The immunological synapse

T cell interactions with B cells during germinal center formation, a three-step model

Establishment of effective immunity against invading microbes depends on continuous generation of antibodies that facilitate pathogen clearance. Long-lived plasma cells with the capacity to produce high affinity antibodies evolve in germinal centers (GCs), where B cells undergo somatic hypermutation and are subjected to affinity-based selection. Here, we focus on the cellular interactions that take place early in the antibody immune response during GC colonization. Clones bearing B-cell receptors with different affinities and specificities compete for entry to the GC, at the boundary between the B-cell and T-cell zones in lymphoid organs. During this process, B cells compete for interactions with T follicular helper cells, which provide selection signals required for differentiation into GC cells and antibody secreting cells. These cellular engagements are long-lasting and depend on activation of adhesion molecules that support persistent interactions and promote transmission of signals between the cells. Here, we discuss how interactions between cognate T and B cells are primarily maintained by three types of molecular interactions: homophilic signaling lymphocytic activation molecule (SLAM) interactions, T-cell receptor: peptide-loaded major histocompatibility class II (pMHCII), and LFA-1:ICAMs. These essential components support a three-step process that controls clonal selection for entry into the antibody affinity maturation response in the GC, and establishment of long-lasting antibody-mediated immunity.

ARL3, a small GTPase with a functionally conserved role in primary cilia and immune synapses

The primary cilium and the immunological synapse are both specialized functional plasma membrane domains that share several similarities. Signalling output of membrane domains is regulated, spatially and temporally, by segregating and focusing lipids and proteins. ARL3, a small GTPase, plays a major role in concentrating lipid-modified proteins in both the immunological synapse and the primary cilia. Here in this review we will introduce the role of ARL3 in health and disease and its role in polarizing signalling at the primary cilia and immunological synapses.

Single-molecule investigations of T-cell activation

T-cell activation is the central event governing its development, differentiation, and effector functions. T-cell activation is initiated by the direct physical interaction of the T cell antigen receptor (TCR) with cognate peptide presented by the major histocompatibility complex (pMHC) molecule expressed on the antigen presenting cell (APC) surface. Since the identification of TCR as the only receptor for antigen on T cells three decades ago, studies have elucidated the major molecular players and signaling events responding to TCR stimulation. However, the question of how the physical event of pMHC binding is converted across the membrane into chemical events to initiate signal transduction remains elusive. Here we review recent investigations of T-cell activation using single-molecule force and fluorescence techniques that shed new light on this key question.

The Major Histocompatibility Complex Class II-CD4 Immunologic Synapse in Alcoholic Hepatitis and Autoimmune Liver Pathology: The Role of Aberrant Major Histocompatibility Complex Class II in Hepatocytes

The major histocompatibility complex class II (MHC II)-CD4 immunologic synapse is classically described between the T-cell receptor of CD4-positive lymphocytes and MHC II on antigen-presenting cells. This interaction and others between surrounding costimulatory and checkpoint molecules promote differentiation of naïve CD4 T lymphocytes into helper T cells subtypes, including types 1, 2, and 17 helper T cells, that have more tailored immunologic responses. Although MHC II is mainly produced by professional antigen-presenting cells, it can be aberrantly produced by other cell types, including hepatocytes in various liver pathologies, such as autoimmune hepatitis and alcoholic hepatitis. This can lead to direct targeting of hepatocytes by CD4-positive lymphocytes, which form an immunologic synapse with the hepatocyte. The lymphocytes internalize the MHC II-CD4 complexes in a phagocytosis-like mechanism and in the process eat the hepatocyte piece by piece. We review the evidence for this mechanism and the role of these autoimmune responses in various liver diseases, including alcoholic hepatitis, autoimmune hepatitis, and primary biliary cirrhosis. The role of aberrant MHC II in malignancy, including hepatocellular carcinoma, is also reviewed. Further understanding of this mechanism can lead to better understanding of the immune mechanisms involved in these liver pathologies, with potential diagnostic and therapeutic applications.

Adhering to adhesion: assessing integrin conformation to monitor T cells

Monitoring T cells is of major importance for the development of immunotherapies. Recent sophisticated assays can address particular aspects of the anti-tumor T-cell repertoire or support very large-scale immune screening for biomarker discovery. Robust methods for the routine assessment of the quantity and quality of antigen-specific T cells remain, however, essential. This review discusses selected methods that are commonly used for T-cell monitoring and summarizes the advantages and limitations of these assays. We also present a new functional assay, which specifically detects activated β2 integrins within a very short time following CD8+ T-cell stimulation. Because of its unique and favorable characteristics, this assay could be useful for implementation into our T-cell monitoring toolbox.

Galectin-3 modulation of T-cell activation: mechanisms of membrane remodelling

Galectin-3 (Gal3) is a multifaceted protein which belongs to a family of lectins and binds β-galactosides. Gal3 expression is altered in many types of cancer, with increased expression generally associated with poor prognosis. Although the mechanisms remain unknown, Gal3 has been implicated in several biological processes involved in cancer progression, including suppression of T cell-mediated immune responses. Extracellular Gal3 binding to the plasma membrane of T cells alters membrane organization and the formation of an immunological synapse. Its multivalent capacity allows Gal3 to interact specifically with different membrane proteins and lipids, influencing endocytosis, trafficking and T cell receptor signalling. The ability of Gal3 to inhibit T cell responses may provide a mechanism by which Gal3 aids in cancer progression. In this review, we seek to give an overview of the mechanisms by which Gal3 alters the spatial organization of cell membranes and how these processes impact on T cell activation.

The emerging role of epigenetic therapeutics in immuno-oncology

The past decade has seen the emergence of immunotherapy as a prime approach to cancer treatment, revolutionizing the management of many types of cancer. Despite the promise of immunotherapy, most patients do not have a response or become resistant to treatment. Thus, identifying combinations that potentiate current immunotherapeutic approaches will be crucial. The combination of immune-checkpoint inhibition with epigenetic therapy is one such strategy that is being tested in clinical trials, encompassing a variety of cancer types. Studies have revealed key roles of epigenetic processes in regulating immune cell function and mediating antitumour immunity. These interactions make combined epigenetic therapy and immunotherapy an attractive approach to circumvent the limitations of immunotherapy alone. In this Review, we highlight the basic dynamic mechanisms underlying the synergy between immunotherapy and epigenetic therapies and detail current efforts to translate this knowledge into clinical benefit for patients.

Loss of human ICOSL results in combined immunodeficiency

Primary immunodeficiencies represent naturally occurring experimental models to decipher human immunobiology. We report a patient with combined immunodeficiency, marked by recurrent respiratory tract and DNA-based viral infections, hypogammaglobulinemia, and panlymphopenia. He also developed moderate neutropenia but without prototypical pyogenic infections. Using whole-exome sequencing, we identified a homozygous mutation in the inducible T cell costimulator ligand gene (ICOSLG; c.657C>G; p.N219K). Whereas WT ICOSL is expressed at the cell surface, the ICOSL^N219K mutation abrogates surface localization: mutant protein is retained in the endoplasmic reticulum/Golgi apparatus, which is predicted to result from deleterious conformational and biochemical changes. ICOSL^N219K diminished B cell costimulation of T cells, providing a compelling basis for the observed defect in antibody and memory B cell generation. Interestingly, ICOSL^N219K also impaired migration of lymphocytes and neutrophils across endothelial cells, which normally express ICOSL. These defects likely contributed to the altered adaptive immunity and neutropenia observed in the patient, respectively. Our study identifies human ICOSLG deficiency as a novel cause of a combined immunodeficiency.

The influence of microenvironment on tumor immunotherapy

Tumor immunotherapy has achieved remarkable efficacy, with immune-checkpoint inhibitors as especially promising candidates for cancer therapy. However, some issues caused by immunotherapy have raised attention, such as limited efficacy for some patients, narrow antineoplastic spectrum, and adverse reactions, suggesting that using regulators of tumor immune response may prove to be more complicated than anticipated. Current evidence indicates that different factors collectively constituting the unique tumor microenvironment promote immune tolerance, and these include the expression of co-inhibitory molecules, the secretion of lactate, and competition for nutrients between tumor cells and immune cells. Furthermore, cancer-associated fibroblasts, the main cellular components of solid tumors, promote immunosuppression through inhibition of T cell function and extracellular matrix remodeling. Here, we summarize the research advances in tumor immunotherapy and the latest insights into the influence of microenvironment on tumor immunotherapy.

The influence of microenvironment on tumor immunotherapy

Tumor immunotherapy has achieved remarkable efficacy, with immune-checkpoint inhibitors as especially promising candidates for cancer therapy. However, some issues caused by immunotherapy have raised attention, such as limited efficacy for some patients, narrow antineoplastic spectrum, and adverse reactions, suggesting that using regulators of tumor immune response may prove to be more complicated than anticipated. Current evidence indicates that different factors collectively constituting the unique tumor microenvironment promote immune tolerance, and these include the expression of co-inhibitory molecules, the secretion of lactate, and competition for nutrients between tumor cells and immune cells. Furthermore, cancer-associated fibroblasts, the main cellular components of solid tumors, promote immunosuppression through inhibition of T cell function and extracellular matrix remodeling. Here, we summarize the research advances in tumor immunotherapy and the latest insights into the influence of microenvironment on tumor immunotherapy.

A Ciliary View of the Immunological Synapse

The primary cilium has gone from being a vestigial organelle to a crucial signaling hub of growing interest given the association between a group of human disorders, collectively known as ciliopathies, and defects in its structure or function. In recent years many ciliogenesis proteins have been observed at extraciliary sites in cells and likely perform cilium-independent functions ranging from regulation of the cytoskeleton to vesicular trafficking. Perhaps the most striking example is the non-ciliated T lymphocyte, in which components of the ciliary machinery are repurposed for the assembly and function of the immunological synapse even in the absence of a primary cilium. Furthermore, the specialization traits described at the immunological synapse are similar to those seen in the primary cilium. Here, we review common regulators and features shared by the immunological synapse and the primary cilium that document the remarkable homology between these structures.

Bispecific T-Cell Redirection versus Chimeric Antigen Receptor (CAR)-T Cells as Approaches to Kill Cancer Cells

The concepts for T-cell redirecting bispecific antibodies (TRBAs) and chimeric antigen receptor (CAR)-T cells are both at least 30 years old but both platforms are just now coming into age. Two TRBAs and two CAR-T cell products have been approved by major regulatory agencies within the last ten years for the treatment of hematological cancers and an additional 53 TRBAs and 246 CAR cell constructs are in clinical trials today. Two major groups of TRBAs include small, short-half-life bispecific antibodies that include bispecific T-cell engagers (BiTE®s) which require continuous dosing and larger, mostly IgG-like bispecific antibodies with extended pharmacokinetics that can be dosed infrequently. Most CAR-T cells today are autologous, although significant strides are being made to develop off-the-shelf, allogeneic CAR-based products. CAR-Ts form a cytolytic synapse with target cells that is very different from the classical immune synapse both physically and mechanistically, whereas the TRBA-induced synapse is similar to the classic immune synapse. Both TRBAs and CAR-T cells are highly efficacious in clinical trials but both also present safety concerns, particularly with cytokine release syndrome and neurotoxicity. New formats and dosing paradigms for TRBAs and CAR-T cells are being developed in efforts to maximize efficacy and minimize toxicity, as well as to optimize use with both solid and hematologic tumors, both of which present significant challenges such as target heterogeneity and the immunosuppressive tumor microenvironment.

Phosphoinositide 3-kinase δ is a regulatory T-cell target in cancer immunotherapy

Tumour infiltration by regulatory T (Treg) cells contributes to suppression of the anti-tumour immune response, which limits the efficacy of immune-mediated cancer therapies. The phosphoinositide 3-kinase (PI3K) pathway has key roles in mediating the function of many immune cell subsets, including Treg cells. Treg function is context-dependent and depends on input from different cell surface receptors, many of which can activate the PI3K pathway. In this review, we explore how PI3Kδ contributes to signalling through several major immune cell receptors, including the T-cell receptor and co-stimulatory receptors such as CD28 and ICOS, but is antagonized by the immune checkpoint receptors CTLA-4 and PD-1. Understanding how PI3Kδ inhibition affects Treg signalling events will help to inform how best to use PI3Kδ inhibitors in clinical cancer treatment.

Circulating T cell-monocyte complexes are markers of immune perturbations

Our results highlight for the first time that a significant proportion of cell doublets in flow cytometry, previously believed to be the result of technical artifacts and thus ignored in data acquisition and analysis, are the result of biological interaction between immune cells. In particular, we show that cell:cell doublets pairing a T cell and a monocyte can be directly isolated from human blood, and high resolution microscopy shows polarized distribution of LFA1/ICAM1 in many doublets, suggesting in vivo formation. Intriguingly, T cell-monocyte complex frequency and phenotype fluctuate with the onset of immune perturbations such as infection or immunization, reflecting expected polarization of immune responses. Overall these data suggest that cell doublets reflecting T cell-monocyte in vivo immune interactions can be detected in human blood and that the common approach in flow cytometry to avoid studying cell:cell complexes should be re-visited.

The role of spectrin in cell adhesion and cell-cell contact

Spectrins are proteins that are responsible for many aspects of cell function and adaptation to changing environments. Primarily the spectrin-based membrane skeleton maintains cell membrane integrity and its mechanical properties, together with the cytoskeletal network a support cell shape. The occurrence of a variety of spectrin isoforms in diverse cellular environments indicates that it is a multifunctional protein involved in numerous physiological pathways. Participation of spectrin in cell–cell and cell–extracellular matrix adhesion and formation of dynamic plasma membrane protrusions and associated signaling events is a subject of interest for researchers in the fields of cell biology and molecular medicine. In this mini-review, we focus on data concerning the role of spectrins in cell surface activities such as adhesion, cell–cell contact, and invadosome formation. We discuss data on different adhesion proteins that directly or indirectly interact with spectrin repeats. New findings support the involvement of spectrin in cell adhesion and spreading, formation of lamellipodia, and also the participation in morphogenetic processes, such as eye development, oogenesis, and angiogenesis. Here, we review the role of spectrin in cell adhesion and cell–cell contact.

Impact statement

This article reviews properties of spectrins as a group of proteins involved in cell surface activities such as, adhesion and cell–cell contact, and their contribution to morphogenesis. We show a new area of research and discuss the involvement of spectrin in regulation of cell–cell contact leading to immunological synapse formation and in shaping synapse architecture during myoblast fusion. Data indicate involvement of spectrins in adhesion and cell–cell or cell–extracellular matrix interactions and therefore in signaling pathways. There is evidence of spectrin’s contribution to the processes of morphogenesis which are connected to its interactions with adhesion molecules, membrane proteins (and perhaps lipids), and actin. Our aim was to highlight the essential role of spectrin in cell–cell contact and cell adhesion.

Antibody therapeutics and immunoregulation in cancer and autoimmune disease

Cancer and autoimmune disease are closely related, and many therapeutic antibodies are widely used in clinics for the treatment of both diseases. Among them, the anti-CD20 antibody has proven to be effective against both lymphoid malignancy and autoimmune disease. Moreover, immune checkpoint blockade using the anti-PD1/PD-L1/CTLA4 antibody has improved the prognosis of patients with refractory solid tumors. At the same time, however, over-enhancement of immunoreaction can induce autoimmune reaction. Although anti-TNF antibody therapies represent a breakthrough in the treatment of autoimmune diseases, optimal management is required to control the serious associated issues, including development and progression of cancer, and it is becoming more and more important to control the immunoreaction. In addition, next-generation antibody therapeutics such as antibody-drug conjugates and bispecific antibodies, are anticipated to treat uncontrolled cancer and autoimmune disease. IL-7R signaling plays an important role in the development and progression of both lymphoid malignancy and autoimmune disease. In addition, abnormal homing activity and steroid resistance caused by IL-7R signaling may worsen prognosis. Therefore, anti-IL-7R targeting antibody therapies that enable suppression of such pathophysiological status have the potential to be beneficial for the treatment of both diseases. In this review, we discuss current antibody therapeutics in cancer and autoimmune disease, and describe a new therapeutic strategy for immunoregulation including IL-7R targeting antibodies.

Multiscale engineering of immune cells and lymphoid organs

Immunoengineering applies quantitative and materials-based approaches for the investigation of the immune system and for the development of therapeutic solutions for various diseases, such as infection, cancer, inflammatory diseases and age-related malfunctions. The design of immunomodulatory and cell therapies requires the precise understanding of immune cell formation and activation in primary, secondary and ectopic tertiary immune organs. However, the study of the immune system has long been limited to in vivo approaches, which often do not allow multidimensional control of intracellular and extracellular processes, and to 2D in vitro models, which lack physiological relevance. 3D models built with synthetic and natural materials enable the structural and functional recreation of immune tissues. These models are being explored for the investigation of immune function and dysfunction at the cell, tissue and organ levels. In this Review, we discuss 2D and 3D approaches for the engineering of primary, secondary and tertiary immune structures at multiple scales. We highlight important insights gained using these models and examine multiscale engineering strategies for the design and development of immunotherapies. Finally, dynamic 4D materials are investigated for their potential to provide stimuli-dependent and context-dependent scaffolds for the generation of immune organ models.

Imaging: Gear up for mechano-immunology

Immune cells including B and T lymphocytes have a remarkable ability to sense the physical perturbations through their surface expressed receptors. At the advent of modern imaging technologies paired with biophysical methods, we have gained the understanding of mechanical forces exerted by immune cells to perform their functions. This review will go over the imaging techniques already being used to study mechanical forces in immune cells. We will also discuss the dire need for new modern technologies for future work.

Actin Cytoskeleton Straddling the Immunological Synapse between Cytotoxic Lymphocytes and Cancer Cells

The immune system is a fundamental part of the tumor microenvironment. In particular, cytotoxic lymphocytes, such as cytolytic T cells and natural killer cells, control tumor growth and disease progression by interacting and eliminating tumor cells. The actin cytoskeleton of cytotoxic lymphocytes engaged in an immunological synapse has received considerable research attention. It has been recognized as a central mediator of the formation and maturation of the immunological synapse, and its signaling and cytolytic activities. In comparison, fewer studies have explored the organization and function of actin filaments on the target cancer cell side of the immunological synapse. However, there is growing evidence that the actin cytoskeleton of cancer cells also undergoes extensive remodeling upon cytotoxic lymphocyte attack, and that such remodeling can alter physical and functional interactions at the immunological synapse. In this article, we review the current knowledge of actin organization and functions at both sides of the immunological synapse between cytotoxic lymphocytes and cancer cells, with particular focus on synapse formation, signaling and cytolytic activity, and immune evasion.

Killing Mechanisms of Chimeric Antigen Receptor (CAR) T Cells

Effective adoptive T cell therapy (ACT) comprises the killing of cancer cells through the therapeutic use of transferred T cells. One of the main ACT approaches is chimeric antigen receptor (CAR) T cell therapy. CAR T cells mediate MHC-unrestricted tumor cell killing by enabling T cells to bind target cell surface antigens through a single-chain variable fragment (scFv) recognition domain. Upon engagement, CAR T cells form a non-classical immune synapse (IS), required for their effector function. These cells then mediate their anti-tumoral effects through the perforin and granzyme axis, the Fas and Fas ligand axis, as well as the release of cytokines to sensitize the tumor stroma. Their persistence in the host and functional outputs are tightly dependent on the receptor's individual components-scFv, spacer domain, and costimulatory domains-and how said component functions converge to augment CAR T cell performance. In this review, we bring forth the successes and limitations of CAR T cell therapy. We delve further into the current understanding of how CAR T cells are designed to function, survive, and ultimately mediate their anti-tumoral effects.

Novel advances on tissue immune dynamics in HIV/simian immunodeficiency virus: lessons from imaging studies

PURPOSE OF REVIEW

To describe recent findings on the effect of HIV/SIV infection on lymph node viral and T-cell dynamics using imaging-based methodologies.

RECENT FINDINGS

Chronic infection, particularly HIV/SIV, alters dramatically the microenvironment, immune cell frequency, distribution, function and tissue organization of secondary lymphoid tissues. These changes are not always reversible. Over the past few years, the implementation of advanced imaging protocols on human lymph node biopsies as well as on longitudinal lymphoid tissues samples from nonhuman primates (NHP) have provided a wealth of information on how local immune responses evolve over time in response to a persisting retroviral pathogen. Most of the information concerns cytotoxic and helper T cells and viral dynamics. In this review, we detail this information focusing on HIV/SIV infection. We also comment on the gaps that imaging technologies have bridged in our understanding and discuss the translational value of these new findings in the light of emerging therapeutic agendas.

SUMMARY

Novel imaging platforms allow for dissecting the spatiotemporal dynamics of immune interactions further improving our understanding of the interplay between virus and host and providing important information for designing successful preventive and curative strategies.

A Protocol to Study T-Cell Signaling in an Immune Synapse by Microscopy

The immune synapse is a complex cellular structure that enables cell-cell communications between immune cells, mainly at the interface of an effector T-cell and an antigen-presenting cell (APC) that expresses the appropriate peptide-MHC complexes. With progressive technological advances, there has been increasing interest in understanding molecular events that take place in motile T-lymphocytes at the immune synapse. Here, we provide an optimized method to induce the formation of an immune synapse between a T-cell and an APC in vitro. The experimental protocol described herein would be useful in characterizing the role of cell surface molecules and downstream signaling pathways in the context of cell-to-cell communications between T-cells and APCs.

Nanomedicine and macroscale materials in immuno-oncology

Immunotherapy is revolutionizing the treatment of cancer. It can achieve unprecedented responses in advanced-stage patients, including complete cures and long-term survival. However, immunotherapy also has limitations, such as its relatively low response rates and the development of severe side effects. These drawbacks are gradually being overcome by improving our understanding of the immune system, as well as by establishing combination regimens in which immunotherapy is combined with other treatment modalities. In addition to this, in recent years, progress made in chemistry, nanotechnology and materials science has started to impact immuno-oncology, resulting in more effective and less toxic immunotherapy interventions. In this context, multiple different nanomedicine formulations and macroscale materials have been shown to be able to boost anti-cancer immunity and the efficacy of immunomodulatory drugs. We here review nanotechnological and materials chemistry efforts related to endogenous and exogenous vaccination, to the engineering of antigen-presenting cells and T cells, and to the modulation of the tumor microenvironment. We also discuss limitations, current trends and future directions. Together, the insights provided and the evidence obtained indicate that there is a bright future ahead for engineering nanomedicines and macroscale materials for immuno-oncology applications.

B cell mechanosensing: A mechanistic overview

B cells are essential to the adaptive immune system for providing the humoral immunity against cohorts of pathogens. The presentation of antigen to the B cell receptor (BCR) leads to the initiation of B cell activation, which is a process sensitive to the stiffness features of the substrates presenting the antigens. Mechanosensing of the B cells, potentiated through BCR signaling and the adhesion molecules, efficiently regulates B cell activation, proliferation and subsequent antibody responses. Defects in sensing of the antigen-presenting substrates can lead to the activation of autoreactive B cells in autoimmune diseases. The use of high-resolution, high-speed live-cell imaging along with the sophisticated biophysical materials, has uncovered the mechanisms underlying the initiation of B cell activation within seconds of its engagement with the antigen presenting substrates. In this chapter, we reviewed studies that have contributed to uncover the molecular mechanisms of B cell mechanosensing during the initiation of B cell activation.

The suppressive effect of co-inhibiting PD-1 and CTLA-4 expression on H22 hepatomas in mice

Objective

We investigated the suppressive effect of siRNA-mediated co-inhibition of PD-1 and CTLA-4 expression on H22 hepatomas in mice.

Methods

Murine H22 cells were cultured in vivo in ICR mice. An allograft tumor model was also established in another ICR mouse group. The tumor-bearing mice were randomly divided into four groups: control, single PD-1 siRNA, single CTLA-4 siRNA, and double PD-1 + CTLA-4 siRNAs. The survival time and physiological condition of the mice were observed after the injection of the siRNAs and placebo. The volume and weight of the solid tumor were measured to assess the inhibition of the tumor. To assess the effects of siRNAs on mouse immune function, the protein levels of IFN-γ and IL-10 in the blood and PD-L1 in the tumor and liver were determined using ELISA, and the mRNA levels of IFN-γ, PD-L1, PD-1, CTLA-4, IL-6 and Survivin in the tumor, liver and spleen were determined using quantitative RT-PCR. The ratios of Bax and Bcl-2 protein were determined via western blot to analyze the effect of siRNAs on tumor cell apoptosis.

Results

The anti-tumor effect appeared in all groups with siRNA-mediated inhibition. The tumor growth suppression was stronger in the group with double inhibition. The weight and volume of the tumors were significantly lower and the survival rate improved in the three siRNA groups. IFN-γ levels increased but IL-10 levels decreased in the blood of the siRNA group mice compared with the results for the control group. In the tumor and spleen tissue, the IFN-γ levels significantly increased, but in the liver tissue they significantly decreased in the three siRNA groups. The results of quantitative RT-PCR showed that the mRNAs for PD-1 and CTLA-4 were downregulated in spleen tissue in the three siRNA groups, while the PD-L1 mRNA and protein levels increased significantly in the tumor, but decreased in the liver. Survivin and IL-6 mRNA levels decreased in the tumor. Western blot results showed that ratio of Bax and Bcl-2 had significantly increased. These results indicated that downregulating PD-1 and CTLA-4 could increase the body’s immune response and promote apoptosis of tumor cells.

Conclusion

Co-inhibiting the expressions of PD-1 and CTLA-4 can effectively suppress the growth of H22 hepatoma and promote the apoptosis of tumor cells in mice. Blocking PD-1 and CTLA-4 can improve the vitality of T cells, and improve the immune environment and response.

The Role of the Immunological Synapse in Differential Effects of APC Subsets in Alloimmunization to Fresh, Non-stored RBCs

Background: Each year, over 5 million red blood cell (RBC) transfusions are administered to patients in the USA. Despite the therapeutic benefits of RBC transfusions, there are associated risks. RBC-specific alloantibodies may form in response to antigenic differences between RBC donors and recipients; these alloantibodies can be a problem as they may mediate hemolysis or pose barriers to future transfusion support. While there is currently no reliable way to predict which RBC recipients will make an alloantibody response, risk factors such as inflammation have been shown to correlate with increased rates of RBC alloimmunization. The underlying mechanisms behind how inflammation mediates alloantibody production are incompletely defined.

Methods: To assess erythrophagocytosis, mice were treated with PBS or inflammatory stimuli followed by a transfusion of allogeneic RBCs labeled with a lipophilic dye. At multiple time points, RBC consumption and expression of activation makers by leukocytes was evaluated. To determine which antigen presenting cell (APC) subset(s) were capable of promoting allogeneic T cell activation, sorted leukocyte populations (which had participated in erythrophagocytosis) were co-cultured in vitro with allogeneic CD4+ T cells; T cell proliferation and ability to form immunological synapses with APCs were determined.

Results: Upon transfusion of fresh allogeneic RBCs, multiple APCs consumed transfused RBCs. However, only CD8+ and CD11b+ dendritic cells formed productive immunological synapses with allogeneic T cells and stimulated proliferation. Importantly, allogeneic T cell activation and RBC alloantibody production occurred in response to RBC transfusion alone, and transfusion in the context of inflammation enhanced RBC consumption, the number of immune synapses, allogeneic T cell proliferation, and the rate and magnitude of alloantibody production.

Conclusions: These data demonstrate that regardless of the ability to participate in RBC consumption, only a subset of APCs are capable of forming an immune synapse with T cells thereby initiating an alloantibody response. Additionally, these data provide mechanistic insight into RBC alloantibody generation.

Bifunctional PD-1 × αCD3 × αCD33 fusion protein reverses adaptive immune escape in acute myeloid leukemia

The CD33-targeting bispecific T-cell engager (BiTE) AMG 330 proved to be highly efficient in mediating cytolysis of acute myeloid leukemia (AML) cells in vitro and in mouse models. Yet, T-cell activation is correlated with upregulation of programmed cell death-ligand 1 (PD-L1) and other inhibitory checkpoints on AML cells that confer adaptive immune resistance. PD-1 and PD-L1 blocking agents may counteract T-cell dysfunction, however, at the expense of broadly distributed immune-related adverse events (irAEs). We developed a bifunctional checkpoint inhibitory T cell-engaging (CiTE) antibody that combines T-cell redirection to CD33 on AML cells with locally restricted immune checkpoint blockade. This is accomplished by fusing the extracellular domain of PD-1 (PD-1_ex), which naturally holds a low affinity to PD-L1, to an αCD3.αCD33 BiTE-like scaffold. By a synergistic effect of checkpoint blockade and avidity-dependent binding, the PD-1_ex attachment increases T-cell activation (3.3-fold elevation of interferon-γ) and leads to efficient and highly selective cytotoxicity against CD33⁺PD-L1⁺ cell lines (50% effective concentration = 2.3-26.9 pM) as well as patient-derived AML cells (n = 8). In a murine xenograft model, the CiTE induces complete AML eradication without initial signs of irAEs as measured by body weight loss. We conclude that our molecule preferentially targets AML cells, whereas high-affinity blockers, such as clinically approved anticancer agents, also address PD-L1⁺ non-AML cells. By combining the high efficacy of T-cell engagers with immune checkpoint blockade in a single molecule, we expect to minimize irAEs associated with the systemic application of immune checkpoint inhibitors and suggest high therapeutic potential, particularly for patients with relapsed/ refractory AML.

Combining Tumor Vaccination and Oncolytic Viral Approaches with Checkpoint Inhibitors: Rationale, Pre-Clinical Experience, and Current Clinical Trials in Malignant Melanoma

The field of tumor immunology has faced many complex challenges over the last century, but the approval of immune checkpoint inhibitors (anti-cytotoxic T-lymphocyte-associated protein 4 [CTLA4] and anti-programmed cell death-1 [PD-1]/PD-ligand 1 [PD-L1]) and talimogene laherparepvec (T-VEC) for the treatment of metastatic melanoma have awakened a new wave of interest in cancer immunotherapy. Additionally, combinations of vaccines and oncolytic viral therapies with immune checkpoint inhibitors and other systemic agents seem to be promising synergistic strategies to further boost the immune response against cancer. These combinations are undergoing clinical investigation, and if successful, will hopefully soon become available to patients. Here, we review key basic concepts of tumor-induced immune suppression in malignant melanoma, the historical perspective around vaccine development in melanoma, and advances in oncolytic viral therapies. We also discuss the emerging role for combination approaches with different immunomodulatory agents as well as new developments in personalized immunization approaches.

Imbalance of immunological synapse-kinapse states reflects tumor escape to immunity in glioblastoma

Since the proper activation of T cells requires the physical interaction with target cells through the formation of immunological synapses (IS), an alteration at this level could be a reason why tumors escape the immune response. As part of their life cycle, it is thought that T cells alternate between a static phase, the IS, and a dynamic phase, the immunological kinapse (IK), depending on high or low antigen sensing. Our investigation performed in tissue samples of human glioma shows that T cells are able to establish synapsing interactions not only with glioma tumorigenic cells, but also with stromal myeloid cells. Particularly, the IS displaying a T cell receptor-rich (TCR-rich) central supramolecular activation cluster (cSMAC) is preferentially established with stromal cells, as opposed to malignant cells. Conversely, T cells in the malignant areas showed distinct morphometric parameters compared with nonneoplastic tissue - the former characterized by an elongated shape, well-suited to kinaptic dynamics. Importantly, high-resolution 3-dimensional analyses demonstrated the existence of bona-fide IK preferentially arranged in malignant areas of the tumor. This imbalance of IS/IK states between these 2 microenvironments reveals the low antigenic sensing of T cells when patrolling tumorigenic cells and reflects the immunoevasive environment of the tumor.

Future prospects of immune checkpoint blockade in cancer: from response prediction to overcoming resistance

Recent advances in the understating of tumor immunology suggest that cancer immunotherapy is an effective treatment against various types of cancer. In particular, the remarkable successes of immune checkpoint-blocking antibodies in clinical settings have encouraged researchers to focus on developing other various immunologic strategies to combat cancer. However, such immunotherapies still face difficulties in controlling malignancy in many patients due to the heterogeneity of both tumors and individual patients. Here, we discuss how tumor-intrinsic cues, tumor environmental metabolites, and host-derived immune cells might impact the efficacy and resistance often seen during immune checkpoint blockade treatment. Furthermore, we introduce biomarkers identified from human and mouse models that predict clinical benefits for immune checkpoint blockers in cancer.

Synaptic Interactions in Germinal Centers

The germinal center (GC) is a complex, highly dynamic microanatomical niche that allows the generation of high-affinity antibody-producing plasma cells and memory B cells. These cells constitute the basis of long-lived highly protective antibody responses. For affinity maturation to occur, B cells undergo multiple rounds of proliferation and mutation of the genes that encode the immunoglobulin V region followed by selection by specialized T cells called follicular helper T (T_FH) cells. In order to achieve this result, the GC requires spatially and temporally coordinated interactions between the different cell types, including B and T lymphocytes and follicular dendritic cells. Cognate interactions between T_FH and GC B cells resemble cellular connections and synaptic communication within the nervous system, which allow signals to be transduced rapidly and effectively across the synaptic cleft. Such immunological synapses are particularly critical in the GC where the speed of T–B cell interactions is faster and their duration shorter than at other sites. In addition, the antigen-based specificity of cognate interactions in GCs is critical for affinity-based selection in which B cells compete for T cell help so that rapid modulation of the signaling threshold determines the outcome of the interaction. In the context of GCs, which contain large numbers of cells in a highly compacted structure, focused delivery of signals across the interacting cells becomes particularly important. Promiscuous or bystander delivery of positive selection signals could potentially lead to the appearance of long-lived self-reactive B cell clones. Cytokines, cytotoxic granules, and more recently neurotransmitters have been shown to be transferred from T_FH to B cells upon cognate interactions. This review describes the current knowledge on immunological synapses occurring during GC responses including the type of granules, their content, and function in T_FH-mediated help to B cells.

Maintenance of CD4 T cell fitness through regulation of Foxo1

Foxo transcription factors play an essential role in regulating specialized lymphocyte functions and in maintaining T cell quiescence. Here, we used a system in which Foxo1 transcription-factor activity, which is normally terminated upon cell activation, cannot be silenced, and we show that enforcing Foxo1 activity disrupts homeostasis of CD4 conventional and regulatory T cells. Despite limiting cell metabolism, continued Foxo1 activity is associated with increased activation of the kinase Akt and a cell-intrinsic proliferative advantage; however, survival and cell division are decreased in a competitive setting or growth-factor-limiting conditions. Via control of expression of the transcription factor Myc and the IL-2 receptor β-chain, termination of Foxo1 signaling couples the increase in cellular cholesterol to biomass accumulation after activation, thereby facilitating immunological synapse formation and mTORC1 activity. These data reveal that Foxo1 regulates the integration of metabolic and mitogenic signals essential for T cell competitive fitness and the coordination of cell growth with cell division.

Piecemeal necrosis is due to the immunologic synapse formation and internalization of intact TCR-MHC II complexes by CD4 T cells

The nature of the immunologic synapse in autoimmune hepatitis is defined. This process involves the T cell receptor (TCR) which binds to the hepatocyte antigen presenting major histocompatibility complex (MHC) on the plasma membrane. This complex is quickly removed from the liver cell and taken into the T cell cytoplasm to be digested by the lysosome. The liver cell is gradually diminished to the point of its total removal by the lymphocytes binding to it.

Disassembling a cancer puzzle: Cell junctions and plasma membrane as targets for anticancer therapy

Despite an enhanced permeability and retention effect typical of many solid tumors, drug penetration is not always sufficient. Possible strategies for the drug delivery improvement are a modification of the tumor cell-to-cell junctions and usage of cell membrane permeabilization proteins. In this review we discuss epithelial cell junctions as targets for a combined anticancer therapy and propose new possible sources of such agents. We suggest considering viral and bacterial pathogens disrupting epithelial layers as plentiful sources of new therapeutic agents for increasing tumor permeability for other effector agents. We also observe the application of pore forming proteins and peptides of different origin for cytoplasmic delivery of anti-cancer agents and consider the main obstacles of their use in vivo.

Hide or defend, the two strategies of lymphoma immune evasion: potential implications for immunotherapy

Evading immune eradication is a prerequisite for neoplastic progression and one of the hallmarks of cancer. Here, we review the different immune escape strategies of lymphoma and classify them into two main mechanisms. First, lymphoma cells may “hide” to become invisible to the immune system. This can be achieved by losing or downregulating MHC and/or molecules involved in antigen presentation (including antigen processing machinery and adhesion molecules), thereby preventing their recognition by the immune system. Second, lymphoma cells may “defend” themselves to become resistant to immune eradication. This can be achieved in several ways: by becoming resistant to apoptosis, by expressing inhibitory ligands that deactivate immune cells and/or by inducing an immunosuppressive (humoral and cellular) microenvironment. These immune escape mechanisms may have therapeutic implications. Their identification may be used to guide “personalized immunotherapy” for lymphoma.

The immunological synapse as a pharmacological target

The development of T cell mediated immunity relies on the assembly of a highly specialized interface between T cell and antigen presenting cell (APC), known as the immunological synapse (IS). IS assembly is triggered when the T cell receptor (TCR) binds to specific peptide antigen presented in association to the major histocompatibility complex (MHC) by the APC, and is followed by the spatiotemporal dynamic redistribution of TCR, integrins, co-stimulatory receptors and signaling molecules, allowing for the fine-tuning and integration of the signals that lead to T cell activation. The knowledge acquired to date about the mechanisms of IS assembly underscores this structure as a robust pharmacological target. The activity of molecules involved in IS assembly and function can be targeted by specific compounds to modulate the immune response in a number of disorders, including cancers and autoimmune diseases, or in transplanted patients. Here, we will review the state-of-the art of the current therapies which exploit the IS to modulate the immune response.

Ceramide and Exosomes: A Novel Target in Cancer Biology and Therapy

Exosomes are secreted extracellular vesicles (EVs) that carry micro RNAs and other factors to reprogram cancer cells and tissues affected by cancer. Exosomes are exchanged between cancer cells and other tissues, often to prepare a premetastatic niche, escape immune surveillance, or spread multidrug resistance. Only a few studies investigated the function of lipids in exosomes although their lipid composition is different from that of the secreting cells. Ceramide is one of the lipids critical for exosome formation, and it is also enriched in these EVs. New research suggests that lipids in the exosomal membrane may organize and transmit "mobile rafts" that turn exosomes into extracellular signalosomes spreading activation of cell signaling pathways in oncogenesis and metastasis. Ceramide may modulate the function of mobile rafts and their effect on these cell signaling pathways. The critical role of lipids and, in particular, ceramide for formation, secretion, and function of exosomes may lead to a radically new understanding of cancer biology and therapy.

PD-L1 immunostaining scoring for non-small cell lung cancer based on immunosurveillance parameters

Non-Small Cell Lung Cancer (NSCLC) is the leading cause of cancer death globally, and new immunotherapies developed and under development targeting PD-1/PD-L1 checkpoint inhibition require accurate patient selection to assure good clinical outcome. PD-L1 immunohistochemistry is the current biomarker assay used for patient selection, but still imprecise in predicting therapy response. Exploring this issue, we performed computational tissue analysis of PD-L1 immunostaining in procured NSCLC tissues (n = 50) using the Merck KGaA anti-PD-L1 clone MKP1A07310. Staining patterns and PD-L1 cut-off points were interrogated using relevant cancer immune-surveillance biomarkers. Groups with high PD-L1 expression levels (above 25/50% staining cut-off points) were enriched for a biomarker profile in the tumor-nest and microenvironment indicating escape from host-immunity, as represented by increased numbers of cells positive for CD8 and Granzyme B (immune-effectors), FOXP3 (immune-suppressive), and CD68 (P < 0.05). Manual analysis of PD-L1 staining patterns identified tumors with an immune-induced reactive pattern relevant for immunotherapy that would ordinarily be excluded by the arbitrary 25% staining threshold (P < 0.05). Conversely, some cases with completely or predominantly immune-independent constitutive PD-L1 staining patterns that indicate insensitivity to immunotherapy may have been incorrectly selected using this staining cut-off point criterion. Therefore, we propose differentiation of reactive vs constitutive PD-L1 staining patterns to improve the accuracy of this biomarker assay in selecting NSCLC patients for PD-1/PD-L1 immunotherapy.

Compartmentalized Cyclic AMP Production by the Bordetella pertussis and Bacillus anthracis Adenylate Cyclase Toxins Differentially Affects the Immune Synapse in T Lymphocytes

A central feature of the immune synapse (IS) is the tight compartmentalization of membrane receptors and signaling mediators that is functional for its ability to coordinate T cell activation. Second messengers centrally implicated in this process, such as Ca²⁺ and diacyl glycerol, also undergo compartmentalization at the IS. Current evidence suggests a more complex scenario for cyclic AMP (cAMP), which acts both as positive and as negative regulator of T-cell antigen receptor (TCR) signaling and which, as such, must be subjected to a tight spatiotemporal control to allow for signaling at the IS. Here, we have used two bacterial adenylate cyclase toxins that produce cAMP at different subcellular localizations as the result of their distinct routes of cell invasion, namely Bordetella pertussis CyaA and Bacillus anthracis edema toxin (ET), to address the ability of the T cell to confine cAMP to the site of production and to address the impact of compartmentalized cAMP production on IS assembly and function. We show that CyaA, which produces cAMP close to the synaptic membrane, affects IS stability by modulating not only the distribution of LFA-1 and its partners talin and L-plastin, as previously partly reported but also by promoting the sustained synaptic accumulation of the A-kinase adaptor protein ezrin and protein kinase A while suppressing the β-arrestin-mediated recruitment of phosphodiesterase 4B. These effects are dependent on the catalytic activity of the toxin and can be reproduced by treatment with a non-hydrolyzable cAMP analog. Remarkably, none of these effects are elicited by ET, which produces cAMP at a perinuclear localization, despite its ability to suppress TCR signaling and T cell activation through its cAMP-elevating activity. These results show that the IS responds solely to local elevations of cAMP and provide evidence that potent compartmentalization mechanisms are operational in T cells to contain cAMP close to the site of production, even when produced at supraphysiological levels.

Exosomes and Immune Response in Cancer: Friends or Foes?

Exosomes are a type of extracellular vesicle whose study has grown exponentially in recent years. This led to the understanding that these structures, far from being inert waste by-products of cellular functioning, are active players in intercellular communication mechanisms, including in the interactions between cancer cells and the immune system. The deep comprehension of the crosstalk between tumors and the immune systems of their hosts has gained more and more importance, as immunotherapeutic techniques have emerged as viable options for several types of cancer. In this review, we present a comprehensive, updated, and elucidative review of the current knowledge on the functions played by the exosomes in this crosstalk. The roles of these vesicles in tumor antigen presentation, immune activation, and immunosuppression are approached as the relevant interactions between exosomes and the complement system. The last section of this review is reserved for the exploration of the results from the first phase I to II clinical trials of exosomes-based cell-free cancer vaccines.

Integrins in T Cell Physiology

From the thymus to the peripheral lymph nodes, integrin-mediated interactions with neighbor cells and the extracellular matrix tune T cell behavior by organizing cytoskeletal remodeling and modulating receptor signaling. LFA-1 (αLβ2 integrin) and VLA-4 (α4β1 integrin) play a key role throughout the T cell lifecycle from thymocyte differentiation to lymphocyte extravasation and finally play a fundamental role in organizing immune synapse, providing an essential costimulatory signal for the T cell receptor. Apart from tuning T cell signaling, integrins also contribute to homing to specific target organs as exemplified by the importance of α4β7 in maintaining the gut immune system. However, apart from those well-characterized examples, the physiological significance of the other integrin dimers expressed by T cells is far less understood. Thus, integrin-mediated cell-to-cell and cell-to-matrix interactions during the T cell lifespan still represent an open field of research.

All-Round Manipulation of the Actin Cytoskeleton by HIV

While significant progress has been made in terms of human immunodeficiency virus (HIV) therapy, treatment does not represent a cure and remains inaccessible to many people living with HIV. Continued mechanistic research into the viral life cycle and its intersection with many aspects of cellular biology are not only fundamental in the continued fight against HIV, but also provide many key observations of the workings of our immune system. Decades of HIV research have testified to the integral role of the actin cytoskeleton in both establishing and spreading the infection. Here, we review how the virus uses different strategies to manipulate cellular actin networks and increase the efficiency of various stages of its life cycle. While some HIV proteins seem able to bind to actin filaments directly, subversion of the cytoskeleton occurs indirectly by exploiting the power of actin regulatory proteins, which are corrupted at multiple levels. Furthermore, this manipulation is not restricted to a discrete class of proteins, but rather extends throughout all layers of the cytoskeleton. We discuss prominent examples of actin regulators that are exploited, neutralized or hijacked by the virus, and address how their coordinated deregulation can lead to changes in cellular behavior that promote viral spreading.

CD45 in human physiology and clinical medicine

CD45 is an evolutionary highly conserved receptor protein tyrosine phosphatase exclusively expressed on all nucleated cells of the hematopoietic system. It is characterized by the expression of several isoforms, specific to a certain cell type and the developmental or activation status of the cell. CD45 is one of the key players in the initiation of T cell receptor signaling by controlling the activation of the Src family protein-tyrosine kinases Lck and Fyn. CD45 deficiency results in T- and B-lymphocyte dysfunction in the form of severe combined immune deficiency. It also plays a significant role in autoimmune diseases and cancer as well as in infectious diseases including fungal infections. The knowledge collected on CD45 biology is rather vast, but it remains unclear whether all findings in rodent immune cells also apply to human CD45. This review focuses on human CD45 expression and function and provides an overview on its ligands and role in human pathology.

αII-spectrin in T cells is involved in the regulation of cell-cell contact leading to immunological synapse formation?

T-lymphocyte activation after antigen presentation to the T-Cell Receptor (TCR) is a critical step in the development of proper immune responses to infection and inflammation. This dynamic process involves reorganization of the actin cytoskeleton and signaling molecules at the cell membrane, leading to the formation of the Immunological Synapse (IS). The mechanisms regulating the formation of the IS are not completely understood. Nonerythroid spectrin is a membrane skeletal protein involved in the regulation of many cellular processes, including cell adhesion, signaling and actin cytoskeleton remodeling. However, the role of spectrin in IS formation has not been explored. We used molecular, imaging and cellular approaches to show that nonerythroid αII-spectrin redistributes to the IS during T-cell activation. The redistribution of spectrin coincides with the relocation of CD45 and LFA-1, two components essential for IS formation and stability. We assessed the role of spectrin by shRNA-mediated depletion from Jurkat T cells and show that spectrin-depleted cells exhibit decreased adhesion and are defective in forming lamellipodia and filopodia. Importantly, IS formation is impaired in spectrin-depleted cells. Thus, spectrin may be engaged in regulation of distinct events necessary for the establishment and maturity of the IS: besides the involvement of spectrin in the control of CD45 and LFA-1 surface display, spectrin acts in the establishment of cell-cell contact and adhesion processes during the formation of the IS.