• Written informed consent after the nature of the trial has been fully explained and before performing any trial related assessments

• Males and females, ≥18 years old

• i. For Cohorts 1, 2, 3, 4a, 4b, 5, 5b, 6 and 7: Diagnosis of symptomatic CSU despite treatment as defined by:

‣ Diagnosis of CSU for ≥ 6 months

⁃ The presence of itch and hives for ≥ 8 consecutive weeks at any time prior to Screening despite current use of H1-antihistamines (as reported by the participant)

⁃ The presence of itch and hives for ≥ 8 consecutive weeks at any time prior to Screening despite treatment with omalizumab or intolerance to omalizumab (as reported by the participant)

⁃ UAS7 of ≥ 16 and ISS7 of ≥ 8 on 7 consecutive days between Day -10 through Day-1 of Screening

• ii. For Cohorts 8 and 9: Diagnosis of symptomatic CSU despite treatment as defined by:

⁃ Diagnosis of CSU for ≥ 6 months (as per local and international guidance)

⁃ The presence of itch and hives for ≥ 8 consecutive weeks at any time prior to Screening despite current use of H1-antihistamines (as reported by the participant)

⁃ Participants may be omalizumab naïve or have been previously exposed to omalizumab independent of treatment duration or response

⁃ UAS7 of ≥ 16 and ISS7 of ≥ 8 on 7 consecutive days between Day -10 through Day -1 of Screening

• Use of H1-antihistamines on stable dose up to four-fold of the approved dose since Screening and not expected to change during first 12 weeks of the trial

• Blood counts at Screening with:

‣ Hemoglobin: ≥ 11 g/dl

⁃ Platelets: ≥ 100,000/mm3

⁃ Leucocytes: ≥ 3,000/mm3

⁃ Neutrophils: ≥ 2,000/mm3

• Willing and able to complete a daily diary for the duration of the trial and adhere to the trial visit schedule