Piezo1 facilitates optimal T cell activation during tumor challenge

Functional effector T cells in the tumor microenvironment (TME) are critical for successful anti-tumor responses. T cell anti-tumor function is dependent on their ability to differentiate from a naïve state, infiltrate into the tumor site, and exert cytotoxic functions. The factors dictating whether a particular T cell can successfully undergo these processes during tumor challenge are not yet completely understood. Piezo1 is a mechanosensitive cation channel with high expression on both CD4+ and CD8+ T cells. Previous studies have demonstrated that Piezo1 optimizes T cell activation and restrains the CD4+ regulatory T cell (Treg) pool in vitro and under inflammatory conditions in vivo. However, little is known about the role Piezo1 plays on CD4+ and CD8+ T cells in cancer. We hypothesized that disruption of Piezo1 on T cells impairs anti-tumor immunity in vivo by hindering inflammatory T cell responses. We challenged mice with T cell Piezo1 deletion (P1KO) with tumor models dependent on T cells for immune rejection. P1KO mice had the more aggressive tumors, higher tumor growth rates and were unresponsive to immune-mediated therapeutic interventions. We observed a decreased CD4:CD8 ratio in both the secondary lymphoid organs and TME of P1KO mice that correlated inversely with tumor size. Poor CD4+ helper T cell responses underpinned the immunodeficient phenotype of P1KO mice. Wild type CD8+ T cells are sub-optimally activated in vivo with P1KO CD4+ T cells, taking on a CD25loPD-1hi phenotype. Together, our results suggest that Piezo1 optimizes T cell activation in the context of a tumor response.

Functional tumor cell-intrinsic STING, not host STING, drives local and systemic antitumor immunity and therapy efficacy following cryoablation

BACKGROUND

Despite its potential utility in delivering direct tumor killing and in situ whole-cell tumor vaccination, tumor cryoablation produces highly variable and unpredictable clinical response, limiting its clinical utility. The mechanism(s) driving cryoablation-induced local antitumor immunity and the associated abscopal effect is not well understood.

METHODS

The aim of this study was to identify and explore a mechanism of action by which cryoablation enhances the therapeutic efficacy in metastatic tumor models. We used the subcutaneous mouse model of the rhabdomyosarcoma (RMS) cell lines RMS 76-9STINGwt or RMS 76-9STING-/-, along with other murine tumor models, in C57BL/6 or STING-/- (TMEM173-/- ) mice to evaluate local tumor changes, lung metastasis, abscopal effect on distant tumors, and immune cell dynamics in the tumor microenvironment (TME).

RESULTS

The results show that cryoablation efficacy is dependent on both adaptive immunity and the STING signaling pathway. Contrary to current literature dictating an essential role of host-derived STING activation as a driver of antitumor immunity in vivo, we show that local tumor control, lung metastasis, and the abscopal effect on distant tumor are all critically dependent on a functioning tumor cell-intrinsic STING signaling pathway, which induces inflammatory chemokine and cytokine responses in the cryoablated TME. This reliance extends beyond cryoablation to include intratumoral STING agonist therapy. Additionally, surveys of gene expression databases and tissue microarrays of clinical tumor samples revealed a wide spectrum of expressions among STING-related signaling components.

CONCLUSIONS

Tumor cell-intrinsic STING pathway is a critical component underlying the effectiveness of cryoablation and suggests that expression of STING-related signaling components may serve as a potential therapy response biomarker. Our data also highlight an urgent need to further characterize tumor cell-intrinsic STING pathways and the associated downstream inflammatory response evoked by cryoablation and other STING-dependent therapy approaches.

A targetable pathway in neutrophils mitigates both arterial and venous thrombosis

Arterial and venous thrombosis constitutes a major source of morbidity and mortality worldwide. Long considered as distinct entities, accumulating evidence indicates that arterial and venous thrombosis can occur in the same populations, suggesting that common mechanisms are likely operative. Although hyperactivation of the immune system is a common forerunner to the genesis of thrombotic events in both vascular systems, the key molecular control points remain poorly understood. Consequently, antithrombotic therapies targeting the immune system for therapeutics gain are lacking. Here, we show that neutrophils are key effectors of both arterial and venous thrombosis and can be targeted through immunoregulatory nanoparticles. Using antiphospholipid antibody syndrome (APS) as a model for arterial and venous thrombosis, we identified the transcription factor Krüppel-like factor 2 (KLF2) as a key regulator of neutrophil activation. Upon activation through genetic loss of KLF2 or administration of antiphospholipid antibodies, neutrophils clustered P-selectin glycoprotein ligand 1 (PSGL-1) by cortical actin remodeling, thereby increasing adhesion potential at sites of thrombosis. Targeting clustered PSGL-1 using nanoparticles attenuated neutrophil-mediated thrombosis in APS and KLF2 knockout models, illustrating the importance and feasibility of targeting activated neutrophils to prevent pathological thrombosis. Together, our results demonstrate a role for activated neutrophils in both arterial and venous thrombosis and identify key molecular events that serve as potential targets for therapeutics against diverse causes of immunothrombosis.

Mechanosensory channel Piezo1 contributes to T lymphocyte migration through direct interaction with integrins

Response to mechanical signals is an important mechanism by which T lymphocytes drive inflammation. A potential contributor in this process is Piezo1, a mechanosensitive cation channel which is abundantly expressed in T lymphocytes. Previously, our lab has shown that Piezo1 colocalizes with high affinity LFA-1 on activated human T lymphocytes during chemokine-activated crawling, suggesting a role for Piezo1 in the adhesion cascade. However, the mechanism by which Piezo1 contributes to the regulation of the adhesion cascade is unknown. We hypothesize that Piezo1 mediates T lymphocyte migration through direct contact with integrin to regulate its function. We investigate the role of Piezo1 in the expression, binding affinity, and turnover of LFA-1 and VLA-4. Co-immunoprecipitation revealed a preferential association of Piezo1 with the alpha subunit of integrins, specifically LFA-1, MAC-1, and VLA-4 in the active forms. Moreover, microfluidic devices were used to study the contribution of Piezo1 on T lymphocytes under laminar flow-induced shear stress. We found that activated T lymphocytes with CRISPR/Cas9-mediated Piezo1 ablation resulted in a reduced chemokine-induced crawling speed that correlates to the efficiency of Piezo1 gene ablation. Finally, in studies of lymph node homing where fluorescently labeled T lymphocytes were tracked in vivo, Piezo1 deficient cells exhibit increased ingress and decreased egress through the lymph node, suggesting an intricate role of Piezo1 on T lymphocyte migration. Taken together, our data support the hypothesis that Piezo1 modulates inflammatory processes through complex integrin interactions and mediates T lymphocyte migration from the lymph node to the site of inflammation.

Case Postbaccalaureate Research Education Program grant NIH/NIGMS 5R25GM075207-15; St. Baldrick’s Foundation; Hyundai Hope-on-Wheels Program; The I’m Not Done Yet Foundation; and Pediatric Cancer Research Foundation

Abstract 971: Effects of tumor cryo-ablation on cGAS-STING pathway and antitumor immunity in syngeneic murine rhabdomyosarcoma

Even with current improvement in cancer therapy, tumor immunosuppressive microenvironment and metastatic tumors are important factors which have shown to be a challenge for cancer treatment. Thus, targeting the tumor microenvironment (TME) locally are required to modify the activation of innate immunity, which can provoke subsequent global adaptive anti-tumor immunity. Tumor cryo-ablation, a medical procedure that utilizes ultra-cold temperatures to destroy in situ local tumor tissues, has the capability to induce the release of immune danger signals that activate antigen-presenting cells to initiate the anti-tumor immunity. To understand the mechanism of immune activation by cryo-ablation, we performed comprehensive analyses on the effects of tumor cryo-ablation on mononuclear phagocytic lineage cells and the antitumor immunity. Here, we show that cryo-ablation of syngeneic Rhabdomyosarcoma (RMS) tumor, an aggressive sarcoma affecting children and young adults, was able to induce both the regression of tumor and the upregulation of the critical immune cytokines and chemokines profile. Moreover, cryo-ablation of RMS tumor initiates cGAS-STING signaling activation and type I interferon production in dendritic cells, which are consequential in pro-inflammatory TME. We also report that antitumor effects of cryo-ablation was more inhibitive, but not completely abrogated, in STING-deficient mice comparing with wild-type mice, demonstrating that both host-derived and tumor-intrinsic cGAS-STING signaling plays an important role in antitumor effects of tumor cryo-ablation. Ongoing experiments will address the efficacy of RMS tumor cryo-ablation on systemic anti-tumor immune activation leading to an abscopal effect on tumor regression at metastatic tumor. Taken together, our results demonstrate that tumor cryo-ablation affects antitumor immunity and cGAS-STING signaling in RMS tumor, and this approach may help guide future immunotherapy to improve cancer treatment outcomes.

Citation Format: Mohammad Abdulaziz Alshebremi, Jay T. Myers, Daniel T. Kingsley, Alex Y. Huang. Effects of tumor cryo-ablation on cGAS-STING pathway and antitumor immunity in syngeneic murine rhabdomyosarcoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 971.

cGAS-STING pathway mediates antitumor immunity of tumor cryoablation in syngeneic murine Rhabdomyosarcoma

Tumor cryoablation, a medical procedure that utilizes ultra-cold temperatures to destroy in situ local tumor tissues, has been established for cure of many tumor types and for stimulation of the immune system. The mechanism of immune response to tumor cryoabltion are not well defined. To understand the molecular pathway of immune activation by cryoablation, we performed comprehensive analyses on the impact of tumor cryoablation on mononuclear phagocytic lineage cells and the antitumor immunity. Here, we show that cryoablation of a murine Rhabdomyosarcoma (RMS) tumor, an aggressive sarcoma affecting children and young adults, was able to induce the regression of tumor and the upregulation of the critical immune cytokines/chemokines profile and maturation markers of CD11c+ DCs. Moreover, cryoablation of RMS tumor initiates cGAS-STING signaling activation and type I interferon production in CD11c+ DCs, which are consequential in pro-inflammatory tumor microenvironment (TME). We also report that antitumor effects of cryoablation were more inhibitive, but not completely abrogated, in STING-deficient mice comparing with wild-type mice, indicating that both host-derived and tumor-intrinsic cGAS-STING signaling plays an important role in antitumor effects of tumor cryoablation. Taken together, our results demonstrate that tumor cryoablation induces antitumor immunity via cGAS-STING signaling in syngeneic Rhabdomyosarcoma (RMS) tumor, and this approach may help guide future immunotherapy to improve cancer treatment outcomes.

Abstract A195: Mechanosensory mechanisms and in vivo tissue topology contribute to rheology of circulating leukocytes resulting in efficient post-capillary vessel wall adhesion and recruitment

Efficient recruitment of circulating immune cells to various tissues plays a critical role in homeostasis and immune surveillance, a process that serves as the basis of any successful cell-based immunotherapeutic strategies in cancer, particularly for solid tumors and cancers residing in body sites outside of blood vessels and sinusoid network. Clinical and experimental observations suggest that in vivo leukocyte adhesion and extravasation are maximal near the transition from capillary to post-capillary venule, through a multistep process that includes the intravascular capture, rolling, arrest, crawling of cells through interactions of adhesion molecules (selectins, integrins, chemokines/receptors, for example), eventually leading to transcellular or paracellular transmigration through intact endothelium. These cellular and molecular processes are strongly influenced by a confluence of scale-dependent physical effects. Mimicking the scale of physiologic vessels using in vitro microfluidic systems allows the capture and investigation of these effects on leukocyte adhesion assays, but imposes practical limits on reproducibility and reliable quantification. We have developed a microfluidic platform that provides multiple (54-512) technical replicates within a 15-minute sample collection time, coupled with an automated computer vision analysis pipeline that captures leukocyte adhesion probabilities as a function of not only shear stress imposed on leukocytes within the vessels as conventional wisdom dictates, but also of the extensional stresses imposed by the topology of post-capillary venules and the rheology of circulating leukocytes in these vessels. We identified that in post-capillary channels of physiologic scale, efficient leukocyte adhesion requires erythrocytes forcing leukocytes against the wall, a phenomenon that is promoted by the transitional flow in post-capillary venule expansions and highly dependent on the adhesion molecule ICAM-1. These studies help identified a mechanosensory mechanism that determines the increased likelihood of leukocyte adhesion in post-capillary venules, and further suggests a significant role of mechanosensory channel(s) in influencing leukocyte integrin affinity for cellular capture to the vessel wall. Through a series of truncation mutants, we have narrowed down a small region of putative interacting domain between integrin and a candidate mechanosensory channel—PIEZO1—on leukocytes. These ongoing investigations offer new insights into immune cellular recruitment and new molecular targets to enhance leukocyte recruitment to peripheral tumor sites.

Citation Format: Alex Y. Huang, Bryan L. Benson, Luis Correa, Lucy Li, Jay T. Myers, Umut A. Gurkan, Richard Ransohoff. Mechanosensory mechanisms and in vivo tissue topology contribute to rheology of circulating leukocytes resulting in efficient post-capillary vessel wall adhesion and recruitment [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A195.

Positively selected enhancer elements endow osteosarcoma cells with metastatic competence

Metastasis results from a complex set of traits acquired by tumor cells, distinct from those necessary for tumorigenesis. Here, we investigate the contribution of enhancer elements to the metastatic phenotype of osteosarcoma. Through epigenomic profiling, we identify substantial differences in enhancer activity between primary and metastatic human tumors and between near isogenic pairs of highly lung metastatic and nonmetastatic osteosarcoma cell lines. We term these regions metastatic variant enhancer loci (Met-VELs). Met-VELs drive coordinated waves of gene expression during metastatic colonization of the lung. Met-VELs cluster nonrandomly in the genome, indicating that activity of these enhancers and expression of their associated gene targets are positively selected. As evidence of this causal association, osteosarcoma lung metastasis is inhibited by global interruptions of Met-VEL-associated gene expression via pharmacologic BET inhibition, by knockdown of AP-1 transcription factors that occupy Met-VELs, and by knockdown or functional inhibition of individual genes activated by Met-VELs, such as that encoding coagulation factor III/tissue factor (F3). We further show that genetic deletion of a single Met-VEL at the F3 locus blocks metastatic cell outgrowth in the lung. These findings indicate that Met-VELs and the genes they regulate play a functional role in metastasis and may be suitable targets for antimetastatic therapies.

CCL3 Enhances Antitumor Immune Priming in the Lymph Node via IFNγ with Dependency on Natural Killer Cells

Lymph node (LN) plays a critical role in tumor cell survival outside of the primary tumor sites and dictates overall clinical response in many tumor types (1, 2). Previously, we and others have demonstrated that CCL3 plays an essential role in orchestrating T cell—antigen-presenting cell (APC) encounters in the draining LN following vaccination, and such interactions enhance the magnitude of the memory T cell pool (3–5). In the current study, we investigate the cellular responses in the tumor-draining lymph nodes (TDLNs) of a CCL3-secreting CT26 colon tumor (L3TU) as compared to wild-type tumor (WTTU) during the priming phase of an antitumor response (≤10 days). In comparison to WTTU, inoculation of L3TU resulted in suppressed tumor growth, a phenomenon that is accompanied by altered in vivo inflammatory responses on several fronts. Autologous tumor-derived CCL3 (aCCL3) secretion by L3TU bolstered the recruitment of T- and B-lymphocytes, tissue-migratory CD103⁺ dendritic cells (DCs), and CD49b⁺ natural killer (NK) cells, resulting in significant increases in the differentiation and activation of multiple Interferon-gamma (IFNγ)-producing leukocytes in the TDLN. During this early phase of immune priming, NK cells constitute the major producers of IFNγ in the TDLN. CCL3 also enhances CD8+ T cell proliferation and differentiation by augmenting DC capacity to drive T cell activation in the TDLN. Our results revealed that CCL3-dependent IFNγ production and CCL3-induced DC maturation drive the priming of effective antitumor immunity in the TDLN.

Plant viral nanoparticles-based HER2 vaccine: Immune response influenced by differential transport, localization and cellular interactions of particulate carriers

Cancer vaccines are designed to elicit an endogenous adaptive immune response that can successfully recognize and eliminate residual or recurring tumors. Such approaches can potentially overcome shortcomings of passive immunotherapies by generating long-lived therapeutic effects and immune memory while limiting systemic toxicities. A critical determinant of vaccine efficacy is efficient transport and delivery of tumor-associated antigens to professional antigen presenting cells (APCs). Plant viral nanoparticles (VNPs) with natural tropism for APCs and a high payload carrying capacity may be particularly effective vaccine carriers. The applicability of VNP platform technologies is governed by stringent structure-function relationships. We compare two distinct VNP platforms: icosahedral cowpea mosaic virus (CPMV) and filamentous potato virus X (PVX). Specifically, we evaluate in vivo capabilities of engineered VNPs delivering human epidermal growth factor receptor 2 (HER2) epitopes for therapy and prophylaxis of HER2⁺ malignancies. Our results corroborate the structure-function relationship where icosahedral CPMV particles showed significantly enhanced lymph node transport and retention, and greater uptake by/activation of APCs compared to filamentous PVX particles. These enhanced immune cell interactions and transport properties resulted in elevated HER2-specific antibody titers raised by CPMV- vs. PVX-based peptide vaccine. The 'synthetic virology' field is rapidly expanding with numerous platforms undergoing development and preclinical testing; our studies highlight the need for systematic studies to define rules guiding the design and rational choice of platform, in the context of peptide-vaccine display technologies.

Abstract A050: Cdk5 disruption attenuates tumor PD-L1 expression via regulation of IFN-γ signaling components and promotes antitumor immunity

In order to escape normal immune surveillance, tumors mimic peripheral tissue tolerance mechanisms such as the expression of programmed cell death-ligand 1 (PD-L1), the inhibition of which can lead to potent anti-tumor responses. Here we show the contribution of cyclin dependent kinase 5 (Cdk5) to immune evasion. Cdk5 is a proline-directed serine/threonine kinase, which is highly expressed in post-mitotic neurons and directs a variety of homeostatic functions from cytoskeletal rearrangement to neurotransmitter signaling. Studies in xenograft models have linked Cdk5 activity to the generation and metabolic activity of primary tumors within the central nervous system (CNS). Here we show that Cdk5, expressed in both murine and human medulloblastoma (MB) cell lines, plays a major role in the ability of MB to avoid immune detection. First, we observed that decreased Cdk5 expression was associated with an increase in the number of infiltrating CD3+ cells in the tumor mass of clinical MB samples. Additionally, using publicly available datasets, we found that decreased Cdk5 expression is correlated with better overall survival or fewer distant metastasis in melanoma, breast cancer, glioma, and lung adenocarcinoma. Next, using a CRISPR/Cas-9 approach, we silenced Cdk5 in a murine model of Sonic Hedgehog (SHH) pathway MB. Rather than causing intrinsic growth defects in MB, interference of Cdk5 activity sensitizes tumors to killing by the normal host immune system in a CD4+ T cell-dependent manner. This rejection is associated with increased IFN-γ expression in the tumor microenvironment, as well as increased PD-L1 expression by myeloid populations in both subcutaneous and intracranial tumors. Mechanistically, we observed an attenuated response to IFN-γ stimulated expression of programmed death ligand 1 (PD-L1) on MB cells. This blunted response was recapitulated when MB cells were treated with Roscovitine, a non-selective Cdk5 inhibitor. Furthermore, using a quantitative global phosphoproteomics approach, we found that Cdk5 knockdown also increased phosphorylation of S-440 and S-443 on interferon regulatory factor binding protein 2 (IRF2BP2), an upstream co-repressor of interferon regulatory factor 2 (IRF-2). Increased phosphorylation of IRF2BP2 corresponded with stable expression of IRF-2 with a concomitant decrease in surface expression of PD-L1. These observations highlight a critical role for Cdk5 in the immune escape mechanisms of primary CNS tumors and provides new therapeutic targets for PD-1/PD-L1 directed immunotherapy.

Citation Format: Rodney D. Dorand, Jr., Joseph Nthale, Jay T. Myers, Deborah S. Barkauskas, Stefanie Avril, Steven M. Chirieleison, Tej K. Pareek, Derek W. Abbott, Duncan S. Stearns, John J. Letterio, Alex Y. Huang, Agne Petrosiute. Cdk5 disruption attenuates tumor PD-L1 expression via regulation of IFN-γ signaling components and promotes antitumor immunity [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A050.

Cdk5 disruption attenuates tumor PD-L1 expression and promotes antitumor immunity

Cancers often evade immune surveillance by adopting peripheral tissue- tolerance mechanisms, such as the expression of programmed cell death ligand 1 (PD-L1), the inhibition of which results in potent antitumor immunity. Here, we show that cyclin-dependent kinase 5 (Cdk5), a serine-threonine kinase that is highly active in postmitotic neurons and in many cancers, allows medulloblastoma (MB) to evade immune elimination. Interferon-γ (IFN-γ)-induced PD-L1 up-regulation on MB requires Cdk5, and disruption of Cdk5 expression in a mouse model of MB results in potent CD4(+) T cell-mediated tumor rejection. Loss of Cdk5 results in persistent expression of the PD-L1 transcriptional repressors, the interferon regulatory factors IRF2 and IRF2BP2, which likely leads to reduced PD-L1 expression on tumors. Our finding highlights a central role for Cdk5 in immune checkpoint regulation by tumor cells.

Abstract LB-151: Positively selected enhancer elements endow tumor cells with metastatic competence

Metastasis results from a complex set of traits acquired by tumor cells, distinct from those necessary for tumorigenesis. Here, we investigate the contribution of enhancer elements to the metastatic phenotype of osteosarcoma. Through epigenomic profiling, we identify substantial differences in signature enhancer-histone marks between near-isogenic pairs of high and low lung-metastatic osteosarcoma cells. We term these regions Metastatic Variant Enhancer Loci (Met-VELs). Met-VELs drive coordinated waves of gene expression during metastatic colonization of the lung. Met-VELs cluster non-randomly, indicating that activity of these enhancers and their associated gene targets is positively selected. Osteosarcoma lung metastasis is inhibited by global interruptions of Met-VEL associated gene expression via pharmacologic BET inhibition, by knockdown of AP-1 transcription factors whose motifs are enriched in Met-VELs, and by knockdown of individual genes activated by Met-VELs. These observations have implications for the discovery and development of targeted anti-metastatic therapies.

Citation Format: James J. Morrow, Tyler E. Miller, Alina Saiakhova, Michael M. Lizardo, Cynthia F. Bartels, Ian Bayles, Stevephen Hung, Arnulfo Mendoza, Jay T. Myers, Frederick Allen, Analisa DiFeo, Brian P. Rubin, Alex Y. Huang, Paul S. Meltzer, Lee J. Helman, Chand Khanna, Peter C. Scacheri. Positively selected enhancer elements endow tumor cells with metastatic competence. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-151.

Multiple Administrations of Viral Nanoparticles Alter in Vivo Behavior-Insights from Intravital Microscopy

Multiple administrations of nanoparticle-based formulations are often a clinical requirement for drug delivery and diagnostic imaging applications. Steady pharmacokinetics of nanoparticles is desirable to achieve efficient therapeutic or diagnostic outcomes over such repeat administrations. While clearance through mononuclear phagocytic system is a key determinant of nanoparticle persistence in vivo, multiple administrations could potentially result in altered pharmacokinetics by evoking innate or adaptive immune responses. Plant viral nanoparticles (VNPs) represent an emerging class of programmable nanoparticle platform technologies that offer a highly organized proteinaceous architecture and multivalency for delivery of large payloads of drugs and molecular contrast agents. These very structural features also render them susceptible to immune recognition and subsequent accelerated systemic clearance that could potentially affect overall efficiency. While the biodistribution and pharmacokinetics of VNPs have been reported, the biological response following repeat administrations remains an understudied area of investigation. Here, we demonstrate that weekly administration of filamentous plant viruses results in the generation of increasing levels of circulating, carrier-specific IgM and IgG antibodies. Furthermore, PVX specific immunoglobulins from the serum of immunized animals quickly form aggregates when incubated with PVX in vitro. Such aggregates of VNP-immune complexes are also observed in the mouse vasculature in vivo following repeat injections when imaged in real time using intravital two-photon laser scanning microscopy (2P-LSM). The size of aggregates diminishes at later time points, coinciding with antibody class switching from IgM to IgG. Together, our results highlight the need for careful in vivo assessment of (viral) nanoparticle-based platform technologies, especially in studying their performance after repeat administration. We also demonstrate the utility of intravital microscopy to aid in this evaluation.

Focal transient CNS vessel leak provides a tissue niche for sequential immune cell accumulation during the asymptomatic phase of EAE induction

Peripheral immune cells are critical to the pathogenesis of neurodegenerative diseases including multiple sclerosis (MS) (Hendriks et al., 2005; Kasper and Shoemaker, 2010). However, the precise sequence of tissue events during the early asymptomatic induction phase of experimental autoimmune encephalomyelitis (EAE) pathogenesis remains poorly defined. Due to the spatial-temporal constrains of traditional methods used to study this disease, most studies had been performed in the spine during peak clinical disease; thus the debate continues as to whether tissue changes such as vessel disruption represent a cause or a byproduct of EAE pathophysiology in the cortex. Here, we provide dynamic, high-resolution information on the evolving structural and cellular processes within the gray matter of the mouse cortex during the first 12 asymptomatic days of EAE induction. We observed that transient focal vessel disruptions precede microglia activation, followed by infiltration of and directed interaction between circulating dendritic cells and T cells. Histamine antagonist minimizes but not completely ameliorates blood vessel leaks. Histamine H1 receptor blockade prevents early microglia function, resulting in subsequent reduction in immune cell accumulation, disease incidence and clinical severity.

Intravital imaging of axonal interactions with microglia and macrophages in a mouse dorsal column crush injury

Traumatic spinal cord injury causes an inflammatory reaction involving blood-derived macrophages and central nervous system (CNS)-resident microglia. Intra-vital two-photon microscopy enables the study of macrophages and microglia in the spinal cord lesion in the living animal. This can be performed in adult animals with a traumatic injury to the dorsal column. Here, we describe methods for distinguishing macrophages from microglia in the CNS using an irradiation bone marrow chimera to obtain animals in which only macrophages or microglia are labeled with a genetically encoded green fluorescent protein. We also describe a injury model that crushes the dorsal column of the spinal cord, thereby producing a simple, easily accessible, rectangular lesion that is easily visualized in an animal through a laminectomy. Furthermore, we will outline procedures to sequentially image the animals at the anatomical site of injury for the study of cellular interactions during the first few days to weeks after injury.

High-resolution intravital imaging reveals that blood-derived macrophages but not resident microglia facilitate secondary axonal dieback in traumatic spinal cord injury

After traumatic spinal cord injury, functional deficits increase as axons die back from the center of the lesion and the glial scar forms. Axonal dieback occurs in two phases: an initial axon intrinsic stage that occurs over the first several hours and a secondary phase which takes place over the first few weeks after injury. Here, we examine the secondary phase, which is marked by infiltration of macrophages. Using powerful time-lapse multi-photon imaging, we captured images of interactions between Cx3cr1(+/GFP) macrophages and microglia and Thy-1(YFP) axons in a mouse dorsal column crush spinal cord injury model. Over the first few weeks after injury, axonal retraction bulbs within the lesion are static except when axonal fragments are lost by a blebbing mechanism in response to physical contact followed by phagocytosis by mobile Cx3Cr1(+/GFP) cells. Utilizing a radiation chimera model to distinguish marrow-derived cells from radio-resistant CNS-resident microglia, we determined that the vast majority of accumulated cells in the lesion are derived from the blood and only these are associated with axonal damage. Interestingly, CNS-resident Cx3Cr1(+/GFP) microglia did not increasingly accumulate nor participate in neuronal destruction in the lesion during this time period. Additionally, we found that the blood-derived cells consisted mainly of singly labeled Ccr2(+/RFP) macrophages, singly labeled Cx3Cr1(+/GFP) macrophages and a small population of double-labeled cells. Since all axon destructive events were seen in contact with a Cx3Cr1(+/GFP) cell, we infer that the CCR2 single positive subset is likely not robustly involved in axonal dieback. Finally, in our model, deletion of CCR2, a chemokine receptor, did not alter the position of axons after dieback. Understanding the in vivo cellular interactions involved in secondary axonal injury may lead to clinical treatment candidates involving modulation of destructive infiltrating blood monocytes.

Utilization of Multiphoton Imaging For Real-Time Fate Determination of Mesenchymal Stem Cells in an Immunocompetent Mouse Model

The clinical application of Mesenchymal Stem Cells (MSCs) for the treatment of a variety of diseases is the focus of intense research. Despite large research efforts many questions regarding MSC biology in vivo remain unanswered. For instance, we do not know for certain whether MSCs exert their therapeutic effects directly within the target tissue or indirectly by influencing the polarization of other cell types, such as macrophages, which can then home to the target tissue microenvironment. To help address this issue, the application of intravital multiphoton microscopy allows for the determination of the dynamic action of intact MSCs versus endogenous host cells at the target tissue site in real time.

Dynamic real-time imaging of marrow-resident neutrophils interacting with human mesenchymal stem cells during systemic lipopolysaccharide challenge

e22158

Background: Human mesenchymal stem cells (hMSCs) have gained intense interest due to their immune-modulatory, tissue differentiating and homing properties to sites of inflammation and tumor microenvironment, as evidenced by more than 200 ongoing clinical trials using hMSCs in a variety of clinical settings. Despite evidence demonstrating the bio-distribution of infused hMSCs in target organs using static fluorescence imaging or whole-body imaging techniques, there is controversy regarding how hMSCs exert their biological effects, and very little is known about how they behave dynamically within host tissues on a single-cell level in vivo. Methods: We infused fluorescently labeled clinical-grade hMSCs into immune-competent mice in which neutrophils and monocytes express a second fluorescent marker under the Lysozyme M (LysM) promoter. The recipient mice were then subjected to serial 4-D (xyzt) imaging of the bone marrow cavity with intravital two-photon microscopy (TPM) during acute systemic Lipopolysaccharide (LPS) challenges to observe changes in MSC and neutrophil migration behavior. Results: We were able, for the first time, to capture dynamic interactions between and migration pattern of hMSCs and LysM+granulocytes in the bone marrow of live mice during systemic LPS challenge. Contrary to some published reports, many of the infused hMSCs remained intact despite repeated cellular contacts with host neutrophils. However, we also observed the destruction and subsequent phagocytosis of some hMSCs by surrounding granulocytes. Conclusions: Our imaging platform provides opportunities to gain insight into the biology and therapeutic mechanisms of hMSCs in vivo at a single-cell level within live hosts.

Cutaneous penetration of the topically applied photosensitizer Pc 4 as detected by intravital 2-photon laser scanning microscopy

The fundamental mechanism of photodynamic therapy (PDT)-induced cell death has been characterized, but early critical PDT events in vivo remain incompletely defined. With the recent development in advanced fluorescence imaging modalities, such as intravital 2-photon laser scanning microscopy (2P-LSM), researchers are now able to investigate and visualize biological processes with high resolution in real time. This powerful imaging technology allows deep tissue visualization with single-cell resolution, thus providing dynamic information on the 3-dimensional architectural makeup of the tissue. The main goal of this study was to determine the cutaneous penetration of a topically applied photosensitizer, the silicon phthalocyanine Pc 4, into the skin of live animals and to assess the effective absorption of Pc 4 through the skin barrier. Our 2P-LSM images indicate that Pc 4 penetrates to the epidermal/dermal junction of mouse skin. The data also indicate that the degree of Pc 4 absorption is dose dependent. These findings represent initial steps that may help in improving the clinical utilization of topical Pc 4-PDT.

Real-time dynamic and sequential tracking of tumor propagation and associated immune responses in the CNS microenvironment

9520

Background: Ex vivo experimental systems are often unable to fully capture complex intercellular communication between tumor cells and surrounding tissues - a critical feature in understanding cancer development and immune evasion. Imaging modality such as bioluminescence lacks the resolution necessary to discern subtle structural differences and heterogeneity in the tumor niche. Microscopic examination of fixed specimens is devoid of the 3-dimensional context or evolution of tumor progression within the same host. Methods: New insights have come from studies involving the use of intravital 2-photon laser scanning microscopy (2P-LSM), which allows deep visualization (>300um) with single-cell resolution (<1um), thus enables direct observation of cellular behavior in intact tissues at a suitable dynamic spatial-time resolution. We study the role of tumor niche in shaping immune repertoire and develop strategies to modify tumor niche to enhance anti-tumor immunity. Results: One example is our study of glioblastoma multiforme (GBM), which contains a cellular hierarchy with a CD133+ sub-population representing self-renewing and tumorigenic GBM stem cells (GSCs). In a xeno-transplant model, GSC was capable of tumor initiation in the mouse brain. To directly test the relative tumorigenic potential of GSCs (CD133+) and non-GSCs (CD133-), we inoculated paired tumor populations from the same primary GBM tumor cells and monitored tumor competition by serial 2P-LSM through implanted cranial windows. Serial 2P-LSM imaging shows that after 35 days, GBM formation was driven exclusively by GSCs but not non-GSCs. To interrogate tumor-associated immune responses, we inoculated syngeneic mouse glioma tumors into C57BL/6 mice. Using this and CNS-inflammatory models, we have begun to undercover the role of perivascular antigen-presenting cells and microglia in guiding the recruitment of CNS-bound lymphocytes. Conclusions: Our data provide the first direct functional evidence that CSCs are responsible for tumor propagation in GBM, and represent an in vivo experimental platform to monitor immunotherapeutic interventions.

Intravital imaging of the mouse popliteal lymph node

Lymph nodes (LNs) are secondary lymphoid organs, which are strategically located throughout the body to allow for trapping and presentation of foreign antigens from peripheral tissues to prime the adaptive immune response. Juxtaposed between innate and adaptive immune responses, the LN is an ideal site to study immune cell interactions. Lymphocytes (T cells, B cells and NK cells), dendritic cells (DCs), and macrophages comprise the bulk of bone marrow-derived cellular elements of the LN. These cells are strategically positioned in the LN to allow efficient surveillance of self antigens and potential foreign antigens. The process by which lymphocytes successfully encounter cognate antigens is a subject of intense investigation in recent years, and involves an integration of molecular contacts including antigen receptors, adhesion molecules, chemokines, and stromal structures such as the fibro-reticular network. Prior to the development of high-resolution real-time fluorescent in vivo imaging, investigators relied on static imaging, which only offers answers regarding morphology, position, and architecture. While these questions are fundamental in our understanding of immune cell behavior, the limitations intrinsic with this technique does not permit analysis to decipher lymphocyte trafficking and environmental clues that affect dynamic cell behavior. Recently, the development of intravital two-photon laser scanning microscopy (2P-LSM) has allowed investigators to view the dynamic movements and interactions of individual cells within live LNs in situ. In particular, we and others have applied this technique to image cellular behavior and interactions within the popliteal LN, where its compact, dense nature offers the advantage of multiplex data acquisition over a large tissue area with diverse tissue sub-structures. It is important to note that this technique offers added benefits over explanted tissue imaging techniques, which require disruption of blood, lymph flow, and ultimately the cellular dynamics of the system. Additionally, explanted tissues have a very limited window of time in which the tissue remains viable for imaging after explant. With proper hydration and monitoring of the animal's environmental conditions, the imaging time can be significantly extended with this intravital technique. Here, we present a detailed method of preparing mouse popliteal LN for the purpose of performing intravital imaging.

Direct in vivo evidence for tumor propagation by glioblastoma cancer stem cells

High-grade gliomas (World Health Organization grade III anaplastic astrocytoma and grade IV glioblastoma multiforme), the most prevalent primary malignant brain tumors, display a cellular hierarchy with self-renewing, tumorigenic cancer stem cells (CSCs) at the apex. While the CSC hypothesis has been an attractive model to describe many aspects of tumor behavior, it remains controversial due to unresolved issues including the use of ex vivo analyses with differential growth conditions. A CSC population has been confirmed in malignant gliomas by preferential tumor formation from cells directly isolated from patient biopsy specimens. However, direct comparison of multiple tumor cell populations with analysis of the resulting phenotypes of each population within a representative tumor environment has not been clearly described. To directly test the relative tumorigenic potential of CSCs and non-stem tumor cells in the same microenvironment, we interrogated matched tumor populations purified from a primary human tumor transplanted into a xenograft mouse model and monitored competitive in vivo tumor growth studies using serial in vivo intravital microscopy. While CSCs were a small minority of the initial transplanted cancer cell population, the CSCs, not the non-stem tumor cells, drove tumor formation and yielded tumors displaying a cellular hierarchy. In the resulting tumors, a fraction of the initial transplanted CSCs maintained expression of stem cell and proliferation markers, which were significantly higher compared to the non-stem tumor cell population and demonstrated that CSCs generated cellular heterogeneity within the tumor. These head-to-head comparisons between matched CSCs and non-stem tumor cells provide the first functional evidence using live imaging that in the same microenvironment, CSCs more than non-stem tumor cells are responsible for tumor propagation, confirming the functional definition of a CSC.

Strain-specific modification of lethality in fucose-deficient mice

The FX locus encodes an essential enzyme in the de novo pathway of GDP-fucose biosynthesis. Mice homozygous for a targeted mutation of the FX gene manifest a host of pleiotropic abnormalities including a lethal phenotype that is almost completely penetrant in heterozygous intercrosses on a mixed genetic background. Here we have investigated genetic suppression of FX-mediated lethality. Reduced recovery of heterozygous mice was observed while backcrossing the null FX allele to C57BL/6J (B6), but was less dramatic in an outcross to CASA/Rk and absent in an outcross to 129S1/SvImJ, indicating that genetic background modifies survival of FX+/- progeny. Substantial strain-specific differences in pre- and postnatal survival of FX-/- progeny were also detected in heterozygous crosses of C57BL/6J congenic, 129S1B6F1, and B6CASAF1 mice. Specifically, intrauterine survival of FX-/- mice was greatly increased during a heterozygous intercross on a uniform C57BL/6J genetic background compared with survival on a hybrid genetic background consisting of a mixture of C57BL/6J and 129S2/SvPas. In addition, statistically significant clustering of FX-/- progeny into litters and specific breeding cages was noted during a B6CASAF1 FX+/- intercross, suggesting a rare mechanism for modifier gene action in which parentally expressed genes define the phenotype, in this case the survival potential, of mutant offspring. Our results disclose that lethality in FX mutant mice is determined by one or more strain-specific modifier loci.

Conditional control of selectin ligand expression and global fucosylation events in mice with a targeted mutation at the FX locus

Glycoprotein fucosylation enables fringe-dependent modulation of signal transduction by Notch transmembrane receptors, contributes to selectin-dependent leukocyte trafficking, and is faulty in leukocyte adhesion deficiency (LAD) type II, also known as congenital disorder of glycosylation (CDG)-IIc, a rare human disorder characterized by psychomotor defects, developmental abnormalities, and leukocyte adhesion defects. We report here that mice with an induced null mutation in the FX locus, which encodes an enzyme in the de novo pathway for GDP-fucose synthesis, exhibit a virtually complete deficiency of cellular fucosylation, and variable frequency of intrauterine demise determined by parental FX genotype. Live-born FX(-/-) mice exhibit postnatal failure to thrive that is suppressed with a fucose-supplemented diet. FX(-/-) adults suffer from an extreme neutrophilia, myeloproliferation, and absence of leukocyte selectin ligand expression reminiscent of LAD-II/CDG-IIc. Contingent restoration of leukocyte and endothelial selectin ligand expression, general cellular fucosylation, and normal postnatal physiology is achieved by modulating dietary fucose to supply a salvage pathway for GDP-fucose synthesis. Conditional control of fucosylation in FX(-/-) mice identifies cellular fucosylation events as essential concomitants to fertility, early growth and development, and leukocyte adhesion.

Fuc-TVII is required for T helper 1 and T cytotoxic 1 lymphocyte selectin ligand expression and recruitment in inflammation, and together with Fuc-TIV regulates naive T cell trafficking to lymph nodes

To determine how the alpha(1,3)fucosyltransferases Fuc-TIV and Fuc-TVII, and the selectin ligands they control may contribute to the adaptive immune response, contact hypersensitivity (CHS) was characterized in mice deficient in either or both enzymes. We find a substantial CHS deficiency in Fuc-TVII(-/-) mice, and a complete deficiency in Fuc-TIV(-/-)/Fuc-TVII(-/-) mice. These defects are not accounted for by alterations in the number or function of epidermal Langerhans cells required for cutaneous antigen processing and presentation. By contrast, defective CHS in Fuc-TVII(-/-) mice or Fuc-TIV(-/-)/Fuc-TVII(-/-) mice is attributed in part to prominent, or nearly complete deficiencies, respectively, in the complement of naive T lymphocytes available in lymph nodes for antigen-dependent activation, expansion, differentiation, and dissemination. Fuc-TVII deficiency also deletes expression of E- and P-selectin ligands by Th1 and T cytotoxic 1 (Tc1) lymphocytes, annuls T cell trafficking to inflamed cutaneous sites in vivo, and thereby controls an essential component of the efferent phase of the cutaneous immune response. These observations indicate that collaborative contributions of Fuc-TIV and Fuc-TVII to L-selectin ligand synthesis, and to lymphocyte recruitment, are requisite components of the primary cellular immune response, and assign an essential role to Fuc-TVII in control of E- and P-selectin ligand expression by Th1 and Tc1 lymphocytes.

Altered membrane trafficking in activated bone marrow-derived macrophages

Activation of macrophages with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) leads to increased intracellular resistance to microbes and increased major histocompatibility complex class II-restricted antigen presentation, processes that both use the vacuolar compartment. Despite the requirement of the macrophage vacuolar compartment for microbicidal activities and antigen processing, the rates of endocytosis and membrane trafficking in activated macrophages are not clearly defined. In this study, vacuolar compartment dynamics were analyzed in murine bone marrow-derived macrophages activated with LPS and/or IFN-gamma, conditions that increased macrophage nitric oxide production and resistance to infection by Listeria monocytogenes. Relative to nonactivated cells, activated macrophages showed diminished rates of fluid-phase pinocytosis and phagocytosis and delayed progression of macropinosomes and phagosomes to late endosomes and lysosomes. In contrast to the slowing of membrane trafficking, rates of macropinosome acidification were similar between activated and nonactivated cells. One consequence of this slowed membrane trafficking in activated macrophages was a prolonged exposure of incoming molecules to an acidic nonlysosomal compartment, a condition which may facilitate microbicidal chemistries or antigen processing.

Cognitive, psychosocial, and physical development in infants and children with end-stage renal disease

The purpose of this article is to synthesize research related to the cognitive, physical, and psychosocial development of children with end-stage renal disease who are receiving conservative management, hemodialysis or peritoneal dialysis, or who have received transplants. An impressive array of research in these three areas of development was found, but more work is needed. Suggestions are made for more multicenter research with larger sample sizes and greater generalizability. In addition, more developmental research that includes measures of renal disease, such as age at onset, severity of disease, and length of time in renal failure, is needed.

Induced stereoscopic motion as an aid in the search for tall targets

Induced stereoscopic motion, ISM, is apparent movement in tall static objects projecting from a reasonably flat background when viewed stereoscopically. ISM is produced by a smooth but extensive variation of the stereo-base (the separation of camera points) in a pair of moving picture films. The two films are projected by two separate but synchronized projectors onto rear view screens which are placed in the field of view of a stereoscope. In a controlled test it was found that subjects located targets faster and with fewer errors with ISM film than with comparable film in which the stereo-base was fixed at the maximum of the ISM film. This improvement of search is due almost entirely to searchs for targets which are difficult to find. Easy targets were always found and found quickly by both methods. ISM is as yet a laboratory production, but plans are being made for developing its field and applicability.