Intravital Imaging of Intestinal Intraepithelial Lymphocytes

Intestinal intraepithelial lymphocytes (IEL) are a numerous population of T cells located within the epithelium of the small and large intestines, being more numerous in the small intestine (SI). They surveil this tissue by interacting with epithelial cells. Intravital microscopy is an important tool for visualizing the patrolling activity of IEL in the SI of live mice. Most IEL express CD8α; therefore, here we describe an established protocol of intravital imaging that tracks lymphocytes labeled with a CD8α-specific monoclonal antibody in the SI epithelium of live mice. We also describe data acquisition and quantification of the movement metrics, including mean speed, track length, displacement length, and paths for each CD8α+ IEL using the available software. The intravital imaging technique for measuring IEL movement will provide a better understanding of the role of IEL in homeostasis and protection from injury or infection in vivo.

Magnetic nanocomposites for biomedical applications

Tissue engineering and regenerative medicine have solved numerous problems related to the repair and regeneration of damaged organs and tissues arising from aging, illnesses, and injuries. Nanotechnology has further aided tissue regeneration science and has provided outstanding opportunities to help disease diagnosis as well as treat damaged tissues. Based on the most recent findings, magnetic nanostructures (MNSs), in particular, have emerged as promising materials for detecting, directing, and supporting tissue regeneration. There have been many reports concerning the role of these nano-building blocks in the regeneration of both soft and hard tissues, but the subject has not been extensively reviewed. Here, we review, classify, and discuss various synthesis strategies for novel MNSs used in medicine. Advanced applications of magnetic nanocomposites (MG-NCs), specifically magnetic nanostructures, are further systematically reviewed. In addition, the scientific and technical aspects of MG-NC used in medicine are discussed considering the requirements for the field. In summary, this review highlights the numerous opportunities and challenges associated with the use of MG-NCs as smart nanocomposites (NCs) in tissue engineering and regenerative medicine.

Stem cell therapy for cuprizone model of multiple sclerosis focusing on the effectiveness of different injection methods and cell labeling

Multiple Sclerosis (MS) is a chronic and autoimmune disease of the central nervous system that causes inflammation in the brain and spinal cord, progressive degeneration of central nervous system tissue, damage to neuronal axons, and loss of function of central nervous system neurons. Experimental encephalomyelitis is an alternative animal model of MS that can simulate the symptoms of this disease. Cuprizone is one of the factors creating this model. Various researchers are testing the use of different cells to reduce the symptoms of cuprizone-demyelinated mice. The different injection methods explained in this article include intracerebral, intraperitoneal, intravenous, and intranasal. The intracerebral method, in contrast to the intranasal method, was widely employed by researchers. In each technique, the researchers try to inject a specific type of stem cell (SC) and monitor their efficiency. For monitoring SCs various labeling procedures are available, however, there is an upward trend in using magnetic resonance imaging (MRI). Two main barriers to using this method are high cost and complexity. In the current review, we try to make review cell therapy in the cuprizone model of MS.

Screening of multifunctional fruit carbon dots for fluorescent labeling and sensing in living immune cells and zebrafishes

Nine kinds of carbon dots (CDs) were synthesized by using fruits with different varieties as carbon sources; meanwhile, the fluorescence characteristics, quantum yield, and response ability to different metal ions and free radicals were systematically studied. These CDs showed similar excitation and emission spectral ranges (λ_ex ≈ 345 nm, λ_em ≈ 435 nm), but very different fluorescence quantum yield (QY), in which orange and cantaloupe CDs have the highest QY around 0.25 and green plum CDs showed the lowest quantum yield around 0.1. Interestingly, the fluorescence of all of these CDs can be significantly quenched by hydroxyl radical (•OH) and iron ion (Fe³⁺); however, these CDs showed very different response characteristics to other metal ions (e.g., Co²⁺, Ni²⁺, Cu²⁺, Ce³⁺, Mn²⁺, Ag⁺, and Fe²⁺). Through in-depth analysis, we found some interesting patterns of the influence of carbon sources on the fluorescence characteristics of CDs. Finally, by using white pitaya CDs as fluorescence probe, we realized sensing of Fe³⁺ and •OH with limits of detection (LOD) of 19.4 μM and 0.7 μM, respectively. Moreover, the CDs were also capable for sensitive detection in immune cells and even in zebrafishes. Our work can provide valuable guidance for the rational design of functional CDs for biological applications.

Genetically encoded dihydroxyphenylalanine coupled with tyrosinase for strain promoted labeling

Protein modifications through genetic code engineering have a remarkable impact on macromolecule engineering, protein translocation, protein-protein interaction, and cell biology. We used the newly developed molecular biology approach, genetic code engineering, for fine-tuning of proteins for biological availability. Here, we have introduced 3, 4-dihydroxy-l-phenylalanine in recombinant proteins by selective pressure incorporation method for protein-based cell labeling applications. The congener proteins treated with tyrosinase convert 3, 4-dihydroxy-l-phenylalanine to dopaquinone for strain-promoted click chemistry. Initially, the single-step Strain-Promoted Oxidation-Controlled Cyclooctyne-1,2-quinone Cycloaddition was studied using tyrosinase catalyzed congener protein and optimized the temporally controlled conjugation with (1R,8S,9s)-Bicyclo[6.1.0]non-4-yn-9-ylmethanol. Then, the feasibility of tyrosinase-treated congener annexin A5 with easily reactive quinone functional moiety was conjugated with fluorescent tag dibenzocyclooctyne-PEG4-TAMRA for labeling of apoptotic cells. Thus, the congener proteins-based products demonstrate selective cell labeling and apoptosis detection in EA.hy926 cells even after the protein modifications. Hence, genetic code engineering can be coupled with click chemistry to develop various protein-based fluorescent labels.

Avians as a Model System of Vascular Development

For more than 2000 years, the avian embryo has helped scientists understand questions of developmental and cell biology. As early as 350 BC Aristotle described embryonic development inside a chicken egg (Aristotle, Generation of animals. Loeb Classical Library (translated), vol. 8, 1943). In the seventeenth century, Marcello Malpighi, referred to as the father of embryology, first diagramed the microscopic morphogenesis of the chick embryo, including extensive characterization of the cardiovascular system (Pearce Eur Neurol 58(4):253-255, 2007; West, Am J Physiol Lung Cell Mol Physiol 304(6):L383-L390, 2016). The ease of accessibility to the embryo and similarity to mammalian development have made avians a powerful system among model organisms. Currently, a unique combination of classical and modern techniques is employed for investigation of the vascular system in the avian embryo. Here, we will introduce the essential techniques of embryonic manipulation for experimental study in vascular biology.

EdU-Based Assay of Cell Proliferation and Stem Cell Quiescence in Skeletal Tissue Sections

Identifying and tracking proliferating and quiescent cells in situ is an important phenotyping component of skeletal tissues in development, physiology and disease. Among all the methods that exist, which include immunostaining for cell cycle-specific proteins, the gold standards use thymidine analogs. These compounds label proliferating cells by being incorporated into de novo-synthesized genomic DNA. 5-bromo-2'-deoxyuridine (BrdU) has traditionally been used for this purpose, but its detection is lengthy and requires harsh treatment of tissue sections to give access of anti-BrdU antibody to DNA. An alternative, more recently developed, uses 5-ethynyl-2'-deoxyuridine (EdU). This thymidine analog is detected by click chemistry, that is, covalent cross-linking of its ethynyl group with a fluorescent azide that is small enough to easily penetrate native tissues and reach DNA. In addition to being simple and quick, this EdU-based assay is compatible with other protocols, such as immunostaining, on the same tissue sections. We here describe an EdU-based protocol optimized to label and functionally assess actively proliferating cells as well as slowly dividing cells, including stem cells, in mouse skeletal tissues.

Effect of Cell Labeling on the Function of Human Pluripotent Stem Cell-Derived Cardiomyocytes

Cell labeling technologies are required to monitor the fate of transplanted cells in vivo and to select target cells for the observation of certain changes in vitro. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been transplanted for the treatment of heart injuries or used in vitro for preclinical cardiac safety assessments. Cardiomyocyte (CM) labeling has been used in these processes to facilitate target cell monitoring. However, the functional effect of the labeling agent on hiPSC-CMs has not been studied. Therefore, we investigated the effects of labeling agents on CM cellular functions. 3'-Dioctadecyloxacarbocyanine perchlorate (DiO), quantum dots (QDs), and a DNA plasmid expressing EGFP using Lipo2K were used to label hiPSC-CMs. We conclude that the hiPSC-CM labeling with DiO and QDs does not induce arrhythmogenic effects but rather improves the mRNA expression of cardiac ion channels and Ca^2＋ influx by L-type Ca^2＋ channels. Thus, DiO and QD labeling agents may be useful tools to monitor transplanted CMs, and further in vivo influences of the labeling agents should be investigated in the future.

Detection limit of 89Zr-labeled T cells for cellular tracking: an in vitro imaging approach using clinical PET/CT and PET/MRI

PURPOSE

Tracking cells in vivo using imaging can provide non-invasive information to understand the pharmacology, efficacy, and safety of novel cell therapies. Zirconium-89 (t1/2 = 78.4 h) has recently been used to synthesize [89Zr]Zr(oxinate)4 for cell tracking using positron emission tomography (PET). This work presents an in vitro approach to estimate the detection limit for in vivo PET imaging of Jurkat T cells directly labeled with [89Zr]Zr(oxinate)4 utilizing clinical PET/CT and PET/MRI.

METHODS

Jurkat T cells were labeled with varying concentrations of [89Zr]Zr(oxinate)4 to generate different cell-specific activities (0.43-31.91 kBq/106 cells). Different concentrations of labeled cell suspensions (104, 105, and 106 cells) were seeded on 6-well plates and into a 3 × 3 cubic-well plate with 1 cm3 cubic wells as a gel matrix. Plates were imaged on clinical PET/CT and PET/MRI scanners for 30 min. The total activity in each well was determined by drawing volumes of interest over each well on PET images. The total cell-associated activity was measured using a well counter and correlated with imaging data. Simulations for non-specific signal were performed to model the effect of non-specific radioactivity on detection.

RESULTS

Using this in vitro model, the lowest cell number that could be visualized on 6-well plate images was 6.8 × 104, when the specific activity was 27.8 kBq/106 cells. For the 3 × 3 cubic-well, a plate of 3.3 × 104 cells could be detected on images with a specific activity of 15.4 kBq/106 cells.

CONCLUSION

The results show the feasibility of detecting [89Zr]Zr(oxinate)4-labeled Jurkat T cells on clinical PET systems. The results provide a best-case scenario, as in vivo detection using PET/CT or PET/MRI will be affected by cell number, specific activity per cell, the density of cells within the target volume, and non-specific signal. This work has important implications for cell labeling studies in patients, particularly when using radiosensitive cells (e.g., T cells), which require detection of low cell numbers while minimizing radiation dose per cell.

Magnetic core-shell nanowires as MRI contrast agents for cell tracking

BACKGROUND

Identifying the precise location of cells and their migration dynamics is of utmost importance for achieving the therapeutic potential of cells after implantation into a host. Magnetic resonance imaging is a suitable, non-invasive technique for cell monitoring when used in combination with contrast agents.

RESULTS

This work shows that nanowires with an iron core and an iron oxide shell are excellent materials for this application, due to their customizable magnetic properties and biocompatibility. The longitudinal and transverse magnetic relaxivities of the core-shell nanowires were evaluated at 1.5 T, revealing a high performance as T2 contrast agents. Different levels of oxidation and various surface coatings were tested at 7 T. Their effects on the T2 contrast were reflected in the tailored transverse relaxivities. Finally, the detection of nanowire-labeled breast cancer cells was demonstrated in T2-weighted images of cells implanted in both, in vitro in tissue-mimicking phantoms and in vivo in mouse brain. Labeling the cells with a nanowire concentration of 0.8 μg of Fe/mL allowed the detection of 25 cells/µL in vitro, diminishing the possibility of side effects. This performance enabled an efficient labelling for high-resolution cell detection after in vivo implantation (~ 10 nanowire-labeled cells) over a minimum of 40 days.

CONCLUSIONS

Iron-iron oxide core-shell nanowires enabled the efficient and longitudinal cellular detection through magnetic resonance imaging acting as T2 contrast agents. Combined with the possibility of magnetic guidance as well as triggering of cellular responses, for instance by the recently discovered strong photothermal response, opens the door to new horizons in cell therapy and make iron-iron oxide core-shell nanowires a promising theranostic platform.

MRI Tracking of Dendritic Cells Loaded with Superparamagnetic Iron Oxide Nanoparticles

Cell tracking via MRI has drawn much attention recently for its sensitive, deep, and real-time properties and high spatial resolution. In a previous chapter, the labeling and tracking of superparamagnetic iron oxide (SPIO)-nanoparticle-loaded stem cells have been well summarized (Sykova et al., Methods Mol Biol 750:79-90, 2011). Thus, in this chapter, we will mainly focus on the tracking of SPIO-nanoparticle-labeled mouse dendritic cells by MRI and provide a detailed protocol for cell labeling and in vivo tracking by a clinical 3.0T MRI scanner. Of note, this protocol is also suitable to be applied on other types of cells.

Gold Nanoparticles as a Computed Tomography Marker for Stem Cell Tracking

Stem cell tracking is an essential prerequisite for effective stem cell therapy. Computed tomography (CT) imaging technique is an emerging quantitative tool to detect real time distribution of transplanted cells. Most of CT labels based on the high atomic number (Z) materials have concern over biocompatibility. The present book chapter describes a protocol for the use of biocompatible gold nanoparticles as a CT marker for efficient labeling of mesenchymal stem cells (MSCs) and subsequent cell tracking in rodent models.

Upconversion Fluorescent Nanoprobe for Highly Sensitive In Vivo Cell Tracking

Near-infrared (NIR)-to-visible upconversion nanomaterials (UCNPs) used as biomedical nanoprobes have considerable advantages over the traditional used "downconversion" fluorescent dyes. Functionalized upconversion nanoparticles (UCNPs) represent high sensitivity and great biocompatibility. Cells labeled with these UCNPs can be tracked for long term in vivo. Here we describe UCNP-PEG-ARG for highly sensitive in vivo cell tracking.

Aggregation-induced emission-based ionic liquids for bacterial killing, imaging, cell labeling, and bacterial detection in blood cells

A series of aggregation-induced emission (AIE)-based imidazolium-type ionic liquids (ILs) were designed and synthesized for bacterial killing and imaging, cell labeling, and bacterial detection in blood cells. The AIE-based ILs showed antibacterial activities against both Escherichia coli and Staphylococcus aureus. The carbon chain length of substitution at the N3 position of the imidazolium cations highly affects the antibacterial properties of ILs. Owing to their AIE characteristics, the ILs could selectively capture fluorescence image of dead bacteria while killing the bacteria. The fluorescence intensity varied with the concentration of bacteria, indicating that AIE-based ILs has potential as an antibacterial material and an efficient probe for bacterial viability assay. In addition, the synthesized AIE-based ILs exhibit relatively low cytotoxicity and hemolysis rate and therefore potential for cell labeling, as well as bacterial detection in blood cells. STATEMENT OF SIGNIFICANCE: Bacteria are ubiquitous, especially the pathogenic bacteria, which pose a serious threat to human health. There is an urgent need for materials with efficient antibacterial properties and biocompatibility and without causing drug resistance. In this work, we synthesized a series of aggregation-induced emission (AIE)-doped imidazolium type ionic liquids (ILs) with multifunction potential of bacterial killing and imaging, cell labeling, and detection of bacteria from blood cells. The synthesized AIE-based ILs can image dead bacteria at the same time of killing these bacteria, which can avoid the fluorescent dyeing process. Simultaneously, the fluorescent imaging of dead bacteria can be distinguished by the naked eye, and the fluorescence intensity from the AIE-based ILs varied with the concentration of bacteria. In addition, the AIE-based ILs exhibit relatively low cytotoxicity and hemolysis rate and therefore potential for cell labeling as well as detection of bacteria from red blood cell suspension.

In Ovo Electroporation of Plasmid DNA and Morpholinos into Specific Tissues During Early Embryogenesis

In ovo electroporation enables transfection of non-viral plasmid DNA and/or morpholinos to fluorescently label and/or perturb gene function in cells of interest. However, targeted electroporation into specific subregions of the embryo can be challenging due to placement and size limitations of the electrodes. Here we describe the basic techniques for in ovo electroporation in the chick embryo and suggest parameters to electroporate cells within different target tissues that with some modifications may be applicable to a wide range of developmental stages and other embryo model organisms.

Labeling of human mesenchymal stem cells with different classes of vital stains: robustness and toxicity

Background

Mesenchymal stem cell (MSC) transplantation has been explored as a new clinical approach to repair injured tissues. However, in order to evaluate the therapeutic activity of MSC, cell tracking techniques are required to determine the fate of transplanted cells in both preclinical and clinical studies. In these aspects, different vital stains offer the potential for labeling and monitoring of grafted cells in vivo. It is desirable to have tracking agents which have long-term stability, are not toxic to the cells, and do not affect cell function.

Methods

Here, we selected three different labels: CellTracker™ Green CMFDA, eGFP-mRNA (genetic pre-tag), and Molday ION Rhodamine B™ (nanoparticle-based fluorescent and magnetic label) and performed extensive analysis of their influence on in vitro expansion of human bone marrow-derived mesenchymal stem cells (hBM-MSCs), as well as potential of affecting therapeutic activity and the impact on the durability of staining.

Results

Our study showed that basic hBM-MSC characteristics and functions might be affected by labeling. We observed strong alterations of metabolic activity and morphology after eGFP and CellTracker™ Green CMFDA hBM-MSC staining. Molday ION Rhodamine B™ labeling revealed superior properties relatively to other vital stains. The relative expression level of most of the investigated growth factors remained stable after cell labeling, but we have observed some changes in the case of EGF, GDNF, HGF, and IGF gene expression.

Conclusions

Taken together, we suggest performing similar to ours extensive analysis prior to using any cell label to tag MSC in experiments, as it can thoroughly bias results.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1296-8) contains supplementary material, which is available to authorized users.

Fluorescence-based tracing of transplanted intestinal epithelial cells using confocal laser endomicroscopy

Background

Intestinal stem cell transplantation has been shown to promote mucosal healing and to engender fully functional epithelium in experimental colitis. Hence, stem cell therapies may provide an innovative approach to accomplish mucosal healing in patients with debilitating conditions such as inflammatory bowel disease. However, an approach to label and trace transplanted cells, in order to assess engraftment efficiency and to monitor wound healing, is a key hurdle to overcome prior to initiating human studies. Genetic engineering is commonly employed in animal studies, but may be problematic in humans due to potential off-target and long-term adverse effects.

Methods

We investigated the applicability of a panel of fluorescent dyes and nanoparticles to label intestinal organoids for visualization using the clinically approved imaging modality, confocal laser endomicroscopy (CLE). Staining homogeneity, durability, cell viability, differentiation capacity, and organoid forming efficiency were evaluated, together with visualization of labeled organoids in vitro and ex vivo using CLE.

Results

5-Chloromethylfluorescein diacetate (CMFDA) proved to be suitable as it efficiently stained all organoids without transfer to unstained organoids in co-cultures. No noticeable adverse effects on viability, organoid growth, or stem cell differentiation capacity were observed, although single-cell reseeding revealed a dose-dependent reduction in organoid forming efficiency. Labeled organoids were easily identified in vitro using CLE for a duration of at least 3 days and could additionally be detected ex vivo following transplantation into murine experimental colitis.

Conclusions

It is highly feasible to use fluorescent dye-based labeling in combination with CLE to trace intestinal organoids following transplantation to confirm implantation at the intestinal target site.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1246-5) contains supplementary material, which is available to authorized users.

Development of a dual-wavelength fluorescent nanoprobe for in vivo and in vitro cell tracking consecutively

Many imaging probes have been developed for a wide variety of imaging modalities. However, no optical imaging probe could be utilized for both microscopic and whole animal imaging. To fill the gap, the dual-wavelength fluorescent imaging nanoprobe was developed to simultaneously carry both visible-range fluorescent dye and near-infrared (NIR) dye. Emission scan confirms that the nanoprobe exhibits two separate peaks with strong fluorescent intensity in both visible and NIR ranges. Furthermore, the dual-wavelength fluorescent nanoprobe has high photostability and colloidal stability, as well as long shelf-life. In vitro cell culture experiments show that the nanoprobe has the ability to label different types of cells (namely, esophageal, prostate, fibroblast and macrophage cell) for fluorescent microscope imaging. More importantly, cell tracking experiments confirm that cell migration and distribution in various organs can be tracked in real time using in vivo whole-body NIR imaging and in vitro microscopic imaging, respectively.

Cellular Magnetic Resonance Imaging for Tracking Metastatic Cancer Cells in the Brain

Cellular magnetic resonance imaging (MRI) enables visualization of cells in vivo. This is accomplished by labeling cells with superparamagnetic iron oxide nanoparticles. Here, we describe the steps for labeling human cancer cells with iron for tracking them after injection into nude mice. We also provide details for validation of cell labeling, ultrasound guided intra-cardiac injection, and MRI.

Nanomaterial-involved neural stem cell research: Disease treatment, cell labeling, and growth regulation

Neural stem cells (NSCs) have been widely investigated for their potential in the treatment of various diseases and transplantation therapy. However, NSC growth regulation, labeling, and its application to disease diagnosis and treatment are outstanding challenges. Recently, nanomaterials have shown promise for various applications including genetic modification, imaging, and controlled drug release. Here we summarize the recent progress in the use of nanomaterials in combination with NSCs for disease treatment and diagnosis, cell labeling, and NSC growth regulation. The toxicity of nanomaterials to NSCs is also discussed.

Recent advances and future prospects of iron oxide nanoparticles in biomedicine and diagnostics

Superparamagnetic iron oxide nanoparticles (SPIONs) are considered as chemically inert materials and, therefore, being extensively applied in the areas of imaging, targeting, drug delivery and biosensors. Their unique properties such as low toxicity, biocompatibility, potent magnetic and catalytic behavior and superior role in multifunctional modalities have epitomized them as an appropriate candidate for biomedical applications. Recent developments in the area of materials science have enabled the facile synthesis of Iron oxide nanoparticles (IONPs) offering easy tuning of surface properties and surface functionalization with desired biomolecules. Such developments have enabled IONPs to be easily accommodated in nanocomposite platform or devices. Additionally, the tag of biocompatible material has realized their potential in myriad applications of nanomedicines including imaging modalities, sensing, and therapeutics. Further, IONPs enzyme mimetic activity pronounced their role as nanozymes in detecting biomolecules like glucose, and cholesterol etc. Hence, based on their versatile applications in biomedicine, the present review article focusses on the current trends, developments and future prospects of IONPs in MRI, hyperthermia, photothermal therapy, biomolecules detection, chemotherapy, antimicrobial activity and also their role as the multifunctional agent in diagnosis and nanomedicines.

Mapping Changes in Cell Surface Protein Expression Through Selective Labeling of Live Cells

ncRNAs are key players in the adaptation of bacteria to new environments, by modulating the composition of the membrane upon changes in the environment. Nevertheless, monitoring the changes in surface protein expression is still a challenge, since these proteins are present in low abundance, and are difficult to extract. Here is described a method to easily, reproducibly, and specifically enrich total protein extracts in surface proteins. This method comprises a direct labeling of surface proteins on living cells using fluorescent dyes, followed by total protein extraction and subsequent separation of these extracts by 2D gel electrophoresis.

Labeling of cell therapies: How can we get it right?

Labeling cells for non-invasive tracking in vivo using magnetic resonance imaging (MRI) is an emerging hot topic garnering ever increasing attention, yet it is fraught with numerous methodological challenges, which merit careful attention. Several of the current procedures used to label cells for tracking by MRI take advantage of the intrinsic phagocytic nature of cells to engulf nanoparticles, though cells with low intrinsic phagocytic capacity are also commonly studied. Before we take the next steps towards administering such cells in vivo, it is essential to understand how the nanolabel is recognized, internalized, trafficked and distributed within the specific host cell. This is even more critical when contemplating labeling of cells that may ultimately be applied in vivo to patients in a therapeutic context.

Detection of intramyocardially injected DiR-labeled mesenchymal stem cells by optical and optoacoustic tomography

The distribution of intramyocardially injected rabbit MSCs, labeled with the near-infrared dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbo-cyanine-iodide (DiR) using hybrid Fluorescence Molecular Tomography-X-ray Computed Tomography (FMT-XCT) and Multispectral Optoacoustic Tomography (MSOT) imaging technologies, was investigated. Viability and induction of apoptosis of DiR labeled MSCs were assessed by XTT- and Caspase-3/-7-testing in vitro. 2 × 10⁶, 2 × 10⁵ and 2 × 10⁴ MSCs labeled with 5 and 10 μg DiR/ml were injected into fresh frozen rabbit hearts. FMT-XCT, MSOT and fluorescence cryosection imaging were performed. Concentrations up to 10 μg DiR/ml did not cause apoptosis in vitro (p > 0.05). FMT and MSOT imaging of labeled MSCs led to a strong signal. The imaging modalities highlighted a difference in cell distribution and concentration correlated to the number of injected cells. Ex-vivo cryosectioning confirmed the molecular fluorescence signal. FMT and MSOT are sensitive imaging techniques offering high-anatomic resolution in terms of detection and distribution of intramyocardially injected stem cells in a rabbit model.

Ultrasmall graphene oxide based T1 MRI contrast agent for in vitro and in vivo labeling of human mesenchymal stem cells

Herein, we report on development of a two-dimensional nanomaterial graphene oxide (GO)-based T₁ magnetic resonance imaging (MRI) contrast agent (CA) for in vitro and in vivo labeling of human mesenchymal stem cells (hMSCs). The CA was synthesized by PEGylation of ultrasmall GO, followed by conjugation with a chelating agent DOTA and then gadolinium(III) to form GO-DOTA-Gd complexes. Thus-prepared GO-DOTA-Gd complexes exhibited significantly improved T₁ relaxivity, and the r₁ value was 14.2 mM^-1s^-1 at 11.7 T, approximately three times higher than Magnevist, a commercially available CA. hMSCs can be effectively labeled by GO-DOTA-Gd, leading to remarkably enhanced cellular MRI effect without obvious adverse effects on proliferation and differentiation of hMSCs. More importantly, in vivo experiment revealed that intracranial detection of 5×10⁵ hMSCs labeled with GO-DOTA-Gd is achieved. The current work demonstrates the feasibility of the GO-based T₁ MRI CA for stem cell labeling, which may find potential applications in regenerative medicine.

Development and Observation of Mature Megagametophyte Cell-Specific Fluorescent Markers

Visualization of the intact embryo sac within the ovular/gynoecial tissues and clear identification of cell types can be logistically difficult and subject to interpretation. Cellular marker technologies have been available for the embryo sac, but have typically labeled only one cell type in a particular line. Here, we describe techniques for simultaneous labeling each cell type in the embryo sac and visualization methods for such in Arabidopsis, soybean, maize, and sorghum.

Self-Assembled Superparamagnetic Iron Oxide Nanoclusters for Universal Cell Labeling and MRI

Superparamagnetic iron oxide (SPIO) nanoparticles have been widely used in a variety of biomedical applications, especially as contrast agents for magnetic resonance imaging (MRI) and cell labeling. In this study, SPIO nanoparticles were stabilized with amphiphilic low molecular weight polyethylenimine (PEI) in an aqueous phase to form monodispersed nanocomposites with a controlled clustering structure. The iron-based nanoclusters with a size of 115.3 ± 40.23 nm showed excellent performance on cellular uptake and cell labeling in different types of cells, moreover, which could be tracked by MRI with high sensitivity. The SPIO nanoclusters presented negligible cytotoxicity in various types of cells as detected using MTS, LDH, and flow cytometry assays. Significantly, we found that ferritin protein played an essential role in protecting stress from SPIO nanoclusters. Taken together, the self-assembly of SPIO nanoclusters with good magnetic properties provides a safe and efficient method for universal cell labeling with noninvasive MRI monitoring capability.

Cytosolic Delivery of Nanolabels Prevents Their Asymmetric Inheritance and Enables Extended Quantitative in Vivo Cell Imaging

Long-term in vivo imaging of cells is crucial for the understanding of cellular fate in biological processes in cancer research, immunology, or in cell-based therapies such as beta cell transplantation in type I diabetes or stem cell therapy. Traditionally, cell labeling with the desired contrast agent occurs ex vivo via spontaneous endocytosis, which is a variable and slow process that requires optimization for each particular label-cell type combination. Following endocytic uptake, the contrast agents mostly remain entrapped in the endolysosomal compartment, which leads to signal instability, cytotoxicity, and asymmetric inheritance of the labels upon cell division. Here, we demonstrate that these disadvantages can be circumvented by delivering contrast agents directly into the cytoplasm via vapor nanobubble photoporation. Compared to classic endocytic uptake, photoporation resulted in 50 and 3 times higher loading of fluorescent dextrans and quantum dots, respectively, with improved signal stability and reduced cytotoxicity. Most interestingly, cytosolic delivery by photoporation prevented asymmetric inheritance of labels by daughter cells over subsequent cell generations. Instead, unequal inheritance of endocytosed labels resulted in a dramatic increase in polydispersity of the amount of labels per cell with each cell division, hindering accurate quantification of cell numbers in vivo over time. The combined benefits of cell labeling by photoporation resulted in a marked improvement in long-term cell visibility in vivo where an insulin producing cell line (INS-1E cell line) labeled with fluorescent dextrans could be tracked for up to two months in Swiss nude mice compared to 2 weeks for cells labeled by endocytosis.

Physicochemical characterization of ferumoxytol, heparin and protamine nanocomplexes for improved magnetic labeling of stem cells

Stem cell-based therapies have become a major focus in regenerative medicine and to treat diseases. A straightforward approach combining three drugs, heparin (H), protamine (P) with ferumoxytol (F) in the form of nanocomplexes (NCs) effectively labeled stem cells for cellular MRI. We report on the physicochemical characteristics for optimizing the H, P, and F components in different ratios, and mixing sequences, producing NCs that varied in hydrodynamic size. NC size depended on the order in which drugs were mixed in media. Electron microscopy of HPF or FHP showed that F was located on the surface of spheroidal shaped HP complexes. Human stem cells incubated with FHP NCs resulted in a significantly greater iron concentration per cell compared to that found in HPF NCs with the same concentration of F. These results indicate that FHP could be useful for labeling stem cells in translational studies in the clinic.

Magnetic Resonance Imaging of Iron Oxide-Labeled Human Embryonic Stem Cell-Derived Cardiac Progenitors

Given the limited regenerative capacity of the heart, cellular therapy with stem cell-derived cardiac cells could be a potential treatment for patients with heart disease. However, reliable imaging techniques to longitudinally assess engraftment of the transplanted cells are scant. To address this issue, we used ferumoxytol as a labeling agent of human embryonic stem cell-derived cardiac progenitor cells (hESC-CPCs) to facilitate tracking by magnetic resonance imaging (MRI) in a large animal model. Differentiating hESCs were exposed to ferumoxytol at different time points and varying concentrations. We determined that treatment with ferumoxytol at 300 μg/ml on day 0 of cardiac differentiation offered adequate cell viability and signal intensity for MRI detection without compromising further differentiation into definitive cardiac lineages. Labeled hESC-CPCs were transplanted by open surgical methods into the left ventricular free wall of uninjured pig hearts and imaged both ex vivo and in vivo. Comprehensive T2*-weighted images were obtained immediately after transplantation and 40 days later before termination. The localization and dispersion of labeled cells could be effectively imaged and tracked at days 0 and 40 by MRI. Thus, under the described conditions, ferumoxytol can be used as a long-term, differentiation-neutral cell-labeling agent to track transplanted hESC-CPCs in vivo using MRI.

SIGNIFICANCE

The development of a safe and reproducible in vivo imaging technique to track the fate of transplanted human embryonic stem cell-derived cardiac progenitor cells (hESC-CPCs) is a necessary step to clinical translation. An iron oxide nanoparticle (ferumoxytol)-based approach was used for cell labeling and subsequent in vivo magnetic resonance imaging monitoring of hESC-CPCs transplanted into uninjured pig hearts. The present results demonstrate the use of ferumoxytol labeling and imaging techniques in tracking the location and dispersion of cell grafts, highlighting its utility in future cardiac stem cell therapy trials.

Fluorescent magnetic nanoparticles for cell labeling: flux synthesis of manganite particles and novel functionalization of silica shell

Novel synthetic approaches for the development of multimodal imaging agents with high chemical stability are demonstrated. The magnetic cores are based on La0.63Sr0.37MnO3 manganite prepared as individual grains using a flux method followed by additional thermal treatment in a protective silica shell allowing to enhance their magnetic properties. The cores are then isolated and covered de novo with a hybrid silica layer formed through the hydrolysis and polycondensation of tetraethoxysilane and a fluorescent silane synthesized from rhodamine, piperazine spacer, and 3-iodopropyltrimethoxysilane. The aminoalkyltrialkoxysilanes are strictly avoided and the resulting particles are hydrolytically stable and do not release dye. The high colloidal stability of the material and the long durability of the fluorescence are reinforced by an additional silica layer on the surface of the particles. Structural and magnetic studies of the products using XRD, TEM, and SQUID magnetometry confirm the importance of the thermal treatment and demonstrate that no mechanical treatment is required for the flux-synthesized manganite. Detailed cell viability tests show negligible or very low toxicity at concentrations at which excellent labeling is achieved. Predominant localization of nanoparticles in lysosomes is confirmed by immunofluorescence staining. Relaxometric and biological studies suggest that the functionalized nanoparticles are suitable for imaging applications.

Advances in using MRI probes and sensors for in vivo cell tracking as applied to regenerative medicine

The field of molecular and cellular imaging allows molecules and cells to be visualized in vivo non-invasively. It has uses not only as a research tool but in clinical settings as well, for example in monitoring cell-based regenerative therapies, in which cells are transplanted to replace degenerating or damaged tissues, or to restore a physiological function. The success of such cell-based therapies depends on several critical issues, including the route and accuracy of cell transplantation, the fate of cells after transplantation, and the interaction of engrafted cells with the host microenvironment. To assess these issues, it is necessary to monitor transplanted cells non-invasively in real-time. Magnetic resonance imaging (MRI) is a tool uniquely suited to this task, given its ability to image deep inside tissue with high temporal resolution and sensitivity. Extraordinary efforts have recently been made to improve cellular MRI as applied to regenerative medicine, by developing more advanced contrast agents for use as probes and sensors. These advances enable the non-invasive monitoring of cell fate and, more recently, that of the different cellular functions of living cells, such as their enzymatic activity and gene expression, as well as their time point of cell death. We present here a review of recent advancements in the development of these probes and sensors, and of their functioning, applications and limitations.

Novel (89)Zr cell labeling approach for PET-based cell trafficking studies

Background

With the recent growth of interest in cell-based therapies and radiolabeled cell products, there is a need to develop more robust cell labeling and imaging methods for in vivo tracking of living cells. This study describes evaluation of a novel cell labeling approach with the positron emission tomography (PET) isotope ⁸⁹Zr (T_1/2 = 78.4 h). ⁸⁹Zr may allow PET imaging measurements for several weeks and take advantage of the high sensitivity of PET imaging.

Methods

A novel cell labeling agent, ⁸⁹Zr-desferrioxamine-NCS (⁸⁹Zr-DBN), was synthesized. Mouse-derived melanoma cells (mMCs), dendritic cells (mDCs), and human mesenchymal stem cells (hMSCs) were covalently labeled with ⁸⁹Zr-DBN via the reaction between the NCS group on ⁸⁹Zr-DBN and primary amine groups present on cell surface membrane protein. The stability of the label on the cell was tested by cell efflux studies for 7 days. The effect of labeling on cellular viability was tested by proliferation, trypan blue, and cytotoxicity/apoptosis assays. The stability of label was also studied in in vivo mouse models by serial PET scans and ex vivo biodistribution following intravenous and intramyocardial injection of ⁸⁹Zr-labeled hMSCs. For comparison, imaging experiments were performed after intravenous injections of ⁸⁹Zr hydrogen phosphate (⁸⁹Zr(HPO₄)₂).

Results

The labeling agent, ⁸⁹Zr-DBN, was prepared in 55% ± 5% decay-corrected radiochemical yield measured by silica gel iTLC. The cell labeling efficiency was 30% to 50% after 30 min labeling depending on cell type. Radioactivity concentrations of labeled cells of up to 0.5 MBq/10⁶ cells were achieved without a negative effect on cellular viability. Cell efflux studies showed high stability of the radiolabel out to 7 days. Myocardially delivered ⁸⁹Zr-labeled hMSCs showed retention in the myocardium, as well as redistribution to the lung, liver, and bone. Intravenously administered ⁸⁹Zr-labeled hMSCs also distributed primarily to the lung, liver, and bone, whereas intravenous ⁸⁹Zr(HPO₄)₂ distributed to the liver and bone with no activity in the lung. Thus, the in vivo stability of the radiolabel on the hMSCs was evidenced.

Conclusions

We have developed a robust, general, and biostable ⁸⁹Zr-DBN-based cell labeling strategy with promise for wide applications of PET-based non-invasive in vivo cell trafficking.

Trypsinization-dependent cell labeling with fluorescent nanoparticles

Trypsin is often used to detach adhered cell subculture from a substrate. However, the proteolytic activity of trypsin may harm cells by cleaving the cell membrane proteins. The present study shows that cellular uptake of fluorescent nanoparticles is remarkably increased within 24 h after trypsinization. These results highlight the trypsin-induced protein digestion, provoking leaky cell plasma membrane which leads to the strongly enhanced cellular uptake of the nanoparticles. To prevent this effect, one should expose cells to the nanoparticle (NP)-based fluorescent labels at least 48 h after trypsinization.

Sensitive in vivo cell detection using size-optimized superparamagnetic nanoparticles

Magnetic nanoparticle (MNP) enabled cell visualization with magnetic resonance imaging (MRI) is currently an intensively studied area of research. In the present study, we have synthesized polyethylene glycolated (PEG) MNPs and validated their suitability as MR cell labeling agents in in vitro and in vivo experiments. The labeling of therapeutic potent mesenchymal stem cells (MSCs) with small core and large core MNPs was evaluated. Both MNPs were, in combination with a transfection agent, stably internalized into the MSCs and didn't show an effect on cell metabolism. The labeled cells showed high contrast in MRI phantom studies. For quantification purposes, the MRI contrast generating properties of cells labeled with small core MNPs were compared with large core MNPs and with the commercial contrast agent Endorem. MSCs labeled with the large core MNPs showed the highest contrast generating properties in in vitro phantom studies and in in vivo intracranial stereotactic injection experiments, confirming the size-relaxivity relationship in biological systems. Finally, the distribution of MSCs pre-labeled with large core PEGylated MNPs was visualized non-invasively with MRI in a glioma model.

Evaluating the effect of ultrasmall superparamagnetic iron oxide nanoparticles for a long-term magnetic cell labeling

In order to evaluate the long-term viability, the iron content stability, and the labeling efficiency of mammalian cells using magnetic cell labeling; dextran-coated ultrasmall superparamagnetic iron oxide (USPIOs) nanoparticles with plain surfaces having a hydrodynamic size of 25 nm were used for this study. Tests were carried out in four groups each containing 5 flasks of 5.5 × 10(6) AD-293 embryonic kidney cells. The cell lines were incubated for 24 h using four different iron concentrations with and without protamine sulfate (Pro), washed with phosphate-buffered saline (PBS) and centrifuged three times to remove the unbounded USPIOs. Cell viability was also verified using USPIOs. There were no significant differences in the cell viability between the control group of cells and those groups with iron uptake at the specified iron concentrations. The average iron uptake ratio compared to that of the control group was (114 ± 1). The magnetic resonance images (MRI) at post-labeling day 1 and day 21 showed (75 ± 4)% and (22 ± 5)% signal decrements compared to that of the control, respectively. The Perl's Prussian blue test showed that 98% of the cells were labeled, and the iron concentration within the media did not affect the cell iron uptake. Magnetic cellular labeling with the USPIO-Pro complex had no short or medium term (3 weeks) toxic effects on AD-293 embryonic kidney cells.

Effects of Quantum Dot Labeling on Endothelial Progenitor Cell Function and Viability

Endothelial progenitor cells (EPC) play an important role in repairing damaged endothelium. An effective imaging method for in vivo tracking of EPCs is essential for understanding EPC-based cell therapy. Fluorescent quantum dots (QDs) have attractive optical characteristics such as extreme brightness and photostability. QDs are currently being investigated as probes for stem cell labeling; however, there is concern about whether QDs can be used safely. We investigated whether quantum dot (QD) labeling would influence EPC viability and function. Rat bone marrow-derived EPCs were cultured and characterized. The cells were labeled with near-infrared-emitting, carboxyl-coated QDs (8 nM) for 24 h. QD labeling efficiency was higher than 97%. Using WST-1 assay, we showed that the viability of the QD-labeled EPCs was not different from that of the control EPCs. Moreover, QD labeling did not influence the ability of EPCs to form capillary tubes on Matrigel and to migrate. The percentage of QD-positive cells decreased with time, probably due to the rapid division of EPCs. These data suggest that the carboxyl-coated QD705 can be useful for labeling EPCs without interrupting their viability and functions.