A Study to Evaluate the Safety and Efficacy (How Well the Study Treatment Works) of ABBV-2294 in Adult Participants With Systemic Sclerosis That Are Currently Receiving Local Standard of Care Treatment, and to Determine the Best Dose of ABBV-2294 to be Evaluated Further.

Systemic sclerosis (SSc), also called scleroderma, is a rare long-term autoimmune disease that causes the body to make too much collagen (scar tissue), leading to hard, thick skin and sometimes damage to organs such as the lungs, heart, kidneys, or digestive system. An autoimmune disease is a condition where the body's immune system, which normally protects against germs, mistakenly attacks its own healthy tissues and organs.

The study has 2 parts. The main goal of Part 1 is to evaluate the safety and efficacy (how well the study treatment works) of ABBV-2294 (combination of ABBV-722 and upadacitinib) in adult participants with SSc that are currently receiving local standard of care treatment, and to determine the best dose of ABBV-2294 to be evaluated further. The main goal of Part 2 is to evaluate the safety and efficacy of the dose of ABBV-2294 determined in Part 1 when compared to placebo (looks like the study treatment but has no medicine in it) in adult patients with SSc that are currently receiving local standard of care treatment. Participants will undergo trial-related procedures throughout the study which may include physical exams, questionnaires, scans and imaging, and blood and urine tests.

ABBV-2294 (combination of ABBV-722 and upadacitinib) is an investigational drug being developed for the treatment of SSc in adult participants. At the start of Part 1, participants will be randomly assigned to receive Dose 1 of ABBV-722 and upadacitinib given together, Dose 2 of ABBV-722 and upadacitinib given together, ABBV-722 given alone, upadacitinib given alone, or placebo for 52 weeks. Participants that complete 52 weeks of treatment will be invited to join a 56-week extension period.

Participants that join Part 2 will be randomly assigned to receive either ABBV-2294 (dose determined in Part 1) or placebo for 52 weeks. Participants that complete 52 weeks of treatment will be invited to join a 104-week extension period. All participants that join the extension will receive ABBV-2294.

Participants 18 years of age and older diagnosed with Systemic sclerosis (SSc). Around 580 participants will be enrolled at approximately 200 sites worldwide.

Participants will receive upadacitinib and/or ABBV-722 oral tablets (or matching placebo) for 52 weeks in Part 1 with an optional 56-week extension period. Part 2 participants will receive ABBV-2294 (dose determined in Part 1) or matching placebo for 52 weeks with an optional 104-week extension period of open label ABBV-2294 (dose determined in Part 1).

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