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Objective: The 48‐week, phase 2 SLEek study (NCT03978520) evaluated the efficacy and safety of upadacitinib (JAK inhibitor) and elsubrutinib (BTK inhibitor) alone or in combination (ABBV‐599) in adults with moderately to severely active systemic lupus erythematosus (SLE). Methods: Patients were randomized 1:1:1:1:1 to elsubrutinib 60 mg and upadacitinib 30 mg once daily (ABBV‐599 high dose), elsubrutinib 60 mg and upadacitinib 15 mg once daily (ABBV‐599 low dose), elsubrutinib 60 mg once daily (QD), upadacitinib 30 mg QD, or placebo QD. The primary endpoint was the proportion of patients achieving both Systemic Lupus Erythematosus Responder Index 4 (SRI‐4) and glucocorticoid dose ≤10 mg QD at week 24. Additional assessments through week 48 included British Isles Lupus Assessment Group‐Based Composite Lupus Assessment (BICLA) and Lupus Low Disease Activity State (LLDAS) responses, number of flares, time to first flare, and adverse events. Results: The study enrolled 341 patients. The ABBV‐599 low dose and elsubrutinib arms were discontinued after a planned interim analysis showed lack of efficacy (no safety concerns). More patients achieved the primary endpoint with upadacitinib (54.8%; P = 0.028) and ABBV‐599 high dose (48.5%; P = 0.081) versus placebo (37.3%). SRI‐4, BICLA, and LLDAS response rates were higher for both upadacitinib and ABBV‐599 high dose versus placebo at weeks 24 and 48. Flares were reduced, and time to first flare through week 48 was substantially delayed with both upadacitinib and ABBV‐599 high dose versus placebo. No new safety signals were observed beyond those previously reported for upadacitinib or elsubrutinib. Conclusion: Upadacitinib 30 mg alone or in combination with elsubrutinib (ABBV‐599 high dose) demonstrated significant improvements in SLE disease activity and reduced flares and were well tolerated through 48 weeks. [ABSTRACT FROM AUTHOR]