Hemophagocytic Lymphohistiocytosis: Lessons Learned from the Dark Side

Precision medicine: The use of tailored therapy in primary immunodeficiencies

Primary immunodeficiencies (PID) are rare, complex diseases that can be characterised by a spectrum of phenotypes, from increased susceptibility to infections to autoimmunity, allergy, auto-inflammatory diseases and predisposition to malignancy. With the introduction of genetic testing in these patients and wider use of next-Generation sequencing techniques, a higher number of pathogenic genetic variants and conditions have been identified, allowing the development of new, targeted treatments in PID. The concept of precision medicine, that aims to tailor the medical interventions to each patient, allows to perform more precise diagnosis and more importantly the use of treatments directed to a specific defect, with the objective to cure or achieve long-term remission, minimising the number and type of side effects. This approach takes particular importance in PID, considering the nature of causative defects, disease severity, short- and long-term complications of disease but also of the available treatments, with impact in life-expectancy and quality of life. In this review we revisit how this approach can or is already being implemented in PID and provide a summary of the most relevant treatments applied to specific diseases.

Pediatric inborn errors of immunity causing hemophagocytic lymphohistiocytosis: Case report and review of the literature

Inborn errors of immunity are a group of genetic disorders caused by mutations that affect the development and/or function of several compartments of the immune system, predisposing patients to infections, autoimmunity, allergy and malignancies. In this regard, mutations that affect proteins involved in trafficking, priming, docking, or membrane fusion will impair the exocytosis of lytic granules of effector NK and cytotoxic T lymphocytes. This may predispose patients to hemophagocytic lymphohistiocytosis, a life-threatening immune disorder characterized by systemic lymphocyte and macrophage activation, and increased levels of cytokines, which lead to an uncontrolled hyperinflammation state and progressive multiorgan damage. In this review, we will describe a clinical case and recent advances in inborn errors of immunity predisposing to hemophagocytic lymphohistiocytosis. Summary sentence: Review of recent advances in inborn errors of immunity predisposing to hemophagocytic lymphohistiocytosis.

Mechanisms of Immune Dysregulation in COVID-19 Are Different From SARS and MERS: A Perspective in Context of Kawasaki Disease and MIS-C

Coronaviruses have led to three major outbreaks to date-Severe Acute Respiratory Syndrome (SARS; 2002), Middle East Respiratory Syndrome (MERS; 2012) and the ongoing pandemic, Coronavirus Disease (COVID-19; 2019). Coronavirus infections are usually mild in children. However, a few children with MERS had presented with a severe phenotype in the acute phase resulting in progressive pneumonic changes with increasing oxygen dependency and acute respiratory distress requiring ventilatory support. A subset of children with a history of SARS-CoV-2 infection develops a multisystem hyper-inflammatory phenotype known as Multisystem Inflammatory Syndrome in Children (MIS-C). This syndrome occurs 4-6 weeks after infection with SARS-CoV-2 and has been reported more often from areas with high community transmission. Children with MIS-C present with high fever and often have involvement of cardiovascular, gastrointestinal and hematologic systems leading to multiorgan failure. This is accompanied by elevation of pro-inflammatory cytokines such as IL-6 and IL-10. MIS-C has several similarities with Kawasaki disease (KD) considering children with both conditions present with fever, rash, conjunctival injection, mucosal symptoms and swelling of hands and feet. For reasons that are still not clear, both KD and MIS-C were not reported during the SARS-CoV and MERS-CoV outbreaks. As SARS-CoV-2 differs from SARS-CoV by 19.5% and MERS by 50% in terms of sequence identity, differences in genomic and proteomic profiles may explain the varied disease immunopathology and host responses. Left untreated, MIS-C may lead to severe abdominal pain, ventricular dysfunction and shock. Immunological investigations reveal reduced numbers of follicular B cells, increased numbers of terminally differentiated CD4+T lymphocytes, and decreased IL-17A. There is still ambiguity about the clinical and immunologic risk factors that predispose some children to development of MIS-C while sparing others. Host-pathogen interactions in SARS, MERS and COVID-19 are likely to play a crucial role in the clinical phenotypes that manifest. This narrative review focuses on the immunological basis for development of MIS-C syndrome in the ongoing SARS-CoV-2 pandemic. To the best of our knowledge, these aspects have not been reviewed before.

The Perfect Storm: A Rheumatologist's Point of View on COVID-19 Infection

The new coronavirus infection (Covid-19) is a pandemic that has affected the whole world and progresses with high morbidity and mortality. It has a high contagion rate and a course capable of rapid lung involvement with severe acute respiratory distress syndrome (ARDS) and pulmonary insufficiency. A severe clinical picture develops as a result of a "perfect cytokine storm" which results from possible immunological mechanisms triggered by the viral infection. Immune system dysregulation and possible autoinflammatory and autoimmune mechanisms are responsible for a higher amount of cytokines release from immune cells. Although no clear treatment of Covid-19 infection has emerged yet, it is argued that some disease-modifying anti-rheumatic drugs (DMARDs) may be effective in addition to anti-viral treatments. These drugs (anti-malarial drugs, colchicum dispert, biologics) have been well known to rheumatologists for years because they are used in the treatment of many inflammatory rheumatologic diseases. Another important issue is whether DMARDs, which can cause severe immunosuppression, pose a risk for Covid-19 infection and whether they have been discontinued beforehand. Although there are insufficient data on this subject, considering the risk of disease reactivation, patients may continue their DMARDs treatment under the supervision of a rheumatologist. In this article, the possible immunological mechanisms in the pathogenesis of Covid-19 infection and the efficacy and safety of various DMARDs used in the treatment are discussed from a rheumatologist's perspective in the light of recent literature data.

Hemophagocytic Lymphohistiocytosis Secondary to Prostatic Adenocarcinoma

Hemophagocytic lymphohistiocytosis (HLH) is caused by excessive immune activation. It can be primary in the setting of genetic defects or secondary in the setting of infection, inflammation, and malignancy. Here we present the fourth reported case of secondary HLH in association with prostatic adenocarcinoma and the diagnostic challenges of this rare, life-threatening condition. This is a 78-year-old male who presented to the hospital with fever and generalized weakness for three days and found to have splenomegaly, pancytopenia, markedly elevated transaminases, and ferritin. Bone marrow biopsy revealed hemophagocytes. He underwent an extensive evaluation to identify the etiology. Para-aortic lymph node biopsy was consistent with prostatic adenocarcinoma. The diagnosis of HLH needs a high index of suspicion because the presentation is nonspecific. HLH is a rapidly progressive and potentially fatal condition underscoring the need for a prompt evaluation if this condition is suspected.