ICOS Human
Description
Introduction to ICOS Human
ICOS (Inducible T-cell Co-Stimulator), also known as CD278, is a critical immune checkpoint protein belonging to the CD28/B7 family. It is expressed on activated T cells and plays a pivotal role in regulating adaptive immune responses, including T-cell activation, cytokine production, and germinal center (GC) reactions. ICOS signaling is essential for maintaining immune homeostasis, and its dysregulation is implicated in autoimmune diseases, cancer, and inflammatory disorders.
Functional Roles in Immunity
ICOS regulates multiple immune processes:
T-Cell Activation and Cytokine Production
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Co-stimulation: ICOS enhances T-cell proliferation and survival by inducing IL-2, IL-4, IL-5, IL-10, IL-17, and IFN-γ .
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Th2/Th17 Balance: Promotes Th2 (IL-4, IL-5) and Th17 (IL-17, IL-21) responses while suppressing Th1 (IFN-γ) in some contexts .
Germinal Center and Tfh Cell Development
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Tfh Cell Differentiation: ICOS-ICOS-L interactions drive follicular helper T (Tfh) cell migration into germinal centers, enabling B-cell affinity maturation .
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Antibody Class Switching: Required for IgG1 and IgE production in response to T-dependent antigens .
Regulatory T-Cell Function
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IL-10 Production: ICOS co-stimulation induces regulatory T cells (Tregs) to secrete IL-10, modulating peripheral tolerance .
Autoimmunity and Mucosal Tolerance
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Oral/Nasal Tolerance: ICOS is essential for mucosal tolerance (e.g., oral MOG peptide administration) but not high-dose tolerance .
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Th17-Driven Autoimmunity: ICOS signaling promotes TH17 cell differentiation and IL-17 production, implicated in multiple sclerosis (MS) and inflammatory bowel disease (IBD) .
Cancer Immunotherapy
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ImmunoPET Imaging: 89Zr-DFO-ICOS mAb enables non-invasive monitoring of activated T cells in tumors, predicting response to therapies like STING agonists .
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Therapeutic Targeting: Monoclonal antibodies (e.g., MSB2311) mimic ICOS-L binding, enhancing tumor-infiltrating T-cell activity .
Table 2: ICOS in Cancer and Autoimmunity
Antibody-Based Strategies
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Agonistic Antibodies: Enhance ICOS signaling to boost antitumor immunity (e.g., MSB2311) .
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Antagonistic Antibodies: Block ICOS-ICOS-L interactions to suppress autoimmune responses .
Fusion Proteins and Biologics
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ICOS-Fc Chimera: Soluble ICOS-Fc (extracellular domain fused to IgG1 Fc) binds ICOS-L, serving as a decoy receptor .
Table 3: Therapeutic Approaches Targeting ICOS
Product Specs
ICOS, short for inducible T-cell costimulatory, is a member of the CD28 family and plays a crucial role in the immune system's stimulatory pathways. As a receptor that forms homodimers, ICOS is essential for effective immune responses. It participates in vital cellular processes like cell signaling and proliferation regulation. Notably, ICOS interacts with B7-H2, an interaction critical for T-cell differentiation, T-B cell communication, and humoral immune responses. This interaction is also vital for forming germinal centers, which are crucial for generating an effective antibody response, and producing the cytokine IL-4. Furthermore, ICOS plays a significant role in inducing the production of IL-10, a cytokine known for its role in the suppressive function of regulatory T cells. ICOS, along with other co-stimulatory pathways like B7-1/B7-2-CD28/CTLA-4, provides essential secondary signals that tightly regulate the activation, suppression, and fine-tuning of T lymphocyte responses. While ICOS stimulates the production of both Th1 and Th2 cytokines, it exhibits a specific role in generating Th2 cells, highlighting its multifaceted role in immune regulation.
Produced using Sf9 insect cells and baculovirus expression system, the recombinant ICOS protein is a single, glycosylated polypeptide chain. It consists of 362 amino acids with a sequence spanning from amino acid 21 to 140a.a. This protein has a molecular weight of 40.8 kDa. However, it appears as a band of approximately 40-57 kDa on SDS-PAGE due to glycosylation. The ICOS protein is engineered with a 242 amino acid His tag at its C-terminus to facilitate purification. After expression, the protein undergoes rigorous purification using proprietary chromatographic methods to ensure high purity.
The provided ICOS protein solution has a concentration of 0.25mg/ml. It is formulated in a buffer containing 20mM MES (pH 5.5), 40% glycerol, 2mM DTT, 1mM EDTA, and 0.1M NaCl to maintain stability and activity.
The purity of the ICOS protein is greater than 90%, as determined by SDS-PAGE analysis, ensuring a high-quality product for research purposes.
Inducible T Cell Costimulator, Activation-Inducible Lymphocyte Immunomediatory Molecule, Inducible T-Cell Costimulator, AILIM, Inducible T-Cell Co-Stimulator, Inducible Costimulator, CD278 Antigen, CD278, CVID1.
ADPEINGSAN YEMFIFHNGG VQILCKYPDI VQQFKMQLLK GGQILCDLTK TKGSGNTVSI KSLKFCHSQL SNNSVSFFLY NLDHSHANYY FCNLSIFDPP PFKVTLTGGY LHIYESQLCC QLKLEPKSCD KTHTCPPCPA PELLGGPSVF LFPPKPKDTL MISRTPEVTC VVVDVSHEDP EVKFNWYVDG VEVHNAKTKP REEQYNSTYR VVSVLTVLHQ DWLNGKEYKC KVSNKALPAP IEKTISKAKG QPREPQVYTL PPSRDELTKN QVSLTCLVKG FYPSDIAVEW ESNGQPENNY KTTPPVLDSD GSFFLYSKLT VDKSRWQQGN VFSCSVMHEA LHNHYTQKSL SLSPGKHHHH
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Q&A
What is the molecular structure of human ICOS and how does it compare to other costimulatory molecules?
Human ICOS is a homodimeric type I transmembrane protein consisting of 199 amino acids with:
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20 amino acid signal sequence
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121 amino acid extracellular domain (Glu21-Phe141)
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23 amino acid transmembrane region
ICOS shares approximately 39% amino acid similarity with CD28 and CTLA-4, other members of the CD28 family of immune costimulatory receptors. Over amino acids 21-141, human and mouse ICOS share approximately 70% sequence identity .
Which human immune cell subsets express ICOS and under what conditions?
ICOS shows differential expression patterns across T cell subsets:
| T Cell Subset | ICOS Expression | CD28 Expression |
|---|---|---|
| Th17 (CCR4+CCR6+) | ~40% constitutive | High (constitutive) |
| Th1 (CXCR3+CCR4−CCR6−) | Minimal constitutive | High (constitutive) |
| Th2 (CCR4+CXCR3−CCR6−) | Minimal constitutive | High (constitutive) |
| Treg (CD25+CD127lo) | Constitutive | High (constitutive) |
| TFH (CXCR5+CD45RO+) | Constitutive | High (constitutive) |
ICOS is expressed on most CD45RO+ cells (memory T cells) and is upregulated within approximately 24-48 hours of activation on primed T helper cells .
How can researchers effectively detect ICOS expression on human cells?
For flow cytometric detection of ICOS on human cells:
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Activate human CD3+ peripheral blood mononuclear cells (PBMCs) with 5 μg/mL PHA for 48 hours
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Stain cells with Mouse Anti-Human ICOS PE-conjugated Monoclonal Antibody (e.g., Clone #669222, Catalog #FAB6975P)
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Include appropriate isotype controls (e.g., Catalog #IC002P) to distinguish specific binding
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Follow standard protocols for staining membrane-associated proteins
For sorting of T cell subsets expressing ICOS, researchers should:
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Use markers such as CXCR3, CCR4, CCR6, CD25, CD127, CXCR5, and CD45RO to identify specific T cell populations
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Incorporate ICOS staining to further subdivide these populations
What experimental approaches can be used to study ICOS function in human T cells?
Several methodological approaches are available:
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Comparative Costimulation: Activate sorted T cell subsets with antibodies to CD3/CD28 or CD3/ICOS beads to compare signaling outcomes
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Engineered Antigen-Presenting Cells: Use OKT3-loaded artificial APCs (aAPCs) engineered to express CD86, CD80, CD70, ICOSL, OX40L, or 4-1BBL for controlled stimulation
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Functional Readouts:
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Gene Modification: Use ICOS-deficient cells or ICOS-overexpressing cells to study gain- and loss-of-function effects
How does ICOS specifically influence human Th17 cell differentiation compared to other costimulatory molecules?
ICOS plays a unique role in human Th17 cell development that distinguishes it from CD28:
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Differential Cytokine Induction: Only ICOS costimulation reproducibly induces IL-17F secretion in human T cells cultured under Th17-polarizing conditions (IL-6, IL-1β, IL-23, neutralizing IFN-γ, and neutralizing IL-4 antibodies)
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Temporal Dynamics:
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Antagonistic Relationship: Combining ICOS and CD28 signals results in CD28 exerting a "veto effect" on IL-17A and IL-17F production, but not on IL-2, IL-10, or IL-22 secretion
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Transcription Factor Expression: ICOS-costimulated Th17 cells coexpress higher levels of both RORC2 and T-bet compared to CD28-costimulated cells, promoting IL-17A+IFN-γ+ double-producing cells
What molecular mechanisms underlie ICOS-mediated enhancement of human Th17 function?
ICOS enhances human Th17 function through several key molecular mechanisms:
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c-MAF Induction: ICOS stimulation induces higher expression of the transcription factor c-MAF compared to CD28 in both cord blood and peripheral blood human Th17 cells
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IL-21 Amplification Loop: Increased c-MAF expression leads to enhanced IL-21 production, which acts in an autocrine manner to amplify Th17 development
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Multiple Transcription Factor Regulation: ICOS induces coordinated expression of c-MAF, RORC2, and T-bet, promoting a robust and stable Th17 phenotype
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STAT5 Activation: The ICOS:ICOS-L interaction influences the activation of transcription factor STAT5, which is crucial for cytokine signaling in T cells
How does the ICOS:ICOS-L interaction regulate type 2 innate lymphoid cells (ILC2s)?
ICOS plays a crucial role in ILC2 biology:
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Expression Pattern: Both human and murine ILC2s express ICOS and ICOS-L on their surface
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Functional Requirement: The ICOS:ICOS-L interaction is essential for:
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Disease Relevance: Disruption of the ICOS:ICOS-L interaction alters ILC2 function, which has implications for allergic asthma pathogenesis
How does ICOS modulate the functionality of human macrophage subpopulations?
ICOS-L activation differentially affects M1 (pro-inflammatory) and M2 (anti-inflammatory) macrophages:
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Migration Effects: Activation of ICOSL with soluble recombinant ICOS-CH3 has opposite effects on macrophage migration:
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Control Verification: A mutant form (F119SICOS-CH3) that does not bind to ICOS has no effect under any experimental conditions, confirming specificity
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Baseline Migration Patterns: Without ICOS stimulation, M1 and M2 cells show distinct migration patterns:
How can researchers reconcile conflicting data on ICOS in Th17 development between human and mouse models?
Researchers face an apparent paradox:
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Species-Specific Effects:
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Temporal Considerations: The increased frequency of Th17 cells in ICOS-deficient mice does not persist throughout disease course, suggesting phase-specific effects
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Methodological Approach to Reconciliation:
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Use side-by-side human and murine experiments with identical protocols
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Employ conditional knockout systems to study temporal effects
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Analyze compensatory mechanisms in constitutive knockout models
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Examine effects of acute ICOS blockade versus genetic deficiency
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What experimental designs would best elucidate the complex role of ICOS in different disease states?
For robust investigation of ICOS biology:
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In Vitro Human Studies:
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Compare primary cells from healthy donors and patients with immune-mediated diseases
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Use CRISPR-Cas9 to generate ICOS-deficient human T cells for mechanistic studies
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Employ single-cell RNA sequencing to identify ICOS-responsive T cell subpopulations
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Humanized Mouse Models:
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Study human ICOS function in NSG mice reconstituted with human immune cells
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Compare effects of anti-human ICOS blocking antibodies versus genetic deficiency
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Examine tissue-specific effects in different organs
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Translational Approaches:
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Correlate ICOS expression patterns with clinical outcomes in patients
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Test ex vivo responses to ICOS manipulation in patient-derived cells
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Develop biomarkers predictive of response to ICOS-targeted therapies
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How might researchers optimize the balance between ICOS and CD28 costimulation for therapeutic T cell expansion?
Based on the antagonistic relationship between ICOS and CD28 in Th17 development , researchers should consider:
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Sequential Stimulation Strategy:
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Initial CD28 stimulation for robust expansion
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Later switch to ICOS stimulation for functional maturation
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Empirical determination of optimal timing for signal switching
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Cytokine Modulation:
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Combine ICOS stimulation with cytokines that enhance desired functional attributes
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Test different IL-21 concentrations to potentially bypass the need for ICOS-induced IL-21
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Comparative Functional Assessment:
Parameter CD28 Costimulation ICOS Costimulation Combined Initial expansion +++ + ++ Long-term IL-17 production + +++ + IL-21 secretion + +++ ++ RORC2 expression + +++ ++ T-bet expression ++ +++ ++ IL-17A+IFN-γ+ cells + +++ + Tumor regression capacity ++ +++ ++ -
Engineered T Cells: Develop T cells with inducible or tunable ICOS signaling to allow temporal control of costimulation
What are the potential clinical applications of targeting the ICOS:ICOS-L pathway in human diseases?
The ICOS:ICOS-L pathway offers several therapeutic opportunities:
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Autoimmune Diseases:
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Cancer Immunotherapy:
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Inflammatory Disorders:
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Allergic Conditions:
What are the most promising research directions for understanding ICOS biology in human health and disease?
Future research should focus on:
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Single-Cell Analysis: Apply single-cell technologies to understand heterogeneity in ICOS expression and responsiveness within immune cell populations
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Structural Biology: Determine crystal structures of human ICOS:ICOS-L complexes to guide development of selective modulators
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Systems Biology: Integrate ICOS signaling with broader immune regulatory networks to predict context-dependent effects
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Biomarker Development: Identify biomarkers predictive of response to ICOS-targeted therapies in different disease states
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Tissue-Specific Effects: Examine ICOS function in different tissue microenvironments, particularly at barrier surfaces and in tumor environments
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Developmental Biology: Investigate the role of ICOS:ICOS-L interactions in thymic development and peripheral tolerance induction
Product Science Overview
Inducible T Cell Costimulator (ICOS), also known as CD278, is a costimulatory receptor that plays a crucial role in the regulation of immune responses. It belongs to the CD28 immunoglobulin (Ig) receptor superfamily, which includes other important receptors such as CTLA-4 and PD-1 . Unlike CD28, ICOS expression is low on naïve T cells but is upregulated upon T-cell receptor (TCR) stimulation .
ICOS is a transmembrane protein that is primarily expressed on activated T cells. It interacts with its ligand, ICOSL (Inducible T Cell Costimulator Ligand), which is a B7-related transmembrane glycoprotein expressed on various cell types including B cells, dendritic cells, monocytes, endothelial cells, and several types of tumor cells . The binding of ICOS to ICOSL delivers a positive costimulatory signal that is essential for optimal T cell function .
The primary function of ICOS is to enhance T cell responses. It plays a critical role in the activation and differentiation of T cells, particularly in the context of immune responses against infections and tumors. ICOS signaling is involved in the production of cytokines, the proliferation of T cells, and the formation of memory T cells . Additionally, ICOS is important for the development and function of follicular helper T cells (Tfh), which are essential for the formation of germinal centers and the production of high-affinity antibodies .
Given its pivotal role in immune regulation, ICOS has been explored as a therapeutic target for various diseases, including cancer and autoimmune disorders. Recent studies have shown that activating ICOS can yield antitumor activity, both alone and in combination with other immunotherapies such as PD-1 blockade . For instance, the use of an anti-ICOS monoclonal antibody (mAb) called feladilimab has demonstrated promising results in preclinical models and early-phase clinical trials . This approach aims to stimulate the growth of antitumor reactive T cells and enhance the overall immune response against tumors .
