Phase 2b 52-Week Extension Results Demonstrate Sustained Hair Regrowth with Rezpegaldesleukin

Nektar Therapeutics has reported 52-week topline results from a blinded 16-week extension of its phase 2b REZOLVE-AA study, demonstrating continued and deepening clinical responses with rezpegaldesleukin (REZPEG) in patients with severe to very severe alopecia areata (AA).¹ Rezpegaldesleukin has already received Fast Track designation from the US Food and Drug Administration for both alopecia areata and atopic dermatitis.²

Rezpegaldesleukin is a first-in-class interleukin-2 (IL-2) pathway agonist designed to selectively expand and activate regulatory T cells (Tregs), thereby restoring immune tolerance. This approach differs fundamentally from currently approved systemic therapies, such as Janus kinase (JAK) inhibitors, which broadly suppress immune signaling. In autoimmune diseases such as AA, insufficient Treg activity contributes to the loss of self-tolerance and subsequent immune-mediated attack on hair follicles. By targeting immune dysregulation at its source, rezpegaldesleukin aims to rebalance pathogenic immune responses implicated in hair follicle destruction.

"The new SALT≤20 responders in this set of patients treated out to 52 weeks reflect how the T regulatory cell mechanism of REZPEG can have more clinical benefit over time, a phenomenon the investigators observed in the Phase 2 study in atopic dermatitis as well," Jonathan Silverberg, MD, PhD, MPH, Professor of Dermatology at The George Washington University School of Medicine and Health Sciences, said in the press release. "Given the prescribing and safety limitations of JAK inhibitors, these new data point to the potential for rezpegaldesleukin to be the first safe and effective biologic in alopecia areata, which may completely transform the management of the disease."¹

The REZOLVE-AA study enrolled 92 patients with severe to very severe disease, defined by high baseline Severity of Alopecia Tool (SALT) scores (mean ~78). During the 36-week induction phase, patients were randomized to receive one of two subcutaneous rezpegaldesleukin dose regimens (18 µg/kg or 24 µg/kg) or placebo, administered twice monthly. Patients demonstrating initial hair regrowth but not achieving a SALT score ≤20 at week 36 were eligible to enter a blinded 16-week extension period, continuing therapy through week 52.

A total of 31 patients entered the extension phase, including 27 receiving active treatment. Results from week 36 to week 52 showed continued clinical improvement with ongoing therapy. Notably, 29% of patients in the low-dose group and 31% in the high-dose group achieved new SALT ≤20 responses during the extension period, compared with no new responders in the placebo arm.

Across the overall study population, response rates also improved over time. After 1 year of treatment, 25.8% and 27.6% of patients in the low- and high-dose groups, respectively, achieved SALT ≤20, compared with 6.7% in the placebo arm (p = 0.049). Similarly, SALT ≤30 responses (≥70% scalp coverage) increased to 30.2% and 35.0% in the active treatment arms versus 8.4% with placebo (p = 0.023).

Additional efficacy endpoints supported these trends. At week 52, SALT50 responses (≥50% improvement from baseline) were observed in 37.7% and 38.8% of patients in the low- and high-dose groups, respectively, compared with 13.6% in the placebo group. SALT30 responses were achieved by 45.6% and 47.6% of treated patients versus 24.2% with placebo. Importantly, treatment persistence was high, with 94% of patients completing the 52-week study period.

The safety profile of rezpegaldesleukin remained favorable and consistent with earlier reports. Most treatment-emergent adverse events were mild to moderate in severity and resolved without intervention. Injection site reactions were the most common adverse events, typically presenting as mild erythema that resolved within several days. No patients discontinued therapy during the extension period due to adverse events, and no new safety signals were identified.

"These extension treatment data to 52 weeks demonstrate the potential of rezpegaldesleukin to deliver truly meaningful clinical outcomes for patients with severe to very severe alopecia areata," David Rosmarin, MD, Chair of the Department of Dermatology and Associate Professor of Dermatology at the Indiana University School of Medicine, said in a statement. "We are in need of a new mechanism for a first-line systemic treatment option as an alternative to the class of agents currently approved for patients. The safety profile combined with a significantly higher number of patients achieving SALT Score ≤20 with continued treatment reinforce that this first-in-class Treg mechanism could emerge as the treatment of choice for patients with alopecia areata, including also those with moderate disease."¹

References

1. 52-Week Topline Results from 16-Week Blinded Treatment Extension of REZOLVE-AA Demonstrate Deepening of Responses in Severe-to-Very-Severe Alopecia Areata with Rezpegaldesleukin. News release. PR Newswire. April 20, 2026. Accessed April 20, 2026. https://www.prnewswire.com/news-releases/52-week-topline-results-from-16-week-blinded-treatment-extension-of-rezolve-aa-demonstrate-deepening-of-responses-in-severe-to-very-severe-alopecia-areata-with-rezpegaldesleukin-302746837.html

2. Nektar Therapeutics receives Fast Track Designation for rezpegaldesleukin for the treatment of severe-to-very severe alopecia areata. News release. Nektar Therapeutics. July 29, 2025. Accessed April 20, 2026. https://www.prnewswire.com/news-releases/nektar-therapeutics-receives-fast-track-designation-for-rezpegaldesleukin-for-the-treatment-of-severe-to-very-severe-alopecia-areata-302515436.html