The 48-week, phase 2 SLEek study (NCT03978520) evaluated the efficacy and safety of upadacitinib (Janus kinase inhibitor) and elsubrutinib (Bruton's tyrosine kinase inhibitor) alone or in combination (ABBV-599) in adults with moderately to severely active systemic lupus erythematosus (SLE). Patients were randomized 1:1:1:1:1 to once-daily (QD) ABBV-599 high dose (HD; elsubrutinib 60mg + upadacitinib 30mg), ABBV-599 low dose (LD; elsubrutinib 60mg + upadacitinib 15mg), elsubrutinib 60mg, upadacitinib 30mg, or placebo. The primary endpoint was the proportion of patients achieving both SLE Responder Index-4 (SRI-4) and glucocorticoid dose ≤10mg 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. The study enrolled 341 patients. The ABBV-599LD 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-599HD (48.5%; P=0.081) versus placebo (37.3%). SRI-4, BICLA, and LLDAS response rates were higher for both upadacitinib and ABBV-599HD 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-599HD versus placebo. No new safety signals were observed beyond those previously reported for upadacitinib or elsubrutinib. Upadacitinib 30mg alone or in combination with elsubrutinib (ABBV-599HD) demonstrated significant improvements in SLE disease activity, reduced flares and were well tolerated through 48 weeks.