CD28 and CD3 have complementary roles in T-cell traction forces

Mechanical regulation of lymphocyte activation and function

Mechanosensing, or how cells sense and respond to the physical environment, is crucial for many aspects of biological function, ranging from cell movement during development to cancer metastasis, the immune response and gene expression driving cell fate determination. Relevant physical stimuli include the stiffness of the extracellular matrix, contractile forces, shear flows in blood vessels, complex topography of the cellular microenvironment and membrane protein mobility. Although mechanosensing has been more widely studied in non-immune cells, it has become increasingly clear that physical cues profoundly affect the signaling function of cells of the immune system. In this Review, we summarize recent studies on mechanical regulation of immune cells, specifically lymphocytes, and explore how the force-generating cytoskeletal machinery might mediate mechanosensing. We discuss general principles governing mechanical regulation of lymphocyte function, spanning from the molecular scale of receptor activation to cellular responses to mechanical stimuli.

Molecular Force Sensors for Biological Application

The mechanical forces exerted by cells on their surrounding microenvironment are known as cellular traction forces. These forces play crucial roles in various biological processes, such as tissue development, wound healing and cell functions. However, it is hard for traditional techniques to measure cellular traction forces accurately because their magnitude (from pN to nN) and the length scales over which they occur (from nm to μm) are extremely small. In order to fully understand mechanotransduction, highly sensitive tools for measuring cellular forces are needed. Current powerful techniques for measuring traction forces include traction force microscopy (TFM) and fluorescent molecular force sensors (FMFS). In this review, we elucidate the force imaging principles of TFM and FMFS. Then we highlight the application of FMFS in a variety of biological processes and offer our perspectives and insights into the potential applications of FMFS.

Preliminary study of the homeostatic regulation of osseointegration by nanotube topology

The ideal implant surface plays a substantial role in maintaining bone homeostasis by simultaneously promoting osteoblast differentiation and limiting overactive osteoclast activity to a certain extent, which leads to satisfactory dynamic osseointegration. However, the rational search for implant materials with an ideal surface structure is challenging and a hot research topic in the field of tissue engineering. In this study, we constructed titanium dioxide titanium nanotubes (TNTs) by anodic oxidation and found that this structure significantly promoted osteoblast differentiation and inhibited osteoclast formation and function while simultaneously inhibiting the total protein levels of proline-rich tyrosine kinase 2 (PYK2) and focal adhesion kinase (FAK). Knockdown of the PYK2 gene by siRNA significantly suppressed the number and osteoclastic differentiation activity of mouse bone marrow mononuclear cells (BMMs), while overexpression of PYK2 inhibited osteogenesis and increased osteoclastic activity. Surprisingly, we found for the first time that neither knockdown nor overexpression of the FAK gene alone caused changes in osteogenesis or osteoclastic function. More importantly, compared with deletion or overexpression of PYK2/FAK alone, coexpression or cosilencing of the two kinases accelerated the effects of TNTs on osteoclastic and osteogenic differentiation on the surface of cells. Furthermore, in vivo experiments revealed a significant increase in positiveexpression-PYK2 cells on the surface of TNTs, but no significant change in positiveexpression -FAK cells was observed. In summary, PYK2 is a key effector molecule by which osteoblasts sense nanotopological mechanical signals and maintain bone homeostasis around implants. These results provide a referable molecular mechanism for the future development and design of homeostasis-based regulatory implant biomaterials.

Antigen density and applied force control enrichment of nanobody-expressing yeast cells in microfluidics

In vitro display technologies such as yeast display have been instrumental in developing the selection of new antibodies, antibody fragments or nanobodies that bind to a specific target, with affinity towards the target being the main factor that influences selection outcome. However, the roles of mechanical forces are being increasingly recognized as a crucial factor in the regulation and activation of effector cell function. It would thus be of interest to isolate binders behaving optimally under the influence of mechanical forces. We developed a microfluidic assay allowing the selection of yeast displaying nanobodies through antigen-specific immobilization on a surface under controlled hydrodynamic flow. This approach enabled enrichment of model yeast mixtures using tunable antigen density and applied force. This new force-based selection method opens the possibility of selecting binders by relying on both their affinity and force resistance, with implications for the design of more efficient immunotherapeutics.

Mechanical control of antigen detection and discrimination by T and B cell receptors

The adaptive immune response is orchestrated by just two cell types, T cells and B cells. Both cells possess the remarkable ability to recognize virtually any antigen through their respective antigen receptors-the T cell receptor (TCR) and B cell receptor (BCR). Despite extensive investigations into the biochemical signaling events triggered by antigen recognition in these cells, our ability to predict or control the outcome of T and B cell activation remains elusive. This challenge is compounded by the sensitivity of T and B cells to the biophysical properties of antigens and the cells presenting them-a phenomenon we are just beginning to understand. Recent insights underscore the central role of mechanical forces in this process, governing the conformation, signaling activity, and spatial organization of TCRs and BCRs within the cell membrane, ultimately eliciting distinct cellular responses. Traditionally, T cells and B cells have been studied independently, with researchers working in parallel to decipher the mechanisms of activation. While these investigations have unveiled many overlaps in how these cell types sense and respond to antigens, notable differences exist. To fully grasp their biology and harness it for therapeutic purposes, these distinctions must be considered. This review compares and contrasts the TCR and BCR, placing emphasis on the role of mechanical force in regulating the activity of both receptors to shape cellular and humoral adaptive immune responses.

Role of immunotherapies and stem cell therapy in the management of liver cancer: A comprehensive review

Liver cancer (LC) is the sixth most common disease and the third most common cause of cancer-related mortality. The WHO predicts that more than 1 million deaths will occur from LC by 2030. Hepatocellular carcinoma (HCC) is a common form of primary LC. Today, the management of LC involves multiple disciplines, and multimodal therapy is typically selected on an individual basis, considering the intricate interactions between the patient's overall health, the stage of the tumor, and the degree of underlying liver disease. Currently, the treatment of cancers, including LC, has undergone a paradigm shift in the last ten years because of immuno-oncology. To treat HCC, immune therapy approaches have been developed to enhance or cause the body's natural immune response to specifically target tumor cells. In this context, immune checkpoint pathway inhibitors, engineered cytokines, adoptive cell therapy, immune cells modified with chimeric antigen receptors, and therapeutic cancer vaccines have advanced to clinical trials and offered new hope to cancer patients. The outcomes of these treatments are encouraging. Additionally, treatment using stem cells is a new approach for restoring deteriorated tissues because of their strong differentiation potential and capacity to release cytokines that encourage cell division and the formation of blood vessels. Although there is no proof that stem cell therapy works for many types of cancer, preclinical research on stem cells has shown promise in treating HCC. This review provides a recent update regarding the impact of immunotherapy and stem cells in HCC and promising outcomes.

Enhancing antitumor response by efficiently generating large-scale TCR-T cells targeting a single epitope across multiple cancer antigens

The need to contrive interventions to curb the rise in cancer incidence and mortality is critical for improving patients' prognoses. Adoptive cell therapy is challenged with quality large-scale production, heightening its production cost. Several cancer types have been associated with the expression of highly-immunogenic CTAG1 and CTAG2 antigens, which share common epitopes. Targeting two antigens on the same cancer could improve the antitumor response of TCR-T cells. In this study, we exploited an efficient way to generate large-fold quality TCR-T cells and also demonstrated that the common epitopes of CTAG1 and CTAG2 antigens provide an avenue for improved cancer-killing via dual-antigen-epitope targeting. Our study revealed that xeno/sera-free medium could expand TCR-T cells to over 500-fold, posing as a better replacement for FBS-supplemented media. Human AB serum was also shown to be a good alternative in the absence of xeno/sera-free media. Furthermore, TCR-T cells stimulated with beads-coated T-activator showed a better effector function than soluble T-activator stimulated TCR-T cells. Additionally, TCR-T cells that target multiple antigens in the same cancer yield better anticancer activity than those targeting a single antigen. This showed that targeting multiple antigens with a common epitope may enhance the antitumor response efficacy of T cell therapies.

A Novel Approach for Colloidal Lithography: From Dry Particle Assembly to High-Throughput Nanofabrication

We introduce a novel approach for colloidal lithography based on the dry particle assembly into a dense monolayer on an elastomer, followed by mechanical transfer to a substrate of any material and curvature. This method can be implemented either manually or automatically and it produces large area patterns with the quality obtained by the state-of-the-art colloidal lithography at a very high throughput. We first demonstrated the fabrication of nanopatterns with a periodicity ranging between 200 nm and 2 μm. We then demonstrated two nanotechnological applications of this approach. The first one is antireflective structures, fabricated on silicon and sapphire, with different geometries including arrays of bumps and holes and adjusted for different spectral ranges. The second one is smart 3D nanostructures for mechanostimulation of T cells that are used for their effective proliferation, with potential application in cancer immunotherapy. This new approach unleashes the potential of bottom-up nanofabrication and paves the way for nanoscale devices and systems in numerous applications.

Evidence and therapeutic implications of biomechanically regulated immunosurveillance in cancer and other diseases

Disease progression is usually accompanied by changes in the biochemical composition of cells and tissues and their biophysical properties. For instance, hallmarks of cancer include the stiffening of tissues caused by extracellular matrix remodelling and the softening of individual cancer cells. In this context, accumulating evidence has shown that immune cells sense and respond to mechanical signals from the environment. However, the mechanisms regulating these mechanical aspects of immune surveillance remain partially understood. The growing appreciation for the 'mechano-immunology' field has urged researchers to investigate how immune cells sense and respond to mechanical cues in various disease settings, paving the way for the development of novel engineering strategies that aim at mechanically modulating and potentiating immune cells for enhanced immunotherapies. Recent pioneer developments in this direction have laid the foundations for leveraging 'mechanical immunoengineering' strategies to treat various diseases. This Review first outlines the mechanical changes occurring during pathological progression in several diseases, including cancer, fibrosis and infection. We next highlight the mechanosensitive nature of immune cells and how mechanical forces govern the immune responses in different diseases. Finally, we discuss how targeting the biomechanical features of the disease milieu and immune cells is a promising strategy for manipulating therapeutic outcomes.

Morphodynamics of T-lymphocytes: Scanning to spreading

Binding of the T cell receptor complex to its ligand, the subsequent molecular rearrangement, and the concomitant cell-scale shape changes represent the very first steps of adaptive immune recognition. The first minutes of the interaction of T cells and antigen presenting cells have been extensively scrutinized; yet, gaps remain in our understanding of how the biophysical properties of the environment may impact the sequence of events. In particular, many pioneering experiments were done on immobilized ligands and gave major insights into the process of T cell activation, whereas later experiments have indicated that ligand mobility was of paramount importance, especially to enable the formation of T cell receptor clusters. Systematic experiments to compare and reconcile the two schools are still lacking. Furthermore, recent investigations using compliant substrates have elucidated other intriguing aspects of T cell mechanics. Here we review experiments on interaction of T cells with planar artificial antigen presenting cells to explore the impact of mechanics on adhesion and actin morphodynamics during the spreading process. We enumerate a sequence tracing first contact to final spread state that is consistent with current understanding. Finally, we interpret the presented experimental results in light of a mechanical model that captures all the different morphodynamic states.

Dynamics of Whole Transcriptome Analysis (WTA) and Surface markers expression (AbSeq) in Immune Cells of COVID-19 Patients and Recovered captured through Single Cell Genomics

Introduction

Single-cell multi-omics studies, such as multidimensional transcriptomics (whole transcriptomic analysis, WTA), and surface marker analysis (antibody sequencing, AbSeq), have turned out to be valuable techniques that offer inaccessible possibilities for single-cell profiling of mRNA, lncRNA, and proteins.

Methods

We used this technique to understand the dynamics of mRNA and protein-level differences in healthy, COVID-19-infected and recovered individuals using peripheral blood mononuclear cells (PBMCs). Our results demonstrate that compared to mRNA expression, protein abundance is a better indicator of the disease state.

Results

We demonstrate that compared to mRNA expression, protein abundance is a better indicator of the disease state. We observed high levels of cell identity and regulatory markers, CD3E, CD4, CD8A, CD5, CD7, GITR, and KLRB1 in healthy individuals, whereas markers related to cell activation, CD38, CD28, CD69, CD62L, CD14, and CD16 elevated in the SARS-CoV-2 infected patients at both WTA and AbSeq levels. Curiously, in recovered individuals, there was a high expression of cytokine and chemokine receptors (CCR5, CCR7, CCR4, CXCR3, and PTGRD2). We also observed variations in the expression of markers within cell populations under different states.

Discussion

Furthermore, our study emphasizes the significance of employing an oligo-based method (AbSeq) that can help in diagnosis, prognosis, and protection from disease/s by identifying cell surface markers that are unique to different cell types or states. It also allows simultaneous study of a vast array of markers, surpassing the constraints of techniques like FACS to query the vast repertoire of proteins.

High-resolution assessment of multidimensional cellular mechanics using label-free refractive-index traction force microscopy

A critical requirement for studying cell mechanics is three-dimensional assessment of cellular shapes and forces with high spatiotemporal resolution. Traction force microscopy with fluorescence imaging enables the measurement of cellular forces, but it is limited by photobleaching and a slow acquisition speed. Here, we present refractive-index traction force microscopy (RI-TFM), which simultaneously quantifies the volumetric morphology and traction force of cells using a high-speed illumination scheme with 0.5-Hz temporal resolution. Without labelling, our method enables quantitative analyses of dry-mass distributions and shear (in-plane) and normal (out-of-plane) tractions of single cells on the extracellular matrix. When combined with a constrained total variation-based deconvolution algorithm, it provides 0.55-Pa shear and 1.59-Pa normal traction sensitivity for a 1-kPa hydrogel substrate. We demonstrate its utility by assessing the effects of compromised intracellular stress and capturing the rapid dynamics of cellular junction formation in the spatiotemporal changes in non-planar traction components.

Preclinical Evaluation of Novel Folate Receptor 1-Directed CAR T Cells for Ovarian Cancer

Treatment options for ovarian cancer patients are limited, and a high unmet clinical need remains for targeted and long-lasting, efficient drugs. Genetically modified T cells expressing chimeric antigen receptors (CAR), are promising new drugs that can be directed towards a defined target and have shown efficient, as well as persisting, anti-tumor responses in many patients. We sought to develop novel CAR T cells targeting ovarian cancer and to assess these candidates preclinically. First, we identified potential CAR targets on ovarian cancer samples. We confirmed high and consistent expressions of the tumor-associated antigen FOLR1 on primary ovarian cancer samples. Subsequently, we designed a series of CAR T cell candidates against the identified target and demonstrated their functionality against ovarian cancer cell lines in vitro and in an in vivo xenograft model. Finally, we performed additional in vitro assays recapitulating immune suppressive mechanisms present in solid tumors and developed a process for the automated manufacturing of our CAR T cell candidate. These findings demonstrate the feasibility of anti-FOLR1 CAR T cells for ovarian cancer and potentially other FOLR1-expressing tumors.

Exploring immunoregulatory properties of a phenolic-enriched maple syrup extract through integrated proteomics and in vitro assays

Our laboratory has established a comprehensive program to investigate the phytochemical composition and nutritional/medicinal properties of phenolic-enriched maple syrup extract (MSX). Previous studies support MSX's therapeutic potential in diverse disease models, primarily through its anti-inflammatory effects. We recently demonstrated MSX's ability to regulate inflammatory signaling pathways and modulate inflammatory markers and proteins in a lipopolysaccharide (LPS)-induced peritonitis mouse model. However, MSX's immunoregulatory properties remain unknown. Herein, we investigated MSX's immunoregulatory properties for the first time using an integrated approach, combining data-dependent acquisition (DDA) and data-independent acquisition (DIA) strategies in a proteomic analysis of spleen tissue collected from the aforementioned peritonitis mouse model. Additionally, we conducted immune cell activation assays using macrophages and T lymphocytes. The DIA analysis unveiled a distinctive expression pattern involving three proteins-Krt83, Thoc2, and Vps16-which were present in both the control and MSX-treated groups but absent in the LPS-induced model group. Furthermore, proteins Ppih and Dpp9 exhibited significant reductions in the MSX-treated group. Ingenuity pathway analysis indicated that MSX may modulate several critical signaling pathways, exerting a suppressive effect on immune responses in various cell types involved in both innate and adaptive immunity. Our in vitro cell assays supported findings from the proteomics, revealing that MSX significantly reduced the levels of interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α) in LPS-stimulated human macrophage cells, as well as the levels of IL-2 in anti-CD3/anti-CD28-induced Jurkat T cells. Taken together, our investigations provide evidence that MSX exerts immune regulatory effects that impact both innate and adaptive immunity, which adds to the data supporting MSX's development as a functional food.

Measurement of Forces Acting on Single T-Cell Receptors

Molecular forces are increasingly recognized as an important parameter to understand cellular signaling processes. In the recent years, evidence accumulated that also T-cells exert tensile forces via their T-cell receptor during the antigen recognition process. To measure such intercellular pulling forces, one can make use of the elastic properties of spider silk peptides, which act similar to Hookean springs: increased strain corresponds to increased stress applied to the peptide. Combined with Förster resonance energy transfer (FRET) to read out the strain, such peptides represent powerful and versatile nanoscopic force sensing tools. In this paper, we provide a detailed protocol how to synthesize a molecular force sensor for application in T-cell antigen recognition and hands-on guidelines on experiments and analysis of obtained single molecule FRET data.

PRKAG2.2 is essential for FoxA1+ regulatory T cell differentiation and metabolic rewiring distinct from FoxP3+ regulatory T cells

Forkhead box A1 (FoxA1)+ regulatory T cells (Tregs) exhibit distinct characteristics from FoxP3+ Tregs while equally effective in exerting anti-inflammatory properties. The role of FoxP3+ Tregs in vivo has been challenged, motivating a better understanding of other Tregs in modulating hyperactive immune responses. FoxA1+ Tregs are generated on activation of the transcription factor FoxA1 by interferon-β (IFNβ), an anti-inflammatory cytokine. T cell activation, expansion, and function hinge on metabolic adaptability. We demonstrated that IFNβ promotes a metabolic rearrangement of FoxA1+ Tregs by enhancing oxidative phosphorylation and mitochondria clearance by mitophagy. In response to IFNβ, FoxA1 induces a specific transcription variant of adenosine 5'-monophosphate-activated protein kinase (AMPK) γ2 subunit, PRKAG2.2. This leads to the activation of AMPK signaling, thereby enhancing mitochondrial respiration and mitophagy by ULK1-BNIP3. This IFNβ-FoxA1-PRKAG2.2-BNIP3 axis is pivotal for their suppressive function. The involvement of PRKAG2.2 in FoxA1+ Treg, not FoxP3+ Treg differentiation, underscores the metabolic differences between Treg populations and suggests potential therapeutic targets for autoimmune diseases.

T Cell Antigen Recognition and Discrimination by Electrochemiluminescence Imaging

Adoptive T lymphocyte (T cell) transfer and tumour-specific peptide vaccines are innovative cancer therapies. An accurate assessment of the specific reactivity of T cell receptors (TCRs) to tumour antigens is required because of the high heterogeneity of tumour cells and the immunosuppressive tumour microenvironment. In this study, we report a label-free electrochemiluminescence (ECL) imaging approach for recognising and discriminating between TCRs and tumour-specific antigens by imaging the immune synapses of T cells. Various T cell stimuli, including agonistic antibodies, auxiliary molecules, and tumour-specific antigens, were modified on the electrode's surface to allow for their interaction with T cells bearing different TCRs. The formation of immune synapses activated by specific stimuli produced a negative (shadow) ECL image, from which T cell antigen recognition and discrimination were evaluated by analysing the spreading area and the recognition intensity of T cells. This approach provides an easy way to assess TCR-antigen specificity and screen both of them for immunotherapies.

Actin cytoskeleton remodeling at the cancer cell side of the immunological synapse: good, bad, or both?

Cytotoxic lymphocytes (CLs), specifically cytotoxic T lymphocytes and natural killer cells, are indispensable guardians of the immune system and orchestrate the recognition and elimination of cancer cells. Upon encountering a cancer cell, CLs establish a specialized cellular junction, known as the immunological synapse that stands as a pivotal determinant for effective cell killing. Extensive research has focused on the presynaptic side of the immunological synapse and elucidated the multiple functions of the CL actin cytoskeleton in synapse formation, organization, regulatory signaling, and lytic activity. In contrast, the postsynaptic (cancer cell) counterpart has remained relatively unexplored. Nevertheless, both indirect and direct evidence has begun to illuminate the significant and profound consequences of cytoskeletal changes within cancer cells on the outcome of the lytic immunological synapse. Here, we explore the understudied role of the cancer cell actin cytoskeleton in modulating the immune response within the immunological synapse. We shed light on the intricate interplay between actin dynamics and the evasion mechanisms employed by cancer cells, thus providing potential routes for future research and envisioning therapeutic interventions targeting the postsynaptic side of the immunological synapse in the realm of cancer immunotherapy. This review article highlights the importance of actin dynamics within the immunological synapse between cytotoxic lymphocytes and cancer cells focusing on the less-explored postsynaptic side of the synapse. It presents emerging evidence that actin dynamics in cancer cells can critically influence the outcome of cytotoxic lymphocyte interactions with cancer cells.

WASP facilitates tumor mechanosensitivity in T lymphocytes

Cytotoxic T lymphocytes (CTLs) carry out immunosurveillance by scanning target cells of diverse physical properties for the presence of antigens. While the recognition of cognate antigen by the T cell receptor is the primary signal for CTL activation, it has become increasingly clear that the mechanical stiffness of target cells plays an important role in antigen-triggered T cell responses. However, the molecular machinery within CTLs that transduces the mechanical information of tumor cells remains unclear. We find that CTL's mechanosensitive ability requires the activity of the actin-organizing protein Wiskott-Aldrich Syndrome Protein (WASP). WASP activation is modulated by the mechanical properties of antigen-presenting contexts across a wide range of target cell stiffnesses and activated WASP then mediates mechanosensitive activation of early TCR signaling markers in the CTL. Our results provide a molecular link between antigen mechanosensing and CTL immune response and suggest that CTL-intrinsic cytoskeletal organizing principles enable the processing of mechanical information from diverse target cells.

Probing mechanical interaction of immune receptors and cytoskeleton by membrane nanotube extraction

The role of force application in immune cell recognition is now well established, the force being transmitted between the actin cytoskeleton to the anchoring ligands through receptors such as integrins. In this chain, the mechanics of the cytoskeleton to receptor link, though clearly crucial, remains poorly understood. To probe this link, we combine mechanical extraction of membrane tubes from T cells using optical tweezers, and fitting of the resulting force curves with a viscoelastic model taking into account the cell and relevant molecules. We solicit this link using four different antibodies against various membrane bound receptors: antiCD3 to target the T Cell Receptor (TCR) complex, antiCD45 for the long sugar CD45, and two clones of antiCD11 targeting open or closed conformation of LFA1 integrins. Upon disruption of the cytoskeleton, the stiffness of the link changes for two of the receptors, exposing the existence of a receptor to cytoskeleton link-namely TCR-complex and open LFA1, and does not change for the other two where a weaker link was expected. Our integrated approach allows us to probe, for the first time, the mechanics of the intracellular receptor-cytoskeleton link in immune cells.

DNA Origami Tension Sensors (DOTS) to study T cell receptor mechanics at membrane junctions

The T cell receptor (TCR) is thought to be a mechanosensor, meaning that it transmits mechanical force to its antigen and leverages the force to amplify the specificity and magnitude of TCR signaling. The past decade has witnessed the development of molecular probes which have revealed many aspects of receptor mechanotransduction. However, most force probes are immobilized on hard substrates, thus failing to reveal mechanics in the physiological context of cell membranes. In this report, we developed DNA origami tension sensors (DOTS) which bear force sensors on a DNA origami breadboard and allow mapping of TCR mechanotransduction at dynamic intermembrane junctions. We demonstrate that TCR-antigen bonds experience 5-10 pN forces, and the mechanical events are dependent on cell state, antigen mobility, antigen potency, antigen height and F-actin activity. We tethered DOTS onto a microparticle to mechanically screen antigen in high throughput using flow cytometry. Finally, DOTS were anchored onto live B cell membranes thus producing the first quantification of TCR mechanics at authentic immune cell-cell junctions.

Bivalent binding of staphylococcal superantigens to the TCR and CD28 triggers inflammatory signals independently of antigen presenting cells

Staphylococcus aureus superantigens (SAgs) such as staphylococcal enterotoxin A (SEA) and B (SEB) are potent toxins stimulating T cells to produce high levels of inflammatory cytokines, thus causing toxic shock and sepsis. Here we used a recently released artificial intelligence-based algorithm to better elucidate the interaction between staphylococcal SAgs and their ligands on T cells, the TCR and CD28. The obtained computational models together with functional data show that SEB and SEA are able to bind to the TCR and CD28 stimulating T cells to activate inflammatory signals independently of MHC class II- and B7-expressing antigen presenting cells. These data reveal a novel mode of action of staphylococcal SAgs. By binding to the TCR and CD28 in a bivalent way, staphylococcal SAgs trigger both the early and late signalling events, which lead to massive inflammatory cytokine secretion.

Mechano-modulation of T cells for cancer immunotherapy

Immunotherapy, despite its promise for future anti-cancer approach, faces significant challenges, such as off-tumor side effects, innate or acquired resistance, and limited infiltration of immune cells into stiffened extracellular matrix (ECM). Recent studies have highlighted the importance of mechano-modulation/-activation of immune cells (mainly T cells) for effective caner immunotherapy. Immune cells are highly sensitive to the applied physical forces and matrix mechanics, and reciprocally shape the tumor microenvironment. Engineering T cells with tuned properties of materials (e.g., chemistry, topography, and stiffness) can improve their expansion and activation ex vivo, and their ability to mechano-sensing the tumor specific ECM in vivo where they perform cytotoxic effects. T cells can also be exploited to secrete enzymes that soften ECM, thus increasing tumor infiltration and cellular therapies. Furthermore, T cells, such as chimeric antigen receptor (CAR)-T cells, genomic engineered to be spatiotemporally controllable by physical stimuli (e.g., ultrasound, heat, or light), can mitigate adverse off-tumor effects. In this review, we communicate these recent cutting-edge endeavors devoted to mechano-modulating/-activating T cells for effective cancer immunotherapy, and discuss future prospects and challenges in this field.

Understanding How Cells Probe the World: A Preliminary Step towards Modeling Cell Behavior?

Cell biologists have long aimed at quantitatively modeling cell function. Recently, the outstanding progress of high-throughput measurement methods and data processing tools has made this a realistic goal. The aim of this paper is twofold: First, to suggest that, while much progress has been done in modeling cell states and transitions, current accounts of environmental cues driving these transitions remain insufficient. There is a need to provide an integrated view of the biochemical, topographical and mechanical information processed by cells to take decisions. It might be rewarding in the near future to try to connect cell environmental cues to physiologically relevant outcomes rather than modeling relationships between these cues and internal signaling networks. The second aim of this paper is to review exogenous signals that are sensed by living cells and significantly influence fate decisions. Indeed, in addition to the composition of the surrounding medium, cells are highly sensitive to the properties of neighboring surfaces, including the spatial organization of anchored molecules and substrate mechanical and topographical properties. These properties should thus be included in models of cell behavior. It is also suggested that attempts at cell modeling could strongly benefit from two research lines: (i) trying to decipher the way cells encode the information they retrieve from environment analysis, and (ii) developing more standardized means of assessing the quality of proposed models, as was done in other research domains such as protein structure prediction.

Polarity in immune cells

Immune cells are responsible for pathogen detection and elimination, as well as for signaling to other cells the presence of potential danger. In order to mount an efficient immune response, they need to move and search for a pathogen, interact with other cells, and diversify the population by asymmetric cell division. All these actions are regulated by cell polarity: cell polarity controls cell motility, which is crucial for scanning peripheral tissues to detect pathogens, and recruiting immune cells to sites of infection; immune cells, in particular lymphocytes, communicate with each other by a direct contact called immunological synapse, which entails a global polarization of the cell and plays a role in activating lymphocyte response; finally, immune cells divide asymmetrically from a precursor, generating a diversity of phenotypes and cell types among daughter cells, such as memory and effector cells. This review aims at providing an overview from both biology and physics perspectives of how cell polarity shapes the main immune cell functions.

Extracellular matrix stiffness-The central cue for skin fibrosis

Skin fibrosis is a physiopathological process featuring the excessive deposition of extracellular matrix (ECM), which is the main architecture that provides structural support and constitutes the microenvironment for various cellular behaviors. Recently, increasing interest has been drawn to the relationship between the mechanical properties of the ECM and the initiation and modulation of skin fibrosis, with the engagement of a complex network of signaling pathways, the activation of mechanosensitive proteins, and changes in immunoregulation and metabolism. Simultaneous with the progression of skin fibrosis, the stiffness of ECM increases, which in turn perturbs mechanical and humoral homeostasis to drive cell fate toward an outcome that maintains and enhances the fibrosis process, thus forming a pro-fibrotic "positive feedback loop". In this review, we highlighted the central role of the ECM and its dynamic changes at both the molecular and cellular levels in skin fibrosis. We paid special attention to signaling pathways regulated by mechanical cues in ECM remodeling. We also systematically summarized antifibrotic interventions targeting the ECM, hopefully enlightening new strategies for fibrotic diseases.

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.

A bead-based method for high-throughput mapping of the sequence- and force-dependence of T cell activation

Adaptive immunity relies on T lymphocytes that use αβ T cell receptors (TCRs) to discriminate among peptides presented by major histocompatibility complex molecules (pMHCs). Identifying pMHCs capable of inducing robust T cell responses will not only enable a deeper understanding of the mechanisms governing immune responses but could also have broad applications in diagnosis and treatment. T cell recognition of sparse antigenic pMHCs in vivo relies on biomechanical forces. However, in vitro screening methods test potential pMHCs without force and often at high (nonphysiological) pMHC densities and thus fail to predict potent agonists in vivo. Here, we present a technology termed BATTLES (biomechanically assisted T cell triggering for large-scale exogenous-pMHC screening) that uses biomechanical force to initiate T cell triggering for peptides and cells in parallel. BATTLES displays candidate pMHCs on spectrally encoded beads composed of a thermo-responsive polymer capable of applying shear loads to T cells, facilitating exploration of the force- and sequence-dependent landscape of T cell responses. BATTLES can be used to explore basic T cell mechanobiology and T cell-based immunotherapies.

Nanotopography modulates cytoskeletal organization and dynamics during T cell activation

Exposure to MHC-antigen complexes on the surface of antigen-presenting cells (APCs) activates T cells, inducing the formation of the immune synapse (IS). Antigen detection at the APC surface is thus a critical step in the adaptive immune response. The physical properties of antigen-presenting surfaces encountered by T cells in vivo are believed to modulate T cell activation and proliferation. Although stiffness and ligand mobility influence IS formation, the effect of the complex topography of the APC surface on this process is not well understood. Here we investigate how nanotopography modulates cytoskeletal dynamics and signaling during the early stages of T cell activation using high-resolution fluorescence microscopy on nanofabricated surfaces with parallel nanoridges of different spacings. We find that although nanoridges reduce the maximum spread area as compared with cells on flat surfaces, the ridges enhance the accumulation of actin and the signaling kinase ZAP-70 at the IS. Actin polymerization is more dynamic in the presence of ridges, which influence the directionality of both actin flows and microtubule (MT) growth. Our results demonstrate that the topography of the activating surface exerts both global effects on T cell morphology and local changes in actin and MT dynamics, collectively influencing T cell signaling.

Microfluidic T Cell Selection by Cellular Avidity

No T cell receptor (TCR) T cell therapies have obtained clinical approval. The lack of strategies capable of selecting and recovering potent T cell candidates may be a contributor to this. Existing protocols for selecting TCR T cell clones for cell therapies such as peptide multimer methods have provided effective measurements on TCR affinities. However, these methods lack the ability to measure the collective strength of intercellular interactions (i.e., cellular avidity) and markers of T cell activation such as immunological synapse formation. This study describes a novel microfluidic fluid shear stress-based approach to identify and recover highly potent T cell clones based on the cellular avidity between living T cells and tumor cells. This approach is capable of probing approximately up to 10 000 T cell-tumor cell interactions per run and can recover potent T cells with up to 100% purity from mixed populations of T cells within 30 min. Markers of cytotoxicity, activation, and avidity persist when recovered high cellular avidity T cells are subsequently exposed to fresh tumor cells. These results demonstrate how microfluidic probing of cellular avidity may fast track the therapeutic T cell selection process and move the authors closer to precision cancer immunotherapy.

May the force be with your (immune) cells: an introduction to traction force microscopy in Immunology

For more than a couple of decades now, “force” has been recognized as an important physical parameter that cells employ to adapt to their microenvironment. Whether it is externally applied, or internally generated, cells use force to modulate their various actions, from adhesion and migration to differentiation and immune function. T lymphocytes use such mechano-sensitivity to decipher signals when recognizing cognate antigens presented on the surface of antigen presenting cells (APCs), a critical process in the adaptive immune response. As such, many techniques have been developed and used to measure the forces felt/exerted by these small, solitary and extremely reactive cells to decipher their influence on diverse T cell functions, primarily activation. Here, we focus on traction force microscopy (TFM), in which a deformable substrate, coated with the appropriate molecules, acts as a force sensor on the cellular scale. This technique has recently become a center of interest for many groups in the “ImmunoBiophysics” community and, as a consequence, has been subjected to refinements for its application to immune cells. Here, we present an overview of TFM, the precautions and pitfalls, and the most recent developments in the context of T cell immunology.

Insights into intercellular receptor-ligand binding kinetics in cell communication

Cell-cell communication is crucial for cells to sense, respond and adapt to environmental cues and stimuli. The intercellular communication process, which involves multiple length scales, is mediated by the specific binding of membrane-anchored receptors and ligands. Gaining insight into two-dimensional receptor-ligand binding kinetics is of great significance for understanding numerous physiological and pathological processes, and stimulating new strategies in drug design and discovery. To this end, extensive studies have been performed to illuminate the underlying mechanisms that control intercellular receptor-ligand binding kinetics via experiment, theoretical analysis and numerical simulation. It has been well established that the cellular microenvironment where the receptor-ligand interaction occurs plays a vital role. In this review, we focus on the advances regarding the regulatory effects of three factors including 1) protein-membrane interaction, 2) biomechanical force, and 3) bioelectric microenvironment to summarize the relevant experimental observations, underlying mechanisms, as well as their biomedical significances and applications. Meanwhile, we introduce modeling methods together with experiment technologies developed for dealing with issues at different scales. We also outline future directions to advance the field and highlight that building up systematic understandings for the coupling effects of these regulatory factors can greatly help pharmaceutical development.

CAR T Cell Locomotion in Solid Tumor Microenvironment

The promising outcomes of chimeric antigen receptor (CAR) T cell therapy in hematologic malignancies potentiates its capability in the fight against many cancers. Nevertheless, this immunotherapy modality needs significant improvements for the treatment of solid tumors. Researchers have incrementally identified limitations and constantly pursued better CAR designs. However, even if CAR T cells are armed with optimal killer functions, they must overcome and survive suppressive barriers imposed by the tumor microenvironment (TME). In this review, we will discuss in detail the important role of TME in CAR T cell trafficking and how the intrinsic barriers contribute to an immunosuppressive phenotype and cancer progression. It is of critical importance that preclinical models can closely recapitulate the in vivo TME to better predict CAR T activity. Animal models have contributed immensely to our understanding of human diseases, but the intensive care for the animals and unreliable representation of human biology suggest in vivo models cannot be the sole approach to CAR T cell therapy. On the other hand, in vitro models for CAR T cytotoxic assessment offer valuable insights to mechanistic studies at the single cell level, but they often lack in vivo complexities, inter-individual heterogeneity, or physiologically relevant spatial dimension. Understanding the advantages and limitations of preclinical models and their applications would enable more reliable prediction of better clinical outcomes.

Mechanically active integrins target lytic secretion at the immune synapse to facilitate cellular cytotoxicity

Cytotoxic lymphocytes fight pathogens and cancer by forming immune synapses with infected or transformed target cells and then secreting cytotoxic perforin and granzyme into the synaptic space, with potent and specific killing achieved by this focused delivery. The mechanisms that establish the precise location of secretory events, however, remain poorly understood. Here we use single cell biophysical measurements, micropatterning, and functional assays to demonstrate that localized mechanotransduction helps define the position of secretory events within the synapse. Ligand-bound integrins, predominantly the αLβ2 isoform LFA-1, function as spatial cues to attract lytic granules containing perforin and granzyme and induce their fusion with the plasma membrane for content release. LFA-1 is subjected to pulling forces within secretory domains, and disruption of these forces via depletion of the adaptor molecule talin abrogates cytotoxicity. We thus conclude that lymphocytes employ an integrin-dependent mechanical checkpoint to enhance their cytotoxic power and fidelity.

Immune-mediated alopecias and their mechanobiological aspects

Alopecia is a non-specific term for hair loss clinically diagnosed by the hair loss pattern and histological analysis of patient scalp biopsies. The immune-mediated alopecia subtypes, including alopecia areata, lichen planopilaris, frontal fibrosing alopecia, and central centrifugal cicatricial alopecia, are common, significant forms of alopecia subtypes. For example, alopecia areata is the most common autoimmune disease with a lifetime incidence of approximately 2% of the world's population. In this perspective, we discuss major results from studies of immune-mediated alopecia subtypes. These studies suggest the key event in disease onset as the collapse in immune privilege, which alters the hair follicle microenvironment, e.g., upregulation of major histocompatibility complex molecules and increase of cytokine production, and results in immune cell infiltration, inflammatory responses, and damage of hair follicles. We note that previous studies have established that the hair follicle has a complex mechanical microenvironment, which may regulate the function of not only tissue cells but also immune cell infiltrates. This suggests a potential for mechanobiology to contribute to alopecia research by adding new methods, new approaches, and new ways of thinking, which is missing in the existing literature. To fill this a gap in the alopecia research space, we develop a mechanobiological hypothesis that alterations in the hair follicle microenvironment, specifically in the mechanically responsive tissues and cells, partially due to loss of immune privilege, may be contributors to disease pathology. We further focus our discussion on the potential for applying mechanoimmunology to the study of T cell infiltrates in the hair follicle, as they are considered primary contributors to alopecia pathology. To establish the connection between the mechanoimmunological hypothesis and immune-mediated alopecia subtypes, we discuss what is known about the role of T cells in immune-mediated alopecia subtypes, using the most extensively studied AA as our model.

Mechanosurveillance: Tiptoeing T Cells

Efficient scanning of tissue that T cells encounter during their migratory life is pivotal to protective adaptive immunity. In fact, T cells can detect even a single antigenic peptide/MHC complex (pMHC) among thousands of structurally similar yet non-stimulatory endogenous pMHCs on the surface of antigen-presenting cells (APCs) or target cells. Of note, the glycocalyx of target cells, being composed of proteoglycans and bulky proteins, is bound to affect and even modulate antigen recognition by posing as a physical barrier. T cell-resident microvilli are actin-rich membrane protrusions that puncture through such barriers and thereby actively place the considerably smaller T-cell antigen receptors (TCRs) in close enough proximity to APC-presented pMHCs so that productive interactions may occur efficiently yet under force. We here review our current understanding of how the plasticity of T-cell microvilli and physicochemical properties of the glycocalyx may affect early events in T-cell activation. We assess insights gained from studies on T-cell plasma membrane ultrastructure and provide an update on current efforts to integrate biophysical aspects such as the amplitude and directionality of TCR-imposed mechanical forces and the distribution and lateral mobility of plasma membrane-resident signaling molecules into a more comprehensive view on sensitized T-cell antigen recognition.

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.

Regulating the discriminatory response to antigen by T-cell receptor

The cell-mediated immune response constitutes a robust host defense mechanism to eliminate pathogens and oncogenic cells. T cells play a central role in such a defense mechanism and creating memories to prevent any potential infection. T cell recognizes foreign antigen by its surface receptors when presented through antigen-presenting cells (APCs) and calibrates its cellular response by a network of intracellular signaling events. Activation of T-cell receptor (TCR) leads to changes in gene expression and metabolic networks regulating cell development, proliferation, and migration. TCR does not possess any catalytic activity, and the signaling initiates with the colocalization of several enzymes and scaffold proteins. Deregulation of T cell signaling is often linked to autoimmune disorders like severe combined immunodeficiency (SCID), rheumatoid arthritis, and multiple sclerosis. The TCR remarkably distinguishes the minor difference between self and non-self antigen through a kinetic proofreading mechanism. The output of TCR signaling is determined by the half-life of the receptor antigen complex and the time taken to recruit and activate the downstream enzymes. A longer half-life of a non-self antigen receptor complex could initiate downstream signaling by activating associated enzymes. Whereas, the short-lived, self-peptide receptor complex disassembles before the downstream enzymes are activated. Activation of TCR rewires the cellular metabolic response to aerobic glycolysis from oxidative phosphorylation. How does the early event in the TCR signaling cross-talk with the cellular metabolism is an open question. In this review, we have discussed the recent developments in understanding the regulation of TCR signaling, and then we reviewed the emerging role of metabolism in regulating T cell function.

Understanding immune signaling using advanced imaging techniques

Advanced imaging is key for visualizing the spatiotemporal regulation of immune signaling which is a complex process involving multiple players tightly regulated in space and time. Imaging techniques vary in their spatial resolution, spanning from nanometers to micrometers, and in their temporal resolution, ranging from microseconds to hours. In this review, we summarize state-of-the-art imaging methodologies and provide recent examples on how they helped to unravel the mysteries of immune signaling. Finally, we discuss the limitations of current technologies and share our insights on how to overcome these limitations to visualize immune signaling with unprecedented fidelity.

Integrin Regulated Autoimmune Disorders: Understanding the Role of Mechanical Force in Autoimmunity

The pathophysiology of autoimmune disorders is multifactorial, where immune cell migration, adhesion, and lymphocyte activation play crucial roles in its progression. These immune processes are majorly regulated by adhesion molecules at cell–extracellular matrix (ECM) and cell–cell junctions. Integrin, a transmembrane focal adhesion protein, plays an indispensable role in these immune cell mechanisms. Notably, integrin is regulated by mechanical force and exhibit bidirectional force transmission from both the ECM and cytosol, regulating the immune processes. Recently, integrin mechanosensitivity has been reported in different immune cell processes; however, the underlying mechanics of these integrin-mediated mechanical processes in autoimmunity still remains elusive. In this review, we have discussed how integrin-mediated mechanotransduction could be a linchpin factor in the causation and progression of autoimmune disorders. We have provided an insight into how tissue stiffness exhibits a positive correlation with the autoimmune diseases’ prevalence. This provides a plausible connection between mechanical load and autoimmunity. Overall, gaining insight into the role of mechanical force in diverse immune cell processes and their dysregulation during autoimmune disorders will open a new horizon to understand this physiological anomaly.

Mechanical Activation of Immune T Cells via a Water Driven Nanomotor

As a key step during immune response, antigen recognition requires direct mechanical interaction between T cells and antigen presenting cells. Upon subjection to mechanical forces, mechanotransduction is triggered. In this study, the mechanical forces generated by water driven synthetic Au-Zn nanomotors are used to activate mechanosensitive Jurkat T cells. The triggering and activation of the cellular Ca^{2 +} channel is observed. It is revealed that the mechanosensitive cells experience different degrees of activation upon receiving different mechanical input signals and demonstrate that external mechanical forces can optimize T cell activation. Compared with T cell activation with cytokines which can lead to the risky widespread activation of T cells and systemic immune storm, nanomotors can present mechanical force and achieve localized immune cell stimulation. It is expected that mechano nanomotors will contribute to the emerging T cell immunology field and facilitate more comprehensive understanding of the T cell mechanical response and function.

Harder, better, faster, stronger: biochemistry and biophysics in the immunosurveillance concert

Antitumor immunosurveillance is triggered by immune cell recognition of characteristic biochemical signals on the surfaces of cancer cells. Recent data suggest that the mechanical properties of cancer cells influence the strength of these signals, with physically harder target cells (more rigid) eliciting better, faster, and stronger cytotoxic responses against metastasis. Using analogies to a certain electronic music duo, we argue that the biophysical properties of cancer cells and their environment can adjust the volume and tone of the antitumor immune response. We also consider the potential influence of biomechanics-based immunosurveillance in disease progression and posit that targeting the biophysical properties of cancer cells in concert with their biochemical features could increase the efficacy of immunotherapy.

Biophysical Approaches for Applying and Measuring Biological Forces

Over the past decades, increasing evidence has indicated that mechanical loads can regulate the morphogenesis, proliferation, migration, and apoptosis of living cells. Investigations of how cells sense mechanical stimuli or the mechanotransduction mechanism is an active field of biomaterials and biophysics. Gaining a further understanding of mechanical regulation and depicting the mechanotransduction network inside cells require advanced experimental techniques and new theories. In this review, the fundamental principles of various experimental approaches that have been developed to characterize various types and magnitudes of forces experienced at the cellular and subcellular levels are summarized. The broad applications of these techniques are introduced with an emphasis on the difficulties in implementing these techniques in special biological systems. The advantages and disadvantages of each technique are discussed, which can guide readers to choose the most suitable technique for their questions. A perspective on future directions in this field is also provided. It is anticipated that technical advancement can be a driving force for the development of mechanobiology.

Pancreatic Ductal Adenocarcinoma Cortical Mechanics and Clinical Implications

Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest cancers due to low therapeutic response rates and poor prognoses. Majority of patients present with symptoms post metastatic spread, which contributes to its overall lethality as the 4th leading cause of cancer-related deaths. Therapeutic approaches thus far target only one or two of the cancer specific hallmarks, such as high proliferation rate, apoptotic evasion, or immune evasion. Recent genomic discoveries reveal that genetic heterogeneity, early micrometastases, and an immunosuppressive tumor microenvironment contribute to the inefficacy of current standard treatments and specific molecular-targeted therapies. To effectively combat cancers like PDAC, we need an innovative approach that can simultaneously impact the multiple hallmarks driving cancer progression. Here, we present the mechanical properties generated by the cell’s cortical cytoskeleton, with a spotlight on PDAC, as an ideal therapeutic target that can concurrently attack multiple systems driving cancer. We start with an introduction to cancer cell mechanics and PDAC followed by a compilation of studies connecting the cortical cytoskeleton and mechanical properties to proliferation, metastasis, immune cell interactions, cancer cell stemness, and/or metabolism. We further elaborate on the implications of these findings in disease progression, therapeutic resistance, and clinical relapse. Manipulation of the cancer cell’s mechanical system has already been shown to prevent metastasis in preclinical models, but it has greater potential for target exploration since it is a foundational property of the cell that regulates various oncogenic behaviors.

Measuring αβ T-Cell Receptor-Mediated Mechanosensing Using Optical Tweezers Combined with Fluorescence Imaging

T-cell antigen receptors (TCRs) are mechanosensors, which initiate a signaling cascade upon ligand recognition resulting in T-cell differentiation, homeostasis, effector and regulatory functions. An optical trap combined with fluorescence permits direct monitoring of T-cell triggering in response to force application at various concentrations of peptide-bound major histocompatibility complex molecules (pMHC). The technique mimics physiological shear forces applied as cells crawl across antigen-presenting surfaces during immune surveillance. True single molecule studies performed on single cells profile force-bond lifetime, typically seen as a catch bond, and conformational change at the TCR-pMHC bond on the surface of the cell upon force loading. Together, activation and single molecule single cell studies provide chemical and physical triggering thresholds as well as insight into catch bond formation and quaternary structural changes of single TCRs. The present methods detail assay design, preparation, and execution, as well as data analysis. These methods may be applied to a wide range of pMHC-TCR interactions and have potential for adaptation to other receptor-ligand systems.

Ion channel mediated mechanotransduction in immune cells

The immune system performs critical functions to defend against invading pathogens and maintain tissue homeostasis. Immune cells reside within or are recruited to a host of mechanically active tissues throughout the body and, as a result, are exposed to varying types and degrees of mechanical stimuli. Despite their abundance in such tissues, the role of mechanical stimuli in influencing immune cell function and the molecular mechanisms responsible for mechanics-mediated changes are still poorly understood. The recent emergence of mechanically-gated ion channels, particularly Piezo1, has provided an exciting avenue of research within the fields of mechanobiology and immunology. Numerous studies have identified roles for mechanically-gated ion channels in mechanotransduction within various different cell types, with a few recent studies in immune cells. These initial studies provide strong evidence that mechanically-gated ion channels play pivotal roles in regulating the immune system. In this review, we discuss characteristics of ion channel mediated force transduction, review the current techniques used to quantify and visualize ion channel activity in response to mechanical stimuli, and finally we provide an overview of recent studies examining the role of mechanically-gated ion channels in modulating immune cell function.

Cancer-cell stiffening via cholesterol depletion enhances adoptive T-cell immunotherapy

Malignant transformation and tumour progression are associated with cancer-cell softening. Yet how the biomechanics of cancer cells affects T-cell-mediated cytotoxicity and thus the outcomes of adoptive T-cell immunotherapies is unknown. Here we show that T-cell-mediated cancer-cell killing is hampered for cortically soft cancer cells, which have plasma membranes enriched in cholesterol, and that cancer-cell stiffening via cholesterol depletion augments T-cell cytotoxicity and enhances the efficacy of adoptive T-cell therapy against solid tumours in mice. We also show that the enhanced cytotoxicity against stiffened cancer cells is mediated by augmented T-cell forces arising from an increased accumulation of filamentous actin at the immunological synapse, and that cancer-cell stiffening has negligible influence on: T-cell-receptor signalling, production of cytolytic proteins such as granzyme B, secretion of interferon gamma and tumour necrosis factor alpha, and Fas-receptor-Fas-ligand interactions. Our findings reveal a mechanical immune checkpoint that could be targeted therapeutically to improve the effectiveness of cancer immunotherapies.

Surface presentation of the noncanonical Wnt5a motif to cytotoxic CD8+ T-cells promotes their mechanotransduction and activation

We report here strategic functionalization of the Wnt5a mimetic peptide ligand Foxy5 on a polydimethylsiloxane elastomer substrate to enhance the mechanotransduction and activation of cytotoxic CD8⁺ T cells by triggering the noncanonical Wnt signaling. This new mechanoregulatory ligand platform can be widely applied in the fundamental research of mechano-immunology and further the development of novel immunotherapies.

Mechanotransduction as a major driver of cell behaviour: mechanisms, and relevance to cell organization and future research

How do cells process environmental cues to make decisions? This simple question is still generating much experimental and theoretical work, at the border of physics, chemistry and biology, with strong implications in medicine. The purpose of mechanobiology is to understand how biochemical and physical cues are turned into signals through mechanotransduction. Here, we review recent evidence showing that (i) mechanotransduction plays a major role in triggering signalling cascades following cell-neighbourhood interaction; (ii) the cell capacity to continually generate forces, and biomolecule properties to undergo conformational changes in response to piconewton forces, provide a molecular basis for understanding mechanotransduction; and (iii) mechanotransduction shapes the guidance cues retrieved by living cells and the information flow they generate. This includes the temporal and spatial properties of intracellular signalling cascades. In conclusion, it is suggested that the described concepts may provide guidelines to define experimentally accessible parameters to describe cell structure and dynamics, as a prerequisite to take advantage of recent progress in high-throughput data gathering, computer simulation and artificial intelligence, in order to build a workable, hopefully predictive, account of cell signalling networks.

Probing T Cell 3D Mechanosensing With Magnetically-Actuated Structures

The ability of cells to recognize and respond to the mechanical properties of their environment is of increasing importance in T cell physiology. However, initial studies in this direction focused on planar hydrogel and elastomer surfaces, presenting several challenges in interpretation including difficulties in separating mechanical stiffness from changes in chemistry needed to modulate this property. We introduce here the use of magnetic fields to change the structural rigidity of microscale elastomer pillars loaded with superparamagnetic nanoparticles, independent of substrate chemistry. This magnetic modulation of rigidity, embodied as the pillar spring constant, changed the interaction of mouse naïve CD4⁺ T cells from a contractile morphology to one involving deep embedding into the array. Furthermore, increasing spring constant was associated with higher IL-2 secretion, showing a functional impact on mechanosensing. The system introduced here thus separates local substrate stiffness and long-range structural rigidity, revealing new facets of T cell interaction with their environment.