A Treg-boosting drug cut eczema severity by 61% in a mid-stage trial

An experimental injection called rezpegaldesleukin reduced the severity of moderate-to-severe eczema by 61% over 16 weeks at its highest dose, against a 31% reduction on placebo, in a mid-stage randomised trial published in The Lancet [s1]. What makes the result worth attention is the mechanism: rather than blocking an inflammatory signal, as most modern eczema drugs do, the drug expands regulatory T cells — the immune cells that dial inflammation down — a different strategy that has so far been tested only through this phase 2b study [s1].

Atopic dermatitis, the most common form of eczema, is driven by an overactive type 2 immune response in the skin. The current biologic and small-molecule options, led by the antibody dupilumab and the oral JAK inhibitors, work by intercepting specific inflammatory messengers. Rezpegaldesleukin, an interleukin-2 receptor agonist, instead selectively expands and strengthens regulatory T cells, or Tregs [s1] — the same broad idea being pursued in cell therapies that engineer Tregs directly, but delivered as a conventional drug rather than a bespoke cell product.

What the trial tested

REZOLVE-AD was a phase 2b, randomised, double-blind, placebo-controlled trial run at 107 sites across ten countries, including Australia, Canada, Germany, Spain and the United States [s1]. It enrolled adults with confirmed moderate-to-severe atopic dermatitis who had not previously received a biologic, defined by an Eczema Area and Severity Index (EASI) score of at least 16 and disease affecting at least 10% of the body surface [s1]. Of 398 patients enrolled between November 2023 and January 2025, 393 were analysed, assigned in a 3:3:3:2 ratio to one of three rezpegaldesleukin dosing schedules or to placebo for a 16-week induction period [s1][s2]. The analysed groups comprised 104 patients on 24 μg/kg every two weeks, 106 on 18 μg/kg every two weeks, 110 on 24 μg/kg every four weeks and 73 on placebo; roughly even by sex, at 203 women (52%) and 190 men (48%) [s1]. The published analysis excluded patients from two sites that were closed for Good Clinical Practice non-compliance well before the database was locked — a transparency detail that cuts both ways, signalling active data-quality oversight but also that not every enrolled participant contributed [s1].

All three drug groups met the primary endpoint, the percentage change in EASI score from baseline at week 16 [s1]. The reductions were dose-dependent: 61% (standard error 3.8) with 24 μg/kg every two weeks, 58% (3.8) with 18 μg/kg every two weeks and 53% (3.7) with 24 μg/kg every four weeks, compared with 31% (4.5) on placebo [s1]. The difference between the highest-dose group and placebo was 30 percentage points (95% confidence interval, 18.0 to 41.3), a statistically significant separation [s1].

On safety, injection-site reactions were the most common side effect and were nearly all mild to moderate and resolved; the trial reported no signal of increased serious or severe adverse events and no deaths during the induction period [s1].

What the result does and does not establish

Two cautions matter. First, this is a phase 2b trial: it is designed to find a dose and a signal, not to confirm a drug works, and its 16-week window is short for a chronic relapsing disease that patients manage for years. The authors frame the data as "supporting further development" [s1] — the language of a promising midpoint, not an endpoint. A phase 3 programme, powered for the standard responder measures and run over longer follow-up, is the test that decides whether rezpegaldesleukin reaches patients.

Second, the trial was funded by Nektar Therapeutics, which is developing the drug [s1]. That the results appear in a peer-reviewed independent journal is a meaningful check, but the reported figures still describe the manufacturer's candidate in a manufacturer-funded study, and the more informative comparison — head-to-head against dupilumab or a JAK inhibitor, rather than against placebo — has not been done. A placebo-controlled EASI reduction says the drug beats nothing; it does not say how it stacks up against what patients can already be prescribed.

The genuinely novel element is the Treg-enhancing approach, which if it holds up could matter beyond eczema, across the autoimmune and inflammatory diseases where restraining rather than blocking immunity is the goal [s1]. For now, rezpegaldesleukin is an encouraging mid-stage result with a distinctive mechanism, awaiting the larger trials that will decide its place. This article describes trial findings and is not medical advice.

Sources

• Rezpegaldesleukin treatment of moderate-to-severe atopic dermatitis (REZOLVE-AD) — The Lancet, published online August 2026
• REZOLVE-AD trial registration (NCT06136741) — ClinicalTrials.gov