CD137 (4-1BB) Signalosome: Complexity Is a Matter of TRAFs

Differential protein-protein interactions underlie signaling mediated by the TCR and a 4-1BB domain-containing CAR

Cells rely on activity-dependent protein-protein interactions to convey biological signals. For chimeric antigen receptor (CAR) T cells containing a 4-1BB costimulatory domain, receptor engagement is thought to stimulate the formation of protein complexes similar to those stimulated by T cell receptor (TCR)-mediated signaling, but the number and type of protein interaction-mediating binding domains differ between CARs and TCRs. Here, we performed coimmunoprecipitation mass spectrometry analysis of a second-generation, CD19-directed 4-1BB:ζ CAR (referred to as bbζCAR) and identified 128 proteins that increased their coassociation after target engagement. We compared activity-induced TCR and CAR signalosomes by quantitative multiplex coimmunoprecipitation and showed that bbζCAR engagement led to the activation of two modules of protein interactions, one similar to TCR signaling that was more weakly engaged by bbζCAR as compared with the TCR and one composed of TRAF signaling complexes that was not engaged by the TCR. Batch-to-batch and interindividual variations in production of the cytokine IL-2 correlated with differences in the magnitude of protein network activation. Future CAR T cell manufacturing protocols could measure, and eventually control, biological variation by monitoring these signalosome activation markers.

Signaling via a CD27-TRAF2-SHP-1 axis during naive T cell activation promotes memory-associated gene regulatory networks

The interaction of the tumor necrosis factor receptor (TNFR) family member CD27 on naive CD8+ T (Tn) cells with homotrimeric CD70 on antigen-presenting cells (APCs) is necessary for T cell memory fate determination. Here, we examined CD27 signaling during Tn cell activation and differentiation. In conjunction with T cell receptor (TCR) stimulation, ligation of CD27 by a synthetic trimeric CD70 ligand triggered CD27 internalization and degradation, suggesting active regulation of this signaling axis. Internalized CD27 recruited the signaling adaptor TRAF2 and the phosphatase SHP-1, thereby modulating TCR and CD28 signals. CD27-mediated modulation of TCR signals promoted transcription factor circuits that induced memory rather than effector associated gene programs, which are induced by CD28 costimulation. CD27-costimulated chimeric antigen receptor (CAR)-engineered T cells exhibited improved tumor control compared with CD28-costimulated CAR-T cells. Thus, CD27 signaling during Tn cell activation promotes memory properties with relevance to T cell immunotherapy.

The dynamic role of immune checkpoint molecules in diagnosis, prognosis, and treatment of head and neck cancers

Head and neck cancer (HNC) is the sixth most common cancer type, accounting for approximately 277,597 deaths worldwide. Recently, the Food and Drug Administration (FDA) has approved immune checkpoint blockade (ICB) agents targeting programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) as a treatment regimen for head and neck squamous cell carcinomas (HNSCC). Studies have reported the role of immune checkpoint inhibitors as targeted therapeutic regimens that unleash the immune response against HNSCC tumors. However, the overall response rates to immunotherapy vary between 14-32% in recurrent or metastatic HNSCC, with clinical response and treatment success being unpredictable. Keeping this perspective in mind, it is imperative to understand the role of T cells, natural killer cells, and antigen-presenting cells in modulating the immune response to immunotherapy. In lieu of this, these immune molecules could serve as prognostic and predictive biomarkers to facilitate longitudinal monitoring and understanding of treatment dynamics. These immune biomarkers could pave the path for personalized monitoring and management of HNSCC. In this review, we aim to provide updated immunological insight on the mechanism of action, expression, and the clinical application of immune cells' stimulatory and inhibitory molecules as prognostic and predictive biomarkers in HNC. The review is focused mainly on CD27 and CD137 (members of the TNF-receptor superfamily), natural killer group 2 member D (NKG2D), tumor necrosis factor receptor superfamily member 4 (TNFRSF4 or OX40), S100 proteins, PD-1, PD-L1, PD-L2, T cell immunoglobulin and mucin domain 3 (TIM-3), cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), lymphocyte-activation gene 3 (LAG-3), indoleamine-pyrrole 2,3-dioxygenase (IDO), B and T lymphocyte attenuator (BTLA). It also highlights the importance of T, natural killer, and antigen-presenting cells as robust biomarker tools for understanding immune checkpoint inhibitor-based treatment dynamics. Though a comprehensive review, all aspects of the immune molecules could not be covered as they were beyond the scope of the review; Further review articles can cover other aspects to bridge the knowledge gap.

The 4-1BBζ costimulatory domain in chimeric antigen receptors enhances CD8+ T-cell functionality following T-cell receptor stimulation

BACKGROUND

Chimeric antigen receptor (CAR) T-cells have revolutionized the treatment of CD19- and B-cell maturation antigen-positive haematological malignancies. However, the effect of a CAR construct on the function of T-cells stimulated via their endogenous T-cell receptors (TCRs) has yet to be comprehensively investigated.

METHODS

Experiments were performed to systematically assess TCR signalling and function in CAR T-cells using anti-mesothelin human CAR T-cells as a model system. CAR T-cells expressing the CD28 or 4-1BB costimulatory endodomains were manufactured and compared to both untransduced T-cells and CAR T-cells with a non-functional endodomain. These cell products were treated with staphylococcal enterotoxin B to stimulate the TCR, and in vitro functional assays were performed by flow cytometry.

RESULTS

Increased proliferation, CD69 expression and IFNγ production were identified in CD8+ 4-1BBζ CAR T-cells compared to control untransduced CD8+ T-cells. These functional differences were associated with higher levels of phosphorylated ZAP70 after stimulation. In addition, these functional differences were associated with a differing immunophenotype, with a more than two-fold increase in central memory cells in CD8+ 4-1BBζ CAR T-cell products.

CONCLUSION

Our data indicate that the 4-1BBζ CAR enhances CD8+ TCR-mediated function. This could be beneficial if the TCR targets epitopes on malignant tissues or infectious agents, but detrimental if the TCR targets autoantigens.

ATOR-1017 (evunzekibart), an Fc-gamma receptor conditional 4-1BB agonist designed for optimal safety and efficacy, activates exhausted T cells in combination with anti-PD-1

BACKGROUND

4-1BB (CD137) is a co-stimulatory receptor highly expressed on tumor reactive effector T cells and NK cells, which upon stimulation prolongs persistence of tumor reactive effector T and NK cells within the tumor and induces long-lived memory T cells. 4-1BB agonistic antibodies have been shown to induce strong anti-tumor effects that synergize with immune checkpoint inhibitors. The first generation of 4-1BB agonists was, however, hampered by dose-limiting toxicities resulting in suboptimal dose levels or poor agonistic activity.

METHODS

ATOR-1017 (evunzekibart), a second-generation Fc-gamma receptor conditional 4-1BB agonist in IgG4 format, was designed to overcome the limitations of the first generation of 4-1BB agonists, providing strong agonistic effect while minimizing systemic immune activation and risk of hepatoxicity. The epitope of ATOR-1017 was determined by X-ray crystallography, and the functional activity was assessed in vitro and in vivo as monotherapy or in combination with anti-PD1.

RESULTS

ATOR-1017 binds to a unique epitope on 4-1BB enabling ATOR-1017 to activate T cells, including cells with an exhausted phenotype, and NK cells, in a cross-linking dependent, FcγR-conditional, manner. This translated into a tumor-directed and potent anti-tumor therapeutic effect in vivo, which was further enhanced with anti-PD-1 treatment.

CONCLUSIONS

These preclinical data demonstrate a strong safety profile of ATOR-1017, together with its potent therapeutic effect as monotherapy and in combination with anti-PD1, supporting further clinical development of ATOR-1017.

Information-Theoretic Analysis of a Model of CAR-4-1BB-Mediated NFκB Activation

Systems biology utilizes computational approaches to examine an array of biological processes, such as cell signaling, metabolomics and pharmacology. This includes mathematical modeling of CAR T cells, a modality of cancer therapy by which genetically engineered immune cells recognize and combat a cancerous target. While successful against hematologic malignancies, CAR T cells have shown limited success against other cancer types. Thus, more research is needed to understand their mechanisms of action and leverage their full potential. In our work, we set out to apply information theory on a mathematical model of NFκB signaling initiated by the CAR following antigen encounter. First, we estimated channel capacity for CAR-4-1BB-mediated NFκB signal transduction. Next, we evaluated the pathway's ability to distinguish contrasting "low" and "high" antigen concentration levels, depending on the amount of variability in protein concentrations. Finally, we assessed the fidelity by which NFκB activation reflects the encountered antigen concentration, depending on the prevalence of antigen-positive targets in tumor population. We found that in most scenarios, fold change in the nuclear concentration of NFκB carries a higher channel capacity for the pathway than NFκB's absolute response. Additionally, we found that most errors in transducing the antigen signal through the pathway skew towards underestimating the concentration of encountered antigen. Finally, we found that disabling IKKβ deactivation could increase signaling fidelity against targets with antigen-negative cells. Our information-theoretic analysis of signal transduction can provide novel perspectives on biological signaling, as well as enable a more informed path to cell engineering.Kindly check and confirm whether the corresponding affiliation is correctly identified.this is correct.

MAIT cells confer resistance to Lenvatinib plus anti-PD1 antibodies in hepatocellular carcinoma through TNF-TNFRSF1B pathway

The combination of antiangiogenic agents and immune checkpoint inhibitors is more efficient than monotherapy in the management of hepatocellular carcinoma (HCC). Lenvatinib plus anti-PD1 antibodies have become the mainstay in HCC treatment. However, more than half the patients with HCC are non-responsive, and the mechanisms underlying drug resistance are unknown. To address this issue, we performed single-cell sequencing on samples from six HCC patients, aiming to explore cellular signals and molecular pathways related to the effect of lenvatinib plus anti-PD1 antibody treatment. GSVA analysis revealed that treatment with lenvatinib plus anti-PD1 antibody led to an increase in the TNF-NFKB pathway across all immune cell types, as compared to the non-treatment group. Mucosal-associated invariant T (MAIT) cells were found to secrete TNF, which activates TNFRSF1B on regulatory T cells, thereby promoting immunosuppression. Additionally, TNFSF9 was highly expressed in anticancer immune cells, including CD8+ effector T cells, MAIT, and γδ T cells in the treatment group. We also detected CD3+ macrophages in both HCC and pan-cancer tissues. Overall, our findings shed light on the potential mechanisms behind the effectiveness of lenvatinib plus anti-PD1 antibody treatment in HCC patients. By understanding these mechanisms better, we may be able to develop more effective treatment strategies for patients who do not respond to current therapies.

Immune interactions in pembrolizumab (PD-1 inhibitor) cancer therapy and cardiovascular complications

The use of immunotherapies like pembrolizumab (PEM) is increasingly common for the management of numerous cancer types. The use of PEM to bolster T-cell response against tumor growth is well documented. However, the interactions PEM has on other immune cells to facilitate tumor regression and clearance is unknown and warrants further investigation. In this review, we present literature findings that have reported the interactions of PEM in stimulating innate and adaptive immune cells, which enhance cytotoxic phenotypes. This triggers secretion of cytokines and chemokines, which have both beneficial and detrimental effects. We also describe how this leads to the development of rare but underreported occurrence of PEM-induced immune-related cardiovascular complications that arise suddenly and progress rapidly to debilitating and fatal consequences. This review encourages further research and investigation of PEM-induced cardiovascular complications and other immune cell interactions in patients with cancer. As PEM therapy in treating cancer types is expanding, we expect that this review will inform health care professionals of diverse specializations of medicine like dermatology (melanoma skin cancers), ophthalmology (eye cancers), and pathology (hematological malignancies) about PEM-induced cardiac complications.

4-1BB Targeting Immunotherapy: Mechanism, Antibodies, and Chimeric Antigen Receptor T

4-1BB (CD137, TNFRSF9) is a type I transmembrane protein which binds its natural ligand, 4-1BBL. This interaction has been exploited to improve cancer immunotherapy. With ligand binding by 4-1BB, the nuclear factor-kappa B signaling pathway is activated, which results in transcription of corresponding genes such as interleukin-2 and interferon-γ, as well as the induction of T cell proliferation and antiapoptotic signals. Moreover, monoclonal antibodies that target-4-1BB, for example, Urelumab and Utomilumab, are widely used in the treatments of B cell non-Hodgkin lymphoma, lung cancer, breast cancer, soft tissue sarcoma, and other solid tumors. Furthermore, 4-1BB as a costimulatory domain, for chimeric antigen receptor T (CAR-T) cells, improves T cell proliferation and survival as well as reduces T cell exhaustion. As such, a deeper understanding of 4-1BB will contribute to improvements in cancer immunotherapy. This review provides a comprehensive analysis of current 4-1BB studies, with a focus on the use of targeting-4-1BB antibodies and 4-1BB activation domains in CAR-T cells for the treatment of cancer.

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.

CD137 (4-1BB) requires physically associated cIAPs for signal transduction and antitumor effects

CD137 (4-1BB) is a member of the TNFR family that mediates potent T cell costimulatory signals upon ligation by CD137L or agonist monoclonal antibodies (mAbs). CD137 agonists attain immunotherapeutic antitumor effects in cancer mouse models, and multiple agents of this kind are undergoing clinical trials. We show that cIAP1 and cIAP2 are physically associated with the CD137 signaling complex. Moreover, cIAPs are required for CD137 signaling toward the NF-κB and MAPK pathways and for costimulation of human and mouse T lymphocytes. Functional evidence was substantiated with SMAC mimetics that trigger cIAP degradation and by transfecting cIAP dominant-negative variants. Antitumor effects of agonist anti-CD137 mAbs are critically dependent on the integrity of cIAPs in cancer mouse models, and cIAPs are also required for signaling from CARs encompassing CD137's cytoplasmic tail.

The benefits of clustering in TNF receptor superfamily signaling

The tumor necrosis factor (TNF) receptor superfamily is a structurally and functionally related group of cell surface receptors that play crucial roles in various cellular processes, including apoptosis, cell survival, and immune regulation. This review paper synthesizes key findings from recent studies, highlighting the importance of clustering in TNF receptor superfamily signaling. We discuss the underlying molecular mechanisms of signaling, the functional consequences of receptor clustering, and potential therapeutic implications of targeting surface structures of receptor complexes.

Agonism of 4-1BB for immune therapy: a perspective on possibilities and complications

Costimulatory receptors on immune cells represent attractive targets for immunotherapy given that these molecules can increase the frequency of individual protective immune cell populations and their longevity, as well as enhance various effector functions. 4-1BB, a member of the TNF receptor superfamily, also known as CD137 and TNFRSF9, is one such molecule that is inducible on several cell types, including T cells and NK cells. Preclinical studies in animal models have validated the notion that stimulating 4-1BB with agonist reagents or its natural ligand could be useful to augment conventional T cell and NK cell immunity to protect against tumor growth and against viral infection. Additionally, stimulating 4-1BB can enhance regulatory T cell function and might be useful in the right context for suppressing autoimmunity. Two human agonist antibodies to 4-1BB have been produced and tested in clinical trials for cancer, with variable results, leading to the production of a wealth of second-generation antibody constructs, including bi- and multi-specifics, with the hope of optimizing activity and selectivity. Here, we review the progress to date in agonism of 4-1BB, discuss the complications in targeting the immune system appropriately to elicit the desired activity, together with challenges in engineering agonists, and highlight the untapped potential of manipulating this molecule in infectious disease and autoimmunity.

TRAFfic signals: High-throughput CAR discovery in NK cells reveals novel TRAF-binding endodomains that drive enhanced persistence and cytotoxicity

Natural killer (NK) cells are a promising alternative therapeutic platform to CAR T cells given their favorable safety profile and potent killing ability. However, CAR NK cells suffer from limited persistence in vivo , which is, in part, thought to be the consequence of limited cytokine signaling. To address this challenge, we developed an innovative high-throughput screening strategy to identify CAR endodomains that could drive enhanced persistence while maintaining potent cytotoxicity. We uncovered a family of TRAF-binding endodomains that outperform benchmarks in primary NK cells along dimensions of persistence and cytotoxicity, even in low IL-2 conditions. This work highlights the importance of cell-type-specific cell therapy engineering and unlocks a wide range of high-throughput molecular engineering avenues in NK cells.

TCR-independent CD137 (4-1BB) signaling promotes CD8+-exhausted T cell proliferation and terminal differentiation

CD137 (4-1BB)-activating receptor represents a promising cancer immunotherapeutic target. Yet, the cellular program driven by CD137 and its role in cancer immune surveillance remain unresolved. Using T cell-specific deletion and agonist antibodies, we found that CD137 modulates tumor infiltration of CD8+-exhausted T (Tex) cells expressing PD1, Lag-3, and Tim-3 inhibitory receptors. T cell-intrinsic, TCR-independent CD137 signaling stimulated the proliferation and the terminal differentiation of Tex precursor cells through a mechanism involving the RelA and cRel canonical NF-κB subunits and Tox-dependent chromatin remodeling. While Tex cell accumulation induced by prophylactic CD137 agonists favored tumor growth, anti-PD1 efficacy was improved with subsequent CD137 stimulation in pre-clinical mouse models. Better understanding of T cell exhaustion has crucial implications for the treatment of cancer and infectious diseases. Our results identify CD137 as a critical regulator of Tex cell expansion and differentiation that holds potential for broad therapeutic applications.

Novel Fas-TNFR chimeras that prevent Fas ligand-mediated kill and signal synergistically to enhance CAR T cell efficacy

The hostile tumor microenvironment limits the efficacy of adoptive cell therapies. Activation of the Fas death receptor initiates apoptosis and disrupting these receptors could be key to increasing CAR T cell efficacy. We screened a library of Fas-TNFR proteins identifying several novel chimeras that not only prevented Fas ligand-mediated kill, but also enhanced CAR T cell efficacy by signaling synergistically with the CAR. Upon binding Fas ligand, Fas-CD40 activated the NF-κB pathway, inducing greatest proliferation and IFN-γ release out of all Fas-TNFRs tested. Fas-CD40 induced profound transcriptional modifications, particularly genes relating to the cell cycle, metabolism, and chemokine signaling. Co-expression of Fas-CD40 with either 4-1BB- or CD28-containing CARs increased in vitro efficacy by augmenting CAR T cell proliferation and cancer target cytotoxicity, and enhanced tumor killing and overall mouse survival in vivo. Functional activity of the Fas-TNFRs were dependent on the co-stimulatory domain within the CAR, highlighting crosstalk between signaling pathways. Furthermore, we show that a major source for Fas-TNFR activation derives from CAR T cells themselves via activation-induced Fas ligand upregulation, highlighting a universal role of Fas-TNFRs in augmenting CAR T cell responses. We have identified Fas-CD40 as the optimal chimera for overcoming Fas ligand-mediated kill and enhancing CAR T cell efficacy.

Information-theoretic analysis of a model of CAR-4-1BB-mediated NFκB activation

Systems biology utilizes computational approaches to examine an array of biological processes, such as cell signaling, metabolomics and pharmacology. This includes mathematical modeling of CAR T cells, a modality of cancer therapy by which genetically engineered immune cells recognize and combat a cancerous target. While successful against hematologic malignancies, CAR T cells have shown limited success against other cancer types. Thus, more research is needed to understand their mechanisms of action and leverage their full potential. In our work, we set out to apply information theory on a mathematical model of cell signaling of CAR-mediated activation following antigen encounter. First, we estimated channel capacity for CAR-4-1BB-mediated NFκB signal transduction. Next, we evaluated the pathway's ability to distinguish contrasting "low" and "high" antigen concentration levels, depending on the amount of intrinsic noise. Finally, we assessed the fidelity by which NFκB activation reflects the encountered antigen concentration, depending on the prevalence of antigen-positive targets in tumor population. We found that in most scenarios, fold change in the nuclear concentration of NFκB carries a higher channel capacity for the pathway than NFκB's absolute response. Additionally, we found that most errors in transducing the antigen signal through the pathway skew towards underestimating the concentration of encountered antigen. Finally, we found that disabling IKKβ deactivation could increase signaling fidelity against targets with antigen-negative cells. Our information-theoretic analysis of signal transduction can provide novel perspectives on biological signaling, as well as enable a more informed path to cell engineering.

Engineering second-generation TCR-T cells by site-specific integration of TRAF-binding motifs into the CD247 locus

BACKGROUND

The incorporation of co-stimulatory signaling domains into second-generation chimeric antigen receptors (CARs) significantly enhances the proliferation and persistence of CAR-T cells in vivo, leading to successful clinical outcomes.

METHODS

To achieve such functional enhancement in transgenic T-cell receptor-engineered T-cell (TCR-T) therapy, we designed a second-generation TCR-T cell in which CD3ζ genes modified to contain the intracellular domain (ICD) of the 4-1BB receptor were selectively inserted into the CD247 locus.

RESULTS

This modification enabled the simultaneous recruitment of key adaptor molecules for signals 1 and 2 on TCR engagement. However, the addition of full-length 4-1BB ICD unexpectedly impaired the expression and signaling of TCRs, leading to suboptimal antitumor activity of the resulting TCR-T cells in vivo. We found that the basic-rich motif (BRM) in the 4-1BB ICD was responsible for the undesirable outcomes, and that fusion of minimal tumor necrosis factor receptor-associated factor (TRAF)-binding motifs at the C-terminus of CD3ζ (zBB^ΔBRM) was sufficient to recruit TRAF2, the key adaptor molecule in 4-1BB signaling, while retaining the expression and proximal signaling of the transgenic TCR. Consequently, TCR-T cells expressing zBB^ΔBRM exhibited improved persistence and expansion in vitro and in vivo, resulting in superior antitumor activity in a mouse xenograft model.

CONCLUSIONS

Our findings offer a promising strategy for improving the intracellular signaling of TCR-T cells and their application in treating solid tumors.

Toward high-throughput engineering techniques for improving CAR intracellular signaling domains

Chimeric antigen receptors (CAR) are generated by linking extracellular antigen recognition domains with one or more intracellular signaling domains derived from the T-cell receptor complex or various co-stimulatory receptors. The choice and relative positioning of signaling domains help to determine chimeric antigen receptors T-cell activity and fate in vivo. While prior studies have focused on optimizing signaling power through combinatorial investigation of native intracellular signaling domains in modular fashion, few have investigated the prospect of sequence engineering within domains. Here, we sought to develop a novel in situ screening method that could permit deployment of directed evolution approaches to identify intracellular domain variants that drive selective induction of transcription factors. To accomplish this goal, we evaluated a screening approach based on the activation of a human NF-κB and NFAT reporter T-cell line for the isolation of mutations that directly impact T cell activation in vitro. As a proof-of-concept, a model library of chimeric antigen receptors signaling domain variants was constructed and used to demonstrate the ability to discern amongst chimeric antigen receptors containing different co-stimulatory domains. A rare, higher-signaling variant with frequency as low as 1 in 1000 could be identified in a high throughput setting. Collectively, this work highlights both prospects and limitations of novel mammalian display methods for chimeric antigen receptors signaling domain discovery and points to potential strategies for future chimeric antigen receptors development.

The emerging landscape of novel 4-1BB (CD137) agonistic drugs for cancer immunotherapy

The clinical development of 4-1BB agonists for cancer immunotherapy has raised substantial interest during the past decade. The first generation of 4-1BB agonistic antibodies entering the clinic, urelumab (BMS-663513) and utomilumab (PF-05082566), failed due to (liver) toxicity or lack of efficacy, respectively. The two antibodies display differences in the affinity and the 4-1BB receptor epitope recognition, as well as the isotype, which determines the Fc-gamma-receptor (FcγR) crosslinking activity. Based on this experience a very diverse landscape of second-generation 4-1BB agonists addressing the liabilities of first-generation agonists has recently been developed, with many entering clinical Phase 1 and 2 studies. This review provides an overview focusing on differences and their scientific rationale, as well as challenges foreseen during the clinical development of these molecules.

Triggering of lymphocytes by CD28, 4-1BB, and PD-1 checkpoints to enhance the immune response capacities

Tumor infiltrating lymphocytes (TILs) usually become exhausted and dysfunctional owing to chronic contact with tumor cells and overexpression of multiple inhibitor receptors. Activation of TILs by targeting the inhibitory and stimulatory checkpoints has emerged as one of the most promising immunotherapy prospectively. We investigated whether triggering of CD28, 4-1BB, and PD-1 checkpoints simultaneously or alone could enhance the immune response capacity of lymphocytes. In this regard, anti-PD-1, CD80-Fc, and 4-1BBL-Fc proteins were designed and produced in CHO-K1 cells as an expression host. Following confirmation of the Fc fusion proteins' ability to bind to native targets expressed on engineered CHO-K1 cells (CHO-K1/hPD-1, CHO-K1/hCD28, CHO-K1/hCTLA4, and CHO-K1/h4-1BB), the effects of each protein, on its own and in various combinations, were assessed in vitro on T cell proliferation, cytotoxicity, and cytokines secretion using the Mixed lymphocyte reaction (MLR) assay, 7-AAD/CFSE cell-mediated cytotoxicity assay, and a LEGENDplex™ Human Th Cytokine Panel, respectively. MLR results demonstrated that T cell proliferation in the presence of the combinations of anti-PD-1/CD80-Fc, CD80-Fc/4-1BBL-Fc, and anti-PD-1/CD80-Fc/4-1BBL-Fc proteins was significantly higher than in the untreated condition (1.83-, 1.91-, and 2.02-fold respectively). Furthermore, anti-PD-1 (17%), 4-1BBL-Fc (19.2%), anti-PD-1/CD80-Fc (18.6%), anti-PD-1/4-1BBL-Fc (21%), CD80-Fc/4-1BBL-Fc (18.5%), and anti-PD-1/CD80-Fc/4-1BBL-Fc (17.3%) significantly enhanced cytotoxicity activity compared to untreated condition (7.8%). However, concerning the cytokine production, CD80-Fc and 4-1BBL-Fc alone or in combination significantly increased the secretion of IFN-γ, TNF-α, and IL-2 compared with the untreated conditions. In conclusion, this research establishes that the various combinations of produced anti-PD-1, CD80-Fc, and 4-1BBL-Fc proteins can noticeably induce the immune response in vitro. Each of these combinations may be effective in killing or destroying cancer cells depending on the type and stage of cancer.

Efficacy of bivalent CEACAM6/4-1BBL genetic vaccine combined with anti-PD1 antibody in MC38 tumor model of mice

We used mouse CRC cell line (MC38) to establish a heterotopic mouse model, and applied [⁸⁹Zr]-labeled PD-L1 antibody KN035 for PET imaging. Attenuated Salmonella typhimurium 3261 was used as an anti-tumor vaccine, and the combined anti-tumor immunotherapy with bivalent genetic vaccine and anti-PD1 antibody Nivolumab was conducted. MicroPET was performed to observe the changes of tumor tissues and expression of PD-L1. We found that the recombinant double-gene plasmids were stably expressed in COS7 cells. Study results showed the combined immunotherapy improved the effectiveness over genetic vaccine alone. This study supports that combination of genetic vaccines and anti-immunocheckpoint immunotherapy can inhibit MC38 tumor growth.

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.

4-1BB: A promising target for cancer immunotherapy

Immunotherapy, powered by its relative efficacy and safety, has become a prominent therapeutic strategy utilized in the treatment of a wide range of diseases, including cancer. Within this class of therapeutics, there is a variety of drug types such as immune checkpoint blockade therapies, vaccines, and T cell transfer therapies that serve the purpose of harnessing the body’s immune system to combat disease. Of these different types, immune checkpoint blockades that target coinhibitory receptors, which dampen the body’s immune response, have been widely studied and established in clinic. In contrast, however, there remains room for the development and improvement of therapeutics that target costimulatory receptors and enhance the immune response against tumors, one of which being the 4-1BB (CD137/ILA/TNFRSF9) receptor. 4-1BB has been garnering attention as a promising therapeutic target in the setting of cancer, amongst other diseases, due to its broad expression profile and ability to stimulate various signaling pathways involved in the generation of a potent immune response. Since its discovery and demonstration of potential as a clinical target, major progress has been made in the knowledge of 4-1BB and the development of clinical therapeutics that target it. Thus, we seek to summarize and provide a comprehensive update and outlook on those advancements in the context of cancer and immunotherapy.

Computational analysis of 4-1BB-induced NFκB signaling suggests improvements to CAR cell design

Background

Chimeric antigen receptor (CAR)-expressing cells are a powerful modality of adoptive cell therapy against cancer. The potency of signaling events initiated upon antigen binding depends on the costimulatory domain within the structure of the CAR. One such costimulatory domain is 4-1BB, which affects cellular response via the NFκB pathway. However, the quantitative aspects of 4-1BB-induced NFκB signaling are not fully understood.

Methods

We developed an ordinary differential equation-based mathematical model representing canonical NFκB signaling activated by CD19scFv-4-1BB. After a global sensitivity analysis on model parameters, we ran Monte Carlo simulations of cell population-wide variability in NFκB signaling and quantified the mutual information between the extracellular signal and different levels of the NFκB signal transduction pathway.

Results

In response to a wide range of antigen concentrations, the magnitude of the transient peak in NFκB nuclear concentration varies significantly, while the timing of this peak is relatively consistent. Global sensitivity analysis showed that the model is robust to variations in parameters, and thus, its quantitative predictions would remain applicable to a broad range of parameter values. The model predicts that overexpressing NEMO and disabling IKKβ deactivation can increase the mutual information between antigen levels and NFκB activation.

Conclusions

Our modeling predictions provide actionable insights to guide CAR development. Particularly, we propose specific manipulations to the NFκB signal transduction pathway that can fine-tune the response of CD19scFv-4-1BB cells to the antigen concentrations they are likely to encounter.

Utomilumab in Patients With Immune Checkpoint Inhibitor-Refractory Melanoma and Non-Small-Cell Lung Cancer

Section Head

Clinical/translational cancer immunotherapy

Background

The goal of this study was to estimate the objective response rate for utomilumab in adults with immune checkpoint inhibitor (ICI)-refractory melanoma and non–small-cell lung cancer (NSCLC).

Methods

Utomilumab was dosed intravenously every 4 weeks (Q4W) and adverse events (AEs) monitored. Tumor responses by RECIST1.1 were assessed by baseline and on-treatment scans. Tumor biopsies were collected for detection of programmed cell death ligand 1, CD8, 4-1BB, perforin, and granzyme B, and gene expression analyzed by next-generation sequencing. CD8+ T cells from healthy donors were stimulated with anti-CD3 ± utomilumab and compared with control.

Results

Patients with melanoma (n=43) and NSCLC (n=20) received utomilumab 0.24 mg/kg (n=36), 1.2 mg/kg (n=26), or 10 mg/kg (n=1). Treatment-emergent AEs (TEAEs) occurred in 55 (87.3%) patients and serious TEAEs in 18 (28.6%). Five (7.9%) patients discontinued owing to TEAEs. Thirty-two (50.8%) patients experienced treatment-related AEs, mostly grade 1–2. Objective response rate: 2.3% in patients with melanoma; no confirmed responses for patients with NSCLC. Ten patients each with melanoma (23.3%) or NSCLC (50%) had stable disease; respective median (95% confidence interval, CI) progression-free survival was 1.8 (1.7–1.9) and 3.6 (1.6–6.5) months. Utomilumab exposure increased with dose. The incidences of antidrug and neutralizing antibodies were 46.3% and 19.4%, respectively. Efficacy was associated with immune-active tumor microenvironments, and pharmacodynamic activity appeared to be blunted at higher doses.

Conclusions

Utomilumab was well tolerated, but antitumor activity was low in patients who previously progressed on ICIs. The potential of 4-1BB agonists requires additional study to optimize efficacy while maintaining the tolerable safety profile.

FBXL20-mediated ubiquitination triggers the proteasomal degradation of 4-1BB

4-1BB [tumor necrosis factor receptor superfamily (TNFRSF9), CD137) is a critical immune stimulator that sustains T cell activity and antitumor immune response. The strategy to eliminate cancers by agonistically targeting 4-1BB is under clinical investigation. As a protein expressed in an inducible manner, 4-1BB is under tight control on both transcription and translation levels to maintain its homeostasis. So far, the mechanisms underlying the transcriptional activation of 4-1BB have been well-interpreted; however, it remains inexplicit how 4-1BB is regulated on the protein level. In this study, we presented experimental evidence supporting that 4-1BB, especially the heavily N-glycosylated (mature) form, is polyubiquitinated and subjected to the ubiquitin-proteasomal system for degradation. By performing proximity-dependent biotin identification screening coupled with biochemical assays, we identified that F-box/LRR-repeat protein 20 acts as the E3 ligase that promotes the polyubiquitination of 4-1BB at the intracellular domain. Our data provided mechanistic insight into 4-1BB regulation on the protein level by unmasking, for the first time, a posttranslational mechanism governing 4-1BB abundance in cells. The findings of this study could potentially guide the development of 4-1BB-targeted therapy for cancers as well as other immune disorders.

The long and winding road: From mouse linkage studies to a novel human therapeutic pathway in type 1 diabetes

Autoimmunity involves a loss of immune tolerance to self-proteins due to a combination of genetic susceptibility and environmental provocation, which generates autoreactive T and B cells. Genetic susceptibility affects lymphocyte autoreactivity at the level of central tolerance (e.g., defective, or incomplete MHC-mediated negative selection of self-reactive T cells) and peripheral tolerance (e.g., failure of mechanisms to control circulating self-reactive T cells). T regulatory cell (Treg) mediated suppression is essential for controlling peripheral autoreactive T cells. Understanding the genetic control of Treg development and function and Treg interaction with T effector and other immune cells is thus a key goal of autoimmunity research. Herein, we will review immunogenetic control of tolerance in one of the classic models of autoimmunity, the non-obese diabetic (NOD) mouse model of autoimmune Type 1 diabetes (T1D). We review the long (and still evolving) elucidation of how one susceptibility gene, Cd137, (identified originally via linkage studies) affects both the immune response and its regulation in a highly complex fashion. The CD137 (present in both membrane and soluble forms) and the CD137 ligand (CD137L) both signal into a variety of immune cells (bi-directional signaling). The overall outcome of these multitudinous effects (either tolerance or autoimmunity) depends upon the balance between the regulatory signals (predominantly mediated by soluble CD137 via the CD137L pathway) and the effector signals (mediated by both membrane-bound CD137 and CD137L). This immune balance/homeostasis can be decisively affected by genetic (susceptibility vs. resistant alleles) and environmental factors (stimulation of soluble CD137 production). The discovery of the homeostatic immune effect of soluble CD137 on the CD137-CD137L system makes it a promising candidate for immunotherapy to restore tolerance in autoimmune diseases.

Cowpea Mosaic Virus and Natural Killer Cell Agonism for In Situ Cancer Vaccination

We have previously shown the plant virus Cowpea mosaic virus (CPMV) to be an efficacious in situ cancer vaccine, providing elimination of tumors and tumor-specific immune memory. Additionally, we have shown that CPMV recruits Natural Killer (NK) cells within the tumor microenvironment. Here we aimed to determine whether a combination of CPMV and anti-4-1BB monoclonal antibody agonist to stimulate tumor-resident and CPMV-recruited NK cells is an effective dual therapy approach to improve NK cell function and in situ cancer vaccination efficacy. Using murine models of metastatic colon carcinomatosis and intradermal melanoma, intratumorally administered CPMV + anti-4-1BB dual therapy provided a robust antitumor response, improved elimination of primary tumors, and reduced mortality compared to CPMV and anti-4-1BB monotherapies. Additionally, on tumor rechallenge there was significant delay/prevention of tumor development and improved survival, highlighting that the CPMV + anti-4-1BB dual therapy enables potent and durable antitumor efficacy.

Galectin-3 Decreases 4-1BBL Bioactivity by Crosslinking Soluble and Membrane Expressed 4-1BB

4-1BB is a T cell costimulatory receptor and a member of the tumor necrosis factor receptor superfamily. Here, we show that Galectin-3 (Gal-3) decreases the cellular response to its ligand (4-1BBL). Gal-3 binds to both soluble 4-1BB (s4-1BB) and membrane-bound 4-1BB (mem4-1BB), without blocking co-binding of 4-1BBL. In plasma, we detected complexes composed of 4-1BB and Gal-3 larger than 100 nm in size; these complexes were reduced in synovial fluid from rheumatoid arthritis. Both activated 4-1BB⁺ T cells and 4-1BB-transfected HEK293 cells depleted these complexes from plasma, followed by increased expression of 4-1BB and Gal-3 on the cell surface. The increase was accompanied by a 4-fold decrease in TNFα production by the 4-1BB^highGal-3⁺ T cells, after exposure to 4-1BB/Gal-3 complexes. In RA patients, complexes containing 4-1BB/Gal-3 were dramatically reduced in both plasma and SF compared with healthy plasma. These results support that Gal-3 binds to 4-1BB without blocking the co-binding of 4-1BBL. Instead, Gal-3 leads to formation of large soluble 4-1BB/Gal-3 complexes that attach to mem4-1BB on the cell surfaces, resulting in suppression of 4-1BBL’s bioactivity.

An anti-PD-1–GITR-L bispecific agonist induces GITR clustering-mediated T cell activation for cancer immunotherapy

Costimulatory receptors such as glucocorticoid-induced tumor necrosis factor receptor–related protein (GITR) play key roles in regulating the effector functions of T cells. In human clinical trials, however, GITR agonist antibodies have shown limited therapeutic effect, which may be due to suboptimal receptor clustering-mediated signaling. To overcome this potential limitation, a rational protein engineering approach is needed to optimize GITR agonist-based immunotherapies. Here we show a bispecific molecule consisting of an anti-PD-1 antibody fused with a multimeric GITR ligand (GITR-L) that induces PD-1-dependent and FcγR-independent GITR clustering, resulting in enhanced activation, proliferation and memory differentiation of primed antigen-specific GITR⁺PD-1⁺ T cells. The anti-PD-1–GITR-L bispecific is a PD-1-directed GITR-L construct that demonstrated dose-dependent, immunologically driven tumor growth inhibition in syngeneic, genetically engineered and xenograft humanized mouse tumor models, with a dose-dependent correlation between target saturation and Ki67 and TIGIT upregulation on memory T cells. Anti-PD-1–GITR-L thus represents a bispecific approach to directing GITR agonism for cancer immunotherapy.

Alvarez and colleagues develop a bispecific anti-PD-1–GITR-L agonist that activates T cells via a mechanism distinct from those found with individual PD-1 and GITR-L agonists and demonstrate its antitumor activity in mice and nonhuman primates.

SILAC Phosphoproteomics Reveals Unique Signaling Circuits in CAR-T Cells and the Inhibition of B Cell-Activating Phosphorylation in Target Cells

Chimeric antigen receptor (CAR) is a single-pass transmembrane receptor designed to specifically target and eliminate cancers. While CARs prove highly efficacious against B cell malignancies, the intracellular signaling events which promote CAR T cell activity remain elusive. To gain further insight into both CAR T cell signaling and the potential signaling response of cells targeted by CAR, we analyzed phosphopeptides captured by two separate phosphoenrichment strategies from third generation CD19-CAR T cells cocultured with SILAC labeled Raji B cells by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Here, we report that CD19-CAR T cells upregulated several key phosphorylation events also observed in canonical T cell receptor (TCR) signaling, while Raji B cells exhibited a significant decrease in B cell receptor-signaling related phosphorylation events in response to coculture. Our data suggest that CD19-CAR stimulation activates a mixture of unique CD19-CAR-specific signaling pathways and canonical TCR signaling, while global phosphorylation in Raji B cells is reduced after association with the CD19-CAR T cells.

Signal Amplification in Highly Ordered Networks Is Driven by Geometry

Here, we hypothesize that, in biological systems such as cell surface receptors that relay external signals, clustering leads to substantial improvements in signaling efficiency. Representing cooperative signaling networks as planar graphs and applying Euler’s polyhedron formula, we can show that clustering may result in an up to a 200% boost in signaling amplitude dictated solely by the size and geometry of the network. This is a fundamental relationship that applies to all clustered systems regardless of its components. Nature has figured out a way to maximize the signaling amplitude in receptors that relay weak external signals. In addition, in cell-to-cell interactions, clustering both receptors and ligands may result in maximum efficiency and synchronization. The importance of clustering geometry in signaling efficiency goes beyond biological systems and can inform the design of amplifiers in nonbiological systems.

The Implementation of TNFRSF Co-Stimulatory Domains in CAR-T Cells for Optimal Functional Activity

The Tumor Necrosis Factor Receptor Superfamily (TNFRSF) is a large and important immunoregulatory family that provides crucial co-stimulatory signals to many if not all immune effector cells. Each co-stimulatory TNFRSF member has a distinct expression profile and a unique functional impact on various types of cells and at different stages of the immune response. Correspondingly, exploiting TNFRSF-mediated signaling for cancer immunotherapy has been a major field of interest, with various therapeutic TNFRSF-exploiting anti-cancer approaches such as 4-1BB and CD27 agonistic antibodies being evaluated (pre)clinically. A further application of TNFRSF signaling is the incorporation of the intracellular co-stimulatory domain of a TNFRSF into so-called Chimeric Antigen Receptor (CAR) constructs for CAR-T cell therapy, the most prominent example of which is the 4-1BB co-stimulatory domain included in the clinically approved product Kymriah. In fact, CAR-T cell function can be clearly influenced by the unique co-stimulatory features of members of the TNFRSF. Here, we review a select group of TNFRSF members (4-1BB, OX40, CD27, CD40, HVEM, and GITR) that have gained prominence as co-stimulatory domains in CAR-T cell therapy and illustrate the unique features that each confers to CAR-T cells.

Remodeling metabolic fitness: Strategies for improving the efficacy of chimeric antigen receptor T cell therapy

The dramatic success of adoptive transfer of engineered T cells expressing chimeric antigen receptor (CAR-T) has been achieved with effective responses in some relapsed or refractory hematologic malignancies, which is not yet met in solid tumors. The efficacy of CAR-T therapy is associated with its fate determination and their interaction with cancer cells in tumor microenvironment (TME), which is closely correlated with T cell metabolism fitness. Indeed, modulating T cell metabolism reprogramming has been proven crucial for their survival and reinvigorating antitumor immunity, and thus is considered as a promising strategy to improve the clinical performance of CAR-T cell therapy in difficult-to-treat cancers. This review briefly summarizes the T cell metabolic profiles and key metabolic challenges it faces in TME such as nutrient depletion, hypoxia, and toxic metabolites, then emphatically discusses the potential strategies to modulate metabolic properties of CAR-T cells including improving CARs construct design, optimizing manufacture process via addition of exogenous cytokines or targeting specific signaling pathway, manipulating ROS levels balance or relieve the unfavorable metabolic TME including adaptation to hypoxia and relieving inhibitory effect of toxic metabolites, eventually strengthening the anti-tumor response.

N-Glycosylation Facilitates 4-1BB Membrane Localization by Avoiding Its Multimerization

Leveraging the T cell immunity against tumors represents a revolutionary type of cancer therapy. 4-1BB is a well-characterized costimulatory immune receptor existing on activated T cells and mediating their proliferation and cytotoxicity under infectious diseases and cancers. Despite the accumulating interest in implementing 4-1BB as a therapeutic target for immune-related disorders, less is known about the pattern of its intracellular behaviors and regulations. It has been previously demonstrated that 4-1BB is heavily modified by N-glycosylation; however, the biological importance of this modification lacks detailed elucidation. Through biochemical, biophysical, and cell-biological approaches, we systematically evaluated the impact of N-glycosylation on the ligand interaction, stability, and localization of 4-1BB. We hereby highlighted that N-glycan functions by preventing the oligomerization of 4-1BB, thus permitting its membrane transportation and fast turn-over. Without N-glycosylation, 4-1BB could be aberrantly accumulated intracellularly and fail to be sufficiently inserted in the membrane. The N-glycosylation-guided intracellular processing of 4-1BB serves as the potential mechanism explicitly modulating the “on” and “off” of 4-1BB through the control of protein abundance. Our study will further solidify the understanding of the biological properties of 4-1BB and facilitate the clinical practice against this promising therapeutic target.

CD137 (4-1BB) costimulation of CD8+ T cells is more potent when provided in cis than in trans with respect to CD3-TCR stimulation

CD137 (4-1BB; TNFSR9) is an activation-induced surface receptor that through costimulation effects provide antigen-primed T cells with augmented survival, proliferation and effector functions as well as metabolic advantages. These immunobiological mechanisms are being utilised for cancer immunotherapy with agonist CD137-binding and crosslinking-inducing agents that elicit CD137 intracellular signaling. In this study, side-by-side comparisons show that provision of CD137 costimulation in-cis with regard to the TCR-CD3-ligating cell is superior to that provided in-trans in terms of T cell activation, proliferation, survival, cytokine secretion and mitochondrial fitness in mouse and human. Cis ligation of CD137 relative to the TCR-CD3 complex results in more intense canonical and non-canonical NF-κB signaling and provides a more robust induction of cell cycle and DNA damage repair gene expression programs. Here we report that the superiority of cis versus trans CD137-costimulation is readily observed in vivo and is relevant for understanding the immunotherapeutic effects of CAR T cells and CD137 agonistic therapies currently undergoing clinical trials, which may provide costimulation either in cis or in trans.

Cancer immune therapy with PD-1-dependent CD137 co-stimulation provides localized tumour killing without systemic toxicity

Expression of the cell surface receptor CD137 has been shown to enhance anti-cancer T cell function via engagement with its natural ligand 4-1BBL. CD137 ligation with engineered ligands has emerged as a cancer immunotherapy strategy, yet clinical development of agonists has been hindered by either toxicity or limited efficacy. Here we show that a CD137/PD-1 bispecific antibody, IBI319, is able to overcome these limitations by coupling CD137 activation to PD-1-crosslinking. In CT26 and MC38 syngeneic mouse tumour models, IBI319 restricts T cell co-stimulation to PD-1-rich microenvironments, such as tumours and tumour-draining lymph nodes, hence systemic (liver) toxicity arising from generalised T cell activation is reduced. Besides limiting systemic T cell co-stimulation, the anti-PD-1 arm of IBI319 also exhibits checkpoint blockade functions, with an overall result of T and NK cell infiltration into tumours. Toxicology profiling in non-human primates shows that IBI319 is a well-tolerated molecule with IgG-like pharmacokinetic properties, thus a suitable candidate for further clinical development.

The toxicity arising from generalised stimulation of T cells restricts applicability of CD137 agonists in cancer immune therapy. Here authors show that a bispecific antibody blocking PD-1 while activating CD137 efficiently restricts T cell activation to the tumour microenvironment, resulting in efficient tumour control and reduced liver toxicity.

A comparison of chimeric antigen receptors containing CD28 versus 4-1BB costimulatory domains

Chimeric antigen receptors (CARs) are engineered proteins designed to target T cells to cancer cells. To effectively activate the T cells in which they are expressed, CARs must contain a costimulatory domain. The CAR T cell products approved for the treatment of B cell lymphomas and/or acute lymphoblastic leukaemia or multiple myeloma incorporate either a CD28-derived or a 4-1BB-derived costimulatory domain. Almost all other clinically tested CARs also use costimulatory domains from CD28 or 4-1BB. In preclinical experiments, cytokine release is usually greater with CARs containing CD28 versus 4-1BB costimulatory domains; however, constructs with either domain confer similar anticancer activity in mouse models. T cell products expressing CARs with either CD28 or 4-1BB costimulatory domains have been highly efficacious in patients with relapsed haematological malignancies, with anti-CD19 products having similar activity regardless of the source of the costimulatory domain. In large-cohort clinical trials, the rates of neurological toxicities have been higher with CD28-costimulated CARs, although this finding is probably the result of a combination of factors rather than due to CD28 signalling alone. Future preclinical and clinical research should aim to compare different costimulatory domains while controlling for confounding variables. Herein, we provide an overview of T cell costimulation by CD28 and 4-1BB and, using the available preclinical and clinical data, compare the efficacy and toxicity profiles associated with CARs containing either costimulatory domain.

Quantitative contributions of TNF receptor superfamily members to CD8+ T-cell responses

T-cell responses to infections and cancers are regulated by co-signalling receptors grouped into the binary categories of co-stimulation or co-inhibition. The co-stimulation TNF receptor superfamily (TNFRSF) members 4-1BB, CD27, GITR and OX40 have similar signalling mechanisms raising the question of whether they have similar impacts on T-cell responses. Here, we screened for the quantitative impact of these TNFRSFs on primary human CD8+ T-cell cytokine production. Although both 4-1BB and CD27 increased production, only 4-1BB was able to prolong the duration over which cytokine was produced, and both had only modest effects on antigen sensitivity. An operational model explained these different phenotypes using shared signalling based on the surface expression of 4-1BB being regulated through signalling feedback. The model predicted and experiments confirmed that CD27 co-stimulation increases 4-1BB expression and subsequent 4-1BB co-stimulation. GITR and OX40 displayed only minor effects on their own but, like 4-1BB, CD27 could enhance GITR expression and subsequent GITR co-stimulation. Thus, different co-stimulation receptors can have different quantitative effects allowing for synergy and fine-tuning of T-cell responses.

A Role for CXCR3 Ligands as Biomarkers of Post-Operative Crohn's Disease Recurrence

BACKGROUND AND AIMS

Crohn's disease [CD] recurrence following ileocolic resection [ICR] is common. We sought to identify blood-based biomarkers associated with CD recurrence.

METHODS

CD patients undergoing ICR were recruited across six centres. Serum samples were obtained at post-operative colonoscopy. A multiplex immunoassay was used to analyse 92 inflammation-related proteins [Olink Proteomics]. Bayesian analysis was used to identify proteins associated with increasing Rutgeerts score. Identified proteins were used in receiver operating characteristic [ROC] analysis to examine the ability to identify CD recurrence [Rutgeerts score ≥i2]. Existing single cell data were interrogated to further elucidate the role of the identified proteins.

RESULTS

Data from 276 colonoscopies in 213 patients were available. Median time from surgery to first and second colonoscopy was 7 (interquartile range [IQR] 6-9) and 19 [IQR 16-23] months, respectively. Disease recurrence was evident at 60 [30%] first and 36 [49%] second colonoscopies. Of 14 proteins significantly associated with Rutgeerts score, the strongest signal was seen for CXCL9 and MMP1. Among patients on anti-tumour necrosis factor drugs, CXCL9 and CXCL11 were most strongly associated with Rutgeerts score. Both are CXCR3 ligands. Incorporation of identified proteins into ROC analysis improved the ability to identify disease recurrence as compared to C-reactive protein alone: area under the curve [AUC] 0.75 (95% confidence interval [CI]: 0.66-0.82] vs 0.64 [95% CI 0.56-0.72], p = 0.012. Single cell transcriptomic data provide evidence that innate immune cells are the primary source of the identified proteins.

CONCLUSIONS

CXCR3 ligands are associated with CD recurrence following ICR. Incorporation of novel blood-based candidate biomarkers may aid in identification of CD recurrence.

Ubiquitination in T-Cell Activation and Checkpoint Inhibition: New Avenues for Targeted Cancer Immunotherapy

The advent of T-cell-based immunotherapy has remarkably transformed cancer patient treatment. Despite their success, the currently approved immunotherapeutic protocols still encounter limitations, cause toxicity, and give disparate patient outcomes. Thus, a deeper understanding of the molecular mechanisms of T-cell activation and inhibition is much needed to rationally expand targets and possibilities to improve immunotherapies. Protein ubiquitination downstream of immune signaling pathways is essential to fine-tune virtually all immune responses, in particular, the positive and negative regulation of T-cell activation. Numerous studies have demonstrated that deregulation of ubiquitin-dependent pathways can significantly alter T-cell activation and enhance antitumor responses. Consequently, researchers in academia and industry are actively developing technologies to selectively exploit ubiquitin-related enzymes for cancer therapeutics. In this review, we discuss the molecular and functional roles of ubiquitination in key T-cell activation and checkpoint inhibitory pathways to highlight the vast possibilities that targeting ubiquitination offers for advancing T-cell-based immunotherapies.

The immunological significance of tumor necrosis factor receptor-associated factors (TRAFs)

The tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family of molecules are intracellular signaling adaptors and control diverse signaling pathways mediated not only by the TNFR superfamily and the Toll-like receptor/interleukin-1 receptor superfamily but also by unconventional cytokine receptors such as IL-6 and IL-17 receptors. There are seven family members, TRAF1 to TRAF7, in mammals. Exaggerated immune responses induced through TRAF signaling downstream of these receptors often lead to inflammatory and autoimmune diseases including rheumatoid arthritis, inflammatory bowel disease, psoriasis and autoinflammatory syndromes, and thus those signals are major targets for therapeutic intervention. For this reason, it has been very important to understand signaling mechanisms regulated by TRAFs that greatly impact on life/death decisions and the activation, differentiation and survival of cells of the innate and adaptive immune systems. Accumulating evidence suggests that dysregulated cellular expression and/or signaling of TRAFs causes overproduction of proinflammatory cytokines, which facilitates aberrant activation of immune cells. In this review, I will explain the structural and functional aspects that are responsible for the cellular activity and disease outcomes of TRAFs, and summarize the findings of recent studies on TRAFs in terms of how individual TRAF family molecules regulates biological and disease processes in the body in both positive and negative ways. This review also discusses how TRAF mutations contribute to human disease.

New emerging targets in cancer immunotherapy: CD137/4-1BB costimulatory axis

CD137 (4-1BB) is a surface glycoprotein that belongs to the tumour necrosis factor receptor family (TNFRSF9). Its expression is induced on activation on a number of leucocyte types. Interestingly, for cancer immunotherapy, CD137 becomes expressed on primed T and natural killer (NK) cells, which on ligation provides powerful costimulatory signals. Perturbation of CD137 by CD137L or agonist monoclonal antibodies on activated CD8 T cells protects such antigen-specific cytotoxic T lymphocytes from apoptosis, enhances effector functionalities and favours persistence and memory differentiation. As a consequence, agonist antibodies exert potent antitumour effects in mouse models and the CD137 signalling domain is critical in chimeric antigen receptors (CAR) of CAR T cells approved to be used in the clinic. New formats of CD137 agonist moieties are being clinically developed, seeking potent costimulation targeted to the tumour microenvironment to avoid liver inflammation side effects, that have thus far limited and delayed clinical development.

Molecular Mechanisms of the Toll-Like Receptor, STING, MAVS, Inflammasome, and Interferon Pathways

Pattern recognition receptors (PRRs) form the front line of defense against pathogens. Many of the molecular mechanisms that facilitate PRR signaling have been characterized in detail, which is critical for the development of accurate PRR pathway models at the molecular interaction level. These models could support the development of therapeutics for numerous diseases, including sepsis and COVID-19. This review describes the molecular mechanisms of the principal signaling interactions of the Toll-like receptor, STING, MAVS, and inflammasome pathways. A detailed molecular mechanism network is included as Data Set S1 in the supplemental material.

Reversing T-cell exhaustion in immunotherapy: a review on current approaches and limitations

Introduction:T cell functions are altered during chronic viral infections and tumor development. This is mainly manifested by significant changes in T cells' epigenetic and metabolic landscapes, pushing them into an 'exhausted' state. Reversing this T cell exhaustion has been emerging as a 'game-changing' therapeutic approach against cancer and chronic viral infection.Areas covered:This review discusses the cellular pathways related to T cell exhaustion, and the clinical development and possible cellular targets that can be exploited therapeutically to reverse this exhaustion. We searched various databases (e.g. Google Scholar, PubMed, Elsevier, and other scientific database sites) using the keywords T cell exhaustion, T cell activation, co-inhibitory receptors, and reversing T cell exhaustion.Expert opinion:The discovery of the immune checkpoints pathways represents a significant milestone toward understanding and reversing T cell exhaustion. Antibodies that target these pathways have already demonstrated promising activities in reversing T cell exhaustion. Nevertheless, there are still many associated limitations. In this context, next-generation alternatives are on the horizon. This includes the use of small molecules to block the immune checkpoints' receptors, combining them with other treatments, and identifying novel, safer and more effective immunotherapeutic targets.

4-1BBL as a Mediator of Cross-Talk between Innate, Adaptive, and Regulatory Immunity against Cancer

The ability of tumor cells to evade the immune system is one of the main challenges we confront in the fight against cancer. Multiple strategies have been developed to counteract this situation, including the use of immunostimulant molecules that play a key role in the anti-tumor immune response. Such a response needs to be tumor-specific to cause as little damage as possible to healthy cells and also to track and eliminate disseminated tumor cells. Therefore, the combination of immunostimulant molecules and tumor-associated antigens has been implemented as an anti-tumor therapy strategy to eliminate the main obstacles confronted in conventional therapies. The immunostimulant 4-1BBL belongs to the tumor necrosis factor (TNF) family and it has been widely reported as the most effective member for activating lymphocytes. Hence, we will review the molecular, pre-clinical, and clinical applications in conjunction with tumor-associated antigens in antitumor immunotherapy, as well as the main molecular pathways involved in this association.

Contributions of Costimulatory Molecule CD137 in Endothelial Cells

CD137 (4-1BB, tumor necrosis factor receptor superfamily 9) is a surface glycoprotein of the tumor necrosis factor receptor family that can be induced on a variety of immunocytes and nonimmune cells, including endothelial cells and smooth muscle cells. The importance of CD137 in immune response has been well recognized; however, the precise biological effects and underlying mechanisms of CD137 in endothelial cells are unclear. A single layer of cells called the endothelium constitutes the innermost layer of blood vessels including larger arteries, veins, the capillaries, and the lymphatic vessels. It not only acts as an important functional interface, but also participates in local inflammatory response. This review covers recent findings to illuminate the role of CD137 in endothelial cells in different pathophysiologic settings.

Glycosylation of Immune Receptors in Cancer

Evading host immune surveillance is one of the hallmarks of cancer. Immune checkpoint therapy, which aims to eliminate cancer progression by reprogramming the antitumor immune response, currently occupies a solid position in the rapidly expanding arsenal of cancer therapy. As most immune checkpoints are membrane glycoproteins, mounting attention is drawn to asking how protein glycosylation affects immune function. The answers to this fundamental question will stimulate the rational development of future cancer diagnostics and therapeutic strategies.

Mechanistic dissection of spatial organization in NF-κB signaling pathways by hybrid simulations

The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is one of the most important transcription factors involved in the regulation of inflammatory signaling pathways. Inappropriate activation of these pathways has been linked to autoimmunity and cancers. Emerging experimental evidences have been showing the existence of elaborate spatial organizations for various molecular components in the pathways. One example is the scaffold protein tumor necrosis factor receptor associated factor (TRAF). While most TRAF proteins form trimeric quaternary structure through their coiled-coil regions, the N-terminal region of some members in the family can further be dimerized. This dimerization of TRAF trimers can drive them into higher-order clusters as a response to receptor stimulation, which functions as a spatial platform to mediate the downstream poly-ubiquitination. However, the molecular mechanism underlying the TRAF protein clustering and its functional impacts are not well-understood. In this article, we developed a hybrid simulation method to tackle this problem. The assembly of TRAF-based signaling platform at the membrane-proximal region is modeled with spatial resolution, while the dynamics of downstream signaling network, including the negative feedbacks through various signaling inhibitors, is simulated as stochastic chemical reactions. These two algorithms are further synchronized under a multiscale simulation framework. Using this computational model, we illustrated that the formation of TRAF signaling platform can trigger an oscillatory NF-κB response. We further demonstrated that the temporal patterns of downstream signal oscillations are closely regulated by the spatial factors of TRAF clustering, such as the geometry and energy of dimerization between TRAF trimers. In general, our study sheds light on the basic mechanism of NF-κB signaling pathway and highlights the functional importance of spatial regulation within the pathway. The simulation framework also showcases its potential of application to other signaling pathways in cells.