Clinical and Biological Markers in Hypereosinophilic Syndromes

Eosinophilic Patterns in Patients with Seasonal Allergy Affected by Bronchial Asthma and Rhinitis/Rhinosinusitis: Efficacy of Benralizumab in Patients with the Persistent Pattern

BACKGROUND

Eosinophilia can be influenced by multiple factors. This study aims to set a protocol for monitoring blood absolute eosinophil count (AEC) in patients with seasonal allergy affected by bronchial asthma (BA), allergic rhinitis (AR), or chronic rhinosinusitis with or without nasal polyposis (CRSw/sNP).

METHODS

We planned a total of four annual blood samples to measure AEC in- and out-seasonal pollen exposure (i.e., one measurement every three months for one year).

RESULTS

We identified two distinct groups of patients (non-eosinophilic and eosinophilic). Patients in the eosinophilic group presented with four different patterns (episodic, transient, floating, and persistent). Most patients with episodic, transient, and floating patterns were affected by mild allergy and the increase in eosinophils was related to allergen exposure. In contrast, patients with the persistent pattern mostly presented with more severe allergy (i.e., severe BA and relapsing CRSwNP) and the eosinophilia was unrelated to allergen exposure. The subgroup of patients with severe BA, relapsing CRSwNP, and persistent eosinophilc pattern were treated with benralizumab, which induced a noteworthy improvement in both severe BA and CRSwNP.

CONCLUSIONS

Multiple AEC measurements in patients with seasonal allergy can better reflect patient's eosinophilic status and help define the relationship of AEC enhancement with allergen exposure.

Management of eosinophil-associated inflammatory diseases: the importance of a multidisciplinary approach

Elevated eosinophil counts in blood and tissue are a feature of many pathological processes. Eosinophils can migrate and accumulate in a wide variety of tissues and, by infiltrating a target organ, can mediate the development of several inflammatory diseases. The normalization of eosinophilia is a common biomarker of a treatable trait and can also be used as a prognostic and predictive biomarker since it implies a reduction in type 2 inflammation that contributes to disease pathogenesis. Biological therapies targeting this cell type and its proinflammatory mediators have been shown to be effective in the management of a number of eosinophilic diseases, and for this reason they constitute a potential common strategy in the treatment of patients with various multimorbidities that present with type 2 inflammation. Various biological options are available that could be used to simultaneously treat multiple target organs with a single drug, bearing in mind the need to offer personalized treatments under the umbrella of precision medicine in all patients with eosinophil-associated diseases (EADs). In addition to reviewing these issues, we also discuss a series of perspectives addressing the management of EAD patients from a multidisciplinary approach, with the collaboration of health professionals from different specialties who manage the different multimorbidities that frequently occur in these patients. We examine the basic principles of care that this multidisciplinary approach must cover and present a multidisciplinary expert opinion regarding the ideal management of patients with EADs, from diagnosis to therapeutic approach and follow-up.

Diagnostic spectrum of hypereosinophilia based on bone marrow pathology: 10 years' experience at a tertiary care hospital

BACKGROUND

Hypereosinophilia (HE) is defined as peripheral blood (PB) eosinophil count exceeding 1.5 × 10⁹ /L. As the causes of HE can be diverse, the work-up of patients was complicated. In this study, we aimed to categorize the underlying diseases associated with HE and demonstrate minimum diagnostic approach.

METHODS

Cases presenting with HE within 7 days of bone marrow (BM) examination conducted between 2008 and 2019 were selected. Cases were classified by the revised 2022 WHO and ICC classification. We also assessed morphologic features of unclassified persisting HE (>4 weeks) patients according to the morphologic criteria suggested a previous study by Wang et al. RESULTS: A total of 364 patients were included. The work-up confirmed primary HE in 38.7%, secondary HE in 48.9%, HE patients with insufficient evaluation in 13.7%. When conducted a slide review of HE patients with sustained HE more than 4 weeks among HE patients with insufficient evaluation, the morphological features showed abnormal eosinophils in PB/BM (69.0%/81.0%), hypercellularity (26.2%), myelofibrosis (7.1%), increased M:E ratio (5.3%), and dysmegakaryopoiesis (4.8%). Of these patients, 14 patients who met all morphologic criteria were suspected of CEL.

CONCLUSIONS

This study demonstrates that HE is associated with variable conditions. BM morphological assessment based on a robust criterion can help to confirm a MN irrespective of the presence of clonal markers. The work-up of patients in whom ruled out the common secondary causes of HE requires a systematic but sufficient approach including at a minimum BM karyotyping, PDGFRA testing, lymphocyte immunophenotyping and TCR gene rearrangement.

Urine eosinophil-derived neurotoxin: A potential marker of activity in select eosinophilic disorders

BACKGROUND

Biomarkers of eosinophilic disease activity, especially in the context of novel therapies that reduce blood eosinophil counts, are an unmet need. Absolute eosinophil count (AEC) does not accurately reflect tissue eosinophilia or eosinophil activation. Therefore, the aims of this study were to compare the reliability of plasma and urine eosinophil major basic protein 1, eosinophil cationic protein, eosinophil-derived neurotoxin (EDN), and eosinophil peroxidase measurement and to evaluate the usefulness of eosinophil granule protein (EGP) measurement for the assessment of disease activity in patients with eosinophil-associated diseases treated with mepolizumab, benralizumab, or dexpramipexole.

METHODS

Eosinophil granule protein concentrations were measured in serum, plasma, and urine from healthy volunteers and patients with hypereosinophilic syndrome (HES), eosinophilic granulomatosis with polyangiitis (EGPA), and eosinophilic asthma using a multiplex assay.

RESULTS

Urine EGP concentrations remained stable, whereas serum and plasma EGP concentrations increased significantly with delayed processing. Plasma (p) EDN, but not urine (u) EDN, concentration correlated with AEC and negatively correlated with prednisone dose. Both pEDN and uEDN decreased significantly following treatment of HES patients with benralizumab and EGPA patients with mepolizumab. uEDN appeared to increase with clinical relapse in both patient groups.

CONCLUSIONS

Measurement of EGP in urine is noninvasive and unaffected by cellular lysis. Although plasma and urine EDN concentrations showed a similar pattern following benralizumab and mepolizumab treatment, the lack of correlation between AEC or prednisone dose and uEDN concentrations suggests that measurement of uEDN may provide a potential biomarker of disease activity in patients with HES and EGPA.

Doxycycline hyclate stimulates inducible nitric oxide synthase and arginase imbalance, potentiating inflammatory and oxidative lung damage in schistosomiasis

BACKGROUND

We investigated the relationship between inducible nitric oxide synthase (iNOS) and arginase pathways, cytokines, macrophages, oxidative damage and lung granulomatous inflammation in S. mansoni-infected and doxycycline-treated mice.

METHODS

Swiss mice were randomized in four groups: (i) uninfected, (ii) infected with S. mansoni, (iii) infected + 200 mg/kg praziquantel (Pzt), (iv) and (v) infected + 5 and 50 mg/kg doxycycline. Pzt (reference drug) was administered in a single dose and doxycycline for 60 days.

RESULTS

S. mansoni-infection determined extensive lung inflammation, marked recruitment of M2 macrophages, cytokines (IL-4, IL-5, IFN-γ, TNF-α) upregulation, intense eosinophil peroxidase (EPO) levels, arginase expression and activity, reduced iNOS expression and nitric oxide (NO) production. The higher dose of doxycycline aggravated lung granulomatous inflammation, downregulating IL-4 levels and M2 macrophages recruitment, and upregulating iNOS expression, EPO, NO, IFN-γ, TNF-α, M1 macrophages, protein carbonyl and malondialdehyde tissue levels. The number and size of granulomas in doxycycline-treated animals was higher than untreated and Pzt-treated mice. Exudative/productive granulomas were predominant in untreated and doxycycline-treated animals, while fibrotic/involutive granulomas were more frequent in Pzt-treated mice. The reference treatment with Pzt attenuated all these parameters.

CONCLUSION

Our findings indicated that doxycycline aggravated lung granulomatous inflammation in a dose-dependent way. Although Th1 effectors are protective against several intracellular pathogens, effective schistosomicidal responses are dependent of the Th2 phenotype. Thus, doxycycline contributes to the worsening of lung granulomatous inflammation by potentiating eosinophils influx and downregulating Th2 effectors, reinforcing lipid and protein oxidative damage in chronic S. mansoni infection.

Distinct features of hypereosinophilic syndrome with neuropathy from eosinophilic granulomatosis with polyangiitis

BACKGROUND AND OBJECTIVES

Hypereosinophilic syndrome (HES) and eosinophilic granulomatosis with polyangiitis (EGPA) have overlapping clinical considerations, which frequently involve peripheral neuropathy. The current study aimed to discriminate between the clinicopathological features of HES and EGPA, focusing on the mechanism of peripheral nerve damage.

METHODS

A total of 53 patients who underwent nerve biopsies at our laboratory were examined: nine patients with idiopathic HES (iHES), three patients with reactive HES, 14 patients with myeloperoxidase-anti-neutrophil cytoplasmic antibody (ANCA)-positive EGPA, and 27 patients with negative EGPA. Nerve biopsies were performed using light and electron microscopy.

RESULTS

Polyneuropathy was more common than mononeuritis multiplex in iHES, which differed from that in ANCA-negative EGPA groups (p = 0.012). Nerve biopsies showed that iHES was associated with neuropathy features such as rare vasculitis and non-vasculitic eosinophilic infiltrates, which differed from those of ANCA-negative EGPA. Fibrinoid necrosis was found only in the reactive HES and ANCA-positive groups. The percentage of endoneurial vessels occluded with eosinophils tended to be higher in iHES (1.8%) than in ANCA-positive EGPA (0%) and negative EGPA (0.7%). In a patient with ANCA-negative EGPA, the endoneurial vessels were occluded with platelets, fibrinoid materials, and eosinophils, demonstrating the morphology of eosinophil extracellular traps.

CONCLUSION

iHES with neuropathy showed a pattern more similar to polyneuropathy than mononeuritis multiplex, which is dominant in ANCA-negative EGPA, and tended to show vasculitis in the peripheral nerves less frequently compared with EGPA. Eosinophilic infiltration and endoneurial vascular occlusion by eosinophils may cause nerve damage.

Case Report: "Area of Focus" Atypical Trichinellosis and Fascioliasis Coinfection

Parasitic co-infection is commonly observed in natural populations, yet rare in the laboratory. Multiparasitism can have negative effects on the host, ranging from the atypical manifestations to increased mortality, consequently, it may be misdiagnosed and treated with unsuitable anthelmintic medicines. Therefore, reliable diagnosis is critical for appropriate treatment of parasitic co-infection. Herein, we report a case of a 31-year-old woman with persistent eosinophilia and hypoechoic liver lesion on ultrasound. The microscopic examination of multiple stool specimens did not find any pathogens. The patient had serum specific anti-Trichinella IgG antibody by Dot enzyme-linked immunosorbent assay (Dot-ELISA). After treatment with albendazole, contrast-enhanced magnetic resonance imaging (MRI) revealed more lesions in the liver. Subsequently, liver biopsy was performed in this patient and Fasciola hepatica was identified using metagenomic next-generation sequencing (mNGS) as well as polymerase chain reaction. After treatment with triclabendazole, which is the only anthelmintic drug specifically available against this fluke, her eosinophil count returned normal, and the liver lesions were significantly regressed. This case highlights the diagnostic challenge posed by parasitic co-infection, which merits more in-depth evaluation to confirm the diagnosis.

Diagnosis and Management of Pediatric Hypereosinophilic Syndrome

Hypereosinophilic syndrome (HES) is a diverse group of disorders characterized by peripheral blood eosinophilia of 1.5 × 10⁹/L (1,500/μL) or greater with evidence of end-organ damage attributable to eosinophilia and no other cause of the end-organ damage. The HES is rare, especially in children. This review aims to provide best practices in diagnosis and treatment of HES in children, including how to differentiate between primary and secondary causes of hypereosinophilia; how to distinguish the differences in clinical presentation, treatment, and prognosis of HES in children and adults; and how to identify key steps in the evaluation and management of HES in children.

Secretory Leukocyte Protease Inhibitor Is Present in Circulating and Tissue-Recruited Human Eosinophils and Regulates Their Migratory Function

Eosinophils and secretory leukocyte protease inhibitor (SLPI) are both associated with Th2 immune responses and allergic diseases, but whether the fact that they are both implicated in these conditions is pathophysiologically related remains unknown. Here we demonstrate that human eosinophils derived from normal individuals are one of the major sources of SLPI among circulating leukocytes. SLPI was found to be stored in the crystalline core of eosinophil granules, and its dislocation/rearrangement in the crystalline core likely resulted in changes in immunostaining for SLPI in these cells. High levels of SLPI were also detected in blood eosinophils from patients with allergy-associated diseases marked by eosinophilia. These include individuals with eosinophilic granulomatosis with polyangiitis (EGPA) and atopic dermatitis (AD), who were also found to have elevated SLPI levels in their plasma. In addition to the circulating eosinophils, diseased skin of AD patients also contained SLPI-positive eosinophils. Exogenous, recombinant SLPI increased numbers of migratory eosinophils and supported their chemotactic response to CCL11, one of the key chemokines that regulate eosinophil migratory cues. Together, these findings suggest a role for SLPI in controlling Th2 pathophysiologic processes via its impact on and/or from eosinophils.

Localized IgG4-related disease manifested on the tongue: a case report

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated fibroinflammatory condition that can affect multiple organs. IgG4-RD may show a variety of initial symptoms. In the oral mucosa, lesions present as inflammatory fibrosis with a large number of IgG4-positive plasma cells. Evaluating treatment is a well-known problem in IgG4-RD due to the absence of an established assessment system. There are difficulties in defining the severity of the disease, which is why treatment is primarily based on its clinical manifestations. We present a case report of localized IgG4-RD with ulcerative and proliferative manifestations on the tongue, which clinically mimicked oral squamous cell carcinoma. A tumor-like lesion on the tongue can indicate something else other than the malignant or reactive changes commonly found in the oral mucosa. Multiple differential diagnoses of these atypical oral lesions, including localized IgG4-RD, should be considered.

Eosinophilia Associated With CD3-CD4+ T Cells: Characterization and Outcome of a Single-Center Cohort of 26 Patients

Background: Lymphocytic variant hypereosinophilic syndrome is characterized by marked over-production of eosinophilopoietic factor(s) by dysregulated T cells leading to eosinophil expansion. In most cases, these T cells are clonal and express a CD3^-CD4⁺ phenotype. As this is a rare disorder, presenting manifestations, disease course, treatment responses, and outcome are not well-characterized. Materials and Methods: In this retrospective single-center observational study, we reviewed medical files of all patients with persistent hypereosinophilia seen between 1994 and 2019 in whom CD3^-CD4⁺ T cells were detected. Data collection included clinical and biological findings at presentation, treatment responses, disease course, and serial CD3^-CD4⁺ T cell counts. Results: Our cohort comprises 26 patients, including 2 with hypereosinophilia of undetermined significance. All 24 symptomatic patients had cutaneous lesions and/or angioedema, and fasciitis was present in several cases. The aberrant T cell subset represented 2% or less total lymphocytes in 11 subjects. TCR gene rearrangement patterns on whole blood were polyclonal in these cases, while they all had serum CCL17/TARC levels above 1,500 pg/ml. Disease manifestations were mild and did not require maintenance therapy in roughly one third of the cohort, while two thirds required long-term oral corticosteroids and/or second-line agents. Among these, interferon-alpha was the most effective treatment option with a response observed in 8/8 patients, one of whom was cured of disease. Treatment had to be interrupted in most cases however due to poor tolerance and/or development of secondary resistance. Anti-interleukin-5 antibodies reduced blood eosinophilia in 5/5 patients, but clinical responses were disappointing. A sub-group of 5 patients had severe treatment-refractory disease, and experienced significant disease- and treatment-related morbidity and mortality, including progression to T cell lymphoma in three. Conclusions: This retrospective longitudinal analysis of the largest monocentric cohort of CD3^-CD4⁺ T cell associated lymphocytic variant hypereosinophilic syndrome published so far provides clinicians confronted with this rare disorder with relevant new data on patient presentation and outcome that should help tailor therapy and follow-up to different levels of disease severity. It highlights the need for novel therapeutic options, especially for the subset of patients with severe treatment-refractory disease. Future research efforts should be made toward understanding CD3^-CD4⁺ T cell biology in order to develop new treatments that target primary pathogenic mechanisms.

Contributions of Eosinophils to Human Health and Disease

The human eosinophil has long been thought to favorably influence innate mucosal immunity but at times has also been incriminated in disease pathophysiology. Research into eosinophil biology has uncovered a number of interesting contributions by eosinophils to health and disease. However, it appears that not all eosinophils from all species are created equal. It remains unclear, for example, exactly how having eosinophils benefits the human host when helminth infections in the developed world have become scarce. This review focuses on our current state of knowledge as it relates to human eosinophils. When information is lacking, we discuss lessons learned from mouse studies that may or may not directly apply to human biology and disease. It is an exciting time to be an "eosinophilosopher" because the use of biologic agents that selectively target eosinophils provides an unprecedented opportunity to define the contribution of this cell to eosinophil-associated human diseases.

Cytokine Diversity in Human Peripheral Blood Eosinophils: Profound Variability of IL-16

Eosinophilic leukocytes develop in the bone marrow and migrate from peripheral blood to tissues, where they maintain homeostasis and promote dysfunction via release of preformed immunomodulatory mediators. In this study, we explore human eosinophil heterogeneity with a specific focus on naturally occurring variations in cytokine content. We found that human eosinophil-associated cytokines varied on a continuum from minimally (coefficient of variation [CV] ≤ 50%) to moderately variable (50% < CV ≤ 90%). Within the moderately variable group, we detected immunoreactive IL-27 (953 ± 504 pg/mg lysate), a mediator not previously associated with human eosinophils. However, our major finding was the distinct and profound variability of eosinophil-associated IL-16 (CV = 103%). Interestingly, eosinophil IL-16 content correlated directly with body mass index (R ² = 0.60, ***p < 0.0001) in one donor subset. We found no direct correlation between eosinophil IL-16 content and donor age, sex, total leukocytes, lymphocytes, or eosinophils (cells per microliter), nor was there any relationship between IL-16 content and the characterized -295T/C IL-16 promoter polymorphism. Likewise, although eosinophil IL-1β, IL-1α, and IL-6 levels correlated with one another, there was no direct association between any of these cytokines and eosinophil IL-16 content. Finally, a moderate increase in total dietary fat resulted in a 2.7-fold reduction in eosinophil IL-16 content among C57BL/6-IL5tg mice. Overall, these results suggest that relationships between energy metabolism, eosinophils, and IL-16 content are not direct or straightforward. Nonetheless, given our current understanding of the connections between asthma and obesity, these findings suggest important eosinophil-focused directions for further exploration.

Idiopathic Hypereosinophilic Syndrome in an Elderly Female: A Case Report

Patient: Female, 83

Final Diagnosis: Idiopathic hypereosinophilic syndrome

Symptoms: Dyspnea

Medication: —

Clinical Procedure: —

Specialty: Allergology

Severe Eosinophilia in Myelodysplastic Syndrome With a Defined and Rare Cytogenetic Abnormality

Myelodysplastic syndromes (MDS) are a heterogeneous group clonal disorders of hematopoietic stem cells (HSC) characterized by ineffective hematopoiesis that lead to variable grades of impaired blood cell production. Chromosomal aberrations are often detected in MDS patients and thus cytogenetic analysis is useful for the diagnosis of these disorders. Common recurring chromosomal defects, such as the −5/5q- and −7/7q- are relatively well characterized cytogenetic abnormalities in MDS, however, the biological significance of uncommon cytogenetic alterations is unknown. We report here, two cases of peripheral blood and bone marrow hypereosinophilia in patients with MDS harboring the unbalanced translocation der(1;7)(q10;p10), a poorly characterized cytogenetic abnormality that is found in certain myeloid malignancies, including MDS. The patients reported here presented hypereosinophilia that was refractory to steroids and cytotoxic therapy, leading to severe target tissue damage that ultimately resulted in fatal end-organ failure. Potential roles of the der(1;7)(q10;p10) aberrations in the pathogenesis of aggressive eosinophilia and disease prognosis are discussed here.

A multimodality work-up of patients with Hypereosinophilia

The work-up of patients with hypereosinophilia (HE) is complex. Following the recently revised World Health Organization criteria, we retrospectively reviewed 125 patients who were referred to us to exclude a neoplastic cause of HE (2003-2016). The clinical laboratory work-up confirmed secondary HE in 25 (20%) patients; myeloid/lymphoid neoplasms with rearrangements of PDGFRA (n = 9) or PDGFRB (n = 2) (9%); HE associated with a well-defined myeloid neoplasm in 8 (6%); and abnormal bone marrow and/or molecular genetic abnormalities consistent with chronic eosinophilic leukemia (CEL), not otherwise specified (NOS) in 21 (17%) patients. For the remaining 60 (48%) patients, a specific diagnosis was not identified, and 56 patients had HE related findings consistent with idiopathic hypereosinophilic syndrome (HES), while 4 patients who were asymptomatic. With a median follow up of 35.3 months (range, <1-104), patients with CEL, not otherwise specified (NOS) had a median OS of 26.1 months, significantly inferior to patients with idiopathic HES (not reached, P < .01). Thus, our experience in a single tertiary cancer center shows that the work-up of HE following WHO recommendations requires a multimodality-based approach; and a correct diagnosis determines risk stratification and proper patient management. However, the causes of HE remain unknown in approximately half of referred patients, indicating the need for further studies.

Consultation for Elevated Blood Eosinophils: Clinical Presentations, High Value Diagnostic Tests, and Treatment Options

The workup of a patient found to have eosinophilia should follow a thorough path with a detailed history and physical examination aimed at eliciting eosinophilic organ involvement, followed by histological confirmation whenever possible. The differential diagnosis of hypereosinophilia is extensive, but a rational approach beyond the history and physical examination including serologic, blood, and bone marrow cell analyses, genetic testing, and radiologic imaging can distinguish many of the causes. Often input from specialists (eg, hematology, dermatology, pulmonary, gastroenterology, and neurology) can help narrow down the possibilities and eventually result in a specific diagnosis. An accurate diagnosis is key to choosing the optimal treatment for a particular condition, and this is certainly true for eosinophilic disorders. Myeloid neoplasms that present with eosinophilia, for example, may respond to medicines that the allergist may be less accustomed to using, such as immunosuppressive agents and kinase inhibitors. Similarly, newly approved biologics that target IL-5 and eosinophils may provide new options for management. What follows is a case-based approach that helps to underscore key features of diagnosis, management, and follow-up when faced with a patient with a potential eosinophil-related disorder.

Long-Term Clinical Outcomes of High-Dose Mepolizumab Treatment for Hypereosinophilic Syndrome

BACKGROUND

Conventional therapies for hypereosinophilic syndromes (HES) have variable efficacy and carry significant long-term toxicities. Anti-IL-5 (mepolizumab) therapy has a glucocorticoid (GC)-sparing effect in GC-sensitive HES, but the efficacy of mepolizumab in treatment-refractory HES patients with severe disease has not been examined to date.

OBJECTIVE

To identify predictors of response to mepolizumab in subjects with severe treatment-refractory HES and compare long-term outcomes in these subjects with HES subjects treated with conventional therapies.

METHODS

Retrospective analysis of clinical and laboratory data from 35 HES subjects treated with mepolizumab and 55 HES subjects on conventional therapy, all followed at a single center, was performed.

RESULTS

Peak eosinophilia, GC sensitivity, pulmonary involvement, HES clinical subtype, and pretreatment serum IL-5 were correlated with mepolizumab response. Despite evidence of more severe disease at baseline, mepolizumab-treated subjects had comparable long-term clinical outcomes to HES subjects treated with conventional therapies and reported improvements in therapy-related comorbidities. Subjects managed with mepolizumab monotherapy had fewer disease flares than HES subjects on conventional therapies or mepolizumab-treated HES subjects requiring additional HES therapies.

CONCLUSIONS

This study confirms that mepolizumab is an effective and well-tolerated therapy for HES, but suggests that response is more likely in GC-responsive subjects with idiopathic or overlap forms of HES. A primary benefit of treatment is the reduction of comorbidity due to discontinuation or the reduction of conventional HES therapies. Although subjects who completely discontinued GC had the most benefit, high-dose mepolizumab was a safe and effective salvage therapy for severe, treatment-refractory HES.

Revisiting the NIH Taskforce on the Research needs of Eosinophil-Associated Diseases (RE-TREAD)

Eosinophil-associated diseases (EADs) are rare, heterogeneous disorders characterized by the presence of eosinophils in tissues and/or peripheral blood resulting in immunopathology. The heterogeneity of tissue involvement, lack of sufficient animal models, technical challenges in working with eosinophils, and lack of standardized histopathologic approaches have hampered progress in basic research. Additionally, clinical trials and drug development for rare EADs are limited by the lack of primary and surrogate endpoints, biomarkers, and validated patient-reported outcomes. Researchers with expertise in eosinophil biology and eosinophil-related diseases reviewed the state of current eosinophil research, resources, progress, and unmet needs in the field since the 2012 meeting of the NIH Taskforce on the Research of Eosinophil-Associated Diseases (TREAD). RE-TREAD focused on gaps in basic science, translational, and clinical research on eosinophils and eosinophil-related pathogenesis. Improved recapitulation of human eosinophil biology and pathogenesis in murine models was felt to be of importance. Characterization of eosinophil phenotypes, the role of eosinophil subsets in tissues, identification of biomarkers of eosinophil activation and tissue load, and a better understanding of the role of eosinophils in human disease were prioritized. Finally, an unmet need for tools for use in clinical trials was emphasized. Histopathologic scoring, patient- and clinician-reported outcomes, and appropriate coding were deemed of paramount importance for research collaborations, drug development, and approval by regulatory agencies. Further exploration of the eosinophil genome, epigenome, and proteome was also encouraged. Although progress has been made since 2012, unmet needs in eosinophil research remain a priority.