The CD28-related molecule ICOS is required for effective T cell-dependent immune responses

Alternative splicing: A key regulator in T cell response and cancer immunotherapy

Alternative splicing (AS), a key post-transcriptional regulatory mechanism, is frequently dysregulated in cancer, driving both tumor progression and immune modulation. Aberrant AS influences antigen presentation, T cell activation, immune checkpoint regulation, and cytokine signaling, contributing to immune evasion but also presenting unique therapeutic vulnerabilities. Targeting AS has emerged as a promising strategy in cancer immunotherapy. Splicing-derived neoantigens have been identified as potent inducers of CD8⁺ T cell responses, offering potential for personalized treatment. AS modulators such as PRMT5 inhibitor GSK3326595 enhance immunotherapy efficacy by upregulating MHC class II expression and promoting T cell infiltration, while RBM39 inhibitor indisulam induces tumor-specific neoantigens. Furthermore, combining AS-targeting drugs with immune checkpoint inhibitors (ICIs) has demonstrated synergistic effects, improved response rates and overcoming resistance in preclinical models. Despite these advances, challenges remain in optimizing drug specificity and minimizing toxicity. Future efforts should focus on refining AS-targeting therapies, identifying predictive biomarkers, and integrating these approaches into clinical applications. This review highlights the therapeutic potential of AS modulation in cancer immunotherapy and its implications for advancing precision oncology.

Aged mice-derived bronchial epithelial cells regulate Th17 cell differentiation in asthma via the MBD2-sICOSL axis

Th17 cells are involved in the pathogenesis of elderly asthma. Bronchial epithelial cells (BECs) can act as antigen-presenting cells, and our previous studies have shown that methyl-CPG binding domain protein 2 (MBD2) in BECs can promote Th17 cell differentiation in asthma. However, the effect of BECs from different age groups (young and old) on Th17 cells remains unclear. In this study, BECs were co-cultured with CD4+ T cells, and it was found that BECs from young mice promoted the biased differentiation of Th2 cells, while BECs from older mice facilitated the biased differentiation of Th17 cells. Interestingly, MBD2 was highly expressed in BECs from older mice compared to BECs from young mice. MBD2 silencing induced inhibition of Th17 cell differentiation, while MBD2 overexpression reversed this change and promoted Th cell differentiation into Th17 cells. Soluble inducible T cell costimulator ligand (sICOSL) is mainly involved in the regulation of T cells after activation. In this study, we found that sICOSL levels were lower in BECs of old mice compared to BECs of young mice. Mechanistically, sICOSL levels increased with MBD2 silencing and decreased with MBD2 overexpression. As expected, the addition of anti-sICOSL antibodies significantly enhanced Th17 cell differentiation and suppressed Th2 cell differentiation, while exogenous sICOSL supplementation promoted Th2 cell differentiation and inhibited Th17 cell differentiation. However, neither anti-sICOSL nor exogenous sICOSL affected the expression of MBD2. Taken together, these results suggest that BECs from older mice regulate Th17 cell differentiation via the MBD2-sICOSL axis. These findings provide new insights into the pathogenesis of Th17-activated asthma in elderly patients.

ICOS+ CD4+ T cells promote antitumor immunity through Akt/STAT1/T-bet axis in MSS/pMMR colorectal cancer

Inducible Co-Stimulator (ICOS), as a T-cell-specific costimulatory receptor that enhances T-cell responses to foreign antigens, plays a crucial role in cancer immunity. However, its role in MSS/pMMR colorectal cancer (CRC) remains unclear. In this study, we demonstrated that ICOS expression decreases as the tumor stages advance and that high ICOS expression is associated with a favorable prognosis in MSS/pMMR CRC. Mechanistically, ICOS promoted the secretion of IFN-γ, TNF-α, and IL-12 in CD4+ T cells through the Akt/STAT1/T-bet axis, leading to the inhibition of MSS/pMMR-CRC-cell proliferation. Importantly, ICOS+ CD4+ T cells enhanced tumor responses to anti-PD-1 therapy in MSS/pMMR CRC. In conclusion, this study revealed that ICOS mediates antitumor immunity by promoting the secretion of cancer-suppressive cytokines. It also suggests that activation of ICOS serves a potential therapeutic strategy for MSS/pMMR CRC.

CD28 Superfamily Costimulatory Molecules in Chronic Pain: Focus on Immunomodulation

Chronic pain has substantial effects on patients' quality of life and psychological well-being. It does not respond satisfactorily to available medicinal therapeutics because its mechanism remains unclear. Recent studies have shown a strong relationship between chronic pain and immunomodulation. As important members of the immune response, CD28 superfamily costimulatory molecules were demonstrated to have an analgesic effect on chronic pain. Based on research on the role of these molecules in chronic pain, new and highly effective analgesic medicines are anticipated that could be used in combination with some previous analgesic medicines to reduce substance abuse and side effects. This review of the literature will examine the pain-regulating mechanisms of CD28 superfamily costimulatory molecules, focusing on immunomodulation. In addition, this review will discuss the potential and difficulties of developing novel analgesic medicines targeting CD28 superfamily costimulatory molecules.

From ex vivo to in vivo chimeric antigen T cells manufacturing: new horizons for CAR T-cell based therapy

In the past decades, Chimeric Antigen Receptor (CAR)-T cell therapy has achieved remarkable success, leading to the approval of six therapeutic products for haematological malignancies. Recently, the therapeutic potential of this therapy has also been demonstrated in non-tumoral diseases. Currently, the manufacturing process to produce clinical-grade CAR-T cells is complex, time-consuming, and highly expensive. It involves multiple steps, including the collection of T cells from patients or healthy donors, in vitro engineering and expansion, and finally reinfusion into patients. Therefore, despite the impressive clinical outcomes, ex vivo manufacturing process makes CAR-T cells out of reach for many cancer patients. Direct in vivo engineering of T cells could be a more rapid solution able to circumvent both the complexity and the costs associated with ex vivo manufactured CAR-T cells. This novel approach allows to completely eliminate ex vivo cell manipulation and expansion while producing therapeutic cell populations directly in vivo. To date, several studies have demonstrated the feasibility of in vivo T cell reprogramming, by employing injectable viral- or nanocarrier-based delivery platforms in tumour animal models. Additionally, in vivo production of CAR-T cells might reduce the incidence, or at least the severity, of systemic toxicities frequently occurring with ex vivo produced CAR-T cells, such as cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome. In this review, we highlight the challenges associated with the current ex vivo manufacturing protocols and review the latest progresses in the emerging field of in vivo CAR-T therapy, by comparing the various platforms so far investigated. Moreover, we offer an overview of the advantages deriving from in vivo reprogramming of other immune cell types, such as Natural Killer and macrophages, with CAR constructs.

HIF1α-regulated glycolysis promotes activation-induced cell death and IFN-γ induction in hypoxic T cells

Hypoxia is a common feature in various pathophysiological contexts, including tumor microenvironment, and IFN-γ is instrumental for anti-tumor immunity. HIF1α has long been known as a primary regulator of cellular adaptive responses to hypoxia, but its role in IFN-γ induction in hypoxic T cells is unknown. Here, we show that the HIF1α-glycolysis axis controls IFN-γ induction in both human and mouse T cells, activated under hypoxia. Specific deletion of HIF1α in T cells (Hif1α-/-) and glycolytic inhibition suppresses IFN-γ induction. Conversely, HIF1α stabilization by hypoxia and VHL deletion in T cells (Vhl-/-) increases IFN-γ production. Hypoxic Hif1α-/- T cells are less able to kill tumor cells in vitro, and tumor-bearing Hif1α-/- mice are not responsive to immune checkpoint blockade (ICB) therapy in vivo. Mechanistically, loss of HIF1α greatly diminishes glycolytic activity in hypoxic T cells, resulting in depleted intracellular acetyl-CoA and attenuated activation-induced cell death (AICD). Restoration of intracellular acetyl-CoA by acetate supplementation re-engages AICD, rescuing IFN-γ production in hypoxic Hif1α-/- T cells and re-sensitizing Hif1α-/- tumor-bearing mice to ICB. In summary, we identify HIF1α-regulated glycolysis as a key metabolic control of IFN-γ production in hypoxic T cells and ICB response.

MiR-155-targeted IcosL controls tumor rejection

Elevated levels of miR-155 in solid and liquid malignancies correlate with aggressiveness of the disease. In this manuscript, we show that miR-155 targets transcripts encoding IcosL, the ligand for Inducible T-cell costimulator (Icos), thus impairing the ability of T cells to recognize and eliminate malignant cells. We specifically found that overexpression of miR-155 in B cells of Eµ-miR-155 mice causes loss of IcosL expression as they progress toward malignancy. Similarly, in mice where miR-155 expression is controlled by a Cre-Tet-OFF system, miR-155 induction led to malignant infiltrates lacking IcosL expression. Conversely, turning miR-155 OFF led to tumor regression and emergence of infiltrates composed of IcosL-positive B cells and Icos-positive T cells forming immunological synapses. Therefore, we next engineered malignant cells to express IcosL, in order to determine whether IcosL expression would increase tumor infiltration by cytotoxic T cells and reduce tumor progression. Indeed, overexpressing an IcosL-encoding cDNA in MC38 murine colon cancer cells before injection into syngeneic C57BL6 mice reduced tumor size and increased intratumor CD8+ T cell infiltration, that formed synapses with IcosL-expressing MC38 cells. Our results underscore the fact that by targeting IcosL transcripts, miR-155 impairs the infiltration of tumors by cytotoxic T cells, as well as the importance of IcosL on enhancing the immune response against malignant cells. These findings should lead to the development of more effective anticancer treatments based on maintaining, increasing, or restoring IcosL expression by malignant cells, along with impairing miR-155 activity.

CAR-NKT Cells in Asthma: Use of NKT as a Promising Cell for CAR Therapy

NKT cells, unique lymphocytes bridging innate and adaptive immunity, offer significant potential for managing inflammatory disorders like asthma. Activating iNKT induces increasing IFN-γ, TGF-β, IL-2, and IL-10 potentially suppressing allergic asthma. However, their immunomodulatory effects, including granzyme-perforin-mediated cytotoxicity, and expression of TIM-3 and TRAIL warrant careful consideration and targeted approaches. Although CAR-T cell therapy has achieved remarkable success in treating certain cancers, its limitations necessitate exploring alternative approaches. In this context, CAR-NKT cells emerge as a promising approach for overcoming these challenges, potentially achieving safer and more effective immunotherapies. Strategies involve targeting distinct IgE-receptors and their interactions with CAR-NKT cells, potentially disrupting allergen-mast cell/basophil interactions and preventing inflammatory cytokine release. Additionally, targeting immune checkpoints like PDL-2, inducible ICOS, FASL, CTLA-4, and CD137 or dectin-1 for fungal asthma could further modulate immune responses. Furthermore, artificial intelligence and machine learning hold immense promise for revolutionizing NKT cell-based asthma therapy. AI can optimize CAR-NKT cell functionalities, design personalized treatment strategies, and unlock a future of precise and effective care. This review discusses various approaches to enhancing CAR-NKT cell efficacy and longevity, along with the challenges and opportunities they present in the treatment of allergic asthma.

Deep Flow Cytometry Unveils Distinct Immune Cell Subsets in Inducible T Cell Co-Stimulator Ligand (ICOSL)- and ICOS-Knockout Mice during Experimental Autoimmune Encephalomyelitis

The inducible T cell co-stimulator ligand (ICOSL), expressed by antigen presenting cells, binds to the inducible T cell co-stimulator (ICOS) on activated T cells. Improper function of the ICOS/ICOSL pathway has been implicated in several autoimmune diseases, including multiple sclerosis (MS). Previous studies showed that ICOS-knockout (KO) mice exhibit severe experimental autoimmune encephalomyelitis (EAE), the animal model of MS, but data on ICOSL deficiency are not available. In our study, we explored the impact of both ICOS and ICOSL deficiencies on MOG35-55 -induced EAE and its associated immune cell dynamics by employing ICOSL-KO and ICOS-KO mice with a C57BL/6J background. During EAE resolution, MOG-driven cytokine levels and the immunophenotype of splenocytes were evaluated by ELISA and multiparametric flow cytometry, respectively. We found that both KO mice exhibited an overlapping and more severe EAE compared to C57BL/6J mice, corroborated by a reduction in memory/regulatory T cell subsets and interleukin (IL-)17 levels. It is noteworthy that an unsupervised analysis showed that ICOSL deficiency modifies the immune response in an original way, by affecting T central and effector memory (TCM, TEM), long-lived CD4+ TEM cells, and macrophages, compared to ICOS-KO and C57BL/6J mice, suggesting a role for other binding partners to ICOSL in EAE development, which deserves further study.

Anti-PD-L1-Based Bispecific Antibodies Targeting Co-Inhibitory and Co-Stimulatory Molecules for Cancer Immunotherapy

Targeting PD-L1 via monospecific antibodies has shown durable clinical benefits and long-term remissions where patients exhibit no clinical cancer signs for many years after treatment. However, the durable clinical benefits and long-term remissions by anti-PD-L1 monotherapy have been limited to a small fraction of patients with certain cancer types. Targeting PD-L1 via bispecific antibodies (referred to as anti-PD-L1-based bsAbs) which can simultaneously bind to both co-inhibitory and co-stimulatory molecules may increase the durable antitumor responses in patients who would not benefit from PD-L1 monotherapy. A growing number of anti-PD-L1-based bsAbs have been developed to fight against this deadly disease. This review summarizes recent advances of anti-PD-L1-based bsAbs for cancer immunotherapy in patents and literatures, and discusses their anti-tumor efficacies in vitro and in vivo. Over 50 anti-PD-L1-based bsAbs targeting both co-inhibitory and co-stimulatory molecules have been investigated in biological testing or in clinical trials since 2017. At least eleven proteins, such as CTLA-4, LAG-3, PD-1, PD-L2, TIM-3, TIGIT, CD28, CD27, OX40, CD137, and ICOS, are involved in these investigations. Twenty-two anti-PD-L1-based bsAbs are being evaluated to treat various advanced cancers in clinical trials, wherein the indications include NSCLC, SNSCLC, SCLC, PDA, MBNHL, SCCHN, UC, EC, TNBC, CC, and some other malignancies. The released data from clinical trials indicated that most of the anti-PD-L1-based bsAbs were well-tolerated and showed promising antitumor efficacy in patients with advanced solid tumors. However, since the approved and investigational bsAbs have shown much more significant adverse reactions compared to PD-L1 monospecific antibodies, anti-PD-L1-based bsAbs may be further optimized via molecular structure modification to avoid or reduce these adverse reactions.

A20 regulates lymphocyte adhesion in murine neuroinflammation by restricting endothelial ICOSL expression in the CNS

A20 is a ubiquitin-modifying protein that negatively regulates NF-κB signaling. Mutations in A20/TNFAIP3 are associated with a variety of autoimmune diseases, including multiple sclerosis (MS). We found that deletion of A20 in central nervous system (CNS) endothelial cells (ECs) enhances experimental autoimmune encephalomyelitis (EAE), a mouse model of MS. A20ΔCNS-EC mice showed increased numbers of CNS-infiltrating immune cells during neuroinflammation and in the steady state. While the integrity of the blood-brain barrier (BBB) was not impaired, we observed a strong activation of CNS-ECs in these mice, with dramatically increased levels of the adhesion molecules ICAM-1 and VCAM-1. We discovered ICOSL to be expressed by A20-deficient CNS-ECs, which we found to function as adhesion molecules. Silencing of ICOSL in CNS microvascular ECs partly reversed the phenotype of A20ΔCNS-EC mice without reaching statistical significance and delayed the onset of EAE symptoms in WT mice. In addition, blocking of ICOSL on primary mouse brain microvascular ECs impaired the adhesion of T cells in vitro. Taken together, we propose that CNS EC-ICOSL contributes to the firm adhesion of T cells to the BBB, promoting their entry into the CNS and eventually driving neuroinflammation.

Harnessing the power of artificial intelligence to advance cell therapy

Cell therapies are powerful technologies in which human cells are reprogrammed for therapeutic applications such as killing cancer cells or replacing defective cells. The technologies underlying cell therapies are increasing in effectiveness and complexity, making rational engineering of cell therapies more difficult. Creating the next generation of cell therapies will require improved experimental approaches and predictive models. Artificial intelligence (AI) and machine learning (ML) methods have revolutionized several fields in biology including genome annotation, protein structure prediction, and enzyme design. In this review, we discuss the potential of combining experimental library screens and AI to build predictive models for the development of modular cell therapy technologies. Advances in DNA synthesis and high-throughput screening techniques enable the construction and screening of libraries of modular cell therapy constructs. AI and ML models trained on this screening data can accelerate the development of cell therapies by generating predictive models, design rules, and improved designs.

Versatile roles of innate lymphoid cells at the mucosal barrier: from homeostasis to pathological inflammation

Innate lymphoid cells (ILCs) are innate lymphocytes that do not express antigen-specific receptors and largely reside and self-renew in mucosal tissues. ILCs can be categorized into three groups (ILC1-3) based on the transcription factors that direct their functions and the cytokines they produce. Their signature transcription factors and cytokines closely mirror those of their Th1, Th2, and Th17 cell counterparts. Accumulating studies show that ILCs are involved in not only the pathogenesis of mucosal tissue diseases, especially respiratory diseases, and colitis, but also the resolution of such diseases. Here, we discuss recent advances regarding our understanding of the biology of ILCs in mucosal tissue health and disease. In addition, we describe the current research on the immune checkpoints by which other cells regulate ILC activities: for example, checkpoint molecules are potential new targets for therapies that aim to control ILCs in mucosal diseases. In addition, we review approved and clinically- trialed drugs and drugs in clinical trials that can target ILCs and therefore have therapeutic potential in ILC-mediated diseases. Finally, since ILCs also play important roles in mucosal tissue homeostasis, we explore the hitherto sparse research on cell therapy with regulatory ILCs. This review highlights various therapeutic approaches that could be used to treat ILC-mediated mucosal diseases and areas of research that could benefit from further investigation.

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.

Granulocyte-Macrophage Colony-Stimulating Factor Influence on Soluble and Membrane-Bound ICOS in Combination with Immune Checkpoint Blockade

With the successful development of immune checkpoint blockade, there remains the continued need to improve efficacy and decrease toxicities. The addition of granulocyte-macrophage colony-stimulating factor (GM-CSF) to ipilimumab has previously demonstrated both an improvement in efficacy and decrease in the incidence of high-grade adverse events. ICOS+CD4+ or ICOS+CD8+ peripheral blood T cells are significantly greater in the patients treated with ipilimumab plus GM-CSF than in the patients treated with ipilimumab alone. To better understand the effects of GM-CSF on inducible T-cell costimulator (ICOS) and clinical outcomes, the relative roles of identified soluble ICOS and membrane-bound ICOS were evaluated. The ICOS splice variant was secreted and found to have immunologic suppressive effects. Changes in soluble ICOS splice variant levels in treated patients correlated with clinical outcomes. GM-CSF enhanced membrane-bound ICOS in an IL12-dependent manner but did not increase soluble ICOS levels. Whereas soluble ICOS plays a role in immune suppression, GM-CSF efficacy involves increasing membrane-bound ICOS and induction of dendritic cell development. Thus, soluble ICOS splice variants may be used as a biomarker for GM-CSF and immune checkpoint blockade-based therapies.

Reciprocal costimulatory molecules control the activation of mucosal type 3 innate lymphoid cells during engagement with B cells

Innate lymphoid cells (ILCs) are the counterpart of T helper cells in the innate immune system and share multiple phenotypes with T helper cells. Inducible T-cell costimulator (ICOS) is recognized on T cells and participates in T-cell activation and T and B-cell engagement in lymphoid tissues. However, the role of ICOS in ILC3s and ILC3-involved interactions with the immune microenvironment remains unclear. Here, we found that ICOS expression on human ILC3s was correlated with the activated state of ILC3s. ICOS costimulation enhanced the survival, proliferation, and capacity of ILC3s to produce cytokines (IL-22, IL-17A, IFN-γ, TNF, and GM-CSF). Via synergistic effects of ICOS and CD40 signaling, B cells promoted ILC3 functions, and ILC3-induced T-cell-independent B-cell IgA and IgM secretion primarily required CD40 signaling. Hence, ICOS is essential for the nonredundant role of ILC3s and their interaction with adjacent B cells.

Immune checkpoint molecules in prevention and development of asthma

Allergic asthma is a respiratory disease initiated by type-2 immune responses characterized by secretion of alarmins, interleukin-4 (IL-4), IL-5, and IL-13, eosinophilic inflammation, and airway hyperresponsiveness (AHR). Immune checkpoints (ICPs) are inhibitory or stimulatory molecules expressed on different immune cells, tumor cells, or other cell types that regulate immune system activation and maintain immune homeostasis. Compelling evidence indicates a key role for ICPs in both the progression and prevention of asthma. There is also evidence of asthma development or exacerbation in some cancer patients receiving ICP therapy. The aim of this review is to provide an updated overview of ICPs and their roles in asthma pathogenesis, and to assess their implications as therapeutic targets in asthma.

CAR-T cell potency: from structural elements to vector backbone components

Chimeric antigen receptor (CAR) T cell therapy, in which a patient’s own T lymphocytes are engineered to recognize and kill cancer cells, has achieved remarkable success in some hematological malignancies in preclinical and clinical trials, resulting in six FDA-approved CAR-T products currently available in the market. Once equipped with a CAR construct, T cells act as living drugs and recognize and eliminate the target tumor cells in an MHC-independent manner. In this review, we first described all structural modular of CAR in detail, focusing on more recent findings. We then pointed out behind-the-scene elements contributing to CAR expression and reviewed how CAR expression can be drastically affected by the elements embedded in the viral vector backbone.

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.

Harnessing the immune system by targeting immune checkpoints: Providing new hope for Oncotherapy

With the goal of harnessing the host's immune system to provide long-lasting remission and cures for various cancers, the advent of immunotherapy revolutionized the cancer therapy field. Among the current immunotherapeutic strategies, immune checkpoint blockades have greatly improved the overall survival rates in certain patient populations. Of note, CTLA4 and PD-1/PD-L1 are two major non-redundant immune checkpoints implicated in promoting cancer immune evasion, and ultimately lead to relapse. Antibodies or inhibitors targeting these two c+heckpoints have achieved some encouraging clinical outcomes. Further, beyond the canonical immune checkpoints, more inhibitory checkpoints have been identified. Herein, we will summarize recent progress in immune checkpoint blockade therapies, with a specific focus on key pre-clinical and clinical results of new immune checkpoint therapies for cancer. Given the crucial roles of immune checkpoint blockade in oncotherapy, drugs targeting checkpoint molecules expressed by both cancer and immune cells are in clinical trials, which will be comprehensively summarized in this review. Taken together, investigating combinatorial therapies targeting immune checkpoints expressed by cancer cells and immune cells will greatly improve immunotherapies that enhance host elimination of tumors.

Inducible Co-Stimulator (ICOS) in transplantation: A review

Prevention of T cell activation is one of the goals of successful organ and tissue transplantation. Blockade of T cell co-stimulation, particularly of the CD28:B7 interaction, has been shown to prolong graft survival. Inducible Co-Stimulator (ICOS) is the third member of the B7 family and here we review the literature on ICOS, its receptor (B7RP-1), and blockade of this pathway in transplant models. ICOS:B7RP-1 are a single receptor:ligand pair with a loss of function of either being implicated in some autoimmune diseases. ICOS has multiple functions, related to its constitutive expression on B cells and activated T cells. In in vitro transplant models, ICOS:B7RP-1 blockade has produced mixed results as to its ability to modulate lymphocyte proliferation. Several in vivo transplant models demonstrate varying degrees of success in prolonging graft survival. Timing and dose of treatment appear important, and combination with other immunosuppressive treatments may also be of benefit. As ICOS has multiple functions, it may be that the observed variable results are due to inadvertent inactivation of graft protective functions. If these barriers can be overcome, ICOS:B7RP-1 blockade could provide an important target for future immunosuppression regimens.

The role of A Disintegrin and Metalloproteinase (ADAM)-10 in T helper cell biology

A Disintegrin and Metalloproteinases (ADAM)-10 is a member of a family of membrane-anchored proteinases that regulate a broad range of cellular functions with central roles within the immune system. This has spurred the interest to modulate ADAM activity therapeutically in immunological diseases. CD4 T helper (Th) cells are the key regulators of adaptive immune responses. Their development and function is strongly dependent on Notch, a key ADAM-10 substrate. However, Th cells rely on a variety of additional ADAM-10 substrates regulating their functional activity at multiple levels. The complexity of both, the ADAM substrate expression as well as the functional consequences of ADAM-mediated cleavage of the various substrates complicates the analysis of cell type specific effects. Here we provide an overview on the major ADAM-10 substrates relevant for CD4 T cell biology and discuss the potential effects of ADAM-mediated cleavage exemplified for a selection of important substrates.

ICOS Gene Polymorphisms (IVS1 + 173 T/C and c. 1624 C/T) in Primary Sjögren's Syndrome Patients: Analysis of ICOS Expression

Background: Primary Sjögren’s syndrome (pSS) is a systemic autoimmune disease, which affects exocrine glands. T cell activation is a trigger mechanism in the immune response. Hyperreactivity of T cells and antibody production are features in pSS. ICOS can be critical in the pathogenesis of pSS. Methods: A total of 134 pSS patients and 134 control subjects (CS) were included. Genotyping was performed by PCR-RFLP. ICOS mRNA expression was quantified by real-time PCR, and CD4+ ICOS+ T cells were determined by flow cytometry. Results: The ICOS IVS1 + 173 T>C polymorphisms were not associated with susceptibility to pSS (p = 0.393, CI = 0.503−1.311). However, the c.1624 C>T polymorphism was associated with a reduction in the risk of development of pSS (p = 0.015, CI = 0.294−0.884). An increase in ICOS mRNA expression in patients was observed (3.7-fold). Furthermore, pSS patients showed an increase in membranal-ICOS expression (mICOS). High expression of mICOS (MFI) was associated with lymphocytic infiltration. Conclusions: The IVS1 + 173 polymorphism is not a genetic marker for the development of pSS, while c.1624 T allele was associated with a low risk. However, elevated mICOS expression in pSS patients with high lymphocytic infiltration was found. ICOS may have an important role in the immunopathogenesis of pSS and should be analyzed in T cell subsets in pSS patients as a possible disease marker.

A review of signaling and transcriptional control in T follicular helper cell differentiation

T follicular helper (Tfh) cells are a critical component of adaptive immunity and assist in optimal Ab-mediated defense. Multiple effector functions of Tfh support germinal center B cell survival, Ab class switching, and plasma cell maturation. In the past 2 decades, the phenotype and functional characteristics of GC Tfh have been clarified allowing for robust studies of the Th subset including activation signals and environmental cues controlling Tfh differentiation and migration during an immune response. A unique, 2-step differentiation process of Tfh has been proposed but the mechanisms underlying transition between unstable Tfh precursors and functional mature Tfh remain elusive. Likewise, newly identified transcriptional regulators of Tfh development have not yet been incorporated into our understanding of how these cells might function in disease. Here, we review the signals and downstream transcription factors that shape Tfh differentiation including what is known about the epigenetic processes that maintain Tfh identity. It is proposed that further evaluation of the stepwise differentiation pattern of Tfh will yield greater insights into how these cells become dysregulated in autoimmunity.

The role of ICOS in allergic disease: Positive or Negative?

With the rapid increase in the incidence of allergic diseases, the mechanisms underlying the development of these diseases have received a great deal of attention, and this is particularly true in regard to the role of ICOS in allergic diseases. Current studies have revealed that ICOS affects the functional activity of multiple immune cells that modulate the adaptive immune system. Additionally, ICOS also plays a crucial role in mediating cellular immunity and coordinating the response of the entire immune system, and thus, it plays a role in allergic reactions. However, the ICOS/ICOS-ligand (ICOS-L) axis functions in a dual role during the development of multiple allergic diseases. In this review, we explore the role of ICOS/ICOSL in the context of different immune cells that function in allergic diseases, and we summarize recent advances in their contribution to these diseases.

Immune Checkpoints and Innate Lymphoid Cells-New Avenues for Cancer Immunotherapy

Immune checkpoints (IC) are broadly characterized as inhibitory pathways that tightly regulate the activation of the immune system. These molecular "brakes" are centrally involved in the maintenance of immune self-tolerance and represent a key mechanism in avoiding autoimmunity and tissue destruction. Antibody-based therapies target these inhibitory molecules on T cells to improve their cytotoxic function, with unprecedented clinical efficacies for a number of malignancies. Many of these ICs are also expressed on innate lymphoid cells (ILC), drawing interest from the field to understand their function, impact for anti-tumor immunity and potential for immunotherapy. In this review, we highlight ILC specificities at different tissue sites and their migration potential upon inflammatory challenge. We further summarize the current understanding of IC molecules on ILC and discuss potential strategies for ILC modulation as part of a greater anti-cancer armamentarium.

Distinct roles of ICOS and CD40L in human T-B cell adhesion and antibody production

CD40-CD40L and inducible co-stimulatory molecule (ICOS)-ICOSL ligations are demonstrated to play critical roles in CD4⁺T-B interaction for B cell activation and differentiation in mouse models. Herein, by using a micropipette adhesion assay and an in vitro CD4⁺T-B cell coculture system simultaneously, we intended to dissect their roles in human CD4⁺T-B adhesion and IgG/IgM production. With the upregulation of CD40L and ICOS expressions on CD4⁺ T cells upon TCR/CD28 stimulation in vitro, activated CD4⁺ T cells exhibited enhanced adhesion with autologous B cells at a single cell level when compared to the resting counterparts. Blockade of ICOS dramatically damped the adhesion between CD4⁺ T and B cells whereas less effect of CD40L blockade was observed. On the contrary, blockade of CD40L led to the dramatic decrease in IgG/IgM production when B cells were cocultured with activated CD4⁺ T cells together with the decrease in the induction of CD19^hi B cells. However, ICOS blockade displayed less attenuation on IgG/IgM production. Distinct roles of CD40-CD40L and ICOS-ICOSL in cell adhesion and IgG/IgM production were also observed in CD4⁺T-B cell interaction in system lupus erythematosus patients. The blockade of CD40L, rather than ICOS, led to the dramatic decrease in the phosphorylation of Pyk2 in CD19^hi B cells and total B cells. Our study thus provides the evidence that CD40L and ICOS on activated CD4⁺ T cells either upon in vitro activation or at the pathogenic state function diversely during CD4⁺T-B cell interactions. While ICOS-ICOSL ligation is more likely to be engaged in cell adhesion, CD40-CD40L provides indispensable signal for B cell differentiation and IgG/IgM production. Our results are thus indicative for the segregating costimulation of CD40-CD40L and ICOS-ICOSL on CD4⁺ T cells for B cell activation and differentiation, which might be helpful for the dissection of SLE pathogenesis.

Cytomegalovirus restricts ICOSL expression on antigen-presenting cells disabling T cell co-stimulation and contributing to immune evasion

Viral infections are controlled, and very often cleared, by activated T lymphocytes. The inducible co-stimulator (ICOS) mediates its functions by binding to its ligand ICOSL, enhancing T-cell activation and optimal germinal center (GC) formation. Here, we show that ICOSL is heavily downmodulated during infection of antigen-presenting cells by different herpesviruses. We found that, in murine cytomegalovirus (MCMV), the immunoevasin m138/fcr-1 physically interacts with ICOSL, impeding its maturation and promoting its lysosomal degradation. This viral protein counteracts T-cell responses, in an ICOS-dependent manner, and limits virus control during the acute MCMV infection. Additionally, we report that blockade of ICOSL in MCMV-infected mice critically regulates the production of MCMV-specific antibodies due to a reduction of T follicular helper and GC B cells. Altogether, these findings reveal a novel mechanism evolved by MCMV to counteract adaptive immune surveillance, and demonstrates a role of the ICOS:ICOSL axis in the host defense against herpesviruses.

Noninvasive Imaging of Cancer Immunotherapy

Immunotherapy has revolutionized the treatment of several malignancies. Notwithstanding the encouraging results, many patients do not respond to treatments. Evaluation of the efficacy of treatments is challenging and robust methods to predict the response to treatment are not yet available. The outcome of immunotherapy results from changes that treatment evokes in the tumor immune landscape. Therefore, a better understanding of the dynamics of immune cells that infiltrate into the tumor microenvironment may fundamentally help in addressing this challenge and provide tools to assess or even predict the response. Noninvasive imaging approaches, such as PET and SPECT that provide whole-body images are currently seen as the most promising tools that can shed light on the events happening in tumors in response to treatment. Such tools can provide critical information that can be used to make informed clinical decisions. Here, we review recent developments in the field of noninvasive cancer imaging with a focus on immunotherapeutics and nuclear imaging technologies and will discuss how the field can move forward to address the challenges that remain unresolved.

Novel targeted therapies of T cell lymphomas

T cell lymphomas (TCL) comprise a heterogeneous group of non-Hodgkin lymphomas (NHL) that often present at an advanced stage at the time of diagnosis and that most commonly have an aggressive clinical course. Treatment in the front-line setting is most often cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) or CHOP-like regimens, which are effective in B cell lymphomas, but in TCL are associated with a high failure rate and frequent relapses. Furthermore, in contrast to B cell NHL, in which substantial clinical progress has been made with the introduction of monoclonal antibodies, no comparable advances have been seen in TCL. To change this situation and improve the prognosis in TCL, new gene-targeted therapies must be developed. This is now possible due to enormous progress that has been made in the last years in the understanding of the biology and molecular pathogenesis of TCL, which enables the implementation of the research findings in clinical practice. In this review, we present new therapies and current clinical and preclinical trials on targeted treatments for TCL using histone deacetylase inhibitors (HDACi), antibodies, chimeric antigen receptor T cells (CARTs), phosphatidylinositol 3-kinase inhibitors (PI3Ki), anaplastic lymphoma kinase inhibitors (ALKi), and antibiotics, used alone or in combinations. The recent clinical success of ALKi and conjugated anti-CD30 antibody (brentuximab-vedotin) suggests that novel therapies for TCL can significantly improve outcomes when properly targeted.

A guide to cancer immunotherapy: from T cell basic science to clinical practice

The T lymphocyte, especially its capacity for antigen-directed cytotoxicity, has become a central focus for engaging the immune system in the fight against cancer. Basic science discoveries elucidating the molecular and cellular biology of the T cell have led to new strategies in this fight, including checkpoint blockade, adoptive cellular therapy and cancer vaccinology. This area of immunological research has been highly active for the past 50 years and is now enjoying unprecedented bench-to-bedside clinical success. Here, we provide a comprehensive historical and biological perspective regarding the advent and clinical implementation of cancer immunotherapeutics, with an emphasis on the fundamental importance of T lymphocyte regulation. We highlight clinical trials that demonstrate therapeutic efficacy and toxicities associated with each class of drug. Finally, we summarize emerging therapies and emphasize the yet to be elucidated questions and future promise within the field of cancer immunotherapy.

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.

ICOS+ Tregs: A Functional Subset of Tregs in Immune Diseases

Recent studies have reported the pathological effect of ICOS⁺ T cells, but ICOS signals also widely participate in anti-inflammatory responses, particularly ICOS⁺ regulatory T (Treg) cells. The ICOS signaling pathway endows Tregs with increased generation, proliferation, and survival abilities. Furthermore, there is enough evidence to suggest a superior capacity of ICOS⁺ Tregs, which is partly attributable to IL-10 induced by ICOS, yet the associated mechanism needs further investigation. In this review, we discuss the complicated role of ICOS⁺ Tregs in several classical autoimmune diseases, allergic diseases, and cancers and investigate the related therapeutic applications in these diseases. Moreover, we identify ICOS as a potential biomarker for disease treatment and prognostic prediction. In addition, we believe that anti-ICOS/ICOSL monoclonal antibodies exhibit excellent clinical application potential. A thorough understanding of the effect of ICOS⁺ Tregs and the holistic role of ICOS toward the immune system will help to improve the therapeutic schedule of diseases.

Resisting Resistance to Immune Checkpoint Therapy: A Systematic Review

The treatment landscape in oncology has witnessed a major revolution with the introduction of checkpoint inhibitors: anti-PD1, anti-PDL1 and anti-CTLA-4. These agents enhance the immune response towards cancer cells instead of targeting the tumor itself, contrary to standard chemotherapy. Although long-lasting durable responses have been observed with immune checkpoints inhibitors, the response rate remains relatively low in many cases. Some patients respond in the beginning but then eventually develop acquired resistance to treatment and progress. Other patients having primary resistance never respond. Multiple studies have been conducted to further elucidate these variations in response in different tumor types and different individuals. This paper provides an overview of the mechanisms of resistance to immune checkpoint inhibitors and highlights the possible therapeutic approaches under investigation aiming to overcome such resistance in order to improve the clinical outcomes of cancer patients.

Beyond the HLA polymorphism: A complex pattern of genetic susceptibility to pemphigus

Pemphigus is a group of autoimmune bullous skin diseases that result in significant morbidity. As for other multifactorial autoimmune disorders, environmental factors may trigger the disease in genetically susceptible individuals. The goals of this review are to summarize the state of knowledge about the genetic variation that may affect the susceptibility and pathogenesis of pemphigus vulgaris and pemphigus foliaceus – both the endemic and the sporadic forms –, to compare and discuss the possible meaning of the associations reported, and to propose recommendations for new research initiatives. Understanding how genetic variants translate into pathogenic mechanisms and phenotypes remains a mystery for most of the polymorphisms that contribute to disease susceptibility. However, genetic studies provide a strong foundation for further developments in this field by generating testable hypotheses. Currently, results still have limited influence on disease prevention and prognosis, drug development, and clinical practice, although the perspectives for future applications for the benefit of patients are encouraging. Recommendations for the continued advancement of our understanding as to the impact of genetic variation on pemphigus include these partially overlapping goals: (1) Querying the functional effect of genetic variants on the regulation of gene expression through their impact on the nucleotide sequence of cis regulatory DNA elements such as promoters and enhancers, the splicing of RNA, the structure of regulatory RNAs and proteins, binding of these regulatory molecules to regulatory DNA elements, and alteration of epigenetic marks; (2) identifying key cell types and cell states that are implicated in pemphigus pathogenesis and explore their functional genomes; (3) integrating structural and functional genomics data; (4) performing disease-progression longitudinal studies to disclose the causal relationships between genetic and epigenetic variation and intermediate disease phenotypes; (5) understanding the influence of genetic and epigenetic variation in the response to treatment and the severity of the disease; (6) exploring gene-gene and genotype-environment interactions; (7) developing improved pemphigus-prone and non-prone animal models that are appropriate for research about the mechanisms that link genotypes to pemphigus. Achieving these goals will demand larger samples of patients and controls and multisite collaborations.

The landscape of CD28, CD80, CD86, CTLA4, and ICOS DNA methylation in head and neck squamous cell carcinomas

CTLA-4 blocking therapeutic antibodies are currently under investigation in head and neck squamous cell carcinoma (HNSCC). A better understanding of the epigenetic regulation of the CD28 superfamily members CD28, CTLA-4, and ICOS and their B7 ligands, CD80 and CD86, could support the development of biomarkers for response prediction to anti-CTLA-4 immunotherapy. We investigated methylation of the encoding genes CD28, CTLA4, ICOS, CD80, and CD86 at single CpG resolution (51 CpG sites) in a cohort of HNSCC (N = 528) and normal adjacent tissue samples (N = 50) provided by The Cancer Genome Research Atlas, in isolated blood leukocytes from healthy individuals (N = 28), and HNSCC cell lines (N = 39). We analysed methylation levels with regard to mRNA expression, overall survival, mutational load, interferon-γ signature, and signatures of immune cell infiltrates. Depending on the location of the CpG sites (promoter, promoter flank, gene body, and intergenic sites), we found significant differences in methylation levels among isolated leukocytes, between leukocytes and HNSCC cell lines, and among HNSCCs. Methylation of all analysed genes correlated inversely or positively with mRNA expression, depending on the CpG site. CD28, CTLA4, and ICOS revealed almost identical correlation patterns. Furthermore, we found significant correlations with survival and features of response to immunotherapy, i.e. interferon-γ signature, signatures of tumour infiltrating immune cells, and mutational load. Our results suggest CD28, CTLA4, ICOS, CD80, and CD86 expression levels are epigenetically co-regulated by DNA methylation. This study provides rationale to test their DNA methylation as potential biomarker for prediction of response to CTLA-4 immune checkpoint inhibitors.

c-MAF, a Swiss Army Knife for Tolerance in Lymphocytes

Beyond its well-admitted role in development and organogenesis, it is now clear that the transcription factor c-Maf has owned its place in the realm of immune-related transcription factors. Formerly introduced solely as a Th2 transcription factor, the role attributed to c-Maf has gradually broadened over the years and has extended to most, if not all, known immune cell types. The influence of c-Maf is particularly prominent among T cell subsets, where c-Maf regulates the differentiation as well as the function of multiple subsets of CD4 and CD8 T cells, lending it a crucial position in adaptive immunity and anti-tumoral responsiveness. Recent research has also revealed the role of c-Maf in controlling Th17 responses in the intestine, positioning it as an essential factor in intestinal homeostasis. This review aims to present and discuss the recent advances highlighting the particular role played by c-Maf in T lymphocyte differentiation, function, and homeostasis.

ICOS-deficient and ICOS YF mutant mice fail to control Toxoplasma gondii infection of the brain

Resistance to chronic Toxoplasma gondii infection requires ongoing recruitment of T cells to the brain. Thus, the factors that promote, sustain, and regulate the T cell response to the parasite in the brain are of great interest. The costimulatory molecule ICOS (inducible T cell costimulator) has been reported to act largely through the PI3K pathway in T cells, and can play pro-inflammatory or pro-regulatory roles depending on the inflammatory context and T cell type being studied. During infection with T. gondii, ICOS promotes early T cell responses, while in the chronic stage of infection ICOS plays a regulatory role by limiting T cell responses in the brain. We sought to characterize the role of ICOS signaling through PI3K during chronic infection using two models of ICOS deficiency: total ICOS knockout (KO) mice and ICOS YF mice that are unable to activate PI3K signaling. Overall, ICOS KO and ICOS YF mice had similar severe defects in parasite-specific IgG production and parasite control compared to WT mice. Additionally, we observed expanded effector T cell populations and a loss of Treg frequency in the brains of both ICOS KO and ICOS YF mice. When comparing the remaining Treg populations in infected mice, ICOS KO Tregs expressed WT levels of Foxp3 and CD25, while ICOS YF Tregs expressed significantly less Foxp3 and CD25 compared to both WT and ICOS KO mice. Together, these results suggest that PI3K-independent signaling downstream of ICOS plays an important role in Treg stability in the context of chronic inflammation.

The ICOSL Expression Predicts Better Prognosis for Nasopharyngeal Carcinoma via Enhancing Oncoimmunity

Nasopharyngeal carcinoma (NPC) is a malignant tumor with poor prognosis, high morbidity, and mortality. Currently, immunocheckpoint therapy has led to new treatment strategies for almost all cancers, including nasopharyngeal carcinoma. Inducible T-cell aggregation ligand (ICOSL) belongs to the b7-cd28 immunoglobulin superfamily, which is a ligand of ICOS, and also begins to draw attention for its potential usage in cancer treatment. Previous studies from our laboratory have suggested that ICOS expression in tumor-infiltrating lymphocytes is correlated with beneficial outcome, but little is known about the role of ICOSL in NPC. In the current study, ICOSL expression in NPC tumor sections was stained by immunohistochemistry (IHC), and both lymphatic metastasis and distant metastasis showed decreased expression, which was negatively correlated with TNM stage of nasopharyngeal carcinoma. Importantly, high ICOSL expression was significantly associated with overall survival (OS) in patients with NPC (n = 225, p < 0.001), and multivariate analysis confirmed that high ICOSL expression was an independent prognostic factor. Fresh nasopharyngeal carcinoma specimens were excised, and the specific expression of cytokines was analyzed by enzyme-linked immunosorbent assay (ELISA). The expression level of ICOSL is positively correlated with interferon-gamma (IFN-γ) concentration in tumor tissues, which is characteristic of T helper 1 (Th1) cells. Knocking down ICOSL by RNAi did not influence the proliferation, migration, and invasion ability of NPC cells. Conclusively, ICOSL expression is associated with increased survival rate in patients with nasopharyngeal carcinoma, which may be a clinical biomarker for prognosis of nasopharyngeal carcinoma.

Molecular and Cellular Functions of CTLA-4

Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is an inhibitory receptor belonging to the CD28 immunoglobulin subfamily, expressed primarily by T-cells. Its ligands, CD80 and CD86, are typically found on the surface of antigen-presenting cells and can either bind CD28 or CTLA-4, resulting in a costimulatory or a co-inhibitory response, respectively. Because of its dampening effect, CTLA-4 is a crucial regulator of T-cell homeostasis and self-tolerance. The mechanisms by which CTLA-4 exerts its inhibitory function can be categorized as either cell-intrinsic (affects the CTLA-4 expressing T-cell) or cell-extrinsic (affects secondary cells). Research from the last decade has shown that CTLA-4 mainly acts in a cell-extrinsic manner via its competition with CD28, CTLA-4-mediated trans-endocytosis of CD80 and CD86, and its direct tolerogenic effects on the interacting cell. Nonetheless, intrinsic CTLA-4 signaling has been implicated in T-cell motility and the regulation of CTLA-4 its subcellular localization amongst others. CTLA-4 is well recognized as a key immune checkpoint and has gained significant momentum as a therapeutic target in the field of autoimmunity and cancer. In this chapter, we describe the role of costimulation in immune response induction as well as the main mechanisms by which CTLA-4 can inhibit this process.

Role of Co-stimulatory Molecules in T Helper Cell Differentiation

CD4⁺ T cells play a central role in orchestrating the immune response to a variety of pathogens but also regulate autoimmune responses, asthma, allergic responses, as well as tumor immunity. To cover this broad spectrum of responses, naïve CD4⁺ T cells differentiate into one of several lineages of T helper cells, including Th1, Th2, Th17, and T_FH, as defined by their cytokine pattern and function. The fate decision of T helper cell differentiation integrates signals delivered through the T cell receptor, cytokine receptors, and the pattern of co-stimulatory signals received. In this review, we summarize the contribution of co-stimulatory and co-inhibitory receptors to the differentiation and maintenance of T helper cell responses.

Immunomodulatory Bonds of the Partnership between Dendritic Cells and T Cells

By acquiring, processing, and presenting both foreign and self-antigens, dendritic cells (DCs) initiate T cell activation that is shaped through the immunomodulatory functions of a variety of cell-membrane-bound molecules including BTLA-HVEM, CD40-CD40L, CTLA-4-CD80/CD86, CD70-CD27, ICOS-ICOS-L, OX40-OX40L, and PD-L1-PD-1, as well as several key cytokines and enzymes such as interleukin-6 (IL-6), IL-12, IL-23, IL-27, transforming growth factor-beta 1 (TGF-β1), retinaldehyde dehydrogenase (Raldh), and indoleamine 2,3-dioxygenase (IDO). Some of these distinct immunomodulatory signals are mediated by specific subsets of DCs, therefore contributing to the functional specialization of DCs in the priming and regulation of immune responses. In addition to responding to the DC-mediated signals, T cells can reciprocally modulate the immunomodulatory capacities of DCs, further refining immune responses. Here, we review recent studies, particularly in experimental mouse systems, that have delineated the integrated mechanisms of crucial immunomodulatory pathways that enable specific populations of DCs and T cells to work intimately together as single functional units that are indispensable for the maintenance of immune homeostasis.

Blockade of CTLA-4 and PD-1 Enhances Adoptive T-cell Therapy Efficacy in an ICOS-Mediated Manner

Adoptive transfer of tumor-reactive T cells (ACT) has led to modest clinical benefit in the treatment of solid tumors. Failures with this therapy are primarily due to inadequate infiltration and poor function of adoptively transferred cells in the tumor microenvironment. To improve the efficacy of ACT, we combined ACT with dual blockade of CTLA-4 and PD-1. Treatment with anti-CTLA-4 plus anti-PD-1 compared with monotherapy resulted in durable antitumor responses, enhanced effector function of ACT, utilizing PMEL-1 transgenic (Tg⁺) CD8⁺ T cells, and improved survival. Using PMEL-1ICOS^-/- mice, we showed that deletion of the inducible T-cell costimulator (ICOS) receptor abolished the therapeutic benefits, with selective downregulation of Eomesodermin (Eomes), interferon gamma (IFNγ), and perforin. Higher expression of IFNγ and Eomes was noted in human ICOS^hi CD8⁺ T cells compared with ICOS^low counterparts. Together, our data provide direct evidence that ACT combined with immune-checkpoint therapy confers durable antitumor responses, which largely depended on CD8⁺ T-cell-intrinsic expression of ICOS. Our study provides a foundation of testing combinatorial therapy of ACT of CD8 T cells and dual blocking of CTLA-4 and PD-1 in patients with melanoma.

miR-29b Reverses T helper 1 cells/T helper 2 cells Imbalance and Alleviates Airway Eosinophils Recruitment in OVA-Induced Murine Asthma by Targeting Inducible Co-Stimulator

Asthma is a complex chronic disease and the pathogenesis is still not entirely clear. In this study, we aimed to clarify the role and mechanism of miR-29b in the development of asthma. We observed that miR-29b levels were decreased in the lung and spleen of OVA-induced asthmatic mice. Reverse transcription-quantitative polymerase chain reaction and flow cytometry demonstrated that the inducible co-stimulator (ICOS) expression at mRNA and protein levels was elevated in the lung of asthmatic mice, and miR-29b expression in the lung of asthmatic mice was negatively associated with ICOS mRNA levels by Pearson Correlation analysis. Additional, flow cytometry showed that the percentage of CD4+ICOS+ T cells in the lung and spleen was regulated by miR-29b, and dual luciferase reporter assay confirmed ICOS was a target gene of miR-29b. Furthermore, miR-29b overexpression in asthmatic mice was induced with miR-29b agomir by intranasal administration; miR-29b alleviated total inflammatory cell infiltration and CCL24 levels, decreased IL-5 levels in bronchoalveolar lavage fluid and serum, and upregulated IFN-γ expression in serum. This study demonstrates that miR-29b targets ICOS, thereby reverses the imbalance of T helper 1 cells (Th1)/Th2 responses and decreases eosinophils recruitment in the airway, which are key features of allergic airway inflammation. Therefore, miR-29b might be an attractive candidate target for asthma treatment.

AP-1 Transcription Factors as Regulators of Immune Responses in Cancer

Immune check point blockade therapy has revolutionized the standard of cancer treatment and is credited with producing remarkable tumor remissions and increase in overall survival. This unprecedented clinical success however is feasible for a limited number of cancer patients due to resistance occurring before or during a course of immunotherapy, which is often associated with activation of oncogenic signaling pathways, co-inhibitory checkpoints upregulation or expansion of immunosuppressive regulatory T-cells (Tregs) in the tumor microenviroment (TME). Targeted therapy aiming to inactivate a signaling pathway such as the Mitogen Activated Protein Kinases (MAPKs) has recently received a lot of attention due to emerging data from preclinical studies indicating synergy with immune checkpoint blockade therapy. The dimeric transcription factor complex Activator Protein-1 (AP-1) is a group of proteins involved in a wide array of cell processes and a critical regulator of nuclear gene expression during T-cell activation. It is also one of the downstream targets of the MAPK signaling cascade. In this review, we will attempt to unravel the roles of AP-1 in the regulation of anti-tumor immune responses, with a focus on the regulation of immune checkpoints and Tregs, seeking to extract useful insights for more efficacious immunotherapy.

Programmed Cell Death-1 Receptor (PD-1)-Mediated Regulation of Innate Lymphoid Cells

Programmed cell death-1 (PD-1) is a cell surface receptor that dampens adaptive immune responses. PD-1 is activated by the engagement of its ligands PDL-1 or PDL-2. This results in the inhibition of T cell proliferation, differentiation, cytokine secretion, and cytolytic function. Although a great deal is known about PD-1 mediated regulation of CD4⁺ and CD8⁺ T cells, its expression and function in innate lymphoid cells (ILCs) are yet to be fully deciphered. This review summarizes the role of PD-1 in (1) modulating ILC development, (2) ILC function, and (3) PD-1 signaling in ILC. Finally, we explore how PD-1 based immunotherapies may be beneficial in boosting ILC responses in cancer, infections, and other immune-related disorders.

Selecting costimulatory domains for chimeric antigen receptors: functional and clinical considerations

Costimulatory signals are required to achieve robust chimeric antigen receptor (CAR) T cell expansion, function, persistence and antitumor activity. These can be provided by incorporating intracellular signalling domains from one or more T cell costimulatory molecules, such as CD28 or 4-1BB, into the CAR. The selection and positioning of costimulatory domains within a CAR construct influence CAR T cell function and fate, and clinical experience of autologous anti-CD19 CAR T cell therapies suggests that costimulatory domains have differential impacts on CAR T cell kinetics, cytotoxic function and potentially safety profile. The clinical impacts of combining costimulatory domains and of alternative costimulatory domains are not yet clearly established, and may be construct- and disease-specific. The aim of this review is to summarise the function and effect of established and emerging costimulatory domains and their combinations within CAR T cells.

ICOS Costimulation Differentially Affects T Cells in Secondary Lymphoid Organs and Inflamed Tissues

B-cell interaction with follicular helper T cells and subsequent differentiation of B cells into high-affinity APCs normally takes place in secondary lymphoid organs. The costimulator ICOS plays a key role in this process and is therefore considered as an attractive target to modulate exaggerated B-cell responses in autoimmune or allergic diseases. Inflamed tissues were recently recognized as additional sites of active T-cell/B-cell interaction. To analyze whether ICOS costimulation is also important there, we employed a mouse airway inflammation model that allows direct comparison of immune reactions in the lung-draining lymph node and the lung tissue as well as assessment of the relative importance of dendritic cells versus B cells as APCs. In both organs, ICOS regulated the pool size of antigen-specific T and B cells and B-cell differentiation into germinal center(-like) cells but not into antibody-secreting cells. In the lymph node, lack of ICOS costimulation drastically reduced the frequency of T follicular helper cells but did not affect production of T-helper cell type 2 (Th2) cytokines. Vice versa in the lung tissue, ICOS did not change PD-1 expression on infiltrating T cells but regulated Th2 cytokine production, a process for which ICOS ligand expression on B cells was of particular importance. Taken together, the results of this study show that ICOS differentially regulates effector T cells in secondary lymphoid organs and inflamed tissues but that blockade of the ICOS pathway is suitable to target T cell-dependent B cell responses at both sites.

Targeting the ICOS/ICOS-L pathway in a mouse model of established allergic asthma disrupts T follicular helper cell responses and ameliorates disease

Background

Allergic asthma is characterized by chronic inflammation and remodelling of the airways, associated with dysregulated type 2 immune responses and allergen‐specific IgE. T follicular helper cells (T_FH) are crucial in T‐dependent B‐cell responses and have been implicated in allergic airway disease (AAD). T_FH, unlike other CD4⁺ T cells, are uniquely reliant on continuous ICOS signalling to maintain their phenotype after T‐cell priming; therefore, disrupting this signal can impair T_FH responses. However, the contribution of T_FH to disease during chronic aero‐allergen exposure and the therapeutic potential of targeting these cells have not been evaluated.

Methods

To establish AAD, female BALB/c mice were repeatedly exposed to house dust mite or Alternaria alternata three times a week for up to 5 weeks. To examine the impact of T_FH on AAD, mice were allergen exposed for 5 weeks and co‐administered anti‐ICOS Ligand‐targeted antibodies, three times a week for the last 2 weeks.

Results

T_FH were first observed in the lung‐draining lymph nodes and with further exposure were also found locally within the lungs. T_FH accumulated with sustained allergen exposure, alongside germinal centre (GC) B cells. Blockade of ICOS signalling after AAD establishment successfully depleted T_FH but did not affect the differentiation of other CD4⁺ T‐cell subsets. This reduced GC responses, allergen‐specific IgE, inflammation, pulmonary IL‐13 and airway hyper‐responsiveness.

Conclusions

T_FH are crucial in the regulation of AAD and the ICOS/ICOS‐L pathway could represent a novel therapeutic target in allergic asthma.