Inducible costimulator (ICOS) potentiates TCR-induced calcium flux by augmenting PLCγ1 activation and actin remodeling

A systems and computational biology perspective on advancing CAR therapy

In the recent decades, chimeric antigen receptor (CAR) therapy signaled a new revolutionary approach to cancer treatment. This method seeks to engineer immune cells expressing an artificially designed receptor, which would endue those cells with the ability to recognize and eliminate tumor cells. While some CAR therapies received FDA approval and others are subject to clinical trials, many aspects of their workings remain elusive. Techniques of systems and computational biology have been frequently employed to explain the operating principles of CAR therapy and suggest further design improvements. In this review, we sought to provide a comprehensive account of those efforts. Specifically, we discuss various computational models of CAR therapy ranging in scale from organismal to molecular. Then, we describe the molecular and functional properties of costimulatory domains frequently incorporated in CAR structure. Finally, we describe the signaling cascades by which those costimulatory domains elicit cellular response against the target. We hope that this comprehensive summary of computational and experimental studies will further motivate the use of systems approaches in advancing CAR therapy.

ICOS costimulation is indispensable for the differentiation of T follicular regulatory cells

ICOS is a T-cell costimulatory receptor critical for Tfh cell generation and function. However, the role of ICOS in Tfr cell differentiation remains unclear. Using Foxp3-Cre-mediated ICOS knockout (ICOS FC) mice, we show that ICOS deficiency in Treg-lineage cells drastically reduces the number of Tfr cells during GC reactions but has a minimal impact on conventional Treg cells. Single-cell transcriptome analysis of Foxp3+ cells at an early stage of the GC reaction suggests that ICOS normally inhibits Klf2 expression to promote follicular features including Bcl6 up-regulation. Furthermore, ICOS costimulation promotes nuclear localization of NFAT2, a known driver of CXCR5 expression. Notably, ICOS FC mice had an unaltered overall GC B-cell output but showed signs of expanded autoreactive B cells along with elevated autoantibody titers. Thus, our study demonstrates that ICOS costimulation is critical for Tfr cell differentiation and highlights the importance of Tfr cells in maintaining humoral immune tolerance during GC reactions.

Co-Stimulatory Receptor Signaling in CAR-T Cells

T cell engineering strategies have emerged as successful immunotherapeutic approaches for the treatment of human cancer. Chimeric Antigen Receptor T (CAR-T) cell therapy represents a prominent synthetic biology approach to re-direct the specificity of a patient's autologous T cells toward a desired tumor antigen. CAR-T therapy is currently FDA approved for the treatment of hematological malignancies, including subsets of B cell lymphoma, acute lymphoblastic leukemia (ALL) and multiple myeloma. Mechanistically, CAR-mediated recognition of a tumor antigen results in propagation of T cell activation signals, including a co-stimulatory signal, resulting in CAR-T cell activation, proliferation, evasion of apoptosis, and acquisition of effector functions. The importance of including a co-stimulatory domain in CARs was recognized following limited success of early iteration CAR-T cell designs lacking co-stimulation. Today, all CAR-T cells in clinical use contain either a CD28 or 4-1BB co-stimulatory domain. Preclinical investigations are exploring utility of including additional co-stimulatory molecules such as ICOS, OX40 and CD27 or various combinations of multiple co-stimulatory domains. Clinical and preclinical evidence implicates the co-stimulatory signal in several aspects of CAR-T cell therapy including response kinetics, persistence and durability, and toxicity profiles each of which impact the safety and anti-tumor efficacy of this immunotherapy. Herein we provide an overview of CAR-T cell co-stimulation by the prototypical receptors and discuss current and emerging strategies to modulate co-stimulatory signals to enhance CAR-T cell function.

Inducible Co-Stimulator ICOS Expression Correlates with Immune Cell Infiltration and Can Predict Prognosis in Lung Adenocarcinoma

Background

Inducible co-stimulator (ICOS) is a cell-enhanced co-stimulatory receptor that has shown great potential in the regulation of innate and adaptive immunity. However, the role of ICOS in lung adenocarcinoma (LUAD) remains unclear.

Methods

We used data from the Cancer Genome Atlas(TCGA) database to identify the expression and prognostic role of ICOS in LUAD. The results were validated using Gene Expression Omnibus(GEO) and Kaplan-Meier plotter databases. A model with predictive performance for overall survival of LUAD patients was constructed using fitted ICOS expression and other clinical parameters. We explored the biological function of ICOS. Subsequently, we further analysed and validated the effect of ICOS expression on tumour immune microenvironment (TIME) and survival. Finally, the CellMiner database was used to determine the relationship between ICOS expression and drug sensitivity.

Results

ICOS expression is significantly associated with poor prognosis in multiple cancers, especially LUAD, and is a good predictor of overall survival in LUAD patients. The biological function is to promote autoimmunity and inhibit cell proliferation. ICOS-related survival prediction model developed to more accurately predict 1-, 3- and 5-year survival probabilities for LUAD patients. In addition, we can use the expression of ICOS to effectively assess patient malignancy, prognosis, TIME status and clinical combination of drugs.

Conclusion

Our results suggest that ICOS is correlated with prognosis and immune infiltrating levels in LUAD. Higher ICOS expression predicts better TIME. This study provides a novel strategy for the development of immunotherapeutic and prognostic markers in LUAD.

Structural characterization of the ICOS/ICOS-L immune complex reveals high molecular mimicry by therapeutic antibodies

The inducible co-stimulator (ICOS) is a member of the CD28/B7 superfamily, and delivers a positive co-stimulatory signal to activated T cells upon binding to its ligand (ICOS-L). Dysregulation of this pathway has been implicated in autoimmune diseases and cancer, and is currently under clinical investigation as an immune checkpoint blockade. Here, we describe the molecular interactions of the ICOS/ICOS-L immune complex at 3.3 Å resolution. A central FDPPPF motif and residues within the CC' loop of ICOS are responsible for the specificity of the interaction with ICOS-L, with a distinct receptor binding orientation in comparison to other family members. Furthermore, our structure and binding data reveal that the ICOS N110 N-linked glycan participates in ICOS-L binding. In addition, we report crystal structures of ICOS and ICOS-L in complex with monoclonal antibodies under clinical evaluation in immunotherapy. Strikingly, antibody paratopes closely mimic receptor-ligand binding core interactions, in addition to contacting peripheral residues to confer high binding affinities. Our results uncover key molecular interactions of an immune complex central to human adaptive immunity and have direct implications for the ongoing development of therapeutic interventions targeting immune checkpoint receptors.

An Antibody Targeting ICOS Increases Intratumoral Cytotoxic to Regulatory T-cell Ratio and Induces Tumor Regression

The immunosuppressive tumor microenvironment constitutes a significant hurdle to immune checkpoint inhibitor responses. Both soluble factors and specialized immune cells, such as regulatory T cells (Treg), are key components of active intratumoral immunosuppression. Inducible costimulatory receptor (ICOS) can be highly expressed in the tumor microenvironment, especially on immunosuppressive Treg, suggesting that it represents a relevant target for preferential depletion of these cells. Here, we performed immune profiling of samples from tumor-bearing mice and patients with cancer to demonstrate differential expression of ICOS in immune T-cell subsets in different tissues. ICOS expression was higher on intratumoral Treg than on effector CD8 T cells. In addition, by immunizing an Icos knockout transgenic mouse line expressing antibodies with human variable domains, we selected a fully human IgG1 antibody called KY1044 that bound ICOS from different species. We showed that KY1044 induced sustained depletion of ICOS^high T cells but was also associated with increased secretion of proinflammatory cytokines from ICOS^low effector T cells (T_eff). In syngeneic mouse tumor models, KY1044 depleted ICOS^high Treg and increased the intratumoral T_Eff:Treg ratio, resulting in increased secretion of IFNγ and TNFα by T_Eff cells. KY1044 demonstrated monotherapy antitumor efficacy and improved anti-PD-L1 efficacy. In summary, we demonstrated that using KY1044, one can exploit the differential expression of ICOS on T-cell subtypes to improve the intratumoral immune contexture and restore an antitumor immune response.

T cell receptor signaling defines the fate and pathway of ICOS internalization

The role of the inducible costimulatory of T cells (ICOS) has been shown to be important for many different T cell outcomes and is indispensable for follicular helper T cell (T_FH) responses. Since its discovery, there have been several studies on the regulation of ICOS at a transcriptional level. However, the post-translational regulation of ICOS has not been well characterized. Here, we demonstrate that ICOS is internalized following ligation. We show that costimulation with CD3 results in differential internalization and fate than stimulation of ICOS alone. Additionally, we show that ICOS internalization is PI3K and clathrin mediated. The studies presented here not only increase the mechanistic understanding of ICOS post-translational regulation but also give insight into the potential mechanisms by which T cells expressing high affinity receptors may be preferentially chosen to become T_FH cells with increased ICOS levels.

RAS and RHO family GTPase mutations in cancer: twin sons of different mothers?

The RAS and RHO family comprise two major branches of the RAS superfamily of small GTPases. These proteins function as regulated molecular switches and control cytoplasmic signaling networks that regulate a diversity of cellular processes, including cell proliferation and cell migration. In the early 1980s, mutationally activated RAS genes encoding KRAS, HRAS and NRAS were discovered in human cancer and now comprise the most frequently mutated oncogene family in cancer. Only recently, exome sequencing studies identified cancer-associated alterations in two RHO family GTPases, RAC1 and RHOA. RAS and RHO proteins share significant identity in their amino acid sequences, protein structure and biochemistry. Cancer-associated RAS mutant proteins harbor missense mutations that are found primarily at one of three mutational hotspots (G12, G13 and Q61) and have been identified as gain-of-function oncogenic alterations. Although these residues are conserved in RHO family proteins, the gain-of-function mutations found in RAC1 are found primarily at a distinct hotspot. Unexpectedly, the cancer-associated mutations found with RHOA are located at different hotspots than those found with RAS. Furthermore, since the RHOA mutations suggested a loss-of-function phenotype, it has been unclear whether RHOA functions as an oncogene or tumor suppressor in cancer development. Finally, whereas RAS mutations are found in a broad spectrum of cancer types, RHOA and RAC1 mutations occur in a highly restricted range of cancer types. In this review, we focus on RHOA missense mutations found in cancer and their role in driving tumorigenesis, with comparisons to cancer-associated mutations in RAC1 and RAS GTPases.

Transmembrane domain-mediated Lck association underlies bystander and costimulatory ICOS signaling

The B7-family inducible costimulator (ICOS) activates phosphoinositide-3 kinase (PI3K) and augments calcium mobilization triggered by the T-cell receptor (TCR). We surprisingly found that the entire cytoplasmic domain of ICOS is dispensable for its costimulation of calcium mobilization. This costimulatory function relies on the unique transmembrane domain (TMD) of ICOS, which promotes association with the tyrosine kinase Lck. TMD-enabled Lck association is also required for p85 recruitment to ICOS and subsequent PI3K activation, and Lck underlies both the bystander and costimulatory signaling activity of ICOS. TMD-replaced ICOS, even with an intact cytoplasmic domain, fails to support T_FH development or GC formation in vivo. When transplanted onto a chimeric antigen receptor (CAR), the ICOS TMD enhances interactions between T cells and antigen-presenting target cells. Therefore, by revealing an unexpected function of the ICOS TMD, our study offers a new perspective for the understanding and potential application of costimulation biology.

Role of TRAFs in Signaling Pathways Controlling T Follicular Helper Cell Differentiation and T Cell-Dependent Antibody Responses

Follicular helper T (T_FH) cells represent a highly specialized CD4⁺ T cell subpopulation that supports the generation of germinal centers (GC) and provides B cells with critical signals promoting antibody class switching, generation of high affinity antibodies, and memory formation. T_FH cells are characterized by the expression of the chemokine receptor CXCR5, the transcription factor Bcl-6, costimulatory molecules ICOS, and PD-1, and the production of cytokine IL-21. The acquisition of a T_FH phenotype is a complex and multistep process that involves signals received through engagement of the TCR along with a multitude of costimulatory molecules and cytokines receptors. Members of the Tumor necrosis factor Receptor Associated Factors (TRAF) represent one of the major classes of signaling mediators involved in the differentiation and functions of T_FH cells. TRAF molecules are the canonical adaptor molecules that physically interact with members of the Tumor Necrosis Factor Receptor Superfamily (TNFRSF) and actively modulate their downstream signaling cascades through their adaptor function and/or E3 ubiquitin ligase activity. OX-40, GITR, and 4-1BB are the TRAF-dependent TNFRSF members that have been implicated in the differentiation and functions of T_FH cells. On the other hand, emerging data demonstrate that TRAF proteins also participate in signaling from the TCR and CD28, which deliver critical signals leading to the differentiation of T_FH cells. More intriguingly, we recently showed that the cytoplasmic tail of ICOS contains a conserved TANK-binding kinase 1 (TBK1)-binding motif that is shared with TBK1-binding TRAF proteins. The presence of this TRAF-mimicking signaling module downstream of ICOS is required to mediate the maturation step during T_FH differentiation. In addition, JAK-STAT pathways emanating from IL-2, IL-6, IL-21, and IL-27 cytokine receptors affect T_FH development, and crosstalk between TRAF-mediated pathways and the JAK-STAT pathways can contribute to generate integrated signals required to drive and sustain T_FH differentiation. In this review, we will introduce the molecular interactions and the major signaling pathways controlling the differentiation of T_FH cells. In each case, we will highlight the contributions of TRAF proteins to these signaling pathways. Finally, we will discuss the role of individual TRAF proteins in the regulation of T cell-dependent humoral responses.

Fundamental Mechanisms of Immune Checkpoint Blockade Therapy

Immune checkpoint blockade is able to induce durable responses across multiple types of cancer, which has enabled the oncology community to begin to envision potentially curative therapeutic approaches. However, the remarkable responses to immunotherapies are currently limited to a minority of patients and indications, highlighting the need for more effective and novel approaches. Indeed, an extraordinary amount of preclinical and clinical investigation is exploring the therapeutic potential of negative and positive costimulatory molecules. Insights into the underlying biological mechanisms and functions of these molecules have, however, lagged significantly behind. Such understanding will be essential for the rational design of next-generation immunotherapies. Here, we review the current state of our understanding of T-cell costimulatory mechanisms and checkpoint blockade, primarily of CTLA4 and PD-1, and highlight conceptual gaps in knowledge.Significance: This review provides an overview of immune checkpoint blockade therapy from a basic biology and immunologic perspective for the cancer research community. Cancer Discov; 8(9); 1069-86. ©2018 AACR.

Mannose Metabolism Is Essential for Th1 Cell Differentiation and IFN-γ Production

Glucose-derived mannose is a common component of glycoproteins, and its deficiency leads to a severe defect in protein glycosylation and failure in basic cell functions. In this work, we show that mannose metabolism is essential for IFN-γ production by mouse Th1 cells. In addition, we demonstrate that the susceptibility of Th1 cells to glycolysis restriction depends on the activation conditions and that under diminished glycolytic flux, mannose availability becomes the limiting factor for IFN-γ expression. This study unravels a new role for glucose metabolism in the differentiation process of Th1 cells, providing a mechanistic explanation for the importance of glycolysis in immune cell functions.

Group 2 Innate Lymphoid Cells in Pulmonary Immunity and Tissue Homeostasis

Group 2 innate lymphoid cells (ILC2) represent an evolutionary rather old but only recently identified member of the family of innate lymphoid cells and have received much attention since their detailed description in 2010. They can orchestrate innate as well as adaptive immune responses as they interact with and influence several immune and non-immune cell populations. Moreover, ILC2 are able to rapidly secrete large amounts of type 2 cytokines that can contribute to protective but also detrimental host immune responses depending on timing, location, and physiological context. Interestingly, ILC2, despite their scarcity, are the dominant innate lymphoid cell population in the lung, indicating a key role as first responders and amplifiers upon immune challenge at this site. In addition, the recently described tissue residency of ILC2 further underlines the importance of their respective microenvironment. In this review, we provide an overview of lung physiology including a description of the most prominent pulmonary resident cells together with a review of known and potential ILC2 interactions within this unique environment. We will further outline recent observations regarding pulmonary ILC2 during immune challenge including respiratory infections and discuss different models and approaches to study ILC2 biology in the lung.

ICOS Signaling Controls Induction and Maintenance of Collagen-Induced Arthritis

ICOS is a key costimulatory receptor facilitating differentiation and function of follicular helper T cells and inflammatory T cells. Rheumatoid arthritis patients were shown to have elevated levels of ICOS⁺ T cells in the synovial fluid, suggesting a potential role of ICOS-mediated T cell costimulation in autoimmune joint inflammation. In this study, using ICOS knockout and knockin mouse models, we found that ICOS signaling is required for the induction and maintenance of collagen-induced arthritis (CIA), a murine model of rheumatoid arthritis. For the initiation of CIA, the Tyr¹⁸¹-based SH2-binding motif of ICOS that is known to activate PI3K was critical for Ab production and expansion of inflammatory T cells. Furthermore, we found that Tyr¹⁸¹-dependent ICOS signaling is important for maintenance of CIA in an Ab-independent manner. Importantly, we found that a small molecule inhibitor of glycolysis, 3-bromopyruvate, ameliorates established CIA, suggesting an overlap between ICOS signaling, PI3K signaling, and glucose metabolism. Thus, we identified ICOS as a key costimulatory pathway that controls induction and maintenance of CIA and provide evidence that T cell glycolytic pathways can be potential therapeutic targets for rheumatoid arthritis.

RHOA G17V Induces T Follicular Helper Cell Specification and Promotes Lymphomagenesis

Angioimmunoblastic T cell lymphoma (AITL) is an aggressive tumor derived from malignant transformation of T follicular helper (Tfh) cells. AITL is characterized by loss-of-function mutations in Ten-Eleven Translocation 2 (TET2) epigenetic tumor suppressor and a highly recurrent mutation (p.Gly17Val) in the RHOA small GTPase. Yet, the specific role of RHOA G17V in AITL remains unknown. Expression of Rhoa G17V in CD4⁺ T cells induces Tfh cell specification; increased proliferation associated with inducible co-stimulator (ICOS) upregulation and increased phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase signaling. Moreover, RHOA G17V expression together with Tet2 loss resulted in development of AITL in mice. Importantly, Tet2^-/-RHOA G17V tumor proliferation in vivo can be inhibited by ICOS/PI3K-specific blockade, supporting a driving role for ICOS signaling in Tfh cell transformation.

FOXP3, ICOS and ICOSL gene polymorphisms in systemic sclerosis: FOXP3 rs2294020 is associated with disease progression in a female Italian population

Systemic sclerosis (SSc), an autoimmune disorder, is characterized by vasculopathy, inflammation, progressive perivascular and interstitial fibrosis. Its pathogenesis is largely unknown, however strong evidences suggest that genetic predisposition may contribute to SSc development. Several gene polymorphisms involved in regulatory T cell function have been identified in many autoimmune diseases, including SSc. Moreover, dysregulation of co-stimulatory and/or co-inhibitory signals, including ICOS signalling, can lead to autoimmunity. The aim of the present study was to investigate the association of the FOXP3 rs2294020, ICOS rs6726035 and ICOSL rs378299 SNPs with both the susceptibility and the progression to SSc in an Italian case-series of patients. SNP genotyping results were successfully obtained from a total of 350 subjects including 166 individuals with SSc and 184 healthy controls. Although analysis tests did not show any significant associations between the SNPs under study and susceptibility to SSc, the occurrence of FOXP3 rs2294020 in female patients was associated with decreased time to progression from early to definite SSc (allelic model: HR=1.43; CI=1.03-1.99; p=0.03; dominant model: HR=1.54; CI=1.04-2.28; p=0.03). The inclusion of presence of ACA autoantibodies in the model did not significantly change the estimates. No conclusions can be drawn for the susceptibility to the disease or the time to progression in men due to the low statistical power. This study provides evidence of the association of rs2294020 with SSc evolution in female patients, modulating the time of progression from the diagnosis of early SSc to the diagnosis of definite SSc, while no effect on SSc susceptibility per se was found. rs2294020 may be considered a disease-modifying gene-variant rather than a disease-susceptibility SNP in SSc.

Cell therapy could be a potential way to improve lipoprotein lipase deficiency

BACKGROUND

Lipoprotein lipase (LPL) deficiency is an autosomal recessive genetic disorder characterized by extreme hypertriglyceridemia, with no cure presently available. The purpose of this study was to test the possibility of using cell therapy to alleviate LPL deficiency.

METHODS

The LPL coding sequence was cloned into the MSCV retrovirus vector, after which MSCV-hLPL and MSCV (empty construct without LPL coding sequence) virion suspensions were made using the calcium chloride method. A muscle cell line (C2C12), kidney cell line (HEK293T) and pre-adipocyte cell line (3 T3-L1) were transfected with the virus in order to express recombinant LPL in vitro. Finally, each transfected cell line was injected subcutaneously into nude mice to identify the cell type which could secret recombinant LPL in vivo. Control cells were transfected with the MSCV empty vector. LPL activity was analyzed using a radioimmunoassay.

RESULTS

After virus infection, the LPL activity at the cell surface of each cell type was significantly higher than in the control cells, which indicates that all three cell types can be used to generate functional LPL. The transfected cells were injected subcutaneously into nude mice, and the LPL activity of the nearby muscle tissue at the injection site in mice injected with 3 T3-L1 cells was more than 5 times higher at the injection sites than at non-injected control sites. The other two types of cells did not show this trend.

CONCLUSION

The subcutaneous injection of adipocytes overexpressing LPL can improve the LPL activity of the adjacent tissue of nude mice. This is a ground-breaking preliminary study for the treatment of LPL deficiency, and lays a good foundation for using cell therapy to correct LPL deficiency.