Long-term Safety and Efficacy of Efavaleukin Alfa in Participants With Moderately to Severely Active Ulcerative Colitis

Inclusion Criteria: * Participant has provided informed consent prior to initiation of any study specific activities/procedures. * Participant has completed the week 52 endoscopy in the phase 2 dose-finding parent study (20170104) and who in the opinion of the investigator may benefit from continued treatment. Exclusion criteria: * Permanent discontinuation of investigational product during the 52- week phase 2 dose finding parent study (20170104) for any reason * Female subjects of reproductive potential must agree not to donate eggs during the study and for 6 weeks after receiving the last dose of investigational product. Disease Related: * Adenoma and dysplasia exclusion criteria: * Any current sporadic adenoma without dysplasia (adenomatous polyps occurring proximal to known areas of colitis) that has not been removed. * Dysplasia occurring in flat mucosa, sporadic adenomas containing dysplasia, and dysplasia-associated lesions or masses will be managed as follows: * Any history or current evidence of high-grade dysplasia. * Any history or current evidence of dysplasia occurring in flat mucosa. * This includes histopathology reporting indefinite for dysplasia, low-grade dysplasia, and high-grade dysplasia. * Any history or current evidence of a nonadenoma like dysplasia associated lesions or masses, with or without evidence of dysplasia. * Any current sporadic adenoma containing dysplasia or any current adenoma-like dysplasia-associated lesions or masses that ha…