The dendritic cell cytoskeleton promotes T cell adhesion and activation by constraining ICAM-1 mobility

Intercellular adhesion molecule-1 (ICAM-1): From molecular functions to clinical applications in cancer investigation

Intercellular adhesion molecule-1 (ICAM-1) is a versatile molecule that plays a critical role in various physiological and pathological processes, particularly in tumor development where its impact is bidirectional. On the one hand, it augments the immune response by promoting immune cell migration, infiltration, and the formation of immunological synapses, thus facilitating potent antitumor effects. Simultaneously, it contributes to tumor immune evasion and influences metastasis by mediating transendothelial migration (TEM), epithelial-to-mesenchymal transition (EMT), and epigenetic modification of tumor cells. Despite its significant potential, the full clinical utility of ICAM-1 has yet to be fully realized. In this review, we thoroughly examine recent advancements in understanding the role of ICAM-1 in tumor development, its relevance in predicting therapeutic efficacy and prognosis, as well as the progress in clinical translational research on anti-ICAM-1-based therapies, encompassing including monoclonal antibodies, immunotherapy, antibody-drug conjugate (ADC), and conventional treatments. By shedding light on these innovative strategies, we aim to underscore ICAM-1's significance as a valuable and multifaceted target for cancer treatment, igniting enthusiasm for further research and facilitating translation into clinical applications.

Functional Integration of Synthetic Cells into 3D Microfluidic Devices for Artificial Organ-On-Chip Technologies

Microfluidics plays a pivotal role in organ-on-chip technologies and in the study of synthetic cells, especially in the development and analysis of artificial cell models. However, approaches that use synthetic cells as integral functional components for microfluidic systems to shape the microenvironment of natural living cells cultured on-chip are not explored. Here, colloidosome-based synthetic cells are integrated into 3D microfluidic devices, pioneering the concept of synthetic cell-based microenvironments for organs-on-chip. Methods are devised to create dense and stable networks of silica colloidosomes, enveloped by supported lipid bilayers, within microfluidic channels. These networks promote receptor-ligand interactions with on-chip cultured cells. Furthermore, a technique is introduced for the controlled release of growth factors from the synthetic cells into the channels, using a calcium alginate-based hydrogel formation within the colloidosomes. To demonstrate the potential of the technology, a modular plug-and-play lymph-node-on-a-chip prototype that guides the expansion of primary human T cells by stimulating receptor ligands on the T cells and modulating their cytokine environment is presented. This integration of synthetic cells into microfluidic systems offers a new direction for organ-on-chip technologies and suggests further avenues for exploration in potential therapeutic applications.

Extracellular matrix rigidity modulates physical properties of subcapsular sinus macrophage-B cell immune synapses

Subcapsular sinus macrophages (SSMs) play a key role in immune defense by forming immunological barriers that control the transport of antigens from lymph into lymph node follicles. SSMs participate in antibody responses by presenting antigens directly to naive B cells and by supplying antigens to follicular dendritic cells to propagate germinal center reactions. Despite the prominent roles that SSMs play during immune responses, little is known about their cell biology because they are technically challenging to isolate and study in vitro. Here, we used multicolor fluorescence microscopy to identify lymph node-derived SSMs in culture. We focused on the role of SSMs as antigen-presenting cells, and found that their actin cytoskeleton regulates the spatial organization and mobility of multivalent antigens (immune complexes [ICs]) displayed on the cell surface. Moreover, we determined that SSMs are mechanosensitive cells that respond to changes in extracellular matrix rigidity by altering the architecture of the actin cytoskeleton, leading to changes in cell morphology, membrane topography, and IC mobility. Changes to extracellular matrix rigidity also modulate actin remodeling by both SSMs and B cells when they form an immune synapse. This alters synapse duration but not IC internalization nor NF-κB activation in the B cell. Taken together, our data reveal that the mechanical microenvironment may influence B cell responses by modulating physical characteristics of antigen presentation by SSMs.

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.

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.

ALCAM-mediated cDC1 CD8 T cells interactions are suppressed in advanced lung tumors

Conventional type 1 dendritic cells (cDC1) are critical regulators of anti-tumoral T-cell responses. The structure and abundance of intercellular contacts between cDC1 and CD8 T cells in cancer tissues is important to determine the outcome of the T-cell response. However, the molecular determinants controlling the stability of cDC1-CD8 interactions during cancer progression remain poorly investigated. Here, we generated a genetic model of non-small cell lung cancer crossed to a fluorescent cDC1 reporter (KP-XCR1venus) to allow the detection of cDC1-CD8T cell clusters in tumor tissues across tumor stages. We found that cDC1-CD8 clusters are abundant and productive at the early stages of tumor development but progressively diminish in advanced tumors. Transcriptional profiling and flow cytometry identified the adhesion molecule ALCAM/CD166 (Activated Leukocyte Cell Adhesion Molecule, ligand of CD6) as highly expressed by lung cDC1 and significantly downregulated in advanced tumors. Analysis of human datasets indicated that ALCAM is downregulated in non-small cell lung cancer and its expression correlates to better prognosis. Mechanistically, triggering ALCAM on lung cDC1 induces cytoskeletal remodeling and contact formation whereas its blockade prevents T-cell activation. Together, our results indicate that ALCAM is important to stabilize cDC1-CD8 interactions at early tumor stages, while its loss in advanced tumors contributes to immune evasion.

ATG-101 Is a Tetravalent PD-L1×4-1BB Bispecific Antibody That Stimulates Antitumor Immunity through PD-L1 Blockade and PD-L1-Directed 4-1BB Activation

Immune checkpoint inhibitors (ICI) have transformed cancer treatment. However, only a minority of patients achieve a profound response. Many patients are innately resistant while others acquire resistance to ICIs. Furthermore, hepatotoxicity and suboptimal efficacy have hampered the clinical development of agonists of 4-1BB, a promising immune-stimulating target. To effectively target 4-1BB and treat diseases resistant to ICIs, we engineered ATG-101, a tetravalent "2+2″ PD-L1×4-1BB bispecific antibody. ATG-101 bound PD-L1 and 4-1BB concurrently, with a greater affinity for PD-L1, and potently activated 4-1BB+ T cells when cross-linked with PD-L1-positive cells. ATG-101 activated exhausted T cells upon PD-L1 binding, indicating a possible role in reversing T-cell dysfunction. ATG-101 displayed potent antitumor activity in numerous in vivo tumor models, including those resistant or refractory to ICIs. ATG-101 greatly increased the proliferation of CD8+ T cells, the infiltration of effector memory T cells, and the ratio of CD8+ T/regulatory T cells in the tumor microenvironment (TME), rendering an immunologically "cold" tumor "hot." Comprehensive characterization of the TME after ATG-101 treatment using single-cell RNA sequencing further revealed an altered immune landscape that reflected increased antitumor immunity. ATG-101 was well tolerated and did not induce hepatotoxicity in non-human primates. According to computational semimechanistic pharmacology modeling, 4-1BB/ATG-101/PD-L1 trimer formation and PD-L1 receptor occupancy were both maximized at around 2 mg/kg of ATG-101, providing guidance regarding the optimal biological dose for clinical trials. In summary, by localizing to PD-L1-rich microenvironments and activating 4-1BB+ immune cells in a PD-L1 cross-linking-dependent manner, ATG-101 safely inhibits growth of ICI resistant and refractory tumors.

SIGNIFICANCE

The tetravalent PD-L1×4-1BB bispecific antibody ATG-101 activates 4-1BB+ T cells in a PD-L1 cross-linking-dependent manner, minimizing the hepatotoxicity of existing 4-1BB agonists and suppressing growth of ICI-resistant tumors. See related commentary by Ha et al., p. 1546.

Theory and Examples of Catch Bonds

We discuss slip bonds, catch bonds, and the tug-of-war mechanism using mathematical arguments. The aim is to explain the theoretical tool of molecular potential energy surfaces (PESs). For this, we propose simple 2-dimensional surface models to demonstrate how a molecule under an external force behaves. Examples are selectins. Catch bonds, in particular, are explained in more detail, and they are contrasted to slip bonds. We can support special two-dimensional molecular PESs for E- and L-selectin which allow the catch bond property. We demonstrate that Newton trajectories (NT) are powerful tools to describe these phenomena. NTs form the theoretical background of mechanochemistry.

Mechanical forces amplify TCR mechanotransduction in T cell activation and function

Adoptive T cell immunotherapies, including engineered T cell receptor (eTCR) and chimeric antigen receptor (CAR) T cell immunotherapies, have shown efficacy in treating a subset of hematologic malignancies, exhibit promise in solid tumors, and have many other potential applications, such as in fibrosis, autoimmunity, and regenerative medicine. While immunoengineering has focused on designing biomaterials to present biochemical cues to manipulate T cells ex vivo and in vivo, mechanical cues that regulate their biology have been largely underappreciated. This review highlights the contributions of mechanical force to several receptor-ligand interactions critical to T cell function, with central focus on the TCR-peptide-loaded major histocompatibility complex (pMHC). We then emphasize the role of mechanical forces in (i) allosteric strengthening of the TCR-pMHC interaction in amplifying ligand discrimination during T cell antigen recognition prior to activation and (ii) T cell interactions with the extracellular matrix. We then describe approaches to design eTCRs, CARs, and biomaterials to exploit TCR mechanosensitivity in order to potentiate T cell manufacturing and function in adoptive T cell immunotherapy.

ICAMs in Immunity, Intercellular Adhesion and Communication

Interactions among leukocytes and leukocytes with immune-associated auxiliary cells represent an essential feature of the immune response that requires the involvement of cell adhesion molecules (CAMs). In the immune system, CAMs include a wide range of members pertaining to different structural and functional families involved in cell development, activation, differentiation and migration. Among them, β2 integrins (LFA-1, Mac-1, p150,95 and αDβ2) are predominantly involved in homotypic and heterotypic leukocyte adhesion. β2 integrins bind to intercellular (I)CAMs, actin cytoskeleton-linked receptors belonging to immunoglobulin superfamily (IgSF)-CAMs expressed by leukocytes and vascular endothelial cells, enabling leukocyte activation and transendothelial migration. β2 integrins have long been viewed as the most important ICAMs partners, propagating intracellular signalling from β2 integrin-ICAM adhesion receptor interaction. In this review, we present previous evidence from pioneering studies and more recent findings supporting an important role for ICAMs in signal transduction. We also discuss the contribution of immune ICAMs (ICAM-1, -2, and -3) to reciprocal cell signalling and function in processes in which β2 integrins supposedly take the lead, paying particular attention to T cell activation, differentiation and migration.

ICAM2 is related to good prognosis in dendritic cell immunotherapy for cancer

Objective: To evaluate the behavior of adhesion molecules ICAM-1 and ICAM-2 in dendritic cell (DC) immunotherapy. Materials & methods: 88 female Balb/c mice were divided into experimental groups. Tumors and lymph nodes were evaluated 7 and 14 days after immunotherapy. Results: Higher mean fluorescence intensity of ICAM-1 in the lymph nodes and tumors in the tumor group at 14 days was observed. Higher mean fluorescence intensity of ICAM-2 in the tumor DC vaccine group was observed after 14 days. A positive correlation was observed in the lymph nodes with ICAM-1 against tumoral volume in the tumor group. A negative correlation was found between ICAM-2 and tumoral volume in the lymph nodes of the tumor group. Conclusion: An increase in ICAM-2 in tumor DC vaccine and a decrease in ICAM-1 suggests the DC vaccine positively influences the immune system and that ICAM-2 could be a marker of good prognosis.

Revisiting regulatory T cells as modulators of innate immune response and inflammatory diseases

Regulatory T cells (Treg) are known to be critical for the maintenance of immune homeostasis by suppressing the activation of auto- or allo-reactive effector T cells through a diverse repertoire of molecular mechanisms. Accordingly, therapeutic strategies aimed at enhancing Treg numbers or potency in the setting of autoimmunity and allogeneic transplants have been energetically pursued and are beginning to yield some encouraging outcomes in early phase clinical trials. Less well recognized from a translational perspective, however, has been the mounting body of evidence that Treg directly modulate most aspects of innate immune response under a range of different acute and chronic disease conditions. Recognizing this aspect of Treg immune modulatory function provides a bridge for the application of Treg-based therapies to common medical conditions in which organ and tissue damage is mediated primarily by inflammation involving myeloid cells (mononuclear phagocytes, granulocytes) and innate lymphocytes (NK cells, NKT cells, γδ T cells and ILCs). In this review, we comprehensively summarize pre-clinical and human research that has revealed diverse modulatory effects of Treg and specific Treg subpopulations on the range of innate immune cell types. In each case, we emphasize the key mechanistic insights and the evidence that Treg interactions with innate immune effectors can have significant impacts on disease severity or treatment. Finally, we discuss the opportunities and challenges that exist for the application of Treg-based therapeutic interventions to three globally impactful, inflammatory conditions: type 2 diabetes and its end-organ complications, ischemia reperfusion injury and atherosclerosis.

T Cell engineering for cancer immunotherapy by manipulating mechanosensitive force-bearing receptors

T cell immune responses are critical for in both physiological and pathological processes. While biochemical cues are important, mechanical cues arising from the microenvironment have also been found to act a significant role in regulating various T cell immune responses, including activation, cytokine production, metabolism, proliferation, and migration. The immune synapse contains force-sensitive receptors that convert these mechanical cues into biochemical signals. This phenomenon is accepted in the emerging research field of immunomechanobiology. In this review, we provide insights into immunomechanobiology, with a specific focus on how mechanosensitive receptors are bound and triggered, and ultimately resulting T cell immune responses.

Mechanosensory feedback loops during chronic inflammation

Epithelial tissues are crucial to maintaining healthy organization and compartmentalization in various organs and act as a first line of defense against infection in barrier organs such as the skin, lungs and intestine. Disruption or injury to these barriers can lead to infiltration of resident or foreign microbes, initiating local inflammation. One often overlooked aspect of this response is local changes in tissue mechanics during inflammation. In this mini-review, we summarize known molecular mechanisms linking disruption of epithelial barrier function to mechanical changes in epithelial tissues. We consider direct mechanisms, such as changes in the secretion of extracellular matrix (ECM)-modulating enzymes by immune cells as well as indirect mechanisms including local activation of fibroblasts. We discuss how these mechanical changes can modulate local immune cell activity and inflammation and perturb epithelial homeostasis, further dysregulating epithelial barrier function. We propose that this two-way relationship between loss of barrier function and altered tissue mechanics can lead to a positive feedback loop that further perpetuates inflammation. We discuss this cycle in the context of several chronic inflammatory diseases, including inflammatory bowel disease (IBD), liver disease and cancer, and we present the modulation of tissue mechanics as a new framework for combating chronic inflammation.

Carbohydrate ligand engagement with CD11b enhances differentiation of tumor-associated myeloid cells for immunotherapy of solid cancers

BACKGROUND

Efforts to modulate the function of tumor-associated myeloid cell are underway to overcome the challenges in immunotherapy and find a cure. One potential therapeutic target is integrin CD11b, which can be used to modulate the myeloid-derived cells and induce tumor-reactive T-cell responses. However, CD11b can bind to multiple different ligands, leading to various myeloid cell functions such as adhesion, migration, phagocytosis, and proliferation. This has created a major challenge in understanding how CD11b converts the differences in the receptor-ligand binding into subsequent signaling responses and using this information for therapeutic development.

METHODS

This study aimed to investigate the antitumor effect of a carbohydrate ligand, named BG34-200, which modulates the CD11b⁺ cells. We have applied peptide microarrays, multiparameter FACS (fluorescence-activated cell analysis) analysis, cellular/molecular immunological technology, advanced microscopic imaging, and transgenic mouse models of solid cancers, to study the interaction between BG34-200 carbohydrate ligand and CD11b protein and the resulting immunological changes in the context of solid cancers, including osteosarcoma, advanced melanoma, and pancreatic ductal adenocarcinoma (PDAC).

RESULTS

Our results show that BG34-200 can bind directly to the activated CD11b on its I (or A) domain, at previously unreported peptide residues, in a multisite and multivalent manner. This engagement significantly impacts the biological function of tumor-associated inflammatory monocytes (TAIMs) in osteosarcoma, advanced melanoma, and PDAC backgrounds. Importantly, we observed that the BG34-200-CD11b engagement triggered endocytosis of the binding complexes in TAIMs, which induced intracellular F-actin cytoskeletal rearrangement, effective phagocytosis, and intrinsic ICAM-1 (intercellular adhesion molecule I) clustering. These structural biological changes resulted in the differentiation in TAIMs into monocyte-derived dendritic cells, which play a crucial role in T-cell activation in the tumor microenvironment.

CONCLUSIONS

Our research has advanced the current understanding of the molecular basis of CD11b activation in solid cancers, revealing how it converts the differences in BG34 carbohydrate ligands into immune signaling responses. These findings could pave the way for the development of safe and novel BG34-200-based therapies that modulate myeloid-derived cell functions, thereby enhancing immunotherapy for solid cancers.

Trail Formation Alleviates Excessive Adhesion and Maintains Efficient Neutrophil Migration

Migrating neutrophils are found to leave behind subcellular trails in vivo, but the underlying mechanisms remain unclear. Here, an in vitro cell migration test plus an in vivo observation was applied to monitor neutrophil migration on intercellular cell adhesion molecule-1 (ICAM-1) presenting surfaces. Results indicated that migrating neutrophils left behind long-lasting, chemokine-containing trails. Trail formation tended to alleviate excessive cell adhesion enhanced by the trans-binding antibody and maintain efficient cell migration, which was associated with differential instantaneous edge velocity between the cell front and rear. CD11a and CD11b worked differently in inducing trail formation with polarized distributions on the cell body and uropod. Trail release at the cell rear was attributed to membrane ripping, in which β2-integrin was disrupted from the cell membrane through myosin-mediated rear contraction and integrin-cytoskeleton dissociation, potentiating a specialized strategy of integrin loss and cell deadhesion to maintain efficient migration. Moreover, neutrophil trails left on the substrate served as immune forerunners to recruit dendritic cells. These results provided an insight in elucidating the mechanisms of neutrophil trail formation and deciphering the roles of trail formation in efficient neutrophil migration.

LFA-1 Activation in T-Cell Migration and Immunological Synapse Formation

Integrin LFA-1 plays a critical role in T-cell migration and in the formation of immunological synapses. LFA-1 functions through interacting with its ligands with differing affinities: low, intermediate, and high. Most prior research has studied how LFA-1 in the high-affinity state regulates the trafficking and functions of T cells. LFA-1 is also presented in the intermediate-affinity state on T cells, however, the signaling to activate LFA-1 to the intermediate-affinity state and the role of LFA-1 in this affinity state both remain largely elusive. This review briefly summarizes the activation and roles of LFA-1 with varied ligand-binding affinities in the regulation of T-cell migration and immunological synapse formation.

Immune cells use active tugging forces to distinguish affinity and accelerate evolution

Cells are known to exert forces to sense their physical surroundings for guidance of motion and fate decisions. Here, we propose that cells might do mechanical work to drive their own evolution, taking inspiration from the adaptive immune system. Growing evidence indicates that immune B cells-capable of rapid Darwinian evolution-use cytoskeletal forces to actively extract antigens from other cells' surfaces. To elucidate the evolutionary significance of force usage, we develop a theory of tug-of-war antigen extraction that maps receptor binding characteristics to clonal reproductive fitness, revealing physical determinants of selection strength. This framework unifies mechanosensing and affinity-discrimination capabilities of evolving cells: Pulling against stiff antigen tethers enhances discrimination stringency at the expense of absolute extraction. As a consequence, active force usage can accelerate adaptation but may also cause extinction of cell populations, resulting in an optimal range of pulling strength that matches molecular rupture forces observed in cells. Our work suggests that nonequilibrium, physical extraction of environmental signals can make biological systems more evolvable at a moderate energy cost.

Quantification of interaction frequency between antigen-presenting cells and T cells by conjugation assay

Interaction between an antigen-presenting cell and a T cell, and their subsequent conjugation are a prerequisite for the formation of the immunological synapse and productive, antigen-dependent activation of T cells. This initial interaction is accompanied by recognition of the presented antigen by the T cell receptor, and by changes in the morphology of the interacting cells and in actin cytoskeleton structure in the site of interaction. The experimental protocol below describes a simple assay for quantitative assessment of antigen-presenting cells-T cell conjugation using confocal microscopy or flow cytometry.

En-Face Imaging of T Cell-Dendritic Cell Immunological Synapses

Imaging of the immunological synapse (IS) between dendritic cells (DCs) and T cells in suspension is hampered by suboptimal alignment of cell-cell contacts along the vertical imaging plane. This requires optical sectioning that often results in unsatisfactory resolution in time and space. Here, we present a workflow where DCs and T cells are confined between a layer of glass and polydimethylsiloxane (PDMS) that orients the cells along one, horizontal imaging plane, allowing for fast en-face-imaging of the DC-T cell IS.

Tuning immunity through tissue mechanotransduction

Immune responses are governed by signals from the tissue microenvironment, and in addition to biochemical signals, mechanical cues and forces arising from the tissue, its extracellular matrix and its constituent cells shape immune cell function. Indeed, changes in biophysical properties of tissue alter the mechanical signals experienced by cells in many disease conditions, in inflammatory states and in the context of ageing. These mechanical cues are converted into biochemical signals through the process of mechanotransduction, and multiple pathways of mechanotransduction have been identified in immune cells. Such pathways impact important cellular functions including cell activation, cytokine production, metabolism, proliferation and trafficking. Changes in tissue mechanics may also represent a new form of 'danger signal' that alerts the innate and adaptive immune systems to the possibility of injury or infection. Tissue mechanics can change temporally during an infection or inflammatory response, offering a novel layer of dynamic immune regulation. Here, we review the emerging field of mechanoimmunology, focusing on how mechanical cues at the scale of the tissue environment regulate immune cell behaviours to initiate, propagate and resolve the immune response.

Rapid increase in transferrin receptor recycling promotes adhesion during T cell activation

Background

T cell activation leads to increased expression of the receptor for the iron transporter transferrin (TfR) to provide iron required for the cell differentiation and clonal expansion that takes place during the days after encounter with a cognate antigen. However, T cells mobilise TfR to their surface within minutes after activation, although the reason and mechanism driving this process remain unclear.

Results

Here we show that T cells transiently increase endocytic uptake and recycling of TfR upon activation, thereby boosting their capacity to import iron. We demonstrate that increased TfR recycling is powered by a fast endocytic sorting pathway relying on the membrane proteins flotillins, Rab5- and Rab11a-positive endosomes. Our data further reveal that iron import is required for a non-canonical signalling pathway involving the kinases Zap70 and PAK, which controls adhesion of the integrin LFA-1 and eventually leads to conjugation with antigen-presenting cells.

Conclusions

Altogether, our data suggest that T cells boost their iron importing capacity immediately upon activation to promote adhesion to antigen-presenting cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01386-0.

IFNγ-primed periodontal ligament cells regulate T-cell responses via IFNγ-inducible mediators and ICAM-1-mediated direct cell contact

Periodontal ligament (PDL) cells help maintain tissue homeostasis by balancing PDL tissue inflammation and regeneration. However, the mechanisms by which interferon γ (IFNγ) modulate this process are not yet fully understood. The present study aimed to examine the effect of primed and non-primed PDL cells with IFNγ on the viability and differentiation of T lymphocytes and its functional consequences. The results showed that IFNγ-primed PDL cells possessed enhanced immunosuppression by suppressing T-lymphocyte viability and directing T-lymphocyte differentiation towards a higher T helper (Th) Th2/Th1 ratio. Suppression of T-cell viability was mainly mediated by IFNγ-inducible secreted mediators, which was prevented in the presence of direct cell contact, probably by intercellular adhesion molecule-1 (ICAM-1)-induced PI3 K-mediated transforming growth factor β1 expression in PDL cells. By contrast, ICAM-1 activation augmented IFNγ-induced IFNγ and interleukin-6 expression in PDL cells, which in turn modulated T-cell differentiation. The resulting interaction between these two cell types activated macrophage and suppressed osteoclast differentiation. In conclusion, the results have shown, for the first time to our knowledge, that primed and non-primed PDL cells with IFNγ differentially control T-cell responses via IFNγ-inducible mediators and ICAM-1-mediated direct cell contact, suggesting the role of PDL cells in shifting an inflammatory phase towards a regenerative phase.

Proteomic and Metabolomic Signatures Associated With the Immune Response in Healthy Individuals Immunized With an Inactivated SARS-CoV-2 Vaccine

CoronaVac (Sinovac), an inactivated vaccine for SARS-CoV-2, has been widely used for immunization. However, analysis of the underlying molecular mechanisms driving CoronaVac-induced immunity is still limited. Here, we applied a systems biology approach to understand the mechanisms behind the adaptive immune response to CoronaVac in a cohort of 50 volunteers immunized with 2 doses of CoronaVac. Vaccination with CoronaVac led to an integrated immune response that included several effector arms of the adaptive immune system including specific IgM/IgG, humoral response and other immune response, as well as the innate immune system as shown by complement activation. Metabolites associated with immunity were also identified implicating the role of metabolites in the humoral response, complement activation and other immune response. Networks associated with the TCA cycle and amino acids metabolic pathways, such as phenylalanine metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, and glycine, serine and threonine metabolism were tightly coupled with immunity. Critically, we constructed a multifactorial response network (MRN) to analyze the underlying interactions and compared the signatures affected by CoronaVac immunization and SARS-CoV-2 infection to further identify immune signatures and related metabolic pathways altered by CoronaVac immunization. These results help us to understand the host response to vaccination of CoronaVac and highlight the utility of a systems biology approach in defining molecular correlates of protection to vaccination.

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.

Cofilin-1 participates in the hyperfunction of myeloid dendritic cells in patients with severe aplastic anaemia

Cofilin‐1 interacts with actin to regulate cell movement. The importance of cofilin‐1 in immunity has been established, and its involvement in a number of autoimmune diseases has been confirmed. However, its role in severe aplastic anaemia (SAA) remains elusive. Thus, the aim of the current study was to investigate the role of cofilin‐1 in patients with SAA. Flow cytometry, Western blotting and real‐time quantitative reverse transcription‐polymerase chain reaction were performed to detect the mRNA and protein expression of cofilin‐1 in myeloid dendritic cells (mDCs) from patients with SAA. The expression of cofilin‐1 was then suppressed via siRNA, and its effects on mDCs and downstream effector T‐cell function were evaluated. Cofilin‐1 expression was higher in mDCs from patients with SAA and correlated with routine blood and immune indexes. Moreover, cofilin‐1 knockdown in mDCs from patients with SAA reduced their phagocytic capacity, migration capacity, and CD86 expression through F‐actin remodelling, downregulating the stimulatory capacity of mDCs on CD4⁺ and CD8⁺ T lymphocytes. Collectively, these findings indicate that cofilin‐1 participates in the hyperfunction of mDCs in patients with SAA and that the downregulation of cofilin‐1 in mDCs from patients with SAA could be a novel treatment approach for SAA.

A B-cell actomyosin arc network couples integrin co-stimulation to mechanical force-dependent immune synapse formation

B-cell activation and immune synapse (IS) formation with membrane-bound antigens are actin-dependent processes that scale positively with the strength of antigen-induced signals. Importantly, ligating the B-cell integrin, LFA-1, with ICAM-1 promotes IS formation when antigen is limiting. Whether the actin cytoskeleton plays a specific role in integrin-dependent IS formation is unknown. Here, we show using super-resolution imaging of mouse primary B cells that LFA-1:ICAM-1 interactions promote the formation of an actomyosin network that dominates the B-cell IS. This network is created by the formin mDia1, organized into concentric, contractile arcs by myosin 2A, and flows inward at the same rate as B-cell receptor (BCR):antigen clusters. Consistently, individual BCR microclusters are swept inward by individual actomyosin arcs. Under conditions where integrin is required for synapse formation, inhibiting myosin impairs synapse formation, as evidenced by reduced antigen centralization, diminished BCR signaling, and defective signaling protein distribution at the synapse. Together, these results argue that a contractile actomyosin arc network plays a key role in the mechanism by which LFA-1 co-stimulation promotes B-cell activation and IS formation.

Regulation of biomaterial implantation-induced fibrin deposition to immunological functions of dendritic cells

The performance of implanted biomaterials is largely determined by their interaction with the host immune system. As a fibrous-like 3D network, fibrin matrix formed at the interfaces of tissue and material, whose effects on dendritic cells (DCs) remain unknown. Here, a bone plates implantation model was developed to evaluate the fibrin matrix deposition and DCs recruitment in vivo. The DCs responses to fibrin matrix were further analyzed by a 2D and 3D fibrin matrix model in vitro. In vivo results indicated that large amount of fibrin matrix deposited on the interface between the tissue and bone plates, where DCs were recruited. Subsequent in vitro testing denoted that DCs underwent significant shape deformation and cytoskeleton reorganization, as well as mechanical property alteration. Furthermore, the immune function of imDCs and mDCs were negatively and positively regulated, respectively. The underlying mechano-immunology coupling mechanisms involved RhoA and CDC42 signaling pathways. These results suggested that fibrin plays a key role in regulating DCs immunological behaviors, providing a valuable immunomodulatory strategy for tissue healing, regeneration and implantation.

The magnitude of LFA-1/ICAM-1 forces fine-tune TCR-triggered T cell activation

T cells defend against cancer and viral infections by rapidly scanning the surface of target cells seeking specific peptide antigens. This key process in adaptive immunity is sparked upon T cell receptor (TCR) binding of antigens within cell-cell junctions stabilized by integrin (LFA-1)/intercellular adhesion molecule-1 (ICAM-1) complexes. A long-standing question in this area is whether the forces transmitted through the LFA-1/ICAM-1 complex tune T cell signaling. Here, we use spectrally encoded DNA tension probes to reveal the first maps of LFA-1 and TCR forces generated by the T cell cytoskeleton upon antigen recognition. DNA probes that control the magnitude of LFA-1 force show that F>12 pN potentiates antigen-dependent T cell activation by enhancing T cell-substrate engagement. LFA-1/ICAM-1 mechanical events with F>12 pN also enhance the discriminatory power of the TCR when presented with near cognate antigens. Overall, our results show that T cells integrate multiple channels of mechanical information through different ligand-receptor pairs to tune function.

Regulation of biomaterial implantation-induced fibrin deposition to immunological functions of dendritic cells

The performance of implanted biomaterials is largely determined by their interaction with the host immune system. As a fibrous-like 3D network, fibrin matrix formed at the interfaces of tissue and material, whose effects on dendritic cells (DCs) remain unknown. Here, a bone plates implantation model was developed to evaluate the fibrin matrix deposition and DCs recruitment in vivo. The DCs responses to fibrin matrix were further analyzed by a 2D and 3D fibrin matrix model in vitro. In vivo results indicated that large amount of fibrin matrix deposited on the interface between the tissue and bone plates, where DCs were recruited. Subsequent in vitro testing denoted that DCs underwent significant shape deformation and cytoskeleton reorganization, as well as mechanical property alteration. Furthermore, the immune function of imDCs and mDCs were negatively and positively regulated, respectively. The underlying mechano-immunology coupling mechanisms involved RhoA and CDC42 signaling pathways. These results suggested that fibrin plays a key role in regulating DCs immunological behaviors, providing a valuable immunomodulatory strategy for tissue healing, regeneration and implantation.

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.

Gene regulation of intracellular adhesion molecule-1 (ICAM-1): A molecule with multiple functions

Intracellular adhesion molecule 1 (ICAM-1) is one of the most extensively studied inducible cell adhesion molecules which is responsible for several immune functions like T cell activation, extravasation, inflammation, etc. The molecule is constitutively expressed over the cell surface and is regulated up / down in response to inflammatory mediators like cellular stress, proinflammatory cytokines, viral infection. These stimuli modulate the expression of ICAM-1 primarily through regulating the ICAM-1 gene transcription. On account of the presence of various binding sites for NF-κB, AP-1, SP-1, and many other transcription factors, the architecture of the ICAM-1 promoter become complex. Transcription factors in union with other transcription factors, coactivators, and suppressors promote their assembly in a stereospecific manner on ICAM-1 promoter which mediates ICAM-1 regulation in response to different stimuli. Along with transcriptional regulation, epigenetic modifications also play a pivotal role in controlling ICAM-1 expression on different cell types. In this review, we summarize the regulation of ICAM-1 expression both at the transcriptional as well as post-transcriptional level with an emphasis on transcription factors and signaling pathways involved.

Characterization of mechanisms positioning costimulatory complexes in immune synapses

Small immunoglobulin superfamily (sIGSF) adhesion complexes form a corolla of microdomains around an integrin ring and secretory core during immunological synapse (IS) formation. The corolla recruits and retains major costimulatory/checkpoint complexes, such as CD28, making forces that govern corolla formation of particular interest. Here, we investigated the mechanisms underlying molecular reorganization of CD2, an adhesion and costimulatory molecule of the sIGSF family during IS formation. Computer simulations showed passive distal exclusion of CD2 complexes under weak interactions with the ramified F-actin transport network. Attractive forces between CD2 and CD28 complexes relocate CD28 from the IS center to the corolla. Size-based sorting interactions with large glycocalyx components, such as CD45, or short-range CD2 self-attraction successfully explain the corolla 'petals.' This establishes a general simulation framework for complex pattern formation observed in cell-bilayer and cell-cell interfaces, and the suggestion of new therapeutic targets, where boosting or impairing characteristic pattern formation can be pivotal.

Large-Sized Graphene Oxide Nanosheets Increase DC-T-Cell Synaptic Contact and the Efficacy of DC Vaccines against SARS-CoV-2

Dendritic cell (DC) vaccines are used for cancer and infectious diseases, albeit with limited efficacy. Modulating the formation of DC-T-cell synapses may greatly increase their efficacy. The effects of graphene oxide (GO) nanosheets on DCs and DC-T-cell synapse formation are evaluated. In particular, size-dependent interactions are observed between GO nanosheets and DCs. GOs with diameters of >1 µm (L-GOs) demonstrate strong adherence to the DC surface, inducing cytoskeletal reorganization via the RhoA-ROCK-MLC pathway, while relatively small GOs (≈500 nm) are predominantly internalized by DCs. Furthermore, L-GO treatment enhances DC-T-cell synapse formation via cytoskeleton-dependent membrane positioning of integrin ICAM-1. L-GO acts as a "nanozipper," facilitating the aggregation of DC-T-cell clusters to produce a stable microenvironment for T cell activation. Importantly, L-GO-adjuvanted DCs promote robust cytotoxic T cell immune responses against SARS-CoV-2 spike 1, leading to >99.7% viral RNA clearance in mice infected with a clinically isolated SARS-CoV-2 strain. These findings highlight the potential value of nanomaterials as DC vaccine adjuvants for modulating DC-T-cell synapse formation and provide a basis for the development of effective COVID-19 vaccines.

Dendritic cell actin dynamics control contact duration and priming efficiency at the immunological synapse

Dendritic cells (DCs) are crucial for the priming of naive T cells and the initiation of adaptive immunity. Priming is initiated at a heterologous cell–cell contact, the immunological synapse (IS). While it is established that F-actin dynamics regulates signaling at the T cell side of the contact, little is known about the cytoskeletal contribution on the DC side. Here, we show that the DC actin cytoskeleton is decisive for the formation of a multifocal synaptic structure, which correlates with T cell priming efficiency. DC actin at the IS appears in transient foci that are dynamized by the WAVE regulatory complex (WRC). The absence of the WRC in DCs leads to stabilized contacts with T cells, caused by an increase in ICAM1-integrin–mediated cell–cell adhesion. This results in lower numbers of activated and proliferating T cells, demonstrating an important role for DC actin in the regulation of immune synapse functionality.

Transmigration across a Steady-State Blood-Brain Barrie Induces Activation of Circulating Dendritic Cells Partly Mediated by Actin Cytoskeletal Reorganization

The central nervous system (CNS) is considered to be an immunologically unique site, in large part given its extensive protection by the blood–brain barrier (BBB). As our knowledge of the complex interaction between the peripheral immune system and the CNS expands, the mechanisms of immune privilege are being refined. Here, we studied the interaction of dendritic cells (DCs) with the BBB in steady–state conditions and observed that transmigrated DCs display an activated phenotype and stronger T cell-stimulatory capacity as compared to non-migrating DCs. Next, we aimed to gain further insights in the processes underlying activation of DCs following transmigration across the BBB. We investigated the interaction of DCs with endothelial cells as well as the involvement of actin cytoskeletal reorganization. Whereas we were not able to demonstrate that DCs engulf membrane fragments from fluorescently labelled endothelial cells during transmigration across the BBB, we found that blocking actin restructuring of DCs by latrunculin-A significantly impaired in vitro migration of DC across the BBB and subsequent T cell-stimulatory capacity, albeit no effect on migration-induced phenotypic activation could be demonstrated. These observations contribute to the current understanding of the interaction between DCs and the BBB, ultimately leading to the design of targeted therapies capable to inhibit autoimmune inflammation of the CNS.

LFA-1 and kindlin-3 enable the collaborative transport of SLP-76 microclusters by myosin and dynein motors

Integrin engagement within the immune synapse enhances T cell activation, but our understanding of this process is incomplete. In response to T cell receptor (TCR) ligation, SLP-76 (LCP2), ADAP (FYB1) and SKAP55 (SKAP1) are recruited into microclusters and activate integrins via the effectors talin-1 and kindlin-3 (FERMT3). We postulated that integrins influence the centripetal transport and signaling of SLP-76 microclusters via these linkages. We show that contractile myosin filaments surround and are co-transported with SLP-76 microclusters, and that TCR ligand density governs the centripetal movement of both structures. Centripetal transport requires formin activity, actomyosin contraction, microtubule integrity and dynein motor function. Although immobilized VLA-4 (α4β1 integrin) and LFA-1 (αLβ2 integrin) ligands arrest the centripetal movement of SLP-76 microclusters and myosin filaments, VLA-4 acts distally, while LFA-1 acts in the lamellum. Integrin β2, kindlin-3 and zyxin are required for complete centripetal transport, while integrin β1 and talin-1 are not. CD69 upregulation is similarly dependent on integrin β2, kindlin-3 and zyxin, but not talin-1. These findings highlight the integration of cytoskeletal systems within the immune synapse and reveal extracellular ligand-independent roles for LFA-1 and kindlin-3. This article has an associated First Person interview with the first author of the paper.

Journey to the Center of the Cell: Cytoplasmic and Nuclear Actin in Immune Cell Functions

Actin cytoskeletal dynamics drive cellular shape changes, linking numerous cell functions to physiological and pathological cues. Mutations in actin regulators that are differentially expressed or enriched in immune cells cause severe human diseases known as primary immunodeficiencies underscoring the importance of efficienct actin remodeling in immune cell homeostasis. Here we discuss recent findings on how immune cells sense the mechanical properties of their environement. Moreover, while the organization and biochemical regulation of cytoplasmic actin have been extensively studied, nuclear actin reorganization is a rapidly emerging field that has only begun to be explored in immune cells. Based on the critical and multifaceted contributions of cytoplasmic actin in immune cell functionality, nuclear actin regulation is anticipated to have a large impact on our understanding of immune cell development and functionality.

The Actin Cytoskeleton at the Immunological Synapse of Dendritic Cells

Dendritic cells (DCs) are considered the most potent antigen-presenting cells. DCs control the activation of T cells (TCs) in the lymph nodes. This process involves forming a specialized superstructure at the DC-TC contact zone called the immunological synapse (IS). For the sake of clarity, we call IS(DC) and IS(TC) the DC and TC sides of the IS, respectively. The IS(DC) and IS(TC) seem to organize as multicentric signaling hubs consisting of surface proteins, including adhesion and costimulatory molecules, associated with cytoplasmic components, which comprise cytoskeletal proteins and signaling molecules. Most of the studies on the IS have focused on the IS(TC), and the information on the IS(DC) is still sparse. However, the data available suggest that both IS sides are involved in the control of TC activation. The IS(DC) may govern activities of DCs that confer them the ability to activate the TCs. One key component of the IS(DC) is the actin cytoskeleton. Herein, we discuss experimental data that support the concept that actin polarized at the IS(DC) is essential to maintaining IS stability necessary to induce TC activation.

LFA-1 in T cell priming, differentiation, and effector functions

The integrin LFA-1 is crucial for T cell entry into mammalian lymph nodes and tissues, and for promoting interactions with antigen-presenting cells (APCs). However, it is increasingly evident that LFA-1 has additional key roles beyond the mere support of adhesion between T cells, the endothelium, and/or APCs. These include roles in homotypic T cell-T cell (T-T) communication, the induction of intracellular complement activity underlying Th1 effector cell polarization, and the support of long-lasting T cell memory. Here, we briefly summarize current knowledge of LFA-1 biology, discuss novel cytoskeletal regulators of LFA-1 functions, and review new aspects of LFA-1 mechanobiology that are relevant to its function in immunological synapses and in specific pathologies arising from LFA-1 dysregulation.

CD97 stabilises the immunological synapse between dendritic cells and T cells and is targeted for degradation by the Salmonella effector SteD

The Salmonella enterica effector SteD depletes mature MHC class II (mMHCII) molecules from the surface of infected antigen-presenting cells through ubiquitination of the cytoplasmic tail of the mMHCII β chain. This requires the Nedd4 family HECT E3 ubiquitin ligase Wwp2 and a tumor-suppressing transmembrane protein adaptor Tmem127. Here, through a proteomic screen of dendritic cells, we found that SteD targets the plasma membrane protein CD97 for degradation by a similar mechanism. SteD enhanced ubiquitination of CD97 on K555 and mutation of this residue eliminated the effect of SteD on CD97 surface levels. We showed that CD97 localises to and stabilises the immunological synapse between dendritic cells and T cells. Removal of CD97 by SteD inhibited dendritic cell-T cell interactions and reduced T cell activation, independently of its effect on MHCII. Therefore, SteD suppresses T cell immunity by two distinct processes.

Shear forces induce ICAM-1 nanoclustering on endothelial cells that impact on T-cell migration

The leukocyte-specific β₂-integrin LFA-1 and its ligand ICAM-1, expressed on endothelial cells (ECs), are involved in the arrest, adhesion, and transendothelial migration of leukocytes. Although the role of mechanical forces on LFA-1 activation is well established, the impact of forces on its major ligand ICAM-1 has received less attention. Using a parallel-plate flow chamber combined with confocal and super-resolution microscopy, we show that prolonged shear flow induces global translocation of ICAM-1 on ECs upstream of flow direction. Interestingly, shear forces caused actin rearrangements and promoted actin-dependent ICAM-1 nanoclustering before LFA-1 engagement. T cells adhered to mechanically prestimulated ECs or nanoclustered ICAM-1 substrates developed a promigratory phenotype, migrated faster, and exhibited shorter-lived interactions with ECs than when adhered to non mechanically stimulated ECs or to monomeric ICAM-1 substrates. Together, our results indicate that shear forces increase ICAM-1/LFA-1 bonds because of ICAM-1 nanoclustering, strengthening adhesion and allowing cells to exert higher traction forces required for faster migration. Our data also underscore the importance of mechanical forces regulating the nanoscale organization of membrane receptors and their contribution to cell adhesion regulation.

Temporal analysis of T-cell receptor-imposed forces via quantitative single molecule FRET measurements

Mechanical forces acting on ligand-engaged T-cell receptors (TCRs) have previously been implicated in T-cell antigen recognition, yet their magnitude, spread, and temporal behavior are still poorly defined. We here report a FRET-based sensor equipped either with a TCR-reactive single chain antibody fragment or peptide-loaded MHC, the physiological TCR-ligand. The sensor was tethered to planar glass-supported lipid bilayers (SLBs) and informed most directly on the magnitude and kinetics of TCR-imposed forces at the single molecule level. When confronting T-cells with gel-phase SLBs we observed both prior and upon T-cell activation a single, well-resolvable force-peak of approximately 5 pN and force loading rates on the TCR of 1.5 pN per second. When facing fluid-phase SLBs instead, T-cells still exerted tensile forces yet of threefold reduced magnitude and only prior to but not upon activation.

Clustering of Major Histocompatibility Complex-Class I Molecules in Healthy and Cancer Colon Cells Revealed from Their Nanomechanical Properties

The activation of the T cell mediated immune response relies on the fine interaction between the T cell receptor on the immune cell and the antigen-presenting major histocompatibility complex (MHC) molecules on the membrane surface of antigen-presenting cells. Both the distribution and quantity of MHC/peptide complexes and their adequate morphological presentation affect the activation of the immune cells. In several types of cancer the immune response is down-regulated due to the low expression of MHC-class I (MHC-I) molecules on the cell's surface, and in addition, the mechanical properties of the membrane seem to play a role. Herein, we investigate the distribution of MHC-I molecules and the related nanoscale mechanical environment on the cell surface of two cell lines derived from colon adenocarcinoma and a healthy epithelial colon reference cell line. Atomic force microscopy (AFM) force spectroscopy analysis using an antibody-tagged pyramidal probe specific for MHC-I molecules and a formula that relates the elasticity of the cell to the energy of adhesion revealed the different population distributions of MHC-I molecules in healthy cells compared to cancer cells. We found that MHC-I molecules are significantly less expressed in cancer cells. Moreover, the local elastic modulus is significantly reduced in cancer cells. We speculate that these results might be related to the proven ability of cancer cells to evade the immune system, not only by reducing MHC-I cell surface expression but also by modifying the local mechanical properties affecting the overall morphology of MHC-I synapse presentation to immune cells.

Biphasic response of T cell activation to substrate stiffness

T cell activation is sensitive to the mechanical properties of an activating substrate. However, there are also contrasting results on how substrate stiffness affects T cell activation, including differences between T cells of mouse and human origin. Towards reconciling these differences, this report examines the response of primary human T cells to polyacrylamide gels with stiffness between 5 and 110 kPa presenting activating antibodies to CD3 and CD28. T cell proliferation and IL-2 secretion exhibited a biphasic functional response to substrate stiffness, which can be shifted by changing density of activating antibodies and abrogated by inhibition of cellular contractility. T cell morphology was modulated by stiffness at early time points. RNA-seq indicates that T cells show differing monotonic trends in upregulated genes and pathways towards both ends of the stiffness spectrum. These studies provide a framework of T cell mechanosensing and suggest an effect of ligand density that may reconcile different, contrasting patterns of stiffness sensing seen in previous studies.

Controlling T cells spreading, mechanics and activation by micropatterning

We designed a strategy, based on a careful examination of the activation capabilities of proteins and antibodies used as substrates for adhering T cells, coupled to protein microstamping to control at the same time the position, shape, spreading, mechanics and activation state of T cells. Once adhered on patterns, we examined the capacities of T cells to be activated with soluble anti CD3, in comparison to T cells adhered to a continuously decorated substrate with the same density of ligands. We show that, in our hand, adhering onto an anti CD45 antibody decorated surface was not affecting T cell calcium fluxes, even adhered on variable size micro-patterns. Aside, we analyzed the T cell mechanics, when spread on pattern or not, using Atomic Force Microscopy indentation. By expressing MEGF10 as a non immune adhesion receptor in T cells we measured the very same spreading area on PLL substrates and Young modulus than non modified cells, immobilized on anti CD45 antibodies, while retaining similar activation capabilities using soluble anti CD3 antibodies or through model APC contacts. We propose that our system is a way to test activation or anergy of T cells with defined adhesion and mechanical characteristics, and may allow to dissect fine details of these mechanisms since it allows to observe homogenized populations in standardized T cell activation assays.

Cytotoxic lymphocytes target characteristic biophysical vulnerabilities in cancer

Immune cells identify and destroy tumors by recognizing cellular traits indicative of oncogenic transformation. In this study, we found that myocardin-related transcription factors (MRTFs), which promote migration and metastatic invasion, also sensitize cancer cells to the immune system. Melanoma and breast cancer cells with high MRTF expression were selectively eliminated by cytotoxic lymphocytes in mouse models of metastasis. This immunosurveillance phenotype was further enhanced by treatment with immune checkpoint blockade (ICB) antibodies. We also observed that high MRTF signaling in human melanoma is associated with ICB efficacy in patients. Using biophysical and functional assays, we showed that MRTF overexpression rigidified the filamentous actin cytoskeleton and that this mechanical change rendered mouse and human cancer cells more vulnerable to cytotoxic T lymphocytes and natural killer cells. Collectively, these results suggest that immunosurveillance has a mechanical dimension, which we call mechanosurveillance, that is particularly relevant for the targeting of metastatic disease.

The epigenetic pioneer EGR2 initiates DNA demethylation in differentiating monocytes at both stable and transient binding sites

The differentiation of human blood monocytes (MO), the post-mitotic precursors of macrophages (MAC) and dendritic cells (moDC), is accompanied by the active turnover of DNA methylation, but the extent, consequences and mechanisms of DNA methylation changes remain unclear. Here, we profile and compare epigenetic landscapes during IL-4/GM-CSF-driven MO differentiation across the genome and detect several thousand regions that are actively demethylated during culture, both with or without accompanying changes in chromatin accessibility or transcription factor (TF) binding. We further identify TF that are globally associated with DNA demethylation processes. While interferon regulatory factor 4 (IRF4) is found to control hallmark dendritic cell functions with less impact on DNA methylation, early growth response 2 (EGR2) proves essential for MO differentiation as well as DNA methylation turnover at its binding sites. We also show that ERG2 interacts with the 5mC hydroxylase TET2, and its consensus binding sequences show a characteristic DNA methylation footprint at demethylated sites with or without detectable protein binding. Our findings reveal an essential role for EGR2 as epigenetic pioneer in human MO and suggest that active DNA demethylation can be initiated by the TET2-recruiting TF both at stable and transient binding sites.

DNA methylation turnover is an essential epigenetic process during development. Here, the authors look at the changes in DNA methylation during the differentiation of post-mitotic human monocytes (MO), and find that EGR2 interacts with TET2 and is required for DNA demethylation at its binding sites; revealing EGR2 as an epigenetic pioneer factor in human MO.