Single-cell RNA sequencing identifies precise tolerogenic cellular and molecular pathways induced by depigmented-polymerized grass pollen allergen extract

T Cell Exhaustion in Allergic Diseases and Allergen Immunotherapy: A Novel Biomarker?

PURPOSE OF REVIEW

This review explores the emerging role of T cell exhaustion in allergic diseases and allergen immunotherapy (AIT). It aims to synthesize current knowledge on the mechanisms of T cell exhaustion, evaluate its potential involvement in allergic inflammation, and assess its implications as a novel biomarker for predicting and monitoring AIT efficacy.

RECENT FINDINGS

Recent studies highlight that T cell exhaustion, characterized by co-expression of inhibitory receptors (e.g., PD-1, CTLA-4, TIM-3), diminished cytokine production, and altered transcriptional profiles, may suppress type 2 inflammation in allergic diseases. In allergic asthma, exhausted CD4 + T cells exhibit upregulated inhibitory receptors, correlating with reduced IgE levels and airway hyperreactivity. During AIT, prolonged high-dose allergen exposure drives allergen-specific Th2 and T follicular helper (Tfh) cell exhaustion, potentially contributing to immune tolerance. Notably, clinical improvements in AIT correlate with depletion of allergen-specific Th2 cells and persistent expression of exhaustion markers (e.g., PD-1, CTLA-4) during maintenance phases. Blockade of inhibitory receptors (e.g., PD-1) enhances T cell activation, underscoring their dual regulatory role in allergy. T cell exhaustion represents a double-edged sword in allergy: it may dampen pathological inflammation in allergic diseases while serving as a mechanism for AIT-induced tolerance. The co-expression of inhibitory receptors on allergen-specific T cells emerges as a promising biomarker for AIT efficacy. Future research should clarify the transcriptional and metabolic drivers of exhaustion in allergy, validate its role across diverse allergic conditions, and optimize strategies to harness T cell exhaustion for durable immune tolerance. These insights could revolutionize therapeutic approaches and biomarker development in allergy management.

Omics in allergy and asthma

This review explores the transformative impact of omics technologies on allergy and asthma research in recent years, focusing on advancements in high-throughput technologies related to genomics and transcriptomics. In particular, the rapid spread of single-cell RNA sequencing has markedly advanced our understanding of the molecular pathology of allergic diseases. Furthermore, high-throughput genome sequencing has accelerated the discovery of monogenic disorders that were previously overlooked as ordinary intractable allergic diseases. We also introduce microbiomics, proteomics, lipidomics, and metabolomics, which are quickly growing areas of research interest, although many of their current findings remain inconclusive as solid evidence. By integrating these omics data, we will gain deeper insights into disease mechanisms, leading to the development of precision medicine approaches that promise to enhance treatment outcomes.

Severe Allergy as a Chronic Inflammatory Condition From a Systems Biology Perspective

Persistent and unresolved inflammation is a common underlying factor observed in several and seemingly unrelated human diseases, including cardiovascular and neurodegenerative diseases. Particularly, in atopic conditions, acute inflammatory responses such as those triggered by insect venom, food or drug allergies possess also a life-threatening potential. However, respiratory allergies predominantly exhibit late immune responses associated with chronic inflammation, that can eventually progress into a severe phenotype displaying similar features as those observed in other chronic inflammatory diseases, as is the case of uncontrolled severe asthma. This review aims to explore the different facets and systems involved in chronic allergic inflammation, including processes such as tissue remodelling and immune cell dysregulation, as well as genetic, metabolic and microbiota alterations, which are common to other inflammatory conditions. Our goal here was to deepen on the understanding of an entangled disease as is chronic allergic inflammation and expose potential avenues for the development of better diagnostic and intervention strategies.

Allergen immunotherapy in asthma

Allergen immunotherapy (AIT), including SCIT and SLIT, is a treatment that involves the administration of allergens to which patients with allergic diseases have been sensitized. HDM-SCIT for asthma is indicated in cases of HDM-sensitized allergic asthma with normal lung function. HDM-SCIT improves asthma symptoms and AHR, and decreases the medication dose. Importantly, AIT can improve other allergic diseases complicated by asthma, such as allergic rhinitis, which can also contribute to the improvement of asthma symptoms. Several studies have suggested that HDM-SLIT also attenuates the risk of asthma exacerbations, and improves lung function in asthma cases with allergic rhinitis. Furthermore, AIT can modify the natural course of allergic diseases, including asthma. For example, the effects of AIT are maintained for at least several years after treatment discontinuation. AIT can prevent the onset of asthma when introduced in allergic rhinitis, and can also inhibit or reduce new allergen sensitizations. Recent data have suggested that AIT may suppress non-targeted allergen-induced immune responses in addition to targeted allergen-induced responses, and suppress infections of the lower respiratory tract by enhancing IFN responses.

Blood Transcriptomics Identifies Multiple Gene Expression Pathways Associated with the Clinical Efficacy of Hymenoptera Venom Immunotherapy

Allergen-specific venom immunotherapy (VIT) is a well-established therapy for Hymenoptera venom allergy (HVA). However, the precise mechanism underlying its clinical effect remains uncertain. Our study aimed to identify the molecular mechanisms associated with VIT efficiency. We prospectively included 19 patients with HVA undergoing VIT (sampled before the beginning of VIT, after reaching the maintenance dose, one year after finishing VIT, and after a sting challenge) and 9 healthy controls. RNA sequencing of whole blood was performed on an Illumina sequencing platform. Longitudinal transcriptomic profiling revealed the importance of the inhibition of the NFκB pathway and the downregulation of DUX4 transcripts for the early protection and induction of tolerance after finishing VIT. Furthermore, successful treatment was associated with inhibiting Th2, Th17, and macrophage alternative signalling pathways in synergy with the inhibition of the PPAR pathway and further silencing of the Th2 response. The immune system became activated when reaching the maintenance dose and was suppressed after finishing VIT. Finally, successful VIT restores the immune system's balance to a state similar to that of healthy individuals. Our results underline the important role of the inhibition of four pathways in the clinical effect of VIT: Th2, Th17, NFκB, and macrophage signalling. Two biomarkers specific for successful VIT, regardless of the time of sampling, were C4BPA and RPS10-NUDT3 and should be further tested as potential biomarkers.

Mechanisms and Predictive Biomarkers of Allergen Immunotherapy in the Clinic

Allergen immunotherapy (AIT) remains to be the only disease-modifying treatment for IgE-mediated allergic diseases such as allergic rhinitis. It can provide long-term clinical benefits when given for 3 years or longer. Mechanisms of immune tolerance induction by AIT are underscored by the modulation of several compartments within the immune system. These include repair of disruption in epithelial barrier integrity, modulation of the innate immune compartment that includes regulatory dendritic cells and innate lymphoid cells, and adaptive immune compartments such as induction of regulatory T and B cells. Altogether, these are also associated with the dampening of allergen-specific TH2 and T follicular helper cell responses and subsequent generation of blocking antibodies. Although AIT is effective in modifying the immune response, there is a lack of validated and clinically relevant biomarkers that can be used to monitor desensitization, efficacy, and the likelihood of response, all of which can contribute to accelerating personalized medication and increasing patient care. Candidate biomarkers comprise humoral, cellular, metabolic, and in vivo biomarkers; however, these are primarily studied in small trials and require further validation. In this review, we evaluate the current candidates of biomarkers of AIT and how we can implement changes in future studies to help us identify clinically relevant biomarkers of safety, compliance, and efficacy.

Biological therapy practice, biomarkers of severe asthma and novel approaches for attaining immunomodulation in upper airway disease

The hybrid rDer p 2231 stimulated in PBMCs isolated from atopic patients, higher levels of IL-2, IL-10, IL-15 and IFN-γ, as well as lower levels of IL-4, IL-5, IL-13, TNF-α and GM-CSF. The use of hybrid molecules as a therapeutic model in D. pteronyssinus allergic mice led to the reduction of IgE production and lower eosinophilic peroxidase activity in the airways. We found increased levels of IgG antibodies, which blocked the IgE binding to the parental allergens in serum of atopic patients. Furthermore, the stimulation of splenocytes from mice treated with rDer p 2231 induced higher levels of IL-10 and IFN-γ and decreased the secretion of IL-4 and IL-5, when compared to parental allergens and D. pteronyssinus extract. (7).