Effects of immunotherapy on the early, late, and rechallenge nasal reaction to provocation with allergen: changes in inflammatory mediators and cells

Subcutaneous allergen immunotherapy in the treatment of allergic respiratory disease

Subcutaneous immunotherapy is recognized as a cornerstone in the management of allergic respiratory disease in patients who are properly characterized with allergy and with allergic rhinoconjunctivis and/or well-controlled asthma, and who are willing to adhere to the rigorous treatment program. A key tenet is that it affords the opportunity to effect long-term clinical remission through its disease-modifying properties. Furthermore, it has the potential to prevent the progression of allergic rhinitis to asthma, prevent new allergen sensitivities, and improve a patient's quality of life.

Sublingual immunotherapy for pediatric patients with mite allergies

Sublingual immunotherapy (SLIT) has been increasingly used instead of subcutaneous immunotherapy. SLIT was initially approved for use among adults; however, it has become more widely accepted for children. Few studies have evaluated the effectiveness of SLIT in the treatment of dust mite allergies among children, including adverse effects. This study aimed to investigate the effectiveness of SLIT in children with dust mite allergies, as well as its adverse effects, at a pediatric general outpatient clinic.I analyzed the data of 181 patients aged 4 to 12 years who tested positive for mite antigen-specific immunoglobulin E, exhibited nasal and/or eye symptoms, and received Miticure. Symptoms were evaluated using the Japanese rhino-conjunctivitis quality of life (QOL) questionnaire no. 1. Wilcoxon tests were used to compare the pretreatment and post-treatment symptom scores. Adverse events were tallied, and Kaplan-Meier curves and Wilcoxon tests were used to assess the proportion of dropouts.The mean QOL score at the baseline was 2.17 (standard deviation [SD] 1.45). After 1 week, the mean symptom QOL score was 1.63 (SD 1.32); the lowest mean score was found in week 41 (0.48, SD 0.63). A significant decline in the occurrence of all symptoms, including sneezing, nasal discharge, nasal congestion, itchy eyes, and teary eyes, was observed. Adverse effects were observed in 76 (42.0%) patients; the most common adverse effect was itchy mouth.SLIT improves symptoms with minimal adverse effects in pediatric patients.

Presentation, diagnosis, and the role of subcutaneous and sublingual immunotherapy in the management of ocular allergy

Allergic eye disease or ocular allergy is a debilitating condition with a significant impact on quality of life and productivity. As atopy continues to be on the rise, primary care providers are likely to encounter increasing numbers of patients with allergic eye disease. This review outlines the classification and pathophysiology of allergic eye disease and its clinical presentation. This paper does not detail traditional first-line therapies of allergic eye disease but describes the interdisciplinary management between the eye-care provider and allergist. It is recommended that patients with ongoing signs and symptoms of ocular allergy despite first-line therapies be referred for allergen immunotherapy, as it is highly effective for treatment of allergic eye disease. Through induction of immune tolerance, allergen immunotherapy is a disease-modifying therapy that can result in long-term improvement of ocular allergy. A thorough literature review was conducted on the efficacy and safety of allergen immunotherapy, including subcutaneous immunotherapy and sublingual immunotherapy, and its role in allergic eye disease.

Mechanisms of allergen-specific immunotherapy for allergic rhinitis and food allergies

Allergen-specific immunotherapy (AIT) is currently the only potential treatment for allergies including allergic rhinitis (AR) and food allergies (FA) that can modify the underlying course of the diseases. Although AIT has been performed for over a century, the precise and detailed mechanism for AIT is still unclear. Previous clinical trials have reported that successful AIT induces the reinstatement of tolerance against the specific allergen. In this review, we aim to provide an updated summary of the knowledge on the underlying mechanisms of IgE-mediated AR and FA as well as the immunological changes observed after AIT and discuss on how better understanding of these can lead to possible identification of biomarkers and novel strategies for AIT.

Nasal allergen challenge and environmental exposure chamber challenge: A randomized trial comparing clinical and biological responses to cat allergen

BACKGROUND

The direct-instillation nasal allergen challenge (NAC) and the environmental exposure chamber (EEC) are 2 methods of conducting controlled allergen provocations. The clinical and biological comparability of these methods has not been thoroughly investigated.

OBJECTIVE

We sought to compare clinical and immunologic responses to cat allergen in NAC versus EEC.

METHODS

Twenty-four participants were randomized to receive either NAC followed by a 2-day challenge in an EEC or a 2-day challenge in an EEC followed by NAC. Challenges were separated by 28-day washout periods. We measured total nasal symptom scores, peak nasal inspiratory flow, nasal (0-8 hours) and serum cytokines, serum antibodies, peripheral blood antigen-specific T lymphocytes, and gene expression in nasal scrapings. The primary outcome was the total nasal symptom score area under the curve for the first 3 hours after allergen exposure in NAC or after initiation of exposure in EEC.

RESULTS

Both challenges increased IL-5 and IL-13 in nasal fluids and serum and resulted in altered nasal cell expression of gene modules related to mucosal biology and transcriptional regulation. Changes in gene modules, more so than cytokine measurements, showed significant associations with total nasal symptom score and peak nasal inspiratory flow. Overall, EEC exposure generated larger responses and more early terminations compared with NAC. Although the 2 challenges did not correlate in symptom magnitude or temporality, striking correlations were observed in cytokine levels.

CONCLUSIONS

Although clinical outcomes of NAC and EEC were temporally different and nonequivalent in magnitude, immunologic responses were similar. Selection of a particular allergen challenge method should depend on considerations of study objectives and cost.

Allergen-Specific Antibodies Regulate Secondary Allergen-Specific Immune Responses

Immunoglobulin E (IgE)-associated allergy is the most common immunologically-mediated hypersensensitivity disease. It is based on the production of IgE antibodies and T cell responses against per se innocuous antigens (i.e., allergens) and subsequent allergen-induced inflammation in genetically pre-disposed individuals. While allergen exposure in sensitized subjects mainly boosts IgE production and T cell activation, successful allergen-specific immunotherapy (AIT) induces the production of allergen-specific IgG antibodies and reduces T cell activity. Under both circumstances, the resulting allergen-antibody complexes play a major role in modulating secondary allergen-specific immune responses: Allergen-IgE complexes induce mast cell and basophil activation and perpetuate allergen-specific T cell responses via presentation of allergen by allergen presenting cells to T cells, a process called IgE-facilitated antigen presentation (FAP). In addition, they may induce activation of IgE memory B cells. Allergen-induced production of specific IgGs usually exerts ameliorating effects but under certain circumstances may also contribute to exacerbation. Allergen-specific IgG antibodies induced by AIT which compete with IgE for allergen binding (i.e., blocking IgG) inhibit formation of IgE-allergen complexes and reduce activation of effector cells, B cells and indirectly T cells as FAP is prevented. Experimental data provide evidence that by binding of allergen-specific IgG to epitopes different from those recognized by IgE, allergen-specific IgG may enhance IgE-mediated activation of mast cells, basophils and allergen-specific IgE⁺ B cells. In this review we provide an overview about the role of allergen-specific antibodies in regulating secondary allergen-specific immune responses.

Ragweed sublingual tablet immunotherapy: part I - evidence-based clinical efficacy and safety

Sublingual tablet immunotherapy provides an attractive alternative approach to allergen immunotherapy, as the allergen is administered as a rapidly dissolving sublingual tablet. Part I of this two-part series on the ragweed sublingual tablet describes the dose-ranging clinical work, the safety studies and the clinical outcomes from the pivotal trials which provide clear evidence for statistically significant and clinically meaningful benefit in the treatment of patients suffering from ragweed-induced seasonal allergic rhinitis-conjunctivitis with or without milder asthma. The robust results observed in the clinical trials performed with the ragweed sublingual tablet are defined by the quality of their study design, their use of a standardized allergen extract, their consistent reproducibility in demonstrating therapeutic efficacy and their properly quantified and graded safety data.

Mechanism of action of allergen immunotherapy

BACKGROUND

Allergen immunotherapy (AIT) leads to the production of antiallergen immunoglobulin (IgG) or "blocking antibody" in the serum and an increase in antiallergen IgG and IgA in nasal secretions. There is also a decrease in the usual rise in antiallergen IgE that occurs after the pollen season.

METHODS

In this paper, mechanisms of action of allergen immunotherapy is reviewed.

RESULTS

Regulatory T (Treg) cells and their cytokines, primarily interleukin (IL) 10 and transforming growth factor beta, suppress T-helper type 2 immune responses and control allergic diseases in many ways. AIT induces a shift in the proportion of IL-4-secreting T-helper type 2 cells in favor of IL-10-secreting inducible Treg cells specific for the same allergenic epitope that increases in number and function. Different types of inducible Treg control several facets of allergic inflammation. There are two main types of immunotherapy: subcutaneous immunotherapy and sublingual immunotherapy. Subcutaneous immunotherapy is efficacious and is indicated for the reduction of seasonal symptoms. Sublingual immunotherapy involves the regular self-administration and retention of allergen extract under the tongue for 1-2 minutes before the extract is swallowed. The allergens cross the mucosa in 15-30 minutes and are then captured by tolerogenic dendritic cells and processed as small peptides. Next, via the lymphatic system, a systemic immune response is created to produce an early decrease in mast cell and basophil degranulation.

CONCLUSION

AIT is indicated for the treatment of moderate-to-severe intermittent or persistent symptoms of allergic rhinitis. AIT can be administered to those >5 years of age and has been shown to be safe in children as young as 3 years of age. In this article, AIT and other types of immunotherapies were discussed as well as the indications for immunotherapy.

Mechanisms of allergen immunotherapy for inhaled allergens and predictive biomarkers

Allergen immunotherapy is effective in patients with IgE-dependent allergic rhinitis and asthma. When immunotherapy is given continuously for 3 years, there is persistent clinical benefit for several years after its discontinuation. This disease-modifying effect is both antigen-specific and antigen-driven. Clinical improvement is accompanied by decreases in numbers of effector cells in target organs, including mast cells, basophils, eosinophils, and type 2 innate lymphoid cells. Immunotherapy results in the production of blocking IgG/IgG₄ antibodies that can inhibit IgE-dependent activation mediated through both high-affinity IgE receptors (FcεRI) on mast cells and basophils and low-affinity IgE receptors (FcεRII) on B cells. Suppression of T_H2 immunity can occur as a consequence of either deletion or anergy of antigen-specific T cells; induction of antigen-specific regulatory T cells; or immune deviation in favor of T_H1 responses. It is not clear whether the altered long-term memory resides within the T-cell or the B-cell compartment. Recent data highlight the role of IL-10-producing regulatory B cells and "protective" antibodies that likely contribute to long-term tolerance. Understanding mechanisms underlying induction and persistence of tolerance should identify predictive biomarkers of clinical response and discover novel and more effective strategies for immunotherapy.

Allergen immunotherapy for allergic rhinoconjunctivitis: A systematic review and meta-analysis

BACKGROUND

The European Academy of Allergy and Clinical Immunology (EAACI) is in the process of developing Guidelines on Allergen Immunotherapy (AIT) for Allergic Rhinoconjunctivitis. To inform the development of clinical recommendations, we undertook a systematic review to assess the effectiveness, cost-effectiveness, and safety of AIT in the management of allergic rhinoconjunctivitis.

METHODS

We searched nine international biomedical databases for published, in-progress, and unpublished evidence. Studies were independently screened by two reviewers against predefined eligibility criteria and critically appraised using established instruments. Our primary outcomes of interest were symptom, medication, and combined symptom and medication scores. Secondary outcomes of interest included cost-effectiveness and safety. Data were descriptively summarized and then quantitatively synthesized using random-effects meta-analyses.

RESULTS

We identified 5960 studies of which 160 studies satisfied our eligibility criteria. There was a substantial body of evidence demonstrating significant reductions in standardized mean differences (SMD) of symptom (SMD -0.53, 95% CI -0.63, -0.42), medication (SMD -0.37, 95% CI -0.49, -0.26), and combined symptom and medication (SMD -0.49, 95% CI -0.69, -0.30) scores while on treatment that were robust to prespecified sensitivity analyses. There was in comparison a more modest body of evidence on effectiveness post-discontinuation of AIT, suggesting a benefit in relation to symptom scores.

CONCLUSIONS

AIT is effective in improving symptom, medication, and combined symptom and medication scores in patients with allergic rhinoconjunctivitis while on treatment, and there is some evidence suggesting that these benefits are maintained in relation to symptom scores after discontinuation of therapy.

Dose-response relationship of a new Timothy grass pollen allergoid in comparison with a 6-grass pollen allergoid

BACKGROUND

Subcutaneous allergen immunotherapy with grass pollen allergoids has been proven to be effective and safe in the treatment of patients with allergic rhinoconjunctivitis. Based on the extensive cross-reactivity among Pooideae species, it has been suggested that grass pollen extracts could be prepared from a single species, rather than from a multiple species mixture.

OBJECTIVE

To find the optimal dose of a Phleum pratense (P. pratense) allergoid preparation and compare its efficacy and safety to a 6-grass pollen allergoid preparation.

METHODS

In this double-blind, placebo-controlled study (EudraCT: 2011-000674-58), three doses of P. pratense allergoid (1800 therapeutic units (TU), standard-dose 6000 TU and 18 000 TU) were compared with placebo and the marketed 6-grass pollen allergoid (6000 TU). In a pre-seasonal dosing regimen, 102 patients were randomized to five treatment groups and received nine subcutaneous injections. The primary efficacy endpoint was the change in weal size (late-phase reaction [LPR]) in response to the intracutaneous testing (ICT) before and after treatment, comparing the active allergoids to placebo. Secondary outcomes were the change in Total Nasal Symptom Score (TNSS) assessed in the allergen exposure chamber (AEC), the changes in P. pratense-serum-specific IgG₄ and the incidence of adverse events (AEs).

RESULTS

All three doses of the P. pratense and the 6-grass pollen allergoid preparations were significantly superior to placebo for the primary outcome, whereas there were no significant differences in the change in TNSS. Compared to the standard-dose, the high-dose of P. pratense did not produce any additional significant benefit, but showed a slight increase in AEs. Yet this increase in AEs was lower than for the 6-grass pollen preparation.

CONCLUSIONS & CLINICAL RELEVANCE

The standard-dose of the new P. pratense allergoid was comparable to the marketed 6-grass pollen preparation at equal dose for the parameters measured.

Applications and mechanisms of immunotherapy in allergic rhinitis and asthma

Clinical and immunologic tolerance are hallmarks of successful allergen immunotherapy (AIT). Clinical benefits such as reduced symptoms, pharmacotherapy intake and improvement of quality of life persist following cessation of treatment. Successful AIT is associated with suppression of allergic inflammatory cells such as mast cells, eosinophils and basophils in target organs. Furthermore, AIT down-regulates type 2 innate lymphoid cells and allergen-specific type 2 T-helper (Th2) cells. The immunologic tolerant state following AIT is associated with the induction of distinct phenotypes of regulatory T-cells (T-regs) including interleukin (IL)-10-, IL-35- and transforming growth factor (TGF)-β- producing T-regs and FoxP3⁺ T-regs. B-cell responses, including the induction of IL-10⁺ regulatory B-cells (B-regs) and the production of IgG4-associated blocking antibodies are also induced following successful AIT. These events are associated with the suppression of antigen-specific Th2 responses and delayed immune deviation in favour of Th1 type responses. Insight into the mechanisms of AIT has allowed identification of novel biomarkers with potential to predict the clinical response to AIT and also novel therapeutic strategies for more effective and safer AIT.

The Effects of Short-Term Immunotherapy Using Molecular Standardized Grass and Rye Allergens Compared with Symptomatic Drug Treatment on Rhinoconjunctivitis Symptoms, Skin Sensitivity, and Specific Nasal Reactivity

BACKGROUND: The efficacy and safety of short-term immunotherapy with molecular standardized allergens (STI) has been demonstrated by double-blind placebo-controlled clinical trials. The aim of this study was to compare STI with symptomatic drug treatment.

METHODS: Forty-eight patients with rhinoconjunctivitis to grass and/or rye pollen were treated either with STI (ALK7, n = 24) plus anti-allergic drugs or anti-allergic drugs, alone (n = 24) in a prospective, randomized study. Symptoms and use of drugs were reported in patient diaries and titrated nasal provocation and skin prick tests were performed at baseline, before, and after season.

RESULTS: Median overall symptom ( P = 0.022, U test) and medication scores ( P = 0.003) were significantly lower in the STI group, as was the result for a simultaneous analysis of conjunctival, nasal, and bronchial symptom scores and medication ( P = 0.005). Sensitivity in the nasal provocation test decreased in the STI group but not in the drug-treated group. These differences became significant directly after STI ( P = 0.027) as well as after the grass pollen season ( P < 0.001). Skin sensitivity did not change in the STI group but increased in the drug-treated group after season, with a significant difference between the two groups for the erythema ( P < 0.001).

CONCLUSIONS: STI reduces grass pollen-induced rhinoconjunctivitis symptoms and drug use, and specific nasal reactivity and skin sensitivity, more efficiently than a standard symptomatic treatment.

The efficacy assessment of a self-administered immunotherapy protocol

Background

We previously reported the safety of a self‐administered subcutaneous immunotherapy (SCIT) protocol. Here we report the results of the retrospective efficacy trial of the United Allergy Service (UAS) self‐administered SCIT protocol. We hypothesized that by utilizing a slow SCIT buildup phase, designed to attain recommended allergen concentrations on a cumulative basis, efficacious outcomes and clinical relevance would be achieved.

Methods

We enrolled 60 SCIT patients and 56 control patients. The study contrasted baseline and treatment period combined symptom plus medication scores (CSMS) as the primary outcome measure and rhinoconjunctivitis quality of life questionnaire (RQLQ) scores as the secondary study outcome measure. Changes in pollen counts were also examined with regard to effects on these efficacy parameters.

Results

The treatment group showed significantly improved CSMS (standardized mean difference [SMD]: −1.57; 95% confidence interval [CI], −1.97 to −1.18; p < 0.001) and RQLQ (SMD: −0.91; 95% CI, −1.23 to −0.59; p < 0.001). These treatment group outcome measures were respectively improved by 33% and 29% compared to baseline and greater than 40% in comparison to the control group (p < 0.0001). Significant results were also shown when examining these outcome measures with regards to either monotherapy or poly‐allergen SCIT. Furthermore, a comparison to recent meta‐analyses of SCIT studies showed equivalent efficacy and clinical relevance. Assessment of pollen counts during the baseline and treatment periods further corroborated the efficacy of the UAS SCIT protocol.

Conclusion

These efficacy results, and our previous safety results, show that a carefully designed and implemented self‐administered SCIT protocol is efficacious and safe.

Effect of grass pollen immunotherapy on clinical and local immune response to nasal allergen challenge

Rationale

Nasal allergen provocations may be useful in investigating the pathophysiology of allergic rhinitis and effects of treatments.

Objective

To use grass pollen nasal allergen challenge (NAC) to investigate the effects of allergen immunotherapy in a cross‐sectional study.

Methods

We studied nasal and cutaneous responses in untreated subjects with seasonal grass‐pollen allergic rhinitis (n = 14) compared with immunotherapy‐treated allergics (n = 14), plus a nonatopic control group (n = 14). Volunteers underwent a standardized NAC with 2000 biological units of timothy grass allergen (equivalent to 1.3 μg major allergen, Phl p5). Nasal fluid was collected and analysed by ImmunoCAP and multiplex assays. Clinical response was assessed by symptom scores and peak nasal inspiratory flow (PNIF). Cutaneous response was measured by intradermal allergen injection. Retrospective seasonal symptom questionnaires were also completed.

Results

Immunotherapy‐treated patients had lower symptom scores (P = 0.04) and higher PNIF (P = 0.02) after challenge than untreated allergics. They had reduced early (P = 0.0007) and late (P < 0.0001) skin responses, and lower retrospective seasonal symptom scores (P < 0.0001). Compared to untreated allergics, immunotherapy‐treated patients had reduced nasal fluid concentrations of IL‐4, IL‐9 and eotaxin (all P < 0.05, 8 h level and/or area under the curve comparison), and trends for reduced IL‐13 (P = 0.07, area under the curve) and early‐phase tryptase levels (P = 0.06).

Conclusions

Nasal allergen challenge is sensitive in the detection of clinical and biological effects of allergen immunotherapy and may be a useful surrogate marker of treatment efficacy in future studies.

The safety of self-administered allergen immunotherapy during the buildup and maintenance phases

BACKGROUND

Self-administered allergen immunotherapy is considered controversial. We believe the implementation of a self-administration protocol characterized by patient preselection and a slow buildup phase is safe.

METHODS

We analyzed 23,614 patient records and associated immunotherapy injections for systemic reactions (SR) during a 1-year period (2011 to 2012). SRs were graded in accordance with the World Allergy Organization (WAO) criteria.

RESULTS

Thirty-seven SRs were reported for 23,614 patients who self-administered 2,021,600 injections yielding an annual SR rate of 0.16% (per patient) or 0.002% (per injection). Only 9 of 4643 pediatric (0.19%) and 28 of 18,971 adult patients (0.15%) experienced 1 or more SRs. No deaths (grade V SR) occurred. From 2009 through early 2014, over 90,000 patients received more than 10 million injections in accordance with the United Allergy Services (UAS) protocol without fatalities.

CONCLUSION

We believe this safety profile is due to a preselection of patients to exclude those with a high risk for adverse reactions and a slow immunotherapy buildup phase. In contrast, previous studies documented office-based SRs ranging from approximately 3% to greater than 14%. Thus, the UAS home-immunotherapy SR rate is significantly lower than office-based immunotherapy SR rates (p < 0.0001). The enhanced safety of this protocol results in a decreased frequency and severity of SRs. This safety report, derived from analyses of one of the largest patient cohorts studied, corroborates and expands the observations of previous studies of self-administered subcutaneous immunotherapy in a low-risk patient population by assessing self-administered allergen immunotherapy during the buildup and maintenance phases.

Subcutaneous and sublingual immunotherapy: Where do we stand?

Though symptoms of allergic diseases can be reduced by the use of drugs such as corticosteroids, antihistamines or leukotrien antagonists, the only treatment directed to change the natural course of allergic disease is allergen-specific immunotherapy (SIT). Its efficacy can last years after the cessassion of the treatment. SIT brings on regulatory T cells with the capacity to generate interleukin-10 and transforming growth factor-b, restricts activation of mast cells and basophils, and shifts antibody isotype from IgE to the noninflammatory type immunoglobulin G4. Subcutaneous (SCIT) and sublingual (SLIT) immunotherapy are the two most used ways at the present for applying SIT. These two treatments were demonstrated to be effective on reducing symptoms and medication use, in prevention of new sensitizations and in protecting from progression of rhinitis to asthma. The safety of SLIT appears to be better than SCIT although there have been a few head to head comparisons. In order to overcome compliance problems or possible systemic side effects which may be faced during this long-term treatment, recent investigations have been focused on the implementation of allergens in quite efficacious and safer ways.

Novel developments in the mechanisms of immune tolerance to allergens

Allergy is the result of a disbalanced immune response to environmental innocuous antigens. Despite of accumulating data to define the pathomechanisms that take place in case of allergic diseases a detailed understanding of sequence of events that lead to the "normal" scenario of tolerance development are still under debate. Allergen-specific immunotherapy is the only causal treatment of allergic diseases. It modifies the immune response to a particular antigen to achieve tolerance against the symptom-causing allergen. This process is considered to mirror physiological peripheral tolerance induction. A number of immunological changes have been described to occur under allergen immunotherapy, including the generation of allergen-specific regulatory T cells, the induction of allergen-specific IgG4, an increase in the Th1/Th2 cytokine ratio and decreased activation and function of effector cells such as mast cells, basophils and eosinophils.

Allergen immunotherapy in allergic respiratory diseases: from mechanisms to meta-analyses

Allergen-specific immunotherapy (SIT) involves the repeated administration of allergenic extracts to atopic individuals over a period of 3 to 5 years either subcutaneously (SCIT) or sublingually (SLIT) for the treatment of allergic respiratory diseases, including asthma and allergic rhinitis (AR). In studies, SCIT and SLIT have been shown to improve existing symptoms of asthma and AR and to also have the capability to cause disease-modifying changes of the underlying atopic condition so as to prevent new allergic sensitization as well as arrest progression of AR to asthma. Recent evidence suggests that immunotherapy brings about these effects through actions that use T-regulatory cells and blocking antibodies such as IgG(4) and IgA(2,) which can then result in an "immune deviation" from a T-helper (Th) 2 cell pattern to a Th1 cell pattern. Numerous meta-analyses and studies have been performed to evaluate the existing data among these studies, with the consensus recommendation favoring the use of immunotherapy because of its potential to modify existing diseases. Significant adverse reactions can occur with immunotherapy, including anaphylaxis and, very rarely, death. A primary factor in considering SIT is its potential to provide long-lasting effects that are able to be sustained well after its discontinuation. Given the significant burden these allergic diseases impose on the health-care system, SIT appears to be a cost-effective adjunctive treatment in modifying the existing disease state.

Novel routes for allergen immunotherapy: safety, efficacy and mode of action

Allergen immunotherapy is the only curative treatment of IgE-mediated type I respiratory allergies. Subcutaneous immunotherapy (SCIT) is used as a reference therapy and has transformed allergic treatments; it improves symptoms (asthma and rhinitis) as well as the quality of life of patients. SCIT requires repetitive administration and carries the risk of severe systemic adverse effects, including anaphylaxis. Sublingual immunotherapy is now a valid noninvasive alternative to SCIT, as a safe and efficacious treatment for respiratory allergies. In this article, we compare various routes of allergen immunotherapy, including SCIT and sublingual immunotherapy, as well as more exploratory routes currently under investigation (i.e., intralymphatic, epicutaneous, intranasal and oral). We discuss their respective advantages, as well as their foreseen modes of action.

Induction of tolerance via the sublingual route: mechanisms and applications

The clinical efficacy of sublingual immunotherapy (SLIT) with natural allergen extracts has been established in IgE-dependent respiratory allergies to grass or tree pollens, as well as house dust mites. Sublingual vaccines have an excellent safety record, documented with approximately 2 billion doses administered, as of today, in humans. The oral immune system comprises various antigen-presenting cells, including Langerhans cells, as well as myeloid and plasmacytoid dendritic cells (DCs) with a distinct localisation in the mucosa, along the lamina propria and in subepithelial tissues, respectively. In the absence of danger signals, all these DC subsets are tolerogenic in that they support the differentiation of Th1- and IL10-producing regulatory CD4(+) T cells. Oral tissues contain limited numbers of mast cells and eosinophils, mostly located in submucosal areas, thereby explaining the good safety profile of SLIT. Resident oral Th1, Th2, and Th17 CD4(+) T cells are located along the lamina propria, likely representing a defence mechanism against infectious pathogens. Second-generation sublingual vaccines are being developed, based upon recombinant allergens expressed in a native conformation, possibly formulated with Th1/T reg adjuvants and/or mucoadhesive particulate vector systems specifically designed to target oral dendritic cells.

Immunotherapy throughout the decades: from Noon to now

OBJECTIVE

To review major milestones in the development of subcutaneous allergen immunotherapy in 20-year segments.

DATA SOURCES

Review of the literature available in textbooks and journals.

STUDY SELECTION

Articles and books addressing major achievements in the development of subcutaneous allergy immunotherapy were selected for inclusion in this review.

RESULTS

Immunotherapy administration has improved the lives of possibly millions of patients with hay fever. Asthmatic symptoms have been relieved if not ablated in millions as well. Insect venom hypersensitivity became treatable and highly effective. In the beginning years of immunotherapy, it was clear that immunotherapy worked; in the later years, the mechanisms for this efficacy were discovered. In this case, the therapy preceded its validation. Methods, materials, and safety have vastly improved. Postulated mechanisms explain much but not everything.

CONCLUSIONS

There is still research to be accomplished, improvements to be made, and, of course, patients to be made well.

Suppression of Th2-driven airway inflammation by allergen immunotherapy is independent of B cell and Ig responses in mice

Allergen-specific immunotherapy (IT) uniquely renders long-term relief from allergic symptoms and is associated with elevated serum levels of allergen-specific IgG and IgA. The allergen-specific IgG response induced by IT treatment was shown to be critical for suppression of the immediate phase of the allergic response in mice, and this suppression was partially dependent on signaling through FcγRIIB. To investigate the relevance of the allergen-specific IgG responses for suppression of the Th2-driven late-phase allergic response, we performed IT in a mouse model of allergic asthma in the absence of FcγRIIB or FcγRI/FcγRIII signaling. We found that suppression of Th2 cell activity, allergic inflammation, and allergen-specific IgE responses is independent of FcγRIIB and FcγRI/FcγRIII signaling. Moreover, we show that the IT-induced allergen-specific systemic IgG or IgA responses and B cell function are dispensable for suppression of the late-phase allergic response by IT treatment. Finally, we found that the secretory mucosal IgA response also is not required for suppression of the Th2-driven allergic inflammation by IT. These data are in contrast to the suppression of the immediate phase of the allergic response, which is critically dependent on the induced allergen-specific serum IgG response. Hence, IT-induced suppression of the immediate and late phases of the allergic response is governed by divergent and independent mechanisms. Our data show that the IT-induced suppression of the Th2 cell-dependent late-phase allergic response is independent of the allergen-specific IgG and IgA responses that are associated with IT treatment.

Immunotherapy with mosquito (Culex quinquefasciatus) extract: a double-blind, placebo-controlled study

BACKGROUND

Mosquito allergy is well established, but mosquito immunotherapy requires validation using clinical and immunologic variables.

OBJECTIVE

To evaluate the tolerability and efficacy of specific immunotherapy with Culex quinquefasciatus (mosquito) extract.

METHODS

We performed a randomized, double-blind, placebo-controlled trial of immunotherapy for 1 year in 40 patients with asthma, rhinitis, or both. Patients were evaluated by means of intradermal testing, symptom and drug scores, and histamine provocation testing before and after 1 year of immunotherapy. Mosquito specific IgE and IgG subclass antibody responses were evaluated at the basal level and after 1 year.

RESULTS

Patients receiving allergen immunotherapy for 1 year showed a significant improvement compared with baseline and patients receiving placebo regarding skin reactions, symptom scores (rhinitis and asthma), and forced expiratory volume in 1 second. Provocation concentration of histamine that caused a decrease in forced expiratory volume in 1 second of 20% by inhalation was elevated in the group receiving immunotherapy. In the active group serologic analysis showed a slight reduction in IgE levels (P = .02) but a significant elevation in IgG4 levels (P = .001), with a significant decrease in the IgE/IgG4 ratio (P = .001). All these changes in the placebo group were nonsignificant.

CONCLUSIONS

Allergen immunotherapy with mosquito extract was well tolerated, with improvement in symptoms and airway reactivity. Good clinical outcome was associated with increased IgG4 antibody levels.

Allergen injection immunotherapy for seasonal allergic rhinitis

BACKGROUND

Allergic rhinitis is the most common of the allergic diseases. Despite improved understanding of the pathophysiology of allergic rhinitis and advances in its pharmacological treatment, its prevalence has increased worldwide. For patients whose symptoms remain uncontrolled despite medical treatment, allergen injection immunotherapy is advised. An allergen-based treatment may reduce symptoms, the need for medication and modify the natural course of this disease.

OBJECTIVES

To evaluate the efficacy and safety of subcutaneous specific allergen immunotherapy, compared with placebo, for reducing symptoms and medication requirements in seasonal allergic rhinitis patients.

SEARCH STRATEGY

We searched the Cochrane Ear, Nose and Throat Disorders Group Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2006), MEDLINE (1950 to 2006), EMBASE (1974 to 2006), Pre-MEDLINE, KOREAMED, INDMED, LILACS, PAKMEDINET, Scisearch, mRCT and the National Research Register. The date of the last search was February 2006.

SELECTION CRITERIA

All studies identified by the searches were assessed to identify randomised controlled trials involving participants with symptoms of seasonal allergic rhinitis and proven allergen sensitivity, treated with subcutaneous allergen specific immunotherapy or corresponding placebo.

DATA COLLECTION AND ANALYSIS

Two independent authors identified all studies reporting double-blind, placebo controlled randomised trials of specific immunotherapy in patients with seasonal allergic rhinitis due to tree, grass or weed pollens. Two authors independently performed quality assessment of studies. Data from identified studies were abstracted onto a standard extraction sheet and subsequently entered into RevMan 4.2.8. Analysis was performed using the Standardised Mean Difference (SMD) method and a random-effects model; P values < 0.05 were considered statistically significant. The primary outcome measures were symptom scores, medication use, quality of life and adverse events.

MAIN RESULTS

We retrieved 1111 publications of which 51 satisfied our inclusion criteria. In total there were 2871 participants (1645 active, 1226 placebo), each receiving on average 18 injections. Duration of immunotherapy varied from three days to three years. Symptom score data from 15 trials were suitable for meta-analysis and showed an overall reduction in the immunotherapy group (SMD -0.73 (95% CI -0.97 to -0.50, P < 0.00001)). Medication score data from 13 trials showed an overall reduction in the immunotherapy group (SMD of -0.57 (95% CI -0.82 to -0.33, p<0.00001)). Clinical interpretation of the effect size is difficult. Adrenaline was given in 0.13% (19 of 14085 injections) of those on active treatment and in 0.01% (1 of 8278 injections) of the placebo group for treatment of adverse events. There were no fatalities.

AUTHORS' CONCLUSIONS

This review has shown that specific allergen injection immunotherapy in suitably selected patients with seasonal allergic rhinitis results in a significant reduction in symptom scores and medication use. Injection immunotherapy has a known and relatively low risk of severe adverse events. We found no long-term consequences from adverse events.

Cluster-Immuntherapie bei allergischer Rhinokonjunktivitis

Apart from allergen avoidance, specific immunotherapy (SIT) represents the only potentially curative treatment available to patients with allergic rhinoconjunctivitis. Evidence for its clinical efficacy has been clearly demonstrated in several controlled clinical trials and depends on the allergen to which the patient is sensitive, the quality and total amount of allergen administered, and the SIT schedule. In classic SIT, gradually ascending dosages of the allergen extract are injected subcutaneously (dose-increase period) until the individual maximum dose is reached (dose-maintenance period). Several dosage schedules have been worked out. In cluster immunotherapy, 2-3 injections per day of treatment are given once a week to rapidly reach the maintenance dose. Several cluster schedules have been described. Recent data demonstrate that the frequency and severity of adverse effects in cluster immunotherapy correspond to those in other dosage schedules. As far as safety goes, cluster immunotherapy is an interesting alternative for the dose-increase period. In addition, recent studies reveal that clinical benefits appear sooner with cluster immunotherapy.

Clinical efficacy and safety of preseasonal sublingual immunotherapy with grass pollen carbamylated allergoid in rhinitic patients. A double-blind, placebo-controlled study

BACKGROUND

The aim of this study was to confirm the clinical efficacy and safety of a preseasonal sublingual immunotherapy (SLIT) in a group of allergic patients with seasonal rhinoconjunctivitis with or without mild intermittent or mild persistent asthma. The immunotherapy was administered through the oral mucosa with a monomeric carbamylated allergoid (allergoid SLIT) for grass pollens. A secondary endpoint was to evaluate the effect of the allergoid SLIT on nasal reactivity.

METHODS AND RESULTS

A single-center, randomized, double-blind, placebo-controlled study was performed. Patients were selected and randomly allocated to two groups: one group received active treatment (allergoid SLIT) for 2 years and the other received placebo. Both groups received the necessary drug treatment throughout the trial. Thirty-three outpatients (20 men and 13 women, mean age: 30 years; range: 19-43) attending our center were enrolled in the study. Symptoms and medications were scored on diary cards during the pollen season. An allergen nasal challenge was performed at baseline and after 2 years of SLIT to evaluate nasal reactivity. Because the clinical scores were non-normally distributed, the Mann-Whitney and the Chi-square tests for intergroup comparisons and the Wilcoxon test for intragroup comparisons were used. The results were evaluated after 1 and 2 years of treatment. Between the first and second years of treatment, no changes in the scores for the placebo group were found, while for the active vaccine group significant decreases were found in rhinorrhea (p < 0.03), sneezing (p < 0.03), and conjunctivitis (p < 0.02). Symptom scores after nasal challenge decreased (p < 0.03) after 2 years' treatment. Nasal steroid use significantly decreased in the active treatment group during May and June in both the years of treatment (p < 0.02). Only two mild local adverse events were reported in the active group and none was reported in the placebo group.

CONCLUSIONS

The results of this study show that the allergoid SLIT is safe and effective in decreasing symptom scores and drug use in rhinitic patients allergic to grass pollen.

Novel ways for immune intervention in immunotherapy: mucosal allergy vaccines

Allergen-specific immunotherapy is currently the only curative treatment for allergy. Subcutaneous immunotherapy (SCIT) has been successfully used to treat patients who are allergic to insect venom, house dust mites, or tree or grass pollens. In the context of potentially severe, albeit infrequent, side effects associated with SCIT, mucosal routes of administration are being investigated to conduct allergenic desensitization. This article reviews recent developments in the field of nasal, oral, and sublingual immunotherapy as they relate to safety, clinical efficacy, and immune mechanisms of action. Implications for the design and development of improved allergy vaccines that could be used through such nonparenteral routes are discussed. Specifically, allergen presentation platforms and adjuvants facilitating the targeting of immune cells at mucosal surfaces to promote tolerance induction are reviewed.

Experimental models for the evaluation of treatment of allergic rhinitis

OBJECTIVE

To review the experimental models used for the clinical evaluation of treatments for allergic rhinitis.

DATA SOURCES

Peer-reviewed clinical studies and review articles were selected from the PubMed database using the following relevant keywords: allergic rhinitis in combination with efficacy, wheal and flare, nasal challenge, park, cat room, or exposure unit. Regulatory guidance documents on allergic rhinitis were also included.

STUDY SELECTION

The authors' knowledge of the field was used to limit references with emphasis on recent randomized and controlled studies. References of historical significance were also included.

RESULTS

Traditional outpatient studies are universally accepted in the evaluation of treatment for allergic rhinitis. Experimental models provide ancillary information on efficacy at different stages of treatment development. Skin histamine and allergen challenge, as well as direct nasal challenge with histamine and allergen, are often used as early steps in assessing drug efficacy. Exposure units, park settings, and cat rooms better approximate real life by drawing on the natural mode of allergen exposure and delivering the sensitizing allergen to allergic individuals in the ambient air. Park studies make use of allergens in the outdoors, whereas cat rooms and exposure units present the sensitizing allergens indoors, with the latter providing consistent predetermined allergen levels. Exposure unit and park studies are acknowledged for the determination of onset of action and are also suited to the measurement of duration of effect and other measures of efficacy. Onset and duration of effect are 2 important pharmacodynamic properties of antihistamines and nasal corticosteroids as determined by the Allergic Rhinitis and Its Impact on Asthma and the European Academy of Allergology and Clinical Immunology workshop group.

CONCLUSIONS

All challenge models serve as important instruments in the evaluation of antiallergic medications and provide additional information to complement traditional studies.

Immune mechanisms of allergen-specific sublingual immunotherapy

Sublingual immunotherapy has been shown in some clinical studies to modulate allergen-specific antibody responses [with a decrease in the immunoglobulin E/immunoglobulin G4 (IgE/IgG4) ratio] and to reduce the recruitment and activation of proinflammatory cells in target mucosa. Whereas a central paradigm for successful immunotherapy has been to reorient the pattern of allergen-specific T-cell responses in atopic patients from a T helper (Th)2 to Th1 profile, there is currently a growing interest in eliciting regulatory T cells, capable of downregulating both Th1 and Th2 responses through the production of interleukin (IL)-10 and/or transforming growth factor (TGF)-beta. We discuss herein immune mechanisms involved during allergen-specific sublingual immunotherapy (SLIT), in comparison with subcutaneous immunotherapy. During SLIT, the allergen is captured within the oral mucosa by Langerhans-like dendritic cells expressing high-affinity IgE receptors, producing IL-10 and TGF-beta, and upregulating indoleamine dioxygenase (IDO), suggesting that such cells are prone to induce tolerance. The oral mucosa contains limited number of proinflammatory cells, such as mast cells, thereby explaining the well-established safety profile of SLIT. In this context, second-generation vaccines based on recombinant allergens in a native conformation formulated with adjuvants are designed to target Langerhans-like cells in the sublingual mucosa, with the aim to induce allergen-specific regulatory T cells. Importantly, such recombinant vaccines should facilitate the identification of biological markers of SLIT efficacy in humans.

Efficacy and safety of subcutaneous immunotherapy with a biologically standardized extract of Ambrosia artemisiifolia pollen: a double-blind, placebo-controlled study

BACKGROUND

The allergological relevance of Ambrosia in Europe is growing but the efficacy of the injective immunotherapy for this allergen has been documented only in Northern America.

OBJECTIVE

We sought to study the safety and efficacy of injective immunotherapy in European patients sensitized to Ambrosia artemisiifolia.

METHODS

Thirty-two patients (18 M/14 F, mean age 36.78, range 23-60 years) suffering from rhinoconjunctivitis and/or asthma and sensitized to Ambrosia were enrolled and randomized in a double-blind, placebo-controlled (DBPC) study lasting 1 year. A maintenance dose corresponding to 7.2 microg of Amb a 1 was administered at 4-week intervals after the build-up. During the second and the third year, all patients were under active therapy in an open fashion. Symptom and medication scores, skin reactivity to Ambrosia (parallel line biological assay), and pollen counts were assessed throughout the trial.

RESULTS

Twenty-three patients completed the trial. No severe adverse event was observed. During the DBPC phase, actively treated patients showed an improvement in asthmatic symptoms (P=0.02) and drug (P=0.0068) scores days with asthmatic symptoms (P=0.003), days with rhinitis symptoms (P=0.05), and days with intake of drugs (P=0.0058), as compared to before therapy. No improvement for any of these parameters was detected in the placebo group. Moreover, the number of days with rhinitis and asthma was significantly higher in the placebo as compared to the active group (P=0.048 and P<0.0001, respectively). Patients who switched from placebo to active therapy improved in rhinoconjunctivitis, asthma, and drug intake. The skin reactivity decreased significantly (12.2-fold, P=0.0001) in the active group whereas a slight increase (1.07-fold, P=0.87) was observed in the placebo group after the DBPC phase. After switching to active therapy, patients previously under placebo showed a significant decrease of this parameter (4.78-fold, P=0.002).

CONCLUSION

Injective immunotherapy is safe and clinically effective in European patients sensitized to Ambrosia.

New approaches in immunotherapy: allergen vaccination with immunostimulatory DNA

Despite its success, conventional immunotherapy is saddled with a number of encumbrances. An allergenic vaccine that could reduce allergenicity, maintain immunogenicity, and be given in a few doses would have important therapeutic implications, as millions of patients with poorly controlled allergic rhinitis and asthma would be candidates for such a form of immunomodulation. This article addresses a specific adjuvant approach to immunotherapy in which highly active immunostimulatory phosphorothioate oligodeoxyribonucleotide moieties are linked to the principal allergenic moiety of a relevant aeroallergen.

[Efficacy of immunotherapy in the treatment of asthma]

Specific immunotherapy consists of the administration of allergen extracts to patients with allergic disease to achieve clinical tolerance to the causative allergens. Currently, it is the only etiologic treatment for respiratory allergy. A World Health Organization opinion paper published in 1997 defines immunotherapy as "the only form of treatment able to modify the natural course of allergic diseases". In patients with allergic rhinitis, several studies suggest that immunotherapy can modify the natural history of respiratory allergy by preventing the development of asthma in children with this disease. Numerous studies demonstrate its efficacy in IgE-mediated asthma and particularly in mild-to-moderate asthma. When complete avoidance of the allergen cannot be achieved with measures that allow the patient to lead a normal life, pharmacological treatment can help to control symptoms, but symptoms immediately return when treatment is interrupted. However, asthma care can be improved by allergen-specific treatment; immunotherapy may shift the immune response from an allergic pattern toward a more protective response, producing persistent improvement with reduction of symptoms and the need for pharmacological treatment. Numerous comparative studies with specific immunotherapy vs. placebo or pharmacological treatment have demonstrated the efficacy of this treatment and its advantages in control of the disease. Specific immunotherapy induces favorable clinical, biological and functional modifications in the course of allergic asthma. Significant improvement in clinical manifestations has been demonstrated, even with levels of allergen exposure higher than those at the beginning of treatment. This improvement is associated with a reduced need for antiinflammatory and bronchodilator treatment. Moreover, specific bronchial reactivity shows a clear improvement with disappearance of delayed response and a clear increase in the threshold for immediate response to the allergen. Reduction in nonspecific bronchial hyperreactivity and improvement in exercise-induced asthma are also observed. Several studies recommend an optimal duration of specific immunotherapy for allergic asthma of between 3 and 5 years to achieve maximal therapeutic efficacy. A direct relationship between treatment duration and the persistence of its effects has been observed. Moreover, the treatment is more effective when started early. The possible adverse effects related to systemic reactions should be borne in mind. Although these effects are infrequent, maximal precautions should be taken when administering this treatment. Immunotherapy is contraindicated in cases of severe asthma, heart disease, autoimmune disease and associated severe neoplastic processes. However, all the beneficial effects of immunotherapy are conditioned by an accurate and early etiological diagnosis confirming the causative allergen. The availability of high-quality allergen extracts is essential to obtain the desired effect. Inappropriate patient selection for this treatment is the main cause of its failure. The integral treatment of allergic asthma includes environmental measures, patient education, pharmacological treatment and, whenever possible, immunotherapy.

Systemic reactions to allergen immunotherapy: a review of the literature

Since its introduction the safety of specific immunotherapy (SIT) was assessed by many well-designed studies. SIT is accepted as an effective treatment of allergic diseases despite the occurrence of side-effects, among which systemic reactions (SRs) are the most dangerous. The reported frequency of SRs after SIT varies among the studies and several factors influence it. Asthma is a particular risk factor for systemic side-effects. Furthermore, SRs occur more often in patients with high allergen sensitivity as determined by skin testing or RAST. Making dosage errors is also considered to be a high risk. It is reported that reactions are more common during rush and clustered induction treatment, whereas a significantly lower incidence of SRs occurred with the use of standardized modified allergen vaccines than with aqueous extracts. On the basis of valuable guidelines, precautions to minimize the risk of SRs from SIT were recommended. Injections should be given or supervised by doctors well-trained in this form of treatment in a clinic where there is the immediate availability of a resuscitative equipment. Consideration should be given to evaluate the patient's conditions and to monitor subjects for a minimum of 30 minutes after the injections. Therefore, if appropriately done, the risk of SIT is negligible.

25. Immunotherapy of allergic disease

Specific immunotherapy involves the administration of allergen extracts to achieve clinical tolerance of the allergens which cause symptoms in patients with allergic conditions. Immunotherapy has been shown to be effective in patients with mild forms of allergic disease, and also in those who do not respond well to standard drug therapy. Recent studies suggest that specific immunotherapy may also modify the course of allergic disease, by reducing the risk of developing new allergic sensitizations, and also inhibiting the development of clinical asthma in children treated for allergic rhinitis. Specific immunotherapy remains the treatment of choice for patients with systemic allergic reactions to wasp and bee stings. The precise mechanisms responsible for the beneficial effects of SIT remain a matter of research and debate. An effect on regulatory T cells seems most probable, associated with switching of allergen-specific B cells towards IgG4 production. Few direct comparisons of specific immunotherapy and drug therapy have been made. Existing data suggest that the effects of specific immunotherapy take longer to come on, but once established, specific immunotherapy will give long-lasting relief of allergic symptoms, whereas the benefits of drugs only last as long as they are continued.

A pre-seasonal birch/hazel sublingual immunotherapy can improve the outcome of grass pollen injective treatment in bisensitized individuals. A case-referent, two-year controlled study

BACKGROUND

The study tests the hypothesis of a reduction of priming due to tree allergy in patients sensitised to both birch/hazel and grass pollen undergoing an associated preseasonal Sublingual/Injective immunotherapy.

METHODS

36 out of 49 bisensitized candidates were pair-matched into 18 case-referent couples. During two years all patients were administered preseasonal grass-SIT and one patient in each couple received also birch/hazel-SLIT. Diary cards were fulfilled for three consecutive grass pollen seasons. Specific Nasal Provocation Test (NPT) for grass and aspecific bronchial challenge were done; sera were analyzed for specific IgE and IgG.

RESULTS

During the peak of the grass pollen season both groups showed a significant improvement in total symptom-score. Conjunctivitis and cough improved significantly more in patients with associated therapies. While antihistamine score decreased significantly in both groups, antiasthmatics did only in the SLIT-SIT group. The follow-up documented a significant increase in grass- and birch-specific IgG and a decrease in grass-specific IgE. Grass-NPT threshold was clearly higher in SLIT-SIT-group (p = 0.01) and only in this group PD20 methacholine improved significantly (p < 0.05).

CONCLUSIONS

Combined birch/hazel-SLIT and grass-SIT are safe and improve clinical outcomes of SIT alone in young bisensitized patients. Priming reduction is supported by specific NPT and bronchial hyperresponsiveness.

The ACVD task force on canine atopic dermatitis (XXIV): allergen-specific immunotherapy

Allergen-specific immunotherapy (ASIT) has been used for years to treat dogs with atopic dermatitis (AD) and humans with atopic diseases. The efficacy of ASIT has been well documented for humans with respiratory atopic diseases and stinging insect allergy, but its effectiveness seems more controversial for patients with AD. In spite of insufficient evidence derived from randomized controlled trials, multiple open studies and a large body of clinical observations suggest that ASIT is effective in controlling the clinical signs of dogs with AD. As a result of the scarcity of evidence from controlled trials, the true efficacy of ASIT, and the optimal protocols for allergen dose and frequency of injection are currently unknown. Allergen-specific immunotherapy nevertheless may be included in the treatment of canine AD because of its potential advantages and limited disadvantages compared to other forms of therapy. There is no evidence, however, for the preference of any specific treatment protocol. The predictive value of historical, clinical and immunologic features related to the efficacy of ASIT in dogs with AD are discussed in this paper. Adverse reactions, and the requirements for monitoring of patients receiving ASIT, then are reviewed and detailed. Finally, this review highlights aspects of ASIT where further research and controlled studies are needed.