Recent advances in the diagnosis and treatment of hypereosinophilic syndromes

Clinical and Therapeutic Intervention of Hypereosinophilia in the Era of Molecular Diagnosis

Hypereosinophilia (HE) presents with an elevated peripheral eosinophilic count of >1.5 × 109/L and is composed of a broad spectrum of secondary non-hematologic disorders and a minority of primary hematologic processes with heterogenous clinical presentations, ranging from mild symptoms to potentially lethal outcome secondary to end-organ damage. Following the introduction of advanced molecular diagnostics (genomic studies, RNA sequencing, and targeted gene mutation profile, etc.) in the last 1-2 decades, there have been deep insights into the etiology and molecular mechanisms involved in the development of HE. The classification of HE has been updated and refined following to the discovery of clinically novel markers and targets in the 2022 WHO classification and ICOG-EO 2021 Working Conference on Eosinophil Disorder and Syndromes. However, the diagnosis and management of HE is challenging given its heterogeneity and variable clinical outcome. It is critical to have a diagnostic algorithm for accurate subclassification of HE and hypereosinophilic syndrome (HES) (e.g., reactive, familial, idiopathic, myeloid/lymphoid neoplasm, organ restricted, or with unknown significance) and to follow established treatment guidelines for patients based on its clinical findings and risk stratification.

Eosinophilic disorders: evaluation of current classification and diagnostic criteria, proposal of a practical diagnostic algorithm

Eosinophilic disorders represent a group of pathologic conditions with highly heterogeneous pathophysiology and clinical presentation and variable prognosis, ranging from asymptomatic or mild, to severe and complex cases, with fatal outcome. Interest in this group of disorders has increased during the last two decades, with consistent progress made regarding understanding of molecular mechanisms, refining of diagnostic criteria, classification and evaluation of therapeutic options. There are still many gaps and difficulties in evaluating eosinophilic syndromes and diseases in medical practice. The disease prognosis depends mainly on the cause and mechanism of eosinophilia, on severity of organ dysfunction and on accurate diagnosis and response to treatment. Besides primary hypereosinophilic syndromes and secondary (reactive) eosinophilias, many associated or idiopathic forms have been described, making this topic a complex and difficult medical entity. An important aim of the experts in the field is to agree upon a more clear and practically useful classification, a better characterization of various phenotypes and endotypes of eosinophilic diseases and to identify novel biomarkers and more effective therapies. The aim of this paper is to review recent data from the literature regarding definition, classification and diagnosis criteria of eosinophilic diseases and to propose a revised and updated diagnostic algorithm useful in clinical practice.

The Eosinophil in Health and Disease: from Bench to Bedside and Back

Historically, eosinophils have been considered as end-stage cells involved in host protection against parasitic infection and in the mechanisms of hypersensitivity. However, later studies have shown that this multifunctional cell is also capable of producing immunoregulatory cytokines and soluble mediators and is involved in tissue homeostasis and modulation of innate and adaptive immune responses. In this review, we summarize the biology of eosinophils, including the function and molecular mechanisms of their granule proteins, cell surface markers, mediators, and pathways, and present comprehensive reviews of research updates on the genetics and epigenetics of eosinophils. We describe recent advances in the development of epigenetics of eosinophil-related diseases, especially in asthma. Likewise, recent studies have provided us with a more complete appreciation of how eosinophils contribute to the pathogenesis of various diseases, including hypereosinophilic syndrome (HES). Over the past decades, the definition and criteria of HES have been evolving with the progress of our understanding of the disease and some aspects of this disease still remain controversial. We also review recent updates on the genetic and molecular mechanisms of HES, which have spurred dramatic developments in the clinical strategies of diagnosis and treatment for this heterogeneous group of diseases. The conclusion from this review is that the biology of eosinophils provides significant insights as to their roles in health and disease and, furthermore, demonstrates that a better understanding of eosinophil will accelerate the development of new therapeutic strategies for patients.

Eosinophilic gastroenteritis: an update

Eosinophilic gastroenteritis (EGE) is characterized by dense eosinophilic inflammation of one or several digestive tract sections. The symptoms include abdominal pain, weight loss, vomiting and diarrhea. Biopsy samples taken during endoscopic examination allows the diagnosis of the disease. An infiltration of >30 eosinophils per high-power field in at least five high-power fields, exhibiting signs of eosinophilic degranulation and extending to the muscularis mucosa or submucosa are all histological indications of EGE. EGE is traditionally classified into three forms depending on the depth of inflammation in the wall (mucosal, muscular or serosal). This, together with the digestive tract segments involved, determines the clinical presentation. The natural history of EGE includes three different evolutionary patterns, since patients may suffer a single outbreak, a recurrent course or even chronic disease. Corticosteroids are the most frequently used therapy for EGE; dietary treatments should be also considered. Surgery has been limited to solving obstruction and small bowel perforation.

Eosinophilic diseases of the gastrointestinal tract

Eosinophilic gastrointestinal disorders (EGIDs) are a diverse group of disorders whose diagnosis is on the rise and are characterized by symptoms caused by infiltration by eosinophils of the different sections of the digestive tract. Although little is known of their etiology, it seems to be multifactorial. Alteration of the immunological capacity of the digestive mucosa is determined by the exposure of genetically predisposed individuals to potential airborne or food allergens. EGIDs are classified based on the location of the inflammatory response even though their symptoms, prognosis, and treatment vary considerably. Eosinophilic esophagitis is the most widely recognized entity in this family and is characterized by exclusive eosinophilic infiltration of the esophagus. Breakthroughs in understanding its etiopathogeny have been extrapolated to eosinophilic gastroenteritis, a rare disease identified many years ago commonly involving the stomach and small bowel which should be distinguished from hypereosinophilic syndrome. Eosinophilic colitis, which usually affects children, could be considered a specific non-IgE-mediated allergy to food protein. The physiopathological bases of these entities need to be established in order to define specific treatment aimed at preventing and altering their clinical evolution.

Current strategies in the management of hypereosinophilic syndrome, including mepolizumab

BACKGROUND

Patients with hypereosinophilic syndrome (HES) vary considerably in their clinical presentation with regard to the severity and pattern of end-organ involvement. Clinical manifestations range from nonspecific symptoms to life-threatening, multisystem damage caused by eosinophil infiltration and local release of proinflammatory mediators and toxic granule products from these invading cells. The primary objective of treatment is to reduce blood and tissue eosinophilia and prevent eosinophil-mediated tissue damage as safely as possible. Systemic corticosteroids, such as prednisone, are first-line therapy for the management of patients with symptomatic HES who lack the Fip1-like 1-platelet-derived growth factor receptor-alpha (FIP1L1-PDGFRA) gene fusion mutation. The tyrosine kinase inhibitor, imatinib, is first-line treatment for FIP1L1-PDGFRA-positive patients). Because of the toxicity and serious side-effects that can occur with oral corticosteroids, alternative therapies may need to be introduced to reduce the cumulative corticosteroid exposure while maintaining disease control.

SCOPE

Among corticosteroid-sparing agents are cytotoxic drugs and interferon-alpha; anti-interleukin-5 (IL-5) monoclonal antibodies are also currently under investigation for the treatment of HES. This manuscript reviews the available treatments for HES and the range of side-effects associated with long-term corticosteroid use, and then focuses on the anti-IL-5 monoclonal antibodies, mepolizumab and reslizumab. Of these, only mepolizumab has been studied in a randomized, placebo-controlled trial. Literature search methodology utilized www.pubmed.gov and www.clinicaltrials.gov with search terms including hypereosinophilic syndrome and corticosteroid side-effects coupled with search terms including eosinophils, mepolizumab and reslizumab through March 2010.

FINDINGS

Three case studies are presented that demonstrate the limitations of corticosteroid therapy in terms of tolerability and quality of life, and the subsequent use of mepolizumab as a corticosteroid-sparing agent in these individuals.

CONCLUSION

Targeted eosinophil-directed therapy with an anti-IL-5 neutralizing monoclonal antibody reduced the need for corticosteroids in these three HES patients without disease exacerbations.

A review of treatment with mepolizumab, an anti-IL-5 mAb, in hypereosinophilic syndromes and asthma

The hypereosinophilic syndromes (HESs) are a heterogeneous group of diseases characterized by peripheral blood eosinophilia with end-organ damage and varying in severity from nonspecific symptoms to life-threatening. Treatment objectives are a safe reduction of blood and tissue eosinophil levels and prevention of eosinophil-mediated tissue damage. Current treatment of patients with HESs, who lack the FIP-1-like 1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRA) fusion gene, is mainly systemic corticosteroid therapy. Eosinophil development from hematopoietic progenitor cells is regulated by IL-5, which influences maturation, differentiation, mobilization, activation, and survival. Consequently, inhibiting IL-5 is a logical therapeutic objective for patients with HESs or selected patients with asthma. Mepolizumab is a fully humanized anti-IL-5 monoclonal IgG(1) antibody that binds to free IL-5 with high affinity and specificity to prevent IL-5 from associating with the IL-5 receptor complex alpha-chain on the surface of eosinophils. In clinical trials with patients with HESs, mepolizumab reduced blood eosinophil counts and the maintenance corticosteroid dose and had no major safety concerns. Mepolizumab reduced airway and blood eosinophils and prevented asthma exacerbations. Thus, mepolizumab may be effective for long-term treatment of patients with selected eosinophilic disorders.

Churg-Strauss syndrome: evidence for disease subtypes?

PURPOSE OF REVIEW

Churg-Strauss syndrome (CSS) is a rare systemic small-vessel necrotizing vasculitis. Its main clinical characteristics, some potentially life-threatening, are now well known, as are its usual successive phases, from allergic rhinitis to asthma, and finally vasculitis. Conversely, physiopathogenetic mechanisms are not completely elucidated and clearly multiple, thereby suggesting the existence of different disease subtypes.

RECENT FINDINGS

Almost 40% of CSS patients have circulating antineutrophil cytoplasm autoantibodies (ANCAs), mostly directed against myeloperoxidase. ANCA-positive patients suffer more frequently from renal disease, peripheral nervous system involvement and/or alveolar hemorrhage, whereas frequent cardiac involvement, lung infiltrates and/or systemic manifestations are more common in those who are ANCA-negative. However, their respective global outcomes do not clearly differ. Patients might also be categorized according to other, more subtle clinical, radiological and/or biological parameters, for example, cardiac magnetic resonance imaging abnormalities or genetic background.

SUMMARY

Because of its practical and therapeutic repercussions, the priority remains the prompt, relatively easy identification of the most severely affected patients at CSS diagnosis, before searching for and trying to classify subsets. Large, collaborative studies are needed to determine whether other subgroups might be associated with outcomes and warrant different, and possibly new, therapeutic strategies.

FIP1L1-PDGFRA molecular analysis in the differential diagnosis of eosinophilia

BACKGROUND

Primary eosinophlia associated with the FIP1L1-PDGFRA rearrangement represents a subset of chronic eosinophilic leukaemia (CEL) and affected patients are very sensitive to imatinib treatment. This study was undertaken in order to examine the prevalence and the associated clinicopathologic and genetic features of FIP1L1-PDGFRA rearrangement in a cohort of 15 adult patients presenting with profound eosinophilia (> 1.5 x 109/L).

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) was used for the detection of FIP1L1-PDGFRA rearrangement and the results confirmed by direct sequencing. C-KIT-D816V mutation was analysed retrospectively by PCR and restriction-fragment-length-polymorphism (PCR-RFLP), in all cases with primary eosinophilia.

RESULTS

Two male patients with splenomegaly carried the FIP1L1-PDGFRA rearrangement, whilst 2 others were ultimately classified as suffering from idiopathic hypereosinophlic syndrome (HES) and one from systemic mastocytosis. These patients were negative for the C-KIT-D816V mutation and received imatinib (100-400 mg daily). Patients with CEL and HES responded to imatinib and remained in complete haematological, clinical and molecular (for carriers of FIP1L1-PDGFRA rearrangement) remission for a median of 28.2 months (range: 11-54), whilst the patient with systemic mastocytosis did not respond. Interestingly, in both patients with FIP1L1-PDGFRA rearrangement, the breakpoints into PDGFRA were located within exon 12 and fused with exons 8 and 8a of FIP1L1, respectively.

CONCLUSION

An early diagnosis of FIPIL1-PDGFRA-positive CEL and imatinib treatment offer to the affected patients an excellent clinical therapeutic result, avoiding undesirable morbidity. Moreover, although the molecular mechanisms underlying disease pathogenesis remain to be determined, imatinib can be effective in patients with idiopathic HES.

Biology of the eosinophil

In this review, we aim to put in perspective the biology of a multifunctional leukocyte, the eosinophil, by placing it in the context of innate and adaptive immune responses. Eosinophils have a unique contribution in initiating inflammatory and adaptive responses, due to their bidirectional interactions with dendritic cells and T cells, as well as their large panel of secreted cytokines and soluble mediators. The mechanisms and consequences of eosinophil responses in experimental inflammatory models and human diseases are discussed.

Pulmonary Eosinophilic Syndromes

Acute eosinophilic pneumonia, chronic eosinophilia, Churg-Strauss syndrome, and the hypereosinophilic syndrome are pulmonary eosinophilic syndromes characterized by an increased number of eosinophils in peripheral blood, in lung tissue, in sputum, in bronchoalveolar lavage fluid, or in all of these. These pulmonary eosinophilic syndromes generally are characterized by increased respiratory symptoms, abnormal radiographic appearance, and the potential for systemic manifestations. It is critical to exclude other causes of eosinophilia in patients who have lung disease, to make a quick diagnosis, and to treat aggressively with corticosteroids and other therapies to prevent long-term sequelae.