This study is looking at a new treatment called RO7790121 for people with ulcerative colitis (UC). UC is a condition where the colon (large intestine) becomes swollen and painful. The study will compare RO7790121 to a placebo, which is a sugar pill with no medicine.

To join, you need to have UC that is moderately to severely active and weigh at least 40 kilograms (about 88 pounds). You should have tried other treatments that didn’t work well for you. You cannot join if you have other similar conditions, certain infections, or if you are pregnant.

• The study is double-blind, meaning neither you nor the researchers will know who is getting the real medicine or the placebo.
• Participants will be monitored for how well the medicine works and any side effects.
• This study is carried out at several locations, so you may need to visit these places for check-ups.

Make sure you talk to your doctor to see if this study is right for you.