A Study With GB004 in Adult Subjects With Active Ulcerative Colitis (UC)

Inclusion Criteria:

• Adult male and female subjects aged ≥ 18 years at the time of signing the informedconsent form (ICF) prior to initiation of any study specific activities/procedures.
• UC diagnosed at least 3 months prior to first dose of investigational product (IP) onDay 1.
• Currently receiving treatment for UC, on a stable dose for at least 2 weeks prior toflexible sigmoidoscopy or colonoscopy, with oral 5-ASA (eg, mesalamine, sulfasalazine)alone or with one of the following oral treatments:

1. prednisone ≤ 20 mg/day or equivalent or
2. beclomethasone ≤ 5 mg/day or
3. budesonide or budesonide multi-matrix (MMX) of ≤ 9 mg/day

Exclusion Criteria:

• Prior approved biologic therapy used for the treatment of UC.
• Diagnosis of Crohn's disease, indeterminate colitis, or pouchitis, or presence ofbacterial or parasitic infection.
• Tofacitinib, oral cyclosporine, sirolimus or mycophenolate mofetil within 8 weeks ofDay 1.
• Azathioprine, or 6-mercaptopurine within 1 day of Day 1. NOTE: Other Inclusion/Exclusion criteria may apply per protocol.