CD25 deficiency: A new conformational mutation prevents the receptor expression on cell surface

Bridging therapy-induced phenotypes and genetic immune dysregulation to study interleukin-2-induced immunotoxicology

Interleukin-2 (IL-2) holds promise for the treatment of cancer and autoimmune diseases, but its high-dose usage is associated with systemic immunotoxicity. Differential IL-2 receptor (IL-2R) regulation might impact function of cells upon IL-2 stimulation, possibly inducing cellular changes similar to patients with hypomorphic IL2RB mutations, presenting with multiorgan autoimmunity. Here, we show that sustained high-dose IL-2 stimulation of human lymphocytes drastically reduces IL-2Rβ surface expression especially on T cells, resulting in impaired IL-2R signaling which correlates with high IL-2Rα baseline expression. IL-2R signaling in NK cells is maintained. CD4+ T cells, especially regulatory T cells are more broadly affected than CD8+ T cells, consistent with lineage-specific differences in IL-2 responsiveness. Given the resemblance of cellular characteristics of high-dose IL-2-stimulated cells and cells from patients with IL-2Rβ defects, impact of continuous IL-2 stimulation on IL-2R signaling should be considered in the onset of clinical adverse events during IL-2 therapy.

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.

Type 1 diabetes and inborn errors of immunity: Complete strangers or 2 sides of the same coin?

Type 1 diabetes (T1D) is a polygenic disease and does not follow a mendelian pattern. Inborn errors of immunity (IEIs), on the other hand, are caused by damaging germline variants, suggesting that T1D and IEIs have nothing in common. Some IEIs, resulting from mutations in genes regulating regulatory T-cell homeostasis, are associated with elevated incidence of T1D. The genetic spectrum of IEIs is gradually being unraveled; consequently, molecular pathways underlying human monogenic autoimmunity are being identified. There is an appreciable overlap between some of these pathways and the genetic variants that determine T1D susceptibility, suggesting that after all, IEI and T1D are 2 sides of the same coin. The study of monogenic IEIs with a variable incidence of T1D has the potential to provide crucial insights into the mechanisms leading to T1D. These insights contribute to the definition of T1D endotypes and explain disease heterogeneity. In this review, we discuss the interconnected pathogenic pathways of autoimmunity, β-cell function, and primary immunodeficiency. We also examine the role of environmental factors in disease penetrance as well as the circumstantial evidence of IEI drugs in preventing and curing T1D in individuals with IEIs, suggesting the repositioning of these drugs also for T1D therapy.

Whole exome sequencing identified a novel splice donor site variant in interleukin 2 receptor alpha chain

Interleukin 2 receptor alpha chain (IL-2Rα or CD25) deficiency (OMIM #606367) is an immune dysregulation disorder segregating in autosomal recessive form. The disease is caused by biallelic variants in the IL-2Rα gene encoding IL-2Rα also known as CD25 protein. IL-2Rα combines with γ and β chains of interleukin 2 receptor to form a functional interleukin 2 receptor (IL-2R). In the present study, we identified a Pakistani family presenting a unique presentation of IL-2Rα deficiency. Clinical whole exome sequencing revealed a novel splice donor site variant (NM_001378789.1 (NP_001365718); c.64 + 1G > A) in the IL-2Rα gene. American College of Medical Genetics (ACMG) guidelines interpreted the identified variant as likely pathogenic. The IL-2Rα gene mutation usually presents with autoimmunity and immunodeficiency but in our patient, it presents with congenital diarrhea, metabolic crisis, and strong family history of death in infancy due to the similar complications. Her congenital diarrhea is attributed to autoimmunity in the form of autoimmune enteropathy and eczema. The laboratory findings revealed severe metabolic acidosis hypokalemia and elevated lactate and ammonia levels. This is a new presentation of IL-2Rα gene mutation. The present study highlights the importance of clinical whole exome sequencing in the correct diagnosis of congenital disorders. The study will also help clinical geneticists for genetic counseling and prevention of the disease in the affected family.

High-yield genome engineering in primary cells using a hybrid ssDNA repair template and small-molecule cocktails

Enhancing CRISPR-mediated site-specific transgene insertion efficiency by homology-directed repair (HDR) using high concentrations of double-stranded DNA (dsDNA) with Cas9 target sequences (CTSs) can be toxic to primary cells. Here, we develop single-stranded DNA (ssDNA) HDR templates (HDRTs) incorporating CTSs with reduced toxicity that boost knock-in efficiency and yield by an average of around two- to threefold relative to dsDNA CTSs. Using small-molecule combinations that enhance HDR, we could further increase knock-in efficiencies by an additional roughly two- to threefold on average. Our method works across a variety of target loci, knock-in constructs and primary human cell types, reaching HDR efficiencies of >80-90%. We demonstrate application of this approach for both pathogenic gene variant modeling and gene-replacement strategies for IL2RA and CTLA4 mutations associated with Mendelian disorders. Finally, we develop a good manufacturing practice (GMP)-compatible process for nonviral chimeric antigen receptor-T cell manufacturing, with knock-in efficiencies (46-62%) and yields (>1.5 × 109 modified cells) exceeding those of conventional approaches.

Soluble CD25 imposes a low-zone IL-2 signaling environment that favors competitive outgrowth of antigen-experienced CD25high regulatory and memory T cells

This study focused on soluble (s)CD25-mediated regulation of IL-2 signaling in murine and human CD4+ T cells. Recombinant sCD25 reversibly sequestered IL-2 to limit acute maximal proliferative responses while preserving IL-2 bioavailability to subsequently maintain low-zone IL-2 signaling during prolonged culture. By inhibiting IL-2 signaling during acute activation, sCD25 suppressed T-cell growth and inhibited IL-2-evoked transmembrane CD25 expression, thereby resulting in lower prevalence of CD25high T cells. By inhibiting IL-2 signaling during quiescent IL-2-mediated growth, sCD25 competed with transmembrane CD25, IL2Rβγ, and IL2Rαβγ receptors for limited pools of IL-2 such that sCD25 exhibited strong or weak inhibitory efficacy in IL-2-stimulated cultures of CD25low or CD25high T cells, respectively. Preferential blocking of IL-2 signaling in CD25low but not CD25high T cells caused competitive enrichment of CD25high memory/effector and regulatory FOXP3+ subsets. In conclusion, sCD25 modulates IL-2 bioavailability to limit CD25 expression during acute activation while enhancing CD25highT-cell dominance during low-zone homeostatic IL-2-mediated expansion, thereby 'flattening' the inflammatory curve over time.

A great disturbance in the force: IL-2 receptor defects disrupt immune homeostasis

PURPOSE OF REVIEW

The current review highlights how inborn errors of immunity (IEI) due to IL-2 receptor (IL-2R) subunit defects may result in children presenting with a wide variety of infectious and inflammatory presentations beyond typical X-linked severe combined immune deficiency (X-SCID) associated with IL-2Rγ.

RECENT FINDINGS

Newborn screening has made diagnosis of typical SCID presenting with severe infections less common. Instead, infants are typically diagnosed in the first days of life when they appear healthy. Although earlier diagnosis has improved clinical outcomes for X-SCID, atypical SCID or other IEI not detected on newborn screening may present with more limited infectious presentations and/or profound immune dysregulation. Early management to prevent/control infections and reduce inflammatory complications is important for optimal outcomes of definitive therapies. Hematopoietic stem cell transplant (HSCT) is curative for IL-2Rα, IL-2Rβ, and IL-2Rγ defects, but gene therapy may yield comparable results for X-SCID.

SUMMARY

Defects in IL-2R subunits present with infectious and inflammatory phenotypes that should raise clinician's concern for IEI. Immunophenotyping may support the suspicion for diagnosis, but ultimately genetic studies will confirm the diagnosis and enable family counseling. Management of infectious and inflammatory complications will determine the success of gene therapy or HSCT.

Clean up by aisle 2: roles for IL-2 receptors in host defense and tolerance

Although IL-2 was first recognized as growth factor for T cells, it is now also appreciated to be a key regulator of T cells through its effects on regulatory T cells (Treg). The IL-2 receptor (IL-2R) subunits' different (i) ligand affinities, (ii) dimerization or trimerization relationships with other cytokine subunits, (iii) expression across multiple cell types, and (iv) downstream signaling effects, largely dictate cellular tolerance and antimicrobial processes. Defects in IL-2Rγ result in profound and almost universally fatal immune deficiency, unless treated with hematopoietic stem cell transplantation (HSCT). Defects in IL-2Rα and IL-2Rβ result in more limited infection susceptibility, particularly to herpesviruses. However, the most prominent clinical symptomatology for IL-2Rα and IL-2Rβ defects include multi-organ autoimmunity and inflammation, consistent with the critical role of IL-2 in establishing and maintaining immune tolerance. Here, we review how we have arrived at our current understanding of the complex roles of IL-2/2R in host defense and tolerance focusing on the insights gained from human clinical immunology.

Cellular and molecular mechanisms breaking immune tolerance in inborn errors of immunity

In addition to susceptibility to infections, conventional primary immunodeficiency disorders (PIDs) and inborn errors of immunity (IEI) can cause immune dysregulation, manifesting as lymphoproliferative and/or autoimmune disease. Autoimmunity can be the prominent phenotype of PIDs and commonly includes cytopenias and rheumatological diseases, such as arthritis, systemic lupus erythematosus (SLE), and Sjogren's syndrome (SjS). Recent advances in understanding the genetic basis of systemic autoimmune diseases and PIDs suggest an at least partially shared genetic background and therefore common pathogenic mechanisms. Here, we explore the interconnected pathogenic pathways of autoimmunity and primary immunodeficiency, highlighting the mechanisms breaking the different layers of immune tolerance to self-antigens in selected IEI.

Efficient IL-2R signaling differentially affects the stability, function, and composition of the regulatory T-cell pool

Signaling via interleukin-2 receptor (IL-2R) is a requisite for regulatory T (Treg) cell identity and function. However, it is not completely understood to what degree IL-2R signaling is required for Treg cell homeostasis, lineage stability and function in both resting and inflammatory conditions. Here, we characterized a spontaneous mutant mouse strain endowed with a hypomorphic Tyr129His variant of CD25, the α-chain of IL-2R, which resulted in diminished receptor expression and reduced IL-2R signaling. Under noninflammatory conditions, Cd25Y129H mice harbored substantially lower numbers of peripheral Treg cells with stable Foxp3 expression that prevented the development of spontaneous autoimmune disease. In contrast, Cd25Y129H Treg cells failed to efficiently induce immune suppression and lost lineage commitment in a T-cell transfer colitis model, indicating that unimpaired IL-2R signaling is critical for Treg cell function in inflammatory environments. Moreover, single-cell RNA sequencing of Treg cells revealed that impaired IL-2R signaling profoundly affected the balance of central and effector Treg cell subsets. Thus, partial loss of IL-2R signaling differentially interferes with the maintenance, heterogeneity, and suppressive function of the Treg cell pool.

IL-2 Signaling Axis Defects: How Many Faces?

CD25, Signal transducer and activator of transcription 5B (STAT5B) and Forkhead box P3 (FOXP3) are critical mediators of Interleukin-2 (IL-2) signaling pathway in regulatory T cells (Tregs). CD25 (i.e., IL-2 Receptor α) binds with high affinity to IL-2, activating STAT5B-mediated signaling that eventually results in transcription of FOXP3, a master regulator of Treg function. Consequently, loss-of-function mutations in these proteins give rise to Treg disorders (i.e., Tregopathies) that clinically result in multiorgan autoimmunity. Immunodysregulation, Polyendocrinopathy Enteropathy X-linked (IPEX), due to mutations in FOXP3, has historically been the prototype of Tregopathies. This review describes current knowledge about defects in CD25, STAT5B, and FOXP3, highlighting that these disorders both share a common biological background and display comparable clinical features. However, specific phenotypes are associated with each of these syndromes, while certain laboratory findings could be helpful tools for clinicians, in order to achieve a prompt genetic diagnosis. Current treatment strategies will be outlined, keeping an eye on gene editing, an interesting therapeutic perspective that could definitely change the natural history of these disorders.

A Review of Autoimmune Enteropathy and Its Associated Syndromes

Autoimmune enteropathy is an extremely rare condition characterized by an abnormal intestinal immune response which typically manifests within the first 6 months of life as severe, intractable diarrhea that does not respond to dietary modification. Affected individuals frequently present with other signs of autoimmunity. The diagnosis is made based on a characteristic combination of clinical symptoms, laboratory studies, and histological features on small bowel biopsy. Autoimmune enteropathy is associated with a number of other conditions and syndromes, most notably immunodysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome and autoimmune polyglandular syndrome type 1 (APS-1). Diagnosis and treatment is challenging, and further research is needed to better understand the pathogenesis, disease progression, and long-term outcomes of these conditions.

CD4+CD25-FoxP3+ T cells: a distinct subset or a heterogeneous population?

In addition to generating effective immunity against infectious agents, the immune system helps to fight against different noninfectious human diseases while maintaining the balance between self and non-self discrimination. The breakdown of tolerance in autoimmune diseases or sustainable tolerance in an abnormal microenvironment such as chronic inflammation may initiate the process of malignancy. Immune system regulation is controlled by a complex, dynamic network of cells and mediators. Understanding the cellular and molecular basis of immune regulation provides better insight into the mechanisms governing the immune pathology of diseases. Among several cellular subsets and mediators with regulatory roles, a subpopulation of CD4⁺ T cells was recently reported to be positive for FoxP3 and negative for CD25, with a suggested range of functional activities in both cancer and autoimmune diseases. This CD4 subset was first reported in 2006 and thought to have a role in the pathogenesis of cancer. However, the spectrum of roles played by this T cell subset is broad, and no consensus has been reached regarding its immunological functions. In this review, we focused on the possible origin of CD4⁺CD25^‒FoxP3⁺ T cells and their function in cancer and autoimmune diseases.

Clinical, Immunological, and Genetic Features in Patients with Immune Dysregulation, Polyendocrinopathy, Enteropathy, X-linked (IPEX) and IPEX-like Syndrome

BACKGROUND

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare inborn error of immunity caused by mutations in the forkhead box P3 (FOXP3) gene.

OBJECTIVE

In this study, we conducted a systematic review of patients with IPEX and IPEX-like syndrome to delineate differences in these 2 major groups.

METHODS

The literature search was performed in PubMed, Web of Science, and Scopus databases, and demographic, clinical, immunologic, and molecular data were compared between the IPEX and IPEX-like groups.

RESULTS

A total of 459 patients were reported in 148 eligible articles. Major clinical differences between patients with IPEX and IPEX-like syndrome were observed in rates of pneumonia (11% vs 31%, P < .001), bronchiectasis (0.3% vs 14%, P < .001), diarrhea (56% vs 42%, P = .020), and organomegaly (10% vs 23%, P = .001), respectively. Eosinophilia (95% vs 100%), low regulatory T-cell count (68% vs 50%), and elevated IgE (87% vs 61%) were the most prominent laboratory findings in patients with IPEX and IPEX-like syndrome, respectively. In the IPEX group, a lower mortality rate was observed among patients receiving hematopoietic stem cell transplantation (HSCT) (24%) compared with other patients (43%), P = .008; however, in the IPEX-like group, it was not significant (P = .189).

CONCLUSIONS

Patients with IPEX syndrome generally suffer from enteropathy, autoimmunity, dermatitis, eosinophilia, and elevated serum IgE. Despite similarities in their clinical presentations, patients with IPEX-like syndrome are more likely to present common variable immunodeficiency-like phenotype such as respiratory tract infections, bronchiectasis, and organomegaly. HSCT is currently the only curative therapy for both IPEX and IPEX-like syndrome and may result in favorable outcome.

Novel Hemizygous IL2RG p.(Pro58Ser) Mutation Impairs IL-2 Receptor Complex Expression on Lymphocytes Causing X-Linked Combined Immunodeficiency

Hypomorphic IL2RG mutations may lead to milder phenotypes than X-SCID, named variably as atypical X-SCID or X-CID. We report an 11-year-old boy with a novel c. 172C>T;p.(Pro58Ser) mutation in IL2RG, presenting with atypical X-SCID phenotype. We also review the growing number of hypomorphic IL2RG mutations causing atypical X-SCID. We studied the patient's clinical phenotype, B, T, NK, and dendritic cell phenotypes, IL2RG and CD25 cell surface expression, and IL-2 target gene expression, STAT tyrosine phosphorylation, PBMC proliferation, and blast formation in response to IL-2 stimulation, as well as protein-protein interactions of the mutated IL2RG by BioID proximity labeling. The patient suffered from recurrent upper and lower respiratory tract infections, bronchiectasis, and reactive arthritis. His total lymphocyte counts have remained normal despite skewed T and B cells subpopulations, with very low numbers of plasmacytoid dendritic cells. Surface expression of IL2RG was reduced on his lymphocytes. This led to impaired STAT tyrosine phosphorylation in response to IL-2 and IL-21, reduced expression of IL-2 target genes in patient CD4+ T cells, and reduced cell proliferation in response to IL-2 stimulation. BioID proximity labeling showed aberrant interactions between mutated IL2RG and ER/Golgi proteins causing mislocalization of the mutated IL2RG to the ER/Golgi interface. In conclusion, IL2RG p.(Pro58Ser) causes X-CID. Failure of IL2RG plasma membrane targeting may lead to atypical X-SCID. We further identified another carrier of this mutation from newborn SCID screening, lost to closer scrutiny.

Rheumatological manifestations in inborn errors of immunity

Rare monogenetic diseases serve as natural models to dissect the molecular pathophysiology of the complex disease traits. Rheumatologic disorders by their nature are considered complex diseases with partially genetic origin, as illustrated by their heterogeneous genetic background and variable phenotypic presentation. Recent advances in genetic technologies have helped uncover multiple variants associated with disease susceptibility; however, a precise understanding of genotype-phenotype relationships is still missing. Inborn errors of immunity (IEIs), in addition to recurrent infections, may also present with autoimmune and autoinflammatory rheumatologic manifestations and have provided insights for understanding the underlying the principles of immune system homeostasis and mechanisms of immune dysregulation. This review discusses the rheumatologic manifestations in IEIs with overlapping and differentiating features in immunodeficiencies and rheumatologic disorders.

Flow Cytometry for Diagnosis of Primary Immune Deficiencies-A Tertiary Center Experience From North India

Flow cytometry has emerged as a useful technology that has facilitated our understanding of the human immune system. Primary immune deficiency disorders (PIDDs) are a heterogeneous group of inherited disorders affecting the immune system. More than 350 genes causing various PIDDs have been identified. While the initial suspicion and recognition of PIDDs is clinical, laboratory tools such as flow cytometry and genetic sequencing are essential for confirmation and categorization. Genetic sequencing, however, are prohibitively expensive and not readily available in resource constrained settings. Flow cytometry remains a simple, yet powerful, tool for multi-parametric analysis of cells. While it is confirmatory of diagnosis in certain conditions, in others it helps in narrowing the list of putative genes to be analyzed. The utility of flow cytometry in diagnosis of PIDDs can be divided into four major categories: (a) Enumeration of lymphocyte subsets in peripheral blood. (b) Detection of intracellular signaling molecules, transcription factors, and cytokines. (c) Functional assessment of adaptive and innate immune cells (e.g., T cell function in severe combined immune deficiency and natural killer cell function in familial hemophagocytic lymphohistiocytosis). (d) Evaluation of normal biological processes (e.g., class switching in B cells by B cell immunophenotyping). This review focuses on use of flow cytometry in disease-specific diagnosis of PIDDs in the context of a developing country.