STAT3 protects hematopoietic stem cells by preventing activation of a deleterious autocrine type-I interferon response

Hematopoietic stem and progenitor cells (HSPCs) maintain blood-forming and immune activity, yet intrinsic regulators of HSPCs remain elusive. STAT3 function in HSPCs has been difficult to dissect as Stat3-deficiency in the hematopoietic compartment induces systemic inflammation, which can impact HSPC activity. Here, we developed mixed bone marrow (BM) chimeric mice with inducible Stat3 deletion in 20% of the hematopoietic compartment to avoid systemic inflammation. Stat3-deficient HSPCs were significantly impaired in reconstitution ability following primary or secondary bone marrow transplantation, indicating hematopoietic stem cell (HSC) defects. Single-cell RNA sequencing of Lin-ckit+Sca1+ BM cells (LSKs) revealed aberrant activation of cell cycle, p53, and interferon (IFN) pathways in Stat3-deficient HSPCs. Stat3-deficient LSKs accumulated γH2AX and showed increased expression of DNA sensors and type-I IFN (IFN-I), while treatment with A151-ODN inhibited expression of IFN-I and IFN-responsive genes. Further, the blockade of IFN-I receptor signaling suppressed aberrant cell cycling, STAT1 activation, and nuclear p53 accumulation. Collectively, our results show that STAT3 inhibits a deleterious autocrine IFN response in HSCs to maintain long-term HSC function. These data signify the importance of ensuring therapeutic STAT3 inhibitors are targeted specifically to diseased cells to avoid off-target loss of healthy HSPCs.

NDUFS4 regulates cristae remodeling in diabetic kidney disease

The mitochondrial electron transport chain (ETC) is a highly adaptive process to meet metabolic demands of the cell, and its dysregulation has been associated with diverse clinical pathologies. However, the role and nature of impaired ETC in kidney diseases remains poorly understood. Here, we generate diabetic mice with podocyte-specific overexpression of Ndufs4, an accessory subunit of mitochondrial complex I, as a model investigate the role of ETC integrity in diabetic kidney disease (DKD). We find that conditional male mice with genetic overexpression of Ndufs4 exhibit significant improvements in cristae morphology, mitochondrial dynamics, and albuminuria. By coupling proximity labeling with super-resolution imaging, we also identify the role of cristae shaping protein STOML2 in linking NDUFS4 with improved cristae morphology. Together, we provide the evidence on the central role of NDUFS4 as a regulator of cristae remodeling and mitochondrial function in kidney podocytes. We propose that targeting NDUFS4 represents a promising approach to slow the progression of DKD.

Abstract 630: Dynamic imaging of T cell surveillance in live tumor fragments using camelid nanobodies

Immunotherapies (ITx) have revolutionized the oncology landscape. However, predicting patient responses to ITx is difficult based solely on static correlates such as TIL localization and molecular signatures. Anti-tumor immune response depends on motile surveillance by tumor infiltrating lymphocytes (TIL) which recognize antigenic determinants and engage target cells in serial stop-and-go interactions that result in cell killing. However, the hostile tumor microenvironment (TME) can cause TIL dysfunction and lack of cytotoxicity which is manifested as either suppressed or aimless TIL motility. To determine which ITx works best for a given patient, we are developing a diagnostic platform using live tumor fragments (LTF) that preserves the TME and its immune cells. Antibody-based labeling of live tissues is hampered by slow diffusion and function-altering cross-linking. To overcome these limitations, we have used small camelid-derived monovalent antibodies (nanobodies) to monitor TIL motility in LTFs. Human tumor excisions were cut into 300 x 300 x 200 µm LTFs, sorted into glass bottom multi-well plates and cultured. CD8+ cells in LTFs were labeled using an anti-hCD8a camelid VHH nanobody covalently labeled with AF594. The same reagent or a mouse anti-hCD8a whole IgG antibody was used to stain human peripheral blood mononuclear cells, and staining patterns were compared by flow cytometry. Immune responsiveness of LTFs to ITx was ascertained by flow cytometry and secreted protein assays (data shown in a companion abstract). Multiphoton microscopy revealed LTF collagen fibrils and cellular autofluorescence. A fluorescent anti-CD8a nanobody, but not a similarly labeled whole IgG, yielded good contrast and fast staining of two cell subsets. The smaller cells were 12 µm in diameter, cell surface-stained, and lacking autofluorescence, consistent with T cells. The larger cells were elongated, ramified, intracellularly stained, and distinctly autofluorescent, consistent with macrophages. 3D motility tracking revealed characteristic translational motility of the smaller cells at ~10 µm/min along collagenous structures. In contrast, larger cells exhibited only slow motility. Our results show that the motility of human CD8+ T lymphocytes can be revealed in LTF culture using a fluorescent CD8-binding camelid nanobody, likely due to its small size and monovalent binding. Further examination is needed to understand if T cell function is altered. The autofluorescence of larger, immotile cells was consistent with tumor-associated macrophages. Based on this distinction, T cells could be distinguished from the macrophages clearly. Our results support the use of camelid-derived VHH and other small monovalent reagents for live tissue lymphocyte tracking, possibly to evaluate TIL response to ITx in an LTF assay.

Citation Format: Leung Kau Tang, Kelsey Tweed, Christina Scribano, David Wahl, Christin Johnson, M. Anna Zal, Jonathan Oliner, Tomasz Zal. Dynamic imaging of T cell surveillance in live tumor fragments using camelid nanobodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 630.

Inhibition of Oxidative Phosphorylation Reverses Bone Marrow Hypoxia Visualized in Imageable Syngeneic B-ALL Mouse Model

Abnormally low level of interstitial oxygen, or hypoxia, is a hallmark of tumor microenvironment and a known promoter of cancer chemoresistance. Inside a solid tumor mass, the hypoxia stems largely from inadequate supply of oxygenated blood through sparse or misshapen tumor vasculature whilst oxygen utilization rates are low in typical tumor's glycolytic metabolism. In acute leukemias, however, markers of intracellular hypoxia such as increased pimonidazole adduct staining and HIF-1α stabilization are observed in advanced leukemic bone marrows (BM) despite an increase in BM vasculogenesis. We utilized intravital fast scanning two-photon phosphorescence lifetime imaging microscopy (FaST-PLIM) in a BCR-ABL B-ALL mouse model to image the extracellular oxygen concentrations (pO₂) in leukemic BM, and we related the extracellular oxygen levels to intracellular hypoxia, vascular markers and local leukemia burden. We observed a transient increase in BM pO₂ in initial disease stages with intermediate leukemia BM burden, which correlated with an expansion of blood-carrying vascular network in the BM. Yet, we also observed increased formation of intracellular pimonidazole adducts in leukemic BM at the same time. This intermediate stage was followed by a significant decrease of extracellular pO₂ and further increase of intracellular hypoxia as leukemia cellularity overwhelmed BM in disease end-stage. Remarkably, treatment of leukemic mice with IACS-010759, a pharmacological inhibitor of mitochondrial Complex I, substantially increased pO₂ in the BM with advanced B-ALL, and it alleviated intracellular hypoxia reported by pimonidazole staining. High rates of oxygen consumption by B-ALL cells were confirmed by Seahorse assay including in ex vivo cells. Our results suggest that B-ALL expansion in BM is associated with intense oxidative phosphorylation (OxPhos) leading to the onset of metabolic BM hypoxia despite increased BM vascularization. Targeting mitochondrial respiration may be a novel approach to counteract BM hypoxia in B-ALL and, possibly, tumor hypoxia in other OxPhos-reliant malignancies.

Merger of dynamic two-photon and phosphorescence lifetime microscopy reveals dependence of lymphocyte motility on oxygen in solid and hematological tumors

Background

Low availability of oxygen in tumors contributes to the hostility of the tumor microenvironment toward the immune system. However, the dynamic relationship between local oxygen levels and the immune surveillance of tumors by tumor infiltrating T-lymphocytes (TIL) remains unclear. This situation reflects a methodological difficulty in visualizing oxygen gradients in living tissue in a manner that is suitable for spatiotemporal quantification and contextual correlation with individual cell dynamics tracked by typical fluorescence reporter systems.

Methods

Here, we devise a regimen for intravital oxygen and cell dynamics co-imaging, termed ‘Fast’ Scanning Two-photon Phosphorescence Lifetime Imaging Microscopy (FaST-PLIM). Using FaST-PLIM, we image the cellular motility of T-lymphocytes in relation to the microscopic distribution of oxygen in mouse models of hematological and solid tumors, namely in bone marrow with or without B-cell acute lymphocytic leukemia (ALL), and in lungs with sarcoma tumors.

Results

Both in bone marrow leukemia and solid tumor models, TILs encountered regions of varying oxygen concentrations, including regions of hypoxia (defined as pO₂ below 5 mmHg), especially in advanced-stage ALL and within solid tumor cores. T cell motility was sustained and weakly correlated with local pO₂ above 5 mmHg but it was very slow in pO₂ below this level. In solid tumors, this relationship was reflected in slow migration of TIL in tumor cores compared to that in tumor margins. Remarkably, breathing 100% oxygen alleviated tumor core hypoxia and rapidly invigorated the motility of otherwise stalled tumor core TILs.

Conclusions

This study demonstrates a versatile and highly contextual FaST-PLIM method for phosphorescence lifetime-based oxygen imaging in living animal tumor immunology models. The initial results of this method application to ALL and solid lung tumor models highlight the importance of oxygen supply for the maintenance of intratumoral T cell migration, define a 5 mmHg local oxygen concentration threshold for TIL motility, and demonstrate efficacy of supplementary oxygen breathing in TIL motility enhancement coincident with reduction of tumor hypoxia.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0543-y) contains supplementary material, which is available to authorized users.

Epidermal T Cell Dendrites Serve as Conduits for Bidirectional Trafficking of Granular Cargo

Dendritic epidermal T cells (DETCs) represent a prototypical lineage of intraepithelial γδ T cells that participate in the maintenance of body barrier homeostasis. Unlike classical T cells, DETCs do not recirculate and they remain persistently activated through their T cell receptors (TCR) at steady state, i.e., in absence of infection or tissue wounding. The steady state TCR signals sustain the formation of immunological synapse-like phosphotyrosine-rich aggregates located on projections (PALPs) which act to anchor and polarize DETC’s long cellular projections toward the apical epidermis while the cell bodies reside in the basal layers. The PALPs are known to contain pre-synaptic accumulations of TCR-containing and lysosomal granules, but how this cargo accumulates there remains unclear. Here, we combined anti-Vγ5 TCR, cholera toxin subunit B (CTB), and LysoTracker (LT)-based intravital labeling of intracellular granules, with high resolution dynamic microscopy and fluorescence recovery after photobleaching (FRAP) to characterize the steady state composition and transport of DETC granules in steady state epidermis. Intradermal fluorescent Vγ5 antibody decorated DETCs without causing cellular depletion, dendrite mobilization or rounding up and became slowly internalized over 48 h into intracellular granules that, after 6 days, colocalized with LAMP-1 and less so with LT or early endosomal antigen-1. Intradermal CTB was likewise internalized predominantly by DETCs in epidermis, labeling a partly overlapping set of largely LAMP-1⁺ intracellular granules. These as well as LT-labeled granules readily moved into newly forming dendrites and accumulated at the apical endings. FRAP and spatiotemporal tracking showed that the inside tubular lengths of DETC cellular projections supported dynamic trafficking of lysosomal cargo toward and away from the PALPs, including internalized TCR and lipid raft component ganglioside GM1 (labeled with CTB). By contrast, the rate of GM1 granules transport through comparable dendrites of non-DETCs was twice slower. Our observations suggest that DETCs use chronic TCR activation to establish a polarized conduit system for long-range trans-epithelial transport aimed to accumulate mature lysosomes at the barrier-forming apical epidermis. The biological strategy behind the steady state lysosome polarization by DETCs remains to be uncovered.

Glioblastoma stem cell-derived exosomes induce M2 macrophages and PD-L1 expression on human monocytes

Exosomes can mediate a dynamic method of communication between malignancies, including those sequestered in the central nervous system and the immune system. We sought to determine whether exosomes from glioblastoma (GBM)-derived stem cells (GSCs) can induce immunosuppression. We report that GSC-derived exosomes (GDEs) have a predilection for monocytes, the precursor to macrophages. The GDEs traverse the monocyte cytoplasm, cause a reorganization of the actin cytoskeleton, and skew monocytes toward the immune suppresive M2 phenotype, including programmed death-ligand 1 (PD-L1) expression. Mass spectrometry analysis demonstrated that the GDEs contain a variety of components, including members of the signal transducer and activator of transcription 3 (STAT3) pathway that functionally mediate this immune suppressive switch. Western blot analysis revealed that upregulation of PD-L1 in GSC exosome-treated monocytes and GBM-patient-infiltrating CD14⁺ cells predominantly correlates with increased phosphorylation of STAT3, and in some cases, with phosphorylated p70S6 kinase and Erk1/2. Cumulatively, these data indicate that GDEs are secreted GBM-released factors that are potent modulators of the GBM-associated immunosuppressive microenvironment.

Visualizing the physiological self-reactivity of epidermal γδ TCR (P3280)

Dendritic epidermal T cells (DETCs) remain activated in vivo at steady state through their monomorphic Vgamma5-Vdelta1 TCR, forming phosphotyrosine-rich aggregates located on projections, called PALPs (Chodaczek et al. 2012). This recent discovery suggests the existence of beneficial self-reactivity on the part of the evolutionarily-preserved γδ TCR. Located at barrier-forming squamous keratinocyte junctions, and remarkably long-lived, the PALPs display multiple hallmarks of true immunological synapses, including TCR clustering and CD3-zeta and ZAP70 tyrosine phosphorylation. Using two independent super-resolution microscopy techniques: the structured illumination microscopy (SIM) and stimulated emission depletion (STED), we show that PALPs consist of several tens of peripherally distributed, tyrosine-phosphorylated TCR microclusters. Individual microclusters are uniformly sized at 150-160 nm and are associated with distinct signaling intermediates, suggesting that they represent supra-molecular signaling assemblies of a defined composition. Intravital fluorescence recovery after photobleaching and high speed time-lapse imaging showed that small intracellular cargo granules trafficked bi-directionally within T cell protrusions between large stationary granules and the PALPs. These studies reveal the PALPs as dynamically active TCR-activatory immunological synapses, and suggest that this novel form of physiological TCR self-reactivity mediates homeostatic secretory functions.

Abstract 4290: Visualizing immune surveillance in lung metastasis progression

As stipulated by the Paget and Fuchs’ “seed and soil” analogy, the establishment of metastases depends on the microenvironment of target tissue; as such, it also depends on the tissue immunosurveillance system. Anti-tumor immune responses are subdued in advanced tumors by various immune suppressory mechanisms, such as by tumor associated CD4 FoxP3 regulatory T-reg cells. But how immune suppression sets in at the sites of metastasis, and how it could be overcome there remains unclear. Using multiphoton and confocal microscopy, we have visualized the immune cell's dynamics that is triggered by various metastatic cancers in the lungs. We found that single, blood-carried cancer cells that settle in the capillary bed triggered strikingly rapid recruitment of CD11c dendritic cells (DCs), which were heterogeneous. Some of those DCs wrapped around the singular cancer cells while other probed their intracellular content by acquiring tumor-derived vesicles. These phagocytic DCs then carried away their cargo towards the draining lymph nodes, thereby initiating tumor antigen cross-presentation. After 24-48 hours, micrometastases became surrounded by T cells that were highly enriched in T-reg. The motility patterns and cell depletion experiments showed that T-reg largely ignored tumor cells but were attracted by the phagocytic tumor-associated DCs. In result of these interactions, the phagocytic DCs became the foci of highly dynamic three-cell interactions between T-reg and the effector T cells, sequestering most T cells at the tumor margin. In this context, we tested the impact of immunomodulatory therapies. The immune cell dynamics that we uncovered in metastases was responsive to therapeutic immune modulation aimed at the tumor-associated phagocytic DCs and also at Programmed Death (PD-1) pathways. Taken together, our intravital dynamic imaging results highlight the duality of metastasis-associated phagocytic DCs. On the one hand, these cells provide tumor antigen cross-presentation and recruit T cells to nascent secondary tumors, but on the other hand, they aid metastasis progression by promoting early on the contact of tumor-infiltrating T cells with T-reg.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4290. doi:1538-7445.AM2012-4290

Body-barrier surveillance by epidermal γδ TCRs

The surveillance of body barriers relies on resident T cells whose repertoires are biased toward particular γδ T cell antigen receptors (TCRs) according to location. These γδ TCRs can recognize ligands that emerge after stress. Through the use of intravital dynamics-immunosignal correlative microscopy, we found that γ-chain variable region 5 (V(γ)5) TCRs expressed by epidermal T cells were constitutively clustered and functionally activated in vivo at steady state, forming true immunological synapses that polarized and anchored T cell projections at squamous keratinocyte tight junctions. This synaptogenesis depended on TCR variable domains, the kinase Lck and the integrin α(E)β(7) but not the γδ lineage or the receptor NKG2D. In response to tissue stress, TCR-proximal signals did not increase substantially but underwent stress mode-dependent relocalization toward the basal epidermis and Langerhans cells. Thus, the γδ TCR orchestrates barrier surveillance proactively, presumably by recognizing tissue ligands expressed in the steady state.

Origin and Dynamics of Tumor-Associated Foxp3+ Regulatory T Cells (49.4)

Regulatory T cells (Tregs) expressing the forkhead transcription factor Foxp3 play a central role in the dominant control of immunological tolerance. Compelling evidence obtained from both animal and clinical studies have now linked the expansion and accumulation of Foxp3+ Tregs at the tumor site to the failure of immune-mediated tumor rejection. However, little is known regarding tumor-associated Foxp3+ Tregs within tumor tissues. Using both subcutaneous (s.c.) tumor and lung metastasis models of MCA-205 fibrosarcoma, we have found that tumor-associated Foxp3+ Tregs are highly activated and undergo vigorous cellular proliferation. Tumor-associated Foxp3+ Tregs were also found to be more potent functionally by in-vitro suppression assays and express higher levels of membrane-bound TGF-b1. To visualize endogenous Foxp3+ Tregs, we have generated Foxp3-GFP transgenic reporter mice by inserting GFP into a bacterial artificial chromosome (BAC) encompassing the Foxp3 locus. Using multi-photon microscopy, we observed a rapid recruitment and accumulation of Foxp3+ Tregs to the nascent lung tumor metastasis as early as 3 days after tumor inoculation. Intravital imaging of established s.c. tumors revealed a distinctive behavior of Foxp3+Tregs: the suppressor cells form a well-defined periperipheral layer encasing the tumor mass, moving rapidly within the superficial plain but not perpendicularly in and out of the tumor. Together, these data highlight that tumor-associated Foxp3+ Tregs are highly dynamic in function, behavior, and origin, perhaps contributing to overall poor immunogenicty of tumors.

Spectral shift of fluorescent dye FM4-64 reveals distinct microenvironment of nuclear envelope in living cells

We report a distinct microenvironment within the nuclear envelope (NE) in living cells revealed by a spectral shift of the fluorescent dye FM4-64 (N-(3-triethylammoniumpropyl)-4-(p-diethylaminophenylhexatrienyl)-pyridinium 2Br). The dye readily translocated to the NE at physiological temperature where it exhibited enhanced fluorescence when excited at 620-650 nm in contrast to 480-520 nm excitation in the endocytic pathway and in the endoplasmic reticulum (ER). In vitro data indicated that the dye reveals an enrichment of negatively charged lipids, presumably due to local phospholipid synthesis. Dual-excitation imaging of FM4-64 in relation to lamina-associated polypeptide-1-green fluorescent protein during mitosis suggested that the disassembly of NE preserves microscale lipid complexes in the ER. Convolutions of NE in cancer or primary cells were readily visualized, and killing of tumor cells by T cells was marked by sudden loss of the long-wavelength excited fluorescence in the NE coincident with apoptosis. This report of FM4-64 as the first vital dye sensitive to the NE environment opens new ways for real-time visualization and functional studies of the NE.

Inhibition of T cell receptor-coreceptor interactions by antagonist ligands visualized by live FRET imaging of the T-hybridoma immunological synapse

The diverse effects of TCR agonists and antagonists on T cell activation are believed to be modified by the differential recruitment of CD4 or CD8 coreceptors to the TCR-MHCp complex. We used three-dimensional live cell imaging of fluorescence resonance energy transfer (FRET) between CD3zeta and CD4 fused to variants of the green fluorescent protein to investigate TCR-CD4 interactions during T cell activation. We demonstrate that recognition of agonist MHCp complexes triggers intermolecular interaction between CD4 and TCR, detectable across the T-hybridoma-APC contact area. This interaction is blocked by the presence of antagonist ligands without decreasing the recruitment of zeta and CD4 or preventing their partial colocalization in the immunological synapse.

T cell receptor binding kinetics and special role of Valpha in T cell development and activation

The kinetics of the interaction between T cell receptor (TCR) and major histocompatibility complex (MHC) has an important role in determining thymocyte-positive and -negative selection in the thymus, as well as in T cell activation. The alpha chain of the TCR is the major player in determining how the TCR fits onto the MHC ligand, and thus has a major role in determining whether a T cell develops as class I or class II restricted. In this article, we summarize recent data from our laboratory and others on the role of polymorphism in the Valpha combining site in determining MHC class restriction, and on kinetic parameters in thymocyte selection.

Selective spectrophotometric determination of glucose and fructose in the presence of aldoses using phenol-acetone reagent and cerium(III) chloride

Aqueous mixtures of glucose and fructose produce red solutions when treated with 2% (w/v) phenol in 5% (v/v) aqueous acetone in the presence of concentrated sulfuric acid. The color is stable for days, and the red chromophore has an absorbance maximum at 568 nm. When the concentration of phenol is raised to 25%, fructose, but not glucose, produces red solutions, allowing for the selective detection of ketoses. Two complementary methods have been developed to remove the interference of ketoses in solutions containing glucose. The first one relies on the selective reduction of ketoses with sodium borohydride in the presence of cerium(III) chloride prior to the addition of the phenol-acetone reagents. The second method is based on the differential specific determination of glucose using 2% versus 25% levels of phenol. The relative sensitivities of different sugars are also presented as well as the applicability of the methods using bacterial polysaccharides for immunochemical analyses. The quantitative determination of glucose or ketoses in the polysaccharides does not require hydrolysis prior to the estimation.