Mechanical force determines chimeric antigen receptor microclustering and signaling.

Chimeric antigen receptor (CAR) T cells are activated to trigger the lytic machinery after antigen engagement, and this has been successfully applied clinically as therapy. The mechanism by which antigen binding leads to the initiation of CAR signaling remains poorly understood. Here, we used a set of short double-stranded DNA (dsDNA) tethers with mechanical forces ranging from ∼12 to ∼51 pN to manipulate the mechanical force of antigen tether and decouple the microclustering and signaling events. Our results revealed that antigen-binding-induced CAR microclustering and signaling are mechanical force dependent. Additionally, the mechanical force delivered to the antigen tether by the CAR for microclustering is generated by autonomous cell contractility. Mechanistically, the mechanical-force-induced strong adhesion and CAR diffusion confinement led to CAR microclustering. Moreover, cytotoxicity may have a lower mechanical force threshold than cytokine generation. Collectively, these results support a model of mechanical-force-induced CAR microclustering for signaling.

Report of the Assay Guidance Workshop on 3-Dimensional Tissue Models for Antiviral Drug Development.

The National Center for Advancing Translational Sciences (NCATS) Assay Guidance Manual (AGM) Workshop on 3D Tissue Models for Antiviral Drug Development, held virtually on 7-8 June 2022, provided comprehensive coverage of critical concepts intended to help scientists establish robust, reproducible, and scalable 3D tissue models to study viruses with pandemic potential. This workshop was organized by NCATS, the National Institute of Allergy and Infectious Diseases, and the Bill and Melinda Gates Foundation. During the workshop, scientific experts from academia, industry, and government provided an overview of 3D tissue models' utility and limitations, use of existing 3D tissue models for antiviral drug development, practical advice, best practices, and case studies about the application of available 3D tissue models to infectious disease modeling. This report includes a summary of each workshop session as well as a discussion of perspectives and challenges related to the use of 3D tissues in antiviral drug discovery.

A PI(4,5)P2-derived "gasoline engine model" for the sustained B cell receptor activation.

To efficiently initiate activation responses against rare ligands in the microenvironment, lymphocytes employ sophisticated mechanisms involving signaling amplification. Recently, a signaling amplification mechanism initiated from phosphatidylinositol (PI) 4, 5-biphosphate [PI(4,5)P2] hydrolysis and synthesis for sustained B cell activation has been reported. Antigen and B cell receptor (BCR) recognition triggered the prompt reduction of PI(4,5)P2 density within the BCR microclusters, which led to the positive feedback for the synthesis of PI(4,5)P2 outside of the BCR microclusters. At single molecule level, the diffusion of PI(4,5)P2 was slow, allowing for the maintenance of a PI(4,5)P2 density gradient between the inside and outside of the BCR microclusters and the persistent supply of PI(4,5)P2 from outside to inside of the BCR microclusters. Here, we review studies that have contributed to uncovering the molecular mechanisms of PI(4,5)P2-derived signaling amplification model. Based on these studies, we proposed a "gasoline engine model" in which the activation of B cell signaling inside the microclusters is similar to the working principle of burning gasoline within the engine chamber of a gasoline engine. We also discuss the evidences showing the potential universality of this model and future prospects.

Interstitial flow promotes the formation of functional microvascular networks in vitro through upregulation of matrix metalloproteinase-2.

Self-organized microvascular networks (MVNs) have become key to the development of many microphysiological models. However, the self-organizing nature of this process combined with variations between types or batches of endothelial cells (ECs) often lead to inconsistency or failure to form functional MVNs. Since interstitial flow (IF) has been reported to play a beneficial role in angiogenesis, vasculogenesis, and 3D capillary morphogenesis, we systematically investigated the role IF plays during neovessel formation in a customized single channel microfluidic chip for which IF has been fully characterized. Compared to static conditions, MVNs formed under IF have higher vessel density and diameters and greater network perfusability. Through a series of inhibitory experiments, we demonstrated that IF treatment improves vasculogenesis by ECs through upregulation of matrix metalloproteinase-2 (MMP-2). We then successfully implemented a novel strategy involving the interplay between IF and MMP-2 inhibitor to regulate morphological parameters of the self-organized MVNs, with vascular permeability and perfusability well maintained. The revealed mechanism and proposed methodology were further validated with a brain MVN model. Our findings and methods have the potential to be widely utilized to boost the development of various organotypic MVNs and could be incorporated into related bioengineering applications where perfusable vasculature is desired.

Imaging: Gear up for mechano-immunology.

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

Utilization of a photoactivatable antigen system to examine B-cell probing termination and the B-cell receptor sorting mechanisms during B-cell activation.

Antigen binding to the B-cell receptor (BCR) induces several responses, resulting in B-cell activation, proliferation, and differentiation. However, it has been difficult to study these responses due to their dynamic, fast, and transient nature. Here, we attempted to solve this problem by developing a controllable trigger point for BCR and antigen recognition through the construction of a photoactivatable antigen, caged 4-hydroxy-3-nitrophenyl acetyl (caged-NP). This photoactivatable antigen system in combination with live cell and single molecule imaging techniques enabled us to illuminate the previously unidentified B-cell probing termination behaviors and the precise BCR sorting mechanisms during B-cell activation. B cells in contact with caged-NP exhibited probing behaviors as defined by the unceasing extension of membrane pseudopods in random directions. Further analyses showed that such probing behaviors are cell intrinsic with strict dependence on F-actin remodeling but not on tonic BCR signaling. B-cell probing behaviors were terminated within 4 s after photoactivation, suggesting that this response was sensitive and specific to BCR engagement. The termination of B-cell probing was concomitant with the accumulation response of the BCRs into the BCR microclusters. We also determined the Brownian diffusion coefficient of BCRs from the same B cells before and after BCR engagement. The analysis of temporally segregated single molecule images of both BCR and major histocompatibility complex class I (MHC-I) demonstrated that antigen binding induced trapping of BCRs into the BCR microclusters is a fundamental mechanism for B cells to acquire antigens.

Substrate stiffness regulates B-cell activation, proliferation, class switch, and T-cell-independent antibody responses in vivo.

B cells use B-cell receptors (BCRs) to sense antigens that are usually presented on substrates with different stiffness. However, it is not known how substrate stiffness affects B-cell proliferation, class switch, and in vivo antibody responses. We addressed these questions using polydimethylsiloxane (PDMS) substrates with different stiffness (20 or 1100 kPa). Live cell imaging experiments suggested that antigens on stiffer substrates more efficiently trigger the synaptic accumulation of BCR and phospho-Syk molecules compared with antigens on softer substrates. In vitro expansion of mouse primary B cells shows different preferences for substrate stiffness when stimulated by different expansion stimuli. LPS equally drives B-cell proliferation on stiffer or softer substrates. Anti-CD40 antibodies enhance B-cell proliferation on stiffer substrates, while antigens enhance B-cell proliferation on softer substrates through a mechanism involving the enhanced phosphorylation of PI3K, Akt, and FoxO1. In vitro class switch differentiation of B cells prefers softer substrates. Lastly, NP67-Ficoll on softer substrates accounted for an enhanced antibody response in vivo. Thus, substrate stiffness regulates B-cell activation, proliferation, class switch, and T cell independent antibody responses in vivo, suggesting its broad application in manipulating the fate of B cells in vitro and in vivo.

Through an ITIM-independent mechanism the FcγRIIB blocks B cell activation by disrupting the colocalized microclustering of the B cell receptor and CD19.

B cell activation is regulated through the interplay of the BCR with the inhibitory coreceptor FcγRIIB and the activating coreceptor CD19. Recent studies suggest that Ag-driven BCR microclusters are efficiently converted to a signaling active state on colocalization with CD19 microclusters. Using total internal reflection fluorescence microscopy-based, high-resolution, high-speed live-cell and molecule imaging approaches, we show that when co-ligated to the BCR, the FcγRIIB can inhibit B cell activation by blocking the colocalization of BCR and CD19 microclusters within the B cell immunological synapse. Remarkably, this inhibitory function of FcγRIIB is dependent not on its well-characterized ITIM-containing cytoplasmic domain, but its transmembrane domain. Indeed, human primary B cells from systemic lupus erythematosus patients homozygous for gene encoding the loss-of-function transmembrane domain mutant FcγRIIB-I232T fail to block the synaptic colocalization of the BCR with CD19, leading to dysregulated recruitment of downstream signaling molecule p-PI3K to membrane proximal signalosome. This inhibitory function of FcγRIIB in impairing the spatial-temporal colocalization of BCR and CD19 microclusters in the B cell immunological synapse may help explain the hyper-reactive features of systemic lupus erythematosus patient B cells in reported studies. These observations may also provide new targets for therapies for systemic autoimmune disease.

B cell activation is regulated by the stiffness properties of the substrate presenting the antigens.

B lymphocytes are activated upon Ag sensing by BCRs. The substrate presenting the Ag can show different degrees of stiffness. It is not clear whether B cells can respond to changes in substrate stiffness. In this study we use high-resolution, high-speed live cell imaging techniques to capture the molecular events in B cell activation after the recognition of Ags tethered to polyacrylamide gel substrates with variable degrees of stiffness as quantified by Young's modulus (2.6-22.1 kPa). We show that the initiation of B cell activation is extremely sensitive to substrate stiffness. B cells exhibit much stronger activation responses when encountering Ags tethered to substrates with a high degree of stiffness as measured by the accumulation of BCR, phospho-spleen tyrosine kinase, and phosphotyrosine molecules into the B cell immunological synapse. Ags tethered to stiff substrates induce the formation of more prominent BCR and phospho-spleen tyrosine kinase microclusters with significantly enhanced colocalization as compared with Ags tethered to soft substrates. Moreover, the expression of the B cell activation marker CD69 is enhanced in B cells encountering Ags on stiffer substrates. Through time-lapse live cell imaging, we find that the different responses of B cells to substrate stiffness are only demonstrated 5 min after BCR and Ag recognition. Using a series of cytoskeleton inhibitors, we determine that the mechanosensing ability of B cells is dependent on microtubules, and only mildly linked to the actin cytoskeleton. These results suggest the importance of the mechanical properties mediated by substrate stiffness in B cell activation.

Transmural Flow Upregulates PD-L1 Expression in Microvascular Networks.

Endothelial programmed death-ligand 1 (PD-L1) expression is higher in tumors than in normal tissues. Also, tumoral vasculatures tend to be leakier than normal vessels leading to a higher trans-endothelial or transmural fluid flow. However, it is not clear whether such elevated transmural flow can control endothelial PD-L1 expression. Here, a new microfluidic device is developed to investigate the relationship between transmural flow and PD-L1 expression in microvascular networks (MVNs). After treating the MVNs with transmural flow for 24 h, the expression of PD-L1 in endothelial cells is upregulated. Additionally, CD8 T cell activation by phytohemagglutinin (PHA) is suppressed when cultured in the MVNs pre-conditioned with transmural flow. Moreover, transmural flow is able to further increase PD-L1 expression in the vessels formed in the tumor microenvironment. Finally, by utilizing blocking antibodies and knock-out assays, it is found that transmural flow-driven PD-L1 upregulation is controlled by integrin αVß3. Overall, this study provides a new biophysical explanation for high PD-L1 expression in tumoral vasculatures.

Ether lipids influence cancer cell fate by modulating iron uptake.

Cancer cell fate has been widely ascribed to mutational changes within protein-coding genes associated with tumor suppressors and oncogenes. In contrast, the mechanisms through which the biophysical properties of membrane lipids influence cancer cell survival, dedifferentiation and metastasis have received little scrutiny. Here, we report that cancer cells endowed with a high metastatic ability and cancer stem cell-like traits employ ether lipids to maintain low membrane tension and high membrane fluidity. Using genetic approaches and lipid reconstitution assays, we show that these ether lipid-regulated biophysical properties permit non-clathrin-mediated iron endocytosis via CD44, leading directly to significant increases in intracellular redox-active iron and enhanced ferroptosis susceptibility. Using a combination of in vitro three-dimensional microvascular network systems and in vivo animal models, we show that loss of ether lipids also strongly attenuates extravasation, metastatic burden and cancer stemness. These findings illuminate a mechanism whereby ether lipids in carcinoma cells serve as key regulators of malignant progression while conferring a unique vulnerability that can be exploited for therapeutic intervention.

Impact of Fibrinogen, Fibrin Thrombi, and Thrombin on Cancer Cell Extravasation Using In Vitro Microvascular Networks.

A bidirectional association exists between metastatic dissemination and the hypercoagulable state associated with many types of cancer. As such, clinical studies have provided evidence that markers associated with elevated levels of coagulation and fibrinolysis correlate with decreased patient survival. However, elucidating the mechanisms underpinning the effects of different components of the coagulation system on metastasis formation is challenging both in animal models and 2D models lacking the complex cellular interactions necessary to model both thrombosis and metastasis. Here, an in vitro, 3D, microvascular model for observing the formation of fibrin thrombi is described, which is in turn used to study how different aspects of the hypercoagulable state associated with cancer affect the endothelium. Using this platform, cancer cells expressing ICAM-1 are shown to form a fibrinogen-dependent bridge and transmigrate through the endothelium more effectively. Cancer cells are also demonstrated to interact with fibrin thrombi, using them to adhere, spread, and enhance their extravasation efficiency. Finally, thrombin is also shown to enhance cancer cell extravasation. This system presents a physiologically relevant model of fibrin clot formation in the human microvasculature, enabling in-depth investigation of the cellular interactions between cancer cells and the coagulation system affecting cancer cell extravasation.

Microphysiological endothelial models to characterize subcutaneous drug absorption.

The high variability in subcutaneous bioavailability of protein therapeutics is poorly understood, contributing to critical delays in patient access to new therapies. Preclinical animal and in vitro models fail to provide a physiologically relevant testbed to parse potential contributors to human bioavailability, therefore new strategies are necessary. Here, we present a microphysiological model of the human hypodermal vasculature at the injection site to study the interactions of administered protein therapeutics within the microenvironment that influence subcutaneous bioavailability. Our model combines human dermal endothelial cells, fibroblasts, and adipocytes, self-assembled into three-dimensional, perfusable microvessels that express relevant extracellular matrix. We demonstrate the utility of the model for measurement of biophysical parameters within the hypodermal microenvironment that putatively impact protein kinetics and distribution at the injection site. We propose that microphysiological models of the subcutaneous space have applications in preclinical development of protein therapeutics intended for subcutaneous administration with optimal bioavailability.

New Strategy for Promoting Vascularization in Tumor Spheroids in a Microfluidic Assay.

Previous studies have developed vascularized tumor spheroid models to demonstrate the impact of intravascular flow on tumor progression and treatment. However, these models have not been widely adopted so the vascularization of tumor spheroids in vitro is generally lower than vascularized tumor tissues in vivo. To improve the tumor vascularization level, a new strategy is introduced to form tumor spheroids by adding fibroblasts (FBs) sequentially to a pre-formed tumor spheroid and demonstrate this method with tumor cell lines from kidney, lung, and ovary cancer. Tumor spheroids made with the new strategy have higher FB densities on the periphery of the tumor spheroid, which tend to enhance vascularization. The vessels close to the tumor spheroid made with this new strategy are more perfusable than the ones made with other methods. Finally, chimeric antigen receptor (CAR) T cells are perfused under continuous flow into vascularized tumor spheroids to demonstrate immunotherapy evaluation using vascularized tumor-on-a-chip model. This new strategy for establishing tumor spheroids leads to increased vascularization in vitro, allowing for the examination of immune, endothelial, stromal, and tumor cell responses under static or flow conditions.

Age-related alterations in meningeal immunity drive impaired CNS lymphatic drainage.

The meningeal lymphatic network enables the drainage of cerebrospinal fluid (CSF) and facilitates the removal of central nervous system (CNS) waste. During aging and in Alzheimer's disease, impaired meningeal lymphatic drainage promotes the buildup of toxic misfolded proteins in the CNS. Reversing this age-related dysfunction represents a promising strategy to augment CNS waste clearance; however, the mechanisms underlying this decline remain elusive. Here, we demonstrate that age-related alterations in meningeal immunity underlie this lymphatic impairment. Single-cell RNA sequencing of meningeal lymphatic endothelial cells from aged mice revealed their response to IFNγ, which was increased in the aged meninges due to T cell accumulation. Chronic elevation of meningeal IFNγ in young mice via AAV-mediated overexpression attenuated CSF drainage-comparable to the deficits observed in aged mice. Therapeutically, IFNγ neutralization alleviated age-related impairments in meningeal lymphatic function. These data suggest manipulation of meningeal immunity as a viable approach to normalize CSF drainage and alleviate the neurological deficits associated with impaired waste removal.

Patient-Specific Vascularized Tumor Model: Blocking TAM Recruitment with Multispecific Antibodies Targeting CCR2 and CSF-1R.

Tumor-associated inflammation drives cancer progression and therapy resistance, with the infiltration of monocyte-derived tumor-associated macrophages (TAMs) associated with poor prognosis in diverse cancers. Targeting TAMs holds potential against solid tumors, but effective immunotherapies require testing on immunocompetent human models prior to clinical trials. Here, we develop an in vitro model of microvascular networks that incorporates tumor spheroids or patient tissues. By perfusing the vasculature with human monocytes, we investigate monocyte trafficking into the tumor and evaluate immunotherapies targeting the human tumor microenvironment. Our findings demonstrate that macrophages in vascularized breast and lung tumor models can enhance monocyte recruitment via TAM-produced CCL7 and CCL2, mediated by CSF-1R. Additionally, we assess a novel multispecific antibody targeting CCR2, CSF-1R, and neutralizing TGF-ß, referred to as CSF1R/CCR2/TGF-ß Ab, on monocytes and macrophages using our 3D models. This antibody repolarizes TAMs towards an anti-tumoral M1-like phenotype, reduces monocyte chemoattractant protein secretion, and effectively blocks monocyte migration. Finally, we show that the CSF1R/CCR2/TGF-ß Ab inhibits monocyte recruitment in patient-specific vascularized tumor models. Overall, this vascularized tumor model offers valuable insights into monocyte recruitment and enables functional testing of innovative therapeutic antibodies targeting TAMs in the tumor microenvironment (TME).

Microfluidic vascular models of tumor cell extravasation.

Emerging microfluidic disease models have amply demonstrated their value in many fields of cancer research. These in vitro technologies recapitulate key aspects of metastatic cancer, including the process of tumor cell arrest and extravasation at the site of the metastatic tumor. To date, extensive efforts have been made to capture key features of the microvasculature to reconstitute the pre-metastatic niche and investigate dynamic extravasation behaviors using microfluidic systems. In this mini-review, we highlight recent microfluidic vascular models of tumor cell extravasation and explore how this approach contributes to development of in vitro disease models to enhance understanding of metastasis in vivo.

A Robust Method for Perfusable Microvascular Network Formation In Vitro.

Micropost-based microfluidic devices are widely used for microvascular network (MVN) formation in diverse research fields. However, consistently generating perfusable MVNs of physiological morphology and dimension has proven to be challenging. Here, how initial seeding parameters determine key characteristics of MVN formation is investigated and a robust two-step seeding strategy to generate perfusable physiological MVNs in microfluidic devices is established.

Vascularized organoids on a chip: strategies for engineering organoids with functional vasculature.

Human organoids, self-organized and differentiated from homogenous pluripotent stem cells (PSC), replicate the key structural and functional characteristics of their in vivo counterparts. Despite the rapid advancement of organoid technology and its diverse applications, major limitations in achieving truly in vivo like functionality have been the lack of matured structural organization and constraints on tissue size, both of which are direct consequences of lacking a functional vasculature. In the absence of perfusable vessels, a core region within organoids quickly becomes necrotic during development due to increased metabolic demands that cannot be met by diffusion alone. Thus, incorporating functional vasculature in organoid models is indispensable for their growth in excess of several hundred microns and maturaturation beyond the embryonic and fetal phase. Here, we review recent advancements in vascularizing organoids and engineering in vitro capillary beds, and further explore strategies to integrate them on a microfluidic based platform, aiming for establishing perfused vasculature throughout organoids in vitro.

The cancer glycocalyx mediates intravascular adhesion and extravasation during metastatic dissemination.

The glycocalyx on tumor cells has been recently identified as an important driver for cancer progression, possibly providing critical opportunities for treatment. Metastasis, in particular, is often the limiting step in the survival to cancer, yet our understanding of how tumor cells escape the vascular system to initiate metastatic sites remains limited. Using an in vitro model of the human microvasculature, we assess here the importance of the tumor and vascular glycocalyces during tumor cell extravasation. Through selective manipulation of individual components of the glycocalyx, we reveal a mechanism whereby tumor cells prepare an adhesive vascular niche by depositing components of the glycocalyx along the endothelium. Accumulated hyaluronic acid shed by tumor cells subsequently mediates adhesion to the endothelium via the glycoprotein CD44. Trans-endothelial migration and invasion into the stroma occurs through binding of the isoform CD44v to components of the sub-endothelial extra-cellular matrix. Targeting of the hyaluronic acid-CD44 glycocalyx complex results in significant reduction in the extravasation of tumor cells. These studies provide evidence of tumor cells repurposing the glycocalyx to promote adhesive interactions leading to cancer progression. Such glycocalyx-mediated mechanisms may be therapeutically targeted to hinder metastasis and improve patient survival.