The purpose of the study is to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of a single dose of UB-221 as an add-on therapy in patients with Chronic Spontaneous Urticaria.

This is a phase I, open-label, dose-escalation study to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of a single dose of UB-221 as an add-on therapy in patients with Chronic Spontaneous Urticaria.

Inclusion Criteria:

• Subjects with age between 20 to 65 years old (inclusive).
• Subjects who are able and willing to provide the informed consent.
• Male subjects with body weight of 50 kilogram (kg) or above; female subjects body weight of 45 kilogram (kg) or above.
• Subjects diagnosed with chronic spontaneous urticaria (CSU).

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 is not suitable to participate in this study.