Nektar Therapeutics (Nasdaq: NKTR) reported that rezpegaldesleukin, its investigational IL-2 pathway agonist, continued to generate new hair growth responses through 52 weeks in patients with severe-to-very-severe alopecia areata, with the proportion achieving a clinically meaningful scalp coverage threshold rising from week 36 to week 52 in both dose arms of the Phase IIb REZOLVE-AA trial.
Nektar indicated that the 52-week data support advancement into late-stage trials in alopecia areata, with specifics of the registrational program not disclosed. Following the data release, Nektar moved to raise USD 250 million through a public offering to support ongoing development.
Trial specifics
The REZOLVE-AA study is a randomized, placebo-controlled, global Phase IIb trial that enrolled 92 patients with severe-to-very-severe alopecia areata who had not previously received a JAK inhibitor or other biologic, across approximately 30 sites in Poland, Canada, and the United States.
At week 52, 25.8% of patients in the 18 µg/kg arm and 27.6% in the 24 µg/kg arm achieved a SALT score ≤20 — meaning at least 80% scalp hair coverage — compared with 6.7% on placebo (exploratory p=0.049). Both figures rose from 14.8% and 15.6%, respectively, at week 36, while the placebo rate was unchanged. Among the 31 patients who entered the blinded 16-week extension, 29% in the low-dose arm and 31% in the high-dose arm achieved new SALT ≤20 responses between weeks 36 and 52, versus none on placebo. SALT ≤30 rates at week 52 were 30.2% and 35.0% for the two active arms versus 8.4% for placebo (exploratory p=0.023). No patients discontinued during the extension due to a treatment-emergent adverse event, and injection site reactions — predominantly mild erythema resolving within five days — were the most common adverse events reported.
Several interpretive caveats apply. The 52-week analyses used a modified intent-to-treat adapted population with carry-forward imputation for patients who did not enter the extension, and the reported p-values are described by the sponsor as exploratory rather than confirmatory. Only 31 of 92 enrolled patients entered the extension, and the placebo extension arm comprised just four individuals, limiting the precision of any cross-arm comparison at that timepoint.
The competitive context
The competitive context for these data is defined almost entirely by oral JAK inhibitors. Baricitinib (Olumiant), approved by the FDA in June 2022 for adults with severe alopecia areata, was the first systemic therapy to reach the market in this indication. Ritlecitinib (Litfulo), a JAK3/TEC kinase inhibitor approved in June 2023 for patients aged 12 and older, and deuruxolitinib (Leqselvi), a deuterium-modified JAK1/JAK2 inhibitor approved in July 2024 for adults, have since followed. All three carry FDA black box warnings covering serious infections, malignancy, major adverse cardiovascular events, and thrombosis — a class-level safety profile that has shaped prescribing patterns and generated sustained clinical interest in mechanistically distinct alternatives.
Rezpegaldesleukin operates through a different pathway entirely. As a PEGylated IL-2 conjugate, it is designed to selectively expand regulatory T cells (Tregs), aiming to restore immune tolerance rather than broadly suppress cytokine signaling. The Treg-restorative approach is mechanistically distinct from JAK inhibition and carries a theoretical rationale for more durable responses, though that hypothesis remains to be tested in registrational trials. The REZOLVE-AA population — JAK inhibitor-naïve patients — does not allow direct inference about how the drug might perform in patients who have failed or are intolerant of the approved oral agents, a question that would be material to its eventual commercial positioning.
Cross-trial comparisons between REZOLVE-AA and the pivotal JAK inhibitor studies are limited by differences in patient populations, baseline disease severity, endpoint definitions, and trial design. The SALT ≤20 response rates observed with baricitinib and ritlecitinib in their respective registrational programs were numerically higher than those reported here at week 52, though the enrolled populations and statistical frameworks differ substantially. What the REZOLVE-AA data do establish is a directional signal of deepening response with continued twice-monthly dosing and a tolerability profile that, based on Phase IIb data, does not carry the cardiovascular and immunosuppressive warnings associated with the approved class.
The FDA granted Fast Track designation for rezpegaldesleukin in severe alopecia areata in July 2025, covering adults and adolescents aged 12 and older weighing at least 40 kg. Nektar is also running Phase IIb programs in atopic dermatitis and a Phase II study in Type 1 diabetes, positioning rezpegaldesleukin as a platform asset across autoimmune conditions driven by Treg deficiency. Data from the atopic dermatitis program were presented at the American Academy of Dermatology meeting in March 2026, and the company has said it plans to submit the REZOLVE-AA results for conference presentation later this year.
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