The structure of interleukin-2 complexed with its alpha receptor

Immunosuppressive effects of triptolide via interleukin-2/receptor signaling

BACKGROUND

Triptolide (TP) has been confirmed to possess many beneficial functions including anti-inflammation and immunosuppression.

OBJECTIVE

The present study aimed to explore the potential involvement of IL-2/IL-2R pathway in the immunosuppressive activities of TP.

METHODS

Cultured CTLL-2 cells were utilized to evaluate the potential benefits of TP. Then cell viability was determined by CCK-8 assay, IFN-γ level by ELISA assay, Annexin V-FITC/PI double-staining and CD25 expression by flow cytometry, and protein expression by western blotting. Additionally, rhIL-2-driven lymphocytes following ConA activation were investigated. The interactions of TP with IL-2 and IL-2Rα were investigated by binding assays and molecular dynamics simulations.

RESULTS

TP treatment attenuated IFN-γ level and cell viability in both rhIL-2-induced CTLL-2 cells and rhIL-2-driven splenic lymphocytes. TP treatment increased cellular apoptosis/necrosis and cleaved PARP-1 level, while suppressed c-Myc level in rhIL-2-induced CTLL-2 cells. Additionally, TP treatment reduced CD25 expression on CTLL-2 cell surface. Notably, the phosphorylation protein levels in IL-2R signaling pathways were inhibited by TP exposure prior to rhIL-2 stimulation. SPR and BLI assays verified TP that directly bound to rhIL-2 and rmIL-2Rα, respectively. Molecular simulations suggested that TP bound at the interface of IL-2 and IL-2Rα near the hydrophobic patch composed of F62, L92 on IL-2 and L23, I46, V139 on IL-2Rα, resulting in decreased binding free energy between IL-2 and IL-2Rα.

CONCLUSIONS

These findings collectively emphasized that TP interfered IL-2/IL-2Rα interactions, down-regulated IL-2Rα expression, and inhibited IL-2R signaling pathways activation, thereby leading to the immune cells being desensitized to rhIL-2 and exhibiting immunosuppressive properties.

Harnessing IL-2 for immunotherapy against cancer and chronic infection: a historical perspective and emerging trends

IL-2 therapy, which enhances the function of CD8 + T cells, was initially employed as the cornerstone of immunotherapy against cancer. However, the impact of this therapy extends beyond CD8 + T cells to cells expressing IL-2R, such as endothelial cells and regulatory T cells (Tregs), resulting in various side effects. Consequently, IL-2 therapy has taken a step back from the forefront of treatment. Immune checkpoint inhibitors (ICIs), such as anti-PD-1/PD-L1 antibodies and CTLA-4 antibodies, are used because of their durable therapeutic responses and the reduced incidence of side effects. Nevertheless, only a small fraction of cancer patients respond to ICIs, and research on IL-2 as a combination treatment to improve the efficacy of these ICIs is ongoing. To mitigate side effects, efforts have focused on developing IL-2 variants that do not strongly bind to cells expressing IL-2Rα and favor signaling through IL-2Rβγ. However, recent studies have suggested that, in the context of persistent antigen stimulation models, effective stimulation of antigen-specific exhausted CD8 + T cells in combination with PD-1 inhibitors requires either 1) binding to IL-2Rα or 2) delivery via a fusion with PD-1. This review explores the historical context of IL-2 as an immunotherapeutic agent and discusses future directions for its use in cancer immunotherapy.

The JAK-STAT pathway: from structural biology to cytokine engineering

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway serves as a paradigm for signal transduction from the extracellular environment to the nucleus. It plays a pivotal role in physiological functions, such as hematopoiesis, immune balance, tissue homeostasis, and surveillance against tumors. Dysregulation of this pathway may lead to various disease conditions such as immune deficiencies, autoimmune diseases, hematologic disorders, and cancer. Due to its critical role in maintaining human health and involvement in disease, extensive studies have been conducted on this pathway, ranging from basic research to medical applications. Advances in the structural biology of this pathway have enabled us to gain insights into how the signaling cascade operates at the molecular level, laying the groundwork for therapeutic development targeting this pathway. Various strategies have been developed to restore its normal function, with promising therapeutic potential. Enhanced comprehension of these molecular mechanisms, combined with advances in protein engineering methodologies, has allowed us to engineer cytokines with tailored properties for targeted therapeutic applications, thereby enhancing their efficiency and safety. In this review, we outline the structural basis that governs key nodes in this pathway, offering a comprehensive overview of the signal transduction process. Furthermore, we explore recent advances in cytokine engineering for therapeutic development in this pathway.

Non-IL-2-blocking anti-CD25 antibody inhibits tumor growth by depleting Tregs and has synergistic effects with anti-CTLA-4 therapy

CD25, also known as the interleukin-2 receptor α chain (IL-2Rα), is highly expressed on regulatory T cells (Tregs), but relatively lower on effector T cells (Teffs). This makes it a potential target for Treg depletion, which can be used in tumor immunotherapy. However, marketed anti-CD25 antibodies (Basiliximab and Daclizumab) were originally developed as immunosuppressive drugs to prevent graft rejection, because these antibodies can block IL-2 binding to CD25 on Teffs, which in turn destroys the function of Teffs. Recent studies have shown that non-IL-2-blocking anti-CD25 antibodies have displayed exciting antitumor effects. Here, we screened out a non-IL-2-blocking anti-CD25 monoclonal antibody (mAb) 7B7 by hybridoma technology, and confirmed its antitumor activity via depleting Tregs in a CD25 humanized mouse model. Subsequently, we verified that the humanized 7B7, named as h7B7-15S, has comparable activities to 7B7, and that its Treg depletion is further increased when combined with anti-CTLA-4, leading to enhanced remodeling of the tumor immune microenvironment. Moreover, our findings reveal that the Fab form of h7B7-15S has the ability to deplete Tregs, independent of the Fc region. Taken together, our studies expand the application of anti-CD25 in tumor immunotherapy and provide insight into the underlying mechanism.

"IL-2 immunotherapy for targeting regulatory T cells in autoimmunity"

FOXP3+ regulatory T cells (Treg) are indispensable for immune homoeostasis and for the prevention of autoimmune diseases. Interleukin-2 (IL-2) signalling is critical in all aspects of Treg biology. Consequences of defective IL-2 signalling are insufficient numbers or dysfunction of Treg and hence autoimmune disorders in human and mouse. The restoration and maintenance of immune homoeostasis remain central therapeutic aims in the field of autoimmunity. Historically, broadly immunosuppressive drugs with serious side-effects have been used for the treatment of autoimmune diseases or prevention of organ-transplant rejection. More recently, ex vivo expanded or in vivo stimulated Treg have been shown to induce effective tolerance in clinical trials supporting the clinical benefit of targeting natural immunosuppressive mechanisms. Given the central role of exogenous IL-2 in Treg homoeostasis, a new and promising focus in drug development are IL-2-based approaches for in vivo targeted expansion of Treg or for enhancement of their suppressive activity. In this review, we summarise the role of IL-2 in Treg biology and consequences of dysfunctional IL-2 signalling pathways. We then examine evidence of efficacy of IL-2-based biological drugs targeting Treg with specific focus on therapeutic candidates in clinical trials and discuss their limitations.

Strategies to therapeutically modulate cytokine action

Cytokines are secreted or membrane-presented molecules that mediate broad cellular functions, including development, differentiation, growth and survival. Accordingly, the regulation of cytokine activity is extraordinarily important both physiologically and pathologically. Cytokine and/or cytokine receptor engineering is being widely investigated to safely and effectively modulate cytokine activity for therapeutic benefit. IL-2 in particular has been extensively engineered, to create IL-2 variants that differentially exhibit activities on regulatory T cells to potentially treat autoimmune disease versus effector T cells to augment antitumour effects. Additionally, engineering approaches are being applied to many other cytokines such as IL-10, interferons and IL-1 family cytokines, given their immunosuppressive and/or antiviral and anticancer effects. In modulating the actions of cytokines, the strategies used have been broad, including altering affinities of cytokines for their receptors, prolonging cytokine half-lives in vivo and fine-tuning cytokine actions. The field is rapidly expanding, with extensive efforts to create improved therapeutics for a range of diseases.

Improving de novo protein binder design with deep learning

Recently it has become possible to de novo design high affinity protein binding proteins from target structural information alone. There is, however, considerable room for improvement as the overall design success rate is low. Here, we explore the augmentation of energy-based protein binder design using deep learning. We find that using AlphaFold2 or RoseTTAFold to assess the probability that a designed sequence adopts the designed monomer structure, and the probability that this structure binds the target as designed, increases design success rates nearly 10-fold. We find further that sequence design using ProteinMPNN rather than Rosetta considerably increases computational efficiency.

CD25: A potential tumor therapeutic target

CD25 is the alpha-chain of the heterotrimer IL-2 receptor. CD25 is expressed on the surface of both immune and non-immune cells with different frequencies. For cancers, CD25 is expressed at high levels in many types of hematological malignancies, but at low levels in most solid tumors. CD25 is also highly expressed in activated circulating immune cells and regulatory T cells (Tregs). Infiltration of Tregs in the tumor microenvironment can lead to an imbalanced ratio of effector T cells (Teffs) and Tregs, which is associated with the progression of cancers. A rescued Teff/Treg cell ratio indicates an efficient anti-tumor response to immunotherapy. CD25 as a potential target for the depletion of Tregs is critical in developing new immunotherapeutic strategies. Few articles have summarized the relationships between CD25 and tumors, or the recent progress of drugs targeting CD25. In this paper, we will discuss the structures of IL-2 and IL-2R, the biological function of CD25 and its important role in tumor therapy. In addition, the latest research on drugs targeting CD25 has been summarized, providing guidance for future drug development.

Crosstalk of Inflammatory Cytokines within the Breast Tumor Microenvironment

Several immune and immunocompetent cells, including dendritic cells, macrophages, adipocytes, natural killer cells, T cells, and B cells, are significantly correlated with the complex discipline of oncology. Cytotoxic innate and adaptive immune cells can block tumor proliferation, and others can prevent the immune system from rejecting malignant cells and provide a favorable environment for tumor progression. These cells communicate with the microenvironment through cytokines, a chemical messenger, in an endocrine, paracrine, or autocrine manner. These cytokines play an important role in health and disease, particularly in host immune responses to infection and inflammation. They include chemokines, interleukins (ILs), adipokines, interferons, colony-stimulating factors (CSFs), and tumor necrosis factor (TNF), which are produced by a wide range of cells, including immune cells, such as macrophages, B-cells, T-cells, and mast cells, as well as endothelial cells, fibroblasts, a variety of stromal cells, and some cancer cells. Cytokines play a crucial role in cancer and cancer-related inflammation, with direct and indirect effects on tumor antagonistic or tumor promoting functions. They have been extensively researched as immunostimulatory mediators to promote the generation, migration and recruitment of immune cells that contribute to an effective antitumor immune response or pro-tumor microenvironment. Thus, in many cancers such as breast cancer, cytokines including leptin, IL-1B, IL-6, IL-8, IL-23, IL-17, and IL-10 stimulate while others including IL-2, IL-12, and IFN-γ, inhibit cancer proliferation and/or invasion and enhance the body's anti-tumor defense. Indeed, the multifactorial functions of cytokines in tumorigenesis will advance our understanding of cytokine crosstalk pathways in the tumor microenvironment, such as JAK/STAT, PI3K, AKT, Rac, MAPK, NF-κB, JunB, cFos, and mTOR, which are involved in angiogenesis, cancer proliferation and metastasis. Accordingly, targeting and blocking tumor-promoting cytokines or activating and amplifying tumor-inhibiting cytokines are considered cancer-directed therapies. Here, we focus on the role of the inflammatory cytokine system in pro- and anti-tumor immune responses, discuss cytokine pathways involved in immune responses to cancer and some anti-cancer therapeutic applications.

Emerging principles of cytokine pharmacology and therapeutics

Cytokines are secreted signalling proteins that play essential roles in the initiation, maintenance and resolution of immune responses. Although the unique ability of cytokines to control immune function has garnered clinical interest in the context of cancer, autoimmunity and infectious disease, the use of cytokine-based therapeutics has been limited. This is due, in part, to the ability of cytokines to act on many cell types and impact diverse biological functions, resulting in dose-limiting toxicity or lack of efficacy. Recent studies combining structural biology, protein engineering and receptor pharmacology have unlocked new insights into the mechanisms of cytokine receptor activation, demonstrating that many aspects of cytokine function are highly tunable. Here, we discuss the pharmacological principles underlying these efforts to overcome cytokine pleiotropy and enhance the therapeutic potential of this important class of signalling molecules.

The potential of regulatory T cell-based therapies for alopecia areata

Cytotoxic T lymphocyte has been a concern for the etiopathogenesis of alopecia areata (AA), some recent evidence suggests that the regulatory T (T_reg) cell deficiency is also a contributing factor. In the lesional scalp of AA, T_reg cells residing in the follicles are impaired, leading to dysregulated local immunity and hair follicle (HF) regeneration disorders. New strategies are emerging to modulate T_reg cells' number and function for autoimmune diseases. There is much interest to boost T_reg cells in AA patients to suppress the abnormal autoimmunity of HF and stimulate hair regeneration. With few satisfactory therapeutic regimens available for AA, T_reg cell-based therapies could be the way forward. Specifically, CAR-T_reg cells and novel formulations of low-dose IL-2 are the alternatives.

SUSD2 suppresses CD8+ T cell antitumor immunity by targeting IL-2 receptor signaling

Dysfunctional CD8+ T cells, which have defective production of antitumor effectors, represent a major mediator of immunosuppression in the tumor microenvironment. Here, we show that SUSD2 is a negative regulator of CD8+ T cell antitumor function. Susd2-/- effector CD8+ T cells showed enhanced production of antitumor molecules, which consequently blunted tumor growth in multiple syngeneic mouse tumor models. Through a quantitative mass spectrometry assay, we found that SUSD2 interacted with interleukin (IL)-2 receptor α through sushi domain-dependent protein interactions and that this interaction suppressed the binding of IL-2, an essential cytokine for the effector functions of CD8+ T cells, to IL-2 receptor α. SUSD2 was not expressed on regulatory CD4+ T cells and did not affect the inhibitory function of these cells. Adoptive transfer of Susd2-/- chimeric antigen receptor T cells induced a robust antitumor response in mice, highlighting the potential of SUSD2 as an immunotherapy target for cancer.

Engineering IL-2 for immunotherapy of autoimmunity and cancer

Preclinical studies of the T cell growth factor activity of IL-2 resulted in this cytokine becoming the first immunotherapy to be approved nearly 30 years ago by the US Food and Drug Administration for the treatment of cancer. Since then, we have learnt the important role of IL-2 in regulating tolerance through regulatory T cells (Treg cells) besides promoting immunity through its action on effector T cells and memory T cells. Another pivotal event in the history of IL-2 research was solving the crystal structure of IL-2 bound to its tripartite receptor, which spurred the development of cell type-selective engineered IL-2 products. These new IL-2 analogues target Treg cells to counteract the dysregulated immune system in the context of autoimmunity and inflammatory disorders or target effector T cells, memory T cells and natural killer cells to enhance their antitumour responses. IL-2 biologics have proven to be effective in preclinical studies and clinical assessment of some is now underway. These studies will soon reveal whether engineered IL-2 biologics are truly capable of harnessing the IL-2-IL-2 receptor pathway as effective monotherapies or combination therapies for autoimmunity and cancer.

Immune checkpoint inhibitors for PD-1/PD-L1 axis in combination with other immunotherapies and targeted therapies for non-small cell lung cancer

It has been widely acknowledged that the use of immune checkpoint inhibitors (ICI) is an effective therapeutic treatment in many late-stage cancers. However, not all patients could benefit from ICI therapy. Several biomarkers, such as high expression of PD-L1, high mutational burden, and higher number of tumor infiltration lymphocytes have shown to predict clinical benefit from immune checkpoint therapies. One approach using ICI in combination with other immunotherapies and targeted therapies is now being investigated to enhance the efficacy of ICI alone. In this review, we summarized the use of other promising immunotherapies and targeted therapies in combination with ICI in treatment of lung cancers. The results from multiple animals and clinical trials were reviewed. We also briefly discussed the possible outlooks for future treatment.

Granulomatous hepatitis in a Saudi child with IL2RA defect: a case report and literature review

Interleukin-2 receptor alpha (IL2RA) defect (OMIM- # 606367) is an immune disease where affected patients are vulnerable to developing recurrent microbial infections in addition to lymphadenopathy and dermatological manifestations. This condition is known to be caused by pathogenic variants in the IL2RA gene, which are inherited in an autosomal recessive fashion. In this case report, we present a patient with IL2RA defect from Saudi Arabia who presented with chronic diarrhea, poor weight gain, mild villous atrophy, malnutrition, hepatomegaly, nonspecific inflammation, and an eczematous skin rash. His genetic analysis revealed a novel, homozygous, and likely pathogenic variant, that is, c.504 C>A (Cys168Ter), located in the exon 4of the IL2RA gene, which was inherited from his parents in an autosomal recessive mode of inheritance. This variant produces a 272-amino-acid shorter IL2RA protein chain, which most likely becomes degraded in the cytosol. Thus, we assume that the c.504 C>A is a null allele that abolishes the synthesis of IL2RA, malforms the IL-2 receptor complex, and eventually causes immunodeficiency manifestations. To our knowledge, this is the first time a person with IL2RA defect has shown signs of granulomatous hepatitis on a liver biopsy.

Signaling new therapeutic opportunities: cytokines in prostate cancer

INTRODUCTION

Despite FDA approval of sipuleucel-T in 2010, endeavors to use immune checkpoint inhibitors in unselected prostate cancer patients have not improved clinical outcomes. These efforts include studies with anti-PD1/PD-L1 and anti-CTLA-4 alone and in combination with existing standards of care. These strategies are generally T-cell centric and disregard the broader complex and pleiotropic components of the prostate cancer tumor microenvironment such as natural killer cells, myeloid-derived suppressor cells and tumor associated macrophages.

AREAS COVERED

We performed an online literature search and undertook a review of existing pre-clinical and clinical literature for cytokine-based therapy relating to prostate cancer, specifically on interleukin (IL)-2, IL-15, IL-12, IL-23, IL-8 and transforming growth factor (TGF)-β.

EXPERT OPINION

Cytokine-based therapies present an alternative immune strategy to target the pleiotropic prostate cancer tumor microenvironment beyond T-cells. Future immunotherapy strategies in prostate cancer should address these immune cell populations which may play more important roles in the prostate cancer tumor microenvironment.

New therapeutic strategies based on biasing IL-2 mutants for cancers and autoimmune diseases

Interleukin-2 (IL-2) is an immunomodulatory multifunctional cytokine. High-dose IL-2 was first approved by the U.S. Food and Drug Administration (FDA) in the 1990s for the treatment of metastatic renal cell carcinoma and metastatic melanoma. However, the short half-life of IL-2 and its toxicity caused by high-dose IL-2 limit the clinical use of IL-2. Recently, the development of cell-type-selective engineered IL-2 products become a hot research filed, mainly because IL-2 stimulates both regulatory T cells (Treg) and effector T cells (Teff) in vivo. The selective effect of IL-2 on Treg and Teff can be improved by designing biased IL-2 mutants, which showed reduced toxicity while being more effective in stimulating anti-tumor effector immunity or ameliorating autoimmune diseases. In this review we summarize the biological properties of IL-2 mutants reported so far. The design process and principle of IL-2 mutants, IL-2 mutant antibody complexes and IL-2 fusion proteins were discussed, which provided research basis for the design and application of IL-2 mutants in the future.

124I Radiolabeled Basiliximab for CD25-Targeted Immuno-PET Imaging of Activated T Cells

Activated T cells played critical roles in immunotherapy and adoptive T cell therapy, and a non-invasive imaging strategy can provide us useful information concerning the transportation, accumulation, and homing of T cells in vivo. In this paper, by utilizing the long half-life radionuclide iodine-124 (¹²⁴I) and CD25 specific monoclonal antibody Basiliximab, we have fabricated a novel probe, namely, ¹²⁴I-Basiliximab, which was highly promising in the immuno-PET imaging of T cells. In vitro, ¹²⁴I-Basiliximab had superior affinity to CD25 protein (Kd = 5.31 nM) and exhibited much higher accumulation in CD25 high-expression lymphoma cell line Karpas299 than that in CD25-negative cell line Daudi. In vivo, ¹²⁴I-Basiliximab was excreted slowly from the body of mice, rendering it a relatively high effective dose (0.393 mSv/MBq) when applied in the immuno-PET imaging. In Karpas299 tumor xenograft, ¹²⁴I-Basiliximab probe was observed to accumulate in the tumor quickly after tracer administration, with the optimal image acquired at 24 h post-injection. More importantly, PHA-activated hPBMC had much higher uptake of ¹²⁴I-Basiliximab, indicating the potential utility of ¹²⁴I-Basiliximab to discriminate activated hPBMC from its non-activated status. In summary, ¹²⁴I-Basiliximab was fabricated for the first time, which can be applied in CD25-targeted immuno-PET imaging of activated T cells in vivo.

Selective Expansion of Tregs Using the IL-2 Cytokine Antibody Complex Does Not Reverse Established Alopecia Areata in C3H/HeJ Mice

Alopecia areata (AA) is an autoimmune disease mediated by NKG2D-expressing cytotoxic T lymphocytes destroying hair follicles in the skin. It is one of the most common autoimmune diseases, but there is no effective treatment modality approved by the FDA. Regulatory T cells (Tregs) are crucial for suppressing autoreactive T cells, and in the skin, they promote hair growth by inducing anagen. Based on this, we tested the therapeutic potential of expanded Tregs in AA using the C3H/HeJ mouse model. In mice with AA, NKG2D-expressing CD8 T cells widely infiltrate both haired and hairless skin areas, which have tissue-resident memory T-cell phenotypes. Tregs in the skin express CD25, CTLA-4, GATA-3, and Jagged1 and efficiently proliferate with IL-2 cytokine antibody complex. However, expanding Tregs in the skin did not induce anagen in normal mice, indicating that they are necessary but not sufficient for anagen induction. Also, they fail to suppress autoreactive CD8 T cells in the skin to reverse established AA in C3H/HeJ mice. These results suggest that Treg expansion alone is not sufficient for AA treatment, and combined immunotherapy is required.

Methods for the Discovery and Identification of Small Molecules Targeting Oxidative Stress-Related Protein–Protein Interactions: An Update

The oxidative stress response pathway is one of the hotspots of current pharmaceutical research. Many proteins involved in these pathways work through protein–protein interactions (PPIs). Hence, targeting PPI to develop drugs for an oxidative stress response is a promising strategy. In recent years, small molecules targeting protein–protein interactions (PPIs), which provide efficient methods for drug discovery, are being investigated by an increasing number of studies. However, unlike the enzyme–ligand binding mode, PPIs usually exhibit large and dynamic binding interfaces, which raise additional challenges for the discovery and optimization of small molecules and for the biochemical techniques used to screen compounds and study structure–activity relationships (SARs). Currently, multiple types of PPIs have been clustered into different classes, which make it difficult to design stationary methods for small molecules. Deficient experimental methods are plaguing medicinal chemists and are becoming a major challenge in the discovery of PPI inhibitors. In this review, we present current methods that are specifically used in the discovery and identification of small molecules that target oxidative stress-related PPIs, including proximity-based, affinity-based, competition-based, structure-guided, and function-based methods. Our aim is to introduce feasible methods and their characteristics that are implemented in the discovery of small molecules for different types of PPIs. For each of these methods, we highlight successful examples of PPI inhibitors associated with oxidative stress to illustrate the strategies and provide insights for further design.

How does a small molecule bind at a cryptic binding site?

Protein-protein interactions (PPIs) are ubiquitous biomolecular processes that are central to virtually all aspects of cellular function. Identifying small molecules that modulate specific disease-related PPIs is a strategy with enormous promise for drug discovery. The design of drugs to disrupt PPIs is challenging, however, because many potential drug-binding sites at PPI interfaces are “cryptic”: When unoccupied by a ligand, cryptic sites are often flat and featureless, and thus not readily recognizable in crystal structures, with the geometric and chemical characteristics of typical small-molecule binding sites only emerging upon ligand binding. The rational design of small molecules to inhibit specific PPIs would benefit from a better understanding of how such molecules bind at PPI interfaces. To this end, we have conducted unbiased, all-atom MD simulations of the binding of four small-molecule inhibitors (SP4206 and three SP4206 analogs) to interleukin 2 (IL2)—which performs its function by forming a PPI with its receptor—without incorporating any prior structural information about the ligands’ binding. In multiple binding events, a small molecule settled into a stable binding pose at the PPI interface of IL2, resulting in a protein–small-molecule binding site and pose virtually identical to that observed in an existing crystal structure of the IL2-SP4206 complex. Binding of the small molecule stabilized the IL2 binding groove, which when the small molecule was not bound emerged only transiently and incompletely. Moreover, free energy perturbation (FEP) calculations successfully distinguished between the native and non-native IL2–small-molecule binding poses found in the simulations, suggesting that binding simulations in combination with FEP may provide an effective tool for identifying cryptic binding sites and determining the binding poses of small molecules designed to disrupt PPI interfaces by binding to such sites.

Small-molecule drugs typically function by binding to and modulating the biological activity of their protein targets. Drug-binding sites resemble pockets or grooves on the surface of the target protein, and are generally present even when the drug is not bound. In the case of “cryptic” binding sites, however, the pocket or groove only takes shape during the drug-binding process, prior to which the geometric features of a typical binding site are absent. Cryptic sites commonly occur at protein-protein interfaces, for example, so targeting such sites could facilitate the design of drugs capable of modulating specific protein-protein interactions—an approach with great therapeutic potential. In practice, targeting cryptic sites is typically difficult, in part because much less is known about how small molecules bind to cryptic sites than to conventional sites. In the work reported here, we used molecular dynamics simulations to study the process of a drug binding at a cryptic binding site, and showed that simulations are capable of predicting the location and geometry of a drug binding. The improved understanding of how small molecules bind at cryptic sites afforded by approaches like the one presented here could aid the rational design of small molecules that target such sites.

Engineering interferons and interleukins for cancer immunotherapy

Cytokines are a class of potent immunoregulatory proteins that are secreted in response to various stimuli and act locally to regulate many aspects of human physiology and disease. Cytokines play important roles in cancer initiation, progression, and elimination, and thus, there is a long clinical history associated with the use of recombinant cytokines to treat cancer. However, the use of cytokines as therapeutics has been limited by cytokine pleiotropy, complex biology, poor drug-like properties, and severe dose-limiting toxicities. Nevertheless, cytokines are crucial mediators of innate and adaptive antitumor immunity and have the potential to enhance immunotherapeutic approaches to treat cancer. Development of immune checkpoint inhibitors and combination immunotherapies has reinvigorated interest in cytokines as therapeutics, and a variety of engineering approaches are emerging to improve the safety and effectiveness of cytokine immunotherapy. In this review we highlight recent advances in cytokine biology and engineering for cancer immunotherapy.

Computational Simulations Highlight the IL2Rα Binding Potential of Polyphenol Stilbenes from Fenugreek

Widely used in global households, fenugreek is well known for its culinary and medicinal uses. The various reported medicinal properties of fenugreek are by virtue of the different natural phytochemicals present in it. Regarded as a promising target, interleukin 2 receptor subunit alpha (IL2Rα) has been shown to influence immune responses. In the present research, using in silico techniques, we have demonstrated the potential IL2Rα binding properties of three polyphenol stilbenes (desoxyrhaponticin, rhaponticin, rhapontigenin) from fenugreek. As the first step, molecular docking was performed to assess the binding potential of the fenugreek phytochemicals with IL2Rα. All three phytochemicals demonstrated interactions with active site residues. To confirm the reliability of our molecular docking results, 100 ns molecular dynamics simulations studies were undertaken. As discerned by the RMSD and RMSF analyses, IL2Rα in complex with the desoxyrhaponticin, rhaponticin, and rhapontigenin indicated stability. The RMSD analysis of the phytochemicals alone also demonstrated no significant structural changes. Based on the stable molecular interactions and comparatively slightly better MM/PBSA binding free energy, rhaponticin seems promising. Additionally, ADMET analysis performed for the stilbenes indicated that all of them obey the ADMET rules. Our computational study thus supports further in vitro IL2Rα binding studies on these stilbenes, especially rhaponticin.

Engineering T cell memory for antitumor immunity

Cancer therapy with the T cell growth factor interleukin (IL)-2 is limited by low response rates and toxicity. Multiple protein engineering strategies have attempted to improve IL-2 therapy, typically through enhanced IL-2 receptor (IL-2R) binding. Intriguingly, Mo et al. show that an IL-2R partial agonist may dramatically improve IL-2 responses by altering T cell differentiation.

Implications of a 'Third Signal' in NK Cells

Innate and adaptive immune systems are evolutionarily divergent. Primary signaling in T and B cells depends on somatically rearranged clonotypic receptors. In contrast, NK cells use germline-encoded non-clonotypic receptors such as NCRs, NKG2D, and Ly49H. Proliferation and effector functions of T and B cells are dictated by unique peptide epitopes presented on MHC or soluble humoral antigens. However, in NK cells, the primary signals are mediated by self or viral proteins. Secondary signaling mediated by various cytokines is involved in metabolic reprogramming, proliferation, terminal maturation, or memory formation in both innate and adaptive lymphocytes. The family of common gamma (γc) cytokine receptors, including IL-2Rα/β/γ, IL-7Rα/γ, IL-15Rα/β/γ, and IL-21Rα/γ are the prime examples of these secondary signals. A distinct set of cytokine receptors mediate a ‘third’ set of signaling. These include IL-12Rβ1/β2, IL-18Rα/β, IL-23R, IL-27R (WSX-1/gp130), IL-35R (IL-12Rβ2/gp130), and IL-39R (IL-23Rα/gp130) that can prime, activate, and mediate effector functions in lymphocytes. The existence of the ‘third’ signal is known in both innate and adaptive lymphocytes. However, the necessity, context, and functional relevance of this ‘third signal’ in NK cells are elusive. Here, we define the current paradigm of the ‘third’ signal in NK cells and enumerate its clinical implications.

A bispecific antibody agonist of the IL-2 heterodimeric receptor preferentially promotes in vivo expansion of CD8 and NK cells

The use of recombinant interleukin-2 (IL-2) as a therapeutic protein has been limited by significant toxicities despite its demonstrated ability to induce durable tumor-regression in cancer patients. The adverse events and limited efficacy of IL-2 treatment are due to the preferential binding of IL-2 to cells that express the high-affinity, trimeric receptor, IL-2Rαβγ such as endothelial cells and T-regulatory cells, respectively. Here, we describe a novel bispecific heavy-chain only antibody which binds to and activates signaling through the heterodimeric IL-2Rβγ receptor complex that is expressed on resting T-cells and NK cells. By avoiding binding to IL-2Rα, this molecule circumvents the preferential T-reg activation of native IL-2, while maintaining the robust stimulatory effects on T-cells and NK-cells in vitro. In vivo studies in both mice and cynomolgus monkeys confirm the molecule's in vivo biological activity, extended pharmacodynamics due to the Fc portion of the molecule, and enhanced safety profile. Together, these results demonstrate that the bispecific antibody is a safe and effective IL-2R agonist that harnesses the benefits of the IL-2 signaling pathway as a potential anti-cancer therapy.

The Potential of Harnessing IL-2-Mediated Immunosuppression to Prevent Pathogenic B Cell Responses

Immunosuppressive drugs can partially control Antibody (Ab)-dependent pathology. However, these therapeutic regimens must be maintained for the patient's lifetime, which is often associated with severe side effects. As research advances, our understanding of the cellular and molecular mechanisms underlying the development and maintenance of auto-reactive B cell responses has significantly advanced. As a result, novel immunotherapies aimed to restore immune tolerance and prevent disease progression in autoimmune patients are underway. In this regard, encouraging results from clinical and preclinical studies demonstrate that subcutaneous administration of low-doses of recombinant Interleukin-2 (r-IL2) has potent immunosuppressive effects in patients with autoimmune pathologies. Although the exact mechanism by which IL-2 induces immunosuppression remains unclear, the clinical benefits of the current IL-2-based immunotherapies are attributed to its effect on bolstering T regulatory (Treg) cells, which are known to suppress overactive immune responses. In addition to Tregs, however, rIL-2 also directly prevent the T follicular helper cells (Tfh), T helper 17 cells (Th17), and Double Negative (DN) T cell responses, which play critical roles in the development of autoimmune disorders and have the ability to help pathogenic B cells. Here we discuss the broader effects of rIL-2 immunotherapy and the potential of combining rIL-2 with other cytokine-based therapies to more efficiently target Tfh cells, Th17, and DN T cells and subsequently inhibit auto-antibody (ab) production in autoimmune patients.

Structural insights into the co-evolution of IL-2 and its private receptor in fish

Interleukin (IL) -2, a member of the four α-helical cytokine family, has broad regulatory roles in mediating vertebrate immune response. In mammals, IL-2 and IL-15 share a common evolutionary origin and possess overlapping but distinct functions. IL-2 and IL-15 bind to distinct private receptors for signaling. However, fish appear to possess a single IL-15Rα like gene whilst lack additional gene(s) coding for IL-2Rα. Whether the IL-2 and IL-15 interact with the same receptor in fish and how their functions and receptors have evolved are not fully understood. In this study, homologues of IL-2 and IL-2/15Rα were sequenced from a teleost species, grass carp (Ctenopharyngodon idella), and the crystal structure of IL-2 was determined. The grass carp IL-2 (termed CiIL-2) displayed a classical cytokine structure consisting of four helical bundles which shares significant similarity with human IL-15. The key amino acids involved in the interface interaction of IL-2/15 and their receptors are well conserved. The CiIL-2 has been shown to bind the IL-2/15Rα like homologue with an affinity of 2.45 nM, supporting the notion that fish IL-2 and IL-15 may share a single common private receptor for exerting functions. Syntenic analysis suggests that the IL-2Rα of tetrapods has evolved from an IL-15Rα like homologue, in which a second sushi domain (D2) in the extracellular region has been duplicated to facilitate the specific interaction with IL-2. The CiIL-2 was predominantly expressed in lymphocyte-rich tissues such as the spleen, kidney and thymus, and could be induced by PHA and IL-21. In vivo challenge with grass carp reovirus and Flavobacterium columnare also resulted in upregulation of CiIL-2 expression. The recombinant CiIL-2 was shown to activate expression of STAT5b, IL-1β, IL-22 and IFN-γ, and to promote the proliferation of the primary cell cultures from head kidney leucocytes. Our results shed lights into the co-evolution of IL-2 and its private receptor, and the functional divergence of IL-2 and IL-15 during evolution.

Computational study for suppression of CD25/IL-2 interaction

Cancer recurrence presents a huge challenge in cancer patient management. Immune escape is a key mechanism of cancer progression and metastatic dissemination. CD25 is expressed in regulatory T (Treg) cells including tumor-infiltrating Treg cells (TI-Tregs). These cells specially activate and reinforce immune escape mechanism of cancers. The suppression of CD25/IL-2 interaction would be useful against Treg cells activation and ultimately immune escape of cancer. Here, software, web servers and databases were used, at which in silico designed small interfering RNAs (siRNAs), de novo designed peptides and virtual screened small molecules against CD25 were introduced for the prospect of eliminating cancer immune escape and obtaining successful treatment. We obtained siRNAs with low off-target effects. Further, small molecules based on the binding homology search in ligand and receptor similarity were introduced. Finally, the critical amino acids on CD25 were targeted by a de novo designed peptide with disulfide bond. Hence we introduced computational-based antagonists to lay a foundation for further in vitro and in vivo studies.

Modulation of CD4 T Cell Response According to Tumor Cytokine Microenvironment

The advancement of knowledge on tumor biology over the past decades has demonstrated a close link between tumor cells and cells of the immune system. In this context, cytokines have a major role because they act as intermediaries in the communication into the tumor bed. Cytokines play an important role in the homeostasis of innate and adaptive immunity. In particular, they participate in the differentiation of CD4 T lymphocytes. These cells play essential functions in the anti-tumor immune response but can also be corrupted by tumors. The differentiation of naïve CD4 T cells depends on the cytokine environment in which they are activated. Additionally, at the tumor site, their activity can also be modulated according to the cytokines of the tumor microenvironment. Thus, polarized CD4 T lymphocytes can see their phenotype evolve, demonstrating functional plasticity. Knowledge of the impact of these cytokines on the functions of CD4 T cells is currently a source of innovation, for therapeutic purposes. In this review, we discuss the impact of the major cytokines present in tumors on CD4 T cells. In addition, we summarize the main therapeutic strategies that can modulate the CD4 response through their impact on cytokine production.

Transcriptional Regulation of NK Cell Development by mTOR Complexes

The mechanistic target of Rapamycin (mTOR) is essential for multiple cellular processes. The unique roles of mTOR complex 1 (mTORC1) or mTOR2 in regulating immune functions are emerging. NK cells are the major lymphocyte subset of innate immunity, and their development and effector functions require metabolic reprogramming. Recent studies demonstrate that in NK cells, conditionally disrupting the formation of mTORC1 or mTOR complex 2 (mTORC2) alters their development significantly. Transcriptomic profiling of NK cells at the single-cell level demonstrates that mTORC1 was critical for the early developmental progression, while mTORC2 regulated the terminal maturation. In this review, we summarize the essential roles of mTOR complexes in NK development and functions.

Structural Understanding of Interleukin 6 Family Cytokine Signaling and Targeted Therapies: Focus on Interleukin 11

Cytokines are small signaling proteins that have central roles in inflammation and cell survival. In the half-century since the discovery of the first cytokines, the interferons, over fifty cytokines have been identified. Amongst these is interleukin (IL)-6, the first and prototypical member of the IL-6 family of cytokines, nearly all of which utilize the common signaling receptor, gp130. In the last decade, there have been numerous advances in our understanding of the structural mechanisms of IL-6 family signaling, particularly for IL-6 itself. However, our understanding of the detailed structural mechanisms underlying signaling by most IL-6 family members remains limited. With the emergence of new roles for IL-6 family cytokines in disease and, in particular, roles of IL-11 in cardiovascular disease, lung disease, and cancer, there is an emerging need to develop therapeutics that can progress to clinical use. Here we outline our current knowledge of the structural mechanism of signaling by the IL-6 family of cytokines. We discuss how this knowledge allows us to understand the mechanism of action of currently available inhibitors targeting IL-6 family cytokine signaling, and most importantly how it allows for improved opportunities to pharmacologically disrupt cytokine signaling. We focus specifically on the need to develop and understand inhibitors that disrupt IL-11 signaling.

IL-15Rα membrane anchorage in either cis or trans is required for stabilization of IL-15 and optimal signaling

Interleukin (IL)-15 plays an important role in the communication between immune cells. It delivers its signal through different modes involving three receptor chains: IL-15Rα, IL-2Rβ and IL-2Rγc. The combination of the different chains result in the formation of IL-15Rα/IL-2Rβ/γc trimeric or IL-2Rβ/γc dimeric receptors. In this study, we have investigated the role of the IL-15Rα chain in stabilizing the cytokine in the IL-2Rβ/γc dimeric receptor. By analyzing the key amino acid residues of IL-15 facing IL-2Rβ, we provide evidence of differential interfaces in the presence or in the absence of membrane-anchored IL-15Rα. Moreover, we found that the anchorage of IL-15Rα to the cell surface regardless its mode of presentation - i.e. cis or trans - is crucial for complete signaling. These observations show how the cells can finely modulate the intensity of cytokine signaling through the quality and the level of expression of the receptor chains.

The cytokine network involved in the host immune response to periodontitis

Periodontitis is an inflammatory disease involving the destruction of both soft and hard tissue in the periodontal region. Although dysbiosis of the local microbial community initiates local inflammation, over-activation of the host immune response directly activates osteoclastic activity and alveolar bone loss. Many studies have reported on the cytokine network involved in periodontitis and its crucial and pleiotropic effect on the recruitment of specific immunocytes, control of pathobionts and induction or suppression of osteoclastic activity. Nonetheless, particularities in the stimulation of pathogens in the oral cavity that lead to the specific and complex periodontal cytokine network are far from clarified. Thus, in this review, we begin with an up-to-date aetiological hypothesis of periodontal disease and summarize the roles of cytokines in the host immune response. In addition, we also summarize the latest cytokine-related therapeutic measures for periodontal disease.

TCB2, a new anti-human interleukin-2 antibody, facilitates heterodimeric IL-2 receptor signaling and improves anti-tumor immunity

IL-2 is a pleiotropic cytokine that plays an essential role in the survival, expansion, and function of CD8 T cells, regulatory T cells (Tregs), and natural killer (NK) cells. Previous studies showed that binding IL-2 with an anti-IL-2 monoclonal antibody (mAb) with a particular specificity could block its interaction with IL-2Rα, which is mainly expressed on Tregs. This selectivity can enhance the anti-tumor effects of IL-2 by activating CD8 T and NK cells, while disfavoring Treg stimulation. Based on this, we newly developed a series of anti-human IL-2 (hIL-2) mAbs (TCB1-3) that selectively stimulate CD8 T and NK cells without overtly activating Tregs. Among them, the hIL-2/TCB2 complex (hIL-2/TCB2c) exerted the best efficacy by inducing a prodigious expansion of host memory phenotype (MP) CD8 T (60-fold) and NK cells (18-fold) with less efficient Treg proliferation (5-fold). As a result, there was an average eightfold increase in the ratio of MP CD8 to Tregs. Accordingly, hIL-2/TCB2c strongly inhibited the growth of B16F10, MC38, and CT26 tumors. More remarkably, hIL-2/TCB2c showed synergy with checkpoint inhibitors such as anti-CTLA-4 or PD1 antibodies, and resulted in almost complete regression of implanted tumors and resistance to secondary tumor challenge. For direct clinical use, we generated a humanized form of TCB2 that had equal immunostimulatory and anti-tumor efficacy as a murine one. Collectively, these results show that TCB2 can provide a potent immunotherapeutic modality either alone or together with checkpoint inhibitors in cancer patients.

Expression and purification of soluble and functional fusion protein DAB389 IL-2 into the E. coli strain Rosetta-gami (DE3)

DAB₃₈₉ IL-2 (Denileukin diftitox) is considered an immunotoxin, and it is the first immunotoxin approved by Food and Drug Administration. It is used for the treatment of a cutaneous form of T-cell lymphoma. This fusion protein has two disulfide bonds in its structure that play an essential role in toxicity and functionality of the immunotoxin. Escherichia coli (E. coli) strain BL21 (DE3) is not capable of making disulfide bonds in its reductive cytoplasm, but the E. coli strain Rosetta-gami (DE3) is a proper strain for the correct expression of the protein due to mutations in glutaredoxin reductase and thioredoxin reductase. In this study, a pET21a vector with the His6-tag fused at the N-terminus of DAB₃₈₉ IL-2 was used to express the soluble immunotoxin in E. coli Rosetta-gami (DE3). After the purification of the soluble protein by two-step column chromatographies, the structure of DAB₃₈₉ IL-2 was analyzed using the Native-PAGE and circular dichroism methods. In the following, the nuclease activity of soluble DAB₃₈₉ IL-2 and its cytotoxicity activity were determined. It is concluded that the soluble recombinant protein expressed in the E. coli Rosetta-gami (DE3) has an intact structure and also functional; hence, this form of immunotoxin could be competitive with its commercial counterparts.

Integral membrane protein expression of human CD25 on the cell surface of HEK293 cell line: the available cellular model of CD25 positive to facilitate in vitro developing assays

Typically, CD25 is expressed on the cellular surface of regulatory T (Treg) cells. These cells are significant in regulating the self-tolerance and also preventing the immune system from attacking a person's own tissues and cells. They promote the cancer progression by playing an important role in evading the immune system. Thus, the experimental procedures was aimed to clone and express human CD25 in HEK293 cell line, as the available cellular model, for the purpose of developing assays to facilitate and enhance the studies on an available CD25 positive cell. The secondary RNA structure of CD25 was evaluated by in silico analysis. Then, cDNA of human CD25 were synthesized from isolated total mRNA of cultured and stimulated PBMCs from blood donors. After cloning the cDNA of CD25 into a pcDNA3.1(+) plasmid, using the effective transfection of the recombinant pcDNA3.1(+) in HEK293, qRT-PCR and flow cytometry methods were used to quantitatively evaluate CD25 transcripts and protein level. There was a 4.8 fold increase in transcripts and a 76.2% increase in protein levels of CD25 when comparing the transfected and control cell lines. The genetically engineered HEK293 cell line expressing Treg cell surface marker of CD25 was introduced in this study for the first time. This cell line can be used to overcome the problematic issues for studying Treg cells including low population of Tregs in peripheral blood, low recovery methods for Treg isolation, time-consuming and non-cost benefit methods in the conditions of in vitro cell culture experiments for the studies focused on the binding of IL-2 to CD25.

The γc Family of Cytokines: Basic Biology to Therapeutic Ramifications

The common cytokine receptor γ chain, γ_c, is a component of the receptors for interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21. Mutation of the gene encoding γ_c results in X-linked severe combined immunodeficiency in humans, and γ_c family cytokines collectively regulate development, proliferation, survival, and differentiation of immune cells. Here, we review the basic biology of these cytokines, highlighting mechanisms of signaling and gene regulation that have provided insights for immunodeficiency, autoimmunity, allergic diseases, and cancer. Moreover, we discuss how studies of this family stimulated the development of JAK3 inhibitors and present an overview of current strategies targeting these pathways in the clinic, including novel antibodies, antagonists, and partial agonists. The diverse roles of these cytokines on a range of immune cells have important therapeutic implications.

Mechanisms of action of low-dose IL-2 restoration therapies in SLE

Interleukin-2 (IL-2) shortage is a hallmark of Systemic Lupus Erythematosus (SLE). Importantly, clinical and preclinical studies demonstrate the potential clinical benefits of IL-2-based restoration therapies for the treatment of SLE. Here we discuss the immunological consequences of IL-2 deficiency in SLE patients and the mechanisms underlying the therapeutic effects of low-dose IL-2 regimens.

Gelatinase B/matrix metalloproteinase-9 and other neutrophil proteases switch off interleukin-2 activity

Interleukin 2 (IL-2) is critical for T cell development and homeostasis, being a key regulator of adaptive immune responses in autoimmunity, hypersensitivity reactions and cancer. Therefore, its abundance in serum and peripheral tissues needs tight control. Here, we described a new mechanism contributing to the immunobiology of IL-2. We demonstrated, both in biochemical and cell-based assays, that IL-2 is subject to proteolytic processing by neutrophil matrix metalloproteinase-9 (MMP-9). IL-2 fragments produced after cleavage by MMP-9 remained linked by a disulfide bond and displayed a reduced affinity for all IL-2 receptor subunits and a distinct pattern and timing of signal transduction. Stimulation of IL-2-dependent cells, including murine CTLL-2 and primary human regulatory T cells, with cleaved IL-2 resulted in significantly decreased proliferation. The concerted action of neutrophil proteases destroyed IL-2. Our data suggest that in neutrophil-rich inflammatory conditions in vivo, neutrophil MMP-9 may reduce the abundance of signaling-competent IL-2 and generate a fragment that competes with IL-2 for receptor binding, whereas the combined activity of granulocyte proteases has the potential to degrade and thus eliminate bioavailable IL-2.

A Rapid Colorimetric Sensor for Soluble Interleukin-2 Receptor α, Based on Aptamer-Adsorbed AuNP

The soluble interleukin-2 receptor α (sIL-2Rα) is a broad indicator of clinical disease activity in various inflammatory diseases. Here we have developed, for the first time, a rapid, washing-free colorimetric aptasensor based on a sIL-2Rα aptamer (K_d =1.33 nm). The aptasensor was fabricated with Au nanoparticles (AuNPs) adsorbing sIL-2Rα aptamers. On addition of sIL-2Rα, the aptamers become desorbed from the AuNPs, and this in turn weakens the absorption corresponding to AuNP-catalyzed oxidation of ortho-phenylenediamine (oPD) with H₂ O₂ . The aptasensor was characterized by TEM imaging, ζ potential measurements, dynamic light scattering (DLS) analysis, and UV/Vis spectrometry, followed by further optimization. The fabricated sensor exhibited great analytical performance, with a linear range of 1 to 100 nm and a detection limit of 1 nm both in buffer and in spiked human serum within 25 min. Other proteins, such as bovine serum albumin (BSA), IL-17Rα, IL-5Rα, IL-13Rα₂ , and CD166, showed negligible effects on the aptasensor. Thanks to the great advantages of the aptamers and AuNPs, this aptasensor provides a rapid, simple, and inexpensive process that might offer insights into various diagnostic applications of sIL-2Rα.

Daclizumab Therapy for Multiple Sclerosis

Daclizumab is a humanized monoclonal antibody that prevents formation of high-affinity interleukin (IL)-2 receptor (IL-2R). Because activated T cells up-regulate high-affinity IL-2R and IL-2 is used to grow activated T cells in vitro, daclizumab was envisioned to selectively inhibit activated T cells. However, the mechanism of action (MOA) of daclizumab is surprisingly broad and it includes many unanticipated effects on innate immunity. Specifically, daclizumab modulates the development of innate lymphoid cells, leading to expansion of immunoregulatory CD56^bright natural killer (NK) cells. Activated CD56^bright NK cells migrate to the intrathecal compartment in multiple sclerosis (MS) and regulate autoreactive T cells via cytotoxicity. Finally, daclizumab also restricts initial steps of T-cell activation by blocking trans-presentation of IL-2 by dendritic cells to antigen-specific T cells. In conclusion, daclizumab has complex immunomodulatory effects with resultant inhibition of central nervous system inflammation in MS.

Structure and Function of an Inflammatory Cytokine, Interleukin-2, Analyzed Using the Bioinformatic Approach

The inflammatory cytokine, interleukin-2 (IL-2), is an important regulator of cellular functions. This relatively less studied member of the interleukin protein family is responsible for multiple immuno-modulatory and immuno-stimulatory tasks, like T cell activation, triggering of natural killer cells, inflammation, as well as proliferation and progression of autoimmune diseases and cancers. In this communication we report the temporally variant structural aspects of the IL-2 ligand and its receptor interfaces, based on the available crystal structures. The intended goal of this effort is to generate simulated results that could potentially aid the designs of novel structure based therapeutics.

Alternative Splicing Rescues Loss of Common Gamma Chain Function and Results in IL-21R-like Deficiency

Inborn errors in interleukin 2 receptor, gamma (IL2RG) perturb signaling of the common gamma chain family cytokines and cause severe combined immunodeficiency (SCID). Here, we report two brothers suffering from chronic cryptosporidiosis, severe diarrhea, and cholangitis. Pan T, B, and NK cell numbers were normal, but immunophenotyping revealed defective B cell differentiation. Using whole exome sequencing, we identified a base pair deletion in the first exon of IL2RG predicted to cause a frameshift and premature stop. However, flow cytometry revealed normal surface expression of the IL-2Rγ chain. While IL-2, IL-7, and IL-15 signaling showed only mild defects of STAT5 phosphorylation in response to the respective cytokines, IL-4- and IL-21-induced phosphorylation of STAT3 and STAT6 was markedly reduced. Examination of RNA isoforms detected alternative splicing downstream of IL2RG exon 1 in both patients resulting in resolution of the predicted frameshift and 16 mutated amino acids. In silico modeling suggested that the IL-2Rγ mutation reduces the stabilization of IL-4 and IL-21 cytokine binding by affecting the N-terminal domain of the IL-2Rγ. Thus, our study shows that IL2RG deficiency can be associated with differential signaling defects. Confounding effects of alternative splicing may partially rescue genetic defects and should be considered in patients with inborn errors of immunity.

Revisiting IL-2: Biology and therapeutic prospects

Interleukin-2 (IL-2), the first cytokine that was molecularly cloned, was shown to be a T cell growth factor essential for the proliferation of T cells and the generation of effector and memory cells. On the basis of this activity, the earliest therapeutic application of IL-2 was to boost immune responses in cancer patients. Therefore, it was a surprise that genetic deletion of the cytokine or its receptor led not only to the expected immune deficiency but also to systemic autoimmunity and lymphoproliferation. Subsequent studies established that IL-2 is essential for the maintenance of Foxp3⁺ regulatory T cells (T_reg cells), and in its absence, there is a profound deficiency of T_reg cells and resulting autoimmunity. We now know that IL-2 promotes the generation, survival, and functional activity of T_reg cells and thus has dual and opposing functions: maintaining T_reg cells to control immune responses and stimulating conventional T cells to promote immune responses. It is well documented that certain IL-2 conformations result in selective targeting of T_reg cells by increasing reliance on CD25 binding while compromising CD122 binding. Recent therapeutic strategies have emerged to use IL-2, monoclonal antibodies to IL-2, or IL-2 variants to boost T_reg cell numbers and function to treat autoimmune diseases while dealing with the continuing challenges to minimize the generation of effector and memory cells, natural killer cells, and other innate lymphoid populations.

The challenges and molecular approaches surrounding interleukin-2-based therapeutics in cancer

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IL2-based cancer therapies are limited by their toxicity and pleiotropy.

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Current engineering approaches target IL2 half-life and cell/receptor specificity.

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IL2 may enhance the efficacy of checkpoint inhibitors and CAR-T-based therapies.

Interleukin-2 has had a long history as a promising cancer therapeutic, being capable of eliciting complete and durable remissions in patients with metastatic renal cell carcinoma and metastatic melanoma. Despite high toxicity and efficacy limited to only certain patient subpopulations and cancer types, the prospective use of novel, engineered IL2 formats in combination with the presently expanding repertoire of immuno-oncological targets remains very encouraging. This is possible due to the significant research efforts in the IL2 field that have yielded critical structural and biological insights that have made IL2 more effective and more broadly applicable in the clinic. In this review, we discuss some of the molecular approaches that have been used to further improve IL2 therapy for cancer.

The tertiary structure of γc cytokines dictates receptor sharing

The γc family of cytokines comprising interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15 and IL-2 is an important group of 4-helix bundle cytokines that signals through receptors incorporating the common gamma chain (γc). These cytokines are involved in lymphocyte biology and their specific functions are contingent on binding to cognate receptor chains. Here, we examined the structural relationships between γc cytokines, aiming to understand the basis for receptor chain usage and sharing. To that end, we obtained tertiary structures of human and mouse γc cytokines plus two other related cytokines, IL-13 and TSLP, which share receptors with IL-4 and IL-7, respectively. Subsequently, we compared the cytokine 3D-structures introducing a structural similarity score that grouped γc cytokines in a manner that mirrored the relationships dictated by receptor sharing. Unlike previously thought, we identified that IL-9 is more closely related to IL-2 and IL-15 than to IL-7, which is actually the most distant member of the γc family of cytokines. Moreover, we found that all the members of the γc family of cytokines share the topology of short-chain 4-helix bundle cytokines but IL-7 that with TSLP has the topology of long-chain 4-helix bundle cytokines. We also carried out Maximun-Likehood and Bayesian phylogenetic analyses that supported these results at the amino acid sequence level. Overall, our findings are of paramount relevance to understand receptor sharing among γc cytokines and can lead to the discovery of new cytokine receptor partners.