Biomarker-guided biologics are changing severe airway disease care
Asthma and chronic obstructive pulmonary disease remain among the most common and most heterogeneous airway diseases seen in practice. Their clinical burden falls hardest on the subgroup with severe disease, where recurrent exacerbations drive hospitalizations, lung function decline, and premature mortality. The central shift in this review is biological rather than semantic: these disorders are increasingly being organized around endotypes, not simply around symptoms or spirometric obstruction.
Engineered monoclonal antibodies now target discrete immune pathways, including IgE, interleukin-5, the IL-4/IL-13 axis, and upstream epithelial alarmins such as TSLP and IL-33. In the right patient, those targets turn a broad diagnosis into a measurable treatment problem. The practical consequence is a precision approach in which the biologic is chosen to match the inflammatory signal, rather than escalating inhaled therapy indefinitely and hoping for the best.
Exacerbation prevention remains the clearest clinical win. Across biomarker-defined populations, biologics consistently reduce attacks, improve lung function, and improve quality of life. Those gains matter most in patients who have already declared themselves high-risk through repeated flares despite standard therapy. Each avoided exacerbation removes a cascade of acute steroid exposure, emergency care, and the downward spiral that often follows repeated airway injury.
Type 2 inflammation remains the most actionable target in asthma
In asthma, the most mature biologic evidence continues to center on type 2 inflammation, a pathway linked to T helper 2 cells and group 2 innate lymphoid cells. Blood eosinophils, fractional exhaled nitric oxide (FeNO), and sputum eosinophils remain the most useful short-term biomarkers for selecting treatment. These markers are not interchangeable, but they often point in the same direction: steroid-responsive airway inflammation that is more likely to benefit from targeted immunomodulation.
Blood eosinophils have the most immediate bedside utility because they are widely available and reproducible. FeNO adds complementary information in selected settings, especially when eosinophilic inflammation is suspected but blood counts alone leave uncertainty. Sputum eosinophils can refine the picture further, although they are less practical outside specialized centers. In day-to-day care, the value of these tests lies in stratifying who is most likely to benefit from a biologic and who may need a different strategy entirely.
The biology behind the response is straightforward. Eosinophil-driven inflammation promotes airway hyperresponsiveness, mucus production, and recurrent injury to the bronchial wall. Suppressing that pathway does not merely reduce symptoms; it can interrupt the inflammatory cycle that keeps patients trapped in repeated exacerbations and persistent airflow limitation.
Eosinophils still identify the patients most likely to benefit in COPD
COPD has been slower to yield to biologic therapy, but the signal is no longer negligible. In selected patients with frequent exacerbations and high eosinophil counts, type 2 biologics have produced benefit. The most robust predictor of response remains a blood eosinophil count of 300 cells/µL or higher. In this setting, eosinophils appear to identify a biologically distinct subset of COPD in which inflammatory amplification is sufficiently type 2–skewed to justify targeted treatment.
The implications are important because COPD has long been treated as a monolith, even though its inflammatory biology is not uniform. Patients with repeated flares despite optimized inhaled treatment represent the group most likely to be considered for escalation. For them, blood eosinophils offer a practical entry point into precision care, helping distinguish a patient with predominantly neutrophilic disease from one whose exacerbation pattern resembles an eosinophilic endotype.
FeNO may provide additional categorization in some cases, though its role remains more limited than eosinophil counts. The review also points to mixed but intriguing signals for anti-IL-33 and TSLP therapies in COPD. Those findings suggest that upstream epithelial danger signaling may be relevant even in a disease traditionally framed as smoking-related and neutrophil-dominant. The clinical meaning is still unsettled, but the pathway is biologically plausible: epithelial stress can amplify downstream immune activation long before symptoms become stable enough to fit classic disease labels.
Longer-term markers may define disease modification, not just response
A major distinction in asthma research is moving beyond short-term response markers toward longer-term measures that may reflect disease modification. Transcriptomic signatures and imaging endpoints are emerging as mechanistic readouts. They may eventually help determine whether a biologic is merely suppressing symptoms or actually altering the trajectory of airway disease.
That question matters because severe asthma is not only episodic; in some patients it is progressive. If a treatment changes airway biology over time, then the goal moves from flare prevention alone to altering the underlying inflammatory architecture. Imaging and transcriptomic tools may help identify that shift, especially in patients whose biomarker profile changes after treatment begins.
In COPD, the same framework could become even more useful, given the disorder’s mixed inflammatory subtypes and the difficulty of predicting which patients will maintain benefit over time. At present, though, the field still lacks enough longitudinal data to support routine use of these tools for treatment decisions. They remain promising mechanistic markers rather than standard-of-care tests.
Referral timing and inhaled therapy decisions remain central
Biologics do not replace comprehensive airway care. Patients with exacerbations despite optimized inhaled therapy still need careful review of inhaler technique, adherence, comorbidity burden, trigger exposure, and self-management capacity. The review places timely referral front and center for exactly that reason: biologic eligibility should be considered before repeated exacerbations harden into long-term disability.
This is also where real-world practice becomes difficult. The field still lacks head-to-head comparisons between biologics, clear criteria for switching or stopping treatment, and solid evidence to guide de-escalation of inhaled therapy once control improves. Those are not academic nuisances; they are the questions clinicians face after the first prescription is written and the first response window closes.
Patients with severe asthma or COPD who continue to exacerbate despite optimized inhaled treatment deserve a structured assessment for treatable traits, not a generic escalation loop. The review argues for precision medicine, but the bedside version of precision still depends on eosinophils, FeNO, and careful clinical judgment. For now, blood eosinophils remain the strongest guide, while type 2 low strategies and de-escalation pathways remain unresolved.