Pleconaril-resistant chronic parechovirus-associated enteropathy in agammaglobulinaemia

FLT3L governs the development of partially overlapping hematopoietic lineages in humans and mice

FMS-related tyrosine kinase 3 ligand (FLT3L), encoded by FLT3LG, is a hematopoietic factor essential for the development of natural killer (NK) cells, B cells, and dendritic cells (DCs) in mice. We describe three humans homozygous for a loss-of-function FLT3LG variant with a history of various recurrent infections, including severe cutaneous warts. The patients' bone marrow (BM) was hypoplastic, with low levels of hematopoietic progenitors, particularly myeloid and B cell precursors. Counts of B cells, monocytes, and DCs were low in the patients' blood, whereas the other blood subsets, including NK cells, were affected only moderately, if at all. The patients had normal counts of Langerhans cells (LCs) and dermal macrophages in the skin but lacked dermal DCs. Thus, FLT3L is required for B cell and DC development in mice and humans. However, unlike its murine counterpart, human FLT3L is required for the development of monocytes but not NK cells.

Ribavirin-resistant chronic norovirus infection-associated enteropathy in common variable immunodeficiency. Case report and review of the literature

Chronic Norovirus infection is particularly challenging in patients with common variable immunodeficiency (CVID) because of their inability to achieve viral clearance and the risk of developing enteropathy leading to intestinal villous atrophy and malabsorption. To date, therapeutic options to eliminate the virus are limited and only ribavirin has been shown to induce viral clearance in norovirus enteropathy associated with CVID. We report a case of a 48-year-old female patient diagnosed with CVID enteropathy possibly related to norovirus infection who failed a ribavirin-based therapy despite dosage optimization through drug plasma level monitoring.

Protein-losing Enteropathy as a Complication and/or Differential Diagnosis of Common Variable Immunodeficiency

As protein-losing enteropathy (PLE) can lead to hypogammaglobulinemia and lymphopenia, and since common variable immunodeficiency (CVID) is associated with digestive complications, we wondered if (1) PLE could occur during CVID and (2) specific features could help determine whether a patient with antibody deficiency has CVID, PLE, or both. Eligible patients were thus classified in 3 groups: CVID + PLE (n = 8), CVID-only (= 19), and PLE-only (n = 13). PLE was diagnosed using fecal clearance of α1-antitrypsin or 111In-labeled albumin. Immunoglobulin (Ig) A, G, and M, naive/memory B and T cell subsets were compared between each group. CVID + PLE patients had multiple causes of PLE: duodenal villous atrophy (5/8), nodular follicular hyperplasia (4/8), inflammatory bowel disease-like (4/8), portal hypertension (4/8), giardiasis (3/8), and pernicious anemia (1/8). Compared to the CVID-only group, CVID + PLE patients had similar serum Ig levels, B cell subset counts, but lower naive T cell proportion and IgG replacement efficiency index. Compared to the CVID-only group, PLE-only patients did not develop infections but had higher serum levels of IgG (p = 0.03), IgA (p < 0.0001), and switched memory B cells (p = 0.001); and decreased naive T cells (CD4⁺: p = 0.005; CD8⁺: p < 0.0001). Compared to the PLE-only group, CVID + PLE patients had higher infection rates (p = 0.0003), and lower serum Ig (especially IgA: p < 0.001) and switched memory B cells levels. In conclusion, PLE can occur during CVID and requires higher IgG replacement therapy dosage. PLE can also mimic CVID and is associated with milder immunological abnormalities, notably mildly decreased to normal serum IgA and switched memory B cell levels.

Gut inflammation in CVID: causes and consequences

INTRODUCTION

There is a wide spectrum of noninfectious gastrointestinal pathology, causing considerable morbidity and mortality in CVID, where both etiology and effective therapy are under debate.

AREAS COVERED

This review will focus on the noninfectious inflammation in the GI tract in CVID patients, covering the both the upper and lower GI tract inflammation, including the liver. The controversy of the CVID enteropathy definition and that of gluten-free diet for celiac-like disease in CVID will be discussed. Furthermore, the review will cover the link between GI inflammation and GI cancer. Finally, the role of gut microbiota, IgA, and genetics and its relationship with CVID enteropathy is scrutinized. The authors reviewed literature from PubMed.

EXPERT OPINION

The heterogeneity and the unknown mechanism behind CVID enteropathy, and thereby the lack of effective treatment, is one of the key challenges in the field of CVID. Celiac-like disease in CVID is due to immune dysregulation, and a gluten-free diet is therefore not indicated. Gut microbial dysbiosis and mucosal IgA can initiate systemic and local inflammation and is involved in the immune dysregulation in CVID. Considering the heterogeneity of CVID enteropathy, personalized medicine is probably the future for these patients.

Identification of a conserved virion-stabilizing network inside the interprotomer pocket of enteroviruses

Enteroviruses pose a persistent and widespread threat to human physical health, with no specific treatments available. Small molecule capsid binders have the potential to be developed as antivirals that prevent virus attachment and entry into host cells. To aid with broad-range drug development, we report here structures of coxsackieviruses B3 and B4 bound to different interprotomer-targeting capsid binders using single-particle cryo-EM. The EM density maps are beyond 3 Å resolution, providing detailed information about interactions in the ligand-binding pocket. Comparative analysis revealed the residues that form a conserved virion-stabilizing network at the interprotomer site, and showed the small molecule properties that allow anchoring in the pocket to inhibit virus disassembly.

Immunoglobulin A and microbiota in primary immunodeficiency diseases

PURPOSE OF REVIEW

With the emergence of the microbiota as a potential driver of host inflammation, the role of iIgA is becoming increasingly important. This review discusses the current evidence regarding the effects of clinical IgA deficiency on the microbiota, and the possible role of microbial dysbiosis in driving inflammation in PID patients.

RECENT FINDINGS

The gut microbiota has been investigated in selective IgA deficiency and common variable immunodeficiency, revealing an important role for IgA in maintaining gut microbiota homeostasis, with disparate effects of IgA on symbionts and pathobionts. Although IgA deficiency is associated with microbial translocation and systemic inflammation, this may be partially compensated by adequate IgG and IgM induction in IgA deficiency but not in common variable immunodeficiency. Therapeutic strategies aimed at correction of the microbiota mostly focus on fecal microbiota transplantation. Whether this may reduce systemic inflammation in PID is currently unknown.

SUMMARY

Clinical IgA deficiency is associated with microbial dysbiosis and systemic inflammation. The evidence for microbiota-targeted therapies in PID is scarce, but indicates that IgA-based therapies may be beneficial, and that fecal microbiota transplantation is well tolerated in patients with antibody deficiency.

Parechovirus A Pathogenesis and the Enigma of Genotype A-3

Parechovirus A is a species in the Parechovirus genus within the Picornaviridae family that can cause severe disease in children. Relatively little is known on Parechovirus A epidemiology and pathogenesis. This review aims to explore the Parechovirus A literature and highlight the differences between Parechovirus A genotypes from a pathogenesis standpoint. In particular, the curious case of Parechovirus-A3 and the genotype-specific disease association will be discussed. Finally, a brief outlook on Parechovirus A research is provided.

Parechovirus: an important emerging infection in young infants

Epidemics of human parechovirus (HPeV) causing disease in young children have occurred every 2 years in Australia since 2013. HPeV genotype 3 caused the epidemic from late 2017 to early 2018. Most HPeV infections cause no or mild symptoms including gastroenteritis or influenza-like illness. Characteristically, young infants present with fever, irritability and on occasions a diffuse rash ("red, hot and angry" babies). Severe disease can manifest as meningoencephalitis, seizures or sepsis-like presentations (including septic shock), or less common presentations including signs of surgical abdomen. Testing for HPeV by specific molecular tests is indicated in children younger than 6 months of age with characteristic presentations without another confirmed diagnosis including febrile illnesses with other suggestive features (eg, rash, seizures), sepsis syndromes (including shock), and suspected meningoencephalitis (which may be detected by magnetic resonance imaging only). There are no effective antiviral therapies. Treatment is primarily supportive, including management of complications. Some infants with severe HPeV infection may have adverse neurodevelopment. Follow-up by a paediatrician is recommended.

Viral infection in primary antibody deficiency syndromes

Patients with primary antibody deficiency syndromes such as X-linked agammaglobulinemia (XLA) and common variable immunodeficiency (CVID) are at increased risk of severe and invasive infection. Viral infection in these populations has been of increasing interest as evidence mounts that viruses contribute significant morbidity and mortality: this is mediated both directly and via aberrant immune responses. We explain the importance of the humoral immune system in defence against viral pathogens before highlighting several significant viral syndromes in patients with antibody deficiency. We explore historical cases of hepatitis C via contaminated immunoglobulin products, the predisposition to invasive enteroviral infections, prolonged excretion of vaccine-derived poliovirus, the morbidity of chronic norovirus infection, and recent literature revealing the importance of respiratory viral infections. We discuss evidence that herpesviruses may play a role in driving the inflammatory disease seen in a subset of patients. We explore the phenomenon of within-host evolution during chronic viral infection and the potential emergence of new pathogenic strains. We highlight novel and emerging viruses identified via deep sequencing techniques. We describe the treatment strategies that have been attempted in all these scenarios and the urgent outstanding questions for research.

Human Parechovirus: an Increasingly Recognized Cause of Sepsis-Like Illness in Young Infants

Human parechovirus (HPeV) is increasingly being recognized as a potentially severe viral infection in neonates and young infants. HPeV belongs to the family Picornaviridae and is currently divided into 19 genotypes. HPeV-1 is the most prevalent genotype and most commonly causes gastrointestinal and respiratory disease. HPeV-3 is clinically the most important genotype due to its association with severe disease in younger infants, which may partly be explained by its distinct virological properties. In young infants, the typical clinical presentation includes fever, severe irritability, and rash, often leading to descriptions of "hot, red, angry babies." Infants with severe central nervous system (CNS) infections are at an increased risk of long-term sequelae. Considering the importance of HPeV as a cause of severe viral infections in young infants, we recommend that molecular diagnostic techniques for early detection be included in the standard practice for the investigation of sepsis-like illnesses and CNS infections in this age group.

Enteroviruses and Parechoviruses

Infections with enteroviruses and human parechoviruses are highly prevalent, particularly in neonates, where they may cause substantial morbidity and mortality. Individuals with B-cell-related immunodeficiencies are at risk for severe enteroviral infections, usually a chronic and fatal meningoencephalitis. In transplant recipients and patients with malignancy, enterovirus infections typically involve the respiratory tract, but cases of severe, disseminated infection have been described. The mainstay of diagnosis for enterovirus and human parechovirus infections involves the use of molecular diagnostic techniques. However, routine nucleic acid-detection methods for enteroviruses will not detect human parechoviruses. Laboratory diagnosis of these viral infections is important in determining a patient's prognosis and guiding clinical management.

Human picornaviruses associated with neurological diseases and their neutralization by antibodies

Picornaviruses are the most commonly encountered infectious agents in mankind. They typically cause mild infections of the gastrointestinal or respiratory tract, but sometimes also invade the central nervous system. There, they can cause severe diseases with long-term sequelae and even be lethal. The most infamous picornavirus is poliovirus, for which significant epidemics of poliomyelitis were reported from the end of the nineteenth century. A successful vaccination campaign has brought poliovirus close to eradication, but neurological diseases caused by other picornaviruses have increasingly been reported since the late 1990s. In this review we focus on enterovirus 71, coxsackievirus A16, enterovirus 68 and human parechovirus 3, which have recently drawn attention because of their links to severe neurological diseases. We discuss the clinical relevance of these viruses and the primary role of humoral immunity in controlling them, and summarize current knowledge on the neutralization of such viruses by antibodies.

Chronic norovirus infection and common variable immunodeficiency

Chronic infection with norovirus is emerging as a significant risk for patients with immunodeficiency - either primary or secondary to therapeutic immunosuppression. Patients with primary immunodeficiency present a range of pathological responses to norovirus infection. Asymptomatic infections occur and differentiating viral carriage or prolonged viral shedding after self-limiting infection from infection causing protracted diarrhoea can be challenging, due to relatively mild pathological changes that may mimic other causes of diarrhoea in such patients (for instance pathogenic bacteria or parasites or graft-versus-host disease). However, a subset of patients with common variable immunodeficiency (CVID) experience a severe norovirus-associated enteropathy leading to intestinal villous atrophy and malabsorption. Symptomatic infection of up to 8 years has been demonstrated with clinical and histological recovery on viral clearance. Although oral immunoglobulins and nitazoxanide have been used to treat noroviral infections associated with immunosuppression, ribavirin is the only agent to date that has been linked to viral clearance in the Noroviral enteropathy associated with CVID.

The Structure of Human Parechovirus 1 Reveals an Association of the RNA Genome with the Capsid

Parechoviruses are human pathogens that cause diseases ranging from gastrointestinal disorders to encephalitis. Unlike those of most picornaviruses, parechovirus capsids are composed of only three subunits: VP0, VP1, and VP3. Here, we present the structure of a human parechovirus 1 (HPeV-1) virion determined to a resolution of 3.1 Å. We found that interactions among pentamers in the HPeV-1 capsid are mediated by the N termini of VP0s, which correspond to the capsid protein VP4 and the N-terminal part of the capsid protein VP2 of other picornaviruses. In order to facilitate delivery of the virus genome into the cytoplasm, the N termini of VP0s have to be released from contacts between pentamers and exposed at the particle surface, resulting in capsid disruption. A hydrophobic pocket, which can be targeted by capsid-binding antiviral compounds in many other picornaviruses, is not present in HPeV-1. However, we found that interactions between the HPeV-1 single-stranded RNA genome and subunits VP1 and VP3 in the virion impose a partial icosahedral ordering on the genome. The residues involved in RNA binding are conserved among all parechoviruses, suggesting a putative role of the genome in virion stability or assembly. Therefore, putative small molecules that could disrupt HPeV RNA-capsid protein interactions could be developed into antiviral inhibitors.

IMPORTANCE

Human parechoviruses (HPeVs) are pathogens that cause diseases ranging from respiratory and gastrointestinal disorders to encephalitis. Recently, there have been outbreaks of HPeV infections in Western Europe and North America. We present the first atomic structure of parechovirus HPeV-1 determined by X-ray crystallography. The structure explains why HPeVs cannot be targeted by antiviral compounds that are effective against other picornaviruses. Furthermore, we found that the interactions of the HPeV-1 genome with the capsid resulted in a partial icosahedral ordering of the genome. The residues involved in RNA binding are conserved among all parechoviruses, suggesting an evolutionarily fixed role of the genome in virion assembly. Therefore, putative small molecules disrupting HPeV RNA-capsid protein interactions could be developed into antiviral inhibitors.

Replication and Inhibitors of Enteroviruses and Parechoviruses

The Enterovirus (EV) and Parechovirus genera of the picornavirus family include many important human pathogens, including poliovirus, rhinovirus, EV-A71, EV-D68, and human parechoviruses (HPeV). They cause a wide variety of diseases, ranging from a simple common cold to life-threatening diseases such as encephalitis and myocarditis. At the moment, no antiviral therapy is available against these viruses and it is not feasible to develop vaccines against all EVs and HPeVs due to the great number of serotypes. Therefore, a lot of effort is being invested in the development of antiviral drugs. Both viral proteins and host proteins essential for virus replication can be used as targets for virus inhibitors. As such, a good understanding of the complex process of virus replication is pivotal in the design of antiviral strategies goes hand in hand with a good understanding of the complex process of virus replication. In this review, we will give an overview of the current state of knowledge of EV and HPeV replication and how this can be inhibited by small-molecule inhibitors.

The role of chronic norovirus infection in the enteropathy associated with common variable immunodeficiency

OBJECTIVES

A severe enteropathy of unknown etiology can be associated with common variable immunodeficiency (CVID).

METHODS

S tool and archived small intestinal mucosal biopsies from patients with CVID enteropathy were analyzed by PCR for the presence of Norovirus RNA. The PCR products were sequenced to determine the relationship of viral isolates. Stool samples from 10 patients with CVID but no enteropathy served as controls.

RESULTS

All eight patients in our CVID cohort with enteropathy showed persistent fecal excretion of Norovirus. Analysis of archived duodenal biopsies revealed a strong association between the presence of Norovirus and villous atrophy over a period of up to 8 years. Analysis of the viral isolates from each patient revealed distinct strains of genogroup II.4. Sequence analysis from consecutive biopsy specimens of one patient demonstrated persistence of the same viral strain over a 6-year period. CVID patients without enteropathy showed no evidence of Norovirus carriage. Viral clearance occurred spontaneously in one patient and followed oral Ribavirin therapy in two further patients, and resulted in complete symptomatic and histological recovery. However, Ribavirin treatment in two further patients was unsuccessful.

CONCLUSIONS

Norovirus is an important pathogen for patients with CVID and a cause of CVID enteropathy, as viral clearance, symptom resolution, and histological recovery coincide. Ribavirin requires further evaluation as a potential therapy.

Viral PCR positivity in stool before allogeneic hematopoietic cell transplantation is strongly associated with acute intestinal graft-versus-host disease

Acute graft-versus-host disease (aGVHD) can be triggered by inflammatory conditions, including infections and mucositis. We investigated the association between PCR positivity for gastrointestinal (GI) viruses in stool before hematopoietic cell transplantation (HCT) and intestinal aGVHD using Cox proportional hazard models. We included 48 consecutive HCT patients (28 with malignancies and 20 with nonmalignancies) without GI symptoms before HCT. Fifteen patients were GI virus positive: 9 adenovirus, 3 norovirus, 2 parechovirus, and 1 astrovirus. Overall survival was 58% ± 8%. The cumulative incidence of aGVHD grade 2 to 4 was 43% ± 8% (n = 18) after a median of 47 days (range, 14 to 140). In univariate analysis, GI virus PCR positivity was the only predictor for aGVHD (P = .008): within the group of GI virus PCR-positive patients, the cumulative incidence of aGVHD 2 to 4 was 70% ± 12% versus 29 ± 8% in the PCR-negative group (P = .004). In conclusion, GI virus PCR positivity before HCT predicted development of intestinal aGVHD. These results may ultimately affect monitoring, aGVHD prophylaxis, and treatment, as well as rescheduling of elective HCTs.

Increased prevalence of gastrointestinal viruses and diminished secretory immunoglobulin a levels in antibody deficiencies

PURPOSE

Gastrointestinal disease occurs frequently in antibody deficiencies. This study aims to explore the relation between gastrointestinal infections and mucosal homeostasis in patients with antibody deficiencies.

METHODS

We performed an observational study including 54 pediatric antibody deficient patients (48 % CVID, 41 % CVID-like, 11 % XLA) and 66 healthy controls. Clinical symptom scores and stool samples were collected prospectively. Stool samples were evaluated for bacteria, parasites, viruses, secretory IgA- and for calprotectin levels. Results were compared between patients and controls.

RESULTS

24 % of antibody deficient patients versus 9 % of healthy controls tested positive for gastrointestinal viruses (p = 0.028). Fecal calprotectin levels were significantly higher in virus positive patients compared to virus negative patients (p = 0.002). However, in controls, fecal calprotectin levels were similar between virus positive and virus negative controls. Moreover, gastrointestinal virus positive patients had low serum IgA levels in 13/14 cases (94 %) versus 40/62 (62 %) patients in the virus negative patient group (p = 0.04). The virus positive patient group also displayed significantly lower secretory IgA levels in stool (median 13 ug/ml) than patients without gastrointestinal viruses detected or healthy controls (median 155 ug/ml) (p = 0.046).

CONCLUSION

We here report an increased prevalence of gastrointestinal viruses and gastrointestinal complaints in antibody deficient patients. Patients that tested positive for gastrointestinal viruses showed diminished serum- and secretory IgA levels, and only in patients, virus positivity was associated with signs of mucosal inflammation. These findings suggest that particularly patients with low IgA are at risk for longstanding replication of gastrointestinal viruses, which may eventually result in CVID-related enteropathy.

A review on guidelines for management and treatment of common variable immunodeficiency

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency in adults. As symptoms of CVID are usually heterogeneous and unspecific, diagnosis and follow-up of CVID can be challenging. In light of this, a broad review of advances in management and treatment of CVID is performed here in order to reach a distinct protocol. However, it should be noted that owing to the nature of the disease, it can only be treated symptomatically but not cured. There is little evidence to guide appropriate or universal guidelines to improve the current status of management of the disease. The most satisfactory treatments of CVID could be achieved by the use of immunoglobulin replacement, antibiotics, immunosuppressants and hematopoietic stem cell transplantation. This review is written based on the importance of clinical surveillance of asymptomatic CVID cases and early recognition of different clinical complications. Moreover, for each complication, appropriate interventions for improving outcomes are mentioned.

Highlights in antiviral drug research: antivirals at the horizon

This review highlights ten "hot topics" in current antiviral research: (i) new nucleoside derivatives (i.e., PSI-352938) showing high potential as a direct antiviral against hepatitis C virus (HCV); (ii) cyclopropavir, which should be further pursued for treatment of human cytomegalovirus (HCMV) infections; (iii) North-methanocarbathymidine (N-MCT), with a N-locked conformation, showing promising activity against both α- and γ-herpesviruses; (iv) CMX001, an orally bioavailable prodrug of cidofovir with broad-spectrum activity against DNA viruses, including polyoma, adeno, herpes, and pox; (v) favipiravir, which is primarily pursued for the treatment of influenza virus infections, but also inhibits the replication of other RNA viruses, particularly (-)RNA viruses such as arena, bunya, and hanta; (vi) newly emerging antiarenaviral compounds which should be more effective (and less toxic) than the ubiquitously used ribavirin; (vii) antipicornavirus agents in clinical development (pleconaril, BTA-798, and V-073); (viii) natural products receiving increased attention as potential antiviral drugs; (ix) antivirals such as U0126 targeted at specific cellular kinase pathways [i.e., mitogen extracellular kinase (MEK)], showing activity against influenza and other viruses; and (x) two structurally unrelated compounds (i.e., LJ-001 and dUY11) with broad-spectrum activity against virtually all enveloped RNA and DNA viruses.

The variable in common variable immunodeficiency: a disease of complex phenotypes

Common variable immunodeficiency (CVID) is the most common and clinically most important severe primary antibody deficiency and is characterized by low levels of IgG, IgA, and/or IgM, with a failure to produce specific antibodies. This diagnostic category represents a heterogeneous group of disorders, which present not only with acute and chronic infections but also with a range of inflammatory and autoimmune disorders as well as an increased incidence of lymphoma and other malignancies. Patients can now be categorized into distinct clinical phenotypes based on analysis of large cohort studies and be further stratified by immunologic laboratory testing. The biologic importance of this categorization is made clear by the 11-fold increase in mortality if even one of these phenotypes (cytopenias, lymphoproliferation, or enteropathy) is present. Limited progress in defining the underlying molecular causes has been made with known causative single gene defects accounting for only 3% of cases, and, for this and the reasons mentioned above, CVID remains resolute in its variability. This review provides a practical approach to risk stratification of these complex phenotypes by using current clinical categories and laboratory biomarkers. The effects of infection as well as inflammatory and autoimmune complications on different organ systems are discussed alongside strategies to reduce diagnostic delay. Recent developments in diagnostics and therapy are also explored.

The role of prolonged viral gastrointestinal infections in the development of immunodeficiency-related enteropathy

Patients with primary immunodeficiencies are prone to develop enteropathy of unknown pathogenesis. We hypothesize that ineffective clearance of gastrointestinal pathogens, particularly viruses, in combination with defective immune regulation may cause inflammatory enteropathy in certain immunodeficient hosts. We reviewed publications related to prolonged enteric viral infection, immunodeficiency, and the subsequent development of inflammatory enteropathy. Prolonged infection with especially enteroviral infections was reported more often in immunocompromised hosts than in healthy individuals. Protracted enteric viral shedding was not always associated with the presence or duration of gastrointestinal symptoms. The development of immunodeficiency-associated enteropathy after prolonged viral infections was described in sporadic cases. Clinical consequences of viral gut infections in immunocompromised hosts comprise isolation issues and supportive care. Prospective studies in cohorts of immunodeficient patients are required to study the impact of prolonged enteric viral replication with respect to the pathogenesis of non-infectious enteropathy.