Functional changes in gut microbiota during hematopoietic stem cell transplantation for severe combined immunodeficiency

[Editorial letter

Too much of a good thing: a review of primary immune regulatory disorders

Primary immune regulatory disorders (PIRDs) are inborn errors of immunity caused by a loss in the regulatory mechanism of the inflammatory or immune response, leading to impaired immunological tolerance or an exuberant inflammatory response to various stimuli due to loss or gain of function mutations. Whilst PIRDs may feature susceptibility to recurrent, severe, or opportunistic infection in their phenotype, this group of syndromes has broadened the spectrum of disease caused by defects in immunity-related genes to include autoimmunity, autoinflammation, lymphoproliferation, malignancy, and allergy; increasing focus on PIRDs has thus redefined the classical ‘primary immunodeficiency’ as one aspect of an overarching group of inborn errors of immunity. The growing number of genetic defects associated with PIRDs has expanded our understanding of immune tolerance mechanisms and prompted identification of molecular targets for therapy. However, PIRDs remain difficult to recognize due to incomplete penetrance of their diverse phenotype, which may cross organ systems and present to multiple clinical specialists prior to review by an immunologist. Control of immune dysregulation with immunosuppressive therapies must be balanced against the enhanced infective risk posed by the underlying defect and accumulated end-organ damage, posing a challenge to clinicians. Whilst allogeneic hematopoietic stem cell transplantation may correct the underlying immune defect, identification of appropriate patients and timing of transplant is difficult. The relatively recent description of many PIRDs and rarity of individual genetic entities that comprise this group means data on natural history, clinical progression, and treatment are limited, and so international collaboration will be needed to better delineate phenotypes and the impact of existing and potential therapies. This review explores pathophysiology, clinical features, current therapeutic strategies for PIRDs including cellular platforms, and future directions for research

Hematopoietic Stem Cell Transplantation for Primary Immunodeficiencies

The field of primary immunodeficiencies has pioneered many of the advances in haematopoietic stem cell transplantation and cellular therapies over the last 50 years. The first patients to demonstrate sustained benefit and prolonged cure from the primary genetic defect following allogeneic haematopoietic stem cell transplantation were patients with primary immunodeficiencies. Although primary immunodeficiency patients began the modern era of haematopoietic stem cell transplantation, the history is nevertheless short-in answer to the question "what is the long term outcome of patients transplanted for primary immunodeficiencies?" we often have to say that we do not know. We believe that most patients who undergo haematopoietic stem cell transplantation for primary immunodeficiencies should live a normal lifespan with a fully corrected immune system. We are now beginning to understanding long term outcomes, the relationship to the underlying genetic defect, age, and pre-morbid condition of the patient at time of transplantation, stem cell source and donor, and effect of pre-transplant cytoreductive chemotherapy conditioning. The long term consequences of post-transplant complications such as graft vs. host disease, veno-occlusive disease, or immune dysregulation are also being recognized. Additionally, some genetic defects have a systemic distribution, and we are learning the natural history of these defects once the immunodeficiency has been removed

Impact of DNA ligase IV on nonhomologous end joining pathways during class switch recombination in human cells

Class switch recombination (CSR) is a region-specific, transcriptionally regulated, nonhomologous recombinational process that is initiated by activation-induced cytidine deaminase (AID). The initial lesions in the switch (S) regions are subsequently processed and resolved, leading to recombination of the two targeted S regions. The mechanisms by which repair and ligation of the broken DNA ends occurs is still elusive. Recently, a small number of patients lacking DNA ligase IV, a critical component of the nonhomologous end joining (NHEJ) machinery, have been identified. We show that these patients display a considerably increased donor/acceptor homology at Sμ–Sα junctions compared with healthy controls. In contrast, Sμ–Sγ junctions show an increased frequency of insertions but no increase in junctional homology. These altered patterns of junctional resolution may be related to differences in the homology between the Sμ and the downstream isotype S regions, and could reflect different modes of switch junction resolution when NHEJ is impaired. These findings link DNA ligase IV, and thus NHEJ, to CSR

COVID-19 and X-linked agammaglobulinemia (XLA) - insights from a monogenic antibody deficiency

Purpose of review The clinical outcomes from COVID-19 in monogenic causes of predominant antibody deficiency have pivotal implications for our understanding of the antiviral contribution of humoral immunity. This review summarizes the lessons learned from COVID-19 infection in X-linked agammaglobulinemia (XLA) due to genetic defects in Bruton's tyrosine kinase (BTK). Recent findings Key molecular pathways underlying the development of severe COVID-19 are emerging, highlighting the possible contribution of BTK to hyperinflammation. SARS-CoV-2 specific T-cell responses and complement activation appear insufficient to achieve viral clearance in some B-cell deficient individuals. Whilst appearing efficacious in this group, use of convalescent plasma has been recently associated with the evolution of viral escape variants. Early data suggests individuals with XLA can mount a viral-specific T-cell vaccine response, however, the clinical significance of this is still emerging. Summary In contrast to reports made early in the pandemic, we show XLA patients remain susceptible to severe disease. Persistent infection was common and is likely to carry a significant symptom burden and risk of novel variant evolution. COVID-19 infection in this vulnerable, antibody deficient group due to genetic, therapeutic or disease causes may require prompt and specific intervention for both patient and societal benefit

Involvement of Artemis in nonhomologous end-joining during immunoglobulin class switch recombination

DNA double-strand breaks (DSBs) introduced in the switch (S) regions are intermediates during immunoglobulin class switch recombination (CSR). These breaks are subsequently recognized, processed, and joined, leading to recombination of the two S regions. Nonhomologous end-joining (NHEJ) is believed to be the principle mechanism involved in DSB repair during CSR. One important component in NHEJ, Artemis, has however been considered to be dispensable for efficient CSR. In this study, we have characterized the S recombinational junctions from Artemis-deficient human B cells. Sμ–Sα junctions could be amplified from all patients tested and were characterized by a complete lack of “direct” end-joining and a remarkable shift in the use of an alternative, microhomology-based end-joining pathway. Sμ–Sγ junctions could only be amplified from one patient who carries “hypomorphic” mutations. Although these Sμ–Sγ junctions appear to be normal, a significant increase of an unusual type of sequential switching from immunoglobulin (Ig)M, through one IgG subclass, to a different IgG subclass was observed, and the Sγ–Sγ junctions showed long microhomologies. Thus, when the function of Artemis is impaired, varying modes of CSR junction resolution may be used for different S regions. Our findings strongly link Artemis to the predominant NHEJ pathway during CSR

Hematopoietic stem cell transplantation and vasculopathy associated with STAT3-dominant-negative hyper-IgE syndrome

Dominant negative mutations in the transcription-factor STAT3 underlie the rare primary immunodeficiency Job's syndrome. Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) has shown promise in correction of the underlying immunological defect, with one report suggesting HSCT can prevent development of wider connective tissue complications. Here, we report the case of a 26 year old male who developed an acute ST-elevation myocardial infarction due to coronary artery ectasia and thrombosis, occurring despite pediatric allogeneic HSCT for STAT3-HIES and a predicted 10-year conventional cardiovascular risk of 0.1%. Vasculopathy associated with STAT3-HIES may persist or arise following HSCT and can precipitate life-threatening complications. This has implications for counseling and vascular surveillance, and highlights the need for further studies to determine the risk, pathogenesis, and optimal management of the vasculopathy associated with STAT3-HIES