Cytotoxic T Cells Use Mechanical Force to Potentiate Target Cell Killing.

The immunological synapse formed between a cytotoxic T lymphocyte (CTL) and an infected or transformed target cell is a physically active structure capable of exerting mechanical force. Here, we investigated whether synaptic forces promote the destruction of target cells. CTLs kill by secreting toxic proteases and the pore forming protein perforin into the synapse. Biophysical experiments revealed a striking correlation between the magnitude of force exertion across the synapse and the speed of perforin pore formation on the target cell, implying that force potentiates cytotoxicity by enhancing perforin activity. Consistent with this interpretation, we found that increasing target cell tension augmented pore formation by perforin and killing by CTLs. Our data also indicate that CTLs coordinate perforin release and force exertion in space and time. These results reveal an unappreciated physical dimension to lymphocyte function and demonstrate that cells use mechanical forces to control the activity of outgoing chemical signals.

IL-4 and IL-13, not eosinophils, drive type 2 airway inflammation, remodeling and lung function decline.

RATIONALE: Type 2 (T2) asthma is characterized by airflow limitations and elevated levels of blood and sputum eosinophils, fractional exhaled nitric oxide, IgE, and periostin. While eosinophils are associated with exacerbations, the contribution of eosinophils to lung inflammation, remodeling and function remains largely hypothetical. OBJECTIVES: To determine the effect of T2 cytokines IL-4, IL-13 and IL-5 on eosinophil biology and compare the impact of depleting just eosinophils versus inhibiting all aspects of T2 inflammation on airway inflammation. METHODS: Human eosinophils or endothelial cells stimulated with IL-4, IL-13 or IL-5 were assessed for gene changes or chemokine release.Mice exposed to house dust mite extract received anti-IL-4Rα (dupilumab), anti-IL-5 or control antibodies and were assessed for changes in lung histological and inflammatory endpoints. MEASUREMENTS AND MAIN RESULTS: IL-4 or IL-13 stimulation of human eosinophils and endothelial cells induced gene expression changes related to granulocyte migration; whereas, IL-5 induced changes reflecting granulocyte differentiation.In a mouse model, blocking IL-4Rα improved lung function by impacting multiple effectors of inflammation and remodeling, except peripheral eosinophil counts, thereby disconnecting blood eosinophils from airway inflammation, remodeling and function. Blocking IL-5 globally reduced eosinophil counts but did not impact inflammatory or functional measures of lung pathology. Whole lung transcriptome analysis revealed that IL-5 or IL-4Rα blockade impacted eosinophil associated genes, whereas IL-4Rα blockade also impacted genes associated with multiple cells, cytokines and chemokines, mucus production, cell:cell adhesion and vascular permeability. CONCLUSIONS: Eosinophils are not the sole contributor to asthma pathophysiology or lung function decline and emphasizes the need to block additional mediators to modify lung inflammation and impact lung function.

Dual blockade of IL-4 and IL-13 with dupilumab, an IL-4Rα antibody, is required to broadly inhibit type 2 inflammation.

BACKGROUND: Dupilumab, a fully human monoclonal antibody that binds IL-4Rα and inhibits signaling of both IL-4 and IL-13, has shown efficacy across multiple diseases with underlying type 2 signatures and is approved for treatment of asthma, atopic dermatitis, and chronic sinusitis with nasal polyposis. We sought to provide a comprehensive analysis of the redundant and distinct roles of IL-4 and IL-13 in type 2 inflammation and report dupilumab mechanisms of action. METHODS: Using primary cell assays and a mouse model of house dust mite-induced asthma, we compared IL-4 vs IL-13 vs IL-4Rα blockers. RESULTS: Intranasal administration of either IL-4 or IL-13 confers an asthma-like phenotype in mice by inducing immune cell lung infiltration, including eosinophils, increasing cytokine/chemokine expression and mucus production, thus demonstrating redundant functions of these cytokines. We further teased out their respective contributions using human in vitro culture systems. Then, in a mouse asthma model by comparing in head-to-head studies, either IL-4 or IL-13 inhibition to dual IL-4/IL-13 inhibition, we demonstrate that blockade of both IL-4 and IL-13 is required to broadly block type 2 inflammation, which translates to protection from allergen-induced lung function impairment. Notably, only dual IL-4/IL-13 blockade prevented eosinophil infiltration into lung tissue without affecting circulating eosinophils, demonstrating that tissue, but not circulating eosinophils, contributes to disease pathology. CONCLUSIONS: Overall, these data support IL-4 and IL-13 as key drivers of type 2 inflammation and help provide insight into the therapeutic mechanism of dupilumab, a dual IL-4/IL-13 blocker, in multiple type 2 diseases.

From lipid second messengers to molecular motors: microtubule-organizing center reorientation in T cells.

In T lymphocytes, polarization of the microtubule-organizing center (MTOC) to the immunological synapse enables the directional secretion of cytokines, cytolytic factors, and other soluble molecules toward the antigen-presenting cell. This is likely to be crucial for maintaining the specificity of T-cell effector responses. Here, we review recent advances in our understanding of MTOC reorientation in T cells, focusing first on the importance of diacylglycerol and protein kinase C isozymes and then on the molecular motor proteins that function downstream to drive MTOC movement.

Molecular mechanisms and functional implications of polarized actin remodeling at the T cell immunological synapse.

Transient,specialized cell-cell interactions play a central role in leukocyte function by enabling specific intercellular communication in the context of a highly dynamic systems level response. The dramatic structural changes required for the formation of these contacts are driven by rapid and precise cytoskeletal remodeling events. In recent years, the immunological synapse that forms between a T lymphocyte and its antigen-presenting target cell has emerged as an important model system for understanding immune cell interactions. In this review, we discuss how regulators of the cortical actin cytoskeleton control synaptic architecture and in this way specify T cell function.

Alpha E beta 7 integrin interaction with E-cadherin promotes antitumor CTL activity by triggering lytic granule polarization and exocytosis.

Various T cell adhesion molecules and their cognate receptors on target cells promote T cell receptor (TCR)-mediated cell killing. In this report, we demonstrate that the interaction of epithelial cell marker E-cadherin with integrin alpha(E)(CD103)beta(7), often expressed by tumor-infiltrating lymphocytes (TILs), plays a major role in effective tumor cell lysis. Indeed, we found that although tumor-specific CD103(+) TIL-derived cytotoxic T lymphocyte (CTL) clones are able to kill E-cadherin(+)/intercellular adhesion molecule 1(-) autologous tumor cells, CD103(-) peripheral blood lymphocyte (PBL)-derived counterparts are inefficient. This cell killing is abrogated after treatment of the TIL clones with a blocking anti-CD103 monoclonal antibody or after targeting E-cadherin in the tumor using ribonucleic acid interference. Confocal microscopy analysis also demonstrated that alpha(E)beta(7) is recruited at the immunological synapse and that its interaction with E-cadherin is required for cytolytic granule polarization and subsequent exocytosis. Moreover, we report that the CD103(-) profile, frequently observed in PBL-derived CTL clones and associated with poor cytotoxicity against the cognate tumor, is up-regulated upon TCR engagement and transforming growth factor beta1 treatment, resulting in strong potentiation of antitumor lytic function. Thus, CD8(+)/CD103(+) tumor-reactive T lymphocytes infiltrating epithelial tumors most likely play a major role in antitumor cytotoxic response through alpha(E)beta(7)-E-cadherin interactions.

Blocking common γ chain cytokine signaling ameliorates T cell-mediated pathogenesis in disease models.

The common γ chain (γc; IL-2RG) is a subunit of the interleukin (IL) receptors for the γc cytokines IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. The lack of appropriate neutralizing antibodies recognizing IL-2RG has made it difficult to thoroughly interrogate the role of γc cytokines in inflammatory and autoimmune disease settings. Here, we generated a γc cytokine receptor antibody, REGN7257, to determine whether γc cytokines might be targeted for T cell-mediated disease prevention and treatment. Biochemical, structural, and in vitro analysis showed that REGN7257 binds with high affinity to IL-2RG and potently blocks signaling of all γc cytokines. In nonhuman primates, REGN7257 efficiently suppressed T cells without affecting granulocytes, platelets, or red blood cells. Using REGN7257, we showed that γc cytokines drive T cell-mediated disease in mouse models of graft-versus-host disease (GVHD) and multiple sclerosis by affecting multiple aspects of the pathogenic response. We found that our xenogeneic GVHD mouse model recapitulates hallmarks of acute and chronic GVHD, with T cell expansion/infiltration into tissues and liver fibrosis, as well as hallmarks of immune aplastic anemia, with bone marrow aplasia and peripheral cytopenia. Our findings indicate that γc cytokines contribute to GVHD and aplastic anemia pathology by promoting these characteristic features. By demonstrating that broad inhibition of γc cytokine signaling with REGN7257 protects from immune-mediated disorders, our data provide evidence of γc cytokines as key drivers of pathogenic T cell responses, offering a potential strategy for the management of T cell-mediated diseases.

Diacylglycerol kinase α establishes T cell polarity by shaping diacylglycerol accumulation at the immunological synapse.

Polarization of the T cell microtubule-organizing center (MTOC) to the immunological synapse between the T cell and an antigen-presenting cell (APC) maintains the specificity of T cell effector responses by enabling directional secretion toward the APC. The reorientation of the MTOC is guided by a sharp gradient of the second messenger diacylglycerol (DAG), which is centered at the immunological synapse. We used a single-cell photoactivation approach to demonstrate that diacylglycerol kinase α (DGK-α), which catalyzes the conversion of DAG to phosphatidic acid, determined T cell polarity by limiting the diffusion of DAG. DGK-α-deficient T cells exhibited enlarged accumulations of DAG at the immunological synapse, as well as impaired reorientation of the MTOC. In contrast, T cells lacking the related isoform DGK-ζ did not display polarization defects. We also found that DGK-α localized preferentially to the periphery of the immunological synapse, suggesting that it constrained the area over which DAG accumulated. Phosphoinositide 3-kinase activity was required for the peripheral localization pattern of DGK-α, which suggests a link between DAG and phosphatidylinositol signaling during T cell activation. These results reveal a previously unappreciated function of DGK-α and provide insight into the mechanisms that determine lymphocyte polarity.

CD103 or LFA-1 engagement at the immune synapse between cytotoxic T cells and tumor cells promotes maturation and regulates T-cell effector functions.

T-cell adhesion/costimulatory molecules and their cognate receptors on target cells play a major role in T-cell receptor (TCR)-mediated activities. Here, we compared the involvement of CD103 and LFA-1, and their respective ligands, in the maturation of the cytotoxic immune synapse (cIS) and in the activation of CTL effector functions. Our results indicate that cytotoxicity toward cancer cells and, to a lesser extent, cytokine production by specific CTL require, together with TCR engagement, the interaction of either CD103 with E-cadherin or LFA-1 with ICAM-1. Flow-based adhesion assay showed that engagement of CD103 or LFA-1, together with TCR, enhances the strength of the T-cell/target cell interaction. Moreover, electron microscopic analyses showed that integrin-dependent mature cIS (mcIS) displays a cohesive ultrastructure, with tight membrane contacts separated by extensive clefts. In contrast, immature cIS (icIS), which is unable to trigger target cell lysis, is loose, with multiple protrusions in the effector cell membrane. Experiments using confocal microscopy revealed polarized cytokine release and degranulation at the mcIS associated with target cell killing, whereas icIS is characterized by failure of IFN-γ and granzyme B relocalization. Thus, interactive forces between CTL and epithelial tumor cells, mainly regulated by integrin engagement, correlate with maturity and the ultrastructure of the cIS and influence CTL effector functions. These results provide new insights into molecular mechanisms regulating antitumor CTL responses and may lead to the development of more efficient cancer immunotherapy strategies.

Annular PIP3 accumulation controls actin architecture and modulates cytotoxicity at the immunological synapse.

The immunological synapse formed by a T lymphocyte on the surface of a target cell contains a peripheral ring of filamentous actin (F-actin) that promotes adhesion and facilitates the directional secretion of cytokines and cytolytic factors. We show that growth and maintenance of this F-actin ring is dictated by the annular accumulation of phosphatidylinositol trisphosphate (PIP3) in the synaptic membrane. PIP3 functions in this context by recruiting the exchange factor Dock2 to the periphery of the synapse, where it drives actin polymerization through the Rho-family GTPase Rac. We also show that synaptic PIP3 is generated by class IA phosphoinositide 3-kinases that associate with T cell receptor microclusters and are activated by the GTPase Ras. Perturbations that inhibit or promote PIP3-dependent F-actin remodeling dramatically affect T cell cytotoxicity, demonstrating the functional importance of this pathway. These results reveal how T cells use lipid-based signaling to control synaptic architecture and modulate effector responses.

IL-2-dependent tuning of NK cell sensitivity for target cells is controlled by regulatory T cells.

The emergence of the adaptive immune system took a toll in the form of pathologies mediated by self-reactive cells. Regulatory T cells (T reg cells) exert a critical brake on responses of T and B lymphocytes to self- and foreign antigens. Here, we asked whether T reg cells are required to restrain NK cells, the third lymphocyte lineage, whose features combine innate and adaptive immune cell properties. Although depletion of T reg cells led to systemic fatal autoimmunity, NK cell tolerance and reactivity to strong activating self- and non-self-ligands remained largely intact. In contrast, missing-self responses were increased in the absence of T reg cells as the result of heightened IL-2 availability. We found that IL-2 rapidly boosted the capacity of NK cells to productively engage target cells and enabled NK cell responses to weak stimulation. Our results suggest that IL-2-dependent adaptive-innate lymphocyte cross talk tunes NK cell reactivity and that T reg cells restrain NK cell cytotoxicity by limiting the availability of IL-2.

Minimal engagement of CD103 on cytotoxic T lymphocytes with an E-cadherin-Fc molecule triggers lytic granule polarization via a phospholipase Cgamma-dependent pathway.

Interaction of the integrin αE(CD103)ß7 expressed on tumor-infiltrating lymphocytes (TIL) with E-cadherin on epithelial tumor cells is required to trigger polarized exocytosis of cytotoxic granules in TIL that elicit tumor cell lysis. In this study, we investigated the functional and signaling properties of CD103 and its individual contribution to T-cell-mediated cancer-cell killing. Our results indicated that the binding of CD103 on tumor-specific CTL to immobilized recombinant E-cadherin-Fc is sufficient to induce the polarization of cytolytic granules, whereas the degranulation of cytolytic granules also requires the coengagement of the T-cell receptor. Moreover, minimal CD103 triggering promotes the phosphorylation of the ERK1/2 kinases and phospholipase Cγ1 (PLCγ1). Inhibiting PLCγ blocks granule relocalization, decreasing T-cell receptor-mediated cytotoxicity. Thus, our results emphasize a unique costimulatory role of CD103 in tumor-specific CTL activation by providing signals that promote T-cell effector functions needed to specifically target and lyse cancer cells.

Intratumoral induction of CD103 triggers tumor-specific CTL function and CCR5-dependent T-cell retention.

We have reported previously that the interaction of alpha(E)(CD103)beta(7) integrin, expressed on a CD8(+) tumor-infiltrating lymphocyte (TIL) clone but not on a peripheral blood lymphocyte (PBL) counterpart, with the epithelial marker E-cadherin on human lung tumor cells plays a crucial role in T-cell receptor-mediated cytotoxicity. We show here that both TIL and PBL clones are able to migrate toward autologous tumor cells and that chemokine receptor CCR5 is involved in this process. Adoptive transfer of the PBL clone in the cognate tumor engrafted in nonobese diabetic/severe combined immunodeficient mice and subsequent coengagement of T-cell receptor and transforming growth factor-beta1 receptor triggers CD103 expression on T-cell surface resulting in strong potentiation of antitumor lytic function. Moreover, interaction of alpha(E)beta(7) integrin with E-cadherin, but not lymphocyte function-associated antigen-1 with intercellular adhesion molecule-1, promotes CCR5 recruitment at the immunologic synapse formed between TIL and tumor cells, leading to inhibition of T-cell sensitivity to CCL5 chemotactic gradient. These results provide evidence for a role of tumor microenvironment, namely MHC class I-restricted antigen presentation and transforming growth factor-beta1 secretion, in regulating the effector phase of tumor-specific CTL response. They also suggest a unique role of CD103 in T-cell retention at the tumor site by a CCR5-dependent mechanism.