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.

Mitophagy Promotes Resistance to BH3 Mimetics in Acute Myeloid Leukemia.

BH3 mimetics are used as an efficient strategy to induce cell death in several blood malignancies, including acute myeloid leukemia (AML). Venetoclax, a potent BCL-2 antagonist, is used clinically in combination with hypomethylating agents for the treatment of AML. Moreover, MCL1 or dual BCL-2/BCL-xL antagonists are under investigation. Yet, resistance to single or combinatorial BH3-mimetic therapies eventually ensues. Integration of multiple genome-wide CRISPR/Cas9 screens revealed that loss of mitophagy modulators sensitizes AML cells to various BH3 mimetics targeting different BCL-2 family members. One such regulator is MFN2, whose protein levels positively correlate with drug resistance in patients with AML. MFN2 overexpression is sufficient to drive resistance to BH3 mimetics in AML. Insensitivity to BH3 mimetics is accompanied by enhanced mitochondria-endoplasmic reticulum interactions and augmented mitophagy flux, which acts as a prosurvival mechanism to eliminate mitochondrial damage. Genetic or pharmacologic MFN2 targeting synergizes with BH3 mimetics by impairing mitochondrial clearance and enhancing apoptosis in AML. SIGNIFICANCE: AML remains one of the most difficult-to-treat blood cancers. BH3 mimetics represent a promising therapeutic approach to eliminate AML blasts by activating the apoptotic pathway. Enhanced mitochondrial clearance drives resistance to BH3 mimetics and predicts poor prognosis. Reverting excessive mitophagy can halt BH3-mimetic resistance in AML. This article is highlighted in the In This Issue feature, p. 1501.

STAT3 protects HSCs from intrinsic interferon signaling and loss of long-term blood-forming activity.

STAT3 function in hematopoietic stem and progenitor cells (HSPCs) has been difficult to discern as Stat3 deficiency in the hematopoietic system induces systemic inflammation, which can impact HSPC activity. To address this, we established mixed bone marrow (BM) chimeric mice with CreER-mediated Stat3 deletion in 20% of the hematopoietic compartment. Stat3-deficient HSPCs had impaired hematopoietic activity and failed to undergo expansion in BM in contrast to Stat3-sufficient (CreER) controls. Single-cell RNA sequencing of Lin-ckit+Sca1+ BM cells revealed altered transcriptional responses in Stat3-deficient hematopoietic stem cells (HSCs) and multipotent progenitors, including intrinsic activation of cell cycle, stress response, and interferon signaling pathways. Consistent with their deregulation, Stat3-deficient Lin-ckit+Sca1+ cells accumulated γH2AX over time. Following secondary BM transplantation, Stat3-deficient HSPCs failed to reconstitute peripheral blood effectively, indicating a severe functional defect in the HSC compartment. Our results reveal essential roles for STAT3 in HSCs and suggest the potential for using targeted synthetic lethal approaches with STAT3 inhibition to remove defective or diseased HSPCs.

Detecting Förster resonance energy transfer in living cells by conventional and spectral flow cytometry.

Assays based on Förster resonance energy transfer (FRET) can be used to study many processes in cell biology. Although this is most often done with microscopy for fluorescence detection, we report two ways to measure FRET in living cells by flow cytometry. Using a conventional flow cytometer and the "3-cube method" for intensity-based calculation of FRET efficiency, we measured the enzymatic activity of specific kinases in cells expressing a genetically-encoded reporter. For both AKT and protein kinase A, the method measured kinase activity in time-course, dose-response, and kinetic assays. Using the Cytek Aurora spectral flow cytometer, which applies linear unmixing to emission measured in multiple wavelength ranges, FRET from the same reporters was measured with greater single-cell precision, in real time and in the presence of other fluorophores. Results from gene-knockout studies suggested that spectral flow cytometry might enable the sorting of cells on the basis of FRET. The methods we present provide convenient and flexible options for using FRET with flow cytometry in studies of cell biology.

Fate of Antibody-Targeted Ultrasmall Gold Nanoparticles in Cancer Cells after Receptor-Mediated Uptake.

Nanoparticles with ultrasmall sizes (less than 10 nm) offer many advantages in biomedical applications compared to their bigger counterparts, including better intratumoral distribution, improved pharmacokinetics (PK), and efficient body clearance. When functionalized with a biocompatible coating and a target-specific antibody, ultrasmall nanoparticles represent an attractive clinical translation platform. Although there is a tremendous body of work dedicated to PK and the biological effects of various nanoparticles, little is known about the fate of different components of functionalized nanoparticles in a biological environment such as in live cells. Here, we used luminescence properties of 5 nm gold nanoparticles (AuNPs) to study the intracellular trafficking and fate of the AuNPs functionalized with an organic layer consisting of a polyethylene glycol (PEG) coating and epidermal growth factor receptor (EGFR)-targeting antibody. We showed that intracellular uptake of the targeted 5 nm AuNPs results in a strong two-photon luminescence (TPL) that is characterized by broad emission and very short lifetimes compared to the fluorescence of the nanoparticle-conjugated fluorophore-tagged antibody, thereby allowing selective imaging of these components using TPL and two-photon excited fluorescence lifetime microscopy (2P-FLIM). Our results indicate that the nanoparticle's coating is detached from the particle's surface inside cells, leading to formation of nanoparticle clusters with a strong TPL. Furthermore, we observed an optically resolved spatial separation of the gold core and the antibody coating of the particles inside cells. We used data from two-photon microscopy, 2P-FLIM, electron microscopy, and in vitro assays to propose a model of interactions of functionalized 5 nm AuNPs with live cells.

Telomerase Reverse Transcriptase Preserves Neuron Survival and Cognition in Alzheimer's Disease Models.

Amyloid-induced neurodegeneration plays a central role in Alzheimer's disease (AD) pathogenesis. Here, we show that telomerase reverse transcriptase (TERT) haploinsufficiency decreases BDNF and increases amyloid-ß (Aß) precursor in murine brain. Moreover, prior to disease onset, the TERT locus sustains accumulation of repressive epigenetic marks in murine and human AD neurons, implicating TERT repression in amyloid-induced neurodegeneration. To test the impact of sustained TERT expression on AD pathobiology, AD mouse models were engineered to maintain physiological levels of TERT in adult neurons, resulting in reduced Aß accumulation, improved spine morphology, and preserved cognitive function. Mechanistically, integrated profiling revealed that TERT interacts with ß-catenin and RNA polymerase II at gene promoters and upregulates gene networks governing synaptic signaling and learning processes. These TERT-directed transcriptional activities do not require its catalytic activity nor telomerase RNA. These findings provide genetic proof-of-concept for somatic TERT gene activation therapy in attenuating AD progression including cognitive decline.

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.

Targeted hypoxia reduction restores T cell infiltration and sensitizes prostate cancer to immunotherapy.

Despite the success of immune checkpoint blockade against melanoma, many "cold" tumors like prostate cancer remain unresponsive. We found that hypoxic zones were prevalent across preclinical prostate cancer and resisted T cell infiltration even in the context of CTLA-4 and PD-1 blockade. We demonstrated that the hypoxia-activated prodrug TH-302 reduces or eliminates hypoxia in these tumors. Combination therapy with this hypoxia-prodrug and checkpoint blockade cooperated to cure more than 80% of tumors in the transgenic adenocarcinoma of the mouse prostate-derived (TRAMP-derived) TRAMP-C2 model. Immunofluorescence imaging showed that TH-302 drives an influx of T cells into hypoxic zones, which were expanded by checkpoint blockade. Further, combination therapy reduced myeloid-derived suppressor cell density by more than 50%, and durably reduced the capacity of the tumor to replenish the granulocytic subset. Spontaneous prostate tumors in TRAMP transgenic mice, which completely resist checkpoint blockade, showed minimal adenocarcinoma tumor burden at 36 weeks of age and no evidence of neuroendocrine tumors with combination therapy. Survival of Pb-Cre4, Ptenpc-/-Smad4pc-/- mice with aggressive prostate adenocarcinoma was also significantly extended by this combination of hypoxia-prodrug and checkpoint blockade. Hypoxia disruption and T cell checkpoint blockade may sensitize some of the most therapeutically resistant cancers to immunotherapy.

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.

Tonic B-cell receptor signaling in diffuse large B-cell lymphoma.

We used clustered regularly interspaced short palindromic repeats/Cas9-mediated genomic modification to investigate B-cell receptor (BCR) signaling in cell lines of diffuse large B-cell lymphoma (DLBCL). Three manipulations that altered BCR genes without affecting surface BCR levels showed that BCR signaling differs between the germinal center B-cell (GCB) subtype, which is insensitive to Bruton tyrosine kinase inhibition by ibrutinib, and the activated B-cell (ABC) subtype. Replacing antigen-binding BCR regions had no effect on BCR signaling in GCB-DLBCL lines, reflecting this subtype's exclusive use of tonic BCR signaling. Conversely, Y188F mutation in the immunoreceptor tyrosine-based activation motif of CD79A inhibited tonic BCR signaling in GCB-DLBCL lines but did not affect their calcium flux after BCR cross-linking or the proliferation of otherwise-unmodified ABC-DLBCL lines. CD79A-GFP fusion showed BCR clustering or diffuse distribution, respectively, in lines of ABC and GCB subtypes. Tonic BCR signaling acts principally to activate AKT, and forced activation of AKT rescued GCB-DLBCL lines from knockout (KO) of the BCR or 2 mediators of tonic BCR signaling, SYK and CD19. The magnitude and importance of tonic BCR signaling to proliferation and size of GCB-DLBCL lines, shown by the effect of BCR KO, was highly variable; in contrast, pan-AKT KO was uniformly toxic. This discrepancy was explained by finding that BCR KO-induced changes in AKT activity (measured by gene expression, CXCR4 level, and a fluorescent reporter) correlated with changes in proliferation and with baseline BCR surface density. PTEN protein expression and BCR surface density may influence clinical response to therapeutic inhibition of tonic BCR signaling in DLBCL.

Epithelial-to-mesenchymal transition drives a pro-metastatic Golgi compaction process through scaffolding protein PAQR11.

Tumor cells gain metastatic capacity through a Golgi phosphoprotein 3-dependent (GOLPH3-dependent) Golgi membrane dispersal process that drives the budding and transport of secretory vesicles. Whether Golgi dispersal underlies the pro-metastatic vesicular trafficking that is associated with epithelial-to-mesenchymal transition (EMT) remains unclear. Here, we have shown that, rather than causing Golgi dispersal, EMT led to the formation of compact Golgi organelles with improved ribbon linking and cisternal stacking. Ectopic expression of the EMT-activating transcription factor ZEB1 stimulated Golgi compaction and relieved microRNA-mediated repression of the Golgi scaffolding protein PAQR11. Depletion of PAQR11 dispersed Golgi organelles and impaired anterograde vesicle transport to the plasma membrane as well as retrograde vesicle tethering to the Golgi. The N-terminal scaffolding domain of PAQR11 was associated with key regulators of Golgi compaction and vesicle transport in pull-down assays and was required to reconstitute Golgi compaction in PAQR11-deficient tumor cells. Finally, high PAQR11 levels were correlated with EMT and shorter survival in human cancers, and PAQR11 was found to be essential for tumor cell migration and metastasis in EMT-driven lung adenocarcinoma models. We conclude that EMT initiates a PAQR11-mediated Golgi compaction process that drives metastasis.

Lysyl hydroxylase 2 induces a collagen cross-link switch in tumor stroma.

Epithelial tumor metastasis is preceded by an accumulation of collagen cross-links that heighten stromal stiffness and stimulate the invasive properties of tumor cells. However, the biochemical nature of collagen cross-links in cancer is still unclear. Here, we postulated that epithelial tumorigenesis is accompanied by changes in the biochemical type of collagen cross-links. Utilizing resected human lung cancer tissues and a p21CIP1/WAF1-deficient, K-rasG12D-expressing murine metastatic lung cancer model, we showed that, relative to normal lung tissues, tumor stroma contains higher levels of hydroxylysine aldehyde-derived collagen cross-links (HLCCs) and lower levels of lysine aldehyde-derived cross-links (LCCs), which are the predominant types of collagen cross-links in skeletal tissues and soft tissues, respectively. Gain- and loss-of-function studies in tumor cells showed that lysyl hydroxylase 2 (LH2), which hydroxylates telopeptidyl lysine residues on collagen, shifted the tumor stroma toward a high-HLCC, low-LCC state, increased tumor stiffness, and enhanced tumor cell invasion and metastasis. Together, our data indicate that LH2 enhances the metastatic properties of tumor cells and functions as a regulatory switch that controls the relative abundance of biochemically distinct types of collagen cross-links in the tumor stroma.

Regulation of T-cell activation and migration by the kinase TBK1 during neuroinflammation.

Development of an immune or autoimmune response involves T-cell activation in lymphoid organs and subsequent migration to peripheral tissues. Here we show that T-cell-specific ablation of the kinase TBK1 promotes T-cell activation but causes retention of effector T cells in the draining lymph node in a neuroinflammatory autoimmunity model, experimental autoimmune encephalomyelitis (EAE). At older ages, the T-cell-conditional TBK1-knockout mice also spontaneously accumulate T cells with activated phenotype. TBK1 controls the activation of AKT and its downstream kinase mTORC1 by a mechanism involving TBK1-stimulated AKT ubiquitination and degradation. The deregulated AKT-mTORC1 signalling in turn contributes to enhanced T-cell activation and impaired effector T-cell egress from draining lymph nodes. Treatment of mice with a small-molecule inhibitor of TBK1 inhibits EAE induction. These results suggest a role for TBK1 in regulating T-cell migration and establish TBK1 as a regulator of the AKT-mTORC1 signalling axis.

Transferring a synthetic gene circuit from yeast to mammalian cells.

The emerging field of synthetic biology builds gene circuits for scientific, industrial and therapeutic needs. Adaptability of synthetic gene circuits across different organisms could enable a synthetic biology pipeline, where circuits are designed in silico, characterized in microbes and reimplemented in mammalian settings for practical usage. However, the processes affecting gene circuit adaptability have not been systematically investigated. Here we construct a mammalian version of a negative feedback-based 'linearizer' gene circuit previously developed in yeast. The first naïve mammalian prototype was non-functional, but a computational model suggested that we could recover function by improving gene expression and protein localization. After rationally developing and combining new parts as the model suggested, we regained function and could tune target gene expression in human cells linearly and precisely as in yeast. The steps we have taken should be generally relevant for transferring any gene circuit from yeast into mammalian cells.

OTUD7B controls non-canonical NF-κB activation through deubiquitination of TRAF3.

The non-canonical NF-κB pathway forms a major arm of NF-κB signalling that mediates important biological functions, including lymphoid organogenesis, B-lymphocyte function, and cell growth and survival. Activation of the non-canonical NF-κB pathway involves degradation of an inhibitory protein, TNF receptor-associated factor 3 (TRAF3), but how this signalling event is controlled is still unknown. Here we have identified the deubiquitinase OTUD7B as a pivotal regulator of the non-canonical NF-κB pathway. OTUD7B deficiency in mice has no appreciable effect on canonical NF-κB activation but causes hyperactivation of non-canonical NF-κB. In response to non-canonical NF-κB stimuli, OTUD7B binds and deubiquitinates TRAF3, thereby inhibiting TRAF3 proteolysis and preventing aberrant non-canonical NF-κB activation. Consequently, the OTUD7B deficiency results in B-cell hyper-responsiveness to antigens, lymphoid follicular hyperplasia in the intestinal mucosa, and elevated host-defence ability against an intestinal bacterial pathogen, Citrobacter rodentium. These findings establish OTUD7B as a crucial regulator of signal-induced non-canonical NF-κB activation and indicate a mechanism of immune regulation that involves OTUD7B-mediated deubiquitination and stabilization of TRAF3.

Imaging of genetically engineered T cells by PET using gold nanoparticles complexed to Copper-64.

Adoptive transfer of primary T cells genetically modified to have desired specificity can exert an anti-tumor response in some patients. To improve our understanding of their therapeutic potential we have developed a clinically-appealing approach to reveal their in vivo biodistribution using nanoparticles that serve as a radiotracer for imaging by positron emission tomography (PET). T cells electroporated with DNA plasmids from the Sleeping Beauty transposon-transposase system to co-express a chimeric antigen receptor (CAR) specific for CD19 and Firefly luciferase (ffLuc) were propagated on CD19(+) K562-derived artificial antigen presenting cells. The approach to generating our clinical-grade CAR(+) T cells was adapted for electro-transfer of gold nanoparticles (GNPs) functionalized with (64)Cu(2+) using the macrocyclic chelator (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, DOTA) and polyethyleneglycol (GNP-(64)Cu/PEG2000). MicroPET/CT was used to visualize CAR(+)EGFPffLucHyTK(+)GNP-(64)Cu/PEG2000(+) T cells and correlated with bioluminescence imaging. These data demonstrate that GNPs conjugated with (64)Cu(2+) can be prepared as a radiotracer for PET and used to image T cells using an approach that has translational implications.

Longitudinal confocal microscopy imaging of solid tumor destruction following adoptive T cell transfer.

A fluorescence-based, high-resolution imaging approach was used to visualize longitudinally the cellular events unfolding during T cell-mediated tumor destruction. The dynamic interplay of T cells, cancer cells, cancer antigen loss variants, and stromal cells-all color-coded in vivo-was analyzed in established, solid tumors that had developed behind windows implanted on the backs of mice. Events could be followed repeatedly within precisely the same tumor region-before, during and after adoptive T cell therapy-thereby enabling for the first time a longitudinal in vivo evaluation of protracted events, an analysis not possible with terminal imaging of surgically exposed tumors. T cell infiltration, stromal interactions, and vessel destruction, as well as the functional consequences thereof, including the elimination of cancer cells and cancer cell variants were studied. Minimal perivascular T cell infiltrates initiated vascular destruction inside the tumor mass eventually leading to macroscopic central tumor necrosis. Prolonged engagement of T cells with tumor antigen-crosspresenting stromal cells correlated with high IFNγ cytokine release and bystander elimination of antigen-negative cancer cells. The high-resolution, longitudinal, in vivo imaging approach described here will help to further a better mechanistic understanding of tumor eradication by T cells and other anti-cancer therapies.