Type 2‑low (T2‑low) asthma is characterized clinically by low blood and sputum eosinophil counts and low fractional exhaled nitric oxide (FeNO). This phenotype is associated with corticosteroid insensitivity and a notable scarcity of well‑validated targeted therapies, which together represent a significant unmet need in asthma management.
Estimates of prevalence vary across populations and age groups. Recent summaries place the proportion of adults with current asthma who meet criteria for T2‑low disease at approximately 14%–39%, whereas pediatric series suggest that up to 60% of children with asthma can be classified as T2‑low. These ranges reflect heterogeneity in study populations, biomarker thresholds, and diagnostic approaches.
The pathogenic landscape of T2‑low asthma is complex and distinct from classical type 2 inflammation. Key non‑T2 mechanisms implicated include signaling through IL‑17, activation of innate immune pathways via cytokines such as IL‑1β and IL‑33, and prominent neutrophilic inflammation in airway samples. Together, these processes contribute to airway dysfunction and reduced responsiveness to inhaled corticosteroids seen in many patients with T2‑low disease.
The review highlights that multiple overlapping immune cascades, rather than a single dominant pathway, appear to underlie T2‑low inflammation. This biological complexity helps explain variable treatment responses and the inconsistent outcomes observed in trials of single‑target interventions.
Beyond airway immune signals, systemic and environmental factors shape the heterogeneity of T2‑low asthma. The authors summarize evidence that obesity and immunosenescence can influence inflammatory patterns and clinical phenotype, possibly promoting non‑T2 pathways. Environmental exposures, notably ozone, are also recognized as modulators of airway inflammation and may skew disease biology toward neutrophilic, non‑eosinophilic endotypes.
These modifying factors underscore the need to consider host physiology and exposure history when interpreting biomarkers and selecting therapies for T2‑low patients.
Among treatments evaluated for T2‑low asthma, two interventions have demonstrated notable efficacy in reducing exacerbations. Long‑term macrolide therapy has been associated with decreased exacerbation rates in certain populations with non‑T2 disease. Similarly, the anti‑TSLP biologic tezepelumab has shown clinically meaningful reductions in exacerbations, including in patients without type 2 biomarker elevation.
These findings suggest that targeting upstream or broad inflammatory pathways can benefit some patients with T2‑low asthma, but identifying which patients are most likely to respond remains a challenge.
The review notes that numerous pathway‑specific therapies targeting discrete non‑T2 mediators have produced inconsistent clinical benefits. Single‑target biologics or small molecules directed at individual cytokines or pathways have not uniformly translated into reliable improvements across T2‑low cohorts, reflecting the underlying heterogeneity and the potential for redundant or parallel inflammatory mechanisms to sustain disease.
As a result, many pathway‑directed strategies remain investigational or have limited applicability until biomarkers or mechanistic classifiers can better define responsive subgroups.
Emerging therapeutic concepts include metabolic modulation as a means to influence airway disease. The review highlights metabolic approaches such as GLP‑1 receptor agonists as potential novel strategies for T2‑low asthma, recognizing that these are early signals of promise rather than established therapies.
Concurrently, multiomics — integrating genomics, transcriptomics, proteomics, metabolomics, and other high‑dimensional data — is positioned as a tool to deconvolute disease heterogeneity. Multiomic profiling may reveal distinct molecular endotypes within T2‑low asthma and identify actionable targets or biomarker signatures for clinical use.
A central conclusion of the review is that progress in T2‑low asthma treatment will depend on robust, mechanism‑based patient classification and the development of clinically deployable biomarkers. Such biomarkers are required to align targeted therapies with the specific biological drivers present in individual patients, thereby improving therapeutic precision and clinical outcomes.
Until mechanism‑guided diagnostics and validated biomarkers are widely available, the management of T2‑low asthma will continue to rely on broader anti‑inflammatory strategies and careful clinical phenotyping.
Type 2‑low asthma represents a significant and prevalent phenotype with distinct non‑T2 immunopathology, frequent corticosteroid insensitivity, and unmet therapeutic needs. Progress will hinge on integrating multiomic insights with clinical biomarkers to enable mechanism‑matched treatments. Current effective options include long‑term macrolides and tezepelumab for selected patients, while other targeted approaches and metabolic strategies such as GLP‑1 receptor agonists remain areas of ongoing investigation.