The study is to evaluate the profiles of safety, tolerability, pharmacokinetics, and pharmacodynamics of UB-221. In this study, safety profile of UB-221 and maximum tolerated dose (MTD) is to be investigated using sentinel dosing strategy. The starting dose of 0.2 mg/kg is selected based on the evaluation and comparison of various approaches including NOAEL, MABEL (minimum anticipated biological effect level), and experiences from other anti-IgE mAb drugs in development.

This is a phase I, randomized, single-blind, placebo-controlled, parallel group, single ascending dose study to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of a single dose of UB-221 as an add-on therapy in chronic spontaneous urticaria (CSU) subjects who fail to respond to the first line H1-antihistamine treatment. Only the qualified subjects will be blinded to receive treatment. Each subject will receive only one dose of UB-221 or placebo.

Inclusion Criteria:

• Subjects aged ≥ 18 years
• Subjects who are able and willing to provide the informed consent
• Subjects diagnosed with chronic spontaneous urticaria (CSU) for more than six weeks prior to the screening visit as confirmed by investigators based on medical history.

Exclusion Criteria:

• History of significant diseases (other than CSU) or major clinical conditions by the investigator's judgment, such as auto-immune disease or psychiatric and behavioral conditions from which the investigator considers the subject not suitable to participate in this study.