This study aims to evaluate the safety, tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) profiles following multiple subcutaneous injections of YH35324 in healthy subjects or subjects with allergic diseases, who have atopy.

YH35324 is a drug under development as a novel therapeutic agent for various IgE-mediated allergic diseases. Since YH35324 has a high binding affinity to human IgE, it prevents serum IgE from binding to receptors on mast cells and basophil, thereby inhibiting histamine release caused by degranulation when exposed to allergens. This study aims to evaluate the safety, tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) profiles following multiple subcutaneous injections of YH35324 in healthy subjects or subjects with allergic diseases, who have atopy.

Inclusion Criteria:

• Male or female adults aged ≥ 19 to ≤ 55 years(Cohort 5, Mald or female adults ≥ 19)
• Serum total IgE level ≥ 30 IU/mL or 30 to 700 IU/mL or >700IU/mL(Not Applicable for Cohort 5)
• Meeting the following cohort-specific disease severity criteria [Cohorts 1-4]: Healthy subjects without any pathological symptoms or findings from medical examination, or subjects with a history of mild allergic diseases (allergic rhinitis, atopic dermatitis, food allergy, urticaria, or allergic asthma) [Cohort 5]: Subject who have been diagnosed with moderate to severe atopic dermatitis

Exclusion Criteria:

• History of malignancy
• Positive drug screen result
• transaminase (AST) or alanine transaminase (ALT) level > 2 X the upper limit of normal
• Estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2 using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula
• Allergy immunotherapy initiated or changed within 6 months prior to randomization(For Cohort 5, within 12 months prior to randomization)
• History of participation in another clinical trial within 6 months prior to randomization

De-identified individual participant data (including data dictionaries) that underline the results reported in study-related publications will be made available during the period beginning 1 year and ending 5 years after all trial primary and secondary endpoints were assessed. Only requests from researchers who provide a methodologically sound proposal will be reviewed and approved by the sponsor. The analysis type should be in accordance with aims in the proposal approved by the sponsor. Proposals should be directed to yhcho@yuhan.co.kr.

A summary of the study results will be posted in the publicly accessible database (i.e. clinicaltrials.gov) no later than 1 year after the study's primary completion date.

Beginning 1 year and ending 5 years after all trial endpoints were assessed

Only requests from researchers who provide a methodologically sound proposal will be reviewed and approved by the sponsor. The analysis type should be in accordance with aims in the proposal approved by the sponsor. Proposals should be directed to yhcho@yuhan.co.kr

As the YH35324 group and placebo group will be double-blinded, YH35324 and placebo will have the same appearance and packaging. Therefore, the double-blind will apply to the subjects, investigators, study coordinators, and study personnel including study pharmacists.

The active control omalizumab has a different appearance and packaging from YH35324 and placebo, and will be administered in an open-label manner.