Nektar Therapeutics announced that its investigational IL-2 agonist, rezpegaldesleukin (rezpeg), did not achieve statistically significant results in reducing disease severity in a Phase IIb trial for alopecia areata. The company stated that the study's failure to meet its primary endpoint was due to enrollment issues, specifically noting that four patients were included despite having major eligibility violations. Nektar did not provide details on the nature of these violations.
The company maintains confidence in rezpeg’s potential and plans to move forward with late-stage development next year. According to Nektar, excluding the four patients from the analysis would have resulted in a successful outcome for the trial. In this adjusted analysis, higher- and lower-dose arms showed SALT score reductions of 29.6% and 30.4%, respectively, compared to a 5.7% reduction for placebo, with p-values of 0.049 and 0.042.
Analysts at William Blair commented on Tuesday, “We believe rezpegaldesleukin exhibits clinical activity in alopecia areata, despite missing statistical significance on the primary endpoint.” They added that there may be further improvements over time: “Since there is not a noticeable plateau, it is conceivable that the proportion of patients achieving less than 20% hair loss could increase with longer follow-up.”
Despite these observations, William Blair analysts noted that “rezpeg’s efficacy is not competitive with low-dose JAK inhibitors.” Even after removing the problematic cases from analysis, the percentage of participants reaching significant improvement was lower than expected.
In the overall study population, treatment with rezpeg at doses of 24 µg/kg and 18 µg/kg led to mean reductions in Severity of Alopecia Tool (SALT) scores by 28.2% and 30.3%, respectively, over 36 weeks; placebo resulted in an 11.2% decrease during the same period.
Shares of Nektar fell by seven percent following Tuesday’s announcement.
Nektar intends to present full findings from REZOLVE-AA at a medical conference next year and expects data from an ongoing extension phase in the second quarter of 2026.
