This is a Phase 1b, randomized, double-blind-, placebo-controlled, multi-center study to evaluate the safety, tolerability, and PK of GB004 in adult subjects with active ulcerative colitis. Target engagement and effect of GB004 on pharmacodynamic biomarkers will be assessed.

The safety, tolerability, pharmacokinetics, and pharmacodynamics of GB004 will be explored in a Phase 1b randomized controlled trial in adults subjects with active ulcerative colitis (UC). Subjects will be evaluated based on incidence of AEs, laboratory parameters, GB004 serum and colonic tissue concentrations, and changes in the signs and symptoms of UC.

Inclusion Criteria:

• Patients aged 18-74, receiving therapy for active ulcerative colitis confirmed by Mayo Score assessment, and evidence of colonic inflammation.

Exclusion Criteria:

• Evidence of Crohn's disease, indeterminate colitis, or presence of bacterial or parasitic infection.
• Patients receiving biologic agents and experimental agents are excluded.