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Respiratory and Allergy Clinic, DIMI—Department of Internal Medicine, University of Genoa, IRCCS Aou San Martino, Largo Rosanna Benzi 10, Genoa 1-16132, Italy
Center for Rhinology and Allergology Wiesbaden, Department of Otorhinolaryngology, Head and Neck Surgery, University Hospital Mannheim, Mannheim, Germany
Department of Paediatrics, University Children’s Medical Institute, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
We have prepared this document, “Sublingual Immunotherapy: World Allergy Organization Position Paper 2013 Update”, according to the evidence-based criteria, revising and updating chapters of the originally published paper, “Sublingual Immunotherapy: World Allergy Organization Position Paper 2009”, available at http://www.waojournal.org. Namely, these comprise: “Mechanisms of sublingual immunotherapy;” “Clinical efficacy of sublingual immunotherapy” – reporting all the data of all controlled trials published after 2009; “Safety of sublingual immunotherapy” – with the recently published Grading System for adverse reactions; “Impact of sublingual immunotherapy on the natural history of respiratory allergy” – with the relevant evidences published since 2009; “Efficacy of SLIT in children” – with detailed analysis of all the studies; “Definition of SLIT patient selection” – reporting the criteria for eligibility to sublingual immunotherapy; “The future of immunotherapy in the community care setting”; “Methodology of clinical trials according to the current scientific and regulatory standards”; and “Guideline development: from evidence-based medicine to patients' views” – including the evolution of the methods to make clinical recommendations.
Additionally, we have added new chapters to cover a few emerging crucial topics: “Practical aspects of schedules and dosages and counseling for adherence” – which is crucial in clinical practice for all treatments; “Perspectives and new approaches” – including recombinant allergens, adjuvants, modified allergens, and the concept of validity of the single products. Furthermore, “Raising public awareness about sublingual immunotherapy”, as a need for our patients, and strategies to increase awareness of allergen immunotherapy (AIT) among patients, the medical community, all healthcare stakeholders, and public opinion, are also reported in detail.
This article was originally published online on 28 March 2014
Foreword
An introductory address by Professor Guido Rasi, Executive Director, European Medicines Agency (EMA)
Immunotherapy and Biologics represent some of the most important hot topics in the field of medicine. In fact, not only is there a tremendous increase in the requests for scientific advice and marketing authorization for biologics and immunological treatments to the European Medicines Agency (EMA), but these therapies call for new methods of research, strategies for development, evaluation, use and pharmacovigilance.
The allergen products used for both the diagnosis and treatment of allergic diseases require particular attention among the immunological and biological therapeutic areas, due to the increase in the prevalence and social relevance of allergies as well as the regulatory actions being requested by the Directive 2001/83/EC and the following amending EC Directives.
In order to discuss the available EMA Guidelines on Allergen Products and to address the many issues that need harmonizing, and the regulatory aspects of allergen products in Europe, the EMA on February 28, 2013 called a workshop in London with the participation of all stakeholders.
The WAO SLIT document presented in this issue of the World Allergy Organization Journal, and the EAACI “Task Force Report on Clinical Outcomes to be used in studies of Allergen Products”, represent relevant contributions to answer the recommendations emerging from this workshop.
From our side, we are working on a document, to be shared with all stakeholders, on possible pathways for facilitating marketing authorization of allergen products. These might include:
▪
a wider utilization of collaborative trials, with the advantage of using the same control group for studies of comparable active products, a substantial advantage for pediatric investigational plans;
▪
new facilitated pathways of marketing authorization allowing a faster access for patients to immunotherapy without affecting an evidence-based risk/benefit ratio;
▪
new study designs for well-conducted post-registration trials, which, with the help of registries, will allow a progressive evaluation of efficacy and safety of new products and a pharmacovigilance in line with the new ad hoc law;
▪
adequate information technology to take full advantage of a wider access to individual data of registration trials.
The harmonization of regulatory aspects of allergen products represents however a work still in progress, as shown by the concordant position on efficacy but the different end-points adopted as well by the different safety considerations in the recent FDA Advisory Committee votes on two SLIT products already approved by EMA and marketed in most European Countries.
Therefore, we expect that the regulatory bodies, scientific societies, manufacturers of allergen products, and allergy patients’ organizations will continue their joint commitment with the common goal of providing worldwide to the many millions of subjects suffering from allergic diseases an early and harmonized access to safe and effective products.
Chapter 1 Introduction and historical background to sublingual immunotherapy
The update of chapter one consists of two figures. Figure 1 provides an overview of the history of the development of the first position paper, which was published in 2009.
Figure 1The historical process leading to the WAO SLIT Position Paper 2009.
The next figure displays the evidence base for sublingual immunotherapy since the publication of the first position paper (Figure 2).
Figure 2Highlights of the evidences in SLIT, from 2009 to 2013, the scientific basis for the updating of “Sublingual Immunotherapy: World Allergy Organization Position Paper 2009”.
There were no changes indicated for this chapter, and related updated details were integrated into other chapters.
Chapter 3 Mechanisms of sublingual immunotherapy
•
Allergen immunotherapy provides an opportunity to study antigen-specific tolerance in humans.
•
Subcutaneous immunotherapy (SCIT) suppresses allergic Th2-mediated inflammation and increases antigen-specific IgG, probably by induction of regulatory T cells (Tregs), immune deviation (Th2 to Th1), and/or apoptosis of effector memory Th2 cells.
•
The oral mucosa is a natural site of immune tolerance (Langerhans cells, FcR1, IL-10, IDO [indoleamine 2,3-dioxygenase]).
•
Sublingual immunotherapy (SLIT) in optimal doses is effective; SLIT has been shown to induce long-term remission after discontinuation and may prevent new sensitizations, features consistent with the induction of tolerance.
•
SLIT induces modest systemic changes consistent with SCIT, but additional local mechanisms in the oral mucosa and/or regional lymph nodes are likely important.
•
Sublingual immunotherapy is associated with
○
retention of allergen in sublingual mucosa for several hours.
○
early increases in antigen-specific IgE and blunting of seasonal IgE.
○
persistent increases in antigen-specific IgG4 and IgE blocking activity that parallel long-term clinical benefits of both SCIT and SLIT.
○
inhibition of eosinophils and reduction of adhesion molecules in target organs.
○
an early (at 4-12 weeks) increase in peripheral phenotypic Tregs and delayed (at 12 months) immune deviation in favor of Th1 responses.
○
detection of CD25 + FOXP + phenotypic Treg cells in the sublingual mucosa.
○
alterations in dendritic cell markers (e.g., increases in expression of complement component C1Q) that correlate with clinical response to treatment and merit further study.
•
Biomarkers that are predictive of or surrogates for the clinical response to immunotherapy are not currently available for routine use.
○
Molecular diagnosis of IgE sensitivities will aid patient selection for immunotherapy.
○
Serum IgG–associated functional blocking activity and basophil activation tests merit further study.
○
Studies of peripheral T cell and dendritic cell signatures have yielded important information, but these tests are currently impractical for routine clinical use.
Clinical evidence for disease modification and induction of tolerance
Since 2009, Cochrane meta-analyses have confirmed the efficacy and safety of SLIT for seasonal and perennial allergic rhinitis [
]. Several large ‘definitive’ trials have now confirmed the efficacy and safety for seasonal rhinitis in both children and adults. Long-term benefits of SLIT for at least 1 [
Sustained 3-year efficacy of pre- and coseasonal 5-grass-pollen sublingual immunotherapy tablets in patients with grass pollen-induced rhinoconjunctivitis.
] years following discontinuation of treatment have been demonstrated in 2 large independent trials of immunotherapy with grass pollen allergen tablets in adults. These studies provide evidence for long-term disease remission and disease modification consistent with the induction of antigen-specific tolerance. In parallel with these novel clinical data, there have been advances in our understanding of the underlying mechanisms of SLIT that may give rise to putative biomarkers to predict the clinical response [
The oral cavity is a naturally tolerogenic environment, remaining noninflamed despite being exposed continuously to multiple foreign proteins. The presence of Langerhans cells and monocytes capable of producing IL-10 and TGF-β are major contributors to the maintenance of tolerance (see Chapter 3 of the 2009 WAO position paper [
] has shown that T cells isolated from the human buccal mucosa, in contrast to those isolated from skin, express TGF-β1, IL-10, interferon-γ and IL-17, particularly in the vestibular region, and markedly express toll-like receptor (TLR) 2 and TLR4. Another study from the same group [
Phl p 5 resorption in human oral mucosa leads to dose-dependent and time-dependent allergen binding by oral mucosal Langerhans cells, attenuates their maturation, and enhances their migratory and TGF-beta1 and IL-10-producing properties.
] confirmed that oral Langerhans cells within fresh human oral mucosal biopsies are capable of rapidly taking up Phl p 5 (within 5 minutes) in a dose-dependent fashion, resulting in their attenuated maturation and enhanced production of inhibitory cytokines (IL-10 and TGF-β). Taken together with the paucity of mast cells in the oral vestibule compared to the sublingual region [
], these data raise the possibility that targeting the vestibule with allergen vaccine with or without adjuvant has the potential to induce enhanced immune deviation or tolerance, possibly with a lower potential for mast cell–related local side effects, although this remains to be tested.
] recently highlighted that the tonsils and surrounding lymphoid tissue are located in the gateway of both the alimentary and respiratory tracts and may be important for local induction of tolerance to both food and inhalant allergens. Abundant FOXP3+ Treg cells were detected in lingual and palatine tonsils. Tonsil-derived plasmacytoid dendritic cells (DCs) were shown to have the ability to generate functional CD4+ CD25+ CD127– FOXP3+ Treg cells. Triggering of tonsil-derived T cells with TLR4 or TLR8 agonists or the proinflammatory cytokines IL-1β or IL-6 was able to break allergen-specific T-cell tolerance through a mechanism dependent on the adaptor molecule myeloid differentiation primary response gene 88 (MyD88) [
Triggering of specific Toll-like receptors and proinflammatory cytokines breaks allergen-specific T-cell tolerance in human tonsils and peripheral blood.
]. In particular, myeloid DCs and stimuli that activate them broke the tolerance of allergen-specific CD4+ T cells, whereas plasmacytoid DCs and stimuli that activate them, such as TLR7 and TLR9 agonists, did not have any effect. These human ex vivo data raise the possibility that immunotherapy strategies that target tonsillar tissue may enhance the induction of tolerance, but this remains to be tested in the context of different strategies of oral immunotherapy.
In a double-blind 18-month controlled trial of high-dose grass pollen SLIT (20 mcg Phl p 5 daily), biopsies of the sublingual mucosa demonstrated more CD3+ FOXP3+ and CD25+ FOXP3+ T cells in SLIT-treated patients than in placebo-treated patients, and some CD3+ FOXP3+ cells were shown with triple immunofluorescence to express IL-10, a direct illustration of the induction of local phenotypic Treg cells following successful treatment [
Sublingual grass pollen immunotherapy is associated with increases in sublingual Foxp3-expressing cells and elevated allergen-specific immunoglobulin G4, immunoglobulin A and serum inhibitory activity for immunoglobulin E-facilitated allergen binding to B cells.
Studies of sublingual grass pollen immunotherapy in general show an increase in serum allergen-specific IgG4 and IgG, although the increase is not as great as that seen with SCIT [
]. In a study of high-dose grass pollen SLIT, increases in grass pollen–specific IgA2 as well as IgG and IgG4 occurred in parallel with local increases in sublingual FOXP3+ Tregs [
Sublingual grass pollen immunotherapy is associated with increases in sublingual Foxp3-expressing cells and elevated allergen-specific immunoglobulin G4, immunoglobulin A and serum inhibitory activity for immunoglobulin E-facilitated allergen binding to B cells.
]. These increases were accompanied by increases in serum inhibitory activity for binding of allergen-IgE complexes to B cells (IgE-FAB), a validated surrogate of IgE-facilitated antigen presentation to T cells. Furthermore, the long-term clinical benefit observed for 2 years following a 3-year course of grass pollen SLIT was associated with persistent elevations in serum levels of both allergen-specific IgG4 [
Sustained 3-year efficacy of pre- and coseasonal 5-grass-pollen sublingual immunotherapy tablets in patients with grass pollen-induced rhinoconjunctivitis.
Eosinophils and inflammatory mediators are elevated in nasal lavage fluid and nasal biopsies after nasal allergen challenge and during seasonal pollen exposure [Chapter 3 of ref. 9]. Recent attempts have been made to standardize the collection of cytokines, mediators, and antibodies in fluid collected on filters and sponges applied directly to the nasal mucosa after nasal challenge [
]. For example, tryptase levels peak at 5 minutes, consistent with early mast cell activation, whereas increases in eosinophil cationic protein (ECP), a marker of eosinophils and Th2 cytokines (IL-4, IL-5, and IL-13), peak at 3 to 8 hours during the late nasal response. Whether alterations in these local mediators, antibodies, and cytokines correlate with the clinical response to immunotherapy remains to be tested.
Effector cells in the periphery
Basophil activation can be measured ex vivo by short-term (1 h) allergen stimulation of freshly harvested whole blood. Techniques include measurement of basophil histamine release and expression of surface activation markers, including CD63 and CD203b. Inhibition of basophil activation has been shown following SLIT with a combined grass and mite extract [
] found no changes in basophil activation and no correlation with clinical response to treatment.
T cells and dendritic cells
Studies of peripheral blood T cell phenotype, proliferation, and cytokine production following SLIT have given variable results. This is in part due to the different allergens, doses, and protocols employed for immunotherapy and the varying methods of T cell purification, processing, and storage, that are difficult to standardize in multicenter studies. Evaluation of T cell phenotype and function overall favor the induction of Tregs and/or immune deviation in favor of Th1 cells. Thus, birch pollen SLIT in one study resulted in the induction of CD25+ FOXP3+ T cells at 4 weeks [
]. CD25+ Tregs suppressed antigen-stimulated CD25– T cell proliferation. This suppression was reversible at 4 weeks but not at 12 months by the addition of an anti-IL-10 antibody to the culture medium. In a study of house dust mite SLIT, suppression of antigen-stimulated purified CD4+ T cell proliferation was reversible at 6 but not 12 months by treatment with soluble TGF-β receptor [
]. These data support that Tregs are induced early, followed by delayed immune deviation in favor of Th1 responses at 12 months. Several other recent studies support these observations [
The induced regulatory T cell level, defined as the proportion of IL-10(+)Foxp3(+) cells among CD25(+)CD4(+) leukocytes, is a potential therapeutic biomarker for sublingual immunotherapy: a preliminary report.
Clinical outcome and IL-17, IL-23, IL-27 and FOXP3 expression in peripheral blood mononuclear cells of pollen-allergic children during sublingual immunotherapy.
Clinical efficacy and immunological mechanisms of sublingual and subcutaneous immunotherapy in asthmatic/rhinitis children sensitized to house dust mite: an open randomized controlled trial.
] of daily SLIT with the combination of house dust mite and timothy grass pollen in dual-sensitized adults (n = 30), clinical improvement and decreased nasal allergen sensitivity were accompanied by an increase in allergen-stimulated CD4+ CD25+ CD127low CD45RO+ Foxp3+ T cells with reduced DNA methylation at CpG sites [
], implying that tolerance might result from epigenetic modification of memory Treg cells at the Foxp3 locus. In contrast, a double-blind placebo-controlled study of 4 months of grass pollen SLIT (n = 89) that examined T cell phenotype and antigen-specific T cells [
Allergen-specific CD4+ T cell responses in peripheral blood do not predict the early onset of clinical efficacy during grass pollen sublingual immunotherapy (ClinicalTrials.gov NCT00619827).
] found that clinical improvement was accompanied by only minor changes in the proportions of CD4+ T cells expressing markers for Th1 (CCR5+, CXCR3+), Th2 (CRTh2+, CCR4+), or Treg (CD25+, CD127–, Foxp3+). A modest downregulation of IL-4 and IL-10 gene expression and IL-10 secretion (P < 0.001) and a decrease in the frequency of potential “pro-allergic” CD27– Th2 cells did not correlate with clinical benefit. Class II-tetramer analyses of antigen-specific T cells failed to show any major impact on either numbers or polarization of circulating CD4+ T cells specific for Phl p 1 or Phl p 5. Further and more prolonged studies are required to confirm or exclude whether tetramer tracking of T cells is valuable as a biomarker of early onset of SLIT efficacy.
Tetramer studies of antigen-specific cells are limited by class II restriction and the need to identify relevant T cell epitopes. For this reason, Wambre and colleagues have used T cell surface/intracellular marker expression with or without associated tetramer staining to characterize subjects allergic to grass pollen and mites, with the aim of distinguishing antigen-specific T cells from bystander T cell responses [
Comparison between major histocompatibility complex class II tetramer staining and surface expression of activation markers for the detection of allergen-specific CD4(+) T cells.
] have identified CD154 (CD40 ligand) as a potentially useful T cell marker for future immunotherapy studies.
Human effector and regulatory dendritic cells are important in directing T cell differentiation, phenotype, and function. Following a detailed evaluation in vitro of human effector and regulatory dendritic cells from human monocytes cultured under deforming conditions, candidate dendritic cell markers were evaluated at the messenger RNA and protein levels before and after grass pollen allergen tablet SLIT [
]. Complement component 1 (C1Q) and Stabilin-1 (STAB1) were increased in PBMCs from clinical responders in contrast to that seen in nonresponders or placebo-treated patients. Further evaluation of C1Q and STAB1 expression as candidate biomarkers during large trials of sublingual allergen immunotherapy are justified.
Biomarkers of clinical response to immunotherapy
A useful biomarker is one that is either predictive of or a surrogate for the clinical response to immunotherapy. A predictive biomarker might aid in selecting patients who will respond (or in excluding potential nonresponders), whereas a surrogate biomarker might be effective in monitoring the clinical response to treatment. Ideally, the biomarker should be practical, easy to measure, technically robust, generalizable, and have good sensitivity and specificity. Skin prick testing and raised serum allergen-specific IgE are essential predictive biomarkers that clearly augment information obtained from the history alone. Nonetheless, these tests produce both false positive and false negative results. One study suggested that the ratio of specific IgE to total IgE might relate to the response to immunotherapy [
]. These hypotheses deserve further evaluation. The advent of molecular diagnosis may enhance predictive value by identifying IgE sensitivity to relevant major allergens [
]. When there is discordance between the history and IgE testing, local provocation to the relevant target organ (eye, nose, bronchi) could be helpful, as might the presence of local IgE in nasal, lacrimal, or bronchoalveolar lavage fluid, although whether provocation testing or local IgE is predictive of response to immunotherapy has not been tested.
Based on knowledge of the mechanisms of SLIT, it is attractive to consider that alterations in peripheral T cell or dendritic cell signatures [
] would be useful for monitoring responses, although the complexity of processing and performing these assays makes them unlikely candidates for routine clinical use. Basophil activation testing is of potential value, although conflicting results have been obtained with SLIT [
]. Basophil testing requires fresh processing of whole blood and access to a flow cytometer within hours. Collection of nasal fluid on sponges or absorbent filters with measurement of mediators and cytokines has been validated in response to nasal provocation, but not in the context of immunotherapy trials [
Serum-based assays are feasible in the context of clinical trials and are largely restricted to measurements of antibodies (specific IgE, IgG, IgG4, and IgA) and functional antibody assays, such as detection of serum inhibitory activity for antigen-stimulated basophil activation tests [
A double-blind placebo-controlled birch allergy vaccination study II: correlation between inhibition of IgE binding, histamine release and facilitated allergen presentation.
The IgE-facilitated allergen binding (FAB) assay: validation of a novel flow-cytometric based method for the detection of inhibitory antibody responses.
Sustained 3-year efficacy of pre- and coseasonal 5-grass-pollen sublingual immunotherapy tablets in patients with grass pollen-induced rhinoconjunctivitis.
Studies on the relationship between the level of specific IgE antibodies and the clinical expression of allergy: I. Definition of levels distinguishing patients with symptomatic from patients with asymptomatic allergy to common aeroallergens.
], there are no biomarkers that can be reliably recommended for selection of individual patients in routine practice for immunotherapy, nor for monitoring the response to treatment. However, rapid advances in the molecular diagnosis of individual allergen IgE sensitivities combined with better information on the constituents of the allergen extracts available for therapy provide an exciting opportunity to relate this new knowledge to prediction of response to immunotherapy [
Chapter 4. Clinical efficacy of sublingual immunotherapy
▪
As of June 2013, there were 77 randomized, double–blind, placebo-controlled (RDBPC) trials of SLIT, of which 62 were conducted with grass or house dust mite (HDM) extracts. The majority of these studies were heterogeneous for allergen dose, duration, and patient selection. All statements on efficacy of SLIT do refer to products which have demonstrated efficacy in appropriate studies.
▪
Seventeen trials, of which one was totally negative, were published after the previous WAO position paper.
▪
The literature suggests that, overall, SLIT is clinically effective in rhinoconjunctivitis and asthma, although differences exist among allergens.
▪
The available meta-analyses are in favor of SLIT (rhinitis and conjunctivitis in adults; asthma and rhinitis in children), although the conclusions are limited by the heterogeneity of the studies in term of doses, duration, and patient selection.
▪
Clinical efficacy and dose dependency have been demonstrated for rhinoconjuntivitis due to grass pollen in adequately powered, well-designed RDBPCs.
▪
Some open, controlled trials suggested that the clinical efficacy of SLIT is similar to that of injection immunotherapy.
▪
Dose-finding trials and large studies with properly defined outcomes and sample sizes are needed for the other relevant individual allergens.
High-dose sublingual immunotherapy with single-dose aqueous grass pollen extract in children is effective and safe: a double-blind, placebo-controlled study.
Fast onset of action of sublingual immunotherapy in house dust mite-induced allergic rhinitis: a multicenter, randomized, double-blind, placebo-controlled trial.
High-dose sublingual immunotherapy with single-dose aqueous grass pollen extract in children is effective and safe: a double-blind, placebo-controlled study.
]. The number of patients enrolled ranged from about 30 to more than 700, and the duration varied from 4 months to 3 years. Five studies enrolled more than 400 patients [
High-dose sublingual immunotherapy with single-dose aqueous grass pollen extract in children is effective and safe: a double-blind, placebo-controlled study.
Fast onset of action of sublingual immunotherapy in house dust mite-induced allergic rhinitis: a multicenter, randomized, double-blind, placebo-controlled trial.
] demonstrated a significant effect of SLIT, independent of the allergen considered. The relative change versus placebo, when reported, ranged between 20% and more than 35%.
Table 1Randomized, double-blind, placebo-controlled trials of SLIT performed since 2009
High-dose sublingual immunotherapy with single-dose aqueous grass pollen extract in children is effective and safe: a double-blind, placebo-controlled study.
Fast onset of action of sublingual immunotherapy in house dust mite-induced allergic rhinitis: a multicenter, randomized, double-blind, placebo-controlled trial.
Only the high dose decreased daily symptom, medication, and combined scores during peak pollen season and whole season versus placebo.
Low dose overall less effective than the 2 other doses on symptoms/medications in peak pollen and whole season
Med 195
43
4.38 mg Amb a 1
High 194
57
Tablets
Pla 198
38
Abbreviations: A/P active/placebo, NS not stated, RC rhinoconjunctivitis, RCA rhinoconjuntivitis/asthma, STA Stallergenes, GRE Greer, ANA Anallergo, ALL Allergopharma, ALK ALK-Abellò, MSD Merck Sharp and Dome, TOR Torii Pharmaceuticals, ZHE Zheng Wolwo Bio Pharma.
] was conducted in more than 200 children recruited in a primary care setting. In this case, the authors hypothesized that the amount of allergen given was too low to produce a clinical benefit.
Of the mentioned trials, one was performed using the Vienna challenge chamber [
] and demonstrated that the effect of SLIT begins quite early (at 4 months). This relatively early onset of the effect was confirmed in another trial with natural allergen exposure [
Fast onset of action of sublingual immunotherapy in house dust mite-induced allergic rhinitis: a multicenter, randomized, double-blind, placebo-controlled trial.
] investigated only immunological parameters and showed a significant effect in the active group but not in the placebo group relative to baseline.
Overall, there have now been 77 RDBPC trials investigating SLIT (Figure 3): 39 with grasses, 23 with mite, 5 with Parietaria, and 10 with other allergens (ragweed, cypress, cat, olive, birch, cedar). Of the 77 trials, 5 were totally negative. Nonetheless, several trials consistently reported efficacy to be dose dependent (for review see [
], which included 22 trials and a total of 979 patients. The overall results favored SLIT over placebo for rhinitis symptoms and medication scores. For symptoms, the standardized mean difference (SMD) was –0.42 (95% CI –0.69 to –0.15, P = 0.002). For medications, the SMD was –0.43 (95% CI –0.63 to –0.23, P = 0.00003). However, great heterogeneity remained (I2 between 40% and 95%, depending on the outcome analyzed) due to the largely different inclusion criteria, outcomes, doses, and durations among the trials. In addition, this analysis did not include the most recent large trials. However, the increasing number of available studies has enabled more detailed meta-analyses, for instance according to the allergen or the disease. One meta-analysis was limited to mite [
] clearly showed the superiority of SLIT over placebo for both symptoms and medications. Finally, another meta-analysis limited to conjunctivitis symptoms [
] confirmed a significant difference in favor of SLIT, with an SMD of 0.41 (95% CI 0.28 to 0.53) and moderate heterogeneity (I2: 59%). The new meta-analyses substantially confirmed the previous results, showing an overall efficacy of SLIT for different outcomes. However, the great heterogeneity of the results (due to the inherent heterogeneity of trials) still limits the reliability of the results [
The problem of comparing the efficacy of subcutaneous immunotherapy (SCIT) and SLIT is still open. The comparison is technically difficult, because head-to-head comparisons need a double-blind, double-dummy design, with a careful choice of outcomes and dosages. Surprisingly, given the technical difficulty, 3 comparative studies [
Clinical efficacy and immunological mechanisms of sublingual and subcutaneous immunotherapy in asthmatic/rhinitis children sensitized to house dust mite: an open randomized controlled trial.
Effect of one-year subcutaneous and sublingual immunotherapy on clinical and laboratory parameters in children with rhinitis and asthma: a randomized, placebo-controlled, double-blind, double-dummy study.
Clinical efficacy and immunological mechanisms of sublingual and subcutaneous immunotherapy in asthmatic/rhinitis children sensitized to house dust mite: an open randomized controlled trial.
] was randomized, open, and controlled and involved 48 children monosensitized to mite. They received SCIT, SLIT, or pharmacotherapy alone for 1 year. The 2 routes of immunotherapy did not differ in terms of clinical efficacy, and both were superior to pharmacotherapy. The second study [
] was a double-blind, double-dummy, 4-parallel-group trial to assess the efficacy and feasibility of SCIT induction followed by SLIT maintenance. The 2 single routes were also compared. The combined regimen did better than the 2 taken separately, with a slight advantage for SCIT alone over SLIT alone on some outcomes. The third study [
Effect of one-year subcutaneous and sublingual immunotherapy on clinical and laboratory parameters in children with rhinitis and asthma: a randomized, placebo-controlled, double-blind, double-dummy study.
] was again a double-dummy study versus placebo in which both treatments achieved a significant clinical improvement versus baseline, with SCIT doing on average better than SLIT in the direct comparison.
Table 2Direct comparisons of SLIT and SCIT for efficacy
Clinical efficacy and immunological mechanisms of sublingual and subcutaneous immunotherapy in asthmatic/rhinitis children sensitized to house dust mite: an open randomized controlled trial.
Significant reduction of total rhinitis and asthma score, medication score, VAS, and skin reactivity P < 0.05 versus pharmacotherapy for both SCIT and SLIT. No difference between routes of administration.
Decreased asthma attacks and use of steroids at 4, 12, 18 mo for SCIT and SCIT+SLIT, at 12 mo only for SLIT. No change in VAS for asthma with SCIT or SIT alone.
Effect of one-year subcutaneous and sublingual immunotherapy on clinical and laboratory parameters in children with rhinitis and asthma: a randomized, placebo-controlled, double-blind, double-dummy study.
173,733 TU (86,866.5 TU D pt. and 86,866.5 TU Df).
RA
Significant reduction in symptom and medication score versus baseline with both treatments. SCIT better than SLIT versus placebo.
10 SLIT
1
Double blind, double dummy, placebo controlled
10 PLA
0
Abbreviations: CON control, PLA placebo, SCIT subcutaneous immunotherapy, SLIT sublingual immunotheapy, RA Rhinitis with asthma, A asthma, VAS visual analog scale.
]. These studies, despite their methodological limitations, provided some interesting insights into the efficacy of SLIT. One study compared coseasonal and continuous regimens in children suffering from grass allergy [
Direct comparison between continuous and coseasonal regimen for sublingual immunotherapy in children with grass allergy: a randomized controlled study.
]. In this study, the continuous (all year long) regimen started in the preseason. The main results were that in the first pollen season the continuous regimen performed better on symptoms, but starting from the second season, the 2 regimens became more and more similar, so that at the third season no difference could be detected. Another study was conducted in a randomized single-blind fashion for 3 years with an Alternaria extract [
Efficacy of sublingual specific immunotherapy in patients with respiratory allergy to Alternaria alternata: a randomised, assessor-blinded, patient-reported outcome, controlled 3-year trial.
]. There was a progressive reduction in symptoms, as measured with a visual analog scale, which became significant after the first year in the active group. Only few mild adverse events were reported. Another open randomized trial in adults (33 patients) showed that a preseasonal regimen was equivalent in efficacy, as measured by visual analog scale, to the continuous administration [
] compared the efficacy of HDM SLIT in 134 monosensitized or polysensitized patients. After 1 year, symptoms and drug scores decreased significantly in both groups, but no difference between groups was detected. The same was observed in another trial comparing the quality of life in patients receiving SLIT who were either mono- or polysensitized, where no difference between the 2 groups could be observed [
]. Therefore, the authors concluded that SLIT can also be effective in patients with multiple sensitizations, provided that the clinically relevant allergen is correctly identified [
Sublingual immunotherapy (SLIT) appears to be better tolerated than subcutaneous immunotherapy (SCIT).
•
SLIT should only be prescribed by physicians with appropriate allergy training and expertise.
•
Specific instructions should be provided to patients regarding the management of adverse reactions, unplanned interruptions in treatment, and situations when SLIT should be withheld.
•
The majority of SLIT adverse events are local reactions (e.g., oromucosal pruritus) that occur during the beginning of treatment and resolve within a few days or weeks without any medical intervention (e.g., dose adjustment, medication).
•
A few cases of SLIT-related anaphylaxis have been reported but there have been no fatalities.
•
Risk factors for the occurrence of SLIT severe adverse events (SAEs) have not yet been established, although there is some suggestion that patients who have had prior systemic reactions to SCIT may be at increased risk.
•
There is a need for a generally accepted system of reporting allergen immunotherapy (AIT) adverse reactions that is applicable to both clinical practice and research.
○
A uniform classification system for grading for AIT systemic reactions has been developed.
○
A classification system for grading SLIT local reactions has also been developed.
○
Consistent use of the Systemic Reaction and SLIT Local Reaction Grading Systems is recommended.
Classification and frequency of SLIT adverse events
One of the purported advantages of SLIT over SCIT is greater safety, which allows for administration of this treatment outside of the medical setting. In a comprehensive review of 104 articles on SLIT, there were 66 studies that provided some information on safety and tolerance, representing 4378 patients who received approximately 1,181,000 SLIT doses [
]. Oromucosal reactions, considered a SLIT local reaction, were relatively common, affecting up to 75% of patients, and were seen most frequently in the build-up phase. In the studies that specified the type of reaction, 169 (0.056%) of 314,959 doses administered were classified as producing systemic reactions. To provide some perspective, in an American Academy of Allergy Asthma & Immunology/American College Of Allergy Asthma & Immunology (AAAAI/ACAAI) 3-year immunotherapy safety surveillance study, the incidence of reported SCIT systemic reactions was 0.1% of injections, the majority of which were classified as Grade 1 (cutaneous or upper respiratory symptoms) [
Immediate and delayed-onset systemic reactions after subcutaneous immunotherapy injections: ACAAI/AAAAI surveillance study of subcutaneous immunotherapy: year 2.
Ann Allergy Asthma Immunol.2011; 107 (e421): 426-431
]. In these trials, the overall occurrence of side effects did not differ from the occurrence in previous studies, and no new safety concerns were raised. Local side effects (oral and gastrointestinal) continue to represent the majority (~80% to 90%) of all reported adverse reactions. Long-term follow-up of some of the large trials indicated that the number and intensity of AEs tend to decline with additional courses of SLIT [
Sustained 3-year efficacy of pre- and coseasonal 5-grass-pollen sublingual immunotherapy tablets in patients with grass pollen-induced rhinoconjunctivitis.
Safety and tolerability of an SQ-standardized GRAss ALlergy immunotherapy tablet (GRAZAX(R)) in a real-life setting for three consecutive seasons - the GRAAL trial.
The amount of information provided about AEs varied greatly in many of the earlier SLIT studies; some included only general summary statements, such as “no relevant side effects,” whereas others provided detailed analyses of the AEs [
]. One consideration with SLIT is that the majority of doses are administered outside of the clinic setting with no direct medical supervision, and the accuracy of the AE reporting depends on the patient’s and/or family’s recall and interpretation of the event. The heterogeneity in classifying and reporting SCIT and SLIT adverse reactions in clinical trials makes comparisons and analysis of safety difficult. In recognition of the need for a uniform classification system for AIT adverse reactions, an international Task Force composed of members of the academic, clinical, and research allergy communities was formed. Using existing grading systems as a template, the Task Force combined information from the members’ clinical experience and data from published studies and safety surveys to develop a 5-grade classification system for systemic AEs (the World Allergy Organization Subcutaneous Immunotherapy Systemic Reaction Grading System, Table 3) [
]. Although the grading system was developed for SCIT, it also applies to SLIT. The grade is based on the organ system(s) involved and severity and is to be determined by the physician’s clinical judgment after the event is over.
Table 3World Allergy Organization subcutaneous systemic reaction grading system
Each Grade is based on organ system involved and severity. Organ systems are defined as: cutaneous, conjunctival, upper respiratory, lower respiratory, gastrointestinal, cardiovascular, and other. A reaction from a single organ system such as cutaneous, conjunctival, or upper respiratory, but not asthma, gastrointestinal, or cardiovascular is classified as a Grade 1. Symptom(s)/sign(s) from more than one organ system or asthma, gastrointestinal, or cardiovascular are classified as Grades 2 or 3. Respiratory failure or hypotension, with or without loss of consciousness, defines Grade 4 and death Grade 5. The grade is determined by the physician’s clinical judgment.
Symptoms(s)/sign(s) of more than one organ system present:
Lower respiratory
Lower or upper respiratory
Death
Asthma (eg, 40% PEF or FEV1 drop, NOT responding to an inhaled bronchodilator)
Respiratory failure with or without loss of consciousness
Cutaneous
Generalized pruritis, urticaria, flushing, or sensation of heat or warmth
Cough perceived to come from the upper airway, not the lung, larynx, or trachea
Abdominal cramps, vomiting, or diarrhea
or
or
Conjunctival
Conjunctival erythema, pruritus, or tearing
Other
Uterine cramps
Other
Nausea, metallic taste, or headache
Patients may also have a feeling of impending doom, especially in grades 2, 3, or 4.
Note: children with anaphylaxis seldom convey a sense of impending doom and their behavior changes may be a sign of anaphylaxis, eg, becoming very quiet or irritable and cranky.
Scoring includes a suffix that denotes if and when epinephrine is administered in relationship to symptom(s)/sign(s) of the SR: a, =5 minutes; b, >5 minutes to =10 minutes; c, >10 to =20 minutes; d, >20 minutes; z, epinephrine not administered.
The final grade of the reaction will not be determined until the event is over, regardless of the medication administered. The final report should include the first symptom(s)/sign(s) and the time of onset after the subcutaneous allergen immunotherapy injection
Symptoms occurring within the first minutes after the injection may be a sign of severe anaphylaxis. Mild symptoms may progress rapidly to severe anaphylaxis and death.
and a suffix reflecting if and when epinephrine was administered, eg, Grade 2a; rhinitis: 10 minutes.
Final report: Grade, a-d or z ________________First symptom ________________ Time of onset of first symptom ________________
Comments
If signs or symptoms are not included in the Table or the differentiation between an systemic response and vasovagal (vasodepressor) reaction, which may occur with any medical intervention, is difficult, please include comment, as appropriate.
]. Reprinted with permission from Elsevier Publishers.
* Each Grade is based on organ system involved and severity. Organ systems are defined as: cutaneous, conjunctival, upper respiratory, lower respiratory, gastrointestinal, cardiovascular, and other. A reaction from a single organ system such as cutaneous, conjunctival, or upper respiratory, but not asthma, gastrointestinal, or cardiovascular is classified as a Grade 1. Symptom(s)/sign(s) from more than one organ system or asthma, gastrointestinal, or cardiovascular are classified as Grades 2 or 3. Respiratory failure or hypotension, with or without loss of consciousness, defines Grade 4 and death Grade 5. The grade is determined by the physician’s clinical judgment.
** This constellation of symptoms may rapidly progress to a more severe reaction.
† Symptoms occurring within the first minutes after the injection may be a sign of severe anaphylaxis. Mild symptoms may progress rapidly to severe anaphylaxis and death.
†† If signs or symptoms are not included in the Table or the differentiation between an systemic response and vasovagal (vasodepressor) reaction, which may occur with any medical intervention, is difficult, please include comment, as appropriate.
Local side effects are the most frequent adverse reactions associated with SLIT, and these local reactions can be severe and/or bothersome enough to cause treatment discontinuation. In the previously discussed review [
], SLIT adverse reactions accounted for treatment withdrawal in 3% of the SLIT patients, compared with 1.4% of the placebo-treated patients. Local adverse reactions are often the reason cited for treatment discontinuation in both RDBPC and observational studies [
]. Similar to the need for a grading system for systemic events, a uniform system for grading the severity of local AEs was perceived as necessary for uniform reporting and classification of SLIT local adverse reactions. A WAO Task Force was formed for the purpose of developing a classification system for grading SLIT local reactions [
] (Table 4) in the development of the clinically based 3-grade classification system for local SLIT reactions (Table 5). This grading system is primarily based on the patient’s subjective reporting, with a severe reaction (Grade 3) being one that leads to treatment discontinuation. Note that gastrointestinal symptoms associated with SLIT can be classified as either local reactions, if only oromucosal symptoms are present, or as a systemic reaction, if occurring in conjunction with other systemic symptoms.
Table 4Description of the local side effects related to SLIT (MedDRA 14.1)[
], there were no fatalities or SLIT-related systemic reactions associated with hypotension, although there were 14 probable SLIT-related SAEs in 3984 patients treated with a total of 1,019,826 doses. This represents 1.4 SAEs per 100,000 SLIT doses. The most common SLIT-related SAEs were asthmatic reactions (n = 7), one of which required hospitalization; the others were abdominal pain/vomiting (n = 3), uvula edema (n = 1), and urticaria lasting 48 hours. Subsequent to this review, there have been a few case reports of systemic reactions of a severity that should be categorized as anaphylaxis (Table 6) [
No clear predictors for SLIT AEs have been identified, although some of the factors in the SLIT anaphylaxis case reports are recognized as risk factors for SCIT: height of season [
]. In addition, most of the patients with SLIT-related SAEs or anaphylaxis had asthma; symptomatic asthma has been identified as a risk factor for AEs with SCIT [
], 5 of 6 patients were female, all were adolescents or young adults, 5 of the 6 had a history of asthma, and 2 had a previous history of severe reactions to SCIT. In a study evaluating the safety of SLIT in 43 patients, 3 of the 5 patients who experienced a SLIT systemic reaction had a history of a previous SCIT systemic reaction [
In general, patients receiving SLIT are not prescribed injectable epinephrine in the event of a rare systemic reaction. However, in the study of 43 patients that identified prior SCIT systemic reaction as a possible predictor for SLIT systemic reaction, injectable epinephrine was prescribed as an ethics committee requirement, and 2 patients used it [
]. The Federal Drug Administration (FDA) has stipulated a similar requirement for prescribing epinephrine autoinjectors for the subjects participating in US SLIT clinical trials. In 2 of these studies, which together included 345 children and 439 adults, a small number of patients in the placebo (n = 2) and SLIT (n = 4) groups used the epinephrine autoinjector [
]. In 3 instances, it was used for symptoms not caused by active treatment. One patient in the placebo group used it 12 hours after the 137th dose because of wheezing related to exposure to a grassy field [
], and another placebo patient used it in response to what was subsequently deemed to be an anxiety attack. In the SLIT group, self-administered epinephrine was used in 4 patients for symptoms diagnosed later as viral pharyngitis [
]. However, in other US clinical trials that collectively included over 1000 patients, there was no use of the epinephrine autoinjectors for SLIT-related reactions [
], and epinephrine autoinjectors are not routinely prescribed or recommended in countries where SLIT is registered and commercially available. The relatively rare and potentially inappropriate use of injectable epinephrine in these studies raises concerns about the benefits and harms of routine prescribing of injectable epinephrine, which may become standard practice if the product information for an FDA- approved SLIT formulation includes this recommendation. In addition, the US clinical trials required that the first SLIT dose be administered in the study site. Administration of the first dose in a medically supervised setting has never been a requirement in the European Union.
Allergen dose, formulation, and adverse reaction rate
The literature does not appear to show a consistent correlation between the administered SLIT dose and the rate or severity of AEs [
]. For example, one study of dust mite–allergic asthmatic children that employed a relatively low-dose dust mite SLIT (15 mcg cumulative monthly dose [CMD] of Der p 1) reported a systemic reaction rate of 0.46% per dose [
]. In contrast, another study of dust mite–allergic asthmatic children treated with a CMD 50 times greater (783 mcg CMD of mixed mite) reported no serious AEs and no significant difference in the incidence of AEs between the SLIT and placebo groups [
Efficacy of sublingual immunotherapy with high-dose mite extracts in asthma: a multi-center, double-blind, randomized, and placebo-controlled study in Taiwan.
], but so far a “maximum tolerated dose” has not been documented for SLIT.
Tolerability may vary with the extract and formulation. A dose-response study compared the safety of 6 doses of ragweed tablets (3, 6, 12, 24, 50, or 100 U Amb a 1) in 53 subjects with ragweed-induced allergic rhinitis. Recruitment to 50 U Amb a 1 was discontinued, and the 100 U Amb a 1 dose was not initiated after 3 subjects experienced systemic reactions at doses ≥24 U Amb a 1 [
]. In contrast, the treatment and placebo groups had similar frequencies of systemic AEs in an RDBPC dose-response study of 115 ragweed-allergic rhinitis patients randomized to receive 4.8 or 48 mcg of Amb a 1 sublingual ragweed extract solution [
]. Similar safety was demonstrated with this same ragweed extract solution in a subsequent RDBPC study of 429 patients who received up to 50 mcg of Amb a 1 or placebo [
]. The difference in tolerability between similar ragweed doses may be a result of the formulation (tablet versus extract solution). However, studies with grass pollen sublingual tablets and extract solution have demonstrated comparable dose efficacy and safety [
High-dose sublingual immunotherapy with single-dose aqueous grass pollen extract in children is effective and safe: a double-blind, placebo-controlled study.
]. One study comparing the safety of 7 doses of grass tablets, with the highest dose equivalent to 200 mcg of Phl p 5, reported no treatment-related AEs that were serious, systemic, or led to withdrawal [
]. These studies reaffirm that an effective and safe dosing regimen will need to be established for each allergen extract formulation.
Induction schedule
In contrast to SCIT, accelerated induction schedules with SLIT do not appear to be associated with a greater risk of systemic reaction. Rush, ultra-rush, and no-induction SLIT schedules seem to be tolerated as well as multi-dose, multi-week induction schedules.
Several large multicenter studies, collectively including over 1000 patients, investigated the safety and efficacy of grass and ragweed tablets administered without an updosing phase. There were few reported systemic allergic reactions, primarily WAO Grade 1 or 2, and no Grade 4 reactions [
]. Similar safety has been reported with SLIT ultra-rush and rush induction schedules, which allow patients to achieve the target maintenance dose within minutes to hours [
Although the induction phase does not seem to influence the SLIT AE rate, many studies have reported that more AEs occurred during the induction phase than during the maintenance phase. Most occur within the first few days to weeks of treatment and infrequently after this initial phase. The local AEs appear to resolve without any medical interventions, such as dose adjustments or antihistamines. In studies that have utilized discontinuous schedules (pre- and coseasonal), the frequency and intensity of AEs appeared to decline in the later courses of SLIT treatment [
Sustained 3-year efficacy of pre- and coseasonal 5-grass-pollen sublingual immunotherapy tablets in patients with grass pollen-induced rhinoconjunctivitis.
Safety and tolerability of an SQ-standardized GRAss ALlergy immunotherapy tablet (GRAZAX(R)) in a real-life setting for three consecutive seasons - the GRAAL trial.
Immunotherapy guidelines do not specify a particular lower age limit for initiating AIT. SCIT is often not prescribed to young children, primarily because of concerns that they may have difficulty cooperating with an immunotherapy program and, in particular, in communicating symptoms of systemic reactions. However, studies that have evaluated the safety of SCIT in children less than 5 years old have reported a similar incidence and severity of AEs as in other age populations [
Immunotherapy can be initiated in young children less than 5 years of age if indicated. Indications should be based on the severity of the disease, risk/benefit ratios, and the ability of the physician to correlate the clinical presentation with appropriate and obtainable allergy testing.
The preventive benefits of AIT may be greater if initiated early in the course of the allergic disease [
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