Understanding differences in allergen immunotherapy products and practices in North America and Europe.

Allergen immunotherapy (AIT) is thought to be clinically effective and safe in treating allergic rhinitis, asthma, and stinging insect allergy in Europe and North America. However, there are intercontinental differences in AIT therapeutic products in terms of their application and regulation. In North America unmodified standardized and nonstandardized aqueous aeroallergen extracts are approved and used almost exclusively for subcutaneous immunotherapy, whereas more product options are available in Europe, including adsorbed allergens, chemically modified allergens, or both. Both liquid extracts and tablets are approved for sublingual immunotherapy in Europe. Nevertheless, within the European Union, there are major differences in AIT products approved and used in individual countries. There are major differences in the clinical approach to subcutaneous immunotherapy in polysensitized patients; in the United States mixed extracts containing multiple aeroallergens are used, whereas European allergists preferably administer separate injections of single allergen sources or homologous groups deemed to be clinically relevant. Moreover, the regulatory approach differs between the European Union and United States. In contrast to the United States, where common allergen standards exist based on biologic activity, no common standards exist in Europe. In terms of development of new investigational products, the United States has followed the European example for phase II and III studies; no formal US Food and Drug Administration guidance has been issued.

An evaluation of veterinary allergen extract content and resultant canine intradermal threshold concentrations.

BACKGROUND: Limited information is available for dogs on threshold concentrations (TCs), and the protein composition of common allergenic extracts produced by different manufacturers. HYPOTHESIS/OBJECTIVES: To characterize the protein heterogeneity of tree, grass, weed and mite allergens from different lots of allergenic extracts, and to determine intradermal TCs for healthy dogs using extracts from two manufacturers. ANIMALS: Twenty five privately owned, clinically healthy dogs and ten purpose-bred beagle dogs. METHODS AND MATERIALS: Protein concentration and heterogeneity of 11 allergens from two manufacturers were evaluated using a Bradford-style assay and SDS-PAGE. Intradermal testing was performed with 11 allergens from each company at four dilutions. Immediate reactions were subjectively scored (0 to 4+), and objectively measured (mm) and their percentage concordance evaluated. Model-based TCs were determined by fitting positive reactions (≥2+) at 15 min to generalized estimating equations. RESULTS: Allergen extract protein quantity and composition varied within and between manufacturers despite sharing the same PNU/mL values. Model-based TCs of one weed, five trees, two grasses and a house dust mite were determined for extracts from Manufacturer 1 (M1), and for extracts of three weeds, three trees and two grasses from Manufacturer 2 (M2). Receiver operating characteristic curve analyses determined a percentage concordance of the objective and subjective measurements of 77.3% for M1 and 75% for M2 allergens. CONCLUSIONS AND CLINICAL IMPORTANCE: Veterinary allergen extracts labelled as the same species and PNU/mL are not standardized; they show heterogeneity in composition and potency within and between manufacturers. Variability in extract content may require adjustment of intradermal testing concentrations.

Hymenoptera venoms used to produce allergen extracts.

OBJECTIVE: To review the methods and materials used for collection, purification, commercial production, and clinical application of Hymenoptera venoms. DATA SOURCES: Most of the sources for this review are the experience and expertise of the authors. Published reports and review articles on Hymenoptera venom collection and production were identified through database searches (PubMed). STUDY SELECTIONS: Studies describing the methods for Hymenoptera venom collection and production were selected for review. RESULTS: Meticulous methods for identification and collection of the insects are required. Collection and purification of the venoms from the insects are based on validated methods and result in a commercial extract that is standardized for the major allergenic proteins required for accurate diagnosis and safe and effective treatment of patients allergic to insect sting. The steps required for mixing, purifying, testing, and standardizing the products are described. CONCLUSION: Hymenoptera venom extracts were developed using many new methods for the collection, purification, and commercial production of the unique materials required for this product. Clinical applications for diagnosis and treatment are affected by the integrity and stability of the allergens after processing and purification.

Major allergen content consistency of SQ house dust mite sublingual immunotherapy tablets and relevance across geographic regions.

BACKGROUND: Consistency in composition and potency, particularly regarding major allergens, is crucial for the quality of extracts for allergen immunotherapy. OBJECTIVE: To characterize the major allergen composition of house dust mite (HDM) extracts commercially available in the United States and the SQ HDM sublingual immunotherapy (SLIT) tablet, and to relate the composition to patient sensitization patterns. METHODS: Der 1/Der 2 ratios were determined in 10,000- and 30,000-AU/mL HDM extracts from 5 US companies and the SQ HDM SLIT-tablet. Allergen content was analyzed by enzyme-linked immunosorbent assay and compared with an in-house reference. Sensitivity toward Der p 1, Der p 2, and Der p 10 was determined in serum from randomly selected subgroups of 220 individuals from North American and European SQ HDM SLIT-tablet trials. RESULTS: Mean Der 1/Der 2 ratios in US HDM extracts ranged from 0.4 to 20.5. For the SQ HDM SLIT-tablet (20 batches), variability did not exceed 12% regarding content of Der f 1 (SD, 11.9%; 95% confidence interval [CI], 0.94-1.06), Der p 1 (SD, 6.1%; 95% CI, 0.97-1.03), and combined Der 2 allergen (SD, 6.4%; 95% CI, 0.97-1.03), indicating a consistent Der 1/Der 2 ratio. High allergen sensitivity frequencies toward Der p 1 and Der p 2 were observed regardless of geographic region. Efficacy of the SQ HDM SLIT-tablet has been demonstrated in 5 clinical trials. CONCLUSION: The SQ HDM SLIT-tablet has efficacy potential for a broad range of patients because it includes a consistent 1:1 ratio of the 2 major HDM allergens to which individuals were most frequently sensitized across geographic regions. Efficacy has been demonstrated.

The Art of Dosing for Subcutaneous Immunotherapy in North America.

Subcutaneous immunotherapy (SCIT) is a long-established treatment option for allergic rhinoconjunctivitis. Proper dosing of the allergens is critical for the efficacy and safety of SCIT. Of the hundreds of liquid allergen extracts in the United States, effective and well-tolerated SCIT dosing has only been established for a small number. Thus, SCIT dosing remains largely empiric and continues to be, by necessity, an art. To highlight the complexity of SCIT dosing, this review summarizes the historical and current landscape of U.S. allergen extracts, differences among U.S. and European allergen extracts, allergen selection for SCIT, considerations for compounding of allergen extract mixtures, and recommended dosing. As of 2021, 18 standardized allergen extracts are available in the United States; all other extracts remain unstandardized without characterization of allergen content or potency. U.S. allergen extracts differ from European extracts in formulation and potency characterization. There is no standardized methodology for SCIT allergen selection, and interpretation of allergen sensitization is not straightforward. Compounding of SCIT mixtures requires consideration of potential dilution effects, allergen cross-reactivity, proteolytic activity, and additives. Probable effective dose ranges for SCIT are recommended in U.S. allergy immunotherapy practice parameters, although there are few studies using U.S. extracts supporting these doses as therapeutic. In contrast, optimized doses of sublingual immunotherapy tablets have been confirmed in North American phase 3 trials. The SCIT dosing for each patient remains an art that requires clinical experience and consideration of polysensitization, tolerability, compounding of allergen extract mixtures, and the range of recommended doses within the context of extract potency variability.

Immunotherapy preparation guidelines, rules, and regulation.

Allergen immunotherapy has been used to treat allergic diseases for more than 100 years. In the U.S., the preparation of diagnostic and therapeutic extracts requires the cooperation of the extract manufacturer, who provides the individual allergen concentrates, and the practicing physician who formulates, dilutes, and administers the final patient-specific treatment extract. The guidelines, rules, and regulations for these activities have been established and continue to be developed as progress is made. The molecular characterization and standardization of allergenic extracts has allowed for improvements in defining the potency of these products. In turn, these advances have led to improved dosing regimens and formulation practices. This review will describe in detail some of these interactions and will identify issues that require more attention.

Extrapolating Evidence-Based Medicine of AIT Into Clinical Practice in the United States.

Allergy/immunology specialists in the United States prescribing allergy immunotherapy (AIT) have placed a heavy value on practical experience and anecdotal evidence rather than research-based evidence. With the extensive research on AIT conducted in the last few decades, the time has come to better implement evidence-based medicine (EBM) for AIT. The goal of this review was to critically assess EBM for debated concepts in US AIT practice for respiratory allergies in the context and quality of today's regulatory standards. Debated topics reviewed were the efficacy and safety of AIT in various subgroups (eg, polyallergic patients, older patients, patients with asthma, and pregnant women), diagnosis topics (eg, skin prick test vs allergen-specific serum IgE, factors affecting skin prick tests, use of nasal or conjunctival allergen challenges, and telemedicine for diagnosis), and dosing topics (eg, optimal dosing for subcutaneous immunotherapy and sublingual immunotherapy tablets, US liquid allergen extract history, duration of treatment, and biomarkers of efficacy). In addition, EBM for patient-centered AIT issues (eg, adherence, use of practice guidelines, and pharmacoeconomics) and the approach to implementation of AIT EBM in future clinical practice were addressed. The EBM for each concept was briefly summarized, and when possible, a practical, concise recommendation was given.

Allergen immunotherapy practice in the United States: guidelines, measures, and outcomes.

To discuss recent issues pertinent to allergen immunotherapy practice in the United States. Allergen extract preparation guidelines, updated allergen immunotherapy practice parameter (AIPP) guidelines, and evolving trends in how immunotherapy outcomes will be measured and assessed. Allergen extract preparation guidelines have been established by 2 entities: the US Pharmacopeia and an American Academy of Allergy, Asthma, and Immunology/American College of Allergy, Asthma, and Immunology/Joint Council of Allergy, Asthma, and Immunology Joint Task Force. Minor differences exist between these guidelines, but both focus on aseptic techniques and require that compounding personnel pass a written examination and annual media fill test. The AIPP third update provides new dosing recommendations for Bermuda grass, imported fire ant, and nonstandardized extracts distinguishing between pollen (0.5 mL of a 1:100 or 1:200 vol/vol) and mold/fungi or cockroach (highest tolerated dose) extracts. Because of limited and sometimes conflicting data on high and low proteolytic-containing extract compatibility, the AIPP continues to recommend against mixing these together. Although the AIPP does not specifically recommend a specific diluent, recent evidence suggests normal saline may not be as effective a stabilizer for extract dilutions as glycerin or human serum albumin. Currently, immunotherapy efficacy is determined with subjective assessments that rely on patient reporting, but this may change as health care reform evolves. It will likely become more important for US allergy/immunology practices to demonstrate immunotherapy comparative-effectiveness and report quality measures. Recent comparative-effectiveness studies have demonstrated the cost-effectiveness of immunotherapy compared with symptomatic drug treatment.

Maintenance dosing for sublingual immunotherapy by prominent European allergen manufacturers expressed in bioequivalent allergy units.

BACKGROUND: Sublingual immunotherapy (SLIT) has become established in Europe, and its efficacy is being evaluated in the United States. The doses used for SLIT in Europe today are difficult to evaluate, because each manufacturer expresses the potency of its extracts differently. OBJECTIVES: To compare in vitro European SLIT maintenance solutions against US licensed standardized allergenic extract concentrates and to determine the monthly SLIT doses delivered expressed in bioequivalent allergy units ([B]AU). METHODS: We studied Dermatophagoides pteronyssinus, timothy grass pollen, cat (hair) and short ragweed pollen allergen extracts. The SLIT maintenance solutions of 4 leading European manufacturers and standardized concentrate extracts of 3 US manufacturers were analyzed with the following assays: protein content, relative potency (immunoglobulin E [IgE]-binding enzyme-linked immunosorbent assay [ELISA] inhibition) and major allergen content. The relative monthly allergen dose in (B)AU was calculated for each recommended SLIT schedule. RESULTS: Relative potency was approximately 10 times higher for US concentrate standardized extracts-which are meant to be diluted-than for European SLIT maintenance solutions of D pteronyssinus and timothy grass pollen. For cat (hair) and short ragweed pollen, the difference was less. Measurements of relative potency and major allergen content correlated well. In our assays, European mite extracts contain a very low quantity of Der p 2 compared with US mites. CONCLUSION: Recommended SLIT doses in Europe vary widely among the manufacturers, but are consistently lower (Eur1) or higher (Eur4) over all four allergens tested. SLIT efficacy probably depends on additional factors apart from the exact dose. SLIT dose finding studies should be done for each product.

Update: stability of allergen extracts to establish expiration dating.

PURPOSE OF REVIEW: The article reviews studies pertaining to US manufactured allergen extract stability that contribute to guidance for expiration dating for bulk concentrates, diluted patient testing and treatment vials, and adjustments following elevated temperature excursions. RECENT FINDINGS: Studies on allergen stability were completed to satisfy the Food and Drug Administration requirements supporting labeled expiration dating for standardized short ragweed, dust mites, cat, grass, and venom extracts and are not published. These studies demonstrated the stability enhancing parameters of 50% glycerin and support the Food and Drug Administration mandated expiration of nonstandardized extracts allowing glycerin extracts twice the dating of nonglycerin aqueous extracts. Patient vials are commonly given 6-12 months dating. There is adequate evidence that human serum albumin stabilizes low protein diluted vials. High protease allergens such as molds and insects compromised potency of pollens when mixed. Subsequent work continued to define the effects of diluents on extract dilutions, temperature excursions that occasionally occur with shipping or refrigerator malfunctions, and allergen compatibility. SUMMARY: Potency has been determined for allergen dilutions with diluents typically used for allergen immunotherapy. These studies along with changes of potency under various storage conditions and mixing designed to improve our guidance on expiration dating of allergen extracts will be discussed.

Allergen stability of testing/treatment boards and immunotherapy vials with various diluents.

BACKGROUND: Otolaryngologists commonly use glycerin and normal saline with phenol (NSP) in diluting solutions to help preserve allergenicity in immunotherapy vials. Studies have shown that diluting with human serum albumin (HSA) may provide better allergen stability. The purpose of this study was to assess the ability of various diluents to preserve allergen content in testing/treatment boards (TTBs) and immunotherapy treatment vials (ITVs) at multiple time points. METHODS: TTBs with 4 allergens were prepared with HSA, NSP, 10% glycerin, and 50% glycerin. The major allergen content of the TTBs was measured at creation (time 0), 3 days, 8 weeks, and 18 weeks. Multiallergen ITVs containing the 4 allergens were prepared from the NSP board (diluted to 10% glycerin) and the HSA board (diluted in HSA) at the time of making the freshly prepared TTBs and again 8 weeks later, simulating the creation of ITVs from a "new" and an "old" TTB. The major allergen content of these ITVs was determined at creation and at interval time points thereafter. RESULTS: TTBs and ITVs showed a substantial loss of allergen at day 3. The loss of allergen was more pronounced in the more dilute (#4, #5, and #6) vials. HSA and 50% glycerin showed superior allergen preservation compared to NSP and 10% glycerin in TTBs. HSA showed superior allergen preservation compared to 10% glycerin-NSP in ITVs. CONCLUSION: The use of HSA as a diluent in TTBs and ITVs showed superior allergen preservation compared to NSP and 10% glycerin, particularly for more dilute vials.

Stability of allergen extracts used in skin testing and immunotherapy.

PURPOSE OF REVIEW: The present article reviews allergen extract stability applied to US manufactured products. Methods used to measure potency of extract concentrates, patient prescription dilute extracts, and mixes containing degrading enzymes will be discussed. RECENT FINDINGS: Information about the allergen extract active ingredient components contributing to potency is increasing. Pertinent stability issues include the type of diluent used for extraction and mixing. Fifty percent glycerin greatly extends the time over which extracts remain potent, including in mixes with fungal and insect extracts known to contain protein-degrading enzymes. Diluents that contain additional protein content such as human serum albumin increase stability of dilute solutions. Many of the most rigorous studies on allergen stability have been performed by allergenic extract manufacturers in support of Food and Drug Administration approved dating for standardized products and are not published. SUMMARY: Studies addressing how antigens in extracts change under various storage conditions have provided general guidance for expiration dating, but the diversity of extracts and testing methods have been less than complete. Additional findings that are increasing our knowledge of extract shelf life will be discussed.