Targeting CD8+ T cells with natural products for tumor therapy: Revealing insights into the mechanisms

BACKGROUND

Despite significant advances in cancer immunotherapy over the past decades, such as T cell-engaging chimeric antigen receptor (CAR)-T cell therapy and immune checkpoint blockade (ICB), therapeutic failure resulting from various factors remains prevalent. Therefore, developing combinational immunotherapeutic strategies is of great significance for improving the clinical outcome of cancer immunotherapy. Natural products are substances that naturally exist in various living organisms with multiple pharmacological or biological activities, and some of them have been found to have anti-tumor potential. Notably, emerging evidences have suggested that several natural compounds may boost the anti-tumor effects through activating immune response of hosts, in which CD8+ T cells play a pivotal role.

METHODS

The data of this review come from PubMed, Web of Science, Google Scholar, and ClinicalTrials (https://clinicaltrials.gov/) with the keywords "CD8+ T cell", "anti-tumor", "immunity", "signal 1", "signal 2", "signal 3", "natural products", "T cell receptor (TCR)", "co-stimulation", "co-inhibition", "immune checkpoint", "inflammatory cytokine", "hesperidin", "ginsenoside", "quercetin", "curcumin", "apigenin", "dendrobium officinale polysaccharides (DOPS)", "luteolin", "shikonin", "licochalcone A", "erianin", "resveratrol", "procyanidin", "berberine", "usnic acid", "naringenin", "6-gingerol", "ganoderma lucidum polysaccharide (GL-PS)", "neem leaf glycoprotein (NLGP)", "paclitaxel", "source", "pharmacological activities", and "toxicity". These literatures were published between 1993 and 2023.

RESULTS

Natural products have considerable advantages as anti-tumor drugs based on the various species, wide distribution, low price, and few side effects. This review summarized the effects and mechanisms of some natural products that exhibit anti-tumor effects via targeting CD8+ T cells, mainly focused on the three signals that activate CD8+ T cells: TCR, co-stimulation, and inflammatory cytokines.

CONCLUSION

Clarifying the role and underlying mechanism of natural products in cancer immunotherapy may provide more options for combinational treatment strategies and benefit cancer therapy, to shed light on identifying potential natural compounds for improving the clinical outcome in cancer immunotherapy.

The best GVHD prophylaxis: Or at least progress towards finding it

Options for GVHD prophylaxis after allogeneic hematopoietic cell transplantation can best be chosen by understanding the pathophysiology of GVHD. Interventions to limit T cell activation, expansion and subsequent tissue injury can each be utilized in designing successful GVHD prevention strategies Depleting, tolerizing or blunting T cells or host antigen presenting cells (APCs), blocking co-stimulation or more broadly suppressing inflammation have all been used. Interventions which spare regulatory T cells (Tregs) may prevent GVHD and facilitate controlled allo-responses and not compromise subsequent relapse risks. Graft manipulations and pharmacologic interventions each have potential to limit the morbidity of GVHD while permitting the immunocompetence to prevent infection or relapse.

Shining a LIGHT on myeloid cell targeted immunotherapy

Despite over a decade of clinical trials combining inhibition of emerging checkpoints with a PD-1/L1 inhibitor backbone, meaningful survival benefits have not been shown in PD-1/L1 inhibitor resistant or refractory solid tumours, particularly tumours dominated by a myelosuppressive microenvironment. Achieving durable anti-tumour immunity will therefore likely require combination of adaptive and innate immune stimulation, myeloid repolarisation, enhanced APC activation and antigen processing/presentation, lifting of the CD47/SIRPα (Cluster of Differentiation 47/signal regulatory protein alpha) 'do not eat me' signal, provision of an apoptotic 'pro-eat me' or 'find me' signal, and blockade of immune checkpoints. The importance of effectively targeting mLILRB2 and SIRPAyeloid cells to achieve improved response rates has recently been emphasised, given myeloid cells are abundant in the tumour microenvironment of most solid tumours. TNFSF14, or LIGHT, is a tumour necrosis superfamily ligand with a broad range of adaptive and innate immune activities, including (1) myeloid cell activation through Lymphotoxin Beta Receptor (LTβR), (2) T/NK (T cell and natural killer cell) induced anti-tumour immune activity through Herpes virus entry mediator (HVEM), (3) potentiation of proinflammatory cytokine/chemokine secretion through LTβR on tumour stromal cells, (4) direct induction of tumour cell apoptosis in vitro, and (5) the reorganisation of lymphatic tissue architecture, including within the tumour microenvironment (TME), by promoting high endothelial venule (HEV) formation and induction of tertiary lymphoid structures. LTBR (Lymphotoxin beta receptor) and HVEM rank highly amongst a range of costimulatory receptors in solid tumours, which raises interest in considering how LIGHT-mediated costimulation may be distinct from a growing list of immunotherapy targets which have failed to provide survival benefit as monotherapy or in combination with PD-1 inhibitors, particularly in the checkpoint acquired resistant setting.

Immunologically modified enzyme-responsive micelles regulate the tumor microenvironment for cancer immunotherapy

Immune checkpoint blockade has been proven to have great therapeutic potential and has revolutionized the treatment of tumors. However, various limitations remain, including the low response rate of exhausted T cells and mutual regulation of multiple immunosuppressive cell types that compromise the effect of single-target therapy. Nano-delivery systems can be used to regulate the tumor immune microenvironment in favor of immunotherapy. In this study, we constructed a polypeptide-based micellar system that encapsulates an aryl hydrocarbon receptor (AhR) inhibitor (CH223191) conjugated to T cell activator anti-CD28. The inhibition of AhR activation downregulates the fraction of immunosuppressive cells and effectively inhibits tumor cell metastasis. In addition, the combination with co-stimulatory antibodies improves T-cell activation and synergistically enhances the antitumor effect of AhR inhibitors. The micellar system developed in this study represents a novel and effective tumor immunotherapy approach.

The Combiome Hypothesis: Selecting Optimal Treatment for Cancer Patients

Existing approaches for cancer diagnosis are inefficient in the use of diagnostic tissue, and decision-making is often sequential, typically resulting in delayed treatment initiation. Future diagnostic testing needs to be faster and optimize increasingly complex treatment decisions. We envision a future where comprehensive testing is routine. Our approach, termed the "combiome," combines holistic information from the tumor, and the patient's immune system. The combiome model proposed here advocates synchronized up-front testing with a panel of sensitive assays, revealing a more complete understanding of the patient phenotype and improved targeting and sequencing of treatments. Development and eventual adoption of the combiome model for diagnostic testing may provide better outcomes for all cancer patients, but will require significant changes in workflows, technology, regulations, and administration. In this review, we discuss the current and future testing landscape, targeting of personalized treatments, and technological and regulatory advances necessary to achieve the combiome.

Extensive functional comparisons between chimeric antigen receptors and T cell receptors highlight fundamental similarities

Though TCRs have been subject to limited engineering in the context of therapeutic design and optimization, they are used largely as found in nature. On the other hand, CARs are artificial, composed of different segments of proteins that function in the immune system. This characteristic raises the possibility of altered response to immune regulatory stimuli. Here we describe a large-scale, systematic comparison of CARs and TCRs across 5 different pMHC targets, with a total of 19 constructs examined in vitro. These functional measurements include CAR- and TCR-mediated activation, proliferation, and cytotoxicity in both acute and chronic settings. Surprisingly, we find no consistent difference between CARs and TCRs as receptor classes with respect to their relative sensitivity to major regulators of T cell activation: PD-L1, CD80/86 and IL-2. Though TCRs often emerge from human blood directly as potent, selective receptors, CARs must be heavily optimized to attain these properties for pMHC targets. Nonetheless, when iteratively improved and compared head to head in functional tests, CARs appear remarkably similar to TCRs with respect to immune modulation.

Targeting CD276 by CAR-T cells induces regression of esophagus squamous cell carcinoma in xenograft mouse models

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CD276 is homogeneously overexpressed in ESCC and EAC.

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CD276-directed CAR-T cells demonstrate remarkable anti-tumor effects in ESCC PDX model.

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CD276-targeting CAR-T cells are successfully generated with patients T cells and show potent cytotoxicity against autologous tumor cells.

Esophageal cancer, including esophageal squamous cell carcinoma (ESCC) and esophageal adenocarcinoma (EAC), has a poor prognosis and limited therapeutic options. Chimeric antigen receptor (CAR)-T cells represent a potential ESCC treatment. In this study, we examined CD276 expression in healthy and esophageal tumor tissues and explored the tumoricidal potential of CD276-targeting CAR-T cells in ESCC. CD276 was strongly and homogenously expressed in ESCC and EAC tumor lesions but mildly in healthy tissues, representing a good target for CAR-T cell therapy. We generated CD276-directed CAR-T cells with a humanized antigen-recognizing domain and CD28 or 4–1BB co-stimulation. CD276-specific CAR-T cells efficiently killed ESCC tumor cells in an antigen-dependent manner both in vitro and in vivo. In patient-derived xenograft models, CAR-T cells induced tumor regression and extended mouse survival. In addition, CAR-T cells generated from patient T cells demonstrated potent cytotoxicity against autologous tumor cells. Our study indicates that CD276 is an attractive target for ESCC therapy, and CD276-targeting CAR-T cells are worth testing in ESCC clinical trials.

Glucocorticoid-induced tumour necrosis factor receptor family-related protein (GITR) drives atherosclerosis in mice and is associated with an unstable plaque phenotype and cerebrovascular events in humans

AIMS

GITR-a co-stimulatory immune checkpoint protein-is known for both its activating and regulating effects on T-cells. As atherosclerosis bears features of chronic inflammation and autoimmunity, we investigated the relevance of GITR in cardiovascular disease (CVD).

METHODS AND RESULTS

GITR expression was elevated in carotid endarterectomy specimens obtained from patients with cerebrovascular events (n = 100) compared to asymptomatic patients (n = 93) and correlated with parameters of plaque vulnerability, including plaque macrophage, lipid and glycophorin A content, and levels of interleukin (IL)-6, IL-12, and C-C-chemokine ligand 2. Soluble GITR levels were elevated in plasma from subjects with CVD compared to healthy controls. Plaque area in 28-week-old Gitr-/-Apoe-/- mice was reduced, and plaques had a favourable phenotype with less macrophages, a smaller necrotic core and a thicker fibrous cap. GITR deficiency did not affect the lymphoid population. RNA sequencing of Gitr-/-Apoe-/- and Apoe-/- monocytes and macrophages revealed altered pathways of cell migration, activation, and mitochondrial function. Indeed, Gitr-/-Apoe-/- monocytes displayed decreased integrin levels, reduced recruitment to endothelium, and produced less reactive oxygen species. Likewise, GITR-deficient macrophages produced less cytokines and had a reduced migratory capacity.

CONCLUSION

Our data reveal a novel role for the immune checkpoint GITR in driving myeloid cell recruitment and activation in atherosclerosis, thereby inducing plaque growth and vulnerability. In humans, elevated GITR expression in carotid plaques is associated with a vulnerable plaque phenotype and adverse cerebrovascular events. GITR has the potential to become a novel therapeutic target in atherosclerosis as it reduces myeloid cell recruitment to the arterial wall and impedes atherosclerosis progression.

The balance of regulatory and stimulatory B cell subsets in breast cancer draining lymph nodes correlates with tumor prognostic factors

AIMS

B cells can promote or inhibit immune responses against breast cancer. We investigated changes in the frequency of B cells with stimulatory or regulatory capacity in breast tumor draining lymph nodes during cancer progression.

MAIN METHODS

We isolated mononuclear cells from fresh axillary lymph nodes (LNs) of 44 patients with breast cancer and stained lymphocytes with antibodies against CD19, CD80, CD86, CD39 and CD73. To assess programmed death-1 (PD-1) and PD-ligand 1 (PD-L1) expression, lymphocytes were briefly stimulated, stained for CD19, PD-1 and PD-L1, and examined with flow cytometry.

KEY FINDINGS

The frequency of CD80⁺ B cells was higher in nonmetastatic lymph nodes, while the percentage of CD86⁺ B cells showed a positive relationship with higher tumor grade and higher numbers of involved LNs. A small proportion of unstimulated B cells expressed PD-1 or PD-L1 but these molecules were rapidly upregulated on B cells following activation. The frequency of stimulated PD-L1⁺ B cells showed an inverse association with estrogen and progesterone receptor expression and a nonsignificant positive association with tumor grade. In addition, the percentage of unstimulated PD-1⁺ B cells was higher in patients with higher-grade tumors. CD73 expression on B cells was associated with lower numbers of involved LNs, and the frequency of CD39⁺ B cells was higher in patients with larger tumors.

SIGNIFICANCE

CD86⁺, CD39⁺, PD-1⁺ and PD-L1⁺ B cells showed associations with poor prognostic factors, therefore their potential role in the suppression of the immune responses against breast cancer should be evaluated in greater detail.

VISTA: an immune regulatory protein checking tumor and immune cells in cancer immunotherapy

VISTA (V-domain immunoglobulin suppressor of T cell activation) is a well-established immune regulatory receptor. However, pre-clinical investigations indicated more complicated influences of VISTA on cancer immunity than previously recognized. Here, we review the current knowledge on the therapeutic phenotypes and molecular mechanisms that underlie the contradictory roles of VISTA in checking anti-cancer immune responses. Furthermore, we highlight the potential indeterminacy of VISTA-targeted strategies in cancer immunotherapy, with in silico analyses. In fact, VISTA functions like a homeostatic regulator that actively normalizes immune responses. Thus, the regulatory role of VISTA in anti-cancer immunity remains to be fully elucidated.

In vitro assays for effector T cell functions and activity of immunomodulatory antibodies

The recent clinical success of cancer immunotherapy with checkpoint blockade has led to renewed interest into the development of immune modulatory agents with the capacity to activate anti-tumor T cell responses. Standardization of optimized in vitro assays for efficient assessment of immune function of such new drugs is thus needed to facilitate clinical development of the optimal drug candidates. Here, we describe an optimized version of T cell suppression assay designed to test the effect of immunomodulatory agents on T cell function and activation. We apply this assay to investigate the agonist activity of the T cell co-stimulatory molecule glucocorticoid-induced TNFR-related protein (GITR). We detail a protocol for concurrent assessment of multiple levels of T cell functional modulation upon GITR engagement, including T cell priming, activation and effector function, in a single assay. As human GITR agonist antibodies are currently under development, availability of standardized cell-based functional assays of GITR agonism is instrumental to translate anti-GITR therapy into the clinical setting.

Co-stimulatory and co-inhibitory pathways in cancer immunotherapy

Cancer remains the leading cause of death worldwide. Traditional treatments such as surgery, radiation, and chemotherapy have had limited efficacy, especially with late stage cancers. Cancer immunotherapy and targeted therapy have revolutionized how cancer is treated, especially in patients with late stage disease. In 2013 cancer immunotherapy was named the breakthrough of the year, partially due to the established efficacy of blockade of CTLA-4 and PD-1, both T cell co-inhibitory molecules involved in tumor-induced immunosuppression. Though early trials promised success, toxicity and tolerance to immunotherapy have hindered long-term successes. Optimizing the use of co-stimulatory and co-inhibitory pathways has the potential to increase the effectiveness of T cell-mediated antitumor immune response, leading to increased efficacy of cancer immunotherapy. This review will address major T cell co-stimulatory and co-inhibitory pathways and the role they play in regulating immune responses during cancer development and treatment.

Genetic Polymorphism in Cytokines and Costimulatory Molecules in Stem Cell and Solid Organ Transplantation

There is growing evidence supporting the genetic variability outside of HLA system that is contributing to the variation in transplant outcomes. Determining novel predictors could help to identify patients at risk and tailor their immunosuppressive regimens. This article discusses the various single nucleotide polymorphisms in costimulatory molecules and cytokines that have been evaluated for their effect on transplantation. An overview of how gene polymorphism studies are conducted and factors to consider in the experimental design to ensure meaningful data can be concluded are discussed.

The CD28-B7 Family of Co-signaling Molecules

Immune responses are controlled by the optimal balance between protective immunity and immune tolerance. T-cell receptor (TCR) signals are modulated by co-signaling molecules, which are divided into co-stimulatory and co-inhibitory molecules. By expression at the appropriate time and location, co-signaling molecules positively and negatively control T-cell differentiation and function. For example, ligation of the CD28 on T cells provides a critical secondary signal along with TCR ligation for naive T-cell activation. In contrast, co-inhibitory signaling by the CD28-B7 family is important to regulate immune homeostasis and host defense, as these signals limit the strength and duration of immune responses to prevent autoimmunity. At the same time, microorganisms or tumor cells can use these pathways to establish an immunosuppressive environment to inhibit the immune responses against themselves. Understanding these co-inhibitory pathways will support the development of new immunotherapy for the treatment of tumors and autoimmune and infectious diseases. Here, we introduce diverse molecules belonging to the members of the CD28-B7 family.

Structures of Immune Checkpoints: An Overview on the CD28-B7 Family

The co-stimulation and co-inhibition signal pathways, immune checkpoints, are among the central mechanisms to regulate the T-cell immunity. Optimal signals involve intricate interactions of numerous ligands and receptors. Manipulation of these signals offers great clinical opportunities and has revolutionized the cancer treatment therapies. The 2018 Nobel Prize in Physiology or Medicine was awarded to James P. Allison and Tasuku Honjo in recognition of their discovery of cancer immunotherapy by inhibition of immune checkpoint molecules. Despite the landmark discovery in cancer immunotherapy, the efforts to harness immunity against cancer are also restricted by the limited knowledge on the co-stimulation and co-inhibition signaling networks. Understanding the structures of these molecules, in particular, tackling the interaction paradigms from the structural perspective, help to provide more accurate insights into the signaling mechanisms, which may further facilitate the development of novel biologics and improve the efficacy of the existing biologics against these targets. Here we review our current understanding on the structures of these co-stimulatory and co-inhibitory molecules. Specifically, we focus on the structural basis of several checkpoint molecules among the CD28-B7 family and discuss the therapeutic drugs against these targets for the treatment of human cancers, autoimmune disorders, and transplantation.

Monoclonal Antibodies for the Treatment of Melanoma: Present and Future Strategies

Metastatic melanoma is a dreadful type of skin cancer arising due to uncontrolled proliferation of melanocytes. It has very poor prognosis, low 5-year survival rates and until recently there were only handful of treatment options for metastatic melanoma patients. The drugs that were approved for the treatment had low response rates and were associated with severe adverse events. With the introduction of monoclonal antibodies against inhibitory immune checkpoints the treatment landscape for metastatic melanoma has changed dramatically. Ipilimumab, the first monoclonal antibody to be approved for the treatment of metastatic melanoma, showed significant improvements in durable response rates in patients and paved the way for next class of monoclonal antibodies. Nivolumab and pembrolizumab, the anti-PD-1 antibodies that were approved 3-years after the approval of ipilimumab, had decent response rates, low relapse rates and showed manageable safety profile. Antibodies against ligands for PD-1 receptors were then developed to overcome the adverse effects of anti-PD-1 antibodies and combination of monoclonal antibodies (ipilimumab plus nivolumab) was tested to increase the response rates. Additional target receptors that regulate T cell activity were identified on T cells and monoclonal antibodies against potential targets such as TIGIT, TIM-3, and LAG-3 were developed. This chapter discusses the details of monoclonal antibodies used for the treatment of melanoma along with the ones that could be introduced in the near future with emphasis on mechanisms by which antibodies stimulate anti-tumor immune response and the specifics of target molecules of the antibodies.

HVEM network signaling in cancer

Somatic mutations in cancer cells may influence tumor growth, survival, or immune interactions in their microenvironment. The tumor necrosis factor receptor family member HVEM (TNFRSF14) is frequently mutated in cancers and has been attributed a tumor suppressive role in some cancer contexts. HVEM functions both as a ligand for the lymphocyte checkpoint proteins BTLA and CD160, and as a receptor that activates NF-κB signaling pathways in response to BTLA and CD160 and the TNF ligands LIGHT and LTα. BTLA functions to inhibit lymphocyte activation, but has also been ascribed a role in stimulating cell survival. CD160 functions to co-stimulate lymphocyte function, but has also been shown to activate inhibitory signaling in CD4⁺ T cells. Thus, the role of HVEM within diverse cancers and in regulating the immune responses to these tumors is likely context specific. Additionally, development of therapeutics that target proteins within this network of interacting proteins will require a deeper understanding of how these proteins function in a cancer-specific manner. However, the prominent role of the HVEM network in anti-cancer immune responses indicates a promising area for drug development.

The role of CD27-CD70-mediated T cell co-stimulation in vasculogenesis, arteriogenesis and angiogenesis

BACKGROUND

T cells have a distinctive role in neovascularization, which consists of arteriogenesis and angiogenesis under pathological conditions and vasculogenesis under physiological conditions. However, the role of co-stimulation in T cell activation in neovascularization has yet to be established. The aim of this study was to investigate the role T cell co-stimulation and inhibition in angiogenesis, arteriogenesis and vasculogenesis.

METHODS AND RESULTS

Hind limb ischemia was induced by double ligation of the left femoral artery in mice and blood flow recovery was measured with Laser Doppler Perfusion Imaging in control, CD70^-/-, CD80/86^-/-, CD70/80/86^-/- and CTLA4^+/- mice. Blood flow recovery was significantly impaired in mice lacking CD70 compared to control mice, but was similar in CD80/86^-/-, CTLA4^+/- and control mice. Mice lacking CD70 showed impaired vasculogenesis, since the number of pre-existing collaterals was reduced as observed in the pia mater compared to control mice. In vitro an impaired capability of vascular smooth muscle cells (VSMC) to activate T cells was observed in VSMC lacking CD70. Furthermore, CD70^-/-, CD80/86^-/- and CD70/80/86^-/- mice showed reduced angiogenesis in the soleus muscle 10 days after ligation. Arteriogenesis was also decreased in CD70^-/- compared to control mice 10 and 28 days after surgery.

CONCLUSIONS

The present study is the first to describe an important role for T cell activation via co-stimulation in angiogenesis, arteriogenesis and vasculogenesis, where the CD27-CD70 T cell co-stimulation pathway appears to be the most important co-stimulation pathway in pre-existing collateral formation and post-ischemic blood flow recovery, by arteriogenesis and angiogenesis.

Increased costimulatory molecule expression of thymic and peripheral B cells and a sensitivity to IL-21 in myasthenia gravis

B cells may contribute to the pathogenesis of myasthenia gravis with anti-acetylcholine antibodies (AChR+ MG) by co-stimulation or selection of T cells. In this study, we investigated costimulatory molecules on B cells in the blood and in the thymus as well as by TLR9 and IL-21 stimulations in AChR+ MG patients with or without immunosuppressive treatment and controls. CD80 and CD86 expression on B cells was increased in the peripheral blood and in the thymus of untreated patients. CD86 was further amplified by IL-21. A role for activated B cells, active thymic environment and IL-21 is implicated in MG.

Agonist anti-GITR antibody significantly enhances the therapeutic efficacy of Listeria monocytogenes-based immunotherapy

Background

We previously demonstrated that in addition to generating an antigen-specific immune response, Listeria monocytogenes (Lm)-based immunotherapy significantly reduces the ratio of regulatory T cells (Tregs)/CD4⁺ and myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment. Since Lm-based immunotherapy is able to inhibit the immune suppressive environment, we hypothesized that combining this treatment with agonist antibody to a co-stimulatory receptor that would further boost the effector arm of immunity will result in significant improvement of anti-tumor efficacy of treatment.

Methods

Here we tested the immune and therapeutic efficacy of Listeria-based immunotherapy combination with agonist antibody to glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) in TC-1 mouse tumor model. We evaluated the potency of combination on tumor growth and survival of treated animals and profiled tumor microenvironment for effector and suppressor cell populations.

Results

We demonstrate that combination of Listeria-based immunotherapy with agonist antibody to GITR synergizes to improve immune and therapeutic efficacy of treatment in a mouse tumor model. We show that this combinational treatment leads to significant inhibition of tumor-growth, prolongs survival and leads to complete regression of established tumors in 60% of treated animals. We determined that this therapeutic benefit of combinational treatment is due to a significant increase in tumor infiltrating effector CD4⁺ and CD8⁺ T cells along with a decrease of inhibitory cells.

Conclusion

To our knowledge, this is the first study that exploits Lm-based immunotherapy combined with agonist anti-GITR antibody as a potent treatment strategy that simultaneously targets both the effector and suppressor arms of the immune system, leading to significantly improved anti-tumor efficacy. We believe that our findings depicted in this manuscript provide a promising and translatable strategy that can enhance the overall efficacy of cancer immunotherapy.

Inhibition of CD40-TRAF6 interactions by the small molecule inhibitor 6877002 reduces neuroinflammation

Background

The influx of leukocytes into the central nervous system (CNS) is a key hallmark of the chronic neuro-inflammatory disease multiple sclerosis (MS). Strategies that aim to inhibit leukocyte migration across the blood-brain barrier (BBB) are therefore regarded as promising therapeutic approaches to combat MS. As the CD40L-CD40 dyad signals via TNF receptor-associated factor 6 (TRAF6) in myeloid cells to induce inflammation and leukocyte trafficking, we explored the hypothesis that specific inhibition of CD40-TRAF6 interactions can ameliorate neuro-inflammation.

Methods

Human monocytes were treated with a small molecule inhibitor (SMI) of CD40-TRAF6 interactions (6877002), and migration capacity across human brain endothelial cells was measured. To test the therapeutic potential of the CD40-TRAF6-blocking SMI under neuro-inflammatory conditions in vivo, Lewis rats and C57BL/6J mice were subjected to acute experimental autoimmune encephalomyelitis (EAE) and treated with SMI 6877002 for 6 days (rats) or 3 weeks (mice).

Results

We here show that a SMI of CD40-TRAF6 interactions (6877002) strongly and dose-dependently reduces trans-endothelial migration of human monocytes. Moreover, upon SMI treatment, monocytes displayed a decreased production of ROS, tumor necrosis factor (TNF), and interleukin (IL)-6, whereas the production of the anti-inflammatory cytokine IL-10 was increased. Disease severity of EAE was reduced upon SMI treatment in rats, but not in mice. However, a significant reduction in monocyte-derived macrophages, but not in T cells, that had infiltrated the CNS was eminent in both models.

Conclusions

Together, our results indicate that SMI-mediated inhibition of the CD40-TRAF6 pathway skews human monocytes towards anti-inflammatory cells with reduced trans-endothelial migration capacity, and is able to reduce CNS-infiltrated monocyte-derived macrophages during neuro-inflammation, but minimally ameliorates EAE disease severity. We therefore conclude that SMI-mediated inhibition of the CD40-TRAF6 pathway may represent a beneficial treatment strategy to reduce monocyte recruitment and macrophage activation in the CNS and has the potential to be used as a co-treatment to combat MS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0875-9) contains supplementary material, which is available to authorized users.

How do I steer this thing? Using dendritic cell targeted vaccination to more effectively guide the antitumor immune response with combination immunotherapy

Mounting an immune response sufficient to eradicate a tumor is the goal of modern immunotherapy. Single agent therapies with checkpoint inhibitors or costimulatory molecule agonists are effective only for a small portion of all treated patients. Combined therapy, e.g., CTLA-4 and PD-1 checkpoint blockade, is a more effective treatment modality, but in preclinical studies OX40 agonism with CTLA-4 blockade using monoclonal antibodies (aOX40/aCTLA-4) failed to induce tumor regression of larger, more established tumors. We hypothesized that administration of a vaccine with a tumor-associated antigen targeted to the appropriate antigen presenting cell could make combined aOX40/aCTLA-4 therapy more effective. We administered an antibody-based vaccine targeting HER2 to the DEC-205 endocytic receptor on cross-presenting dendritic cells (anti-DEC-205/HER2; aDEC-205/HER2) and a potent adjuvant (poly (I:C)) to assist with maturation, along with aOX40/aCTLA-4 therapy. This therapy induced complete regression of established tumors and a pronounced infiltration of effector CD8 and CD4 T cells, with no effect on regulatory T cell infiltration compared to aOX40/aCTLA-4 alone. To be maximally effective, this therapy required expression of both OX40 and CTLA-4 on CD8 T cells. These data indicate that vaccination targeting cross-presenting dendritic cells with a tumor-associated antigen is a highly effective immunization strategy that can overcome some of the limitations of current systemic immunotherapeutic approaches that lack defined tumor-directed antigenic targets.

Lymph nodes from HIV-infected individuals harbor mature dendritic cells and increased numbers of PD-L1+ conventional dendritic cells

The immune response induced by dendritic cells (DC) during the HIV infection has been of remarkable interest because of the therapeutic potential of DC for vaccine development. However, their beneficial or detrimental contribution in HIV infection remains unclear. The activation state of DC in lymph nodes (LN) is essential to induce T cell responses against HIV. In the present study, we characterized the immunophenotype and function of conventional (cDC) and plasmacytoid (pDC) dendritic cells from peripheral blood (PB) and LN of HIV(+) individuals. We observed that the frequency of PB pDC was decreased and exhibited an immature phenotype; whereas in the LN, activated pDC accumulated (CD40(+) and CD83(+)). In addition, the frequency of PB cDC from HIV(+) individuals was decreased and exhibited an immature phenotype, whereas LN harbored activated and mature cDC (CD40(+), CD83(+), CD80(+) and CD86(+)). However, an increased number of PD-L1(+) cDC was also observed in the LN. Moreover, pDC and cDC were able to produce inflammatory cytokines (IFN-α, TNF-α and IL-12) after TLR stimulation. These findings suggests that LN cDC expressing PD-L1 from HIV(+) individuals may negatively impact the generation of HIV-specific T cells and that DC might be contributing to tissue chronic immune activation.

The immunomodulatory properties of human bone marrow-derived mesenchymal stromal cells are defined according to multiple immunobiological criteria

OBJECTIVE

Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) are well known to modulate T cells. However, the molecular mechanisms that mark hBM-MSCs immunomodulation of T cells are not fully resolved.

MATERIALS AND METHODS

hBM-MSCs harvested from sternum or iliac crest of five healthy donors and characterized in accordance with the International Society of Cellular Therapy (ISCT) guidelines are co-cultured with T cells. Additionally, modulatory effects of MSCs on T-cell viability, proliferation, cytokine profile, co-stimulatory pathway, activation and immunomodulation are also determined.

RESULTS

hBM-MSCs significantly reduced the expression of T-cell activation marker CD38 as well as co-stimulatory markers CD134 and CD154, whilst that of CD27 remained unchanged. BrdU, CFSE and Ki67 proliferation assays showed that hBM-MSCs reduced T-cell proliferation. Moreover, viability of T cells remained unchanged when co-cultured with hBM-MSCs. Finally, T cells when co-cultured with hBM-MSCs showed increased secretion of IL-10 and IL-11.

CONCLUSION

Collectively, hBM-MSCs are able to modulate the main steps involved in T-cell response toward a tolerogenic state. Thus, establishing immunobiological criteria defining the immunosuppressive effect of hBM-MSCs is of importance to reach efficient immunotherapeutic intervention.

TLR Function in Murine CD4(+) T Lymphocytes and Their Role in Inflammation

Toll-like receptor (TLR) signaling represents an evolutionary-conserved mechanism allowing for the rapid detection of broad molecular patterns that are common to different groups of pathogens. TLRs are traditionally associated with cells of the innate immune response where ligation of a TLR alone can lead to cellular activation and the initialization of an immune response. Cells of adaptive immunity, namely different classes of T and B lymphocytes, are also known to express a variety of TLRs. Conversely, the functional and signaling outcomes of TLRs are decidedly different in cells of the adaptive immune response. T lymphocytes generally have substantially lower TLR expression compared to innate cells, suggesting that TLRs function in a highly specialized capacity in this cell type. Certain TLRs act in a co-stimulatory capacity on T cells, amplifying activation only in the presence of simultaneous T-cell receptor engagement. However, the full array of TLR signaling events and outcomes in T lymphocytes remains poorly understood. Here, we describe a few methods for investigating the general function of TLRs on T lymphocytes in vitro and in vivo with an emphasis on the study of CD4(+) T cells. Most of these procedures can be adapted for the study of TLR signaling on other classes of lymphocytes as well.

Dysregulated co-stimulatory molecule expression in a Sjögren's syndrome mouse model with potential implications by microRNA-146a

Sjögren's syndrome (SjS) is an autoimmune condition that primarily affects salivary and lacrimal glands, causing loss of secretion. We have previously shown that microRNA-146a (miR-146a) is over-expressed in the salivary glands and peripheral blood mononuclear cells (PBMC) of SjS-prone mice (C57BL/6.NOD-Aec1Aec2, B6DC) and in PBMC of SjS patients. The purpose of this research was to identify a target molecule of miR-146a and identify subpopulations of cells affected by altered miR-146a in the salivary glands of SjS-prone mice. In silico analyses identified costimulatory molecule CD80 as a potential target of miR-146a. Luciferase assay of the human CD80 3'untranslated region demonstrated miR-146a directly inhibited CD80 protein expression as indicated by reduced luciferase reporter expression and an examination of B6DC salivary glands revealed a reduction in CD80 protein. More interestingly, the specific reduction in CD80 protein was detected from the salivary gland epithelial cell population and in interstitial dendritic cells in the glands as well. The reduction in CD80 protein levels in salivary gland epithelial cells were negatively associated with elevated miR-146a expression. Therefore, this study provides the first indication that salivary gland epithelial cells may be critically involved in SjS progression by altering CD86:CD80 protein ratio in response to miR-146a upregulation.

Co-stimulation Therapy in Rheumatoid Arthritis: Today and Tomorrow

Abatacept is the only T cell co-stimulation modulator approved thus far for the treatment of moderate-to-severe rheumatoid arthritis (RA) and is licensed for use in patients with an inadequate response to methotrexate (MTX) and/or anti-tumor necrosis factor (anti-TNF) therapy. The upstream mechanism of action of abatacept leads to downstream effects in a variety of cell types associated with the production of autoantibodies and pro-inflammatory cytokines implicated in RA. Accumulating data also suggest effects on other cells involved in the pathogenesis of RA, including regulatory T cells and osteoclasts. Clinical trials have demonstrated that abatacept is an effective and well-tolerated treatment in RA. More recently, evidence from the Assessing Very Early Rheumatoid arthritis Treatment (AVERT) trial showed that complete drug-free remission following treatment with abatacept may be a possibility in some patients with early RA, indicating that the disease course could be altered by early intervention. Equivalent efficacy and onset of action of abatacept and anti-TNF therapy have also been demonstrated in patients with an inadequate response to MTX in the Abatacept versus adaliMumab comParison in bioLogic-naïvE rheumatoid arthritis subjects with background methotrexate (AMPLE) trial. Together, these findings support the use of abatacept in early and established RA.

Concurrent loss of co-stimulatory molecules and functional cytokine secretion attributes leads to proliferative senescence of CD8(+) T cells in HIV/TB co-infection

The role of T-cell immunosenescence and functional CD8(+) T-cell responses in HIV/TB co-infection is unclear. We examined and correlated surrogate markers of HIV disease progression with immune activation, immunosenescence and differentiation using T-cell pools of HIV/TB co-infected, HIV-infected and healthy controls. Our investigations showed increased plasma viremia and reduced CD4/CD8 T-cell ratio in HIV/TB co-infected subjects relative to HIV-infected, and also a closer association with changes in the expression of CD38, a cyclic ADP ribose hydrolase and CD57, which were consistently expressed on late-senescent CD8(+) T cells. Up-regulation of CD57 and CD38 were directly proportional to lack of co-stimulatory markers on CD8(+) T cells, besides diminished expression of CD127 (IL-7Rα) on CD57(+)CD4(+) T cells. Notably, intracellular IFN-γ, perforin and granzyme B levels in HIV-specific CD8(+) T cells of HIV/TB co-infected subjects were diminished. Intracellular CD57 levels in HIV gag p24-specific CD8(+) T cells were significantly increased in HIV/TB co-infection. We suggest that HIV-TB co-infection contributes to senescence associated with chronic immune activation, which could be due to functional insufficiency of CD8(+) T cells.

The CD28-B7 Family in Anti-Tumor Immunity: Emerging Concepts in Cancer Immunotherapy

The interactions between B7 molecules and CD28-family receptors are crucial in the regulation of adaptive cellular immunity. In cancer, the aberrant expression of co-inhibitory B7 molecules has been attributed to reduced anti-tumor immunity and cancer immune evasion, prompting the development of cancer therapeutics that can restore T cell function. Murine tumor models have provided significant support for the targeting of multiple immune checkpoints involving CTLA-4, PD-1, ICOS, B7-H3 and B7-H4 during tumor growth, and clinical studies investigating the therapeutic effects of CTLA-4 and PD-1 blockade have shown exceptionally promising results in patients with advanced melanoma and other cancers. The expression pattern of co-inhibitory B7 ligands in the tumor microenvironment has also been largely correlated with poor patient prognosis, and recent evidence suggests that the presence of several B7 molecules may predict the responsiveness of immunotherapies that rely on pre-existing tumor-associated immune responses. While monotherapies blocking T cell co-inhibition have beneficial effects in reducing tumor burden, combinatorial immunotherapy targeting multiple immune checkpoints involved in various stages of the anti-tumor response has led to the most substantial impact on tumor reduction. In this review, we will examine the contributions of B7- and CD28-family members in the context of cancer development, and discuss the implications of current human findings in cancer immunotherapy.

Macrophages enhance tumor-derived autophagosomes (DRibbles)-induced B cells activation by TLR4/MyD88 and CD40/CD40L

Our previous studies have showed that tumor-derived autophagosomes (termed "DRibbles") induce B cell activation, resulting in antibody production and cytokine secretion. Unexpectedly, we found that unfractionated splenocytes produced a higher level of antibody and cytokine than that of purified B cells. In the current study, we investigated the role of accessory cells in DRibbles-induced B cell activation. We found that cognate macrophages, but not T cells, significantly enhanced the B cell activities. Such an enhancement required cell-cell contact. Furthermore, DRibbles stimulation up-regulated CD40L expression on macrophages, resulting in increased level of CD40 expressed on B cells. The accessory role of macrophages in DRibbles-activated B cells is critically dependent on the CD40/CD40L interaction. In addition, the effects of macrophages were found to be largely dependent on TLR4 and MyD88 signaling pathway. Finally, our results showed that macrophages were able to enhance the antigen presentation function of B cells for specific T cell stimulation. Thus, these results suggest that macrophages play an important accessory role for DRibbles-induced B cell immune function.

TCR stimulation without co-stimulatory signals induces expression of "tolerogenic" genes in memory CD4 T cells but does not compromise cell proliferation

Memory T cells resist co-stimulatory blockade and present a unique therapeutic challenge in transplantation and autoimmune diseases. Herein, we determined whether memory T cells express less "tolerogenic" genes than naïve T cells to reinforce a proliferative response under the deprivation of co-stimulatory signals. The expression of ∼40 tolerogenic genes in memory and naïve CD4(+) T cells was thus assessed during an in vitro TCR stimulation without co-stimulation. Briefly, upon TCR stimulation with an anti-CD3 mAb alone, memory CD4(+) T cells exhibited more proliferation than naïve CD4(+) T cells. To our surprise, at 24h upon anti-CD3 mAb stimulation, memory CD4(+) T cells expressed more than a 5-fold higher level of the transcription factor Egr2 and a 20-fold higher level of the transmembrane E3 ubiquitin ligase GRAIL than those in naïve T cells. Hence, the high-level expression of tolerogenic genes, Egr2 and GRAIL, in memory CD4(+) T cells does not prevent cell proliferation. Importantly, anti-CD3 mAb-stimulated memory CD4(+) T cells expressed high protein/gene levels of phosphorylated STAT5, Nedd4, Bcl-2, and Bcl-XL. Therefore, co-stimulation-independent proliferation of memory CD4(+) T cells may be due to elevated expression of molecules that support cell proliferation and survival, but not lack of tolerogenic molecules.

Parallels between immune driven-hematopoiesis and T cell activation: 3 signals that relay inflammatory stress to the bone marrow

Quiescence, self-renewal, lineage commitment and differentiation of hematopoietic stem cells (HSCs) towards fully mature blood cells are a complex process that involves both intrinsic and extrinsic signals. During steady-state conditions, most hematopoietic signals are provided by various resident cells inside the bone marrow (BM), which establish the HSC micro-environment. However, upon infection, the hematopoietic process is also affected by pathogens and activated immune cells, which illustrates an effective feedback mechanism to hematopoietic stem and progenitor cells (HSPCs) via immune-mediated signals. Here, we review the impact of pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs), costimulatory molecules and pro-inflammatory cytokines on the quiescence, proliferation and differentiation of HSCs and more committed progenitors. As modulation of HSPC function via these immune-mediated signals holds an interesting parallel with the "three-signal-model" described for the activation and differentiation of naïve T-cells, we propose a novel "three-signal" concept for immune-driven hematopoiesis. In this model, the recognition of PAMPs and DAMPs will activate HSCs and induce proliferation, while costimulatory molecules and pro-inflammatory cytokines confer a second and third signal, respectively, which further regulate expansion, lineage commitment and differentiation of HSPCs. We review the impact of inflammatory stress on hematopoiesis along these three signals and we discuss whether they act independently from each other or that concurrence of these signals is important for an adequate response of HSPCs upon infection.

Heme oxygenase-1 regulates dendritic cell function through modulation of p38 MAPK-CREB/ATF1 signaling

Dendritic cells (DCs) are critical for the initiation of immune responses including activation of CD8 T cells. Intracellular reactive oxygen species (ROS) levels influence DC maturation and function. Intracellular heme, a product of catabolism of heme-containing metalloproteins, is a key inducer of ROS. Intracellular heme levels are regulated by heme oxygenase-1 (HO-1), which catalyzes the degradation of heme. Heme oxygenase-1 has been implicated in regulating DC maturation; however, its role in other DC functions is unclear. Furthermore, the signaling pathways modulated by HO-1 in DCs are unknown. In this study, we demonstrate that inhibition of HO-1 activity in murine bone marrow-derived immature DCs (iDCs) resulted in DCs with raised intracellular ROS levels, a mature phenotype, impaired phagocytic and endocytic function, and increased capacity to stimulate antigen-specific CD8 T cells. Interestingly, our results reveal that the increased ROS levels following HO-1 inhibition did not underlie the changes in phenotype and functions observed in these iDCs. Importantly, we show that the p38 mitogen-activated protein kinase (p38 MAPK), cAMP-responsive element binding protein (CREB), and activating transcription factor 1 (ATF1) pathway is involved in the mediation of the phenotypic and functional changes arising from HO-1 inhibition. Furthermore, up-regulation of HO-1 activity rendered iDCs refractory to lipopolysaccharide-induced activation of p38 MAPK-CREB/ATF1 pathway and DC maturation. Finally, we demonstrate that treatment of iDC with the HO-1 substrate, heme, recapitulates the effects that result from HO-1 inhibition. Based on these results, we conclude that HO-1 regulates DC maturation and function by modulating the p38 MAPK-CREB/ATF1 signaling axis.

Emerging Co-signaling Networks in T Cell Immune Regulation

Co-signaling molecules are surface glycoproteins that positively or negatively regulate the T cell response to antigen. Co-signaling ligands and receptors crosstalk between the surfaces of antigen-presenting cells (APCs) and T cells, and modulate the ultimate magnitude and quality of T cell receptor (TCR) signaling. In the past 10 years, the field of co-signaling research has been advanced by the understanding of underlying mechanisms of the immune modulation led by newly identified co-signaling molecules and the successful preclinical and clinical trials targeting co-inhibitory molecules called immune checkpoints in the treatment of autoimmune diseases and cancers. In this review, we briefly describe the characteristics of well-known B7 co-signaling family members regarding the expression, functions and therapeutic implications and to introduce newly identified B7 members such as B7-H5, B7-H6, and B7-H7.

Nuclear factor-erythroid 2 (NF-E2) p45-related factor-2 (Nrf2) modulates dendritic cell immune function through regulation of p38 MAPK-cAMP-responsive element binding protein/activating transcription factor 1 signaling

Nrf2 is a redox-responsive transcription factor that has been implicated in the regulation of DC immune function. Loss of Nrf2 results in increased co-stimulatory molecule expression, enhanced T cell stimulatory capacity, and increased reactive oxygen species (ROS) levels in murine immature DCs (iDCs). It is unknown whether altered immune function of Nrf2-deficient DCs (Nrf2^−/− iDCs) is due to elevated ROS levels. Furthermore, it is unclear which intracellular signaling pathways are involved in Nrf2-mediated regulation of DC function. Using antioxidant vitamins to reset ROS levels in Nrf2^−/− iDCs, we show that elevated ROS is not responsible for the altered phenotype and function of these DCs. Pharmacological inhibitors were used to explore the role of key MAPKs in mediating the altered phenotype and function in Nrf2^−/− iDCs. We demonstrate that the increased co-stimulatory molecule expression (MHC II and CD86) and antigen-specific T cell activation capacity observed in Nrf2^−/− iDCs was reversed by inhibition of p38 MAPK but not JNK. Importantly, we provide evidence for increased phosphorylation of cAMP-responsive element binding protein (CREB) and activating transcription factor 1 (ATF1), transcription factors that are downstream of p38 MAPK. The increased phosphorylation of CREB/ATF1 in Nrf2^−/− iDCs was sensitive to p38 MAPK inhibition. We also show data to implicate heme oxygenase-1 as a potential molecular link between Nrf2 and CREB/ATF1. These results indicate that dysregulation of p38 MAPK-CREB/ATF1 signaling axis underlies the altered function and phenotype in Nrf2-deficient DCs. Our findings provide new insights into the mechanisms by which Nrf2 mediates regulation of DC function.

PD-L1/PD-1 Co-Stimulation, a Brake for T cell Activation and a T cell Differentiation Signal

For T cell activation, three signals have to be provided from the antigen presenting cell; Signal 1 (antigen recognition), signal 2 (co-stimulation) and signal 3 (cytokine priming). Blocking negative co-stimulation during antigen presentation to T cells is becoming a promising therapeutic strategy to enhance cancer immunotherapy. Here we will focus on interference with PD-1/PD-L1 negative co-stimulation during antigen presentation to T cells as a therapeutic approach. We will discuss the potential mechanisms and the therapeutic consequences by which interference/inhibition with this interaction results in anti-tumour immunity. Particularly, we will comment on whether blocking negative co-stimulation provides differentiation signals to T cells undergoing antigen presentation. A major dogma in immunology states that T cell differentiation signals are given by cytokines and chemokines (signal 3) rather than co-stimulation (signal 2). We will discuss whether this is the case when blocking PD-L1/PD-1 negative co-stimulation.