A role for TASK2 channels in the human immunological synapse.

To initiate T cell-mediated immunity, dendritic cells (DCs) present antigens to T cells through the establishment of an immune synapse (IS). While events behind IS formation in T cells are well understood, the organization of IS components at the DC membrane remains ill-defined. Galectins modulate immune responses via glycan-(in)dependent interactions but the molecular mechanisms underlying their function in DC-mediated T cell activation, are poorly described. Here, we demonstrate that intracellular galectin-9 (gal9) in DCs is required for CD4+ T cell activation through its interaction with the HLA-DR alpha- and beta- cytoplasmic domains, as supported by coimmunoprecipitation, mass spectrometry, and NMR analyses. Live-cell imaging revealed gal9-depleted DCs fail to establish stable ISs with T cells, reducing T cell activation and proliferation. Notably, HLA-DR membrane lateral mobility and recruitment to the IS was diminished in DCs lacking gal9. Conditional gal9 knockout in DCs led to enhanced tumor growth in vivo, underscoring a role for gal9 in T cell-dependent antitumor immunity. Collectively, this study reports gal9-mediated HLA-DR organization at the DC synapse, uncovering a mechanism through which intracellular galectins coordinate immune receptor positioning to enhance CD4+ T cell activation.

The diffraction of light imposes a fundamental limit on the resolution of light microscopes. This limit can be circumvented by creating and exploiting independent behaviors of the sample at length scales below the diffraction limit. In super-resolution single molecule localization microscopy (SMLM), the independence arises from individual fluorescent labels stochastically switching between dark and fluorescent states, which in turn allows the pinpointing of fluorophores post experimentally using a sequence of acquired sparse image frames. Finally, the resulting list of fluorophore coordinates is utilized to produce high resolution images or to gain quantitative insight into the underlying biological structures. Therefore, image processing and post-processing are essential stages of SMLM. Here, we review the latest progress on SMLM data processing and post-processing.

Impaired Actin Polymerization Results in Defective Immunological Synapse Formation in T Cells in Chronic Lymphocytic Leukemia.

Article Figures and data Abstract eLife digest Introduction Results Discussion Materials and methods Data availability References Decision letter Author response Article and author information Metrics Abstract Supramolecular signaling assemblies are of interest for their unique signaling properties. A µm scale signaling assembly, the central supramolecular signaling cluster (cSMAC), forms at the center of the interface of T cells activated by antigen-presenting cells. We have determined that it is composed of multiple complexes of a supramolecular volume of up to 0.5 µm3 and associated with extensive membrane undulations. To determine cSMAC function, we have systematically manipulated the localization of three adaptor proteins, LAT, SLP-76, and Grb2. cSMAC localization varied between the adaptors and was diminished upon blockade of the costimulatory receptor CD28 and deficiency of the signal amplifying kinase Itk. Reconstitution of cSMAC localization restored IL-2 secretion which is a key T cell effector function as dependent on reconstitution dynamics. Our data suggest that the cSMAC enhances early signaling by facilitating signaling interactions and attenuates signaling thereafter through sequestration of a more limited set of signaling intermediates. eLife digest Cells receive dozens of signals at different times and in different places. Integrating incoming information and deciding how to respond is no easy task. Signaling molecules on the cell surface pass messages inwards using chemical messengers that interact in complicated networks within the cell. One way to unravel the complexity of these networks is to look at specific groups of signaling molecules in test tubes to see how they interact. But the interior of a living cell is a very different environment. Molecules inside cells are tightly packed and, under certain conditions, they interact with each other by the thousands. They form structures known as ‘supramolecular complexes’, which changes their behavior. One such supramolecular complex is the ‘central supramolecular activation cluster’, or cSMAC for short. It forms under the surface of immune cells called T cells when they are getting ready to fight an infection. Under the microscope, the cSMAC looks like the bullseye of a dartboard, forming a crowd of signaling molecules at the center of the interface between the T cell and another cell. Its exact role is not clear, but evidence suggests it helps to start and stop the signals that switch T cells on. The cSMAC contains two key protein adaptors called LAT and SLP-76 that help to hold the structure together. So, to find out what the cSMAC does, Clark et al. genetically modified these adaptors to gain control over when the cSMAC forms. Clark et al. examined mouse T cells using super-resolution microscopy and electron microscopy, watching as other immune cells delivered the signal to switch on. As the T cells started to activate, the composition of the cSMAC changed. In the first two minutes after the cells started activating, the cSMAC included a large number of different components. This made T cell activation more efficient, possibly because the supramolecular complex was helping the network of signals to interact. Later, the cSMAC started to lose many of these components. Separating components may have helped to stop the activation signals. Understanding how T cells activate could lead to the possibility of turning them on or off in immune-related diseases. But these findings are not just relevant to immune cells. Other cells also use supramolecular complexes to control their signaling. Investigating how these complexes change over time could help us to understand how other cell types make decisions. Introduction T cell activation is governed by spatiotemporal organization of signal transduction across scales. At the nanoscale, receptors form clusters of dozens of molecules that can coalesce into microclusters and are commonly associated with active forms of signaling intermediates (Boyle et al., 2011; Hu et al., 2016; Lillemeier et al., 2006; Schamel et al., 2005; Sherman et al., 2011; Varma et al., 2006; Yokosuka et al., 2005). This association suggests that such receptor clusters mediate efficient T cell signaling. Larger, µm scale assemblies were first described at the center and periphery of T cells activated by antigen-presenting cells (APC) for the TCR, PKCθ and LFA-1, talin, respectively, as central and peripheral supramolecular activation clusters (cSMAC and pSMAC) (Grakoui et al., 1999; Monks et al., 1998; Monks et al., 1997). µm scale of assemblies, in particular in the form of supramolecular protein complexes, provides unique biophysical and signaling properties (Banani et al., 2016; Li et al., 2012; Shin and Brangwynne, 2017). Supramolecular protein complexes play critical roles in viral sensing (Cai et al., 2014), inflammation (Franklin et al., 2014), embryonic development (Brangwynne et al., 2009), protein folding in cancer (Rodina et al., 2016), nuclear ubiquitinoylation (Marzahn et al., 2016), and chromatin compaction (Larson et al., 2017). Such complexes are readily observed by fluorescence microscopy, held together by a network of multivalent protein interactions and often have distinct phase properties (Banani et al., 2016; Li et al., 2012; Shin and Brangwynne, 2017). The cSMAC has many properties of such supramolecular protein complexes: It contains various multivalent signaling intermediates (Balagopalan et al., 2015), prominently LAT (linker of activation of T cells), components of this complex including LAT and PKCθ exchange with the remainder of the cell to a moderate extent and slowly (Roybal et al., 2015), and components of this complex can be assembled into supramolecular structures in vitro (Su et al., 2016). Therefore, understanding biophysical properties of the cSMAC and how it regulates T cell activation is of substantial importance. cSMAC function is controversial despite decades of work. Limitations in investigating the cSMAC are that its properties are largely unresolved and that its composition and/or assembly have not been systematically manipulated inside live T cells. Based on association of cSMAC formation with T cell activation conditions, the cSMAC has been proposed to enhance T cell signaling, terminate it, not be related to signaling or only upon weak stimulation or at late time points (Čemerski et al., 2008; Freiberg et al., 2002; Grakoui et al., 1999; Lee et al., 2002; Monks et al., 1997). cSMAC formation is often associated with efficient T cell activation conditions, fitting with a role in enhancing T cell signaling. Accumulation of signaling intermediates at the T cell:APC interface center is substantially reduced by blockade of the costimulatory receptor CD28 (Singleton et al., 2009; Wülfing et al., 2002), in regulatory T cells (Zanin-Zhorov et al., 2010), during thymic selection (Ebert et al., 2008), or in the absence of the signal amplifying kinase Itk (IL-2 inducible T cell kinase) (Singleton et al., 2011). To determine cSMAC properties, we have used stimulated emission depletion (STED) super-resolution microscopy and correlative light electron microscopy (CLEM). The cSMAC was composed of multiple complexes of supramolecular dimensions and associated with extensive membrane undulations. To investigate cSMAC function, we have systematically manipulated the localization of three adaptor proteins in live primary T cells: LAT (Balagopalan et al., 2015) is an integral component of the cSMAC. SLP-76 (SH2 domain-containing leucocyte protein of 76 kD) (Koretzky et al., 2006) is associated with it only during the first minute of T cell activation (Roybal et al., 2015). Grb2 (growth factor receptor-bound 2) (Jang et al., 2009) association with the cSMAC is less prevalent (Roybal et al., 2015). Interface recruitment of all three adaptors was diminished upon attenuation of T cell activation by costimulation blockade and Itk-deficiency as was IL-2 secretion, a critical T cell effector function. By fusing these adaptors with various protein domains with a strong interface localization preference we brought them back to the interface under the attenuated T cell activation conditions and restored cSMAC formation. Such restoration enhanced IL-2 secretion but only when executed to the extent and with dynamics seen under full stimulus conditions. Results μm scale LAT accumulation at the center of the T cell APC interface is associated with efficient T cell activation To investigate the function of µm scale protein accumulation at the center of the T cell:APC interface, we first cataloged protein localization events that were consistently associated with efficient T cell activation. We attenuated T cell activation through costimulation blockade (Singleton et al., 2009; Wülfing et al., 2002) and Itk deficiency. The 5C.C7 T cell receptor (TCR) recognizes the moth cytochrome C (MCC) 89–103 peptide presented by I-Ek. In the restimulation of in vitro primed 5C.C7 T cells with CH27 B cell lymphoma APCs and MCC peptide IL-2 amounts in the supernatant were reduced upon blockade of the CD28 ligands CD80 and CD86 (‘costimulation blockade’) and in T cells from Itk knock out 5C.C7 TCR transgenic mice, in particular at lower peptide concentrations (Figure 1A). As IL-2 amounts in T cell culture supernatants are determined by the difference between IL-2 generation and consumption we also determined IL-2 mRNA levels. Even at an MCC peptide concentration of 10 µM the level of IL-2 mRNA in T cells was significantly (p<0.001) reduced to less than 50% upon costimulation blockade and Itk-deficiency (Figure 1B). 10 µM MCC was used for the remainder of the study. To more precisely relate the determination of IL-2 amounts in T cell culture supernatants to IL-2 mRNA generation, we determined the time course of both (Figure 1—figure supplement 1). IL-2 mRNA generation occurred during the first six hours of T cell activation, consistent with transient nuclear localization of NFkB and previous data establishing that APC contact times of less than one hour are sufficient to commit a primed T cells to proliferation (Iezzi et al., 1998). We used IL-2 mRNA generation for the remainder of the study because of its greater sensitivity to stimulus attenuation. Figure 1 with 4 supplements see all Download asset Open asset CD28 and Itk regulate IL-2 secretion and signaling organization. (A) In vitro primed 5C.C7 T cells, wild type or Itk-deficient (‘Itk ko’), were activated by CH27 APCs and the indicated concentration of MCC peptide in the absence or presence of 10 µg/ml anti-CD80 plus anti-CD86 (‘full stimulus’ or ‘costimulation blockade’). IL-2 levels in the supernatant are given relative to stimulation of wild type 5C.C7 T cells under full stimulus conditions with 10 µM MCC with SEM. 4–8 experiments were averaged per condition. Statistical significance as determined separately for each MCC peptide concentration by 1-way ANOVA is indicated. (B) Relative levels of IL-2 mRNA are given upon 5C.C7 T cell activation similar to A with only 10 µM MCC. 3–18 experiments were averaged per condition. Statistical significance as determined by 1-way ANOVA is indicated. (C) Wild type and Itk-deficient ('Itk ko') 5C.C7 T cells expressing the indicated sensors were activated by CH27 B cell APCs (10 µM MCC) in the absence or presence of 10 µg/ml anti-CD80 plus anti-CD86 ((‘full stimulus’ or ‘costimulation blockade’) and percentage occurrence of patterns of interface enrichment (Figure 1—figure supplement 2A) is given in shades of red from −40 to 420 s relative to tight cell coupling. Cluster trees are given in pink.Sensors used and source data for panel Care given in Figure 1—figure supplements 2B–4, Figure 1—source data 1. Figure 1—source data 1 Sensors used in Figure 1C,D. Publications describing the sensors used in Figure 1C,D and representative 5C.C7 T cell imaging data are given. https://cdn.elifesciences.org/articles/45789/elife-45789-fig1-data1-v2.pdf Download elife-45789-fig1-data1-v2.pdf We characterized T cell signaling organization as extensively described before (Ambler et al., 2017; Roybal et al., 2015; Singleton et al., 2009). Briefly, in vitro primed 5C.C7 T cells are retrovirally transduced to express fluorescent signaling intermediates or sensors, FACS sorted to low expression as close as possible to endogenous signaling intermediate concentrations and imaged in three dimensions over time during restimulation with APC and 10 µM MCC peptide (‘full stimulus’). In image analysis the frequency of occurrence of geometrically quantified µm scale subcellular distributions that represent underlying cell biological structures is determined (Figure 1—figure supplement 2A) (Roybal et al., 2013). Of particular interest here are accumulation at the center of the T cell APC interface (‘central’), the cSMAC, and accumulation in a µm deep ‘invagination’ at the center of the interface that likely mediates termination of early central signaling (Singleton et al., 2006). Upon costimulation blockade most sensors that displayed frequent central accumulation upon full T cell stimulation, in particular during the first two minutes of cell coupling, did less so. In Itk-deficient 5C.C7 T cells sensors with only transient early central accumulation in wild type T cells lost much of that accumulation (Figure 1C,D; Figure 1—figure supplements 2B–4, Figure 1—source data 1). Both phenotypes are indicative of reduced cSMAC formation. Efficient IL-2 secretion thus was associated with µm scale central signaling localization. LAT as a key cSMAC component displayed µm scale central localization (Figure 2A) in a biphasic pattern. At the time of tight cell coupling under full stimulus conditions 49 ± 6% of cell couples showed central LAT accumulation. After 2 min of cell coupling central LAT accumulation was only found in about 25% of cell couples (Figure 2B) and remained stable at that level. In the absence of Itk, the initial peak of central LAT accumulation was significantly (p=0.005) diminished to 26 ± 6% of cell couples with central LAT accumulation. Such reduction was more pronounced (11 ± 4%, p<0.001) upon costimulation blockade (Figure 2B; Figure 2—source data 1). Combining costimulation blockade and Itk deficiency yielded the least interface LAT accumulation (Figure 2B). Impaired activation of cytoskeletal transport processes is a likely contributor to diminished central LAT accumulation upon costimulation blockade and Itk deficiency, as enhancement of actin dynamics with active Rac and Cofilin (Roybal et al., 2016) significantly (p<0.001, Figure 2C; Figure 2—source data 1)(Roybal et al., 2016) increased central and overall LAT accumulation. Figure 2 with 2 supplements see all Download asset Open asset LAT localization and activation is regulated by costimulation and Itk. (A) An interaction of a LAT-GFP-transduced 5C.C7 T cell with a CH27 APC (10 μM MCC) is shown at the indicated time points (in minutes) relative to the time of formation of a tight cell couple. Differential interference contrast (DIC) images are shown in the top row, with top-down, maximum projections of 3-dimensional LAT-GFP fluorescence data in the bottom row. LAT-GFP fluorescence intensities are displayed in a rainbow-like false-color scale (increasing from blue to red). The scale bar corresponds to 5 µm. A corresponding video is available as Figure 2—Video 1. (B) The graphs display the percentage of cell couples with LAT accumulation in the indicated patterns (Figure 1—figure supplement 2A, ‘periphery’ is the sum of asymmetric and peripheral) relative to tight cell couple formation for wild type or Itk-deficient 5C.C7 T cells activated with CH27 APCs (10 µM MCC) in the absence or presence of 10 µg/ml anti-CD80 plus anti-CD86 (‘costimulation blockade’) as indicated. 47–77 cell couples from 2 to 5 independent experiments were analyzed per condition, 226 total. A statistical analysis is given in Figure 2—source data 1. (C) Itk-deficient 5C.C7 T cells were activated with CH27 APCs (10 µM MCC) in the presence of 10 µg/ml anti-CD80 plus anti-CD86 and 250 nM constitutively active Cofilin plus 1 µM constitutively active Rac1 as protein transduction reagents. LAT interface accumulation is given as in B. 30 cell couples from a single experiment were analyzed. Statistical significance is given in Figure 2—source data 1. (D) 5C.C7 T cells were activated as in B for the indicated times. Band intensities of α-LAT pY191 blots (Figure 2—figure supplement 1) as normalized to the 1 min time point under full stimulus conditions are given. 5–7 experiments were averaged per condition. Statistical significance as determined separately for each time point by 1-way ANOVA is indicated. Figure 2—source data 1 Statistical significance of differences in LAT accumulation under different T cell activation conditions is given for the indicated patterns as determined by proportion’s z-test. No entry indicates p>0.05. 0.000 indicates p<0.0005. Gray scale is used to visualize the level of significance. https://cdn.elifesciences.org/articles/45789/elife-45789-fig2-data1-v2.pdf Download elife-45789-fig2-data1-v2.pdf Attenuation of T cell activation was associated with diminished LAT phosphorylation at Y191 (Figure 2D; Figure 2—source data 1) upon costimulation blockade, in particular in combination with Itk deficiency. At 2, 5, and 10 min after tight cell coupling LAT phosphorylation was significantly (p≤0.02) reduced in Itk-deficient 5C.C7 T cells upon costimulation blockade compared to wild type 5C.C7 T cells under full stimulus conditions by 39%, 61%, and 70%, respectively. The cSMAC consists of multiple complexes of supramolecular dimensions and is associated with extensive membrane undulations To determine cSMAC properties, we stained 5C.C7 T cell:CH27 B cell APC couples for LAT and LAT phosphorylated at Y191 (‘pLAT’) and imaged them using STED super-resolution microscopy (Figure 3A). Multiple LAT/pLAT complexes formed in the cSMAC and/or beyond, on average four per cell. LAT complexes were significantly larger (p=0.04) in the cSMAC region with a supramolecular volume of 0.23 ± 0.03 µm3 than in T cells without a cSMAC (0.12 ± 0.01 µm3)(Figure 3B). pLAT complexes were similarly larger in the cSMAC region with volumes of 0.25 ± 0.03 µm3 (cSMAC) versus 0.13 ± 0.01 µm3 (non-cSMAC, p=0.007)(Figure 3B). Figure 3 with 3 supplements see all Download asset Open asset The cSMAC consists of multiple smaller complexes and is associated with extensive membrane undulations. (A) Two representative STED midplane images are given of 5C.C7 T cells activated by CH27 APCs (10 µm MCC) for 4.5 min and stained with α-LAT pY191. Staining fluorescence intensity is given in rainbow-like false-color scale (increasing from blue to red). The T cell outline is given in yellow. The scale bars correspond to 1 µm. (B) For experiments as in A LAT and LAT pY191 cluster size is given separately for cell couples with central or diffuse LAT accumulation as indicated (number of cell couples analyzed in two independent experiments in parentheses). Statistical significance as determined separately for ‘LAT’ and ‘pLAT’ by Student’s test is indicated. (C) Midplane sections are given for two EM tomograms from a CLEM experiment. 5C.C7 T cells expressing LAT-GFP (top) or LAT V3-GFP (bottom)(see Figure 4B) were activated by CH27 APCs under full stimulus (top) or costimulation blocked (bottom) conditions, respectively. Upon formation of a cell couple with central LAT-GFP or LAT V3-GFP accumulation cell were fixed and processed for EM. The T cell plasma membrane at the cellular interface is traced in blue. Videos of the entire EM tomogram reconstructions are given as Figure 3—Videos 1 and 2. (D) In cell couples processed as in C membrane undulations were determined as the ratio of the length of the plasma membrane (‘length’) to a straight-line interface diameter of the same region (‘diameter) in single images of EM sections. In cell couples with central LAT-GFP (black symbols) or LAT V3-GFP (red symbols) accumulation the interface center (‘cSMAC’) and periphery (‘pSMAC’) were measured separately. Peripheral regions were measured twice per cell, once to the left and once to the right of the central region. In control cell couples without central LAT-GFP (black symbols) or LAT V3-GFP (red symbols) accumulation (‘no the entire interface was analyzed. couples are from two independent experiments per condition. Statistical significance as determined by 1-way ANOVA is indicated To understand how LAT as a protein could the formation of multiple supramolecular complexes, we related cSMAC formation to plasma membrane with CLEM (Figure Figure supplement 1). live cell imaging of 5C.C7 T cells activated by CH27 B cell APCs we fixed upon of central LAT and processed them for electron microscopy We used two conditions, a full stimulus and activation of 5C.C7 T cells expressing a protein of LAT with the PKCθ upon costimulation blockade as an to enhanced cSMAC formation upon attenuation of T cell activation, as in in the In EM sections we measured the extent of membrane undulations in cSMAC and interface regions as the ratio of the plasma membrane length to the straight-line diameter of the region. This ratio was significantly (p<0.001) larger in the cSMAC ± than in the of the same T cell ± In control cell couples without cSMAC formation the ratio as measured across the entire interface was as ± as that in regions of cell couples with central LAT (Figure The data are consistent with diminished membrane undulations in 5C.C7 T cells upon costimulation blockade with a ratio of ± (Roybal et al., 2016). The cSMAC thus is a cellular region membrane undulations and multiple supramolecular complexes are associated with enhanced of signaling intermediates. To the for cSMAC in the remainder of these we used microscopy to determine central protein accumulation as a of cSMAC formation. of LAT with protein domains with pronounced interface localization preference LAT localization To determine cSMAC function, we to its formation upon costimulation blockade and in Itk-deficient T cells. To we to how cSMAC components interact within the a supramolecular complex could function through formation of protein interactions or by enhancing signaling through complex formation such that the same proteins can be assembled using and protein interaction of the large number of cSMAC components of which are (Figure 1) we the as most Impaired cSMAC formation upon costimulation blockade and Itk-deficiency at least in be by a reduction in the number of protein interaction that is the of key components such as LAT as by diminished phosphorylation (Figure We be to cSMAC formation by enhancing through the of protein interaction this and protein interaction the live cell signaling through the formation of the central region of increased protein be We increased LAT by three protein PKCθ or The PKCθ is for central interface accumulation of PKCθ et al., it central localization by (Figure supplement 1A). The domains strong central accumulation only within the first minute of cell coupling (Figure supplement as consistent with the localization of full length (Figure 1—figure supplement The interface accumulation on the first two minutes of cell coupling without a central preference (Figure supplement 1A). the of protein interaction domains to LAT is to their initial experiments to this remained as in the expression of LAT and the three LAT proteins was by FACS for the same level of proteins were at ± the endogenous level of LAT in T cells (Figure supplement with change to endogenous LAT levels in the transduced T cells. of LAT to the PKCθ yielded efficient central accumulation that was over the entire imaging time under all conditions at levels 50% of cell couples with central accumulation (Figure s after tight cell coupling such central accumulation was significantly Figure data 1) more frequent than central accumulation of LAT under full stimulus at time of LAT to the PKCθ thus central LAT accumulation the levels seen for LAT under condition. in formed upon LAT expression membrane undulations were similarly enhanced as in T cells expressing LAT (Figure cSMAC properties. Figure 4 with 4 supplements see all Download asset Open asset LAT localization can be by with protein domains with a strong interface localization (A) A of LAT-GFP is given (top) with LAT accumulation data under full stimulus conditions from Figure 2B) as a for the of the (B) top are given for the three proteins of LAT with protein localization domains as indicated. imaging data are given in the wild type or Itk-deficient 5C.C7 T cells transduced to express the LAT indicated on the top of the were activated with CH27 APCs (10 µM MCC) in the absence or presence of 10 µg/ml anti-CD80 plus anti-CD86 (‘costimulation blockade’) with different T cell activation conditions given in as indicated. the percentage of cell couples that displayed accumulation of the LAT with the indicated patterns as in Figure relative to tight cell couple formation in and red accumulation of LAT-GFP in or the central interface respectively, under the same T cell activation conditions Figure 2B) for For costimulation blocked conditions representative imaging data are given similar to Figure are available as Figure cell couples from 2 to 5 independent experiments were analyzed per condition, total. Statistical analysis is given in Figure data 1. Figure data 1 Statistical significance of differences in accumulation of as compared to LAT under different T cell activation conditions is given for the indicated patterns as determined by proportion’s z-test. No entry indicates p>0.05. 0.000 indicates p<0.0005. Gray scale is used to visualize the level of significance. Download of LAT to the domains yielded different on the T cell activation conditions. Upon a full T cell stimulus LAT in diminished central and overall accumulation compared to LAT that was across many time points (Figure Figure data that LAT not enhance assembled signaling Upon the three attenuated LAT consistently enhanced central most at most time for costimulation blockade in wild type and Itk cells (Figure Figure data 1). LAT accumulation upon attenuated T cell stimulation in was largely from LAT accumulation under full stimulus conditions Figure data 1) and central accumulation was enhanced only between 1 and 3 min after tight cell coupling. of LAT to the thus for close reconstitution of full LAT localization upon attenuated T cell of LAT to the LAT but was less (Figure Figure data 1). Upon the three attenuated T cell LAT enhanced central and overall LAT accumulation but consistently the same extent as LAT under full stimulus conditions. For in Itk-deficient 5C.C7 T cells upon costimulation blockade interface accumulation in was consistently enhanced for time point and from upon expression of LAT accumulation at the interface center only increased from a of to To that overall interface accumulation of the LAT

Innate immune cells recognize and elicit responses against pathogens by integrating signals from different types of cell-surface receptors. How the receptors interact in the membrane to enable their signaling crosstalk is poorly understood. Here, we reveal the nanoscale organization of TLR2 and Dectin-1, a receptor pair known to cooperate in regulating antifungal immunity, through their synergistic signaling crosstalk at macrophage cell membranes. Using super-resolution single-molecule localization microscopy, we show that discrete noncolocalized nanoclusters of Dectin-1 and TLR2 are partially overlapped during their synergistic crosstalk. Compared to when one type of receptor is activated alone, the simultaneous activation of Dectin-1 and TLR2 leads to a higher percentage of both receptors being activated by their specific ligands and consequently an increased level of tyrosine phosphorylation. Our results depict, in nanoscale detail, how Dectin-1 and TLR2 achieve synergistic signaling through the spatial organization of their receptor nanoclusters.

392. Super-Resolution (STED) Imaging Reveals Simultaneous Co-Docking of Tandem Chimeric Antigen Receptors to Two Target Antigens Enhancing T Cell Functionality and Mitigating Antigen Escape

Background: In anti-tumor immunity, T cells play a central role to eliminate cancer cells. Immune responses of T cells are initiated by communication with antigen presenting cells (APCs). It became clear that an immunological synapse (IS) is formed at the T cell-APC interface and is made up of a supramolecular activation cluster (SMAC) containing the T cell receptors (TCR) microclusters (MCs) and CD28 MCs. TCR MCs consist of TCR, kinases, and adaptor molecules, and are the minimal unit of T cell signal transduction. CD28 MCs also function as the signalosomes of CD28 activation. By using total internal reflection fluorescence microscopy to observe the interaction of T cell and planar bilayer, it was elucidated that TCR activation is regulated by the amount of MCs aggregation, which shows the extent of IS formation. Based on this finding, we hypothesized that ex vivo T cells could be examined IS formation and that exhausted T cells of advanced cancer patients should be low in response to a stimulus. Method: To simplify IS formation of T cells, we used human monoclonal T cells by αCD3 and/or αCD28 antibody and replaced to evaluate the aggregation of MCs by detecting the CD3 or CD28 molecules on the surface of T cells. This phenomenon was defined as IS-like formation. In this method, IS-like formation was detected by confirming an image of each cell with imaging cytometry. After these conditions was established, it was verified whether it is possible to measure IS-like formation rate of T cells. Additionally, the correlation between IS-like formation and interferon-γ cytokine production after this activation was examined. In the same manner as above, IS - like formation rates of T cells derived from PBMCs of healthy donors or esophageal and gastric cancer patients were measured. Result: We have succeeded in observing that CD3 or CD28 molecules on a T cell aggregated in one area after stimulation as IS-like formation by imaging cytometry. In dot plot study, positive area of CD3 or CD28 decreased after the stimulation, which showed the aggregation of these molecules. Accordingly, we could measure IS-like formation rate of a population of T cell clones. In addition, the rate of IS-like formation showed a positive correlation with interferon-γ production. Similar results were obtained T cell from PBMC in healthy donors. Moreover, IS-like formation rate of T cell from cancer patients decreased compared with healthy donors. Conclusion: IS-like formation of T cell succeeded to observe by CD3 and/or CD28 antibody stimulation. We established the evaluation method of IS-like formation degree by imaging cytometry. Moreover, IS-like formation rate correlated with cytokine production of IFN-g. We established new method to evaluate the strength of T cell after activation. Citation Format: Tomoko Tanaka, Kimihiro Yamashita, Yutaka Sugita, Eiji Fukuoka, Akira Arimoto, Yoshihiro Kakeji. A new method for evaluating T cell response after stimulation on gastrointestinal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5699.

Description Signal-Transducing Adaptor Protein-1 (STAP-1) is an adaptor protein that contains pleckstrin and Src homology-2 domains, specifically expressed in immune cells such as T cells. Therefore, we hypothesized that STAP-1 plays some roles in T cell functions and analyzed the role of STAP-1 in human/murine T cells. STAP-1 deficiency downregulated T cell activation, determined by impaired TCR-mediated phosphorylation of downstream molecules, IL-2 production and cell proliferation both in human cells and murine CD4+ T cells. In molecular analysis, we found that STAP-1 plays a critical role for T cell activation by interacting with LCK and PLC-γ1 as a scaffold upon TCR engagement. Furthermore, STAP-1 KO mice exhibited lower pathogenesis in experimental autoimmune encephalomyelitis (EAE) by downregulating the activation of Th1 and Th17, as well as infiltration of these cells into CNS. Conversely, STAP-1 overexpression promotes T cell activation in vitro, as well as pathogenesis of EAE in vivo. Taken together, we hypothesized that pharmacological inhibition of STAP-1-LCK binding can be a new therapeutic target of T cell-mediated autoimmune diseases. Therefore, we generated STAP-1-derived peptide which inhibits STAP-1-LCK binding. STAP-1 inhibitor successfully suppressed TCR-mediated T cell activation both in human and murine T cells. Our findings indicate that STAP-1 is a key regulator of T cells and is a promising target of T cell-mediated autoimmune and inflammatory diseases. Funding Sources Supported by Japan Society for the Promotion of Science Grants- in-Aid for Scientific Research 19H03364,16K09872,21K08451 and Japan Agency for Medical Research and Development Grant 23ym0126801j0002 through the Translational Research Program, Strategic Promotion for Practical Application of Innovative Medical Technology. Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)

Defense from infection or cancer is provided by coordinated actions of the innate and adaptive immune system, including B lymphocytes that generate antibodies (Abs) against pathogens or tumor antigens. B cells establish immune synapses with antigen-presenting cells during activation to initiate Ab-production, which may include entrance into a germinal center (GC) reaction to generate very high-affinity Abs. Establishment of an immune synapse requires polarity proteins to coordinate uptake and processing of external antigens. For this, there is a highly conserved family of partitioning defective (Par) proteins that mediates cell polarity in multiple cell types. In particular, Par-3, a member of the Par polarity complex (Par-3, aPKC, Par-6), is a key protein that localizes to the immune synapse and is required for B cell polarization and immune synapse formation. Recently, we showed that LKB1, the mammalian homolog of Par-4 and a regulator of energy metabolism, controls B cell activation, GC formation and differentiation into Ab-producing plasma cells. However, roles for LKB1 in B cell polarity, immune synapse formation and anti-tumor immunity are unknown. Based on previous studies showing that LKB1 induces cell polarity and co-localizes with Par-3, we hypothesize that LKB1 is required for Par complex assembly and controls immune synapse formation during B cell activation. Subcellular analysis of LKB1 by immunofluorescence microscopy in mouse primary B cells reveals LKB1 co-localization with aPKC in membrane protrusions required for immune synapse formation. Interestingly, B cell specific LKB1 knock out (BKO) mice exhibit mislocalization of aPKC/Par complex, loss of lymphoid tissue polarity and spontaneous B cell activation that results in the formation of giant GCs and secretion of proinflammatory cytokines and chemokines. Similar inflammatory profiles with T cell chemoattractants are known to recruit CD8+ cytotoxic T lymphocytes (CTLs) into solid tumors, such as melanoma. These similarities suggest that LKB1 inactivated B cells in the tumor microenvironment could stimulate T cell infiltrates into solid tumors. Our studies suggest that physiologic inactivation of LKB1 in B cells controls B cell activation, GC formation and potentially infiltration of T cells in the tumor microenvironment during anti-tumor responses. We are currently utilizing an exciting genetic mouse melanoma model to examine the role of LKB1 in promoting anti-tumor immunity. Together, our studies assess LKB1 as a target for augmenting adaptive immunity against cancer. Citation Format: Laura Jimenez, Lynnea Waters, Diane N.H. Kim, Nicole Walsh, Michael A. Teitell. Roles for LKB1 at the immune synapse during B-cell activation and antitumor responses [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr B46.

T cell activation and function require physical contact with antigen presenting cells at a specialized junctional structure known as the immunological synapse. Once formed, the immunological synapse leads to sustained T cell receptor-mediated signalling and stabilized adhesion. High resolution microscopy indeed had a great impact in understanding the function and dynamic structure of immunological synapse. Trends of recent research are now moving towards understanding the mechanical part of immune system, expanding our knowledge in mechanosensitivity, force generation, and biophysics of cell-cell interaction. Actin cytoskeleton plays inevitable role in adaptive immune system, allowing it to bear dynamic and precise characteristics at the same time. The regulation of mechanical engine seems very complicated and overlapping, but it enables cells to be very sensitive to external signals such as surface rigidity. In this review, we focus on actin regulators and how immune cells regulate dynamic actin rearrangement process to drive the formation of immunological synapse.

The immunological synapse (IS) is an intercellular communication platform, organized at the contact site of two adjacent cells, where at least one is an immune cell. Functional IS formation is fundamental for the modulation of the most relevant immune system activities, such as T cell activation by antigen presenting cells and T cell/natural killer (NK) cell-mediated target cell (infected or cancer) killing. Extensive evidence suggests that connexins, in particular connexin-43 (Cx43) hemichannels and/or gap junctions, regulate signaling events in different types of IS. Although the underlying mechanisms are not fully understood, the current evidence suggests that Cx43 channels could act as facilitators for calcium ions, cyclic adenosine monophosphate, and/or adenosine triphosphate uptake and/or release at the interface of interacting cells. These second messengers have relevant roles in the IS signaling during dendritic cell-mediated T and NK cell activation, regulatory T cell-mediated immune suppression, and cytotoxic T lymphocyte or NK cell-mediated target tumor cell killing. Additionally, as the cytoplasmic C-terminus domain of Cx43 interacts with a plethora of proteins, Cx43 may act as scaffolds for integration of various regulatory proteins at the IS, as suggested by the high number of Cx43-interacting proteins that translocate at these cell-cell interface domains. In this review, we provide an updated overview and analysis on the role and possible underlying mechanisms of Cx43 in IS signaling.

Although tens of immune synapse (IS) protein species are known, there remain many unknown IS-localized protein species. Understanding the proteome of the IS between a target cell and a lymphocyte is crucial for advancing immuno-oncology. The low abundance of ISs and the lack of a definitive enrichment marker have limited efficient proteomic profiling. Here, we used Microscoop™, an innovative system that integrates microscopy, machine learning, and targeted photo-biotinylation to enable precise and spatially specific enrichment of IS proteins, thereby facilitating proteomic discovery of the IS. We utilized Raji B cells as antigen-presenting cells (APCs) and induced IS formation with Jurkat T cells. The system first employed immunofluorescence imaging of CD3, a common IS marker in Jurkat T cells, and used a convolutional neural network-based deep learning algorithm to train the recognition of ISs from CMTPX-stained Raji B cells. Our automated system then successfully achieved spatially-targeted biotin-tagging of proteins at ISs through thousands of fields of view of imaging, deep learning-driven pattern generation, and photochemical labeling. Subsequent streptavidin pull-down and mass spectrometry analysis enabled the identification of IS-specific proteins. Remarkably, our spatial proteomic approach led to the isolation and identification of hundreds of different species at the IS interface, including proteins associated with key components of T-cell receptor (TCR) signaling pathways such as the TCR/CD3 complex, Src and Tec family tyrosine kinases, and pivotal NF-kB signaling proteins. Beyond these, we also identified a significant enrichment of proteins not previously associated with the IS. Our study not only illuminates previously unknown aspects of immune regulation at the IS interface, but also shedded light on proteins potentially important for immuno-oncology. These insights have significant implications for cancer research, particularly in understanding and manipulating immune responses for therapeutic purposes. Citation Format: Weng-Man Chong, Cecile Li, Chun-Kai Huang, Chantal Hoi Yin Cheung, Hsiao-Jen Chang, Chia-Wen Chung, Jung-Chi Liao. Identification of the novel immune synapse-localized proteome for immuno-oncology using Microscoop-induced targeted photo-biotinylation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1043.

The antigen specific immune response is initiated by molecular interactions in the nanometer scale gap between the T cell and antigen-presenting cell (APC). This specialized cell-cell junction has been aptly described as an immunological synapse (Norcross, 1984; Paul and Seder, 1994). The immunological synapse is the site of key signaling events that set thresholds for T cell activation. If these thresholds are appropriately set the T cell is defended against a wide array of pathogens and toxins. If these thresholds are incorrectly set the host is susceptible to pathogen escape, at one extreme, and destructive autoimmunity at the other extreme. The immunological synapse is the site of a sensitive molecular search where as few as 10-100 agonist MHC-peptide complexes are sufficient to activate a T cell (Peterson, et al., 1999). The immunological synapse is also the product of an extensive cellular search that brings the T cell and APC together in the secondary lymphoid tissues. The interaction of T cells agonist MHCpeptide complexes on an appropriate surface generates a robust stop signal (Dustin, et al., 1997; Dustin, et al., 1996; Negulescu, et al., 1996). The common characteristic of the stop signal is that the TCR signal appears to control the polarity of the T cell cytoskeleton and maintains a balance of integrin mediated traction forces to hold the T cell in place-an apparently delicate balance (Dustin, et al., 1997). Subsequent studies on the molecular interactions in the immunological synapse reveal a complex signaling landscape in which molecular topology and dynamic assemblies of cytoskeletal molecules and adhesion molecules create distinct supramolecular activation clusters (SMACs) in a bull’s eye pattern (Grakoui, et al., 1999;Monks, et al., 1998). The T cell receptor (TCR) and CD28 occupy the center of the bull’s eye, whereas the adhesion molecules LFA-1 and CD2 occupy the surrounding ring (Bromley, et al., 2001; Grakoui, et al., 1999; Monks, et al., 1998). The immunological synapse is formed through a distinct intermediate in which the6.KeywordsStop SignalImmunological SynapseCD28 EngagementImmunological Synapse FormationAntigen Induce Cell DeathThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The T cell integrin receptor LFA-1 orchestrates adhesion between T cells and antigen-presenting cells (APCs), resulting in formation of a contact zone known as the immune synapse (IS) which is supported by the cytoskeleton. L-plastin is a leukocyte-specific actin bundling protein that rapidly redistributes to the immune synapse following T cell-APC engagement. We used single domain antibodies (nanobodies, derived from camelid heavy-chain only antibodies) directed against functional and structural modules of L-plastin to investigate its contribution to formation of an immune synapse between Raji cells and human peripheral blood mononuclear cells or Jurkat T cells. Nanobodies that interact either with the EF hands or the actin binding domains of L-plastin both trapped L-plastin in an inactive conformation, causing perturbation of IS formation, MTOC docking towards the plasma membrane, T cell proliferation and IL-2 secretion. Both nanobodies delayed Ser(5) phosphorylation of L-plastin which is required for enhanced bundling activity. Moreover, one nanobody delayed LFA-1 phosphorylation, reduced the association between LFA-1 and L-plastin and prevented LFA-1 enrichment at the IS. Our findings reveal subtle mechanistic details that are difficult to attain by conventional means and show that L-plastin contributes to immune synapse formation at distinct echelons.

CRAC channels have a vital role in the activation of T lymphocytes, through their calcium influx. CRAC is composed of the ER-membrane resident STIM1 (stromal interaction molecule 1) and the plasma membrane Orai1 pore-forming subunit. Both are accumulated at the interface of the immunological synapse (IS) between a T cell and an antigen-presenting cell (APC). CRAC channelopathies due to mutations in either Orai1 or STIM1 are characterized by severe combined immunodeficiency (SCID)-like disease, autoimmunity, muscular hypotonia, and ectodermal dysplasia. The down-regulation of actin-binding protein expression (e.g. HS1), which may be responsible for the immobilization of ion channels, hampers Ca2+-signaling and IS formation of T lymphocytes. We hypothesized that actin-binding proteins modulate the trafficking of the CRAC channels to the IS, which is crucial for the Ca2+-signaling. By means of GST-affinity assay we could show that HS1, which is an actin-regulatory adaptor protein, binds to the N-terminus of the Orai1. N-terminal truncated Orai1 channels (ΔN1: 1–74, ΔN2: 1–88) were created and expressed in Jurkat cells. Then Orai1 channel expressing Jurkat cells were conjugated to CD3/CD28 beads as an APC and Orai1 polarization was determined: the Orai1-ΔN1 mutant similar to the wild-type Orai1 redistributed to the IS but the Orai1-ΔN2 did not. Furthermore, the HS1 protein did not show IS-accumulation in cells expressing the Orai1-ΔN2 subunits unlike for those transfected with the Orai1-ΔN1 or the wild-type constructs. Overall, these data indicate that Orai1-HS1 interaction could contribute to the anchoring of the Orai1 in the IS and can affect the Ca2+-signaling upon T cell activation.