Specialized T cells may trigger asthma in older men

Key takeaways:

• Researchers defined eight subsets of airway CD4+ tissue-resident memory T cells.
• Nearly 65% of all CD4+ T cells in men with severe asthma expressed the integrin CD103.

A cytotoxic CD4+ tissue-resident memory T-cell subset may be critical in driving airway inflammation and remodeling among men with severe asthma, according to a study published in Med.

“If you are male and you develop asthma after age 40, there’s a high chance this T-cell population is in your lungs,” Gregory Seumois, PhD, research assistant professor and director of immunogenomics at La Jolla Institute for Immunology, said in a press release.

These results suggest that classifying patients only by whether they have low or high levels of type 2 inflammation may inadequately capture different asthma phenotypes, which may be targeted by different treatments, according to the researchers.

“Once you understand the role of cells like these T cells better, you can start to develop treatments that target those cells,” Ramesh Kurukulaaratchy, BM, DM, FRCP, associate professor at University of Southampton, said in the press release.

Eight subsets

The study involved 16 patients (50% men) with severe asthma who required high doses or continuous or frequent use of oral corticosteroids as well as 14 patients (64% men) with mild asthma, including 10 with significantly lower doses of inhaled steroids, all of whom underwent bronchoscopy with bronchoalveolar lavage collection.

Researchers performed a single-cell RNA sequencing assay on CD4+ T cells collected from these specimens. A clustering analysis of 27,771 airway CD4+ tissue-resident memory T cells (T_RM), including a median of approximately 1,304 cells per patient, revealed eight transcriptionally distinct subsets.

Clusters 1 and 2, which represented 71% of all the CD4+ T cells analyzed, were significantly enriched for T_RM signature genes. Because cluster 1 had higher levels of the ITGAE T_RM marker gene, which encodes for the alpha chain of the integrin CD103, researchers called it the CD103+ cluster and cluster 2 the CD103– cluster.

Defining features of the other clusters included:

• Cluster 3 (representing 13% of the airway CD4+ T cells: enriched for the expression of gene signatures linked to central memory T cells;
• Cluster 4 (4%): enriched for gene signatures linked to regulatory T cells (T_REG);
• Cluster 5 (4%): enriched for gene signatures linked to follicular helper T cells;
• Cluster 6 (3%): highly enriched for type I and II interferon response gene signatures;
• Cluster 7 (1%): enriched for cell-cycle signature genes representing proliferating cells; and
• Cluster 8 (1%): expressed high levels of several transcripts encoding for cytotoxicity molecules and represented cytotoxic CD4+ T cells.

Although these subsets indicate substantial levels of heterogeneity in CD4+ T cells in asthmatic airways, the researchers wrote, the T_RM subsets are major contributors.

“We have to think of severe asthma as having different subtypes, and the treatment has to be tailored according to these subtypes, because one size does not fit all,” S. Hasan Arshad, MBBS, DM, FRCP, chair in allergy and clinical immunology at University of Southampton, said in the press release.

T_RM subsets

Proportions of CD103+ cells were significantly increased in the airways of patients with severe asthma (46%) compared with patients with mild asthma (21%; P < .05), but proportions of CD103^– cells were significantly decreased in those patients with severe asthma (22% vs. 44%; P < .05).

When evaluated by sex, researchers only found a significant increase in the proportion of CD103+ T_RM subset in the CD4+ T cells of men with severe vs. mild asthma (64% vs. 13%; P < .01).

Further analysis revealed this association was not dependent on drug treatments.

The researchers additionally noted a positive correlation between proportions of CD103+ cells and composite asthma severity scores among men but not women (r_s = 0.8; P < .01).

Men had a significant positive correlation with the severity of airflow obstruction as well (r_s = .07; P < .01), along with a negative correlation between proportions of airway T_REG cells and proportions of CD103+ cells (r_s = .07; P < .05) and severity of airflow obstruction, suggesting an imbalance of these cells in men with severe asthma.

Age had a positive correlation with proportions of CD103+ cells in airways of men with severe asthma as well (r_s = 0.7; P < .05), with seven of the eight men with severe asthma developing the disease after age 40 years, indicating that late onset may be linked to this specific immune profile too.

Cytotoxicity

Next, researchers conducted further analyses comparing clusters 1 and 2 using sex as a covariate to determine the molecular properties of the cells in the CD103+ T_RM subset that contribute to asthma severity. Separate differential gene expression analysis on the more than 1,300 differentially expressed transcripts indicated increases in the expression of several genes involved in cytotoxic function in the CD103+ subset, along with indicators that treatment was not a major confounding factor.

In fact, the researchers continued, treatment with high-dose corticosteroids and/or biologics may have failed to curtail the activation and functional responses of airway CD103+ cells in severe asthma based on the sustained expression of transcripts linked to T cell receptor (TCR) activation and cytokines in the CD103+ subset.

Further, the researchers found significant positive enrichment of cytotoxicity signature genes in the CD103+ subset, indicating enriched cytotoxic CD4+ cells, potentially driving airway inflammation and remodeling in severe asthma.

Overall, the researchers said that CD103+ cells exhibit a T_H1-like phenotype with increased TCR activation, cytotoxicity and pro-inflammatory effector properties.

Men also had significantly enriched levels of the most differentially expressed genes that were increased in severe asthma, the researchers added, particularly those linked with cytotoxicity, although these cytotoxicity genes only were differentially expressed in the CD103+ subset.

The CD103+ subset was enriched in the genes that were linked with TCR signaling and cytotoxicity as well, the researchers said, but there were no significant differences in these features between men and women or between patients with mild or severe asthma.

Pro-inflammatory cytokines

The researchers then stimulated the cell samples and found increased expression of transcripts that encode for chemokines released by cytotoxic CD4+ cells in stimulated airway CD4+ T cells in patients with severe asthma compared with those with mild asthma.

These chemokines are key in recruiting several immune cell types expressing CCR1, CCR3 and CCR5 that can drive airway inflammation and remodeling, the researchers continued.

Patients with severe asthma also had significantly fewer cells expressing IL-4, IL-5, IL-13 and IL-17A transcripts compared with patients with mild asthma, the researchers found, whereas a larger fraction of airway CD4+ T cells expressed pro-inflammatory non-T_H2 cytokine transcripts.

These findings indicate that high doses of corticosteroids do not fully curtail the effector potential of airway CD4+ T cells, the researchers wrote, and non-T_H2 cytokines may be a contributing factor in severe asthma pathogenesis.

In addition to their potential for directly killing target cells, the researchers wrote, cytotoxic CD4+ cells also can express pro-inflammatory molecules that may be important in sustaining airway inflammation and remodeling.

For example, the researchers wrote, stimulated CD103+ cells expressed high levels of transcripts that encoded for cytotoxicity-associated molecules and cytokines.

Conclusions, next steps

Men with severe asthma had a “striking increase” in proportions of CD103+ cells with cytotoxic properties in their airways, which may drive airway inflammation and remodeling, the researchers wrote.

Current assessments classify patients with asthma with low or high levels of type 2 inflammation, the researchers added, which is not enough to explain asthma diversity such as the men with late-onset severe asthma in this study at the pathophysiological level.

This role that cytotoxic CD4+ cells have in driving disease may represent an attractive target and an expanded portfolio of treatable traits for therapeutic development, the researchers wrote, with sex and airway CD4+ cell profiles guiding disease assessment, prognosis and treatment.

Reference:

• Army of specialized T cells may trigger asthma attacks in older men. https://www.lji.org/news-events/news/post/army-of-specialized-t-cells-may-trigger-asthma-attacks-in-older-men/. Published Oct. 20, 2023. Accessed Oct. 24, 2023.