Efficacy and Safety of GDC-0853 in Participants With Refractory Chronic Spontaneous Urticaria (CSU)

Inclusion Criteria:

- Aged 18−75 years, inclusive

- Diagnosis of chronic spontaneous urticaria (CSU) refractory to H1 antihistamines at
the time of randomization

- Willing and able to complete an Urticaria Participant Daily eDiary for the duration of
the study

- No evidence of active or latent or inadequately treated infection with tuberculosis
(TB)

- Partcipants with a history of Bacille Calmette-Guérin (BCG) vaccination should be
screened using the QuantiFERON-TB-Gold (QFT) test

- Only for participants currently receiving proton-pump inhibitors (PPIs) or H2 receptor
antagonists (H2RAs): Treatment must be at a stable dose during the 2-week screening
period prior to randomization and with a plan to remain at a stable dose for the
duration of the study

- For women of childbearing potential: Agreement to remain abstinent (refrain from
heterosexual intercourse) or use contraceptive methods that result in a failure rate
of <1% per year during the treatment period and for at least 4 weeks after the last
dose of study drug. Women must refrain from donating eggs during this same period.

Exclusion Criteria:

- Treatment with omalizumab or other monoclonal antibody therapies used to treat CSU
within 4 months prior to screening or primary nonresponse to omalizumab

- Use of a non-biologic investigational drug or participation in an investigational
study with a non-biologic drug within 30 days prior to study drug administration on
Day 1 (or within 5 half-lives of the investigational product, whichever is greater)

- Use of a biologic investigational therapy or participation in an investigational study
involving biologic therapy within 90 days or 5 half-lives, whichever is greater, prior
to study drug administration on Day 1

- Previous treatment with GDC-0853 or other Bruton's tyrosine kinase (BTK) inhibitors

- Participants whose urticaria is solely due to physical urticaria

- Other diseases with symptoms of urticaria or angioedema, including urticarial
vasculitis, urticaria pigmentosa, erythema multiforme, mastocytosis, hereditary or
acquired angioedema, lymphoma, or leukemia

- Atopic dermatitis, bullous pemphigoid, dermatitis herpetiformis, or other skin disease
associated with itch such as psoriasis

- Routine doses of the following medications within 30 days prior to screening: systemic
or cutaneous (topical) corticosteroids (prescription or over the counter),
hydroxychloroquine, methotrexate, cyclosporine, or cyclophosphamide

- Prior utilization of intravenous (IV) steroids for treatment of laryngeal angioedema

- Intravenous immunoglobulin G (IV IG) or plasmapheresis within 30 days prior to
screening

- History of anaphylactic shock without clearly identifiable avoidable antigen

- Hypersensitivity to GDC-0853 or any component of the formulation

- Major surgery within 8 weeks prior to screening or surgery planned prior to end of
study (12 weeks after randomization)

- Require any prohibited concomitant medications

- History of live attenuated vaccine within 6 weeks prior to randomization or
requirement to receive these vaccinations at any time during study drug treatment

- Evidence of clinically significant cardiac, neurologic, psychiatric, pulmonary, renal,
hepatic, endocrine, metabolic, or gastrointestinal (GI) disease that, in the
investigator's opinion, would compromise the safety of the participant, interfere with
the interpretation of the study results or otherwise preclude participant
participation

- Current treatment with astemizole, terfenadine, and/or ebastine

- Uncontrolled disease states, such as asthma, psoriasis, or inflammatory bowel disease,
where flares are commonly treated with oral or parenteral corticosteroids