Every systemic option in atopic dermatitis works by blocking something — a cytokine, a receptor, a kinase. Rezpegaldesleukin does the opposite: it is an interleukin-2 receptor agonist designed to selectively expand and enhance regulatory T cells, restoring immune regulation rather than suppressing effector signalling. REZOLVE-AD is the phase 2b test of that idea.
Across 107 sites in ten countries, 398 biologic-naive adults with moderate-to-severe atopic dermatitis — EASI at least 16, investigator global assessment at least 3, at least 10% body surface area — were randomised 3:3:3:2 to rezpegaldesleukin 24 micrograms/kg every two weeks, 18 micrograms/kg every two weeks, 24 micrograms/kg every four weeks, or placebo for a 16-week induction period. Three hundred and ninety-three were analysed.
All three dose arms met the primary endpoint, with a clean dose-response. Mean EASI change at week 16 was -61% (SE 3.8), -58% (3.8) and -53% (3.7) against -31% (4.5) for placebo, giving treatment differences of 30 percentage points (95% CI -41.3 to -18.0, p<0.0001), 27 points (-38.5 to -15.7, p<0.0001) and 22 points (-33.3 to -10.3, p=0.0002).
The tolerability signal is specific and worth knowing. Injection-site reactions occurred in 223 of 320 treated patients (70%) against 3 of 73 on placebo (4%) — though over 99% were mild to moderate and resolved. Eosinophilia, pyrexia, headache and arthralgia were each modestly commoner. There was no increase in serious or severe adverse events and no deaths during induction.
What this changes today is not prescribing — this is phase 2b, 16 weeks, and the drug is years from availability. What it changes is the mental model. If enhancing regulatory T cell function produces a 30-point EASI improvement over placebo, that validates immune restoration as a therapeutic strategy in a disease treated entirely by blockade, and the same approach becomes worth watching in other autoimmune skin disease. Two things to weigh before enthusiasm: the placebo arm improved 31%, which is high and typical of atopic dermatitis trials, and a 70% injection-site reaction rate will matter for adherence in a chronic condition however mild each reaction is.
- Phase 2b, 16 weeks — this is a mechanism validated, not a treatment available.
- Dose-response was clean across three regimens, which strengthens the causal claim.
- Expect injection-site reactions in about 7 in 10 patients if this reaches practice.
- The placebo arm improved 31%, a reminder of how much moves in atopic dermatitis trials without active drug.
- Watch this mechanism in other autoimmune skin disease, where blockade is also the only current strategy.
The statistics, in plain English
The clean dose-response is the most persuasive feature: three regimens producing 61%, 58% and 53% improvement in descending order of exposure is the pattern a real pharmacological effect makes, and it is much harder to produce by chance or bias than a single positive comparison. The confidence intervals are wide — 41.3 to 18.0 percentage points for the top dose — which is expected in a phase 2b trial with about 100 patients per arm. Note that missing data were handled by multiple imputation, and that patients from two sites closed for Good Clinical Practice non-compliance were excluded from analysis, which is the right call but means the analysed population is not quite the randomised one.
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