This study is testing a medicine called Rezpegaldesleukin (Rezpeg) for adults with Severe to Very Severe Alopecia Areata, a condition causing hair loss. The study is randomized, double-blind, and placebo-controlled. This means participants are randomly assigned to groups, neither they nor the researchers know which group they are in, and some participants will receive a placebo, which has no active medicine.

The study lasts up to 81 weeks and includes initial screening, treatment, and follow-up. Participants must be adults, have significant hair loss, and not have used specific treatments before. Women must test negative for pregnancy and use birth control if needed. The study excludes those unwilling to use birth control, those with other forms of alopecia, or those with certain medical conditions or past treatments.

• Study duration is about 81 weeks, including treatment and follow-up.
• Participants must not have used specific alopecia treatments before.
• Women must use effective birth control and test negative for pregnancy.