A Study of the Efficacy and Safety of Risankizumab in Subjects With Crohn's Disease Who Responded to Induction Treatment in M16-006 or M15-991

The study consists of 3 sub-studies, as follows: - Sub-study 1 (Randomized, double-blind, placebo controlled study) to evaluate the efficacy and safety of risankizumab versus placebo as maintenance therapy in subjects with moderately to severely active Crohn's disease (CD) who responded to risankizumab induction treatment in Study M16-006 or Study M15-991 - Sub-study 2 (Randomized, exploratory maintenance study) to evaluate the efficacy and safety of two different dosing regimens for risankizumab as maintenance therapy in subjects who responded to induction treatment in Study M16-006 or Study M15-991; - Sub-study 3 (Open-label, long-term extension study) to evaluate long-term safety of risankizumab in subjects who completed Sub-study 1 or 2.