Evaluation of effector cell fate and function by in vivo bioluminescence imaging

The effector functions of immune cells have typically been examined using assays that require sampling of tissues or cells to reveal specific aspects of an immune response (e.g., antigen-specificity, cytokine expression or killing of target cells). The outcome of an immune response in vivo, however, is not solely determined by a single effector function of a specific cell population, but is the result of numerous cellular and molecular interactions that occur in the complex environment of intact organ systems. These interactions influence survival, migration, and activation, as well as final effector function of a given population of cells. Efforts to reveal the cellular and molecular basis of biological processes have resulted in a number of technologies that combine molecular biology and imaging sciences that are collectively termed as Molecular Imaging. This emerging field has developed to reveal functional aspects of cells, genes, and proteins in real time in living animals and humans and embraces multiple modalities, including established clinical imaging methods such as magnetic resonance imaging, single photon emission computed tomography, and positron emission tomography, as well as novel methodologies specifically designed for research animals. Here, we highlight one of the newer modalities, in vivo bioluminescence imaging, as a method for evaluating effector T cell proliferation, migration, and function in model systems of malignant and non-malignant diseases.     

In vivo bioluminescence imaging

In vivo bioluminescent imaging (BLI) is a versatile and sensitive tool that is based on detection of light emission from cells or tissues. Bioluminescence, the biochemical generation of light by a living organism, is a naturally occurring phenomenon. Luciferase enzymes, such as that from the North American firefly (Photinus pyralis), catalyze the oxidation of a substrate (luciferin), and photons of light are a product of the reaction. Optical imaging by bioluminescence allows a low-cost, noninvasive, and real-time analysis of disease processes at the molecular level in living organisms. Bioluminescence has been used to track tumor cells, bacterial and viral infections, gene expression, and treatment response. Bioluminescence in vivo imaging allows longitudinal monitoring of a disease course in the same animal, a desirable alternative to analyzing a number of animals at many time points during the course of the disease. We provide a brief introduction to BLI technology, specific examples of in vivo BLI studies investigating bacterial/viral pathogenesis and tumor growth in animal models, and highlight some future perspectives of BLI as a molecular imaging tool.     

In vivo bioluminescence imaging for integrated studies of infection

Understanding biological processes in the context of intact organ systems with fine temporal resolution has required the development of imaging strategies that reveal cellular and molecular changes in the living body. Reporter genes that confer optical signatures on a given biological process have been used widely in cell biology and have been used more recently to interrogate biological processes in living animal models of human biology and disease. The use of internal biological sources of light, luciferases, to tag cells, pathogens, and genes has proved to be a versatile tool to provide in vivo indicators that can be detected externally. The application of this technology to the study of animal models of infectious disease has not only provided insights into disease processes, but has also revealed new mechanisms by which pathogens may avoid host defences during infection.     

In vivo bioluminescence: A cellular reporter for research and industry

The detection of specific bacterial pathogens, indicator microorganisms and antimicrobial substances, and the recovery of microorganisms from sub-lethal injury, are all aspects of importance to industry which are currently being targeted using in vivo bioluminescence. In all instances, a key requirement for the application of bioluminescence is the establishment of a strict correlation between in vivo bioluminescence and cell viability, as determined by colony counting on agar plates. Comparative studies for biocides (phenol, chlorhexidine diacetate, phenol thioether), for a virucide (hypochlorite) and for cellular recovery of S. typhimurium from sub-lethal injury, all indicate that such a correlation is valid. Furthermore, real-time measurements of in vivo bioluminescence reveal a major population of bacterial cells that retain functional intracellular biochemistry, but are defective in their ability to replicate post of freeze injury.     

In vivo imaging platform for tracking immunotherapeutic cells

Cellular therapeutics show great promise for the treatment of disease, but few noninvasive techniques exist for monitoring the cells after administration. Here we present a magnetic resonance imaging (MRI) technology that uses perfluoropolyether (PFPE) agents to track cells in vivo. Fluorine MRI selectively images only the labeled cells, and a 'conventional' (1)H image places the cells in their anatomical context. We labeled phenotypically defined dendritic cells (DCs) with PFPE ex vivo and observed efficient intracellular uptake of the PFPE with little effect on DC function. We injected labeled DCs into tissue or intravenously in mice and then tracked the cells in vivo using (19)F MRI. Although we focused on DCs, which are being developed as immunotherapeutics for cancer and autoimmune diseases, this technology should be useful for monitoring a wide range of cell types in vivo.     

In vivo imaging using bioluminescence: a tool for probing graft-versus-host disease

Immunological reactions have a key role in health and disease and are complex events characterized by coordinated cell trafficking to specific locations throughout the body. Clarification of these cell-trafficking events is crucial for improving our understanding of how immune reactions are initiated, controlled and recalled. As we discuss here, an emerging modality for revealing cell trafficking is bioluminescence imaging, which harnesses the light-emitting properties of enzymes such as luciferase for quantification of cells and uses low-light imaging systems. This strategy could be useful for the study of a wide range of biological processes, such as the pathophysiology of graft-versus-host and graft-versus-leukaemia reactions.     

In vivo cell tracking of mouse embryonic myoblasts and fast fibers during development

Fast and slow TnI are co‐expressed in E11.5 embryos, and fast TnI is present from the very beginning of myogenesis. A novel green fluorescent protein (GFP) reporter mouse lines (FastTnI/GFP lines) that carry the primary and secondary enhancer elements of the mouse fast troponin I (fast TnI), in which reporter expression correlates precisely with distribution of the endogenous fTnI protein was generated. Using the FastTnI/GFP mouse model, we characterized the early myogenic events in mice, analyzing the migration of GFP+ myoblasts, and the formation of primary and secondary myotubes in transgenic embryos. Interestingly, we found that the two contractile fast and slow isoforms of TnI are expressed during the migration of myoblasts from the somites to the limbs and body wall, suggesting that both participate in these events. Since no sarcomeres are present in myoblasts, we speculate that the function of fast TnI in early myogenesis is, like Myosin and Tropomyosin, to participate in cell movement during the initial myogenic stages. genesis 52:793–808, 2014. © 2014 Wiley Periodicals, Inc.     

In vivo bioluminescence imaging of bone marrow-derived cells in brain inflammation

It has been accepted that bone marrow cells infiltrate the brain and play important roles in neuroinflammation. However, there is no good tool for the visualization of these cells in living animals. In this study, we generated mice that were transplanted with GFP- or luciferase-expressing bone marrow cells, and performed in vivo fluorescence imaging (FLI) and in vivo bioluminescence imaging (BLI) to visualize the infiltrated cells. Brain inflammation was induced by intrahippocampal injection of lipopolysaccharide (LPS). Immunohistochemical investigation demonstrated an increase in the infiltration of bone marrow cells into the hippocampus because of the LPS injection and differentiation of the infiltrated cells into microglia, but not into neurons or astrocytes. BLI, but not FLI, successfully detected an increase in signal intensity with the LPS injection, and the increase of BLI coincided with that of luciferase activity in hippocampus. BLI could quantitatively and continuously monitor bone marrow-derived cells in vivo.     

In vivo bioluminescence imaging to evaluate estrogenic activities of endocrine disrupters

Reporter gene technology is widely used to measure activity of hormone analogs, and bioluminescent in vitro assays have allowed rapid screening of numerous chemicals either to identify new agonists or antagonists of hormones or to detect the presence of endocrine disrupters in the environment. Stable bioluminescent cell lines have been established and they provide reproducible dose–response curves and accurate determination of in vitro efficiencies of various chemicals. In vivo, however, these molecules can be metabolized, bound by proteins, or stored in fats and thus could display efficiencies different from those observed in vitro. In vivo assays, such as the uterotrophic bioassay, require numerous sacrificed animals, and responses not only are dependent on an estrogenic action but also imply other factors. For a faster assay and to avoid the use of numerous animals, we developed an in vivo biosensor constituted of stable bioluminescent cells implanted in nude mice. MCF-7 bioluminescent cell lines were chosen since their proliferation is low in the absence of estrogen and the xenograft size can thus be stable for several weeks. Luciferase gene expression was monitored noninvasively with a cooled charge-coupled device camera. Quantitative analysis allowed us to compare in vitro and in vivo actions of different estrogenic compounds (estradiol, estrone) and endocrine disruptors (ethynylestradiol, genistein, octylphenol, and 2,4′-dichlorodiphenyldichloroethylene) in the same cell lines and to follow hormone action on a living animal as a function of time. Different administration protocols have been used and good correlation was observed for most products. However, we found that ethynylestradiol was the most efficient chemical when orally administered.     

In vivo N-glycosylation and fate of Asn-X-Ser/Thr tripeptides

The minimum primary structural requirement for a tripeptide to serve as a substrate for oligosaccharyl transferase is the sequence -Asn-X-Ser/Thr-. In the present study the activities of three structurally different tripeptides containing acceptor sequences for oligosaccharyl transferase were compared in three systems: Xenopus oocytes, in which they were introduced into the cytoplasm by microinjection, cultured mammalian cells, and isolated rat liver microsomes. In the last two systems, the peptides were added exogenously to the culture or to the incubation medium, respectively. On the basis of lectin column and paper chromatographic analysis it was established that the microinjected acceptor tripeptides were glycosylated in Xenopus oocytes. However, lectin column analysis and retention of sensitivity to endoglycosidase H revealed that none of the three glycopeptides was processed to complex oligosaccharide chains and none was subsequently secreted. Rather, over a 24-h period the glycopeptides were degraded. Chloroquine was found to block this degradation process, but even under these conditions, the glycopeptides were not secreted into the medium. In the isolated microsomes the glycosylation of the acceptor tripeptides was time-dependent and the tripeptide with an iodotyrosine residue in the X position was found to be a poor substrate. When added to cultured mammalian cells, all three of the tripeptides were taken up, glycosylated, and subsequently secreted. These results are discussed in the context of the wide differences in glycosylation of the three peptides and their lack of secretion after glycosylation in Xenopus oocytes.     

In vivo divisional tracking of hematopoietic stem cells

Hematopoietic stem cell (HSC) division leads to self-renewal, differentiation, or death of HSCs, and adequate balance of this process results in sustained, lifelong, high-throughput hematopoiesis. Despite their contribution to hematopoietic cell production, the majority of cells within the HSC population are quiescent at any given time. Recent studies have tackled the questions of how often HSCs divide, how divisional history relates to repopulating potential, and how many HSCs contribute to hematopoiesis. Here, we summarize these recent findings on HSC turnover from different experimental systems and discuss hypothetical models for HSC cycling and maintenance in steady-state and upon hematopoietic challenge.     

In vivo tracking of the human patella.

The purpose of this study was to describe the dynamic, in vivo, three-dimensional tracking pattern of the patella for one normal male subject. Intracortical pins were inserted into the patella, tibia, and femur. The subject performed seated and squatting knee flexion/extension, and maximum voluntary quadriceps contractions. In addition, the vastus medialis oblique was subjected to maximal electrical stimulation. Motions of the markers attached to the intracortical pins were analyzed using an automated video system. Patellar and tibial motions were determined relative to a femoral reference system. While the tibia flexed 50 degrees from full extension (seated condition), the patella flexed 30.3 degrees, tilted laterally 10.3 degrees, and shifted laterally 8.6 mm. In general, these results show qualitative agreement with the data collected from cadaveric specimens [van Kampen and Huiskes, J. orthop. Res. 8, 372-382 (1990)]. The differences present may reflect different passive constraints to patellar motions, and different relative loading of the individual quadriceps components, in our study compared to the cadaveric study. Only small differences were found between patellar motions in the seated and squatting conditions. Differences in patellar displacements produced by (1) maximal electrical stimulation of the vastus medialis oblique, and (2) maximum voluntary quadriceps contraction, at 30 degrees knee flexion and full extension, may reflect the dominant influence of passive constraints, and the vastus lateralis, on normal patellar motions. Further in vivo study of patellar tracking seems warranted to evaluate surgical and conservative interventions for patellofemoral disorders.     

In vivo bioluminescence visualization of antitumor effects by human MUC1 vaccination

Recently, the use of a cancer deoxyribonucleic acid (DNA) vaccine encoding tumor-associated antigens has emerged as an immunotherapeutic strategy. In this study, we monitored tumor growth inhibition by pcDNA3-hMUC1 immunization in mice using optical imaging. To determine the anti-hMUC1-associated immune response generated by pcDNA3.1 or pcDNA3-hMUC1, we determined the concentration of interferon-gamma (IFN-gamma) protein and CD8+IFN-gamma cell numbers among lymphocytes from the draining lymph nodes of mice immunized with pcDNA3.1 or pcDNA3-hMUC1. After subcutaneously injecting CT26/hMUC1-Fluc into mice immunized with pcDNA3-hMUC1, we monitored in vivo tumor growth inhibition using an optical imaging method. The concentration of IFN-gamma protein in pcDNA3-hMUC1 was higher than that of the pcDNA3.1 group (2.7 < or = 0.08 ng/mL and 1.6 +/- 0.07 ng/mL, respectively, p < .001. The number of hMUC1-associated CD8+IFN-gamma cells in pcDNA3-hMUC1-immunized animals was 30-fold higher than in the pcDNA3.1 group. Bioluminescent images showed tumor growth inhibition in pcDNA3-hMUC1 immunized animals up to 25 days after immunization. A good correlation (r2 = .9076: pcDNA3/hMUC1 group; r2 = .7428: pcDNA3.1 group) was observed between bioluminescence signals and tumor weights in two mice in each group. We conclude that optical bioluminescent imaging offers a useful means of monitoring the antitumor effects of cancer DNA immunization in living animals.     

In vivo bioluminescence imaging of Ca signalling in the brain of Drosophila

Many different cells' signalling pathways are universally regulated by Ca(2+) concentration [Ca(2+)] rises that have highly variable amplitudes and kinetic properties. Optical imaging can provide the means to characterise both the temporal and spatial aspects of Ca(2+) signals involved in neurophysiological functions. New methods for in vivo imaging of Ca(2+) signalling in the brain of Drosophila are required for probing the different dynamic aspects of this system. In studies here, whole brain Ca(2+) imaging was performed on transgenic flies with targeted expression of the bioluminescent Ca(2+) reporter GFP-aequorin (GA) in different neural structures. A photon counting based technique was used to undertake continuous recordings of cytosolic [Ca(2+)] over hours. Time integrals for reconstructing images and analysis of the data were selected offline according to the signal intensity. This approach allowed a unique Ca(2+) response associated with cholinergic transmission to be identified by whole brain imaging of specific neural structures. Notably, [Ca(2+)] transients in the Mushroom Bodies (MBs) following nicotine stimulation were accompanied by a delayed secondary [Ca(2+)] rise (up to 15 min. later) in the MB lobes. The delayed response was sensitive to thapsigargin, suggesting a role for intra-cellular Ca(2+) stores. Moreover, it was reduced in dunce mutant flies, which are impaired in learning and memory. Bioluminescence imaging is therefore useful for studying Ca(2+) signalling pathways and for functional mapping of neurophysiological processes in the fly brain.     

In vivo analysis of uropod function during physiological T cell trafficking

Migrating lymphocytes acquire a polarized phenotype with a leading and a trailing edge, or uropod. Although in vitro experiments in cell lines or activated primary cell cultures have established that Rho-p160 coiled-coil kinase (ROCK)-myosin II-mediated uropod contractility is required for integrin de-adhesion on two-dimensional surfaces and nuclear propulsion through narrow pores in three-dimensional matrices, less is known about the role of these two events during the recirculation of primary, nonactivated lymphocytes. Using pharmacological antagonists of ROCK and myosin II, we report that inhibition of uropod contractility blocked integrin-independent mouse T cell migration through narrow, but not large, pores in vitro. T cell crawling on chemokine-coated endothelial cells under shear was severely impaired by ROCK inhibition, whereas transendothelial migration was only reduced through endothelial cells with high, but not low, barrier properties. Using three-dimensional thick-tissue imaging and dynamic two-photon microscopy of T cell motility in lymphoid tissue, we demonstrated a significant role for uropod contractility in intraluminal crawling and transendothelial migration through lymph node, but not bone marrow, endothelial cells. Finally, we demonstrated that ICAM-1, but not anatomical constraints or integrin-independent interactions, reduced parenchymal motility of inhibitor-treated T cells within the dense lymphoid microenvironment, thus assigning context-dependent roles for uropod contraction during lymphocyte recirculation.     

In vivo cell electrofusion

In vitro electrofusion of cells brought into contact and exposed to electric pulses is an established procedure. Here we report for the first time the occurrence of fusion of cells within a tissue exposed in vivo to permeabilizing electric pulses. The dependence of electrofusion on the ratio of applied voltage to distance between the electrodes, and thus on the achievement of in vivo cell electropermeabilization (electroporation) is demonstrated in the metastasizing B16 melanoma tumor model. The kinetics of the morphological changes induced by cell electrofusion (appearance of syncytial areas or formation of giant cells) are also described, as well as the kinetics of mitosis and cell death occurrence. Finally, tissue dependence of in vivo cell electrofusion is reported and discussed, since electrofusion has been observed neither in liver nor in another tumor type. Particular microenvironmental conditions, such as the existence of reduced extracellular matrices, could be necessary for electrofusion achievement. Since biomedical applications of in vivo cell electropermeabilization are rapidly developing, we also discuss the influence of cell electrofusion on the efficacy of DNA electrotransfer for gene therapy and of antitumor electrochemotherapy, in which electrofusion could be an interesting advantage to treat metastasizing tumors.     

Cellular senescence impact on immune cell fate and function

Cellular senescence occurs not only in cultured fibroblasts, but also in undifferentiated and specialized cells from various tissues of all ages, in vitro and in vivo. Here, we review recent findings on the role of cellular senescence in immune cell fate decisions in macrophage polarization, natural killer cell phenotype, and following T‐lymphocyte activation. We also introduce the involvement of the onset of cellular senescence in some immune responses including T‐helper lymphocyte‐dependent tissue homeostatic functions and T‐regulatory cell‐dependent suppressive mechanisms. Altogether, these data propose that cellular senescence plays a wide‐reaching role as a homeostatic orchestrator.