Host ranges of Sf-rhabdoviruses harbored by lepidopteran insects and insect cell lines.

Cell lines derived from Spodoptera frugiperda (Sf), which are the most widely used hosts in the baculovirus-insect cell system, are contaminated with Sf-rhabdoviruses (Sf-RVs). In this study, we identified a closely related virus (Sf-CAT-RV) in the caterpillar species used to isolate the original Sf cell line. We then evaluated the Sf-RV and Sf-CAT-RV host ranges, found Sf-CAT-RV could infect Vero cells, and obtained results suggesting both variants can infect mouse ear fibroblasts. In addition, we found both variants could establish pantropic infections in severely immunocompromised (RAG2/IL2RG-/-) mice. However, both variants were cleared by two weeks post-inoculation and neither produced any symptoms or obvious adverse outcomes in these hosts. We conclude the caterpillars used to isolate Sf21 cells were the most likely source of the Sf-RV contaminant, Sf-RVs and their Sf-CAT-RV progenitor have broader host ranges than expected from previous work, but neither variant poses a serious threat to human health.

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 ß 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.

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-2Rß, 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.

The IL-2A receptor pathway and its role in lymphocyte differentiation and function.

Murine myeloid cells are developed from hemopoietic stem/progenitor cells. Different types of progenitor cells have variable differentiation potentials. Among the ten main types of cells differentiated from lymphoid progenitor cells, regulatory T cells (Tregs), an important cell subpopulation regulating immune and inflammatory responses, arise from the hematopoietic stem cells in the bone marrow. Tregs then differentiate into T lymphocytes and migrate to the thymus and finally generate Treg subsets, which are subsequently activated and regulated by inflammatory cytokines in the peripheral blood. Tregs also have different phenotypes and immunomodulatory functions. The cytokine interleukin-2/interleukin-2 receptor (IL-2/IL-2R) pathway is an important regulatory signaling pathway of Tregs. Besides, different types of CD4+ and CD8+ cells have different immune effects in the absence of IL-2. IL-2R consists of three subunits, α chain (CD25), ß chain (CD122), and γ chain (CD132). Different subunit combinations have different effects on the activation of immune cells. Multiple studies have shown that IL2RA deficiency has various effects on the immune function in mice. This article reviews the subunit composition and signaling pathway of IL-2R, the classification of Tregs in a murine myeloid cell line and the regulatory effect of IL-2/IL-2R on them, the regulatory impact and signaling mechanism of IL-2/IL-2R on CD4+/CD8+ lymphocyte differentiation, the primary manifestations and molecular mechanism of immune dysfunction in IL-2- and IL-2R-deficient mice, soluble IL-2Rα as a biomarker for diagnosis, prognosis and therapeutic efficacy of treatment in immune system disorders, and the development and clinical application of IL-2 mutants.

NFAT Factors Are Dispensable for the Development but Are Critical for the Maintenance of Foxp3+ Regulatory T Cells.

The transcription factors of the nuclear factor of activated T cell (NFAT) family play a crucial role in multiple aspects of T cell function. It has recently been reported that NFATs play an important role in the suppressive function of CD4+CD25+Foxp3+ regulatory T (Treg) cells. In this study, we have investigated the role of NFATs in the thymic development of Treg cells in mice. We show that NFAT factors are dispensable for the development of Foxp3+ Treg cells in the thymus but are critical for the maintenance of both the phenotype and survival of Treg cells in the thymus as well as in peripheral lymphoid organs. Specifically, the homeostasis of CD4+CD25+Foxp3+ but not the CD4+CD25-Foxp3+ fraction is severely perturbed when NFAT signaling is blocked, leading to a strongly reduced Treg population. We underscored this intriguing effect of NFAT on CD4+CD25+Foxp3+ Treg cells to the disruption of survival signals provided by interleukin 2 (IL-2). Accordingly, blocking Treg cell death by abolishing the activity of pro-apoptotic Bcl-2 family member Bim, compensated for the survival defects induced due to a lack of NFAT-IL-2-IL-2R signaling. Inhibition of NFAT activity led to a strong reduction in the number of Foxp3+ Treg cells; however, it did not influence the level of Foxp3 expression on an individual cell basis. In addition, we show a differential effect of IL-2 and IL-7 signaling on Foxp3+ Treg versus CD4+CD25- T cell development, again underlining the dispensability of NFAT signaling in the development, but not in the maintenance of Foxp3+ Treg cells.

Dynamic transcriptional activity and chromatin remodeling of regulatory T cells after varied duration of interleukin-2 receptor signaling.

Regulatory T (Treg) cells require (interleukin-2) IL-2 for their homeostasis by affecting their proliferation, survival and activation. Here we investigated transcriptional and epigenetic changes after acute, periodic and persistent IL-2 receptor (IL-2R) signaling in mouse peripheral Treg cells in vivo using IL-2 or the long-acting IL-2-based biologic mouse IL-2-CD25. We show that initially IL-2R-dependent STAT5 transcription factor-dependent pathways enhanced gene activation, chromatin accessibility and metabolic reprogramming to support Treg cell proliferation. Unexpectedly, at peak proliferation, less accessible chromatin prevailed and was associated with Treg cell contraction. Restimulation of IL-2R signaling after contraction activated signature IL-2-dependent genes and others associated with effector Treg cells, whereas genes associated with signal transduction were downregulated to somewhat temper expansion. Thus, IL-2R-dependent Treg cell homeostasis depends in part on a shift from more accessible chromatin and expansion to less accessible chromatin and contraction. Mouse IL-2-CD25 supported greater expansion and a more extensive transcriptional state than IL-2 in Treg cells, consistent with greater efficacy to control autoimmunity.

The metalloprotease ADAM10 generates soluble interleukin-2 receptor alpha (sCD25) in vivo.

The cytokine interleukin-2 (IL-2) plays a critical role in controlling the immune homeostasis by regulating the proliferation and differentiation of immune cells, especially T cells. IL-2 signaling is mediated via the IL-2 receptor (IL-2R) complex, which consists of the IL-2Rα (CD25), the IL-2Rß, and the IL-2Rγ. While the latter are required for signal transduction, IL-2Rα controls the ligand-binding affinity of the receptor complex. A soluble form of the IL-2Rα (sIL-2Rα) is found constitutively in human serum, though its levels are increased under various pathophysiological conditions. The sIL-2Rα originates partly from activated T cells through proteolytic cleavage, but neither the responsible proteases nor stimuli that lead to IL-2Rα cleavage are known. Here, we show that the metalloproteases ADAM10 and ADAM17 can cleave the IL-2Rα and generate a soluble ectodomain, which functions as a decoy receptor that inhibits IL-2 signaling in T cells. We demonstrate that ADAM10 is mainly responsible for constitutive shedding of the IL-2Rα, while ADAM17 is involved in IL-2Rα cleavage upon T cell activation. In vivo, we found that mice with a CD4-specific deletion of ADAM10, but not ADAM17, show reduced steady-state sIL-2Rα serum levels. We propose that the identification of proteases involved in sIL-2Rα generation will allow for manipulation of IL-2Rα cleavage, especially as constitutive and induced cleavage of IL-2Rα are executed by different proteases, and thus offer a novel opportunity to alter IL-2 function.

Interleukin 2 receptor subunit beta as a novel hub gene plays a potential role in the immune microenvironment of abdominal aortic aneurysms.

BACKGROUND: Abdominal aortic aneurysm (AAA) is potentially life threatening and characterized by immune-inflammatory cell infiltration and extracellular matrix degradation. Currently, pharmacotherapy mainly aims to control risk factors without reversion of the dilated aorta. This study analyzed the immune-inflammatory response and identified the immune-related hub genes of AAA. METHOD: Gene Expression Omnibus datasets (GSE57691, GSE47472 and GSE7084) were downloaded. After identification of GSE57691 differentially expressed genes (DEGs), weighted gene co-expression network analysis of the DEGs was performed. Through enrichment analysis of each module and screening in Immunology Database and Analysis Portal, immune-related hub genes were identified via protein-protein interaction (PPI) network construction and lasso regression. CIBERSORT was utilized to analyze AAA immune infiltration. The correlations between the immune-related hub genes and infiltrating immune cells were investigated. Receiver operating characteristic (ROC) curve analysis was performed to determine immune-related hub gene cutoff values, which were validated in GSE47472 and GSE7084. RESULT: In GSE57691, 1,018 DEGs were identified. Five modules were identified in the co-expression network. The blue and green modules were found to be related to immune-inflammatory responses, and 61 immune-related genes were identified. PPI and lasso regression analyses identified FOS, IL-6 and IL2RB as AAA immune-related hub genes. CIBERSORT analysis indicated significantly increased infiltration of naive B cells, memory activated CD4 T cells, follicular helper T cells, monocytes and M1 macrophages and significantly decreased infiltration of M2 macrophages in AAA compared with normal samples. IL2RB was more strongly associated with immune infiltration in AAA than were FOS and IL6. The IL2RB area under the ROC curve (AUC) value was > 0.9 in both the training and validation set, demonstrating its strong, stable diagnostic value in AAA. CONCLUSION: AAA and normal samples had different immune infiltration statuses. IL2RB was identified as an immune-related hub gene and a potential hub gene with significant diagnostic value in AAA.

Super-enhancer-based identification of a BATF3/IL-2R-module reveals vulnerabilities in anaplastic large cell lymphoma.

Anaplastic large cell lymphoma (ALCL), an aggressive CD30-positive T-cell lymphoma, comprises systemic anaplastic lymphoma kinase (ALK)-positive, and ALK-negative, primary cutaneous and breast implant-associated ALCL. Prognosis of some ALCL subgroups is still unsatisfactory, and already in second line effective treatment options are lacking. To identify genes defining ALCL cell state and dependencies, we here characterize super-enhancer regions by genome-wide H3K27ac ChIP-seq. In addition to known ALCL key regulators, the AP-1-member BATF3 and IL-2 receptor (IL2R)-components are among the top hits. Specific and high-level IL2R expression in ALCL correlates with BATF3 expression. Confirming a regulatory link, IL-2R-expression decreases following BATF3 knockout, and BATF3 is recruited to IL2R regulatory regions. Functionally, IL-2, IL-15 and Neo-2/15, a hyper-stable IL-2/IL-15 mimic, accelerate ALCL growth and activate STAT1, STAT5 and ERK1/2. In line, strong IL-2Rα-expression in ALCL patients is linked to more aggressive clinical presentation. Finally, an IL-2Rα-targeting antibody-drug conjugate efficiently kills ALCL cells in vitro and in vivo. Our results highlight the importance of the BATF3/IL-2R-module for ALCL biology and identify IL-2Rα-targeting as a promising treatment strategy for ALCL.

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-2Rß result in more limited infection susceptibility, particularly to herpesviruses. However, the most prominent clinical symptomatology for IL-2Rα and IL-2Rß 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.

Selective expansion of regulatory T cells using an orthogonal IL-2/IL-2 receptor system facilitates transplantation tolerance.

Adoptive transfer of Tregs has been shown to improve alloengraftment in animal models. However, it is technically challenging to expand Tregs ex vivo for the purpose of infusing large numbers of cells in the clinic. We demonstrate an innovative approach to engineering an orthogonal IL-2/IL-2 receptor (IL-2R) pair, the parts of which selectively interact with each other, transmitting native IL-2 signals, but do not interact with the natural IL-2 or IL-2R counterparts, thereby enabling selective stimulation of target cells in vivo. Here, we introduced this orthogonal IL-2R into Tregs. Upon adoptive transfer in a murine mixed hematopoietic chimerism model, orthogonal IL-2 injection significantly promoted orthogonal IL-2R+Foxp3GFP+CD4+ cell proliferation without increasing other T cell subsets and facilitated donor hematopoietic cell engraftment followed by acceptance of heart allografts. Our data indicate that selective target cell stimulation enabled by the engineered orthogonal cytokine receptor improves Treg potential for the induction of organ transplantation tolerance.

Exploring the Pathogenic Role and Therapeutic Implications of Interleukin 2 in Autoimmune Hepatitis.

Interleukin 2 is essential for the expansion of regulatory T cells, and low-dose recombinant interleukin 2 has improved the clinical manifestations of diverse autoimmune diseases in preliminary studies. The goals of this review are to describe the actions of interleukin 2 and its receptor, present preliminary experiences with low-dose interleukin 2 in the treatment of diverse autoimmune diseases, and evaluate its potential as a therapeutic intervention in autoimmune hepatitis. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Interleukin 2 is critical for the thymic selection, peripheral expansion, induction, and survival of regulatory T cells, and it is also a growth factor for activated T cells and natural killer cells. Interleukin 2 activates the signal transducer and activator of transcription 5 after binding with its trimeric receptor on regulatory T cells. Immune suppressor activity is increased; anti-inflammatory interleukin 10 is released; pro-inflammatory interferon-gamma is inhibited; and activation-induced apoptosis of CD8+ T cells is upregulated. Preliminary experiences with cyclic injections of low-dose recombinant interleukin 2 in diverse autoimmune diseases have demonstrated increased numbers of circulating regulatory T cells, preserved regulatory function, improved clinical manifestations, and excellent tolerance. Similar improvements have been recognized in one of two patients with refractory autoimmune hepatitis. In conclusion, interferon 2 has biological actions that favor the immune suppressor functions of regulatory T cells, and low-dose regimens in preliminary studies encourage its rigorous investigation in autoimmune hepatitis.

IL-2 and IL-2R gene polymorphisms and immune function in people residing in areas with high background radiation, Yangjiang, China.

PURPOSE: Long-term exposure to low dose radiation may trigger immune response and stimulate hormesis. Interleukin-2 (IL-2) and interleukin-2 receptor (IL-2R) play a crucial role in immune function. We aimed to explore the possible association of IL-2 and IL-2R gene polymorphisms with low dose radiation exposure, as well as the relationship with IL-2 gene expression in people residing in areas with a high background radiation in Yangjiang, China. MATERIALS AND METHODS: We recruited and assigned 54 native men residing in Yangxi County, Yangjiang city to the high natural background radiation (HNBR) group, and 53 native men residing in Hengpi County, Enping city to the control area (CA) group. All the participants wore a thermoluminescent dosimeter (TLD) for 90 days, and answered questionnaires. The serum levels of IL2, IL4, IL5, sIL2R, and tumor growth factor (TGF), and expression levels of IL2RA, IL2RB, IL2RG, and IL2 were also analyzed. Additionally, we tested 10 polymorphic loci associated with the IL-2 gene. RESULTS: The annual effective radiation doses in the HNBR and CA groups were 6.24 mSv y-1 and 1.95 mSv y-1, respectively. After adjusting for potential confounding factors, the serum levels of IL-2 and IL-5 were higher in the HNBR group than the CA group (p < .05), while the serum level of TGFß was lower in the HNBR group (p < .05). The IL-2 gene mRNA expression level was higher in the HNBR group than the CA group (p < .05). The IL-2RB rs76206423 AA allele showed significant variations in the HNBR group (p = .0381). CONCLUSIONS: Long-term exposure to low dose radiation may enhance immune function, and IL-2RB rs76206423 may be related to the expression of IL-2 by other coding variants. Moreover, our data provide a better understanding of the molecular mechanism of the immune response to low dose radiation.

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.

Persistence of adoptively transferred T cells with a kinetically engineered IL-2 receptor agonist.

Interleukin-2 (IL-2) is a component of most protocols of adoptive cell transfer (ACT) therapy for cancer, but is limited by short exposure and high toxicities. NKTR-214 is a kinetically-engineered IL-2 receptor ßγ (IL-2Rßγ)-biased agonist consisting of IL-2 conjugated to multiple releasable polyethylene glycol chains resulting in sustained signaling through IL-2Rßγ. We report that ACT supported by NKTR-214 increases the proliferation, homing and persistence of anti-tumor T cells compared to ACT with IL-2, resulting in superior antitumor activity in a B16-F10 murine melanoma model. The use of NKTR-214 increases the number of polyfunctional T cells in murine spleens and tumors compared to IL-2, and enhances the polyfunctionality of T and NK cells in the peripheral blood of patients receiving NKTR-214 in a phase 1 trial. In conclusion, NKTR-214 may have the potential to improve the antitumor activity of ACT in humans through increased in vivo expansion and polyfunctionality of the adoptively transferred T cells.

Bempegaldesleukin selectively depletes intratumoral Tregs and potentiates T cell-mediated cancer therapy.

High dose interleukin-2 (IL-2) is active against metastatic melanoma and renal cell carcinoma, but treatment-associated toxicity and expansion of suppressive regulatory T cells (Tregs) limit its use in patients with cancer. Bempegaldesleukin (NKTR-214) is an engineered IL-2 cytokine prodrug that provides sustained activation of the IL-2 pathway with a bias to the IL-2 receptor CD122 (IL-2Rß). Here we assess the therapeutic impact and mechanism of action of NKTR-214 in combination with anti-PD-1 and anti-CTLA-4 checkpoint blockade therapy or peptide-based vaccination in mice. NKTR-214 shows superior anti-tumor activity over native IL-2 and systemically expands anti-tumor CD8+ T cells while inducing Treg depletion in tumor tissue but not in the periphery. Similar trends of intratumoral Treg dynamics are observed in a small cohort of patients treated with NKTR-214. Mechanistically, intratumoral Treg depletion is mediated by CD8+ Teff-associated cytokines IFN-γ and TNF-α. These findings demonstrate that NKTR-214 synergizes with T cell-mediated anti-cancer therapies.

Interleukin 2 regulates the activation of human basophils.

Basophils are important effector cells in allergic disorders and anti-parasitic immune response. A number of activators including interleukin 3 (IL-3) and IgE have been identified in the regulation of human basophils expressing mediators such as histamine and leukotriene C4 (LTC4) and cytokines, including IL-4 and IL-13. Human basophils express high levels of IL-2 receptors. However, the function of the IL-2 pathway in basophils remains unknown. Here, we identified that IL-2 induced the activation of human basophils in vitro to express a variety of inflammatory cytokines and chemokines including IL-5, IL-13, GM-CSF and CCL-17. This effect by IL-2 is confirmed by an upstream regulator analysis using Ingenuity pathway analysis. Of note, one of the top regulated cytokines, IL-5, was for the first time identified to be induced by IL-2 in human basophils rather than IL-3 or anti-IgE. Immunofluorescence analysis of skin specimens from bullous pemphigoid and eczema revealed that infiltrating basophils in skin lesions widely expressed IL-5 and GM-CSF. Together, our findings reveal IL-2 as a novel regulator of human basophils. This adds a new layer to support the importance of basophils in allergic disorders.

Regulation of autoimmune disease by the E3 ubiquitin ligase Itch.

Itch is a HECT type E3 ubiquitin ligase that is required to prevent the development of autoimmune disease in both mice and humans. Itch is expressed in most mammalian cell types, and, based on published data, it regulates many cellular pathways ranging from T cell differentiation to liver tumorigenesis. Since 1998, when Itch was first discovered, hundreds of publications have described mechanisms through which Itch controls various biologic activities in both immune and non-immune cells. Other studies have provided insight into how Itch catalytic activity is regulated. However, while autoimmunity is the primary clinical feature that occurs in both mice and humans lacking Itch, and Itch control of immune cell function has been well-studied, it remains unclear how Itch prevents the emergence of autoimmune disease. In this review, we explore recent discoveries that advance our understanding of how Itch regulates immune cell biology, and the extent to which these clarify how Itch prevents autoimmune disease. Additionally, we discuss how molecular regulators of Itch impact its ability to control these processes, as this may provide clues on how to therapeutically target Itch to treat patients with autoimmune disease.

CD25 and Protein Phosphatase 2A Cooperate to Enhance IL-2R Signaling in Human Regulatory T Cells.

Low-dose IL-2 therapy is a direct approach to boost regulatory T cells (Tregs) and promote immune tolerance in autoimmune patients. However, the mechanisms responsible for selective response of Tregs to low-dose IL-2 is not fully understood. In this study we directly assessed the contribution of CD25 and protein phosphatase 2A (PP2A) in promoting IL-2R signaling in Tregs. IL-2-induced tyrosine phosphorylation of STAT5 (pSTAT5) was proportional to CD25 levels on human CD4+ T cells and YT human NK cell line, directly demonstrating that CD25 promotes IL-2R signaling. Overexpression of the PP2A catalytic subunit (PP2Ac) by lentiviral transduction in human Tregs increased the level of IL-2R subunits and promoted tyrosine phosphorylation of Jak3 and STAT5. Interestingly, increased expression of CD25 only partially accounted for this enhanced activation of pSTAT5, indicating that PP2A promotes IL-2R signaling through multiple mechanisms. Consistent with these findings, knockdown of PP2Ac in human Tregs and impaired PP2Ac activity in mouse Tregs significantly reduced IL-2-dependent STAT5 activation. In contrast, overexpression or knockdown of PP2Ac in human T effector cells did not affect IL-2-dependent pSTAT5 activation. Overexpression of PP2Ac in human Tregs also increased the expressions of proteins related to survival, activation, and immunosuppressive function, and upregulated several IL-2-regulated genes. Collectively, these findings suggest that CD25 and PP2A cooperatively enhance the responsiveness of Tregs to IL-2, which provide potential therapeutic targets for low-dose IL-2 therapy.