Dynamic polarization of the microtubule cytoskeleton during CTL-mediated killing

Principles of organelle positioning in motile and non-motile cells

Cells are equipped with asymmetrically localised and functionally specialised components, including cytoskeletal structures and organelles. Positioning these components to specific intracellular locations in an asymmetric manner is critical for their functionality and affects processes like immune responses, tissue maintenance, muscle functionality, and neurobiology. Here, we provide an overview of strategies to actively move, position, and anchor organelles to specific locations. By conceptualizing the cytoskeletal forces and the organelle-to-cytoskeleton connectivity, we present a framework of active positioning of both membrane-enclosed and membrane-less organelles. Using this framework, we discuss how different principles of force generation and organelle anchorage are utilised by different cells, such as mesenchymal and amoeboid cells, and how the microenvironment influences the plasticity of organelle positioning. Given that motile cells face the challenge of coordinating the positioning of their content with cellular motion, we particularly focus on principles of organelle positioning during migration. In this context, we discuss novel findings on organelle positioning by anchorage-independent mechanisms and their advantages and disadvantages in motile as well as stationary cells.

Factors contributing to the potency of CD8+ T cells

CD8+ cytotoxic T lymphocytes (CTLs) play a crucial role in targeting virus-infected and cancer cells. Although other cytotoxic lymphocytes such as CD4+ T and natural killer (NK) cells, as well as chimeric antigen receptor (CAR)-T cells, can also identify and destroy aberrant cells, they seem to be significantly less potent based on available experimental data. Here, I contemplate the molecular mechanisms controlling the sensitivity and kinetics of granule-mediated CD8+ T cell cytolytic responses. I posit that the clustering of MHC-I molecules and T cell receptors (TCRs) on the cell surface, as well as the contribution of the CD8 co-receptor, are major factors driving exceptionally potent cytolytic responses. I also contend that CD8+ T cells with known specificity and engineered TCR-T cells might be among the most efficient cytolytic effectors for treating patients suffering from viral infections or cancer.

Regulation of CD8 T-cell signaling, metabolism, and cytotoxic activity by extracellular lysophosphatidic acid

Lysophosphatidic acid (LPA) is an endogenous bioactive lipid that is produced extracellularly and signals to cells via cognate LPA receptors, which are G-protein coupled receptors (GPCRs). Mature lymphocytes in mice and humans express three LPA receptors, LPA2 , LPA5, and LPA6 , and work from our group has determined that LPA5 signaling by T lymphocytes inhibits specific antigen-receptor signaling pathways that ultimately impair lymphocyte activation, proliferation, and function. In this review, we discuss previous and ongoing work characterizing the ability of an LPA-LPA5 axis to serve as a peripheral immunological tolerance mechanism that restrains adaptive immunity but is subverted during settings of chronic inflammation. Specifically, LPA-LPA5 signaling is found to regulate effector cytotoxic CD8 T cells by (at least) two mechanisms: (i) regulating the actin-microtubule cytoskeleton in a manner that impairs immunological synapse formation between an effector CD8 T cell and antigen-specific target cell, thus directly impairing cytotoxic activity, and (ii) shifting T-cell metabolism to depend on fatty-acid oxidation for mitochondrial respiration and reducing metabolic efficiency. The in vivo outcome of LPA5 inhibitory activity impairs CD8 T-cell killing and tumor immunity in mouse models providing impetus to consider LPA5 antagonism for the treatment of malignancies and chronic infections.

Recent advances in CD8+ T cell-based immune therapies for HIV cure

Achieving a cure for HIV infection is a global priority. There is substantial evidence supporting a central role for CD8⁺ T cells in the natural control of HIV, suggesting the rationale that these cells may be exploited to achieve remission or cure of this infection. In this work, we review the major challenges for achieving an HIV cure, the models of HIV remission, and the mechanisms of HIV control mediated by CD8⁺ T cells. In addition, we discuss strategies based on this cell population that could be used in the search for an HIV cure. Finally, we analyze the current challenges and perspectives to translate this basic knowledge toward scalable HIV cure strategies.

Study of Effector CD8+ T Cell Interactions with Cortical Neurons in Response to Inflammation in Mouse Brain Slices and Neuronal Cultures

Cytotoxic CD8+ T cells contribute to neuronal damage in inflammatory and degenerative CNS disorders, such as multiple sclerosis (MS). The mechanism of cortical damage associated with CD8+ T cells is not well understood. We developed in vitro cell culture and ex vivo brain slice co-culture models of brain inflammation to study CD8+ T cell-neuron interactions. To induce inflammation, we applied T cell conditioned media, which contains a variety of cytokines, during CD8+ T cell polyclonal activation. Release of IFNγ and TNFα from co-cultures was verified by ELISA, confirming an inflammatory response. We also visualized the physical interactions between CD8+ T cells and cortical neurons using live-cell confocal imaging. The imaging revealed that T cells reduced their migration velocity and changed their migratory patterns under inflammatory conditions. CD8+ T cells increased their dwell time at neuronal soma and dendrites in response to added cytokines. These changes were seen in both the in vitro and ex vivo models. The results confirm that these in vitro and ex vivo models provide promising platforms for the study of the molecular details of neuron-immune cell interactions under inflammatory conditions, which allow high-resolution live microscopy and are readily amenable to experimental manipulation.

Current state of NK cell-mediated immunotherapy in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) has become one of the most common hematological diseases in western countries, with an annual incidence of 42/100,000. Conventional chemotherapy and targeted therapeutic drugs showed limitations in prognosis or in efficiency in high-risk patients. Immunotherapy represented is one of the most effective therapeutic approaches with the potential of better effect and prognosis. Natural killer (NK) cells are good options for immunotherapy as they can effectively mediate anti-tumor activity of immune system by expressing activating and inhibiting receptors and recognizing specific ligands on various tumor cells. NK cells are critical in the immunotherapy of CLL by enhancing self-mediated antibody-dependent cytotoxicity (ADCC), allogeneic NK cell therapy and chimeric antigen receptor-natural killer (CAR-NK) cell therapy. In this article, we reviewed the features, working mechanisms, and receptors of NK cells, and the available evidence of the advantages and disadvantages of NK cell-based immunotherapies, and put forward future study directions in this field.

The T Cell Journey: A Tour de Force

T cells act as the puppeteers in the adaptive immune response, and their dysfunction leads to the initiation and progression of pathological conditions. During their lifetime, T cells experience myriad forces that modulate their effector functions. These forces are imposed by interacting cells, surrounding tissues, and shear forces from fluid movement. In this review, a journey with T cells is made, from their development to their unique characteristics, including the early studies that uncovered their mechanosensitivity. Then the studies pertaining to the responses of T cell activation to changes in antigen-presenting cells' physical properties, to their immediate surrounding extracellular matrix microenvironment, and flow conditions are highlighted. In addition, it is explored how pathological conditions like the tumor microenvironment can hinder T cells and allow cancer cells to escape elimination.

The immune synapses reveal aberrant functions of CD8 T cells during chronic HIV infection

Chronic HIV infection causes persistent low-grade inflammation that induces premature aging of the immune system including senescence of memory and effector CD8 T cells. To uncover the reasons of gradually diminished potency of CD8 T cells from people living with HIV, here we expose the T cells to planar lipid bilayers containing ligands for T-cell receptor and a T-cell integrins and analyze the cellular morphology, dynamics of synaptic interface formation and patterns of the cellular degranulation. We find a large fraction of phenotypically naive T cells from chronically infected people are capable to form mature synapse with focused degranulation, a signature of a differentiated T cells. Further, differentiation of aberrant naive T cells may lead to the development of anomalous effector T cells undermining their capacity to control HIV and other pathogens that could be contained otherwise.

Targeting Microtubules for the Treatment of Heart Disease

Heart disease remains the leading cause of morbidity and mortality worldwide. With the advancement of modern technology, the role(s) of microtubules in the pathogenesis of heart disease has become increasingly apparent, though currently there are limited treatments targeting microtubule-relevant mechanisms. Here, we review the functions of microtubules in the cardiovascular system and their specific adaptive and pathological phenotypes in cardiac disorders. We further explore the use of microtubule-targeting drugs and highlight promising druggable therapeutic targets for the future treatment of heart diseases.

Locked and Loaded: Mechanisms Regulating Natural Killer Cell Lytic Granule Biogenesis and Release

NK cell-mediated cytotoxicity is a critical element of our immune system required for protection from microbial infections and cancer. NK cells bind to and eliminate infected or cancerous cells via direct secretion of cytotoxic molecules toward the bound target cells. In this review, we summarize the current understanding of the molecular regulations of NK cell cytotoxicity, focusing on lytic granule development and degranulation processes. NK cells synthesize apoptosis-inducing proteins and package them into specialized organelles known as lytic granules (LGs). Upon activation of NK cells, LGs converge with the microtubule organizing center through dynein-dependent movement along microtubules, ultimately polarizing to the cytotoxic synapse where they subsequently fuse with the NK plasma membrane. From LGs biogenesis to degranulation, NK cells utilize several strategies to protect themselves from their own cytotoxic molecules. Additionally, molecular pathways that enable NK cells to perform serial killing are beginning to be elucidated. These advances in the understanding of the molecular pathways behind NK cell cytotoxicity will be important to not only improve current NK cell-based anti-cancer therapies but also to support the discovery of additional therapeutic opportunities.

Cytotoxic T Lymphocyte Activation Signals Modulate Cytoskeletal Dynamics and Mechanical Force Generation

Cytotoxic T lymphocytes (CTLs) play an integral role in the adaptive immune response by killing infected cells. Antigen presenting cells (APCs), such as dendritic cells, present pathogenic peptides to the T cell receptor on the CTL surface and co-stimulatory signals required for complete activation. Activated CTLs secrete lytic granules containing enzymes that trigger target cell death at the CTL-target contact, also known as the immune synapse (IS). The actin and microtubule cytoskeletons are instrumental in the killing of CTL targets. Lytic granules are transported along microtubules to the IS, where granule secretion is facilitated by actin depletion and recovery. Furthermore, actomyosin contractility promotes target cell death by mediating mechanical force exertion at the IS. Recent studies have shown that inflammatory cytokines produced by APCs, such as interleukin-12 (IL-12), act as a third signal for CTL activation and enhance CTL proliferation and effector function. However, the biophysical mechanisms mediating such enhanced effector function remain unclear. We hypothesized that the third signal for CTL activation, IL-12, modulates cytoskeletal dynamics and force exertion at the IS, thus potentiating CTL effector function. Here, we used live cell total internal reflection fluorescence (TIRF) microscopy to study actomyosin and microtubule dynamics at the IS of murine primary CTLs activated in the presence of peptide-MHC and co-stimulation alone (two signals), or additionally with IL-12 (three signals). We found that three signal-activated CTLs have altered actin flows, myosin dynamics and microtubule growth rates as compared to two signal-activated CTLs. We further showed that lytic granules in three-signal activated CTLs are less clustered and have lower velocities than in two-signal activated CTLs. Finally, we used traction force microscopy to show that three signal-activated CTLs exert greater traction forces than two signal-activated CTLs. Our results demonstrate that activation of CTLs in the presence of IL-12 leads to differential modulation of the cytoskeleton, thereby augmenting the mechanical response of CTLs to their targets. This indicates a potential physical mechanism via which the third signal can enhance the CTL response.

Sorting Nexin 27 Enables MTOC and Secretory Machinery Translocation to the Immune Synapse

Sorting nexin 27 (SNX27) association to the retromer complex mediates intracellular trafficking of cargoes containing PSD95/Dlg1/ZO-1 (PDZ)-binding C-terminal sequences from endosomes to the cell surface, preventing their lysosomal degradation. Antigen recognition by T lymphocyte leads to the formation of a highly organized structure named the immune synapse (IS), which ensures cell-cell communication and sustained T cell activation. At the neuronal synapse, SNX27 recycles PDZ-binding receptors and its defective expression is associated with synaptic dysfunction and cognitive impairment. In T lymphocytes, SNX27 was found localized at recycling endosomal compartments that polarized to the IS, suggesting a function in polarized traffic to this structure. Proteomic analysis of PDZ-SNX27 interactors during IS formation identify proteins with known functions in cytoskeletal reorganization and lipid regulation, such as diacylglycerol (DAG) kinase (DGK) ζ, as well as components of the retromer and WASH complex. In this study, we investigated the consequences of SNX27 deficiency in cytoskeletal reorganization during IS formation. Our analyses demonstrate that SNX27 controls the polarization towards the cell-cell interface of the PDZ-interacting cargoes DGKζ and the retromer subunit vacuolar protein sorting protein 26, among others. SNX27 silencing abolishes the formation of a DAG gradient at the IS and prevents re-localization of the dynactin complex component dynactin-1/p150^Glued, two events that correlate with impaired microtubule organizing center translocation (MTOC). SNX27 silenced cells show marked alteration in cytoskeleton organization including a failure in the organization of the microtubule network and defects in actin clearance at the IS. Reduced SNX27 expression was also found to hinder the arrangement of signaling microclusters at the IS, as well as the polarization of the secretory machinery towards the antigen presenting cells. Our results broaden the knowledge of SNX27 function in T lymphocytes by showing a function in modulating IS organization through regulated trafficking of cargoes.

Stochastic model of T Cell repolarization during target elimination (II)

Cytotoxic T lymphocytes (T cells) and natural killer cells form a tight contact, the immunological synapse (IS), with target cells, where they release their lytic granules containing perforin/granzyme and cytokine-containing vesicles. During this process the cell repolarizes and moves the microtubule organizing center (MTOC) toward the IS. In the first part of our work we developed a computational model for the molecular-motor-driven motion of the microtubule cytoskeleton during T cell polarization and analyzed the effects of cortical-sliding and capture-shrinkage mechanisms. Here we use this model to analyze the dynamics of the MTOC repositioning in situations in which 1) the IS is in an arbitrary position with respect to the initial position of the MTOC and 2) the T cell has two IS at two arbitrary positions. In the case of one IS, we found that the initial position determines which mechanism is dominant and that the time of repositioning does not rise monotonously with the MTOC-IS distance. In the case of two IS, we observe several scenarios that have also been reported experimentally: the MTOC alternates stochastically (but with a well-defined average transition time) between the two IS; it wiggles in between the two IS without transiting to one of the two; or it is at some point pulled to one of the two IS and stays there. Our model allows one to predict which scenario emerges in dependency of the mechanisms in action and the number of dyneins present. We report that the presence of capture-shrinkage mechanism in at least one IS is necessary to assure the transitions in every cell configuration. Moreover, the frequency of transitions does not decrease with the distance between the two IS and is the highest when both mechanisms are present in both IS.

Multifaceted roles of centrosomes in development, health, and disease

The centrosome is a membrane-less organelle consisting of a pair of barrel-shaped centrioles and pericentriolar material and functions as the major microtubule-organizing center and signaling hub in animal cells. The past decades have witnessed the functional complexity and importance of centrosomes in various cellular processes such as cell shaping, division, and migration. In addition, centrosome abnormalities are linked to a wide range of human diseases and pathological states, such as cancer, reproductive disorder, brain disease, and ciliopathies. Herein, we discuss various functions of centrosomes in development and health, with an emphasis on their roles in germ cells, stem cells, and immune responses. We also discuss how centrosome dysfunctions are involved in diseases. A better understanding of the mechanisms regulating centrosome functions may lead the way to potential therapeutic targeting of this organelle in disease treatment.

Actin Dynamics at the T Cell Synapse as Revealed by Immune-Related Actinopathies

The actin cytoskeleton is composed of dynamic filament networks that build adaptable local architectures to sustain nearly all cellular activities in response to a myriad of stimuli. Although the function of numerous players that tune actin remodeling is known, the coordinated molecular orchestration of the actin cytoskeleton to guide cellular decisions is still ill defined. T lymphocytes provide a prototypical example of how a complex program of actin cytoskeleton remodeling sustains the spatio-temporal control of key cellular activities, namely antigen scanning and sensing, as well as polarized delivery of effector molecules, via the immunological synapse. We here review the unique knowledge on actin dynamics at the T lymphocyte synapse gained through the study of primary immunodeficiences caused by mutations in genes encoding actin regulatory proteins. Beyond the specific roles of individual actin remodelers, we further develop the view that these operate in a coordinated manner and are an integral part of multiple signaling pathways in T lymphocytes.

Microtubule destabilization is a critical checkpoint of chemotaxis and transendothelial migration in melanoma cells but not in T cells

Microtubules (MTs) control cell shape and intracellular cargo transport. The role of MT turnover in the migration of slow-moving cells through endothelial barriers remains unclear. To irreversibly interfere with MT disassembly, we have used the MT-stabilizing agent zampanolide (ZMP) in Β16F10 melanoma as amodel of slow-moving cells. ZMP-treated B16 cells failed to follow chemotactic gradients across rigid confinements and could not generate stable sub-endothelial pseudopodia under endothelial monolayers. In vivo, ZMP-treated Β16 cells failed to extravasate though lung capillaries. In contrast to melanoma cells, the chemotaxis and transendothelial migration of ZMP-treated Tcells were largely conserved. This is afirst demonstration that MT disassembly is akey checkpoint in the directional migration of cancer cells but not of lymphocytes.

NK cells integrate signals over large areas when building immune synapses but require local stimuli for degranulation

Immune synapses are large-scale, transient molecular assemblies that serve as platforms for antigen presentation to B and T cells and for target recognition by cytotoxic T cells and natural killer (NK) cells. The formation of an immune synapse is a tightly regulated, stepwise process in which the cytoskeleton, cell surface receptors, and intracellular signaling proteins rearrange into supramolecular activation clusters (SMACs). We generated artificial immune synapses (AIS) consisting of synthetic and natural ligands for the NK cell-activating receptors LFA-1 and CD16 by microcontact printing the ligands into circular-shaped SMAC structures. Live-cell imaging and analysis of fixed human NK cells in this reductionist system showed that the spatial distribution of activating ligands influenced the formation, stability, and outcome of NK cell synapses. Whereas engagement of LFA-1 alone promoted synapse initiation, combined engagement of LFA-1 and CD16 was required for the formation of mature synapses and degranulation. Organizing LFA-1 and CD16 ligands into donut-shaped AIS resulted in fewer long-lasting, symmetrical synapses compared to dot-shaped AIS. NK cells spreading evenly over either AIS shape exhibited similar arrangements of the lytic machinery. However, degranulation only occurred in regions containing ligands that therefore induced local signaling, suggesting the existence of a late checkpoint for degranulation. Our results demonstrate that the spatial organization of ligands in the synapse can affect its outcome, which could be exploited by target cells as an escape mechanism.

Dynein self-organizes while translocating the centrosome in T-cells

T-cells massively restructure their internal architecture upon reaching an antigen-presenting cell (APC) to form the immunological synapse (IS), a cell-cell interface necessary for efficient elimination of the APC. This reorganization occurs through tight coordination of cytoskeletal processes: actin forms a peripheral ring, and dynein motors translocate the centrosome toward the IS. A recent study proposed that centrosome translocation involves a microtubule (MT) bundle that connects the centrosome perpendicularly to dynein at the synapse center: the "stalk." The synapse center, however, is actin-depleted, while actin was assumed to anchor dynein. We propose that dynein is attached to mobile membrane anchors, and investigate this model with computer simulations. We find that dynein organizes into a cluster in the synapse when translocating the centrosome, aligning MTs into a stalk. By implementing both a MT-capture-shrinkage and a MT-sliding mechanism, we explicitly demonstrate that this organization occurs in both systems. However, results obtained with MT-sliding dynein are more robust and display a stalk morphology consistent with our experimental data obtained with expansion microscopy. Thus, our simulations suggest that actin organization in T-cells during activation defines a specific geometry in which MT-sliding dynein can self-organize into a cluster and cause stalk formation.

Lipid Rafts Interaction of the ARID3A Transcription Factor with EZRIN and G-Actin Regulates B-Cell Receptor Signaling

Several diseases originate via dysregulation of the actin cytoskeleton. The ARID3A/Bright transcription factor has also been implicated in malignancies, primarily those derived from hematopoietic lineages. Previously, we demonstrated that ARID3A shuttles between the nucleus and the plasma membrane, where it localizes within lipid rafts. There it interacts with components of the B-cell receptor (BCR) to reduce its ability to transmit downstream signaling. We demonstrate here that a direct component of ARID3A-regulated BCR signal strength is cortical actin. ARID3A interacts with actin exclusively within lipid rafts via the actin-binding protein EZRIN, which confines unstimulated BCRs within lipid rafts. BCR ligation discharges the ARID3A-EZRIN complex from lipid rafts, allowing the BCR to initiate downstream signaling events. The ARID3A-EZRIN interaction occurs almost exclusively within unpolymerized G-actin, where EZRIN interacts with the multifunctional ARID3A REKLES domain. These observations provide a mechanism by which a transcription factor directly regulates BCR signaling via linkage to the actin cytoskeleton with consequences for B-cell-related neoplasia.

Dynamic Microtubule Arrays in Leukocytes and Their Role in Cell Migration and Immune Synapse Formation

The organization of microtubule arrays in immune cells is critically important for a properly operating immune system. Leukocytes are white blood cells of hematopoietic origin, which exert effector functions of innate and adaptive immune responses. During these processes the microtubule cytoskeleton plays a crucial role for establishing cell polarization and directed migration, targeted secretion of vesicles for T cell activation and cellular cytotoxicity as well as the maintenance of cell integrity. Considering this large spectrum of distinct effector functions, leukocytes require flexible microtubule arrays, which timely and spatially reorganize allowing the cells to accommodate their specific tasks. In contrast to other specialized cell types, which typically nucleate microtubule filaments from non-centrosomal microtubule organizing centers (MTOCs), leukocytes mainly utilize centrosomes for sites of microtubule nucleation. Yet, MTOC localization as well as microtubule organization and dynamics are highly plastic in leukocytes thus allowing the cells to adapt to different environmental constraints. Here we summarize our current knowledge on microtubule organization and dynamics during immune processes and how these microtubule arrays affect immune cell effector functions. We particularly highlight emerging concepts of microtubule involvement during maintenance of cell shape and physical coherence.

Coordinating Cytoskeleton and Molecular Traffic in T Cell Migration, Activation, and Effector Functions

Dynamic localization of receptors and signaling molecules at the plasma membrane and within intracellular vesicular compartments is crucial for T lymphocyte sensing environmental cues, triggering membrane receptors, recruiting signaling molecules, and fine-tuning of intracellular signals. The orchestrated action of actin and microtubule cytoskeleton and intracellular vesicle traffic plays a key role in all these events that together ensure important steps in T cell physiology. These include extravasation and migration through lymphoid and peripheral tissues, T cell interactions with antigen-presenting cells, T cell receptor (TCR) triggering by cognate antigen-major histocompatibility complex (MHC) complexes, immunological synapse formation, cell activation, and effector functions. Cytoskeletal and vesicle traffic dynamics and their interplay are coordinated by a variety of regulatory molecules. Among them, polarity regulators and membrane-cytoskeleton linkers are master controllers of this interplay. Here, we review the various ways the T cell plasma membrane, receptors, and their signaling machinery interplay with the actin and microtubule cytoskeleton and with intracellular vesicular compartments. We highlight the importance of this fine-tuned crosstalk in three key stages of T cell biology involving cell polarization: T cell migration in response to chemokines, immunological synapse formation in response to antigen cues, and effector functions. Finally, we discuss two examples of perturbation of this interplay in pathological settings, such as HIV-1 infection and mutation of the polarity regulator and tumor suppressor adenomatous polyposis coli (Apc) that leads to familial polyposis and colorectal cancer.

The DISC1-Girdin complex - a missing link in signaling to the T cell cytoskeleton

In this study, using Jurkat cells, we show that DISC1 (disrupted in schizophrenia 1) and Girdin (girders of actin filament) are essential for typical actin accumulation at the immunological synapse. Furthermore, DISC1, Girdin and dynein are bound in a complex. Although this complex initially forms as a central patch at the synapse, it relocates to a peripheral ring corresponding to the peripheral supramolecular activation cluster (pSMAC). In the absence of DISC1, the classic actin ring does not form, cell spreading is blocked, and the dynein complex fails to relocate to the pSMAC. A similar effect is seen when Girdin is deleted. When cells are treated with inhibitors of actin polymerization, the dynein-NDE1 complex is lost from the synapse and the microtubule-organizing center fails to translocate, suggesting that actin and dynein might be linked. Upon stimulation of T cell receptors, DISC1 becomes associated with talin, which likely explains why the dynein complex colocalizes with the pSMAC. These results show that the DISC1-Girdin complex regulates actin accumulation, cell spreading and distribution of the dynein complex at the synapse.This article has an associated First Person interview with the first author of the paper.

Stochastic Model of T Cell Repolarization during Target Elimination I

Cytotoxic T lymphocytes (T) and natural killer cells are the main cytotoxic killer cells of the human body to eliminate pathogen-infected or tumorigenic cells (i.e., target cells). Once a natural killer or T cell has identified a target cell, they form a tight contact zone, the immunological synapse (IS). One then observes a repolarization of the cell involving the rotation of the microtubule (MT) cytoskeleton and a movement of the MT organizing center (MTOC) to a position that is just underneath the plasma membrane at the center of the IS. Concomitantly, a massive relocation of organelles attached to MTs is observed, including the Golgi apparatus, lytic granules, and mitochondria. Because the mechanism of this relocation is still elusive, we devise a theoretical model for the molecular-motor-driven motion of the MT cytoskeleton confined between plasma membrane and nucleus during T cell polarization. We analyze different scenarios currently discussed in the literature, the cortical sliding and capture-shrinkage mechanisms, and compare quantitative predictions about the spatiotemporal evolution of MTOC position and MT cytoskeleton morphology with experimental observations. The model predicts the experimentally observed biphasic nature of the repositioning due to an interplay between MT cytoskeleton geometry and motor forces and confirms the dominance of the capture-shrinkage over the cortical sliding mechanism when the MTOC and IS are initially diametrically opposed. We also find that the two mechanisms act synergistically, thereby reducing the resources necessary for repositioning. Moreover, it turns out that the localization of dyneins in the peripheral supramolecular activation cluster facilitates their interaction with the MTs. Our model also opens a way to infer details of the dynein distribution from the experimentally observed features of the MT cytoskeleton dynamics. In a subsequent publication, we will address the issue of general initial configurations and situations in which the T cell established two ISs.

Chitosan Nanoparticles Strengthen Vγ9Vδ2 T-Cell Cytotoxicity Through Upregulation Of Killing Molecules And Cytoskeleton Polarization

Background

During the past few years, immune cell therapy for malignant cancer has benefited a considerable amount of patients worldwide. As one of several promising candidates for immunotherapy, Vγ9Vδ2 γδ T cells have many unique biological advantages, such as non-MHC restriction and have been noted as the earliest source of IFN-γ. However, potentiating anti-tumor functions of γδ T cells has become of particular interest to researchers studying γδ T cell applications.

Purpose

In this study, we proposed a nanotechnology-based methodology for strengthening γδ T cell functions.

Methods

As a type of reliable, biocompatible material, chitosan nanoparticles (CSNPs) were used to enhance anti-tumor immunity of γδ T cells.

Results

First, we found that the size of prepared CSNPs distributed 50 to 100 nm, and that CSNPs had optimal immunocompatibility. Then, we observed that CSNPs could induce α-tubulin cytoskeleton polarization and rearrangement, correlating with a higher killing ability of γδ T cells. Furthermore, we revealed that CSNPs could enhance Vγ9Vδ2 T cell anti-tumor functions by upregulating killing of related receptors, including NKG2D, CD56, FasL, and perforin secretion.

Conclusion

Our work provided evidence of application for CSNPs based bio-carrier in immunotherapy. More importantly, we proposed a new strategy for enhancing γδ T cell anti-tumor activity using nanobiomaterial, which could benefit future clinical applications of γδ T cells.

A numerical mechanical model integrating actin treadmilling and receptor recycling to explain selective disengagement of immune cells

T-killer cells of the immune system eliminate virus-infected cells by releasing toxic granules through a direct cell to cell surface interface (synapse). The release of toxic granules only through the cell surface interface assures the specificity of the immune response. The toxic granule releasing apparatus, however, may not be aligned toward the synapse at the moment of the synapse formation. Therefore, mechanisms for reorienting the killing apparatus inside the T-killer cell to the interface with the target is required. Numerous research works were reported to suggest the mechanisms with direct and indirect evidence, but the most adversary situation, that is when the cell's initial orientation is the complete opposite of the desired direction, either remained answered or brought skepticism toward the suggested mechanisms. To address this issue, a computational mechanical model of T-killer cell synapse formation is constructed to test previously suggested models in a more realistic setting and at the same time to test previously neglected component in the model, namely the actin network formation on the synapse. In this model, by capturing the mechanical interaction between T-killer cell surface receptor dynamics and mechanical properties of synapse formation, it is shown that T-killer cells can selectively engage or disengage from the target cell depending on the killing apparatus alignment with the target. The mechanism works as a safeguard measure ensuring target-cell killing and specificity, so it will be effective when T-killer cells are stranded in situations where the alignment of the killing apparatus is challenging.

Selenium nanoparticles as new strategy to potentiate γδ T cell anti-tumor cytotoxicity through upregulation of tubulin-α acetylation

Immune cell therapy presents a paradigm for the treatment of malignant tumors. Human Vγ9Vδ2 T cells, a subset of peripheral γδ T cells, have been shown to have promising anti-tumor activity. However, new methodology on how to achieve a stronger anti-tumor activity of Vγ9Vδ2 T cells is under continuous investigation. In this work, we used selenium nanoparticles (SeNPs) to strengthen the anti-tumor cytotoxicity of Vγ9Vδ2 T cells. We found SeNPs pretreated γδ T cells had significantly stronger cancer killing and tumor growth inhibition efficacy when compared with γδ T cells alone. Simultaneously, SeNPs pretreatment could significantly upregulate the expression of cytotoxicity related molecules including NKG2D, CD16, and IFN-γ, meanwhile, downregulate PD-1 expression of γδ T cells. Importantly, we observed that SeNPs promoted tubulin acetylation modification in γδ T cells through interaction between microtubule network and lysosomes since the latter is the primary resident station of SeNPs shown by confocal visualization. In conclusion, SeNPs could significantly potentiate anti-tumor cytotoxicity of Vγ9Vδ2 T cells, and both cytotoxicity related molecules and tubulin acetylation were involved in fine-tuning γδ T cell toxicity against cancer cells. Our present work demonstrated a new strategy for further enhancing anti-tumor cytotoxicity of human Vγ9Vδ2 T cells by using SeNPs-based nanotechnology, not gene modification, implicating SeNPs-based nanotechnology had a promising clinical perspective in the γδ T cell immunotherapy for malignant tumors.

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.

Search and Capture Efficiency of Dynamic Microtubules for Centrosome Relocation during IS Formation

Upon contact with antigen-presenting cells, cytotoxic T lymphocytes (T cells) establish a highly organized contact zone denoted as the immunological synapse (IS). The formation of the IS implies relocation of the microtubule organizing center (MTOC) toward the contact zone, which necessitates a proper connection between the MTOC and the IS via dynamic microtubules (MTs). The efficiency of the MTs finding the IS within the relevant timescale is, however, still illusive. We investigate how MTs search the three-dimensional constrained cellular volume for the IS and bind upon encounter to dynein anchored at the IS cortex. The search efficiency is estimated by calculating the time required for the MTs to reach the dynein-enriched region of the IS. In this study, we develop simple mathematical and numerical models incorporating relevant components of a cell and propose an optimal search strategy. Using the mathematical model, we have quantified the average search time for a wide range of model parameters and proposed an optimized set of values leading to the minimal capture time. Our results show that search times are minimal when the IS formed at the nearest or at the farthest sites on the cell surface with respect to the perinuclear MTOC. The search time increases monotonically away from these two specific sites and is maximal at an intermediate position near the equator of the cell. We observed that search time strongly depends on the number of searching MTs and distance of the MTOC from the nuclear surface.

Chemokine-triggered microtubule polymerization promotes neutrophil chemotaxis and invasion but not transendothelial migration

Microtubules (MTs) are critically involved in the transport of material within cells, but their roles in chemotactic leukocyte motility and effector functions are still obscure. Resting neutrophils contain few MTs assembled in an MT organizing center (MTOC) behind their multilobular nuclei. Using a probe of real-time tubulin polymerization, SiR-tubulin, we found that neutrophils elongated their MTs within minutes in response to signals from the two prototypic chemotactic peptides, CXCL1 and fMLP. Taxol, a beta-tubulin binding and MT stabilizing drug, was found to abolish this CXCL1- and fMLP-stimulated MT polymerization. Nevertheless, taxol treatment as well as disruption of existing and de novo generated MTs did not impair neutrophil protrusion and squeezing through IL-1β-stimulated endothelial monolayers mediated by endothelial deposited CXCL1 and neutrophil CXCR2. Notably, CXCL1-dependent neutrophil TEM was not associated with neutrophil MT polymerization. Chemokinetic neutrophil motility on immobilized CXCL1 was also not associated with MT polymerization, and taxol treatment did not interfere with this motility. Nevertheless, and consistent with its ability to suppress MT polymerization induced by soluble CXCL1 and fMLP, taxol treatment inhibited neutrophil chemotaxis toward both chemotactic peptides. Taxol treatment also suppressed CXCL1- and fMLP-triggered elastase-dependent neutrophil invasion through collagen I barriers. Collectively, our results highlight de novo chemoattractant-triggered MT polymerization as key for neutrophil chemotaxis and elastase-dependent invasion but not for chemotactic neutrophil crossing of inflamed endothelial barriers.

Positioning of the Centrosome and Golgi Complex

For over a century, the centrosome has been an organelle more easily tracked than understood, and the study of its peregrinations within the cell remains a chief underpinning of its functional investigation. Increasing attention and new approaches have been brought to bear on mechanisms that control centrosome localization in the context of cleavage plane determination, ciliogenesis, directional migration, and immunological synapse formation, among other cellular and developmental processes. The Golgi complex, often linked with the centrosome, presents a contrasting case of a pleiomorphic organelle for which functional studies advanced somewhat more rapidly than positional tracking. However, Golgi orientation and distribution has emerged as an area of considerable interest with respect to polarized cellular function. This chapter will review our current understanding of the mechanism and significance of the positioning of these organelles.

The MTOC/Golgi Complex at the T-Cell Immunological Synapse

T cells effectively explore the tissue in search for antigens. When activated, they dedicate a big amount of energy and resources to arrange a complex structure called immunological synapse (IS), containing a particular distribution of molecules defined as supramolecular activation clusters (SMACs), and become polarized toward the target cell in a manner that channels the information specifically. This arrangement is symmetrical and requires the polarization of the MTOC and the Golgi to be operational, especially for the proper delivery of lytic granules and the recycling of molecules three dimensionally segregated at the clustered interface. Alternatively, after the productive encounter, T cells need to rearrange again to newly navigate through the tissue, changing back to a motile state called immunological kinapse (IK). In this IK state, the MTOC and the Golgi apparatus are repositioned and recruited at the back of the T cell to facilitate motility, while the established symmetry of the elements of the SMACs is broken and distributed in a different pattern. Both states, IS and IK, are interchangeable and are mainly orchestrated by the MTOC/Golgi complex, being critical for an effective immune response.

CLIP-170 is essential for MTOC repositioning during T cell activation by regulating dynein localisation on the cell surface

The microtubule-organizing centre (MTOC) is repositioned to the centre of the contacted cell surface, the immunological synapse, during T cell activation. However, our understanding of its molecular mechanism remains limited. Here, we found that the microtubule plus-end tracking cytoplasmic linker protein 170 (CLIP-170) plays a novel role in MTOC repositioning using fluorescence imaging. Inhibition of CLIP-170 phosphorylation impaired both MTOC repositioning and interleukin-2 (IL-2) expression. T cell stimulation induced some fraction of dynein to colocalise with CLIP-170 and undergo plus-end tracking. Concurrently, it increased dynein in minus-end-directed movement. It also increased dynein relocation to the centre of the contact surface. Dynein not colocalised with CLIP-170 showed both an immobile state and minus-end-directed movement at a velocity in good agreement with the velocity of MTOC repositioning, which suggests that dynein at the immunological synapse may pull the microtubules and the MTOC. Although CLIP-170 is phosphorylated by AMP-activated protein kinase (AMPK) irrespective of stimulation, phosphorylated CLIP-170 is essential for dynein recruitment to plus-end tracking and for dynein relocation. This indicates that dynein relocation results from coexistence of plus-end- and minus-end-directed translocation. In conclusion, CLIP-170 plays an indispensable role in MTOC repositioning and full activation of T cells by regulating dynein localisation.

LFA-1 in T Cell Migration and Differentiation

Maintenance of homeostatic immune surveillance and development of effective adaptive immune responses require precise regulation of spatial and temporal lymphocyte trafficking throughout the body to ensure pathogen clearance and memory generation. Dysregulation of lymphocyte activation and migration can lead to impaired adaptive immunity, recurrent infections, and an array of autoimmune diseases and chronic inflammation. Central to the recruitment of T cells, integrins are cell surface receptors that regulate adhesion, signal transduction, and migration. With 24 integrin pairs having been discovered to date, integrins are defined not only by the composition of the heterodimeric pair but by cell-type specific expression and their ligands. Furthermore, integrins not only facilitate adhesion but also induce intracellular signaling and have recently been uncovered as mechanosensors providing additional complexity to the signaling pathways. Among several leukocyte-specific integrins, lymphocyte function-associated antigen-1 (LFA-1 or α_Lβ₂; CD11a/CD18) is a key T cell integrin, which plays a major role in regulating T cell activation and migration. Adhesion to LFA-1's ligand, intracellular adhesion receptor 1 (ICAM-1) facilitates firm endothelium adhesion, prolonged contact with antigen-presenting cells, and binding to target cells for killing. While the downstream signaling pathways utilized by LFA-1 are vastly conserved they allow for highly disparate responses. Here, we summarize the roles of LFA-1 and ongoing studies to better understand its functions and regulation.

Visualizing the Actin and Microtubule Cytoskeletons at the B-cell Immune Synapse Using Stimulated Emission Depletion (STED) Microscopy

B cells that bind to membrane-bound antigens (e.g., on the surface of an antigen-presenting cell) form an immune synapse, a specialized cellular structure that optimizes B-cell receptor (BCR) signaling and BCR-mediated antigen acquisition. Both the remodeling of the actin cytoskeleton and the reorientation of the microtubule network towards the antigen contact site are essential for immune synapse formation. Remodeling of the actin cytoskeleton into a dense peripheral ring of F-actin is accompanied by polarization of the microtubule-organizing center towards the immune synapse. Microtubule plus-end binding proteins, as well as cortical plus-end capture proteins mediate physical interactions between the actin and microtubule cytoskeletons, which allow them to be reorganized in a coordinated manner. Elucidating the mechanisms that control this cytoskeletal reorganization, as well as understanding how these cytoskeletal structures shape immune synapse formation and BCR signaling, can provide new insights into B cell activation. This has been aided by the development of super-resolution microscopy approaches that reveal new details of cytoskeletal network organization. We describe here a method for using stimulated emission depletion (STED) microscopy to simultaneously image actin structures, microtubules, and transfected GFP-tagged microtubule plus-end binding proteins in B cells. To model the early events in immune synapse formation, we allow B cells to spread on coverslips coated with anti-immunoglobulin (anti-Ig) antibodies, which initiate BCR signaling and cytoskeleton remodeling. We provide step-by-step protocols for expressing GFP fusion proteins in A20 B-lymphoma cells, for anti-Ig-induced cell spreading, and for subsequent cell fixation, Immunostaining, image acquisition, and image deconvolution steps. The high-resolution images obtained using these procedures allow one to simultaneously visualize actin structures, microtubules, and the microtubule plus-end binding proteins that may link these two cytoskeletal networks.

The Rap2c GTPase facilitates B cell receptor-induced reorientation of the microtubule-organizing center

When B lymphocytes encounter antigen-bearing surfaces, B-cell receptor (BCR) signaling initiates remodeling of the F-actin network and reorientation of the microtubule-organizing center (MTOC) towards the antigen contact site. We have previously shown that the Rap1 GTPase, an evolutionarily conserved regulator of cell polarity, is essential for these processes and that Rap1-regulated actin remodeling is required for MTOC polarization. The role of Rap2 proteins in establishing cell polarity is not well understood. We now show that depleting Rap2c, the only Rap2 isoform expressed in the A20 B-cell line, impairs BCR-induced MTOC reorientation as well as the actin remodeling that supports MTOC polarization. Thus Rap1 and Rap2 proteins may have similar but non-redundant functions in coupling the BCR to MTOC polarization.

Follicular CD8+ T Cells: Origin, Function and Importance during HIV Infection

The lymphoid follicle is critical for the development of humoral immune responses. Cell circulation to this site is highly regulated by the differential expression of chemokine receptors. This feature contributes to the establishment of viral reservoirs in lymphoid follicles and the development of some types of malignancies that are able to evade immune surveillance, especially conventional CD8⁺ T cells. Interestingly, a subtype of CD8⁺ T cells located within the lymphoid follicle (follicular CD8⁺ T cells) was recently described; these cells have been proposed to play an important role in viral and tumor control, as well as to modulate humoral and T follicular helper cell responses. In this review, we summarize the knowledge on this novel CD8⁺ T cell population, its origin, function, and potential role in health and disease, in particular, in the context of the infection by the human immunodeficiency virus.

Smyd1C Mediates CD8 T Cell Death via Regulation of Bcl2-Mediated Restriction of outer Mitochondrial Membrane Integrity

The SET and Mynd domain 1 (Smyd1) locus encodes three tissue-restricted isoforms. Two previously characterized isoforms, Smyd1A and Smyd1B, are heart and skeletal muscle-restricted histone methyl transferases. Here we report that a third, non-catalytic isoform, Smyd1C, is expressed predominantly in activated CD8 T cells. While Smyd1C- deficient CD8 T cells undergo activation-induced apoptosis, neither of two classical mechanisms activation-induced cell death nor activated cell autonomous death are utilized. Instead, Smyd1C accumulates within both mitochondria and the immunological synapse where it associates with Bcl-2, FK506-Binding Protein 8/38 (FKBP38) and Calcineurin. This complex maintains Bcl-2 phosphorylation, enhanced mitochondrial localization, and restricted apoptosis of activated CD8 T cells. We suggest that CD8 T cell death is governed, in part, by Smyd1C regulation of Bcl2-mediated restriction of outer mitochondrial membrane integrity.

The cytotoxic T lymphocyte immune synapse at a glance

The immune synapse provides an important structure for communication with immune cells. Studies on immune synapses formed by cytotoxic T lymphocytes (CTLs) highlight the dynamic changes and specialised mechanisms required to facilitate focal signalling and polarised secretion in immune cells. In this Cell Science at a Glance article and the accompanying poster, we illustrate the different steps that reveal the specialised mechanisms used to focus secretion at the CTL immune synapse and allow CTLs to be such efficient and precise serial killers.

NDR1-Dependent Regulation of Kindlin-3 Controls High-Affinity LFA-1 Binding and Immune Synapse Organization

Antigen-specific adhesion between T cells and antigen-presenting cells (APC) during the formation of the immunological synapse (IS) is mediated by LFA-1 and ICAM-1. Here, LFA-1–ICAM-1 interactions were measured at the single-molecule level on supported lipid bilayers. High-affinity binding was detected at low frequencies in the inner peripheral supramolecular activation cluster (SMAC) zone that contained high levels of activated Rap1 and kindlin-3. Rap1 was essential for T cell attachment, whereas deficiencies of ste20-like kinases, Mst1/Mst2, diminished high-affinity binding and abrogated central SMAC (cSMAC) formation with mislocalized kindlin-3 and vesicle transport regulators involved in T cell receptor recycling/releasing machineries, resulting in impaired T cell-APC interactions. We found that NDR1 kinase, activated by the Rap1 signaling cascade through RAPL and Mst1/Mst2, associated with and recruited kindlin-3 to the IS, which was required for high-affinity LFA-1/ICAM-1 binding and cSMAC formation. Our findings reveal crucial roles for Rap1 signaling via NDR1 for recruitment of kindlin-3 and IS organization.

The Rap1-cofilin-1 pathway coordinates actin reorganization and MTOC polarization at the B cell immune synapse

B cells that bind antigens displayed on antigen-presenting cells (APCs) form an immune synapse, a polarized cellular structure that optimizes the dual functions of the B cell receptor (BCR), signal transduction and antigen internalization. Immune synapse formation involves polarization of the microtubule-organizing center (MTOC) towards the APC. We now show that BCR-induced MTOC polarization requires the Rap1 GTPase (which has two isoforms, Rap1a and Rap1b), an evolutionarily conserved regulator of cell polarity, as well as cofilin-1, an actin-severing protein that is regulated by Rap1. MTOC reorientation towards the antigen contact site correlated strongly with cofilin-1-dependent actin reorganization and cell spreading. We also show that BCR-induced MTOC polarization requires the dynein motor protein as well as IQGAP1, a scaffolding protein that can link the actin and microtubule cytoskeletons. At the periphery of the immune synapse, IQGAP1 associates closely with F-actin structures and with the microtubule plus-end-binding protein CLIP-170 (also known as CLIP1). Moreover, the accumulation of IQGAP1 at the antigen contact site depends on F-actin reorganization that is controlled by Rap1 and cofilin-1. Thus the Rap1-cofilin-1 pathway coordinates actin and microtubule organization at the immune synapse.

Granule-Dependent Natural Killer Cell Cytotoxicity to Fungal Pathogens

Natural killer (NK) cells kill or inhibit the growth of a number of fungi including Cryptococcus, Candida, Aspergillus, Rhizopus, and Paracoccidioides. Although many fungi are not dangerous, invasive fungal pathogens, such as Cryptococcus neoformans, cause life-threatening disease in individuals with impaired cell-mediated immunity. While there are similarities to cell-mediated killing of tumor cells, there are also important differences. Similar to tumor killing, NK cells directly kill fungi in a receptor-mediated and cytotoxic granule-dependent manner. Unlike tumor cell killing where multiple NK cell-activating receptors cooperate and signal events that mediate cytotoxicity, only the NKp30 receptor has been described to mediate signaling events that trigger the NK cell to mobilize its cytolytic payload to the site of interaction with C. neoformans and Candida albicans, subsequently leading to granule exocytosis and fungal killing. More recently, the NKp46 receptor was reported to bind Candida glabrata adhesins Epa1, 6, and 7 and directly mediate fungal clearance. A number of unanswered questions remain. For example, is only one NK cell-activating receptor sufficient for signaling leading to fungal killing? Are the signaling pathways activated by fungi similar to those activated by tumor cells during NK cell killing? How do the cytolytic granules traffic to the site of interaction with fungi, and how does this process compare with tumor killing? Recent insights into receptor use, intracellular signaling and cytolytic granule trafficking during NK cell-mediated fungal killing will be compared to tumor killing, and the implications for therapeutic approaches will be discussed.

Antigen Export Reduces Antigen Presentation and Limits T Cell Control of M. tuberculosis

Persistence of Mycobacterium tuberculosis results from bacterial strategies that manipulate host adaptive immune responses. Infected dendritic cells (DCs) transport M. tuberculosis to local lymph nodes but activate CD4 T cells poorly, suggesting bacterial manipulation of antigen presentation. However, M. tuberculosis antigens are also exported from infected DCs and taken up and presented by uninfected DCs, possibly overcoming this blockade of antigen presentation by infected cells. Here we show that the first stage of this antigen transfer, antigen export, benefits M. tuberculosis by diverting bacterial proteins from the antigen presentation pathway. Kinesin-2 is required for antigen export and depletion of this microtubule-based motor increases activation of antigen-specific CD4 T cells by infected cells and improves control of intracellular infection. Thus, although antigen transfer enables presentation by bystander cells, it does not compensate for reduced antigen presentation by infected cells and represents a bacterial strategy for CD4 T cell evasion.

Dynein Separately Partners with NDE1 and Dynactin To Orchestrate T Cell Focused Secretion

Helper and cytotoxic T cells accomplish focused secretion through the movement of vesicles toward the microtubule organizing center (MTOC) and translocation of the MTOC to the target contact site. In this study, using Jurkat cells and OT-I TCR transgenic primary murine CTLs, we show that the dynein-binding proteins nuclear distribution E homolog 1 (NDE1) and dynactin (as represented by p150(Glued)) form mutually exclusive complexes with dynein, exhibit nonoverlapping distributions in target-stimulated cells, and mediate different transport events. When Jurkat cells expressing a dominant negative form of NDE1 (NDE1-enhanced GFP fusion) were activated by Staphylococcus enterotoxin E-coated Raji cells, NDE1 and dynein failed to accumulate at the immunological synapse (IS) and MTOC translocation was inhibited. Knockdown of NDE1 in Jurkat cells or primary mouse CTLs also inhibited MTOC translocation and CTL-mediated killing. In contrast to NDE1, knockdown of p150(Glued), which depleted the alternative dynein/dynactin complex, resulted in impaired accumulation of CTLA4 and granzyme B-containing intracellular vesicles at the IS, whereas MTOC translocation was not affected. Depletion of p150(Glued) in CTLs also inhibited CTL-mediated lysis. We conclude that the NDE1/Lissencephaly 1 and dynactin complexes separately mediate two key components of T cell-focused secretion, namely translocation of the MTOC and lytic granules to the IS, respectively.

LAG3 and PD1 co-inhibitory molecules collaborate to limit CD8+ T cell signaling and dampen antitumor immunity in a murine ovarian cancer model

The immune co-inhibitory receptors lymphocyte activation gene-3 (LAG3) and programmed cell death 1 (PD1) synergistically contribute to autoimmunity and tumor evasion. Here we demonstrate how they collaborate and interact to regulate T cell function. We first show that LAG3 and PD1 are co-expressed on both OVA-specific and non-specific T cells infiltrating murine ovarian tumors. Dual antibody blockade or genetic knockout of LAG3 and PD1 significantly enhanced T effector function and delayed tumor growth. LAG3 and PD1 co-localized in activated CD8⁺ T cells in vitro at the trans-Golgi vesicles, early/recycling endosomal compartments, lysosomes, and microtubule organizing center. Importantly, LAG3 and PD1 cluster with pLck at the immunological synapse. Reciprocal immunoprecipitation of T cell extracts revealed physical interaction between LAG3 and PD1. Mutational analyses indicate that the cytoplasmic domain of LAG3 is not absolutely required for its association with PD1, while the ITIM and ITSM of PD1 are necessary for its association with LAG3. Finally, LAG3 protein also associates with the Src-homology-2 domain-containing phosphatases (SHP1/2) which are known to be recruited by PD1 during T cell signaling. Our data indicate that the association of LAG3 with PD1 contributes to their rapid trafficking to the immunological synapse, leading to a synergistic inhibitory effect on T cell signaling.

Signaling and Polarized Communication Across the T Cell Immunological Synapse

T cells express a somatically recombined antigen receptor (αβTCR) that is calibrated during development to respond to changes in peptides displayed by major histocompatibility complex proteins (pMHC) on the surface of antigen-presenting cells (APC). A key characteristic of pMHC for adaptive immunity is the ability to sample internal states of cells and tissues to sensitively detect changes associated with infection, cell derangement, or tissue injury. Physical T cell-APC contact sets up an axis for polarization of TCR, adhesion molecules, kinases, cytoskeletal elements, and organelles inherent in this mode of juxtacrine signaling. The discovery of further lateral organization of the TCR and adhesion molecules into radially symmetric compartments, the immunological synapse, revealed an intersecting plane of symmetry and potential for regulated symmetry breaking to control duration of T cell-APC interactions. In addition to organizing signaling machinery, the immunological synapse directs the polarized transport and secretion of cytokines and cytolytic agents across the synaptic cleft and is a site for the generation and exocytic release of bioactive microvesicles that can functionally affect recipient APC and other cells in the environment. This machinery is coopted by retroviruses, and human immune deficiency virus-1 may even use antigen-specific synapses for infection of healthy T cells. Here, we discuss recent advances in the molecular and cell biological mechanisms of immunological synapse assembly and signaling and its role in intercellular communication across the synaptic cleft.