Structure and function of the interleukin 2 receptor: affinity conversion model

Can iron, zinc, copper and selenium status be a prognostic determinant in COVID-19 patients?

In severe COVID-19, the levels of iron (Fe), copper (Cu), zinc (Zn) and selenium (Se), do not only regulate host immune responses, but modify the viral genome, as well. While low serum Fe concentration is an independent risk factor for the increased death rate, Zn controls oxidative stress, synthesis of inflammatory cytokines and viral replication. Therefore, Zn deficiency associates with a worse prognosis. Although Cu exposure inactivates the viral genome and exhibits spike protein dispersal, increase in Cu/Zn due to high serum Cu levels, are correlated with enhanced risk of infections. Se levels are significantly higher in surviving COVID-19 patients. Meanwhile, both Zn and Se suppress the replication of SARS-CoV-2. Since the balance between the deficiency and oversupply of these metals due to a reciprocal relationship, has decisive effect on the prognosis of the SARS-CoV-2 infection, monitoring their concentrations may facilitate improved outcomes for patients suffering from COVID-19.

FOXP3-based immune risk model for recurrence prediction in small-cell lung cancer at stages I-III

BACKGROUND

Immunotherapies may prolong the survival of patients with small-cell lung cancer (SCLC) to some extent. The role of forkhead box protein P3 (FOXP3) in tumor microenvironment (TME) remains controversial. We aimed to examine FOXP3-related expression characteristics and prognostic values and to develop a clinically relevant predictive system for SCLC.

METHODS

We enrolled 102 patients with histologically confirmed SCLC at stages I-III. Through immunohistochemistry, we determined the expression pattern of FOXP3 and its association with other immune biomarkers. By machine learning and statistical analysis, we constructed effective immune risk score models. Furthermore, we examined FOXP3-related enrichment pathways and TME traits in distinct cohorts.

RESULTS

In SCLC, FOXP3 level was significantly associated with status of programmed death-ligand 1 (PD-L1), programmed cell death protein 1 (PD-1), CD4, CD8, and CD3 (p=0.002, p=0.001, p=0.002, p=0.030, and p<0.001). High FOXP3 expression showed longer relapse-free survival (RFS) than the low-level group (41.200 months, 95% CI 26.937 to 55.463, vs 14.000 months, 95% CI 8.133 to 19.867; p=0.008). For tumor-infiltrating lymphocytes (TILs), subgroup analysis demonstrated FOXP3 and PD-1, PD-L1, lymphocyte activation gene-3, CD3, CD4, or CD8 double positive were significantly correlated with longer RFS. We further performed importance evaluation for immune biomarkers, constructed an immune risk score incorporating the top three important biomarkers, FOXP3, TIL PD-L1, and CD8, and found their independently prognostic role to predict SCLC relapse. Better predictive performance was achieved in this immune risk model compared with single-indicator-based or two-indicator-based prediction systems (area under the curve 0.715 vs 0.312-0.711). Then, relapse prediction system integrating clinical staging and immune risk score was established, which performed well in different cohorts. High FOXP3-related genes were enriched in several immune-related pathways, and the close relationships of interleukin-2, CD28, basic excision repair genes MUTYH, POLD1, POLD2, and oxidative phosphorylation related gene cytochrome c oxidase subunit 8A with FOXP3 expression were revealed. Moreover, we found low-immune risk score group had statistically higher activated CD4⁺ memory T cells (p=0.014) and plasma cells (p=0.049) than the high-risk group. The heterogeneity of tumor-infiltrating immune cells might represent a promising feature for risk prediction in SCLC.

CONCLUSION

FOXP3 interacts closely with immune biomarkers on tumor-infiltrating cells in TME. This study highlighted the crucial prognostic value and promising clinical applications of FOXP3 in SCLC.

T-cell dysregulation in COVID-19

T-cells play key roles in immunity to COVID-19 as well as the development of severe disease. T-cell immunity to COVID-19 is mediated through differentiated CD4⁺ T-cells and cytotoxic CD8⁺ T-cells, although their differentiation is often atypical and ambiguous in COVID-19 and single cell dynamics of key genes need to be characterized. Notably, T-cells are dysregulated in severe COVID-19 patients, although their molecular features are still yet to be fully revealed. Importantly, it is not clear which T-cell activities are beneficial and protective and which ones can contribute to the development of severe COVID-19. In this article, we examine the latest evidence and discuss the key features of T-cell responses in COVID-19, showing how T-cells are dysregulated in severe COVID-19 patients. Particularly, we highlight the impairment of FOXP3 induction in CD4⁺ T-cells and how the impaired FOXP3 expression can lead to the differentiation of abnormally activated (hyperactivated) T-cells and the dysregulated T-cell responses in severe patients. Furthermore, we characterise the feature of hyperactivated T-cells, showing their potential contribution to T-cell dysregulation and immune-mediated tissue destruction (immunopathology) in COVID-19.

T-Cell Hyperactivation and Paralysis in Severe COVID-19 Infection Revealed by Single-Cell Analysis

Severe COVID-19 patients show various immunological abnormalities including T-cell reduction and cytokine release syndrome, which can be fatal and is a major concern of the pandemic. However, it is poorly understood how T-cell dysregulation can contribute to the pathogenesis of severe COVID-19. Here we show single cell-level mechanisms for T-cell dysregulation in severe COVID-19, demonstrating new pathogenetic mechanisms of T-cell activation and differentiation underlying severe COVID-19. By in silico sorting CD4+ T-cells from a single cell RNA-seq dataset, we found that CD4+ T-cells were highly activated and showed unique differentiation pathways in the lung of severe COVID-19 patients. Notably, those T-cells in severe COVID-19 patients highly expressed immunoregulatory receptors and CD25, whilst repressing the expression of FOXP3. Furthermore, we show that CD25⁺ hyperactivated T-cells differentiate into multiple helper T-cell lineages, showing multifaceted effector T-cells with Th1 and Th2 characteristics. Lastly, we show that CD25-expressing hyperactivated T-cells produce the protease Furin, which facilitates the viral entry of SARS-CoV-2. Collectively, CD4⁺ T-cells from severe COVID-19 patients are hyperactivated and FOXP3-mediated negative feedback mechanisms are impaired in the lung, which may promote immunopathology. Therefore, our study proposes a new model of T-cell hyperactivation and paralysis that drives immunopathology in severe COVID-19.

Control of regulatory T-cell differentiation and function by T-cell receptor signalling and Foxp3 transcription factor complexes

The transcription factor Foxp3 controls the differentiation and function of regulatory T-cells (Treg). Studies in the past decades identified numerous Foxp3-interacting protein partners. However, it is still not clear how Foxp3 produces the Treg-type transcriptomic landscape through cooperating with its partners. Here I show the current understanding of how Foxp3 transcription factor complexes regulate the differentiation, maintenance and functional maturation of Treg. Importantly, T-cell receptor (TCR) signalling plays central roles in Treg differentiation and Foxp3-mediated gene regulation. Differentiating Treg will have recognized their cognate antigens and received TCR signals before initiating Foxp3 transcription, which is triggered by TCR-induced transcription factors including NFAT, AP-1 and NF-κB. Once expressed, Foxp3 seizes TCR signal-induced transcriptional and epigenetic mechanisms through interacting with AML1/Runx1 and NFAT. Thus, Foxp3 modifies gene expression dynamics of TCR-induced genes, which constitute cardinal mechanisms for Treg-mediated immune suppression. Next, I discuss the following key topics, proposing new mechanistic models for Foxp3-mediated gene regulation: (i) how Foxp3 transcription is induced and maintained by the Foxp3-inducing enhanceosome and the Foxp3 autoregulatory transcription factor complex; (ii) molecular mechanisms for effector Treg differentiation (i.e. Treg maturation); (iii) how Foxp3 activates or represses its target genes through recruiting coactivators and corepressors; (iv) the 'decision-making' Foxp3-containing transcription factor complex for Th17 and Treg differentiation; and (v) the roles of post-translational modification in Foxp3 regulation. Thus, this article provides cutting-edge understanding of molecular biology of Foxp3 and Treg, integrating findings by biochemical and genomic studies.

The effects of interleukin-2 on immune response regulation

The immune system has many adaptive and dynamic components that are regulated to ensure appropriate, precise and rapid response to a foreign pathogen. A delayed or inadequate immune response can lead to prolonged disease, while an excessive or under-regulated response can lead to autoimmunity. The cytokine, interleukin-2 (IL-2) and its receptor IL-2R play an important role in maintaining this balance.The IL-2 receptor transduces pSTAT5 signal through both the intermediate and high affinity receptors, which differ from each other by the presence of CD25 chain in IL-2 receptor. We present experimental data on the kinetics of pSTAT5 signalling through both of the receptors and develop a model that captures this kinetics. We then use this model to parameterize key aspects of two additional models in which we propose and study two different mechanisms by which IL-2 receptor can transduce distinct signals leading to either an activated or a non-activated cell state. We speculate that this initial state differentiation, perhaps enhanced by downstream feedbacks, may eventually lead to differential cell fates.Our result shows that non-linear dynamical models can suggest resolution of a puzzling array of seemingly contradictory experimental results on IL-2 effect on proliferation and differentiation of T-cells.

From stability to dynamics: understanding molecular mechanisms of regulatory T cells through Foxp3 transcriptional dynamics

Studies on regulatory T cells (T_reg) have focused on thymic T_reg as a stable lineage of immunosuppressive T cells, the differentiation of which is controlled by the transcription factor forkhead box protein 3 (Foxp3). This lineage perspective, however, may constrain hypotheses regarding the role of Foxp3 and T_regin vivo, particularly in clinical settings and immunotherapy development. In this review, we synthesize a new perspective on the role of Foxp3 as a dynamically expressed gene, and thereby revisit the molecular mechanisms for the transcriptional regulation of Foxp3. In particular, we introduce a recent advancement in the study of Foxp3‐mediated T cell regulation through the development of the Timer of cell kinetics and activity (Tocky) system, and show that the investigation of Foxp3 transcriptional dynamics can reveal temporal changes in the differentiation and function of T_regin vivo. We highlight the role of Foxp3 as a gene downstream of T cell receptor (TCR) signalling and show that temporally persistent TCR signals initiate Foxp3 transcription in self‐reactive thymocytes. In addition, we feature the autoregulatory transcriptional circuit for the Foxp3 gene as a mechanism for consolidating T_reg differentiation and activating their suppressive functions. Furthermore, we explore the potential mechanisms behind the dynamic regulation of epigenetic modifications and chromatin architecture for Foxp3 transcription. Lastly, we discuss the clinical relevance of temporal changes in the differentiation and activation of T_reg.

A temporally dynamic Foxp3 autoregulatory transcriptional circuit controls the effector Treg programme

Regulatory T cells (Treg) are negative regulators of the immune response; however, it is poorly understood whether and how Foxp3 transcription is induced and regulated in the periphery during T‐cell responses. Using Foxp3‐Timer of cell kinetics and activity (Tocky) mice, which report real‐time Foxp3 expression, we show that the flux of new Foxp3 expressors and the rate of Foxp3 transcription are increased during inflammation. These persistent dynamics of Foxp3 transcription determine the effector Treg programme and are dependent on a Foxp3 autoregulatory transcriptional circuit. Persistent Foxp3 transcriptional activity controls the expression of coinhibitory molecules, including CTLA‐4 and effector Treg signature genes. Using RNA‐seq, we identify two groups of surface proteins based on their relationship to the temporal dynamics of Foxp3 transcription, and we show proof of principle for the manipulation of Foxp3 dynamics by immunotherapy: new Foxp3 flux is promoted by anti‐TNFRII antibody, and high‐frequency Foxp3 expressors are targeted by anti‐OX40 antibody. Collectively, our study dissects time‐dependent mechanisms behind Foxp3‐driven T‐cell regulation and establishes the Foxp3‐Tocky system as a tool to investigate the mechanisms behind T‐cell immunotherapies.

The common γ-chain cytokine receptor: tricks-and-treats for T cells

Originally identified as the third subunit of the high-affinity IL-2 receptor complex, the common γ-chain (γc) also acts as a non-redundant receptor subunit for a series of other cytokines, collectively known as γc family cytokines. γc plays essential roles in T cell development and differentiation, so that understanding the molecular basis of its signaling and regulation is a critical issue in T cell immunology. Unlike most other cytokine receptors, γc is thought to be constitutively expressed and limited in its function to the assembly of high-affinity cytokine receptors. Surprisingly, recent studies reported a series of findings that unseat γc as a simple housekeeping gene, and unveiled γc as a new regulatory molecule in T cell activation and differentiation. Cytokine-independent binding of γc to other cytokine receptor subunits suggested a pre-association model of γc with proprietary cytokine receptors. Also, identification of a γc splice isoform revealed expression of soluble γc proteins (sγc). sγc directly interacted with surface IL-2Rβ to suppress IL-2 signaling and to promote pro-inflammatory Th17 cell differentiation. As a result, endogenously produced sγc exacerbated autoimmune inflammatory disease, while the removal of endogenous sγc significantly ameliorated disease outcome. These data provide new insights into the role of both membrane and soluble γc in cytokine signaling, and open new venues to interfere and modulate γc signaling during immune activation. These unexpected discoveries further underscore the perspective that γc biology remains largely uncharted territory that invites further exploration.

Reprogrammed cell delivery for personalized medicine

In most approaches, personalized medicine requires time- and cost-intensive characterization of an individual's genetic background in order to achieve the best-adapted therapy. For this purpose, cell-based drug delivery offers a promising alternative. In particular, synthetic biology has introduced the vision of cells being programmable therapeutic production facilities that can be introduced into patients. This review highlights the progress made in synthetic biology-based cell engineering toward advanced drug delivery entities. Starting from basic one-input responsive transcriptional or post-transcriptional gene control systems, the field has reached a level on which cells can be engineered to detect cancer cells, to obtain control over T-cell proliferation, and to restore blood glucose homeostasis upon blue light illumination. Furthermore, a cellular implant was developed that detects blood urate level disorders and acts accordingly to restore homeostasis while another cellular implant was engineered as an artificial insemination device that releases bull sperm into bovine ovarian only during ovulation time by recording endogenous luteinizing hormone levels. Soon, the field will reach a stage at which cells can be reprogrammed to detect multiple metabolic parameters and self-sufficiently treat any disorder connected to them.

Highly concentrated urine-purified Tac peptide fails to inhibit IL-2-dependent cell proliferation in vitro

Tac peptide, i.e., the p55 chain of the human interleukin-2 receptor (IL-2R) complex, is detectable as a soluble from (sIL-2R) in normal sera and, at increased levels, in patients with different diseases. Since several immunological abnormalities are observed in most conditions associated with an increase in sIL-2R levels, a down-regulatory effect on IL-2-dependent functions has been postulated as a consequence of binding and functional block of IL-2 by the excess of sIL-2R. To test this hypothesis, we purified sIL-2R from the urine of a patient with hairy cell leukemia and investigated the possible inhibitory effect of this peptide on the in vitro IL-2-induced cell proliferation. The urine-purified molecule was detectable by the specific immunoassay utilized to measure the serum Tac peptide and was constructed by a single polypeptide of about 50 kDa which was able to bind IL-2. Experiments performed with the IL-2-dependent murine CTLL-2 cell line and with PHA-stimulated human peripheral blood mononuclear cells showed that the purified sIL-2R at concentrations up to about 300 nM was unable to block IL-2-dependent cell proliferation. According to these data, which can be explained by the low affinity for IL-2 of the p55 IL-2R chain, it seems unlikely that in vivo the soluble Tac peptide can exert a down regulatory effect on IL-2-induced phenomena through a functional block of IL-2.

Immune dysfunction in the elderly: effect of thymic hormone administration on several in vivo and in vitro immune function parameters

The effects of short-term thymic hormone administration on age-associated immune function were evaluated. Two groups of individuals greater than 65 years of age were treated for 30 days with thymic extracts (TP1) or placebo; before and after this treatment a panel of in vitro and in vivo parameters was determined according to a very rigorous experimental protocol. In most individuals, TP1 treatment was associated with an improvement in cutaneous delayed-type response to PPD. Moreover, an increase in a circulating T cell subpopulation bearing the CD45R surface antigen ("virgin" T cells), and in NK cell cytotoxic activity was also observed in some subjects. Finally, lymphocyte responsiveness to PHA tended to increase, while no effect on lymphocyte ability to produce IL-2 following mitogen stimulation was observed. These findings suggest that TP1 treatment may influence age-related alterations in immune function parameters in some subjects.

Ligand-dependent selection of the receptor gene: segregation of IL-2 binding activity and anti-Tac reactivity by a single amino acid alteration in the Tac antigen (p55)

The Tac antigen (p55, CD25) is a 55 kDa glycoprotein that binds interleukin 2 at low affinity (Kd congruent to 10-50 nM). Expression of the Tac antigen is induced in the activated human T cells to constitute the functional, high-affinity IL-2 receptors (IL-2Rs) (Kd congruent to 10 pM) in conjunction with p70-75. A monoclonal antibody, anti-Tac, recognizes this molecule and inhibits the binding of IL-2 to both high- and low-affinity IL-2Rs. This observation indicates that IL-2 and anti-Tac binding sites are located close to each other within the Tac molecule. In this report, by utilizing a novel approach, we selected cDNAs encoding the Tac antigen variants whose reactivity with anti-Tac is greatly reduced, while retaining their IL-2 binding activity. Each of the mutant cDNAs contained a point (G----A) mutation resulting in an amino acid substitution at the particular amino-terminal portion of the Tac molecule (Asp-4). These results demonstrate that N-terminal amino acid Asp-4 is involved in the epitope recognized by anti-Tac, and that IL-2 binding site and anti-Tac binding site are structurally separable from each other in the Tac molecule.

Activation of murine CD8+ lymphocytes: two distinct signals regulate c-myc and interleukin 2 receptor RNA expression

Resting cytotoxic T lymphocyte precursors (CTL-P; CD8+) constitutively express T cell receptors (TcR) on their cell surfaces. CTL-P are preactivated if binding of the corresponding antigen (mitogens, allogeneic major histocompatibility complex (MHC) determinants, viral proteins or haptens in conjunction with self MHC structures) to the TcR takes place. Using a myc-specific probe I show that within 12 h first antigen binding leads to optimal c-myc RNA expression which seems to be the first sign that resting CTL-P are preactivated. Thereafter, c-myc RNA expression was remarkably reduced only at day 5. Antigen alone, however, is not sufficient for interleukin 2 receptor (IL2R) RNA expression. A monocyte-derived, soluble mediator termed IL2R-inducing factor (RIF) acts in conjunction with antigen to induced the expression of IL2R RNA and functional IL2R on the cell surface. RIF is a 44-kDa heat-labile protein produced by accessory cells and its function is restricted to CD8+ lymphocytes. IL2R RNA is first expressed 12 h after onset of culture, maximally expressed on day 3 and it decreases thereafter. Cells kept in long-term culture without mitogen but in the presence of IL2 do not express high amounts of IL2R RNA. Expression of IL2R RNA can be very efficiently reinduced, however, by mitogenic stimulation. In contrast to primary cultures, IL2R RNA expression peaks earlier and is independent of RIF. The results obtained here show that (a) for CD8+ lymphocytes of primary cultures two distinct activation signals (mitogen and RIF) are necessary for c-myc and IL2R RNA expression and (b) for CD8+ lymphocytes of secondary cultures the mitogenic signal alone is sufficient for re-expression of IL2R RNA.

Immunological studies in patients with HBsAg-positive chronic active hepatitis--spontaneous lymphocyte transformation and natural killer cell activity

The present study was to address the nature of cells which are responsible for enhanced spontaneous lymphocyte transformation (SLT) observed in patients with HBsAg-positive chronic active hepatitis (CAH). The subjects consisted of 34 cases with HBsAg-positive CAH (group I), 31 HBsAg carrier (group II), and 27 normal persons (group III) who had no serological evidence of hepatitis B virus (HBV) infection. SLT values and the number of cells bearing HLA-DR antigens in group I (1021.45±276.40 cpm, 36.94±4.90%) were significantly (p<0.01) elevated as compared to group II (103.74±30.44 cpm, 13.26± 4.72%) and III (118.92 ± 30.84 cpm, 14.93±5.10%), but there was no difference of the number of the IL-2 receptor-bearing cells among each groups. Though natural killer (NK) cell activity in both group I (65.42±15.77%) and II (59.14±14.89%) were significantly enhanced as compared to group III (46.25±20.20%), there was no difference in between group I and II. These findings indicate that the cells bearing HLA-DR antigen, but not NK cells, are responsible for the enhanced SLT in patients with CAH.

Determination of cell-free interleukin 2 receptor level in the serum of normal animals and of animals bearing IL-2 receptor positive tumours with high or low metastatic capacity

Serum levels of cell-free interleukin-2 receptors were elevated above normal in mice bearing the IL-2R positive T-cell lymphoma Eb or its highly metastatic variant ESb. Although ESb cells expressed less IL-2R molecules than Eb cells on their cell surface, serum receptor levels were raised more quickly in ESb than in Eb tumour bearing animals. Elevated IL-2R serum levels were a sensitive tumour marker in animals bearing the aggressive variant ESb but not in animals bearing the low metastatic line Eb. Peritoneal ascites tumour-bearing animals had higher serum IL-2R levels than corresponding animals with subcutaneously growing tumours. Thus, serum IL-2R levels in tumour-bearing animals were dependent on the tumour line and influenced by the site and mode of tumour growth.

Bone marrow pro-T and pro-B lymphocyte clones express functional receptors for interleukin (IL) 3 and IL 4/BSF-1 and nonfunctional receptors for IL 2

It is shown here that the C4-77 and C4-86 bone marrow clones with properties of pro-T lymphocytes and the Bc/Bm11 and CB/Bm7 clones with characteristics of pro-B lymphocytes grow in recombinant interleukin 4 (rIL4)/BSF-1 and IL3, but not in rIL2. The proliferative cell responses to rIL4/BSF-1 were always less that approximately 50% of those achieved by the clones in response to IL3. The CC11 monoclonal antibody (mAb) specific for IL3-sensitive mouse cells did not affect the action of rIL4/BSF-1, but it did inhibit the action of IL3 on the clones. The PC61 mAb against IL2 receptors had no effect on either rIL4/BSF-1- or IL3-driven responses. All four clones carry on the cell membrane the glycoproteins recognized by the CC11 mAb and by the PC61 mAb as assessed by immunofluorescence staining and flow cytometry. We conclude that the pro-T and the pro-B clones express functional receptors for IL3 and rIL4/BSF-1 and nonfunctional receptors for IL2, that rIL4/BSF-1 promotes growth of these clones via an IL3- and IL2-independent pathway and discuss the possible biological significance of these findings.