A Phase 2, Randomized, Placebo-controlled, Double-blind Clinical Study to Evaluate Efficacy and Safety of LAD603 in Adult Subjects With Severe to Very Severe Alopecia Areata

Inclusion Criteria: * Participant is a male or female between 18 and 65 years old at the time of signing the informed consent. * Severe to very severe AA criteria: 1. Greater than or equal to (\>=) 50% hair loss of the scalp as measured by SALT without evidence of terminal hair regrowth within 6 months at both the Screening and Baseline (Day 1) visits. 2. Current episode of hair loss lasting at least 6 months and not exceeding 7 years. * Participants who are WOCBP or male must agree to the requirements for the avoidance of pregnancy and exposure of the participant's partner to LAD603 dur…