The alpha gal story: Lessons learned from connecting the dots

Anaphylaxis is a severe allergic reaction that can be rapidly progressing and fatal; thus, establishing the etiology of anaphylaxis is pivotal to long-term risk management. Recently, Steinke and colleagues have identified a novel IgE antibody response to a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (alpha-gal) (J Allergy Clin Immunol 2015; 135: 589-596). IgE to alpha-gal has been associated with two distinct forms of anaphylaxis: i) immediate onset anaphylaxis during first exposure to intravenous cetuximab which is a monoclonal antibody specific for the epidermal growth factor receptor (EGFR), and ii) delayed onset anaphylaxis 3-6 hours after ingestion of mammalian food products (e.g., beef and pork). Results from their studies and those of others strongly suggest that tick bites are a cause, if not the only significant cause, of IgE antibody responses to alpha-gal in the southern, eastern and central United States, Europe, Australia and parts of Asia.

In 2004, cetuximab was in clinical trials for the treatment of metastatic colorectal cancer and was causing hypersensitivity reactions, but they were occurring primarily in a group of southern US states. Patients who had reactions to cetuximab also had IgE antibodies specific for this molecule before they started treatment. It was later determined that the antigen was alpha-gal which represents a major transplantation barrier between primates and other mammals. Humans and higher primates cannot produce alpha-gal which makes it possible for these animals to make IgG antibodies directed towards this oligosaccharide. The antibodies causing reactions to cetuximab overlapped the same geographical area where allergic reactions to red meat were occurring. It was later discovered that tick bites represent the most important cause of alpha-gal sensitization and that epidemiological evidence in the USA would suggest that the rise in the deer population has played an important role.

The results described in this review provide evidence that: IgE responses to an oligosaccharide can induce significant or severe allergic symptoms, demonstration of sensitization to this epitope by skin test often requires intradermal as well as prick test, ticks can induce high titer food specific IgE responses in adult life, and also that eating mammalian products carrying this epitope does not give rise to any symptoms during the first hour or more. The delay in onset of symptoms following eating red meat is best explained by delayed arrival of the relevant form of antigen in the circulation, but the question remains as to what form of glycoprotein or more likely glycolipid takes 3 hours or more to appear in the circulation. Finally, the often-rapid production of IgE antibodies to alpha-gal after tick bites provides a striking model of a parasite induced IgE response; however, it remains a challenge to identify why the response is so strong and why it is directed so consistently against the alpha-gal carbohydrate residue. 

Current biologics to treat inflammatory skin diseases

Psoriasis and atopic dermatitis (AD) are the most common inflammatory skin conditions that share similarities, including epidermal hyperplasia, marked T-cell and dendritic cell infiltration, and a relatively increased Th1 axis. However, T cell polarization differs and therapeutic targeting has confirmed that TNF-α, IL-17, and IL-23 are the main cytokine drivers of psoriasis while AD has been recently characterized as Th2/Th22 polarized, with some Th17 involvement. Noda et al detail the different therapeutic approaches that have been approved or being tested for these diseases (J Allergy Clin Immunol 2015; 135: 324-336).

Up to 3% of adults have psoriasis, which is associated with red scaly lesions, a shorter life span, and a high risk for cardiovascular diseases, obesity, and diabetes. Up to 20% of these patients have severe disease which requires systemic therapies. Conventional treatments for psoriasis such as phototherapy, methotrexate, cyclosporine, and aceitretin are associated with loss of efficacy, side effects and toxicity. This led to the introduction of biologics, selective immune antagonists, such as TNF-α and IL-12/IL-23p40, and IL-17A which have demonstrated higher efficacy and a better safety profile. Various biologics are FDA approved and have revolutionized the treatment of psoriasis and psoriatic arthritis. Despite the rapid improvements associated with biologics, high cost has driven the development of small-molecule, orally available treatments which provide alternatives to injection therapies.

AD is the most common inflammatory skin disorder affecting up to 25% of children and up to 7% of adults characterized by highly pruritic erythematous plaques that are prone to infections, which is rarely seen in patients with psoriasis.  Severe AD resistant to topical medications is treated with oral steroids, phototherapy and other immunosuppressants that are associated with inconvenience or toxicity, much like the conventional treatments for psoriasis. The inflammatory AD profile has only recently been established, characterized by overexpression of the Th2 cytokines (IL-4, IL-5, and IL-13) and chemokines (CCL17, CCL18, and CCL26), as well as the Th22 cytokine IL-22. The Th17 axis is also activated in patients with AD and might have a role in promoting Th2 differentiation.  Studies on the effects of biologics in patients with AD are lagging behind psoriasis by about a decade, and selective antagonists are only recently being examined for the treatment of AD in clinical trials.  The drug dupilumab is currently in phase III trials for AD, which binds to IL-4 receptor alpha (IL-4Rα) and blocks IL-4 and IL-13 activity. The drug significantly reduced levels of the Th2 chemokines and reversed epidermal hyperplasia in phase I and II studies. Other phase I or II trials are underway that target various antagonists such as IL-12/23p40, IL-22, IL-31, IgE and TSLP.

The authors summarize that while psoriasis develops through well-understood mechanisms and has many targeted biologics with proved efficacy, clinical trials and subsequent molecular analyses using human samples will be able to clarify the relative roles of polar cytokines in patients with AD.

Are there any known side effects of immune suppression from the long term use of biologics? For example, is there data from the long term use of biologics that have been successful in other diseases such as arthritis or Crohn’s disease?

Reactivation of tuberculosis is the concern with the use of TNF blockers. No cumulative toxicity has been reported with up to 5-year exposure to ustekinumab in psoriasis patients (Papp KA et al. Br J Dermatol 2013).

Asthma phenotypes and the use of biologic medications in asthma and allergic disease

Asthma has traditionally been defined using non-specific clinical and physiologic variables which encompass multiple different phenotypes and is treated with non-specific anti-inflammatory therapies. However, it is increasingly recognized that human asthma is a heterogeneous disease. In their review, Fajt and Wenzel analyzed randomized double blind placebo controlled trials of molecularly targeted therapies in defined allergic disease and asthma phenotypes (J Allergy Clin Immunol 2015; 135: 299-310).

There is an increasing appreciation of heterogeneity within asthma and allergic diseases, based primarily on recent cluster analyses, molecular phenotyping, biomarkers and differential responses to targeted and non-targeted therapies. These pioneering studies have led to successful therapeutic trials of molecularly targeted therapies in defined phenotypes. Pathobiologic studies combined with therapeutic trials of type-2 targeted therapies either approved or in clinical trials include those targeted to IgE, IL-5, IL-13, the IL-4 receptor alpha (IL-4Rα) and thymic stromal lymphopoietin (TSLP). IgE was the first successful biological target used in allergic disease and asthma with the overall success of the drug omalizumab (humanized monoclonal anti-IgE antibody) by reducing the allergic asthmatic response. Omalizumab has been shown to be effective in treating allergic rhinitis and peanut allergy although it is not FDA approved for these indications. The authors review other therapies targeting the canonical type-2 cytokines IL-4, IL-5, and IL-13 that have shown consistent efficacy especially in asthma with evidence for a Th2/type-2 inflammation (“type-2 high asthma”).

Recent clustering, molecular studies and treatment trials have begun to suggest that type-2 asthma itself represents several different molecular phenotypes. Data are emerging that late onset, less allergic but highly eosinophilic asthma may respond better to IL-5 targeted therapies than earlier onset (allergic) asthma, while in allergic models of asthma, anti-IL-4/13 approaches appear superior. However, approximately half of all asthmatics do not have evidence for type-2 inflammation, called “type-2 low asthma” which is defined by the absence of type-2 cytokines and their downstream signatures. This group is poorly defined, clinically heterogeneous and without specific biomarkers making molecular phenotyping and targeted therapy approaches difficult.  Non-type-2 patients generally have adult onset disease, often in association with obesity, post-infectious, neutrophilic and smoking related factors and are less likely to be atopic/allergic.

As the results of these studies summarized in this manuscript are varied even for antibodies directed towards the same biologic pathway, it is appreciated that the response to a biologic medication can be confounded by multiple factors including treatment duration, dose, phenotype and differing outcome measures assessed. Moving forward, it will be critical to determine the optimal biomarkers necessary to determine which patients will derive the best therapeutic benefit from each specific targeted medication. 



Question for the authors:
Considering many who suffer from allergic asthma can have multiple allergic diseases such as atopic dermatitis, allergic rhinitis and food allergy, are there studies that resulted in improvement of multiple atopic diseases in the same patient?


There are a few studies which come to mind:

In the Corren et al. (JACI, 2011), in patients with a history of cat allergen–induced asthma, treatment with omalizumab reduced the severity of acute airway reactions and symptoms (including  allergic rhinoconjunctivitis)  caused by controlled cat room exposure to allergens.

In the SOLAR study (Vignola, Allergy, 2004), asthmatic patients with allergic rhinitis treated with omalizumab not only experienced fewer asthma exacerbations but also had clinically significant improvement in both Asthma Quality of Life Questionnaire and Rhinitis Quality of Life Questionnaire scores.

In terms of the monoclonal antibody to IL4R, dupilumab, 2 separate studies showed strong efficacy in atopic dermatitis and in asthma. In adults with moderate-to-severe atopic dermatitis despite treatment with topical corticosteroids and calcineurin inhibitors, Beck et al. (NEJM, 2014) showed that dupilumab treatment resulted in marked clinical efficacy and medication reduction.  In moderate-severe asthma on mid-high dose ICS/LABA with Type-2 High Phenotype, Wenzel et al. (NEJM, 2013) showed that dupilimab therapy resulted in a ↓ in asthma exacerbation, rescue beta agonist use, upper airway symptoms and exhaled nitric oxide.

These studies suggest that the same biologic target may be efficacious in more than 1 allergic disease, but further studies are needed to specifically address this question.

Biologics and food allergy

Food allergy is an immune-mediated response to food proteins leading to symptoms affecting the skin, gastrointestinal tract or respiratory tract. Up to 8% if children and 5% if adults self-reported an allergy to at least one food. The incidence of food allergy has steadily increased over 18% between 1997-2007, suggesting that environmental influences may play a role. Despite this increase in prevalence, there are currently no approved treatments beyond allergen avoidance and treatment of reactions to accidental ingestion. Though the incidence of food allergy-related mortality is low, avoidance and fear of accidental ingestion significantly impairs the quality of life for children with food allergy and their caregivers. In their review, Bauer et al discuss the mechanisms that contribute to allergy with emphasis on future targets for biologics for the treatment of IgE mediated food allergy (J Allergy Clin Immunol 2015; 135(2): 312-323).

Recently there has been increased interest in the use of biologics which are selective immune antagonists for the treatment of allergic diseases, particularly asthma. Dupilumab, a biologic that binds to IL-4Rα and blocks the Th2 cytokines IL-4 and IL-13 activity has been successful in clinical trials for the treatment of asthma and atopic dermatitis. However, relatively few studies have investigated applications of biologics for the treatment of food allergy and no reported clinical trials have investigated the effectiveness of anti-Th2 cytokine treatments in context of food allergy. Recent basic and clinical studies have identified attractive new targets for food allergy therapeutics, including epithelial cell-derived mediators (such as IL-33 and TSLP), IgE-binding receptors (such as CD23) and IgE signaling pathways. A promising therapeutic for the treatment of food allergy is the drug omalizumab which binds IgE and reduces serum levels by 99%. If successful, omalizumab could allow for the use of rapid dose escalation protocols for allergen immunotherapy for food allergic patients. A new drug similar to omalizumab, ligelizumab is an anti-IgE antibody that binds free serum IgE, but with up to 12-times higher affinity, making it much more potent. Phase II trials are planned to assess the clinical efficacy of ligelizumab in subjects with atopic dermatitis and asthma.

Despite the increasing prevalence of food allergy and adverse impact on human health and quality of life, there is an unmet need for effective therapeutic options to treat food allergy. The authors detail a variety of potential treatment options for food allergy, although most studies have focused on asthma, allergic rhinitis, and atopic dermatitis, and future studies are needed to determine the effects on food allergic patients. 

The gut microbiota and inflammatory non-communicable diseases: Associations and potentials for gut microbiota therapies

The health of our modern society is being threatened by a plethora of chronic inflammatory non-communicable diseases (NCDs) which share in common, an underlying low-grade inflammation. These include early onset NCDs such as allergy, asthma and some autoimmune diseases and later onset NCDs including cardiovascular disease (CVD), metabolic disease and neurodegenerative disorders. While inflammation and the pathways to disease are multifactorial, the altered gut colonization patterns associated with declining microbial diversity is a central theme, and increasingly implicated in the physiological, immunological and metabolic dysregulation seen in many NCDs. Upon review of the current literature, West et al discuss the relationships between gut colonization and inflammatory NCDs, and gut microbiota modulation strategies for their treatment and prevention (J Allergy Clin Immunol 2015; 135: 3-13).

The critical role of the gut microbiota in immune development has been well documented in germ free animal models, demonstrating the failure of normal maturation and, in particular, failure of the systemic immune regulatory networks that result in both allergic and autoimmune phenomena. Data from several animal models have formed a basis to further explore the role of gut microbiota in early programming of host responses in humans. Collectively, recent literature suggests that the imprinting of human gut microbiota may commence already in utero and is then further shaped by postnatal exposures such as cesarean or vaginal delivery, antibiotics to the mother or infant, breastfeeding, and introduction to solid foods.

Culture independent DNA-based studies have demonstrated associations between reduced gut microbiota diversity and early onset NCDs including atopy, eczema, and asthma. Furthermore, inflammatory bowel disease (IBD), celiac disease, and type 1 diabetes have been shown to be associated with dysbiosis. It is also suggested that the early microbial environment drives more sustained predisposition to low-grade inflammation into adulthood and the propensity for later onset NCDs. Aberrations in the gut microbiota may also have implications for obesity-associated NCDs.

The most widely used approach for treatment and prevention of NCDs has been to administer probiotics. For example, specific probiotics promote favorable intestinal colonization and their fermented products have anti-inflammatory, immunomodulatory, and metabolic effects, although the effects are variable when evaluated in clinical trials. Fecal microbiota transplantation (FMT) is an emerging therapy that has been successful in the treatment of Clostridium difficile infection and possibly IBD. While much remains unknown, multidisciplinary and integrative approaches may ultimately lead to improved strategies to overcome the disease epidemic of modern civilizations. 

Question for the authors:

 

Most treatment and prevention research focuses on early development and manipulation of the gut microbiota. What is known about treatment of allergic and autoimmune diseases in adults through diet and lifestyle modifications that directly alter the gut microbiota composition?

Most treatment and prevention research focuses on early development and manipulation of the gut microbiota. What is known about treatment of allergic and autoimmune diseases in adults through diet and lifestyle modifications that directly alter the gut microbiota composition?

There is clear evidence that diet impacts gut microbiota composition, however intervention studies aiming at modulating the gut microbiota in adults with allergic or autoimmune disease are scarce.  Dietary patterns such as the Mediterranean diet have been associated with increased asthma control in cross-sectional studies although the effect on gut microbiota composition was not studied. However, there is some support that a Mediterranean-style diet may influence gut microbiota.  In a small pilot study, Marlow et al 2013, examined the effects of a Mediterranean-influenced dietary intervention on inflammatory biomarkers and gut microbiota in eight Crohn’s disease patients. This 6-week dietary intervention resulted in a trend for reduced inflammation and ”normalised” gut microbiota with an increase in Bacteroidetes and the Clostridium clusters, and a decrease in Proteobacteria and Bacillaceae.

Even though most probiotic prevention and treatment studies have targeted a pediatric population, there are also randomized controlled trials with probiotics (although most commonly given as supplements and not incorporated in the diet) for treatment of allergic disease also in adults. The results have been variable, although meta-analyses generally show no benefit of probiotics for treatment of allergic disease.

The impact of lifestyle modifications other than diet in this context is even less studied. Benjamin et al 2012, reported smoking to be associated with an increase in Bacteroides-Prevotella both in patients with active Crohn’s disease and in healthy controls suggesting that smoking may at least partially contribute to the dysbiotic state. Stress is another lifestyle  factor with potential to impact gut microbiota composition via the gut-brain axis, however there is a paucity of studies in the context of allergic and autoimmune disease.

Clearly, there is need for well-designed dietary and life-style intervention studies targeting gut microbiota in both allergic and autoimmune disease.

The Microbiome in Asthma

Newly developed culture-independent methods for microbial detection are deepening the understanding of their role in lung disease. A persuasive body of evidence suggests that the microbiome of the lower airways differs distinctly in the obstructive lung disease, including asthma. Huang and Boushey provide their perspective on the findings of studies of differences in the airway microbiome in patients with asthma vs. healthy subjects, and of studies of relationships between environmental microbiota, gut microbiota, immune function, and the development of asthma (J Allergy Clin Immunol 2015; 135: 25-30). Additionally, they provide a rationale for approaches involving directed manipulation of the gut and airway microbiome for treatment and prevention of allergic asthma.

Alterations in respiratory tract immune function are at least theoretically linked to the immunomodulatory activity of gut microbiota through the concept of a “common mucosal response”. This proposes that antigen presentation at one mucosal site stimulates migration of lymphoid cells to other mucosal sites, shaping immune responsiveness at those sites as well. Studies in mice provide strong support for the concept that bacterial community composition of the gut can shape developing immune function to foster or protect against allergic sensitization.   Similarly, studies focused exclusively on lung microbiota suggest that establishment of a lung microbiome occurs and is a dynamic process after birth. The authors discuss relationships of gut microbiota in response to viral respiratory infection, and provide findings that bacteria regulate immune defense against viral infections in mouse models. For example, interaction between exposure to allergens and microbial exposure has been seen in inner city children. Surprisingly, children with the highest rates of atopic sensitization and recurrent, presumably virus induced wheeze were found in children exposed to the lowest levels of cockroach, mouse and cat allergen and the lowest levels of bacterial diversity in their first year of life. On the contrary, the lowest rates of atopy and wheezing were found in those who had been exposed to the highest levels of these allergens and bacterial diversity. These results suggest that the bacteria served as a tolerance-inducing adjuvant for allergens.

The authors emphasize that dissecting the role of the microbiome in asthma is challenged by the heterogeneity of the disease at multiple levels. These levels include asthma’s clinical and inflammatory heterogeneity, genetic factors that contribute to asthma risk, and the multiplicity of immune pathways involved in asthma. To progress to clinical studies of oral or aerosol administration of microbiota for treatment and especially for prevention of asthma which will necessarily involve enrollment of pregnant women or of newborn infants will likely require overcoming ethical, legal, and cultural hurdles as high as the scientific ones we currently face.

Question for the authors:

 

The studies described in your review focus on the early development of the mucosal microbiota. Is there evidence that manipulating the microbiota in adults with allergic asthma may be a potential therapeutic?

We are a long way from human studies of the effects on allergic or asthmatic symptoms of manipulating the microbiota in adults with the condition. So the evidence available is largely from studies of mice, like Karimi et al’s study showing that dietary supplementation with L. reuteri increased Treg cell number and activity and reduced the allergic inflammation induced by allergen challenge in previously sensitized and challenged BALB/c mice (Am J Respir Crit Care Med Vol 179. pp 186–193, 2009).  Nothing comparable has been done in humans with established allergic asthma.

Update on Epigenetics in allergic disease

Chronic inflammatory diseases, including allergies and asthma, are the result of complex interactions between the genetic predisposition and environmental factors.  Epigenetics comprises the umbrella of such biochemical reactions and mechanisms including DNA methylation and chromatin modifications on histones and other structures. In their review, Harb and Renz review the recent developments in this context with emphasis on allergy and asthma research (J Allergy Clin Immunol 2015; 135: 15-24) .

There are many different epigenetic modifications affecting the status of the transcription of genes. For example, epigenetic modifications of T-cells start very early during the activation/differentiation program with naïve non-committed precursors during fetal immune development. DNA methylation is a biochemical process by the addition of a methyl group to the DNA nucleotides cysteine or adenine. This process leads mainly to gene silencing and subsequently to the inhibition of gene transcription. Histones are highly alkaline proteins found in eukaryotic cells nuclei that package and order the DNA into structural units called nucleosomes. Histone modifications range from gene activation to gene silencing and can have some DNA repair functions as well. The authors have previously shown that allergen sensitization and development of the TH2 immune response is closely linked to epigenetic programming of the previously naïve T-cell during development of the effector status. Moreover, house dust mite can also elucidate epigenetic modifications in asthmatic patients. Furthermore, environmental microbes are also considered to play an important role in shaping the immune response particularly early in life. For example, regulatory T-cell function was shown to be more efficient with farming exposure and was associated with demethylation of the FOXP3 promoter in offspring of mothers with farm milk exposure compared to controls. On the other hand,tobacco smoke has also been shown to impact epigenetic programming of different cell types.

There are many studies suggesting that different diet and nutrients exert their effect through epigenetic mechanisms, such as folic acid and vitamin B12 which are prominent methyl donors and can affect the DNA methylation status universally. In addition to that, fish oil is the main source of Omega-3 fatty acids that are precursors of a large number of anti-inflammatory mediators including defensins and resolvins, and recent data provides mechanisms toward an altered expression of NF-KB affecting important inflammatory regulatory pathways through deacetylation. The authors discuss a variety of examples indicating a role of epigenetic alteration as a mechanism linking obesity and the effect on altered gene expression leading to an asthma phenotype. Moreover, stress represents an additional environmental factor through epigenetic modifications, with evidence of altered gene expression that modifies the allergic phenotype.

The authors emphasize that questions remain on the role of different epigenetic regulator mechanisms in various areas. More clinical studies are needed to unmask the exact mechanism of epigenetic modifications and their role in disease development. Other questions relate to the regulation of gene-specific epigenetic modifications and the control of the events through the underlying enzymatic machinery. Reversibility and stability of these effects also require further attention together with the question about the inheritance of different epigenetic marks.