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Background: Uncontrolled/refractory gout patients are recalcitrant/intolerant to oral urate-lowering therapies (ULTs), experiencing frequent gout flares, functionally limiting tophi, and low quality of life. Pegloticase lowers urate, but anti-pegloticase antibodies limit urate-lowering efficacy and increase infusion reaction (IR) risk. Immunomodulator + pegloticase co-administration may improve treatment response rates, with 79% of MIRROR open-label trial (MIRROR-OL, pegloticase + oral methotrexate) participants meeting 6-month response criteria. Exploratory outcomes from MIRROR-OL are described here., Methods: Adults with uncontrolled gout (serum urate [SU] ≥ 6 mg/dL and ULT-intolerance/recalcitrance or functionally limiting tophi) were included. Oral methotrexate (15 mg/week) was administered 4 weeks before and during pegloticase treatment (biweekly 8 mg infusion, ≤ 52 weeks). Exploratory outcomes included change from baseline (CFB) in number of affected joints, Health Assessment Questionnaires (HAQs), and Gout Global Assessments., Results: Fourteen patients received ≥ 1 pegloticase infusion, with 13 included in 52-week analyses (1 enrolled before treatment-extension amendment, exited at 24 weeks). Three patients prematurely exited due to SU rise; 10 completed 52-week evaluations (8 completed 52 weeks of co-therapy, 2 completed 24 weeks [met treatment goals]). At 52 weeks, SU averaged 1.1 ± 2.5 mg/dL, with improvements in HAQ pain and health (CFB: - 33.6 and - 0.7, respectively), Patient and Physician Global Assessments (CFB: - 4.6 and - 5.7, respectively), and joint involvement (CFB: - 5.6, - 8.4, - 6.0 tender, swollen, tophi-affected joints, respectively). Two patients underwent dual-energy computed tomography, showing concomitant monosodium urate volume reductions. All patients had ≥ 1 AE, with 92.9% experiencing acute flare. One mild IR ("cough") occurred and no new safety signals were identified., Conclusion: Pegloticase + methotrexate co-therapy resulted in sustained SU-lowering with meaningful improvements in clinical measures, urate burden, and patient-reported outcomes., Trial Registration: ClinicalTrials.gov (NCT03635957)., (© 2022. The Author(s).)