Rezpeg Produces Meaningful Hair Regrowth at One Year in Severe Alopecia Areata, Phase 3 Plans Announced

Alopecia areata is an autoimmune disease in which the immune system mistakenly targets hair follicles, causing hair to fall out in patches or, in severe cases, across the entire scalp or body. It is unpredictable, can be deeply distressing, and until recently had very few treatment options beyond watchful waiting. The approval of JAK inhibitors in recent years represented a genuine turning point, but those drugs come with safety concerns that have made physicians cautious about prescribing them broadly. Now, new data from a mid-stage clinical trial suggest that a different type of drug, one that works by reshaping immune regulation rather than broadly suppressing it, may offer comparable results with a more favorable tolerability profile.

Nektar Therapeutics announced on April 20, 2026, that extended treatment with its investigational drug rezpegaldesleukin, commonly referred to as rezpeg, promoted meaningful hair regrowth in people with severe-to-very-severe alopecia areata after one year. The results come from a blinded treatment extension of the Phase 2b REZOLVE-AA study. The primary benchmark the trial used is the SALT score, a standardized scale that measures what percentage of the scalp is affected by hair loss. The headline outcome, SALT Score 20, means that 80 percent or more of the scalp is covered by hair, which represents a clinically meaningful level of regrowth for someone who may have lost most or all of their scalp hair. At the 52-week mark, 27 percent of participants in both the low-dose and high-dose rezpeg groups achieved that threshold.

The trial also measured a slightly less stringent marker, SALT Score 30, meaning at least 70 percent of the scalp is covered. At 52 weeks, 30.2 percent of participants on the low dose and 35 percent on the high dose achieved this outcome, compared to just 8.4 percent in the placebo group. Nektar noted that the drug's results compare favorably to those seen with low-dose baricitinib, a JAK inhibitor sold under the brand name Olumiant and currently approved for severe alopecia areata, though the two drugs have not been tested head to head in a direct comparison trial.

Rezpeg works through a different mechanism than JAK inhibitors. It is a modified version of interleukin-2, a signaling protein that plays a central role in immune regulation, and it works specifically by expanding regulatory T cells, the branch of the immune system responsible for preventing the immune response from overreacting and attacking the body's own tissues. The idea is that by reinforcing this self-regulating immune pathway rather than broadly blocking immune activity, rezpeg could restore tolerance to hair follicles without the systemic immune suppression that raises infection and cancer-related safety flags. The safety profile observed in the REZOLVE-AA trial was described as favorable and consistent with earlier results. Nektar has said it plans to advance rezpeg into a Phase 3 pivotal trial for alopecia areata later in 2026, which would be the next required step toward a potential approval. Three JAK inhibitors are currently FDA-approved for severe alopecia areata: baricitinib, ritlecitinib, and deuruxolitinib. Rezpeg, if it continues to perform well in larger studies, would represent the first approved treatment for the condition that works through an IL-2 regulatory mechanism, potentially offering an important option for patients who cannot tolerate or do not respond to the existing therapies.