Cue Biopharma's shares plunged nearly 24% Monday after reporting Phase II data for its anti-IgE antibody CUE-221 in chronic spontaneous urticaria (CSU) as investors seemed sceptical of the drug's apparent edge over Roche and Novartis' Xolair (omalizumab).Still, based on the data, Cue said it is advancing CUE-221 into a Phase IIb/III study in CSU and in a Phase II study in food allergy.The five-arm trial, conducted in China by Ascendant Health Sciences, enrolled 145 participants with moderate-to-severe CSU that was inadequately controlled despite treatment with H1 antihistamines. Participants were randomised to one of three doses of CUE-221 once every four weeks, placebo or Xolair.Cue said the drug hit its main goal across all three doses. At week 12, complete hive resolution as measured by Hives Severity Score over 7 days (HSS7=0) was achieved by 54%, 53% and 43% of patients at the 4 mg/kg, 2 mg/kg and 1 mg/kg doses, respectively, versus 11% for placebo (p<0.005 for the two higher doses).All three CUE-221 groups also posted numerically higher rates than the 41% seen with Xolair. The trial's primary goal was to demonstrate superiority over placebo; Xolair was included to compare efficacy, though it wasn't part of the formal statistical analysis plan.Meanwhile, complete response on the Urticaria Activity Score over 7 days (UAS7) scale, a secondary endpoint, was seen in 46% of patients at the highest dose, meeting the bar for statistical significance, versus 11% for placebo and 29% for Xolair.Staying powerAnother positive signal came after treatment stopped. CUE-221 was administered through week 16, but the rate of complete hive resolution continued to rise, reaching a peak of 69% at week 22 for patients on the 4-mg/kg dose. At week 28, or 12 weeks after the last dose, 60% of patients at the highest dose remained hive-free versus 24% for Xolair, a 36 percentage-point difference that Cue said was statistically significant in a post-hoc analysis. The 1 and 2 mg/kg arms fell to hive-free rates of 24% and 31%, respectively, over that time."Results support that the effects of CUE-221 on IgE function could result in substantial efficacy in CSU that persists for several months, even after dosing ends," said Dale Umetsu, a professor of medicine at Stanford University and former global lead for Xolair development.No treatment-related serious adverse events or cases of hypersensitivity, including anaphylaxis, were reported with CUE-221. Injection-site reactions were infrequent, with only one exceeding grade 1 severity and none leading to treatment discontinuations.A vote of confidenceDespite the negative market reaction, analysts at B. Riley Securities liked what they saw. They had two bars for success — matching Xolair's level of hives control at 12 weeks, with higher doses producing consistently better results, and showing that benefits persisted after patients stopped taking the drug — and "the symptom response endpoints cleared both," the analysts said."Lower exposures of the same molecule losing the effect, while the top dose retained it, is the threshold pattern the [Phase I] predicted and the clinical shape a CD23-sparing mechanism should produce," according to the analysts, adding that "safety was clean and leaves dosing headroom."They also pointed to some competing anti-IgE programmes — namely, LongBio Pharma's LP-003 and RAPT Therapeutics' ozureprubart (RPT904/JYB1904) — and suggested CUE-221's "three-month offdrug tail" could be a differentiator when it comes to durability. GSK acquired RAPT earlier this year for $2.2 billion.In 2025, RAPT reported that efficacy was sustained at week 16 after a single dose of its drug, whereas no follow-up has so far been reported for LP-003, according to the analysts.