Allergen Immunotherapy: Biomarkers and Clinical Outcome Measures

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.

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.

Horse allergy: Curly Horses can mediate immune tolerance

American Bashkir Curly Horses are claimed to be hypoallergenic, but this has not been clinically proven. In the present study, the effect of exposure to Curly Horses was investigated in 141 patients allergic to horses by measuring their lung function and nasal patency during Curly Horse contact. Continuous contact with Curly Horses, including riding and brushing, decreased the allergic riders' reactivity as measured by FEV1, PEF, and PNIF. Subsequent visits (up to 40 or more hours of riding) further reduced reactivity to the Curly Horses. Allergic events to horses occurred only in 72 out of 1312 riding hours, mainly in the first ten riding hours.In 41 out of the 141 patients, it was further investigated whether repeated exposure to Curly Horses could induce tolerance to other horses. Patients in the tolerance induction study were tested annually for horse allergy using a nasal provocation test. The tolerance induction study showed that exposure to Curly Horses induced immune tolerance to other horses in 88% of patients who completed the study.To understand the mechanism causing hypoallergenicity, we performed IgE immunoblots to determine whether Curly Horse hairs contain IgE binding proteins. However, no differences in IgE reactivity were found between Curly and non-Curly Horses. Moreover, the immune tolerance induction study patients did not show decreased IgE reactivity to hairs from Curly or non-Curly Horses even though patients had developed tolerance. However, we did find increasing levels of anti-horse IgG antibodies in the study patients.Overall, our data strongly suggests that continuous exposure to Curly Horses can induce immune tolerance, rendering these patients non-reactive to horses. The reason for the reduced clinical allergenicity of Curly Horses remains unclear, but the data suggest that blocking IgG antibodies may be of importance for immune tolerance development.

Lack of Harmonized Adherence Criteria in Allergen Immunotherapy Prevents Comparison of Dosing and Application Strategies: A Scoping Review

Allergen immunotherapy (AIT) involves the application of increasing doses of allergen extract (as oral, sublingual, or subcutaneous immunotherapy) until immunologic tolerance is reached. Successful AIT relies on the consistent administration of allergen extract; therefore, adherence to these treatments is vital for compelling long-term results. Our review discusses the current terminology from adherence research in general, summarizes 25 current studies on adherence research in AIT in a scoping literature review, and delineates recommendations for tools and parameters for adherence research, aiming to improve outcomes in AIT. Almost every adherence study in AIT published to date used different tools, parameters, and data sources for measuring adherence and persistence rates. Unfortunately, an easily accessible, objective parameter or biomarker for monitoring treatment adherence and success has not yet been established for AIT. This situation calls for the development of an international core outcomes set for AIT that defines what is exactly meant by AIT adherence and how AIT adherence should be consistently measured. Therefore, we exemplarily present results and conclusions from adherence research in chronic diseases other than allergology. We aim to facilitate the development of advanced methods, considering the challenging disease specificities of these parameters in a routine care setting of AIT.

A single center retrospective study of systemic reactions' distribution and risk factors to subcutaneous immunotherapy with dust mite extract in patients with allergic rhinitis and/ or asthma

To analyze various risk factors including causes that may lead to adverse reactions, especially systemic adverse reactions（SRs）, before and after mite allergen subcutaneous immunotherapy (SCIT), so as to provide real-world reference data for further improving the safety of mite allergen SCIT. Methods: The local adverse reactions（LRs）and SRs of 230 patients with allergic rhinitis and/or asthma who received SCIT in Weifang people's hospital were analyzed retrospectively. The data of patient characteristics, drug factors and environmental elements of adverse reactions were collected and statistically analyzed. Results: There were 28 cases (12.2%) of SRs in 230 patients. All the patients received a total of 7515 injections and 37 SRs (0.49%) were observed. 32.4% (12/37) of SRs could identify their external and subjective triggers. SRs patients had higher 2-year SCIT compliance than no-SRs patients (p = 0.026). The prevalence of SRs in SCIT patients with atopic dermatitis or simple allergic asthma are no statistical significance (P = 0.111). Conclusion: the incidence of SRs in this study is within an ideal range. Through professional patient education and pre injection risk factor assessment, Compliance is still well-controlled and guaranteed although SRs occurred.

Mast Cell Desensitization in Allergen Immunotherapy

Allergen immunotherapy (AIT) is the only treatment with disease-transforming potential for allergic disorders. The immunological mechanisms associated with AIT can be divided along time in two phases: short-term, involving mast cell (MC) desensitization; and long-term, with a regulatory T cell (Treg) response with significant reduction of eosinophilia. This regulatory response is induced in about 70% of patients and lasts up to 3 years after AIT cessation. MC desensitization is characteristic of the initial phase of AIT and it is often related to its success. Yet, the molecular mechanisms involved in allergen-specific MC desensitization, or the connection between MC desensitization and the development of a Treg arm, are poorly understood. The major AIT challenges are its long duration, the development of allergic reactions during AIT, and the lack of efficacy in a considerable proportion of patients. Therefore, reaching a better understanding of the immunology of AIT will help to tackle these short-comings and, particularly, to predict responder-patients. In this regard, omics strategies are empowering the identification of predictive and follow-up biomarkers in AIT. Here, we review the immunological mechanisms underlying AIT with a focus on MC desensitization and AIT-induced adverse reactions. Also, we discuss the identification of novel biomarkers with predictive potential that could improve the rational use of AIT.

Predictive Response to Immunotherapy Score: A Useful Tool for Identifying Eligible Patients for Allergen Immunotherapy

A specific predictive tool of allergen immunotherapy (AIT) outcome has not been identified yet. This study aims to evaluate the efficacy of a disease score referred to as Predictive Response to Immunotherapy Score (PRIS) to predict the response to AIT and identify eligible patients. A total of 110 patients diagnosed with allergic rhinitis with or without concomitant asthma were enrolled in this study. Before beginning sublingual immunotherapy (SLIT), patients were evaluated by analyzing clinical and laboratory parameters. A specific rating was assigned to each parameter to be combined in a total score named PRIS. At baseline (T0) and follow-up [after 12 (T12) and 24 months (T24) of SLIT], a Visual Analogue Scale (VAS) was used to calculate a mean symptom score (MSS). Finally, the percentage variation between the MSS at T0 and at T12 [ΔMSS-12(%)] and T24 [ΔMSS-24 (%)] was measured. We observed a significant improvement of symptoms at T12 and T24 compared to T0 in all groups undergoing SLIT. PRIS was effective in predicting ΔMSS-24 (%) in patients treated with single-allergen SLIT. In addition, PRIS was effective in predicting ΔMSS-24 (%) in both patients with only rhinitis and with concomitant asthma. PRIS assessment can represent a useful tool to individuate potential responders before SLIT prescription.

Intralymphatic Immunotherapy (ILIT) With Bee Venom Allergens: A Clinical Proof-of-Concept Study and the Very First ILIT in Humans

Background

Subcutaneous venom immunotherapy (VIT) represents an effective treatment against bee venom allergy. However, it involves long treatment times, high costs, and the risk of adverse events (AEs). Shorter, safer, and cheaper treatment options are therefore pursued.

Objective

To determine the safety, immunogenicity, and efficacy of bee venom intralymphatic immunotherapy (ILIT).

Methods

In an open pilot study, 12 patients received bee venom ILIT in three sessions with 14-day intervals: 0.1–5 μg/dose. Ultrasound imaging was applied to guide an injection and to document the lymph node structure. In a second study, 67 patients from 15 centers in Europe and Australia were randomized to receive four doses of either 10- or 20-μg bee venom ILIT with 28-day intervals. Clinical endpoints included specific IgE and IgG and protection after a bee sting challenge. These studies were performed in the years 2000–2003.

Results

In a proof-of-concept study, no serious AEs were observed. An increase in allergen-specific IgG1 but no IgG4 and IgE was observed. ILIT induced the protection against a bee sting challenge in 7 out of 8 challenged patients. In a multicenter study, an increase in allergen-specific IgG and IgE was observed, with the highest increase in patients receiving a higher ILIT dose. The study was terminated due to several serious AEs upon the sting challenge provocation after the completion of treatment. However, out of 45 patients challenged, 15 (65%) and 18 (82%) patients in the 10- and 20-μg group, respectively, showed an improvement of two grades or more. No correlation was observed between antibody levels and sting protection.

Conclusions

While a pilot study suggested the safety and efficacy of bee venom ILIT, a high number of AEs seen after the sting challenge following a randomized study indicate that the immunology protection offered by bee venom ILIT is insufficient. Of note, the bee venom allergen extract used in the two studies were from the two different providers. While the first study used a formulation approved for use in subcutaneous VIT, the second study used a nonapproved formulation never tested in humans. Further studies on approved formulations should be performed to generate conclusive results regarding the safety and efficacy of bee venom ILIT.

Workup and Clinical Assessment for Allergen Immunotherapy Candidates

Allergen Immunotherapy (AIT) is a well-established, efficient, and safe way to treat respiratory and insect-venom allergies. After determining the diagnosis of the clinically relevant culprit allergen, AIT can be prescribed. However, not all patients are eligible for AIT, since some diseases/conditions represent contraindications to AIT use, as described in several guidelines. Allergists are often preoccupied on whether an extensive workup should be ordered in apparently healthy AIT candidates in order to detect contra-indicated diseases and conditions. These preoccupations often arise from clinical, ethical and legal issues. The aim of this article is to suggest an approach to the workup and assessment of the presence of any underlying diseases/conditions in patients with no case history before the start of AIT. Notably, there is a lack of published studies on the appropriate evaluation of AIT candidates, with no globally accepted guidelines. It appears that Allergists are mostly deciding based on their AIT training, as well as their clinical experience. Guidance is based mainly on experts’ opinions; the suggested preliminary workup can be divided into mandatory and optional testing. The evaluation for possible underlying neoplastic, autoimmune, and cardiovascular diseases, primary and acquired immunodeficiencies and pregnancy, might be helpful but only in subjects for whom the history and clinical examination raise suspicion of these conditions. A workup without any reasonable correlation with potential contraindications is useless. In conclusion, the evaluation of each individual candidate for possible medical conditions should be determined on a case-by-case basis.

Advances and highlights in biomarkers of allergic diseases

During the past years, there has been a global outbreak of allergic diseases, presenting a considerable medical and socioeconomical burden. A large fraction of allergic diseases is characterized by a type 2 immune response involving Th2 cells, type 2 innate lymphoid cells, eosinophils, mast cells, and M2 macrophages. Biomarkers are valuable parameters for precision medicine as they provide information on the disease endotypes, clusters, precision diagnoses, identification of therapeutic targets, and monitoring of treatment efficacies. The availability of powerful omics technologies, together with integrated data analysis and network‐based approaches can help the identification of clinically useful biomarkers. These biomarkers need to be accurately quantified using robust and reproducible methods, such as reliable and point‐of‐care systems. Ideally, samples should be collected using quick, cost‐efficient and noninvasive methods. In recent years, a plethora of research has been directed toward finding novel biomarkers of allergic diseases. Promising biomarkers of type 2 allergic diseases include sputum eosinophils, serum periostin and exhaled nitric oxide. Several other biomarkers, such as pro‐inflammatory mediators, miRNAs, eicosanoid molecules, epithelial barrier integrity, and microbiota changes are useful for diagnosis and monitoring of allergic diseases and can be quantified in serum, body fluids and exhaled air. Herein, we review recent studies on biomarkers for the diagnosis and treatment of asthma, chronic urticaria, atopic dermatitis, allergic rhinitis, chronic rhinosinusitis, food allergies, anaphylaxis, drug hypersensitivity and allergen immunotherapy. In addition, we discuss COVID‐19 and allergic diseases within the perspective of biomarkers and recommendations on the management of allergic and asthmatic patients during the COVID‐19 pandemic.