Mechanisms and Predictive Biomarkers of Allergen Immunotherapy in the Clinic

Biomarker-driven drug development for allergic diseases and asthma: An FDA public workshop

The US Food and Drug Administration (FDA) hosted a workshop on February 22, 2024, to discuss the status of biomarkers in drug development for allergic asthma and food allergy. The workshop provided a forum for open discussion among regulators, academicians, National Institutes of Health staff and industry to inform stakeholders of the requirements for the FDA to adopt a biomarker as a surrogate end point for a clinical trial, and to inform FDA of the status of various biomarkers in development. The workshop was divided into 3 sessions: (1) FDA and European Union regulators discussing regulatory perspectives on use of biomarkers in drug development programs, (2) investigators discussing biomarkers for pediatric and adult asthma, and (3) investigators discussing biomarkers for food allergy. In this report, we review the information presented at the workshop and summarize the current status of potential biomarkers for these allergic diseases.

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.

Polymerised mite allergoids with glutaraldehyde reduce proteolytic activity and enhance the stability of allergen mixtures: a proof of concept with grass mixtures

Background

Polysensitized patients require allergen immunotherapy (AIT) targeting multiple allergens. However, combining allergen extracts can lead to instability and reduced efficacy particularly due to the high proteolytic activity of house dust mite (HDM) allergens. While is known that glutaraldehyde cross-linking may reduce enzymatic activity, its ability to stabilize multi-allergen formulations and protect key allergens from degradation remains unexplored.

Objective

To evaluate the impact of glutaraldehyde polymerization on the stability and immunogenicity of HDM and grass pollen allergen formulations, addressing proteolytic activity challenges in multi-allergen vaccines.

Methods

Stability was assessed over 24 months through protein quantification and antigenic activity assays. Proteolytic activity of HDM-containing extracts was measured using Azocoll, and peptide substrate-based enzymatic assays. Grass pollen allergen degradation was evaluated by SDS-PAGE, immunoblotting, and ELISA Immunogenicity was assessed in mice immunized with grass allergoids alone or in combination with glutaraldehyde-polymerised HDM, measuring IgG responses, splenocyte proliferation, and IL-10 production.

Results

Glutaraldehyde polymerization significantly reduced HDM proteolytic activity (p < 0.0001), achieving reductions of 97.7%, 77.9%, and 89.9% in total protease activity, cysteine protease activity, and serine protease activity, respectively. This inhibition protected grass pollen allergens when mixed with HDM from degradation, ensuring consistent protein content and antigenic activity over 24 months. Mice immunized with grass allergoids alone or combined with polymerised mite extracts showed similar IgG responses and T-cell activation, indicating no compromise in the immune response to grass allergens, with IL-10 secretion confirming preserved regulatory responses.

Conclusions

Polymerised allergen extracts address the challenges of proteolytic degradation in multi-allergen formulations, offering stable, immunogenic vaccines that maintain efficacy and provide a reliable treatment option for polyallergic patients.

The role of allergen-specific regulatory T cells in the control of allergic disease

Allergies result from an antigen-specific loss of tolerance against innocuous foreign substances. Allergen immunotherapy (AIT) aims to reverse the pathogenic response and to re-establish physiological tolerance. However, the tolerogenic mechanisms that prevent allergy in healthy and act during AIT are still obscure. Foxp3 expressing 'regulatory' CD4 T cells (Tregs) are essential mediators of tolerance against allergens. It remains controversial which antigen specificity of Tregs is required to prevent allergy and the role of allergen-specific Tregs during AIT. Recent work provided precise insight into physiological T cell responses against environmental and food compounds. This identified Treg responses mainly against peptides and proteins not involved in immune pathology, revealing an unexpected role of Treg antigen specificity for tolerance. This review will focus on antigen-specific Treg responses against food and airborne allergens, and the impact of the technological approach utilized for antigen-specific Treg characterization is discussed, with critical points to be addressed in future research.

[Mechanisms of allergen-specific immunotherapy]

Allergen-specific immunotherapy (AIT) has been a longstanding treatment for allergic diseases. Historically, subcutaneous immunotherapy was the main approach, but with the development of sublingual preparations, which are associated with fewer systemic side effects, sublingual immunotherapy is gaining global popularity. In Japan, the approval of standardized sublingual immunotherapy preparations in 2014 has significantly accelerated its adoption. The mechanism of allergic inflammation is divided into sensitization and elicitation phases. The sensitization phase involves the production of antigen-specific IgE antibodies against a particular antigen. These IgE antibodies bind to FcεRI on mast cells and basophils, preparing the body for an allergic response. The elicitation phase occurs when the body, already primed with these antibodies, is re-exposed to the same antigen, triggering inflammation and symptoms. This phase includes mechanisms where IgE-mediated mast cell activation leads to degranulation and where local Th2 cell activation induces inflammation. While the mechanisms of AIT are not fully understood, they are categorized into desensitization and immune tolerance. Desensitization is induced by reducing the responsiveness of mast cells and basophils to the antigen. Immune tolerance involves the production of antigen-specific IgG4 antibodies that compete with IgE for antigen binding, and the induction of regulatory T cells and other anti-inflammatory immune cells producing cytokines such as IL-10. AIT still faces challenges, such as the lack of predictive biomarkers for efficacy. Recent studies indicate that HLA genotypes influence AIT responsiveness. Advances in genetic and single-cell analysis are expected to address these challenges, paving the way for improved treatment outcomes.

Allergen-specific immunotherapy at the extremes of age: below 5 years and elderly: evidence beyond indications?

PURPOSE OF REVIEW

Allergen-specific immunotherapy (AIT) has been used in clinical practice to treat allergic diseases for over 100 years. The effectiveness and safety of AIT have been substantiated in numerous studies; however, children before 5 years of age and elderly are not encompassed generally. This review aims to present the current understanding of AIT in the extremes of age.

RECENT FINDINGS

Early allergen immunotherapy during infancy or early childhood may prevent the development of allergic sensitization to common allergens, thereby reducing the risk of developing allergic diseases later in life. In the elderly, improved symptoms and quality of life and reduced dependence on medication are indicated the importance on the implementation of AIT. Both clinical and immunological parameters demonstrated that the treatment was effective at the time of cessation and trend to sustained tolerance.

SUMMARY

There is no specific lower or upper age limit for initiating immunotherapy; however, it is important to thoroughly evaluate the severity of disease and the risks and benefits in each case.

A Modern Approach to Clinical Outcome Assessment in Allergy Management: Advantages of Allergen Exposure Chambers

Allergic diseases triggered by airborne allergens such as allergic rhinitis and conjunctivitis are increasingly prevalent, posing significant challenges for both patients and healthcare systems. Assessing the efficacy of allergen immunotherapy and other anti-allergic treatments requires precise and reproducible methods. Allergen exposure chambers (AECs) have emerged as advanced tools for evaluating clinical outcomes, offering controlled conditions that address many limitations of traditional field-based studies. This review explores the advantages of AECs in allergy management, emphasizing their role in providing standardized allergen exposure for both clinical research and routine assessments. AECs deliver consistent and reproducible data comparable to the nasal allergen challenge and natural allergen exposure, making them a valuable addition to the diagnosis and treatment effectiveness of allergic diseases. Although they are well suited to early-stage clinical trials, further standardization and validation are needed to gain broader acceptance in pivotal phase III studies. Future research should focus on refining AEC protocols and integrating them into regulatory frameworks, ensuring their role in the advancement of therapeutic approaches for allergic diseases.

Green carbon dots derived from Zingiberis Rhizoma Carbonisatum alleviate ovalbumin-induced allergic rhinitis

Background

Allergic rhinitis (AR) affects up to 40% of the population, leading to significant healthcare expenditures. Current mainstream treatments, while effective, can lead to side effects and do not address the underlying immunological imbalances. Zingiberis Rhizoma Carbonisatum (ZRC), the partially charred product of Zingiberis Rhizoma (ZR), has been widely used clinically in China since ancient times to treat respiratory disorders.

Methods

Inspired by the similarity between high-temperature pyrolysis and carbonization processing of herbal medicine, ZRC derived CDs (ZRC-CDs) were extracted and purified through several procedures. Then, the physicochemical characteristics of CDs were delineated through a suite of characterization methods. Moreover, our investigation zeroed in on elucidating the ameliorative impacts of CDs on ovalbumin-induced rat models alongside their underlying mechanisms.

Results

ZRC-CDs with particle sizes ranging from 1.0 to 3.5 nm and rich surface functional groups. Additionally, we observed that ZRC-CDs significantly attenuated nasal symptoms and pathological damage in ovalbumin-induced AR rats, and modulated lipid metabolism and type 2 inflammatory responses. They also inhibit PI3K/AKT and JAK/STAT pathways, which are associated with metabolism and inflammation. Importantly, ZRC-CDs demonstrated high biocompatibility, underscoring their potential as a novel therapeutic agent.

Conclusion

ZRC-CDs offer a promising alternative for AR treatment and could help facilitate broader clinical use of the ZRC. In addition, the exploration of the inherent bioactivity of CDs can help to broaden their biological applications.

Novel Approaches to Allergen Immunotherapy for Respiratory Allergies

Allergen immunotherapy (AIT) remains the cornerstone for managing respiratory allergies, offering long-term symptom relief, disease modification, and prevention of disease progression. While novel approaches like intralymphatic and epicutaneous immunotherapy and the combination of allergens with adjuvants show promise, traditional methods remain effective and safe. Hypoallergenic T-cell peptide vaccines and recombinant allergens require further research to confirm their clinical benefits. Passive immunotherapy, while demonstrating effectiveness in specific cases, needs exploration of its long-term efficacy and broader applicability. Combining AIT with biologics may enhance safety and treatment outcomes. Despite emerging innovations, allergen-specific immunotherapy with natural allergen extracts remains the primary disease-modifying treatment, offering long-term symptom relief and prevention of disease progression. Continued research is essential to refine and optimize allergen immunotherapy strategies, providing patients with more effective and personalized treatment options.

Single-Domain Antibodies-Novel Tools to Study and Treat Allergies

IgE-mediated allergies represent a major health problem in the modern world. Apart from allergen-specific immunotherapy (AIT), the only disease-modifying treatment, researchers focus on biologics that target different key molecules such as allergens, IgE, or type 2 cytokines to ameliorate allergic symptoms. Single-domain antibodies, or nanobodies, are the newcomers in biotherapeutics, and their huge potential is being investigated in various research fields since their discovery 30 years ago. While they are dominantly applied for theranostics of cancer and treatment of infectious diseases, nanobodies have become increasingly substantial in allergology over the last decade. In this review, we discuss the prerequisites that we consider to be important for generating useful nanobody-based drug candidates for treating allergies. We further summarize the available research data on nanobodies used as allergen monitoring and detection probes and for therapeutic approaches. We reflect on the limitations that have to be addressed during the development process, such as in vivo half-life and immunogenicity. Finally, we speculate about novel application formats for allergy treatment that might be available in the future.

Is allergen immunotherapy a model of personalized treatment in pediatric respiratory allergy?

PURPOSE OF REVIEW

To review recent evidence on allergen immunotherapy (AIT) as a model of personalized medicine in the treatment of children and adolescents with respiratory allergies.

RECENT FINDINGS

Meta-analysis and systematic review studies continue to point out that AIT is an effective treatment for children with respiratory allergies. Molecular allergy allows the understanding of patient sensitization profiles that frequently change the prescription of AIT. There is still a lack of evidence showing that this personalized prescription of AIT is associated with better clinical outcomes. The nasal allergen challenge has extended the indications of AIT for a new group of subjects with local allergic rhinitis. Patient selection of allergens involved in the increasingly personalized composition of extracts to be used in AIT increasingly characterizes it as personalized medicine.

SUMMARY

Despite the numerous studies carried out to identify the best biomarker to evaluate the response to AIT, there is still much disagreement, and clinical assessment (symptoms, quality of life, among others) continues to be the best way to evaluate the therapeutic success of AIT.