SAN FRANCISCO, April 20, 2026

Nektar Therapeutics has reported compelling 52-week topline results from the Phase 2b REZOLVE-AA trial, demonstrating sustained and deepening clinical responses with rezpegaldesleukin, a first-in-class IL-2 pathway agonist, in patients with severe-to-very-severe alopecia areata. The findings highlight significant improvements in hair regrowth outcomes, strong patient retention, and a favorable safety profile, supporting advancement into late-stage clinical development.

Sustained Efficacy with Deepening Hair Regrowth Responses

The REZOLVE-AA study evaluated rezpegaldesleukin, a novel regulatory T-cell (Treg) biologic, administered as a twice-monthly subcutaneous injection over a 52-week treatment period. The results demonstrated progressive improvement in hair regrowth, with increasing proportions of patients achieving clinically meaningful thresholds over time.

Between weeks 36 and 52, 29% and 31% of patients in the low-dose (18 µg/kg) and high-dose (24 µg/kg) groups, respectively, achieved a SALT score ≤20, indicating ≥80% scalp hair coverage, compared to no new responders in the placebo group. At week 52, overall response rates further improved, with 25.8% and 27.6% of patients in the respective dose groups achieving this endpoint, significantly outperforming placebo.

Additional efficacy endpoints reinforced these findings, including SALT50 responses (≥50% improvement) observed in approximately 38% of treated patients, and SALT30 responses (≥30% improvement) in nearly 47% of patients, highlighting robust clinical benefit. These results demonstrate that continued treatment leads to deeper and more durable responses, a critical factor in managing chronic autoimmune conditions like alopecia areata.

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Favorable Safety Profile Supports Long-Term Use

The study also confirmed a strong safety and tolerability profile for rezpegaldesleukin, consistent with earlier clinical findings. Nearly all treatment-emergent adverse events (TEAEs) were mild-to-moderate in severity and resolved without intervention. Importantly, 94% of patients completed the 52-week treatment period, with no discontinuations due to adverse events during the extension phase.

The most commonly reported side effects were injection site reactions, primarily mild erythema that resolved within days. Crucially, no dose-limiting toxicities or serious safety concerns were observed, reinforcing the therapy’s potential as a safe long-term treatment option.

This safety profile is particularly significant in comparison to existing treatments such as JAK inhibitors, which are associated with safety limitations and monitoring requirements, highlighting rezpegaldesleukin’s potential as a differentiated and safer alternative.

First-in-Class Mechanism Targets Immune Imbalance

Rezpegaldesleukin operates through a novel mechanism of action, targeting the interleukin-2 receptor pathway to selectively expand regulatory T cells (Tregs). These cells play a critical role in maintaining immune system balance and preventing autoimmune attacks on healthy tissues.

In alopecia areata, the immune system mistakenly attacks hair follicles, leading to hair loss. By enhancing Treg activity, rezpegaldesleukin helps restore immune tolerance, addressing the underlying cause of the disease rather than just its symptoms.

The therapy has already received Fast Track designation from the U.S. FDA for both alopecia areata and atopic dermatitis, underscoring its potential to address significant unmet medical needs in autoimmune diseases.

The 52-week results from the REZOLVE-AA trial position rezpegaldesleukin as a potential first-in-class biologic therapy for alopecia areata, offering sustained efficacy, deepening clinical responses, and a favorable safety profile. As Nektar Therapeutics advances the program into late-stage development, this innovative therapy has the potential to transform the treatment landscape for patients suffering from severe autoimmune hair loss disorders, marking a significant step forward in precision immunology and biopharmaceutical innovation.

Source: Nektar Therapeutics press release