A Study of LAD603 in Adults With Alopecia Areata

Inclusion Criteria:

• Participant is a male or female between 18 and 65 years old at the time of signingthe informed consent.

• Severe to very severe AA criteria:

1. Greater than or equal to (>=) 50% hair loss of the scalp as measured by SALTwithout evidence of terminal hair regrowth within 6 months at both theScreening and Baseline (Day 1) visits.

2. Current episode of hair loss lasting at least 6 months and not exceeding 7years.

• Participants who are WOCBP or male must agree to the requirements for the avoidanceof pregnancy and exposure of the participant's partner to LAD603 during the study,

Exclusion Criteria:

AA, Skin Specific, and Other Inflammatory Diseases

• Participants have other types of alopecia (including but not limited to traction,scarring alopecia).

• Participants with "diffuse" type AA.

• Currently has an active form of other inflammatory skin disease(s) or evidence ofskin condition (e.g., psoriasis, seborrheic dermatitis, lupus) at the time of theScreening or Baseline (Day 1) visits that is expected to interfere with theassessment of alopecia areata severity.

Other Medical Conditions

• Participant has previous severe adverse reaction to subcutaneously administeredmedication.

• Participant has any of the following liver safety laboratory results at Screening

1. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) greater thanor equal to (>=) 2.5 × upper limit of normal (ULN)

2. Total bilirubin (TBL) >=1.5 × ULN (TBL >=3 × ULN in participants with Gilbert'ssyndrome)

3. Alkaline phosphatase (ALP) >=1.5 × ULNPrior/Concomitant Therapy

• Intention to use any concomitant medication that is not permitted by this protocolor failure to undergo the required washout period for a particular prohibitedmedication.