A Study of the Safety of Oral Elsubrutinib Capsules and Oral Upadacitinib Tablets Given Alone or in Combination (ABBV-599) for Adult Participants With Moderately to Severely Active Systemic Lupus Erythematosus to Assess Change in Disease State

Systemic Lupus Erythematosus (SLE) is an immune-mediated disease associated with inflammation of multiple organ systems. This study will evaluate how well elsubrutinib and upadacitinib given alone or as the ABBV-599 combination (elsubrutinib/upadacitinib) works within the body, in participants who completed study M19-130. This study will assess the change in disease symptoms.

ABBV-599 is an investigational drug being developed for the treatment of Systemic Lupus Erythematosus (SLE). This study is "double-blinded", which means that neither the trial participants nor the study doctors will know who will be given which study drug. Study doctors put the participants into 1 of 4 groups called treatment arms. Each group receives a different treatment. Adult participants with a diagnosis of SLE will be enrolled. Around 260 participants will be enrolled in the study in approximately 100 sites worldwide.

Participants will receive the following for up to 56 weeks:

Participants will receive oral elsubrutinib capsules and/or oral upadacitinib tablets once daily for up to 56 weeks. Participants who were receiving elsubrutinib and/or upadacitnib in M19-130 will continue to receive the same treatment in this study. Participants who were receiving placebo in M19-130 will be re-randomized to one of the 2 combination treatment arms in this study.

Arm 1: Elsubrutinib Dose A and Upadacitinib Dose A Arm 2: Elsubrutinib Dose A and Upadacitinib Dose B

There may be higher burden for participants in this trial compared to their standard of care. Participants will attend monthly visits during the course of the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires.