaxis regimen for ≥ 1 week before the first infusion.

- Any other organ transplant beside kidney; - Any severe infection, unless treated and completely resolved at least 2 weeks prior to Day 1; - Chronic or active hepatitis B virus infection; - Known history of hepatitis C virus ribonucleic acid (RNA) positivity unless treated and viral load is negative; - Known history of human immunodeficiency virus (HIV) positivity; - Glucose-6-phosphate dehydrogenase (G6PD) deficiency (tested at the Screening Visit); - Decompensated congestive heart failure or hospitalization for congestive heart failure within 3 months of the Screening Visit, uncontrolled arrhythmia, treatment for acute coronary syndrome (myocardial infarction or unstable angina), or uncontrolled blood pressure (> 160/100 mm Hg) at the end of the Screening Period (Day 1 prior to infusion); - Pregnant, planning to become pregnant, breastfeeding, planning to impregnate female partner, or not using an effective form of birth control, as determined by the Investigator; - Prior treatment with pegloticase, another recombinant uricase (rasburicase), or concomitant therapy with a polyethylene glycol-conjugated drug; - Known allergy to pegylated products or history of anaphylactic reaction to a recombinant protein or porcine product; - Receipt of an investigational drug within 4 weeks or 5 half-lives, whichever is longer, prior to Day 1, or plans to take an investigational drug during the study; - Currently receiving systemic or radiologic treatment for ongoing cancer; - History of malignancy within 5 years other than non-melanoma skin cancer, in situ carcinoma of cervix, early stage renal cell cancer or early stage prostate cancer that has been completely resected > 2 years prior to screening; - Uncontrolled hyperglycemia with a plasma glucose value > 240 mg/dL at Screening that is not subsequently controlled by the end of the Screening Period; - Diagnosis of osteomyelitis; - Known history of hypoxanthine-guanine phosphoribosyl-transferase deficiency, such as Lesch-Nyhan and Kelley-Seegmiller syndrome; - Unsuitable candidate for the study, based on the opinion of the Investigator (e.g., cognitive impairment), such that participation might create undue risk to the subject or interfere with the subject’s ability to comply with the protocol requirements or complete the study; - Currently receiving allopurinol, febuxostat or other urate lowering medications and unable to discontinue medication 7 days prior to Day 1; or - Currently receiving probenecid and unable to discontinue medication within 3 days, prior to Day 1.