Shifting foci of hematopoiesis during reconstitution from single stem cells

Delivery of monocyte lineage cells in a biomimetic scaffold enhances tissue repair

The monocyte lineage is essential to normal wound healing. Macrophage inhibition or knockout in mice results in impaired wound healing through reduced neovascularization, granulation tissue formation, and reepithelialization. Numerous studies have either depleted macrophages or reduced their activity in the context of wound healing. Here, we demonstrate that by increasing the number of macrophages or monocytes in the wound site above physiologic levels via pullulan-collagen composite dermal hydrogel scaffold delivery, the rate of wound healing can be significantly accelerated in both wild-type and diabetic mice, with no adverse effect on the quality of repair. Macrophages transplanted onto wounds differentiate into M1 and M2 phenotypes of different proportions at various time points, ultimately increasing angiogenesis. Given that monocytes can be readily isolated from peripheral blood without in vitro manipulation, these findings hold promise for translational medicine aimed at accelerating wound healing across a broad spectrum of diseases.

A PET Imaging Strategy to Visualize Activated T Cells in Acute Graft-versus-Host Disease Elicited by Allogenic Hematopoietic Cell Transplant

A major barrier to successful use of allogeneic hematopoietic cell transplantation is acute graft-versus-host disease (aGVHD), a devastating condition that arises when donor T cells attack host tissues. With current technologies, aGVHD diagnosis is typically made after end-organ injury and often requires invasive tests and tissue biopsies. This affects patient prognosis as treatments are dramatically less effective at late disease stages. Here, we show that a novel PET radiotracer, 2'-deoxy-2'-[18F]fluoro-9-β-D-arabinofuranosylguanine ([18F]F-AraG), targeted toward two salvage kinase pathways preferentially accumulates in activated primary T cells. [18F]F-AraG PET imaging of a murine aGVHD model enabled visualization of secondary lymphoid organs harboring activated donor T cells prior to clinical symptoms. Tracer biodistribution in healthy humans showed favorable kinetics. This new PET strategy has great potential for early aGVHD diagnosis, enabling timely treatments and improved patient outcomes. [18F]F-AraG may be useful for imaging activated T cells in various biomedical applications. Cancer Res; 77(11); 2893-902. ©2017 AACR.

Reactive Oxygen Species Imaging in a Mouse Model of Inflammatory Bowel Disease

Purpose

Reactive oxygen species (ROS) are important contributors to inflammatory bowel disease (IBD); however, there are insufficient tools for their in vivo evaluation.

Procedures

To determine if a chemiluminescent ROS reporter, coelenterazine, would be a useful tool for the detection of immune cell activation, the macrophage cell line (RAW 264.7) was treated with phorbol myristate acetate (PMA). Additionally, coelenterazine was used to monitor the changes in ROS production over time in a mouse model of IBD.

Results

In vitro, coelenterazine enabled the dynamic monitoring of the RAW 264.7 cell oxidative burst. In vivo, there were early, preclinical, changes in the localization and magnitude of coelenterazine chemiluminescent foci.

Conclusions

Coelenterazine offers a high-throughput method for assessing immune cell activation in culture and provides a means for the in vivo detection and localization of ROS during IBD disease progression.

Quo vadis chimerism?

Although immunity in multicellular organisms is efficient in dealing with alien agents, it may fail for allogeneic chimerism. Natural chimerism is widely documented in nature, distributed in at least ten phyla of protists, invertebrates and plants, vertebrates and mammals, including humans; it is an important ecological/evolutionary tool manipulating metazoans' life history portraits. Instead of purging allogeneic nascent selfish cells, a 'double edged sword' chimerism emerges, displaying environmental dictated costs and benefits for the genotypes involved. Benefits include the development of synergistic complementation, the increase of genetic variability, the assurance of mate location, improved size-dependent ecological qualities (growth rates, reproduction, survivorship, competition, environmental tolerance) and more. Costs include the threat of somatic and germ cell parasitism, developmental instability, death, diseases, autoimmunity, sexual sterility and organ malformations, which develop as well in mammalian natural chimerism, including humans. Because of its importance, medical sciences should study and harness natural chimerism properties for clinical purposes.

Image-guided transplantation of single cells in the bone marrow of live animals

Transplantation of a single hematopoietic stem cell is an important method for its functional characterization, but the standard transplantation protocol relies on cell homing to the bone marrow after intravenous injection. Here, we present a method to transplant single cells directly into the bone marrow of live mice. We developed an optical platform that integrates a multiphoton microscope with a laser ablation unit for microsurgery and an optical tweezer for cell micromanipulation. These tools allow image-guided single cell transplantation with high spatial control. The platform was used to deliver single hematopoietic stem cells. The engraftment of transplants was tracked over time, illustrating that the technique can be useful for studying both normal and malignant stem cells in vivo.

Bioluminescence Assays for Monitoring Chondrogenic Differentiation and Cartilage Regeneration

Since articular cartilage has a limited regeneration potential, for developing biological therapies for cartilage regeneration it is important to study the mechanisms underlying chondrogenesis of stem cells. Bioluminescence assays can visualize a wide range of biological phenomena such as gene expression, signaling, metabolism, development, cellular movements, and molecular interactions by using visible light and thus contribute substantially to elucidation of their biological functions. This article gives a concise review to introduce basic principles of bioluminescence assays and applications of the technology to visualize the processes of chondrogenesis and cartilage regeneration. Applications of bioluminescence assays have been highlighted in the methods of real-time monitoring of gene expression and intracellular levels of biomolecules and noninvasive cell tracking within animal models. This review suggests that bioluminescence assays can be applied towards a visual understanding of chondrogenesis and cartilage regeneration.

T cell progenitor therapy-facilitated thymopoiesis depends upon thymic input and continued thymic microenvironment interaction

Infusion of in vitro-derived T cell progenitor (proT) therapy with hematopoietic stem cell transplant aids the recovery of the thymus damaged by total body irradiation. To understand the interaction between proTs and the thymic microenvironment, WT mice were lethally irradiated and given T cell-deficient (Rag1-/-) marrow with WT in vitro-generated proTs, limiting mature T cell development to infused proTs. ProTs within the host thymus led to a significant increase in thymic epithelial cells (TECs) by day 21 after transplant, increasing actively cycling TECs. Upon thymus egress (day 28), proT TEC effects were lost, suggesting that continued signaling from proTs is required to sustain TEC cycling and cellularity. Thymocytes increased significantly by day 21, followed by a significant improvement in mature T cell numbers in the periphery by day 35. This protective surge was temporary, receding by day 60. Double-negative 2 (DN2) proTs selectively increased thymocyte number, while DN3 proTs preferentially increased TECs and T cells in the spleen that persisted at day 60. These findings highlight the importance of the interaction between proTs and TECs in the proliferation and survival of TECs and that the maturation stage of proTs has unique effects on thymopoiesis and peripheral T cell recovery.

Mutant KRAS promotes malignant pleural effusion formation

Malignant pleural effusion (MPE) is the lethal consequence of various human cancers metastatic to the pleural cavity. However, the mechanisms responsible for the development of MPE are still obscure. Here we show that mutant KRAS is important for MPE induction in mice. Pleural disseminated, mutant KRAS bearing tumour cells upregulate and systemically release chemokine ligand 2 (CCL2) into the bloodstream to mobilize myeloid cells from the host bone marrow to the pleural space via the spleen. These cells promote MPE formation, as indicated by splenectomy and splenocyte restoration experiments. In addition, KRAS mutations are frequently detected in human MPE and cell lines isolated thereof, but are often lost during automated analyses, as indicated by manual versus automated examination of Sanger sequencing traces. Finally, the novel KRAS inhibitor deltarasin and a monoclonal antibody directed against CCL2 are equally effective against an experimental mouse model of MPE, a result that holds promise for future efficient therapies against the human condition.

Intrathymic injection of hematopoietic progenitor cells establishes functional T cell development in a mouse model of severe combined immunodeficiency

BACKGROUND

Even though hematopoietic stem cell transplantation can be curative in patients with severe combined immunodeficiency, there is a need for additional strategies boosting T cell immunity in individuals suffering from genetic disorders of lymphoid development. Here we show that image-guided intrathymic injection of hematopoietic stem and progenitor cells in NOD-scid IL2rγ^null mice is feasible and facilitates the generation of functional T cells conferring protective immunity.

METHODS

Hematopoietic stem and progenitor cells were isolated from the bone marrow of healthy C57BL/6 mice (wild-type, Luciferase⁺, CD45.1⁺) and injected intravenously or intrathymically into both male and female, young or aged NOD-scid IL2rγ^null recipients. The in vivo fate of injected cells was analyzed by bioluminescence imaging and flow cytometry of thymus- and spleen-derived T cell populations. In addition to T cell reconstitution, we evaluated mice for evidence of immune dysregulation based on diabetes development and graft-versus-host disease. T cell immunity following intrathymic injection of hematopoietic stem and progenitor cells in NOD-scid IL2rγ^null mice was assessed in a B cell lymphoma model.

RESULTS

Despite the small size of the thymic remnant in NOD-scid IL2rγ^null mice, we were able to accomplish precise intrathymic delivery of hematopoietic stem and progenitor cells by ultrasound-guided injection. Thymic reconstitution following intrathymic injection of healthy allogeneic hematopoietic cells was most effective in young male recipients, indicating that even in the setting of severe immunodeficiency, sex and age are important variables for thymic function. Allogeneic T cells generated in intrathymically injected NOD-scid IL2rγ^null mice displayed anti-lymphoma activity in vivo, but we found no evidence for severe auto/alloreactivity in T cell-producing NOD-scid IL2rγ^null mice, suggesting that immune dysregulation is not a major concern.

CONCLUSIONS

Our findings suggest that intrathymic injection of donor hematopoietic stem and progenitor cells is a safe and effective strategy to establish protective T cell immunity in a mouse model of severe combined immunodeficiency.

A Functional Bioluminescent Zebrafish Screen for Enhancing Hematopoietic Cell Homing

To discover small molecules that modulate hematopoietic cell homing after adoptive transfer, we created a transgenic zebrafish expressing firefly luciferase downstream of the ubiquitin promoter (ubi:luc) to serve as a hematopoietic donor. Bioluminescence imaging (BLI) was used to detect and follow ubi:luc hematopoietic cells that homed to the marrow as early as 1 day post-transplant. BLI was able to detect the biological effect of prostaglandin E₂ on early homing/engraftment of donor hematopoietic cells. This system was utilized in a functional screen of small molecules to enhance homing/engraftment. We discovered a phytosterol, ergosterol, that could increase hematopoietic cell homing in zebrafish and mice. In addition, ergosterol increased CXCR4 expression and promoted expansion of Lin⁻SCA-1⁺KIT⁺ cells in vitro. We have demonstrated the utility of in vivo BLI to non-invasively monitor donor hematopoietic cell activity in adult zebrafish as a functional screen for mediators of cellular homing.

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Bioluminescent imaging (BLI) can track engrafting hematopoietic cells

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BLI can be used for screening of enhancers of hematopoietic cell homing

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Using BLI, ergosterol was found to increase hematopoietic cell homing

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Ergosterol affects hematopoietic progenitor migration, growth, and viability in vitro

A synthetic luciferin improves in vivo bioluminescence imaging of gene expression in cardiovascular brain regions

Bioluminescence imaging is an effective tool for in vivo investigation of molecular processes. We have demonstrated the applicability of bioluminescence imaging to spatiotemporally monitor gene expression in cardioregulatory brain nuclei during the development of cardiovascular disease, via incorporation of firefly luciferase into living animals, combined with exogenous d-luciferin substrate administration. Nevertheless, d-luciferin uptake into the brain tissue is low, which decreases the sensitivity of bioluminescence detection, particularly when considering small changes in gene expression in tiny central areas. Here, we tested the hypothesis that a synthetic luciferin, cyclic alkylaminoluciferin (CycLuc1), would be superior to d-luciferin for in vivo bioluminescence imaging in cardiovascular brain regions. Male C57B1/6 mice underwent targeted delivery of an adenovirus encoding the luciferase gene downstream of the CMV promoter to the subfornical organ (SFO) or paraventricular nucleus of hypothalamus (PVN), two crucial cardioregulatory neural regions. While bioluminescent signals could be obtained following d-luciferin injection (150 mg/kg), CycLuc1 administration resulted in a three- to fourfold greater bioluminescent emission from the SFO and PVN, at 10- to 20-fold lower substrate concentrations (7.5-15 mg/kg). This CycLuc1-mediated enhancement in bioluminescent emission was evident early following substrate administration (i.e., 6-10 min) and persisted for up to 1 h. When the exposure time was reduced from 60 s to 1,500 ms, minimal signal in the PVN was detectable with d-luciferin, whereas bioluminescent images could be reliably captured with CycLuc1. These findings demonstrate that bioluminescent imaging with the synthetic luciferin CycLuc1 provides an improved physiological genomics tool to investigate molecular events in discrete cardioregulatory brain nuclei.

Dynamic Immune Cell Recruitment After Murine Pulmonary Aspergillus fumigatus Infection under Different Immunosuppressive Regimens

Humans are continuously exposed to airborne spores of the saprophytic fungus Aspergillus fumigatus. However, in healthy individuals pulmonary host defense mechanisms efficiently eliminate the fungus. In contrast, A. fumigatus causes devastating infections in immunocompromised patients. Host immune responses against A. fumigatus lung infections in immunocompromised conditions have remained largely elusive. Given the dynamic changes in immune cell subsets within tissues upon immunosuppressive therapy, we dissected the spatiotemporal pulmonary immune response after A. fumigatus infection to reveal basic immunological events that fail to effectively control invasive fungal disease. In different immunocompromised murine models, myeloid, notably neutrophils, and macrophages, but not lymphoid cells were strongly recruited to the lungs upon infection. Other myeloid cells, particularly dendritic cells and monocytes, were only recruited to lungs of corticosteroid treated mice, which developed a strong pulmonary inflammation after infection. Lymphoid cells, particularly CD4⁺ or CD8⁺ T-cells and NK cells were highly reduced upon immunosuppression and not recruited after A. fumigatus infection. Moreover, adoptive CD11b⁺ myeloid cell transfer rescued cyclophosphamide immunosuppressed mice from lethal A. fumigatus infection but not cortisone and cyclophosphamide immunosuppressed mice. Our findings illustrate that CD11b⁺ myeloid cells are critical for anti-A. fumigatus defense under cyclophosphamide immunosuppressed conditions.

Tracking and Quantification of Magnetically Labeled Stem Cells using Magnetic Resonance Imaging

Stem cell based therapies have critical impacts on treatments and cures of diseases such as neurodegenerative or cardiovascular disease. In vivo tracking of stem cells labeled with magnetic contrast agents is of particular interest and importance as it allows for monitoring of the cells' bio-distribution, viability, and physiological responses. Herein, recent advances are introduced in tracking and quantification of super-paramagnetic iron oxide (SPIO) nanoparticles-labeled cells with magnetic resonance imaging, a noninvasive approach that can longitudinally monitor transplanted cells. This is followed by recent translational research on human stem cells that are dual-labeled with green fluorescence protein (GFP) and SPIO nanoparticles, then transplanted and tracked in a chicken embryo model. Cell labeling efficiency, viability, and cell differentiation are also presented.

Systemic Mesenchymal Stromal Cell Transplantation Prevents Functional Bone Loss in a Mouse Model of Age-Related Osteoporosis

Age-related osteoporosis is driven by defects in the tissue-resident mesenchymal stromal cells (MSCs), a heterogeneous population of musculoskeletal progenitors that includes skeletal stem cells. MSC decline leads to reduced bone formation, causing loss of bone volume and the breakdown of bony microarchitecture crucial to trabecular strength. Furthermore, the low-turnover state precipitated by MSC loss leads to low-quality bone that is unable to perform remodeling-mediated maintenance--replacing old damaged bone with new healthy tissue. Using minimally expanded exogenous MSCs injected systemically into a mouse model of human age-related osteoporosis, we show long-term engraftment and markedly increased bone formation. This led to improved bone quality and turnover and, importantly, sustained microarchitectural competence. These data establish proof of concept that MSC transplantation may be used to prevent or treat human age-related osteoporosis.

SIGNIFICANCE

This study shows that a single dose of minimally expanded mesenchymal stromal cells (MSCs) injected systemically into a mouse model of human age-related osteoporosis display long-term engraftment and prevent the decline in bone formation, bone quality, and microarchitectural competence. This work adds to a growing body of evidence suggesting that the decline of MSCs associated with age-related osteoporosis is a major transformative event in the progression of the disease. Furthermore, it establishes proof of concept that MSC transplantation may be a viable therapeutic strategy to treat or prevent human age-related osteoporosis.

Type I IFN Does Not Promote Susceptibility to Foodborne Listeria monocytogenes

Type I IFN (IFN-α/β) is thought to enhance growth of the foodborne intracellular pathogen Listeria monocytogenes by promoting mechanisms that dampen innate immunity to infection. However, the type I IFN response has been studied primarily using methods that bypass the stomach and, therefore, fail to replicate the natural course of L. monocytogenes infection. In this study, we compared i.v. and foodborne transmission of L. monocytogenes in mice lacking the common type I IFN receptor (IFNAR1(-/-)). Contrary to what was observed using i.v. infection, IFNAR1(-/-) and wild-type mice had similar bacterial burdens in the liver and spleen following foodborne infection. Splenocytes from wild-type mice infected i.v. produced significantly more IFN-β than did those infected by the foodborne route. Consequently, the immunosuppressive effects of type I IFN signaling, which included T cell death, increased IL-10 secretion, and repression of neutrophil recruitment to the spleen, were all observed following i.v. but not foodborne transmission of L. monocytogenes. Type I IFN was also previously shown to cause a loss of responsiveness to IFN-γ through downregulation of the IFN-γ receptor α-chain on macrophages and dendritic cells. However, we detected a decrease in surface expression of IFN-γ receptor α-chain even in the absence of IFN-α/β signaling, suggesting that in vivo, this infection-induced phenotype is not type I IFN-dependent. These results highlight the importance of using the natural route of infection for studies of host-pathogen interactions and suggest that the detrimental effects of IFN-α/β signaling on the innate immune response to L. monocytogenes may be an artifact of the i.v. infection model.

Bioluminescent imaging of ABCG2 efflux activity at the blood-placenta barrier

Physiologic barriers such as the blood placenta barrier (BPB) and the blood brain barrier protect the underlying parenchyma from pathogens and toxins. ATP-binding cassette (ABC) transporters are transmembrane proteins found at these barriers, and function to efflux xenobiotics and maintain chemical homeostasis. Despite the plethora of ex vivo and in vitro data showing the function and expression of ABC transporters, no imaging modality exists to study ABC transporter activity in vivo at the BPB. In the present study, we show that in vitro models of the placenta possess ABCG2 activity and can specifically transport D-luciferin, the endogenous substrate of firefly luciferase. To test ABCG2 transport activity at the BPB, we devised a breeding strategy to generate a bioluminescent pregnant mouse model to demonstrate transporter function in vivo. We found that coadministering the ABCG2 inhibitors Ko143 and gefitinib with D-luciferin increased bioluminescent signal from fetuses and placentae, whereas the control P-gp inhibitor DCPQ had no effect. We believe that our bioluminescent pregnant mouse model will facilitate greater understanding of the BPB and ABCG2 activity in health and disease.

Hyaluronan synthesis is necessary for autoreactive T-cell trafficking, activation, and Th1 polarization

The extracellular matrix polysaccharide hyaluronan (HA) accumulates at sites of autoimmune inflammation, including white matter lesions in multiple sclerosis (MS), but its functional importance in pathogenesis is unclear. We have evaluated the impact of 4-methylumbelliferone (4-MU), an oral inhibitor of HA synthesis, on disease progression in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS. Treatment with 4-MU decreases the incidence of EAE, delays its onset, and reduces the severity of established disease. 4-MU inhibits the activation of autoreactive T cells and prevents their polarization toward a Th1 phenotype. Instead, 4-MU promotes polarization toward a Th2 phenotpye and induction of Foxp3(+) regulatory T cells. Further, 4-MU hastens trafficking of T cells through secondary lymphoid organs, impairs the infiltration of T cells into the CNS parenchyma, and limits astrogliosis. Together, these data suggest that HA synthesis is necessary for disease progression in EAE and that treatment with 4-MU may be a potential therapeutic strategy in CNS autoimmunity. Considering that 4-MU is already a therapeutic, called hymecromone, that is approved to treat biliary spasm in humans, we propose that it could be repurposed to treat MS.

Neutrophils support lung colonization of metastasis-initiating breast cancer cells

Despite progress in the development of drugs that efficiently target cancer cells, treatments for metastatic tumours are often ineffective. The now well-established dependency of cancer cells on their microenvironment suggests that targeting the non-cancer-cell component of the tumour might form a basis for the development of novel therapeutic approaches. However, the as-yet poorly characterized contribution of host responses during tumour growth and metastatic progression represents a limitation to exploiting this approach. Here we identify neutrophils as the main component and driver of metastatic establishment within the (pre-)metastatic lung microenvironment in mouse breast cancer models. Neutrophils have a fundamental role in inflammatory responses and their contribution to tumorigenesis is still controversial. Using various strategies to block neutrophil recruitment to the pre-metastatic site, we demonstrate that neutrophils specifically support metastatic initiation. Importantly, we find that neutrophil-derived leukotrienes aid the colonization of distant tissues by selectively expanding the sub-pool of cancer cells that retain high tumorigenic potential. Genetic or pharmacological inhibition of the leukotriene-generating enzyme arachidonate 5-lipoxygenase (Alox5) abrogates neutrophil pro-metastatic activity and consequently reduces metastasis. Our results reveal the efficacy of using targeted therapy against a specific tumour microenvironment component and indicate that neutrophil Alox5 inhibition may limit metastatic progression.

Selection via pluripotency-related transcriptional screen minimizes the influence of somatic origin on iPSC differentiation propensity

The value of induced pluripotent stem cells (iPSCs) within regenerative medicine is contingent on predictable and consistent iPSC differentiation. However, residual influence of the somatic origin or reprogramming technique may variegate differentiation propensity and confound comparative genotype/phenotype analyses. The objective of this study was to define quality control measures to select iPSC clones that minimize the influence of somatic origin on differentiation propensity independent of the reprogramming strategy. More than 60 murine iPSC lines were derived from different fibroblast origins (embryonic, cardiac, and tail tip) via lentiviral integration and doxycycline-induced transgene expression. Despite apparent equivalency according to established iPSC histologic and cytomorphologic criteria, clustering of clonal variability in pluripotency-related gene expression identified transcriptional outliers that highlighted cell lines with unpredictable cardiogenic propensity. Following selection according to a standardized gene expression profile calibrated by embryonic stem cells, the influence of somatic origin on iPSC methylation and transcriptional patterns was negated. Furthermore, doxycycline-induced iPSCs consistently demonstrated earlier differentiation than lentiviral-reprogrammed lines using contractile cardiac tissue as a measure of functional differentiation. Moreover, delayed cardiac differentiation was predominately associated with upregulation in pluripotency-related gene expression upon differentiation. Starting from a standardized pool of iPSCs, relative expression levels of two pluripotency genes, Oct4 and Zfp42, statistically correlated with enhanced cardiogenicity independent of somatic origin or reprogramming strategy (R(2)  = 0.85). These studies demonstrate that predictable iPSC differentiation is independent of somatic origin with standardized gene expression selection criteria, while the residual impact of reprogramming strategy greatly influences predictable output of tissue-specification required for comparative genotype/phenotype analyses.

Establishment of Green Fluorescent Protein and Firefly Luciferase Expressing Mouse Primary Macrophages for In Vivo Bioluminescence Imaging

Macrophages play a key role in tissue homeostasis as well as in a range of pathological conditions including atherosclerosis, cancer, and autoimmunity. Many aspects of their in vivo behavior are, however, poorly understood. Bioluminescence imaging (BLI) with green fluorescent protein (GFP) and firefly luciferase (FLUC) labelled autologous reporter macrophages could potentially offer a powerful tool to study macrophage biology, but this approach has been hindered by the relative difficulty of efficient gene transfer into primary macrophages. Here we describe a straightforward method for producing large numbers of GFP/FLUC expressing mouse primary macrophages utilizing lentivirus vector, cyclosporine, and a double infection strategy. Using this method we achieved up to 60% of macrophages to express GFP with correspondingly high FLUC signal. When injected into the circulation using a mouse model of local biomaterial induced inflammation and osteolysis, macrophages were initially detectable within the lungs, followed by systemic homing to the local area of chronic inflammation in the distal femur. In addition, transduced macrophages maintained their ability to assume M1 and M2 phenotypes although the GFP/FLUC expression was altered by the polarizing signals. These reporter macrophages could prove to be valuable tools to study the role of macrophages in health and disease.

Luciferin Amides Enable in Vivo Bioluminescence Detection of Endogenous Fatty Acid Amide Hydrolase Activity

Firefly luciferase is homologous to fatty acyl-CoA synthetases. We hypothesized that the firefly luciferase substrate d-luciferin and its analogs are fatty acid mimics that are ideally suited to probe the chemistry of enzymes that release fatty acid products. Here, we synthesized luciferin amides and found that these molecules are hydrolyzed to substrates for firefly luciferase by the enzyme fatty acid amide hydrolase (FAAH). In the presence of luciferase, these molecules enable highly sensitive and selective bioluminescent detection of FAAH activity in vitro, in live cells, and in vivo. The potency and tissue distribution of FAAH inhibitors can be imaged in live mice, and luciferin amides serve as exemplary reagents for greatly improved bioluminescence imaging in FAAH-expressing tissues such as the brain.

Treatment with agonistic DR3 antibody results in expansion of donor Tregs and reduced graft-versus-host disease

The paucity of regulatory T cells (Tregs) limits clinical translation to control aberrant immune reactions including graft-versus-host disease (GVHD). Recent studies showed that the agonistic antibody to DR3 (αDR3) expanded CD4(+)FoxP3(+) Tregs in vivo. We investigated whether treating donor mice with a single dose of αDR3 could alleviate acute GVHD in a MHC-mismatched bone marrow transplantation model. αDR3 induced selective proliferation of functional Tregs. CD4(+) T cells isolated from αDR3-treated mice contained higher numbers of Tregs and were less proliferative to allogeneic stimuli. In vivo GVHD studies confirmed that Tregs from αDR3-treated donors expanded robustly and higher frequencies of Tregs within donor CD4(+) T cells were maintained, resulting in improved survival. Conventional T cells derived from αDR3-treated donors showed reduced activation and proliferation. Serum levels of proinflammatory cytokines (IFNγ, IL-1β, and TNFα) and infiltration of donor T cells into GVHD target tissues (gastrointestinal tract and liver) were decreased. T cells from αDR3-treated donors retained graft-vs-tumor (GVT) effects. In conclusion, a single dose of αDR3 alleviates acute GVHD while preserving GVT effects by selectively expanding and maintaining donor Tregs. This novel strategy will facilitate the clinical application of Treg-based therapies.

Combinations of Kinase Inhibitors Protecting Myoblasts against Hypoxia

Cell-based therapies to treat skeletal muscle disease are limited by the poor survival of donor myoblasts, due in part to acute hypoxic stress. After confirming that the microenvironment of transplanted myoblasts is hypoxic, we screened a kinase inhibitor library in vitro and identified five kinase inhibitors that protected myoblasts from cell death or growth arrest in hypoxic conditions. A systematic, combinatorial study of these compounds further improved myoblast viability, showing both synergistic and additive effects. Pathway and target analysis revealed CDK5, CDK2, CDC2, WEE1, and GSK3β as the main target kinases. In particular, CDK5 was the center of the target kinase network. Using our recently developed statistical method based on elastic net regression we computationally validated the key role of CDK5 in cell protection against hypoxia. This method provided a list of potential kinase targets with a quantitative measure of their optimal amount of relative inhibition. A modified version of the method was also able to predict the effect of combinations using single-drug response data. This work is the first step towards a broadly applicable system-level strategy for the pharmacology of hypoxic damage.

Donor Requirements for Regulatory T Cell Suppression of Murine Graft-versus-Host Disease

Adoptive transfer of freshly isolated natural occurring CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg) prevents graft-versus-host disease (GVHD) in several animal models and following hematopoietic cell transplantation (HCT) in clinical trials. Donor-derived Treg have been mainly used, as they share the same MHC with CD4(+) and CD8(+) conventional T cells (Tcon) that are primarily responsible for GVHD. Third party-derived Treg are a promising alternative for cellular therapy, as they can be prepared in advance, screened for pathogens and activity, and banked. We explored MHC disparities between Treg and Tcon in HCT to evaluate the impact of different Treg populations in GVHD prevention and survival. Third-party Treg and donor Treg are equally suppressive in ex vivo assays, whereas both donor and third-party but not host Treg protect from GVHD in allogeneic HCT, with donor Treg being the most effective. In an MHC minor mismatched transplantation model (C57BL/6 → BALB/b), donor and third-party Treg were equally effective in controlling GVHD. Furthermore, using an in vivo Treg depletion mouse model, we found that Treg exert their main suppressive activity in the first 2 d after transplantation. Third-party Treg survive for a shorter period of time after adoptive transfer, but despite the shorter survival, they control Tcon proliferation in the early phases of HCT. These studies provide relevant insights on the mechanisms of Treg-mediated protection from GVHD and support for the use of third-party Treg in clinical trials.

Skin fibrosis. Identification and isolation of a dermal lineage with intrinsic fibrogenic potential

Dermal fibroblasts represent a heterogeneous population of cells with diverse features that remain largely undefined. We reveal the presence of at least two fibroblast lineages in murine dorsal skin. Lineage tracing and transplantation assays demonstrate that a single fibroblast lineage is responsible for the bulk of connective tissue deposition during embryonic development, cutaneous wound healing, radiation fibrosis, and cancer stroma formation. Lineage-specific cell ablation leads to diminished connective tissue deposition in wounds and reduces melanoma growth. Using flow cytometry, we identify CD26/DPP4 as a surface marker that allows isolation of this lineage. Small molecule-based inhibition of CD26/DPP4 enzymatic activity during wound healing results in diminished cutaneous scarring. Identification and isolation of these lineages hold promise for translational medicine aimed at in vivo modulation of fibrogenic behavior.

Mast cells mediate malignant pleural effusion formation

Mast cells (MCs) have been identified in various tumors; however, the role of these cells in tumorigenesis remains controversial. Here, we quantified MCs in human and murine malignant pleural effusions (MPEs) and evaluated the fate and function of these cells in MPE development. Evaluation of murine MPE-competent lung and colon adenocarcinomas revealed that these tumors actively attract and subsequently degranulate MCs in the pleural space by elaborating CCL2 and osteopontin. MCs were required for effusion development, as MPEs did not form in mice lacking MCs, and pleural infusion of MCs with MPE-incompetent cells promoted MPE formation. Once homed to the pleural space, MCs released tryptase AB1 and IL-1β, which in turn induced pleural vasculature leakiness and triggered NF-κB activation in pleural tumor cells, thereby fostering pleural fluid accumulation and tumor growth. Evaluation of human effusions revealed that MCs are elevated in MPEs compared with benign effusions. Moreover, MC abundance correlated with MPE formation in a human cancer cell-induced effusion model. Treatment of mice with the c-KIT inhibitor imatinib mesylate limited effusion precipitation by mouse and human adenocarcinoma cells. Together, the results of this study indicate that MCs are required for MPE formation and suggest that MC-dependent effusion formation is therapeutically addressable.

Systemically delivered adipose stromal vascular fraction cells disseminate to peripheral artery walls and reduce vasomotor tone through a CD11b+ cell-dependent mechanism

Vasoactivity, an important aspect of tissue healing, is often compromised in disease and tissue injury. Dysfunction in the smaller vasoactive arteries is most impactful, given the role of these vessels in controlling downstream tissue perfusion. The adipose stromal vascular fraction (SVF) is a mix of homeostatic cells shown to promote tissue healing. Our objective was to test the hypothesis that autologous SVF cells therapeutically modulate peripheral artery vasoactivity in syngeneic mouse models of small artery function. Analysis of vasoactivity of saphenous arteries isolated from normal mice 1 week after intravenous injection of freshly isolated SVF cells revealed that pressure-dependent artery vasomotor tone was decreased by the SVF cell isolate, but not one depleted of CD11b(+) cells. Scavenging hydrogen peroxide in the vessel wall abrogated the artery relaxation promoted by the SVF cell isolate. Consistent with a CD11b(+) cell being the relevant cell type, SVF-derived F4/80-positive macrophages were present within the adventitia of the artery wall coincident with vasorelaxation. In a model of artery inflammation mimicking a common disease condition inducing vasoactive dysfunction, the SVF cells potentiated relaxation of saphenous arteries without structurally remodeling the artery via a CD11b(+) cell-dependent manner. Our findings demonstrate that freshly isolated, adipose SVF cells promote vasomotor relaxation in vasoactive arteries via a hydrogen peroxide-dependent mechanism that required CD11b(+) cells (most likely macrophages). Given the significant impact of small artery dysfunction in disease, we predict that the intravenous delivery of this therapeutic cell preparation would significantly improve tissue perfusion, particularly in diseases with diffuse vascular involvement.

Development of reporter gene imaging techniques for long-term assessment of human circulating angiogenic cells

The use of biomaterials and tracking the long-term fate of the transplanted cells is expected to help improve the clinical translation of cell therapies for cardiac regeneration. To this end, reporter gene strategies are promising for monitoring the fate of cells transplanted with or without a delivery biomaterial; however, their application with primary adult progenitor cells (such as human circulating angiogenic cells (CACs)) has not been extensively evaluated. In this study, human CACs were transduced with reporter genes via one of two lentiviral (LV) vectors: LV-GFP-iresTK or LV-Fluc-RFP-tTK. The mean transduction efficiency was 15% (LV-GFP-iresTK) and 13% (LV-Fluc-RFP-tTK) at multiplicities of infection (MOI) of 10 and 50, respectively. Western blot analysis confirmed HSV1-tk protein expression in transduced CACs. There was no significant difference in viability between the transduced CACs and the untreated controls at a MOI of 50 or below. However, a reduction was observed in cell viability of CACs transduced with LV-Fluc-RFP-tTK at an MOI of 100. Cell migration and angiogenic potential were not affected by transduction protocol. After 4 weeks, 80.3 ± 8.4% of the labeled cells continued to express the reporters and could be visualized when embedded within a collagen matrix scaffold. Therefore, quiescent human CACs can be stably transduced to express reporter genes without affecting their function. This reporter gene technique is a promising approach to be further tested for tracking transplanted CACs (±delivery matrix) non-invasively and longitudinally.

Single thrombopoietin dose alleviates hematopoietic stem cells intrinsic short- and long-term ionizing radiation damage. In vivo identification of anatomical cell expansion sites

Hematopoietic stem cells (HSC) are essential for maintaining the integrity of complex and long-lived organisms. HSC, which are self-renewing, reconstitute the hematopoietic system through out life and facilitate long-term repopulation of myeloablated recipients. We have previously demonstrated that when mice are exposed to sublethal doses of ionizing radiation, subsets of the stem/progenitor compartment are affected. In this study we examine the role of thrombopoietin (TPO) on the regenerative capacities of HSC after irradiation and report the first demonstration of efficacy of a single injection of TPO shortly after in vivo exposure to ionizing radiation for reducing HSC injury and improving their functional outcome. Our results demonstrate that TPO treatment not only reduced the number of apoptotic cells but also induced a significant modification of their intrinsic characteristics. These findings were supported by transplantation assays with long-term HSC that were irradiated or unirradiated, TPO treated or untreated, in CD45.1/CD45.2 systems and by using luciferase-labeled HSC for direct bioluminescence imaging in living animals. Of particular importance, our data demonstrate the skull to be a highly favorable site for the TPO-induced emergence of hematopoietic cells after irradiation, suggesting a TPO-mediated relationship of primitive hematopoietic cells to an anatomical component. Together, the data presented here: provide novel findings about aspects of TPO action on stem cells, open new areas of investigation for therapeutic options in patients who are treated with radiation therapy, and show that early administration of a clinically suitable TPO-agonist counteracts the previously observed adverse effects.

Effect of DiD Carbocyanine Dye Labeling on Immunoregulatory Function and Differentiation of Mice Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) have been used to treat a variety of degenerative disorders. Labeling of MSCs with an appropriate tracer is vital to demonstrate the in vivo engraftment and differentiation of transplanted MSCs. DiD is a lipophilic fluorescent dye with near infrared emission spectra that makes it suitable for in vivo tracing. Therefore, in the present study the consequences of DiD labeling on induction of oxidative stress and apoptosis as well as inhibition of biological functions of mesenchymal stem cells (MSCs) were investigated. DiD labeling did not provoke the production of ROS, induction of apoptosis, or inhibition of production of immunosuppressive factors (PGE2 and IL-10) by MSCs. In addition, there were no statistical differences between DiD-labeled and unlabeled MSCs in suppression of proliferation and cytokine production (IFN-γ and IL-17) by in vitro stimulated splenocytes or improvement of clinical score in EAE after in vivo administration. In addition, DiD labeling did not alter the differentiation capacity of MSCs. Taken together, DiD can be considered as a safe dye for in vivo tracking of MSCs.

Cardiac tissue slice transplantation as a model to assess tissue-engineered graft thickness, survival, and function

BACKGROUND

Cell therapies offer the potential to improve cardiac function after myocardial infarction. Although injection of single-cell suspensions has proven safe, cell retention and survival rates are low. Tissue-engineered grafts allow cell delivery with minimal initial cell loss and mechanical support to the heart. However, graft performance cannot be easily compared, and optimal construct thickness, vascularization, and survival kinetics are unknown.

METHODS AND RESULTS

Cardiac tissue slices (CTS) were generated by sectioning mouse hearts (n=40) expressing firefly luciferase and green fluorescent protein into slices of defined size and thickness using a vibrating blade microtome. Bioluminescence imaging of CTS transplanted onto hearts of immunodeficient mice demonstrated survival of ≤30% of transplanted cells. Cardiac slice perfusion was re-established within 3 days, likely through anastomosis of pre-existing vessels with the host vasculature and invasion of vessels from the host. Immunofluorescence showed a peak in cell death 3 days after transplantation and a gradual decline thereafter. MRI revealed preservation of contractile function and an improved ejection fraction 1 month after transplantation of CTS (28±2% CTS versus 22±2% control; P=0.05). Importantly, this effect was specific to CTS because transplantation of skeletal muscle tissue slices led to faster dilative remodeling and higher animal mortality.

CONCLUSIONS

In summary, this is the first study to use CTS as a benchmark to validate and model tissue-engineered graft studies. CTS transplantation improved cell survival, established reperfusion, and enhanced cardiac function after myocardial infarction. These findings also confirm that dilative remodeling can be attenuated by topical transplantation of CTS but not skeletal muscle tissue grafts.

A biocompatible "split luciferin" reaction and its application for non-invasive bioluminescent imaging of protease activity in living animals

The great complexity of many human pathologies, such as cancer, diabetes, and neurodegenerative diseases, requires new tools for studies of biological processes on the whole organism level. The discovery of novel biocompatible reactions has tremendously advanced our understanding of basic biology; however, no efficient tools exist for real-time non-invasive imaging of many human proteases that play very important roles in multiple human disorders. We recently reported that the "split luciferin" biocompatible reaction represents a valuable tool for evaluation of protease activity directly in living animals using bioluminescence imaging (BLI). Since BLI is the most sensitive in vivo imaging modality known to date, this method can be widely applied for the evaluation of the activity of multiple proteases, as well as identification of their new peptide-specific substrates. In this unit, we describe several applications of this "split luciferin" reaction for quantification of protease activities in test tube assays and living animals.

Donor CD4+ Foxp3+ regulatory T cells are necessary for posttransplantation cyclophosphamide-mediated protection against GVHD in mice

Posttransplantation cyclophosphamide (PTCy) is an effective prophylaxis against graft-versus-host disease (GVHD). However, it is unknown whether PTCy works singularly by eliminating alloreactive T cells via DNA alkylation or also by restoring the conventional (Tcon)/regulatory (Treg) T-cell balance. We studied the role of Tregs in PTCy-mediated GVHD prophylaxis in murine models of allogeneic blood or marrow transplantation (alloBMT). In 2 distinct MHC-matched alloBMT models, infusing Treg-depleted allografts abrogated the GVHD-prophylactic activity of PTCy. Using allografts in which Foxp3(+) Tregs could be selectively depleted in vivo, either pre- or post-PTCy ablation of donor thymus-derived Tregs (tTregs) abolished PTCy protection against GVHD. PTCy treatment was associated with relative preservation of donor Tregs. Experiments using combinations of Foxp3(-) Tcons and Foxp3(+) Tregs sorted from different Foxp3 reporter mice indicated that donor Treg persistence after PTCy treatment was predominantly caused by survival of functional tTregs that retained Treg-specific demethylation and also induction of peripherally derived Tregs. Finally, adoptive transfer of tTregs retrieved from PTCy-treated chimeras rescued PTCy-treated, Treg-depleted recipients from lethal GVHD. Our findings indicate that PTCy-mediated protection against GVHD is not singularly dependent on depletion of donor alloreactive T cells but also requires rapidly recovering donor Tregs to initiate and maintain alloimmune regulation.

Beyond D-luciferin: expanding the scope of bioluminescence imaging in vivo

The light-emitting chemical reaction catalyzed by the enzyme firefly luciferase is widely used for noninvasive imaging in live mice. However, photon emission from the luciferase is crucially dependent on the chemical properties of its substrate, D-luciferin. In this review, we describe recent work to replace the natural luciferase substrate with synthetic analogs that extend the scope of bioluminescence imaging.

Autologous apoptotic cells preceding transplantation enhance survival in lethal murine graft-versus-host models

Acute graft-versus-host disease (GVHD) is induced by alloreactivity of donor T cells toward host antigens presented on antigen-presenting cells (APCs). Apoptotic cells are capable of inducing tolerance by altering APC maturation. Apoptosis can be induced by extracorporeal photopheresis (ECP). We demonstrate that the use of ECP as a prophylaxis prior to conditioning significantly improves survival (P < .0001) after bone marrow transplantation (BMT) by inhibiting the initiation phase of acute GVHD in a murine BMT model. ECP-treated autologous splenocytes resulted in immune tolerance in the host, including reduced dendritic cell activation with decreased nuclear factor-κB engagement, increased regulatory T-cell (Treg) numbers with enhanced expression of cytolytic T lymphocyte-associated antigen 4, potentiating their suppressive function. The protective effect required host production of interleukin-10 and host Tregs. Conventional T cells that entered this tolerant environment experienced reduced proliferation, as well as a reduction of tissue homing and expression of activation markers. The induction of this tolerant state by ECP was obviated by cotreatment with lipopolysaccharide, suggesting that the inflammatory state of the recipient prior to treatment would play a role in potential clinical translation. The use of prophylactic ECP may provide an alternative and safe method for immunosuppression in the bone marrow transplant setting.

A synthetic luciferin improves bioluminescence imaging in live mice

Firefly luciferase is the most widely used optical reporter for noninvasive bioluminescence imaging (BLI) in rodents. BLI relies on the ability of the injected luciferase substrate D-luciferin to access luciferase-expressing cells and tissues within the animal. Here we show that injection of mice with a synthetic luciferin, CycLuc1, improves BLI with existing luciferase reporters and enables imaging in the brain that could not be achieved with D-luciferin.

Image-guided intrathymic injection of multipotent stem cells supports lifelong T-cell immunity and facilitates targeted immunotherapy

T-cell deficiency related to disease, medical treatment, or aging represents a major clinical challenge and is associated with significant morbidity and mortality in cancer and bone marrow transplantation recipients. This study describes several innovative and clinically relevant strategies to manipulate thymic function based on an interventional radiology technique for intrathymic injection of cells or drugs. We show that intrathymic injection of multipotent hematopoietic stem/progenitor cells into irradiated syngeneic or allogeneic young or aged recipients resulted in efficient and long-lasting generation of functional donor T cells. Persistence of intrathymic donor cells was associated with intrathymic presence of cells resembling long-term hematopoietic stem cells, suggesting a self-renewal capacity of the intrathymically injected cells. Furthermore, our approach enabled the induction of long-term antigen-specific T-cell-mediated antitumor immunity following intrathymic injection of progenitor cells harboring a transgenic T-cell receptor gene. The intrathymic injection of interleukin-7 prior to irradiation conferred radioprotection. In addition, thymopoiesis of aged mice improved with a single intrathymic administration of low-dose keratinocyte growth factor, an effect that was sustained even in the setting of radiation-induced injury. Taken together, we established a preclinical framework for the development of novel clinical protocols to establish lifelong antigen-specific T-cell immunity.

Stem cell decisions: a twist of fate or a niche market?

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Extrinsic and intrinsic cues that impact on stem cell biology.

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The importance to establish methods that allow to compare spindle orientation measurements.

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Mechanisms of centrosome segregation in asymmetrically dividing cells.

Establishing and maintaining cell fate in the right place at the right time is a key requirement for normal tissue maintenance. Stem cells are at the core of this process. Understanding how stem cells balance self-renewal and production of differentiating cells is key for understanding the defects that underpin many diseases. Both, external cues from the environment and cell intrinsic mechanisms can control the outcome of stem cell division. The role of the orientation of stem cell division has emerged as an important mechanism for specifying cell fate decisions. Although, the alignment of cell divisions can dependent on spatial cues from the environment, maintaining stemness is not always linked to positioning of stem cells in a particular microenvironment or `niche'. Alternate mechanisms that could contribute to cellular memory include differential segregation of centrosomes in asymmetrically dividing cells.

Bioluminescence: a versatile technique for imaging cellular and molecular features

Bioluminescence is a ubiquitous imaging modality for visualizing biological processes in vivo. This technique employs visible light and interfaces readily with most cell and tissue types, making it a versatile technology for preclinical studies. Here we review basic bioluminescence imaging principles, along with applications of the technology that are relevant to the medicinal chemistry community. These include noninvasive cell tracking experiments, analyses of protein function, and methods to visualize small molecule metabolites. In each section, we also discuss how bioluminescent tools have revealed insights into experimental therapies and aided drug discovery. Last, we highlight the development of new bioluminescent tools that will enable more sensitive and multi-component imaging experiments and, thus, expand our broader understanding of living systems.

Analyzing hematopoietic stem cell homing, lodgment, and engraftment to better understand the bone marrow niche

The existence of a bone marrow (BM) niche--the location in which hematopoietic stem cells (HSCs) reside--was proposed more than 30 years ago. Recent data suggest that the interaction of HSCs with cellular and extracellular components within the BM is critical for HSC regulation. The tracking of immunofluorescently labeled, prospectively isolated HSCs to and within the BM cavity allows the assessment of the regulatory processes involved in (1) homing, which involves transendothelial migration into the BM; (2) lodgment, including transmarrow migration through the extravascular space; and (3) BM reconstitution. Together, such analyses provide a better understanding of the cellular and extracellular components involved in the regulation of HSC quiescence and differentiation. Homing and lodgment of transplanted HSCs, the first critical steps in engraftment, involve multiple interactions between HSCs and the BM microenvironment. Herein, we describe a refined method of analyzing homing efficiency and spatial distribution of HSCs harvested from endosteal and/or central BM regions; we also review alternate methods. Using these techniques, microenvironment modifications within the recipient or surface protein-expression modifications on donor HSCs in animal models provide insights into components influencing the homing, lodgment, and engraftment processes.

Intravital imaging of hematopoietic stem cells in the mouse skull

Over the past 50 years, much insight has been gained into the biology of hematopoietic stem cells (HSCs). Much of this information has been gained though isolation of specific bone marrow populations, and transplantation into irradiated recipients followed by characterization of chimeras months later. These studies have yielded insights into the function of HSCs, but have shed little light on the interactions of individual stem cells with their environment. Characterization of the behavior of single HSCs awaited the use of relatively noninvasive intravital microscopy, which allows one to identify rare cells in real time and follow them in multiple imaging sessions. Here we describe techniques used to image transplanted HSCs in the mouse calvarium using hybrid confocal/multi-photon microscopy and second harmonic imaging. For detection, fluorescently tagged HSCs are transplanted into a recipient mouse. The architecture of the bone marrow can be delineated using a combination of fluorescent probes and vascular dyes, second harmonic generation to detect the collagen signal from bone, and transgenic recipient mice containing specific fluorescent support cell populations.

Reporter gene technologies for imaging cell fates in hematopoiesis

Advances in noninvasive imaging technologies that allow for in vivo dynamic monitoring of cells and cellular function in living research subjects have revealed new insights into cell biology in the context of intact organs and their native environment. In the field of hematopoiesis and stem cell research, studies of cell trafficking involved in injury repair and hematopoietic engraftment have made great progress using these new tools. Stem cells present unique challenges for imaging since after transplantation, they proliferate dramatically and differentiate. Therefore, the imaging modality used needs to have a large dynamic range, and the genetic regulatory elements used need to be stably expressed during differentiation. Multiple imaging technologies using different modalities are available, and each varies in sensitivity, ease of data acquisition, signal to noise ratios (SNR), substrate availability, and other parameters that affect utility for monitoring cell fates and function. For a given application, there may be several different approaches that can be used. For mouse models, clinically validated technologies such as magnetic resonance imaging (MRI) and positron emission tomography (PET) have been joined by optical imaging techniques such as in vivo bioluminescence imaging (BLI) and fluorescence imaging (FLI), and all have been used to monitor bone marrow and stem cells after transplantation into mice. Photoacoustic imaging that utilizes the sound created by the thermal expansion of absorbed light to generate an image best represents hybrid technologies. Each modality requires that the cells of interest be marked with a genetic reporter that acts as a label making them uniquely visible using that technology. For each modality, there are several labels to choose from. Multiple methods for applying these different labels are available. This chapter provides an overview of the imaging technologies and commonly used labels for each, as well as detailed protocols for gene delivery into hematopoietic cells for the purposes of applying these specific labels to cell trafficking. The goal of this chapter is to provide adequate background information to allow the design and implementation of an experimental system for in vivo imaging in mice.

CD133 is a positive marker for a distinct class of primitive human cord blood-derived CD34-negative hematopoietic stem cells

The identification of human CD34-negative (CD34(-)) hematopoietic stem cells (HSCs) provides a new concept for the hierarchy in the human HSC compartment. Previous studies demonstrated that CD34(-) severe combined immunodeficiency (SCID)-repopulating cells (SRCs) are a distinct class of primitive HSCs in comparison to the well-characterized CD34(+)CD38(-) SRCs. However, the purification level of rare CD34(-) SRCs in 18 lineage marker-negative (Lin(-)) CD34(-) cells (1/1000) is still very low compared with that of CD34(+)CD38(-) SRCs (1/40). As in the mouse, it will be necessary to identify useful positive markers for a high degree of purification of rare human CD34(-) SRCs. Using 18Lin(-)CD34(-) cells, we analyzed the expression of candidate positive markers by flow cytometric analysis. We finally identified CD133 as a reliable positive marker of human CB-derived CD34(-) SRCs and succeeded in highly purifying primitive human CD34(-) HSCs. The limiting dilution analysis demonstrated that the incidence of CD34(-) SRCs in 18Lin(-)CD34(-)CD133(+) cells was 1/142, which is the highest level of purification of these unique CD34(-) HSCs to date. Furthermore, CD133 expression clearly segregated the SRC activities of 18Lin(-)CD34(-) cells, as well as 18Lin(-)CD34(+) cells, in their positive fractions, indicating its functional significance as a common cell surface maker to isolate effectively both CD34(+) and CD34(-) SRCs.

IL-17 gene ablation does not impact Treg-mediated suppression of graft-versus-host disease after bone marrow transplantation

Regulatory T cell (Treg) immunotherapy is a promising strategy for the treatment of graft rejection responses and autoimmune disorders. Our and other laboratories have shown that the transfer of highly purified CD4(+)CD25(+)Foxp3(+) natural Treg can prevent lethal graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation across both major and minor histocompatibility barriers. However, recent evidence suggests that the Treg suppressive phenotype can become unstable, a phenomenon that can culminate in Treg conversion into IL-17-producing cells. We hypothesized that the intense proinflammatory signals released during an ongoing alloreaction might redirect a fraction of the transferred Treg to the Th17 cell fate, thereby losing immunosuppressive potential. We therefore sought to evaluate the impact of Il17 gene ablation on Treg stability and immunosuppressive capacity in a major MHC mismatch model. We show that although Il17 gene ablation results in a mildly enhanced Treg immunosuppressive ability in vitro, such improvement is not observed when IL-17-deficient Treg are used for GVHD suppression in vivo. Similarly, when we selectively blocked IL-1 signaling in Treg, that was shown to be necessary for Th17 conversion, we did not detect any improvement on Treg-mediated GVHD suppressive ability in vivo. Furthermore, upon ex vivo reisolation of transferred wild-type Treg, we detected little or no Treg-mediated IL-17 production upon GVHD induction. Our results indicate that blocking Th17 conversion does not affect the GVHD suppressive ability of highly purified natural Treg in vivo, suggesting that IL-17 targeting is not a valuable strategy to improve Treg immunotherapy after hematopoietic cell transplantation.

The fate of nonvascularized fat grafts: histological and bioluminescent study

Background:

Nonvascularized fat grafting has become one of the most popular options for breast contouring. However, the survival process of the grafts remains to be elucidated. In this study, we tracked the fate of nonvascularized fat grafts with in vivo bioluminescence and immunohistochemistry.

Methods:

Nonvascularized fat grafts or vascularized adiposal flaps from luciferase transgenic rats were transplanted to Lewis rats. The bioluminescent signals from the grafts were monitored longitudinally. In addition, nonvascularized fat grafts from Lewis rats were engrafted to Lewis rats and the viability of the adipocytes in the grafts was evaluated with immunohistochemical staining for perilipin at postoperative week 1, 2, 3, 4, and 6.

Results:

The bioluminescent signals from the nonvascularized fat grafts increased drastically from postoperative day 3 to 7, stayed flat from day 7 to 12, and declined from day 12 to 17, whereas those from the vascularized fat flaps remained throughout the entire postoperative period. Immunohistochemistry revealed that the survival zones with large adipocytes were decreased within 2 weeks and the regenerating zones with small adipocytes appeared after 3 weeks.

Conclusions:

Our study showed the process of survival and regeneration of nonvascularized fat grafts and suggested that graft-derived stromal cells proliferated within 7 days after transplantation and differentiated into adipocytes after postoperative week 3.

Mast cells suppress murine GVHD in a mechanism independent of CD4+CD25+ regulatory T cells

To investigate the role of mast cells in hematopoietic cell transplantation, we assessed graft-versus-host disease (GVHD) in C57BL/6-Kit(W-sh/W-sh) recipients, which virtually lack mast cells, compared with C57BL/6 WT recipients. GVHD was severely exacerbated in C57BL/6-Kit(W-sh/W-sh) mice (median survival time = 13 vs 60 days in wild-type [WT] mice; P < .0001). The increased mortality risk in C57BL/6-Kit(W-sh/W-sh) hosts correlated with increased T-cell numbers in lymph nodes, liver, and gastrointestinal tract sites, as indicated by bioluminescence imaging (P < .001). We did not detect any deficit in the number or function of CD4(+)CD25(+) regulatory T cells (Tregs) in C57BL/6-Kit(W-sh/W-sh) mice. Furthermore, Tregs were equally effective at reducing GVHD in C57BL/6-Kit(W-sh/W-sh) recipients compared with WT recipients containing mast cells. Furthermore, we found that survival of C57BL/6-Kit(W-sh/W-sh) mice during GVHD was significantly improved if the mice were engrafted with bone marrow-derived cultured mast cells from WT C57BL/6 mice but not from interleukin (IL)-10-deficient C57BL/6 mice. These data indicate that the presence of mast cells can significantly reduce GVHD independently of Tregs, by decreasing conventional T-cell proliferation in a mechanism involving IL-10. These experiments support the conclusion that mast cells can mediate a novel immunoregulatory role during hematopoietic cell transplantation.