A New Antibody Cut COPD Flare-Ups Without an Eosinophil Gate

The most interesting number in two new COPD trials may be zero: the number of blood-eosinophil cutoffs patients had to clear before enrolling.

That matters because the two antibody treatments currently approved in the United States for chronic obstructive pulmonary disease, dupilumab and mepolizumab, are labeled for people with an eosinophilic form of the disease. Eosinophils are white blood cells associated with one type of airway inflammation. Patients with low eosinophil counts fall outside those COPD indications.

Tozorakimab may offer another route. In two matching Phase 3 trials published in the New England Journal of Medicine, the experimental antibody reduced the annualized rate of moderate or severe COPD exacerbations by 29% to 34% among former smokers. The combined population of current and former smokers also had significantly lower exacerbation rates, although that analysis does not prove a separate effect among current smokers considered alone.

Those percentages are relative reductions. The absolute results show more clearly what happened.

In the OBERON trial, former smokers receiving tozorakimab had an estimated 1.34 moderate or severe exacerbations per year, compared with 1.90 among those receiving placebo. In TITANIA, the rates were 1.37 and 2.07. The differences were approximately 0.56 and 0.70 fewer exacerbations per patient-year.

The participants were not people with mild disease trying an antibody instead of an inhaler. They had symptomatic COPD and had experienced at least two moderate exacerbations or one severe exacerbation during the previous year despite stable maintenance treatment with dual or triple inhaled therapy.

A moderate event meant worsening that required systemic steroids, antibiotics or an emergency visit with intensified treatment. A severe one required hospitalization for at least 24 hours or resulted in death, according to the trial-program design.

Two attempts at the same answer

OBERON and TITANIA were designed as replicate trials: randomized, double-blind studies using matching interventions and endpoints. That is valuable because a result appearing in two planned trials is generally more persuasive than a single positive experiment.

In OBERON, the rate ratio among former smokers was 0.71, with a 95% confidence interval from 0.57 to 0.88. In TITANIA, it was 0.66, with an interval from 0.55 to 0.80. Both results were statistically significant.

The first key secondary analysis included current and former smokers together. It produced rate ratios of 0.70 in OBERON and 0.71 in TITANIA, relative reductions of 30% and 29%.

That wording matters. The significant result belongs to the combined population; it should not be translated into a claim that current smokers were independently proved to benefit.

The principal published comparison covered 1,750 participants: 877 in OBERON and 873 in TITANIA across the monthly-tozorakimab and placebo groups. A larger figure of 2,306 appears in company and conference materials because the original trials also contained a 300-milligram-every-eight-weeks group outside the paper's principal comparison.

Every four weeks for 52 weeks, participants in the reported treatment group received a 300-milligram injection under the skin in addition to their usual inhaled therapy.

Why the blood test matters

The FDA-approved COPD indications for dupilumab and mepolizumab specify an eosinophilic phenotype. OBERON and TITANIA enrolled patients without requiring an elevated eosinophil count.

A pooled, prespecified analysis of patients with fewer than 150 eosinophils per microliter found a 23% reduction in moderate or severe exacerbations. The rate ratio was 0.77, with a 95% confidence interval from 0.62 to 0.94. At 300 or more cells per microliter, the estimated reduction was larger, 43%, according to results released by AstraZeneca.

That does not prove the antibody works equally well at every eosinophil level. The estimates were larger at higher counts, and subgroup results are less definitive than the trials' main outcomes. But the below-150 result is the unusual one: an efficacy signal from two pooled Phase 3 trials in a group outside the eosinophilic labels of existing COPD biologics.

Whether that evidence produces a broad treatment indication is now a question for regulators, not the trial sponsor.

Blocking an airway alarm

Tozorakimab targets interleukin-33, or IL-33. One way to think of IL-33 is as a molecular alarm released by stressed or damaged barrier tissue, including the lining of the airways. Once active, it can trigger inflammatory signaling.

The antibody was designed to bind IL-33 before it drives two proposed pathways. In laboratory and animal work, it inhibited the reduced form of IL-33 from signaling through a receptor called ST2. It also prevented the formation and downstream activity of oxidized IL-33, which has been linked in laboratory models to excessive mucus and defective epithelial repair.

Those mechanistic findings come from preclinical research. They offer a possible explanation for the drug's effects, not direct proof that altered mucus production or airway repair caused the clinical result.

The clinical finding is simpler: people receiving the antibody experienced fewer treated or hospitalized flare-ups.

The safety results need the uncompressed version

Overall adverse-event rates looked similar. In OBERON, at least one adverse event occurred in 70.4% of tozorakimab recipients and 77.2% of placebo recipients. In TITANIA, the figures were 80.1% and 79.8%.

Serious adverse events were also broadly balanced: 23.3% versus 27.0% in OBERON and 31.1% versus 32.4% in TITANIA. Injection-site reactions were more frequent with the antibody, 5.2% versus 1.4% in OBERON and 6.6% versus 1.6% in TITANIA.

There were also small numerical imbalances that should not disappear beneath a general statement that the treatment was well tolerated. Adverse events resulting in death occurred in 1.3% of tozorakimab recipients and 1.2% of placebo recipients in OBERON. In TITANIA, the figures were 2.5% and 0.9%.

AJMC's report from the European Respiratory Society presentation also described pooled major adverse cardiovascular events as rare but somewhat more frequent with tozorakimab. Exact adjudicated counts were not available in the accessible primary material reviewed for this article.

Small numbers can produce chance imbalances, and these results do not establish that the drug caused the events. They do mean that the underlying cases, longer follow-up and regulatory analysis matter.

The sponsor relationship matters too. AstraZeneca developed tozorakimab, funded both trials and employs several of the paper's authors. The published report also acknowledges company-supported medical-writing assistance. Two consistent randomized trials are strong evidence, but sponsor descriptions such as first-in-class or highly clinically meaningful remain promotional judgments rather than trial outcomes.

What the trials did not show

Tozorakimab did not cure COPD, restore damaged lungs or demonstrate that patients lived longer. OBERON and TITANIA lasted 52 weeks and focused on recurrent moderate or severe exacerbations.

A separate long-term extension supplies another caution. In an April clinical-trial update, AstraZeneca disclosed that PROSPERO produced a numerical but not statistically significant reduction in severe exacerbations among former smokers, missing its primary endpoint. The company described the result in the combined current-and-former-smoker population as nominally significant. Full data have not been published.

PROSPERO measured a different, narrower outcome over a longer period, so its miss does not erase the positive OBERON and TITANIA findings. It does leave the durability of the effect against the most serious attacks less settled than a simple Phase 3 success label might suggest.

Tozorakimab is not approved. AstraZeneca says the FDA has accepted its biologics license application for Priority Review, with a decision anticipated in the first quarter of 2027. Priority Review accelerates the agency's target timetable; it does not lower the approval standard or guarantee a favorable decision.

If the drug is eventually approved without an eosinophil restriction, its most consequential feature may not be that it is another antibody for COPD. It may be that the treatment door no longer begins with the same blood-test gate.