Tracking transplanted cells using dual-radionuclide SPECT

Visualization of Acute Inflammation through a Macrophage-Camouflaged Afterglow Nanocomplex

Acute inflammation is a basic innate, immediate, and stereotyped immune response to injury, which is characterized by rapid recruitment of immune cells to the vasculature and extravasation into the damaged parenchyma. Visualization of acute inflammation plays an important role in monitoring the disease course and understanding pathogenesis, which lacks specific targeted and observing tools in vivo. Here, we report a Trojan horse strategy of a macrophage-camouflaged afterglow nanocomplex (UCANPs@RAW) to specifically visualize acute inflammation. Due to the advantages of optical antibackground interference elimination, as well as particular immune homing and long-term tracking capacity, UCANPs@RAW demonstrates an excellent acute inflammatory recognition ability. In an arthritis model, previously intravenously injected UCANPs@RAW could directionally migrate from the liver to the inflammation site as soon as 3 h after the model was induced, which could be continuously lighted for at least 36 h with the highest imaging signal-to-background ratio (SBR) as 382 at the time point of 9 h. Additionally, UCANPs@RAW is observed to penetrate the blood-brain barrier and image the deep brain inflamed region covered by the thick skull in an acute brain inflammation model with an SBR_max of 258, which is based on the strong recruiting ability of macrophages to immune response. In view of this smart nanocomplex, our strategy holds great potential for inflammatory detection and treatments.

Hot spot 19 F magnetic resonance imaging of inflammation

Among the preclinical molecular imaging approaches, lately fluorine (¹⁹ F) magnetic resonance imaging (MRI) has garnered significant scientific interest in the biomedical research community, due to the unique properties of fluorinated materials and the ¹⁹ F nucleus. Fluorine is an intrinsically sensitive nucleus for MRI-there is negligible endogenous ¹⁹ F in the body and, thus, no background signal which allows the detection of fluorinated materials as "hot spots" by combined ¹ H/¹⁹ F MRI and renders fluorine-containing molecules as ideal tracers with high specificity. In addition, perfluorocarbons are a family of compounds that exhibit a very high fluorine payload and are biochemically as well as physiologically inert. Perfluorocarbon nanoemulsions (PFCs) are well known to be readily taken up by immunocompetent cells, which can be exploited for the unequivocal identification of inflammatory foci by tracking the recruitment of PFC-loaded immune cells to affected tissues using ¹ H/¹⁹ F MRI. The required ¹⁹ F labeling of immune cells can be accomplished either ex vivo by PFC incubation of isolated endogenous immune cells followed by their re-injection or by intravenous application of PFCs for in situ uptake by circulating immune cells. With both approaches, inflamed tissues can unambiguously be detected via background-free ¹⁹ F signals due to trafficking of PFC-loaded immune cells to affected organs. To extend ¹⁹ F MRI tracking beyond cells with phagocytic properties, the PFC surface can further be equipped with distinct ligands to generate specificity against epitopes and/or types of immune cells independent of phagocytosis. Recent developments also allow for concurrent detection of different PFCs with distinct spectral signatures allowing the simultaneous visualization of several targets, such as various immune cell subtypes labeled with these PFCs. Since ligands and targets can easily be adapted to a variety of problems, this approach provides a general and versatile platform for inflammation imaging which will strongly extend the frontiers of molecular MRI. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease.

Fluorine-19 MRI Contrast Agents for Cell Tracking and Lung Imaging

Fluorine-19 (¹⁹F)-based contrast agents for magnetic resonance imaging stand to revolutionize imaging-based research and clinical trials in several fields of medical intervention. First, their use in characterizing in vivo cell behavior may help bring cellular therapy closer to clinical acceptance. Second, their use in lung imaging provides novel noninvasive interrogation of the ventilated airspaces without the need for complicated, hard-to-distribute hardware. This article reviews the current state of ¹⁹F-based cell tracking and lung imaging using magnetic resonance imaging and describes the link between the methods across these fields and how they may mutually benefit from solutions to mutual problems encountered when imaging ¹⁹F-containing compounds, as well as hardware and software advancements.

Fluorescent silica nanoparticles improve optical imaging of stem cells allowing direct discrimination between live and early-stage apoptotic cells

Highly bright and photostable cyanine dye-doped silica nanoparticles, IRIS Dots, are developed, which can efficiently label human mesenchymal stem cells (hMSCs). The application procedure used to label hMSCs is fast (2 h), the concentration of IRIS Dots for efficient labeling is low (20 μg mL(-1) ), and the labeled cells can be visualized by flow cytometry, confocal microscopy, and transmission electron microscopy. Labeled hMSCs are unaffected in their viability and proliferation, as well as stemness surface marker expression and differentiation capability into osteocytes. Moreover, this is the first report that shows nonfunctionalized IRIS Dots can discriminate between live and early-stage apoptotic stem cells (both mesenchymal and embryonic) through a distinct external cell surface distribution. On the basis of biocompatibility, efficient labeling, and apoptotic discrimination potential, it is suggested that IRIS Dots can serve as a promising stem cell tracking agent.

Biocompatible nanoparticle labeling of stem cells and their distribution in brain

Nanolabeling is an invaluable novel technique in biology to detect and characterize different parts of biological systems including microscopic entities, viz., cells inside the living systems. Stem cells (SCs) are multipotent cells with the potential to differentiate into bone, cartilage, fat, muscle cells, and neurons and are being investigated for their utility in cell-based transplantation therapy. Yet, adequate methods to track transplanted SCs in vivo are limited, precluding functional studies. Nanoparticles (quantum dots) offer an alternative to organic dyes and fluorescent proteins to label and track cells in vitro and in vivo. These nanoparticles are resistant to chemical and metabolic degradation, demonstrating long-term photo stability. Here, we describe the technology of labeling the stem cells with silver nitrate nanoparticles in an in vitro coculture model. This is followed by defining the procedure of administering these cells in vivo and studying the distribution pattern and resultant regenerative effects of the "tagged" stem cells.

Comparison of the myocardial clearance of endothelial progenitor cells injected early versus late into reperfused or sustained occlusion myocardial infarction

Stem cell transplantation following AMI has shown promise for the repair or reduction of the amount of myocardial injury. There is some evidence that these treatment effects appear to be directly correlated to cell residence time. This study aims to assess the effects of (a) the timing of stem cell injection following myocardial infarction, and (b) flow milieu, on cell residence times at the site of transplantation by comparing three time points (day of infarction, week 1 and week 4–5), and two models of acute myocardial infarction (sustained occlusion or reperfusion). Twenty-one dogs received 2 injections of 30 million endothelial progenitor cells. The first injections were administered by epicardial (n = 8) or endocardial injection (n = 13) either on the day of infarction (n = 15) or at 1 week (n = 6). The second injections were administered by only endocardial injection (n = 18) 4 weeks following the first injection. Cell clearance half-lives were comparable between early and late injections. However, transplants into sustained occlusion infarcts resulted in slower cell clearance 77.1 ± 6.1 (n = 18) versus reperfused 59.4 ± 2.9 h (n = 21) p = 0.009. Sustained occlusion infarcts had longer cell retention in comparison to reperfusion whereas the timing of injection did not affect clearance rates. If the potential for myocardial regeneration associated with cell transplantation is, at least in part, linked to cell residence times, then greater benefit may be observed with transplants into infarcts associated with persistent coronary artery occlusion.

Functional assessment of human dendritic cells labeled for in vivo (19)F magnetic resonance imaging cell tracking

BACKGROUND AIMS

Dendritic cells (DC) are increasingly being used as cellular vaccines to treat cancer and infectious diseases. While there have been some promising results in early clinical trials using DC-based vaccines, the inability to visualize non-invasively the location, migration and fate of cells once adoptively transferred into patients is often cited as a limiting factor in the advancement of these therapies. A novel perflouropolyether (PFPE) tracer agent was used to label human DC ex vivo for the purpose of tracking the cells in vivo by (19)F magnetic resonance imaging (MRI). We provide an assessment of this technology and examine its impact on the health and function of the DC.

METHODS

Monocyte-derived DC were labeled with PFPE and then assessed. Cell viability was determined by examining cell membrane integrity and mitochondrial lipid content. Immunostaining and flow cytometry were used to measure surface antigen expression of DC maturation markers. Functional tests included bioassays for interleukin (IL)-12p70 production, T-cell stimulatory function and chemotaxis. MRI efficacy was demonstrated by inoculation of PFPE-labeled human DC into NOD-SCID mice.

RESULTS

DC were effectively labeled with PFPE without significant impact on cell viability, phenotype or function. The PFPE-labeled DC were clearly detected in vivo by (19)F MRI, with mature DC being shown to migrate selectively towards draining lymph node regions within 18 h.

CONCLUSIONS

This study is the first application of PFPE cell labeling and MRI cell tracking using human immunotherapeutic cells. These techniques may have significant potential for tracking therapeutic cells in future clinical trials.

Combined fluorescence and X-Ray tomography for quantitative in vivo detection of fluorophore

Initial results from a novel dual modality preclinical imager which combines non-contact fluorescence tomography (FT) and x-ray computed tomography (CT) for preclinical functional and anatomical in vivo imaging are presented. The anatomical data from CT provides a priori information to the FT reconstruction to create overlaid functional and anatomical images with accurate localization and quantification of fluorophore distribution. Phantoms with inclusions containing Indocyanine-Green (ICG), and with heterogeneous backgrounds including iodine in compartments at different concentrations for CT contrast, have been imaged with the dual modality FT/CT system. Anatomical information from attenuation maps and optical morphological information from absorption and scattering maps are used as a priori information in the FT reconstruction. Although ICG inclusions can be located without the a priori information, the recovered ICG concentration shows 75% error. When the a priori information is utilized, the ICG concentration can be recovered with only 15% error. Developing the ability to accurately quantify fluorophore concentration in anatomical regions of interest may provide a powerful tool for in vivo small animal imaging.

Cell tracking and therapy evaluation of bone marrow monocytes and stromal cells using SPECT and CMR in a canine model of myocardial infarction

BACKGROUND

The clinical application of stem cell therapy for myocardial infarction will require the development of methods to monitor treatment and pre-clinical assessment in a large animal model, to determine its effectiveness and the optimum cell population, route of delivery, timing, and flow milieu.

OBJECTIVES

To establish a model for a) in vivo tracking to monitor cell engraftment after autologous transplantation and b) concurrent measurement of infarct evolution and remodeling.

METHODS

We evaluated 22 dogs (8 sham controls, 7 treated with autologous bone marrow monocytes, and 7 with stromal cells) using both imaging of 111Indium-tropolone labeled cells and late gadolinium enhancement CMR for up to12 weeks after a 3 hour coronary occlusion. Hearts were also examined using immunohistochemistry for capillary density and presence of PKH26 labeled cells.

RESULTS

In vivo Indium imaging demonstrated an effective biological clearance half-life from the injection site of ~5 days. CMR demonstrated a pattern of progressive infarct shrinkage over 12 weeks, ranging from 67-88% of baseline values with monocytes producing a significant treatment effect. Relative infarct shrinkage was similar through to 6 weeks in all groups, following which the treatment effect was manifest. There was a trend towards an increase in capillary density with cell treatment.

CONCLUSION

This multi-modality approach will allow determination of the success and persistence of engraftment, and a correlation of this with infarct size shrinkage, regional function, and left ventricular remodeling. There were overall no major treatment effects with this particular model of transplantation immediately post-infarct.

Noninvasive imaging of transplanted cells

PURPOSE OF REVIEW

Transplantation of cells is an urgent clinical need that is increasingly providing an alternative to solid-organ transplants. This review discusses the state-of-the-art in-vivo imaging of cell transplantation with a special focus on recent developments.

RECENT FINDINGS

Noninvasive imaging modalities, such as magnetic resonance imaging (MRI), nuclear (positron emission tomography and single-photon emission computed tomography), acoustical, and optical imaging can investigate the biodistribution, fate, and functional integration of grafted cells. Especially, multimodal imaging is emerging as an important development to provide complimentary and confirmatory information.

SUMMARY

The development of noninvasive imaging of transplanted cells has progressed rapidly over the last few years. Translating these techniques into clinical protocols remains the focus of ongoing investigations.

MRI characterization of agarose gel micro-droplets at acute time-points within the rabbit lumbar muscle

Agarose gel micro-droplets supplemented with provisional matrix proteins have been shown to enhance encapsulated cell survival for cell therapy applications. This study evaluated micro-droplet T(1) and T(2) relaxation on a 1.5 T clinical MRI scanner to guide the optimization of encapsulated cell delivery to intermediate-sized animals. Preliminary in vitro experiments using encapsulated human blood-derived endothelial progenitor cells (EPCs) documented a negligible impact of EPC encapsulation on agarose micro-droplet T(1) and T(2) relaxation, even following transient immersion in 2.3 mm Gd-DTPA. Furthermore, Gd-DTPA immersion did not adversely impact encapsulated cell viability. These results allowed for efficient pre-clinical methodological development using direct injections into the rabbit lumbar region of agarose droplets without cells (n=6). At time-points to 6 h, in vivo injection sites displayed elevated T(2) and T(1) (1.8%: DeltaT(2)=53+/-28%, DeltaT(1)=50+/-25%, n=13; 2.5%: DeltaT(2)=41+/-10%, DeltaT(1)=41+/-26%, n=11). Rapid imaging sequences displayed high conspicuity at sites of Gd-DTPA-immersed capsule injection, which persisted for less than 4 h. Therefore, basic differences of micro-droplet T(1) and T(2) when compared to tissue provide a platform for acute tracking of encapsulated cell fate. Transient Gd-DTPA encapsulation accentuates T(1) differences.

Molecular pathology of malignant gliomas

Malignant gliomas, the most common type of primary brain tumor, are a spectrum of tumors of varying differentiation and malignancy grades. These tumors may arise from neural stem cells and appear to contain tumor stem cells. Early genetic events differ between astrocytic and oligodendroglial tumors, but all tumors have an initially invasive phenotype, which complicates therapy. Progression-associated genetic alterations are common to different tumor types, targeting growth-promoting and cell cycle control pathways and resulting in focal hypoxia, necrosis, and angiogenesis. Knowledge of malignant glioma genetics has already impacted clinical management of these tumors, and researchers hope that further knowledge of the molecular pathology of malignant gliomas will result in novel therapies.

Quantum dot labeling of mesenchymal stem cells

Background

Mesenchymal stem cells (MSCs) are multipotent cells with the potential to differentiate into bone, cartilage, fat and muscle cells and are being investigated for their utility in cell-based transplantation therapy. Yet, adequate methods to track transplanted MSCs in vivo are limited, precluding functional studies. Quantum Dots (QDs) offer an alternative to organic dyes and fluorescent proteins to label and track cells in vitro and in vivo. These nanoparticles are resistant to chemical and metabolic degradation, demonstrating long term photostability. Here, we investigate the cytotoxic effects of in vitro QD labeling on MSC proliferation and differentiation and use as a cell label in a cardiomyocyte co-culture.

Results

A dose-response to QDs in rat bone marrow MSCs was assessed in Control (no-QDs), Low concentration (LC, 5 nmol/L) and High concentration (HC, 20 nmol/L) groups. QD yield and retention, MSC survival, proinflammatory cytokines, proliferation and DNA damage were evaluated in MSCs, 24 -120 hrs post QD labeling. In addition, functional integration of QD labeled MSCs in an in vitro cardiomyocyte co-culture was assessed. A dose-dependent effect was measured with increased yield in HC vs. LC labeled MSCs (93 ± 3% vs. 50% ± 15%, p < 0.05), with a larger number of QD aggregates per cell in HC vs. LC MSCs at each time point (p < 0.05). At 24 hrs >90% of QD labeled cells were viable in all groups, however, at 120 hrs increased apoptosis was measured in HC vs. Control MSCs (7.2% ± 2.7% vs. 0.5% ± 0.4%, p < 0.05). MCP-1 and IL-6 levels doubled in HC MSCs when measured 24 hrs after QD labeling. No change in MSC proliferation or DNA damage was observed in QD labeled MSCs at 24, 72 and 120 hrs post labeling. Finally, in a cardiomyocyte co-culture QD labeled MSCs were easy to locate and formed functional cell-to-cell couplings, assessed by dye diffusion.

Conclusion

Fluorescent QDs label MSC effectively in an in vitro co-culture model. QDs are easy to use, show a high yield and survival rate with minimal cytotoxic effects. Dose-dependent effects suggest limiting MSC QD exposure.