Seeing stem cells at work in vivo

Engineering colloidal systems for cell manipulation, delivery, and tracking

Men-made colloidal systems are widely presented across various aspects of biomedical science. There is a strong demand for engineering colloids to tailor their functions and properties to meet the requirements of biological and medical tasks. These requirements are not only related to size, shape, capacity to carry bioactive compounds as drug delivery systems, and the ability to navigate via chemical and physical targeting. Today, the more challenging aspects of colloid design are how the colloidal particles interact with biological cells, undergo internalization by cells, how they reside in the cell interior, and whether we can explore cells with colloids, intervene with biochemical processes, and alter cell functionality. Cell tracking, exploitation of cells as natural transporters of internalized colloidal carriers loaded with drugs, and exploring physical methods as external triggers of cell functions are ongoing topics in the research agenda. In this review, we summarize recent advances in these areas, focusing on how colloidal particles interact and are taken up by mesenchymal stem cells, dendritic cells, neurons, macrophages, neutrophils and lymphocytes, red blood cells, and platelets. The engineering of colloidal vesicles with cell membrane fragments and exosomes facilitates their application. The perspectives of different approaches in colloid design, their limitations, and obstacles on the biological side are discussed.

Optimization of a nanoparticle uptake protocol applied to amniotic-derived cells: unlocking the therapeutic potential

Stem cell-based therapy implementation relies heavily on advancements in cell tracking. The present research has been designed to develop a gold nanorod (AuNR) labeling protocol applied to amniotic epithelial cells (AECs) leveraging the pro-regenerative properties of this placental stem cell source which is widely used for both human and veterinary biomedical regenerative applications, although not yet exploited with tracking technologies. Ovine AECs, in native or induced mesenchymal (mAECs) phenotypes via epithelial-mesenchymal transition (EMT), served as the model. Initially, various uptake methods validated on other sources of mesenchymal stromal cells (MSCs) were assessed on mAECs before optimization for AECs. Furthermore, the protocol was implemented by adopting the biological strategy of MitoCeption to improve endocytosis. The results indicate that the most efficient, affordable, and easy protocol leading to internalization of AuNRs in living mAECs recognized the combination of the one-step uptake condition (cell in suspension), centrifugation-mediated internalization method (G-force) and MitoCeption (mitochondrial isolated from mAECs). This protocol produced labeled vital mAECs within minutes, suitable for preclinical and clinical trials. The optimized protocol has the potential to yield feasible labeled amniotic-derived cells for biomedical purposes: up to 10 million starting from a single amniotic membrane. Similar and even higher efficiency was found when the protocol was applied to ovine and human AECs, thereby demonstrating the transferability of the method to cells of different phenotypes and species-specificity, hence validating its great potential for the development of improved biomedical applications in cell-based therapy and diagnostic imaging.

Evidence of a pan-tissue decline in stemness during human aging

Despite their biological importance, the role of stem cells in human aging remains to be elucidated. In this work, we applied a machine learning methodology to GTEx transcriptome data and assigned stemness scores to 17,382 healthy samples from 30 human tissues aged between 20 and 79 years. We found that ~60% of the studied tissues exhibit a significant negative correlation between the subject's age and stemness score. The only significant exception was the uterus, where we observed an increased stemness with age. Moreover, we observed that stemness is positively correlated with cell proliferation and negatively correlated with cellular senescence. Finally, we also observed a trend that hematopoietic stem cells derived from older individuals might have higher stemness scores. In conclusion, we assigned stemness scores to human samples and show evidence of a pan-tissue loss of stemness during human aging, which adds weight to the idea that stem cell deterioration may contribute to human aging.

Therapeutic potential of stem cells in regeneration of liver in chronic liver diseases: Current perspectives and future challenges

The deposition of extracellular matrix and hyperplasia of connective tissue characterizes chronic liver disease called hepatic fibrosis. Progression of hepatic fibrosis may lead to hepatocellular carcinoma. At this stage, only liver transplantation is a viable option. However, the number of possible liver donors is less than the number of patients needing transplantation. Consequently, alternative cell therapies based on non-stem cells (e.g., fibroblasts, chondrocytes, keratinocytes, and hepatocytes) therapy may be able to postpone hepatic disease, but they are often ineffective. Thus, novel stem cell-based therapeutics might be potentially important cutting-edge approaches for treating liver diseases and reducing patient' suffering. Several signaling pathways provide targets for stem cell interventions. These include pathways such as TGF-β, STAT3/BCL-2, NADPH oxidase, Raf/MEK/ERK, Notch, and Wnt/β-catenin. Moreover, mesenchymal stem cells (MSCs) stimulate interleukin (IL)-10, which inhibits T-cells and converts M1 macrophages into M2 macrophages, producing an anti-inflammatory environment. Furthermore, it inhibits the action of CD4+ and CD8+ T cells and reduces the activity of TNF-α and interferon cytokines by enhancing IL-4 synthesis. Consequently, the immunomodulatory and anti-inflammatory capabilities of MSCs make them an attractive therapeutic approach. Importantly, MSCs can inhibit the activation of hepatic stellate cells, causing their apoptosis and subsequent promotion of hepatocyte proliferation, thereby replacing dead hepatocytes and reducing liver fibrosis. This review discusses the multidimensional therapeutic role of stem cells as cell-based therapeutics in liver fibrosis.

The decisive early phase of bone regeneration

Bone has a remarkable endogenous regenerative capacity that enables scarless healing and restoration of its prior mechanical function, even under challenging conditions such as advanced age and metabolic or immunological degenerative diseases. However - despite much progress - a high number of bone injuries still heal with unsatisfactory outcomes. The mechanisms leading to impaired healing are heterogeneous, and involve exuberant and non-resolving immune reactions or overstrained mechanical conditions that affect the delicate regulation of the early initiation of scar-free healing. Every healing process begins phylogenetically with an inflammatory reaction, but its spatial and temporal intensity must be tightly controlled. Dysregulation of this inflammatory cascade directly affects the subsequent healing phases and hinders the healing progression. This Review discusses the complex processes underlying bone regeneration, focusing on the early healing phase and its highly dynamic environment, where vibrant changes in cellular and tissue composition alter the mechanical environment and thus affect the signalling pathways that orchestrate the healing process. Essential to scar-free healing is the interplay of various dynamic cascades that control timely resolution of local inflammation and tissue self-organization, while also providing sufficient local stability to initiate endogenous restoration. Various immunotherapy and mechanobiology-based therapy options are under investigation for promoting bone regeneration.

Impact of Nanotechnology on Differentiation and Augmentation of Stem Cells for Liver Therapy

The liver is one of the crucial organs of the body that performs hundreds of chemical reactions needed by the body to survive. It is also the largest gland of the body. The liver has multiple functions, including the synthesis of chemicals, metabolism of nutrients, and removal of toxins. It also acts as a storage unit. The liver has a unique ability to regenerate itself, but it can lead to permanent damage if the injury is beyond recovery. The only possible treatment of severe liver damage is liver transplant which is a costly procedure and has several other drawbacks. Therefore, attention has been shifted towards the use of stem cells that have shown the ability to differentiate into hepatocytes. Among the numerous kinds of stem cells (SCs), the mesenchymal stem cells (MSCs) are the most famous. Various studies suggest that an MSC transplant can repair liver function, improve the signs and symptoms, and increase the chances of survival. This review discusses the impact of combining stem cell therapy with nanotechnology. By integrating stem cell science and nanotechnology, the information about stem cell differentiation and regulation will increase, resulting in a better comprehension of stem cell-based treatment strategies. The augmentation of SCs with nanoparticles has been shown to boost the effect of stem cell-based therapy. Also, the function of green nanoparticles in liver therapies is discussed.

Role of adipose tissue grafting and adipose-derived stem cells in peripheral nerve surgery

The application of autologous fat grafting in reconstructive surgery is commonly used to improve functional form. This review aims to provide an overview of the scientific evidence on the biology of adipose tissue, the role of adipose-derived stem cells, and the indications of adipose tissue grafting in peripheral nerve surgery. Adipose tissue is easily accessible through the lower abdomen and inner thighs. Non-vascularized adipose tissue grafting does not support oxidative and ischemic stress, resulting in variable survival of adipocytes within the first 24 hours. Enrichment of adipose tissue with a stromal vascular fraction is purported to increase the number of adipose-derived stem cells and is postulated to augment the long-term stability of adipose tissue grafts. Basic science nerve research suggests an increase in nerve regeneration and nerve revascularization, and a decrease in nerve fibrosis after the addition of adipose-derived stem cells or adipose tissue. In clinical studies, the use of autologous lipofilling is mostly applied to secondary carpal tunnel release revisions with promising results. Since the use of adipose-derived stem cells in peripheral nerve reconstruction is relatively new, more studies are needed to explore safety and long-term effects on peripheral nerve regeneration. The Food and Drug Administration stipulates that adipose-derived stem cell transplantation should be minimally manipulated, enzyme-free, and used in the same surgical procedure, e.g. adipose tissue grafts that contain native adipose-derived stem cells or stromal vascular fraction. Future research may be shifted towards the use of tissue-engineered adipose tissue to create a supportive microenvironment for autologous graft survival. Shelf-ready alternatives could be enhanced with adipose-derived stem cells or growth factors and eliminate the need for adipose tissue harvest.

Establishment and characterization of a novel human induced pluripotent stem cell line stably expressing the iRFP720 reporter

Stem cell therapy has great potential for replacing beta-cell loss in diabetic patients. However, a key obstacle to cell therapy’s success is to preserve viability and function of the engrafted cells. While several strategies have been developed to improve engrafted beta-cell survival, tools to evaluate the efficacy within the body by imaging are limited. Traditional labeling tools, such as GFP-like fluorescent proteins, have limited penetration depths in vivo due to tissue scattering and absorption. To circumvent this limitation, a near-infrared fluorescent mutant version of the DrBphP bacteriophytochrome, iRFP720, has been developed for in vivo imaging and stem/progenitor cell tracking. Here, we present the generation and characterization of an iRFP720 expressing human induced pluripotent stem cell (iPSC) line, which can be used for real-time imaging in various biological applications. To generate the transgenic cells, the CRISPR/Cas9 technology was applied. A puromycin resistance gene was inserted into the AAVS1 locus, driven by the endogenous PPP1R12C promoter, along with the CAG-iRFP720 reporter cassette, which was flanked by insulator elements. Proper integration of the transgene into the targeted genomic region was assessed by comprehensive genetic analysis, verifying precise genome editing. Stable expression of iRFP720 in the cells was confirmed and imaged by their near-infrared fluorescence. We demonstrated that the reporter iPSCs exhibit normal stem cell characteristics and can be efficiently differentiated towards the pancreatic lineage. As the genetically modified reporter cells show retained pluripotency and multilineage differentiation potential, they hold great potential as a cellular model in a variety of biological and pharmacological applications.

CT/bioluminescence dual-modal imaging tracking of stem cells labeled with Au@PEI@PEG nanotracers and RfLuc in nintedanib-assisted pulmonary fibrosis therapy

Mesenchymal stem cells (MSCs) are promising in idiopathic pulmonary fibrosis (IPF) therapy. However, low survival rate and ambiguous behavior of MSCs after transplantation impede their clinical translation. To this end, we have developed a new strategy to improve the survival rate and monitor the behavior of the transplanted MSCs simultaneously. In our strategy, nintedanib, a tyrosine kinase inhibitor, is employed to protect the human MSCs (hMSCs) from excessive oxidative stress responses and inflammatory environment in the damaged lung. Moreover, by labeling of the transplanted hMSCs with a computed tomography (CT) nanotracer, Au nanoparticles functionalized with polyethylenimine (PEI) and polyethylene glycol (PEG) (Au@PEI@PEG), in combination with red-emitting firefly luciferase (RfLuc), in vivo CT/bioluminescence (BL) dual-modal imaging tracking of the location, distribution, and survival of the transplanted hMSCs in presence of nintedanib were achieved, which facilitates the profound understanding of the role the stem cells play in IPF therapy.

Stem Cell Transplantation Therapy and Neurological Disorders: Current Status and Future Perspectives

Neurodegenerative diseases are a global health issue with inadequate therapeutic options and an inability to restore the damaged nervous system. With advances in technology, health scientists continue to identify new approaches to the treatment of neurodegenerative diseases. Lost or injured neurons and glial cells can lead to the development of several neurological diseases, including Parkinson's disease, stroke, and multiple sclerosis. In recent years, neurons and glial cells have successfully been generated from stem cells in the laboratory utilizing cell culture technologies, fueling efforts to develop stem cell-based transplantation therapies for human patients. When a stem cell divides, each new cell has the potential to either remain a stem cell or differentiate into a germ cell with specialized characteristics, such as muscle cells, red blood cells, or brain cells. Although several obstacles remain before stem cells can be used for clinical applications, including some potential disadvantages that must be overcome, this cellular development represents a potential pathway through which patients may eventually achieve the ability to live more normal lives. In this review, we summarize the stem cell-based therapies that have been explored for various neurological disorders, discuss the potential advantages and drawbacks of these therapies, and examine future directions for this field.

Visualizing stem cells in vivo using magnetic resonance imaging

Stem cell (SC) therapies displayed encouraging efficacy and clinical outcome in various disorders. Despite this huge hype, clinical translation of SC therapy has been disheartening due to contradictory results from clinical trials. The ability to monitor migration and engraftment of cells in vivo represents an ideal strategy in cell therapy. Therefore, suitable imaging approach to track MSCs would allow understanding of migratory and homing efficiency, optimal route of delivery and engraftment of cells at targeted location. Hence, longitudinal tracking of SCs is crucial for the optimization of treatment parameters, leading to improved clinical outcome and translation. Magnetic resonance imaging (MRI) represents a suitable imaging modality to observe cells non-invasively and repeatedly. Tracking is achieved when cells are incubated prior to implantation with appropriate contrast agents (CA) or tracers which can then be detected in an MRI scan. This review explores and emphasizes the importance of monitoring the distribution and fate of SCs post-implantation using current contrast agents, such as positive CAs including paramagnetic metals (gadolinium), negative contrast agents such as superparamagnetic iron oxides and ¹⁹ F containing tracers, specifically for the in vivo tracking of MSCs using MRI. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Synthetic Antiferromagnetic Gold Nanoparticles as Bimodal Contrast Agents in MRI and CT-An Experimental In Vitro and In Vivo Study

The use of multimodal contrast agents can potentially overcome the intrinsic limitations of individual imaging methods. We have validated synthetic antiferromagnetic nanoparticles (SAF-NPs) as bimodal contrast agents for in vitro cell labeling and in vivo cell tracking using magnetic resonance imaging (MRI) and computed tomography (CT). SAF-NP-labeled cells showed high contrast in MRI phantom studies (r₂* = 712 s⁻¹ mM⁻¹), while pelleted cells showed clear contrast enhancement in CT. After intravenous SAF-NP injection, nanoparticles accumulated in the liver and spleen, as visualized in vivo by significant MRI contrast enhancement. Intravenous injection of SAF-NP-labeled cells resulted in cell accumulation in the lungs, which was clearly detectable by using CT but not by using MRI. SAF-NPs proved to be very efficient cell labeling agents for complementary MRI- and CT-based cell tracking. Bimodal monitoring of SAF-NP labeled cells is in particular of interest for applications where the applied imaging methods are not able to visualize the particles and/or cells in all organs.

In vivo Cell Tracking Using Non-invasive Imaging of Iron Oxide-Based Particles with Particular Relevance for Stem Cell-Based Treatments of Neurological and Cardiac Disease

Stem cell-based therapeutics is a rapidly developing field associated with a number of clinical challenges. One such challenge lies in the implementation of methods to track stem cells and stem cell-derived cells in experimental animal models and in the living patient. Here, we provide an overview of cell tracking in the context of cardiac and neurological disease, focusing on the use of iron oxide-based particles (IOPs) visualized in vivo using magnetic resonance imaging (MRI). We discuss the types of IOPs available for such tracking, their advantages and limitations, approaches for labeling cells with IOPs, biological interactions and effects of IOPs at the molecular and cellular levels, and MRI-based and associated approaches for in vivo and histological visualization. We conclude with reviews of the literature on IOP-based cell tracking in cardiac and neurological disease, covering both preclinical and clinical studies.

Tracking of Labelled Stem Cells Using Molecular MR Imaging in a Mouse Burn Model in Vivo as an Approach to Regenerative Medicine

Therapies based on stem cell transplants offer significant potential in the field of regenerative medicine. Monitoring the fate of the transplanted stem cells in a timely manner is considered one of the main limitations for long-standing success of stem cell transplants. Imaging methods that visualize and track stem cells in vivo non-invasively in real time are helpful towards the development of successful cell transplantation techniques. Novel molecular imaging methods which are non-invasive particularly such as MRI have been of great recent interest. Hence, mouse models which are of clinical relevance have been studied by injecting contrast agents used for labelling cells such as super-paramagnetic iron-oxide (SPIO) nanoparticles for cellular imaging. The MR techniques which can be used to generate positive contrast images have been of much relevance recently for tracking of the labelled cells. Particularly when the off-resonance region in the vicinity of the labeled cells is selectively excited while suppressing the signals from the non-labeled regions by the method of spectral dephasing. Thus, tracking of magnetically labelled cells employing positive contrast in vivo MR imaging methods in a burn mouse model in a non-invasive way has been the scope of this study. The consequences have direct implications for monitoring labeled stem cells at some stage in wound healing. We suggest that our approach can be used in clinical trials in molecular and regenerative medicine.

Illuminating the Regenerative Properties of Stem Cells In Vivo with Bioluminescence Imaging

Preclinical animal studies are essential to the development of safe and effective stem cell therapies. Bioluminescence imaging (BLI) is a powerful tool in animal studies that enables the real-time longitudinal monitoring of stem cells in vivo to elucidate their regenerative properties. This review describes the application of BLI in preclinical stem cell research to address critical challenges in producing successful stem cell therapeutics. These challenges include stem cell survival, proliferation, homing, stress response, and differentiation. The applications presented here utilize bioluminescence to investigate a variety of stem and progenitor cells in several different in vivo models of disease and implantation. An overview of luciferase reporters is provided, along with the advantages and disadvantages of BLI. Additionally, BLI is compared to other preclinical imaging modalities and potential future applications of this technology are discussed in emerging areas of stem cell research.

Labeling and tracking cells with gold nanoparticles

Gold nanoparticles (AuNPs) have garnered much attention as contrast agents for computerized tomography (CT) because of their facile synthesis and surface functionalization, in addition to their significant X-ray attenuation and minimal cytotoxicity. Cell labeling using AuNPs and tracking of the labeled cells using CT has become a time-efficient and cost-effective method. Actively targeted AuNPs can enhance CT contrast and sensitivity, and further reduce the radiation dosage needed during CT imaging. In this review, we summarize the state-of-the-art use of AuNPs in CT for cell tracking, including the precautionary steps necessary for their use and the difficulty in translating the process into clinical use.

Cellular and molecular imaging for stem cell tracking in neurological diseases

Stem cells (SCs) are cells with strong proliferation ability, multilineage differentiation potential and self-renewal capacity. SC transplantation represents an important therapeutic advancement for the treatment strategy of neurological diseases, both in the preclinical experimental and clinical settings. Innovative and breakthrough SC labelling and tracking technologies are widely used to monitor the distribution and viability of transplanted cells non-invasively and longitudinally. Here we summarised the research progress of the main tracers, labelling methods and imaging technologies involved in current SC tracking technologies for various neurological diseases. Finally, the applications, challenges and unresolved problems of current SC tracing technologies were discussed.

Simultaneous in vivo PET/MRI using fluorine-18 labeled Fe3O4@Al(OH)3 nanoparticles: comparison of nanoparticle and nanoparticle-labeled stem cell distribution

BACKGROUND

Mesenchymal stem cells (MSCs) have shown potential for treatment of different diseases. However, their working mechanism is still unknown. To elucidate this, the non-invasive and longitudinal tracking of MSCs would be beneficial. Both iron oxide-based nanoparticles (Fe₃O₄ NPs) for magnetic resonance imaging (MRI) and radiotracers for positron emission tomography (PET) have shown potential as in vivo cell imaging agents. However, they are limited by their negative contrast and lack of spatial information as well as short half-life, respectively. In this proof-of-principle study, we evaluated the potential of Fe₃O₄@Al(OH)₃ NPs as dual PET/MRI contrast agents, as they allow stable binding of [¹⁸F]F^- ions to the NPs and thus, NP visualization and quantification with both imaging modalities.

RESULTS

¹⁸F-labeled Fe₃O₄@Al(OH)₃ NPs (radiolabeled NPs) or mouse MSCs (mMSCs) labeled with these radiolabeled NPs were intravenously injected in healthy C57Bl/6 mice, and their biodistribution was studied using simultaneous PET/MRI acquisition. While liver uptake of radiolabeled NPs was seen with both PET and MRI, mMSCs uptake in the lungs could only be observed with PET. Even some initial loss of fluoride label did not impair NPs/mMSCs visualization. Furthermore, no negative effects on blood cell populations were seen after injection of either the NPs or mMSCs, indicating good biocompatibility.

CONCLUSION

We present the application of novel ¹⁸F-labeled Fe₃O₄@Al(OH)₃ NPs as safe cell tracking agents for simultaneous PET/MRI. Combining both modalities allows fast and easy NP and mMSC localization and quantification using PET at early time points, while MRI provides high-resolution, anatomic background information and long-term NP follow-up, hereby overcoming limitations of the individual imaging modalities.

Integration of nano- and biotechnology for beta-cell and islet transplantation in type-1 diabetes treatment

Regenerative medicine using human or porcine β‐cells or islets has an excellent potential to become a clinically relevant method for the treatment of type‐1 diabetes. High‐resolution imaging of the function and faith of transplanted porcine pancreatic islets and human stem cell–derived beta cells in large animals and patients for testing advanced therapy medicinal products (ATMPs) is a currently unmet need for pre‐clinical/clinical trials. The iNanoBIT EU H2020 project is developing novel highly sensitive nanotechnology‐based imaging approaches allowing for monitoring of survival, engraftment, proliferation, function and whole‐body distribution of the cellular transplants in a porcine diabetes model with excellent translational potential to humans. We develop and validate the application of single‐photon emission computed tomography (SPECT) and optoacoustic imaging technologies in a transgenic insulin‐deficient pig model to observe transplanted porcine xeno‐islets and in vitro differentiated human beta cells. We are progressing in generating new transgenic reporter pigs and human‐induced pluripotent cell (iPSC) lines for optoacoustic imaging and testing them in transplantable bioartificial islet devices. Novel multifunctional nanoparticles have been generated and are being tested for nuclear imaging of islets and beta cells using a new, high‐resolution SPECT imaging device. Overall, the combined multidisciplinary expertise of the project partners allows progress towards creating much needed technological toolboxes for the xenotransplantation and ATMP field, and thus reinforces the European healthcare supply chain for regenerative medicinal products.

Recent Advances in Molecular Imaging with Gold Nanoparticles

Gold nanoparticles (AuNP) have been extensively developed as contrast agents, theranostic platforms, and probes for molecular imaging. This popularity has yielded a large number of AuNP designs that vary in size, shape, surface functionalization, and assembly, to match very closely the requirements for various imaging applications. Hence, AuNP based probes for molecular imaging allow the use of computed tomography (CT), fluorescence, and other forms of optical imaging, photoacoustic imaging (PAI), and magnetic resonance imaging (MRI), and other newer techniques. The unique physicochemical properties, biocompatibility, and highly developed chemistry of AuNP have facilitated breakthroughs in molecular imaging that allow the detection and imaging of physiological processes with high sensitivity and spatial resolution. In this Review, we summarize the recent advances in molecular imaging achieved using novel AuNP structures, cell tracking using AuNP, targeted AuNP for cancer imaging, and activatable AuNP probes. Finally, the perspectives and current limitations for the clinical translation of AuNP based probes are discussed.

ZeOncoTest: Refining and Automating the Zebrafish Xenograft Model for Drug Discovery in Cancer

The xenograft of human cancer cells in model animals is a powerful tool for understanding tumor progression and metastatic potential. Mice represent a validated host, but their use is limited by the elevated experimental costs and low throughput. To overcome these restrictions, zebrafish larvae might represent a valuable alternative. Their small size and transparency allow the tracking of transplanted cells. Therefore, tumor growth and early steps of metastasis, which are difficult to evaluate in mice, can be addressed. In spite of its advantages, the use of this model has been hindered by lack of experimental homogeneity and validation. Considering these facts, the aim of our work was to standardize, automate, and validate a zebrafish larvae xenograft assay with increased translatability and higher drug screening throughput. The ZeOncoTest reliability is based on the optimization of different experimental parameters, such as cell labeling, injection site, automated individual sample image acquisition, and analysis. This workflow implementation finally allows a higher precision and experimental throughput increase, when compared to previous reports. The approach was validated with the breast cancer cell line MDA-MB-231, the colorectal cancer cells HCT116, and the prostate cancer cells PC3; and known drugs, respectively RKI-1447, Docetaxel, and Mitoxantrone. The results recapitulate growth and invasion for all tested tumor cells, along with expected efficacy of the compounds. Finally, the methodology has proven useful for understanding specific drugs mode of action. The insights gained bring a step further for zebrafish larvae xenografts to enter the regulated preclinical drug discovery path.

Long-term in vivo CT tracking of mesenchymal stem cells labeled with Au@BSA@PLL nanotracers

Human mesenchymal stem cells (hMSCs) transplantation has attracted considerable interest for the treatment of pulmonary injury. Noninvasive and long-term tracking of hMSCs after transplantation in vivo, which is important for our understanding of the stem cell therapy, still remains a big challenge. Herein, we report on the development of a novel gold nanoparticle-based nanotracer to track by CT imaging the transplantation of hMSCs in vivo. Gold nanoparticles (AuNPs) were synthesized on bovine serum albumin (BSA) via an in situ growth method and modified with a poly-l-lysine (PLL) layer, yielding Au@BSA@PLL nanotracers with enhanced biocompatibility and intracellular uptake. Au@BSA@PLL nanotracers were explored for in vitro and in vivo tracking of hMSCs with computer tomography (CT). Our results showed that the endocytosis of Au@BSA@PLL by hMSCs was as high as ∼293 pg per cell. Meanwhile, the nanotracers had a negligible influence on the viability, proliferation, and osteogenic and adipogenic differentiation of the labeled hMSCs. Using a pulmonary fibrosis injury mouse model induced by bleomycin, the labeled hMSCs could be tracked by CT imaging up to 23 d after transplanted in vivo, suggesting the feasibility of Au@BSA@PLL as a potential cellular nanotracer for noninvasive and long-term CT tracking of hMSCs in lung tissue repair.

Non-Invasive Cell Tracking with Brighter and Red-Transferred Luciferase for Potential Application in Stem Cell Therapy

This study investigated the safety of a novel cell-labeling technology with mKATE and Renilla reniformis luciferase (mKATE-renLUC) and assessed the efficacy on tracking implanted human placental stromal cells (PSC) in an erectile dysfunction (ED) animal model. Human PSC were labeled with mKATE-renLUC using a lentivirus. Cell viability, apoptosis, proliferation, migration, surface marker expression and differentiation potential of the labeled PSC were evaluated and compared with non-labeled PSC. The paracrine profile of labeled cells was examined using an angiogenesis protein array. The brightness and duration of labeled cells with different densities were evaluated. An ED rat model was established and labeled PSC were injected into cavernosal tissue of the penis. The migration and distribution of transplanted PSC were monitored using an IVIS imaging system in real time. Implanted PSC were identified in isolated tissues via detection of mKATE fluorescence. The cell viability, morphology, proliferation, migration, surface marker expression and differentiation potential of mKATE-renLUC-labeled PSC were similar to those of non-labeled cells in vitro (no statistical difference p>0.05). Similar expressions of trophic factors were found between labeled and non-labeled PSC. The migration and distribution of PSC expressing renLUC were tracked in vivo using IVIS imaging system. mKATE-positive PSC were detected in penile, kidney, prostate and hepatic tissues using histological methods. This labeling technology provides a safe and effective cell-tracking approach with a brighter fluorophore and codon-optimized luciferase.

Intravenous transplantation of olfactory bulb ensheathing cells for a spinal cord hemisection injury rat model

Cellular transplantation strategies utilizing intraspinal or intrathecal olfactory ensheathing cells (OECs) have been reported as beneficial for spinal cord injury (SCI). However, there are many disadvantages of these methods, including additional trauma to the spinal cord parenchyma and technical challenges. Therefore, we investigated the feasibility and potential benefits of intravenous transplantation of OECs in a rat hemisection SCI model. OECs derived from olfactory bulb tissue were labeled with quantum dots (QDs), and their biodistribution after intravenous transplantation was tracked using a fluorescence imaging system. Accumulation of the transplanted OECs was observed in the injured spinal cord within 10 min, peaked at seven days after cell transplantation, and decreased gradually thereafter. This time window corresponded to the blood–spinal cord barrier (BSCB) opening time, which was quantitated with the Evans blue leakage assay. Using immunohistochemistry, we examined neuronal growth (GAP-43), remyelination (MBP), and microglia (Iba-1) reactions at the lesion site. Motor function recovery was also measured using a classic open field test (Basso, Beattie and Bresnahan score). Compared with the group injected only with QDs, the rats that received OEC transplantation exhibited a prominent reduction in inflammatory responses, increased neurogenesis and remyelination, and significant improvement in motor function. We suggest that intravenous injection could also be an effective method for delivering OECs and improving functional outcomes after SCI. Moreover, the time course of BSCB disruption provides a clinically relevant therapeutic window for cell-based intervention.

Optical fluorescence imaging with shortwave infrared light emitter nanomaterials for in vivo cell tracking in regenerative medicine

In vivo tracking and monitoring of adoptive cell transfer has a distinct importance in cell‐based therapy. There are many imaging modalities for in vivo monitoring of biodistribution, viability and effectiveness of transferred cells. Some of these procedures are not applicable in the human body because of low sensitivity and high possibility of tissue damages. Shortwave infrared region (SWIR) imaging is a relatively new technique by which deep biological tissues can be potentially visualized with high resolution at cellular level. Indeed, scanning of the electromagnetic spectrum (beyond 1000 nm) of SWIR has a great potential to increase sensitivity and resolution of in vivo imaging for various human tissues. In this review, molecular imaging modalities used for monitoring of biodistribution and fate of administered cells with focusing on the application of non‐invasive optical imaging at shortwave infrared region are discussed in detail.

Gadolinium-Labelled Cell Scaffolds to Follow-up Cell Transplantation by Magnetic Resonance Imaging

Cell scaffolds are often used in cell transplantation as they provide a solid structural support to implanted cells and can be bioengineered to mimic the native extracellular matrix. Gadolinium fluoride nanoparticles (Gd-NPs) as a contrast agent for Magnetic Resonance Imaging (MRI) were incorporated into poly(lactide-co-glycolide)/chitosan scaffolds to obtain Imaging Labelled Cell Scaffolds (ILCSs), having the shape of hollow spherical/ellipsoidal particles (200-600 μm diameter and 50-80 μm shell thickness). While Gd-NPs incorporated into microparticles do not provide any contrast enhancement in T1-weighted (T1w) MR images, ILCSs can release Gd-NPs in a controlled manner, thus activating MRI contrast. ILCSs seeded with human mesenchymal stromal cells (hMSCs) were xenografted subcutaneously into either immunocompromised and immunocompetent mice without any immunosuppressant treatments, and the transplants were followed-up in vivo by MRI for 18 days. Immunocompromised mice showed a progressive activation of MRI contrast within the implants due to the release of Gd-NPs in the extracellular matrix. Instead, immunocompetent mice showed poor activation of MRI contrast due to the encapsulation of ILCSs within fibrotic capsules and to the scavenging of released Gd-NPs by phagocytic cells. In conclusion, the MRI follow-up of cell xenografts can report the host cell response to the xenograft. However, it does not strictly report on the viability of transplanted hMSCs.

Indocyanine green labeling for optical and photoacoustic imaging of mesenchymal stem cells after in vivo transplantation

The transplantation of mesenchymal stem cells (MSCs) holds great promise for the treatment of a plethora of human diseases, but new noninvasive procedures are needed to monitor the cell fate in vivo. Already largely used in medical diagnostics, the fluorescent dye indocyanine green (ICG) is an established dye to track limited numbers of cells by optical imaging (OI), but it can also be visualized by photoacoustic imaging (PAI), which provides a higher spatial resolution than pure near infrared fluorescence imaging (NIRF). Because of its successful use in clinical and preclinical examinations, we chose ICG as PAI cell labeling agent. Optimal incubation conditions were defined for an efficient and clinically translatable MSC labeling protocol, such that no cytotoxicity or alterations of the phenotypic profile were observed, and a consistent intracellular uptake of the molecule was achieved. Suspensions of ICG-labeled cells were both optically and optoacoustically detected in vitro, revealing a certain variability in the photoacoustic spectra acquired by varying the excitation wavelength from 680 to 970 nm. Intramuscular engraftments of ICG-labeled MSCs were clearly visualized by both PAI and NIRF over few days after transplantation in the hindlimb of healthy mice, suggesting that the proposed technique retains a considerable potential in the field of transplantation-focused research and therapy. Stem cells were labeled with the Food and Drug Administration (FDA)-approved fluorescent dye ICG, and detected by both PAI and OI, enabling to monitor the cell fate safely, in dual modality, and with good sensitivity and improved spatial resolution.

Superparamagnetic graphene quantum dot as a dual-modality contrast agent for confocal fluorescence microscopy and magnetomotive optical coherence tomography

A magnetic graphene quantum dot (MGQD) nanoparticle, synthesized by hydrothermally reducing and cutting graphene oxide-iron oxide sheet, was demonstrated to possess the capabilities of simultaneous confocal fluorescence and magnetomotive optical coherence tomography (MMOCT) imaging. This MGQD shows low toxicity, significant tunable blue fluorescence and superparamagnetism, which can thus be used as a dual-modality contrast agent for confocal fluorescence microscopy (CFM) and MMOCT. The feasibility of applying MGQD as a tracer of cells is shown by imaging and visualizing MGQD labeled cells using CFM and our in-house MMOCT. Since MMOCT and CFM can offer anatomical structure and intracellular details, respectively, the MGQD for cell tracking could provide a more comprehensive diagnosis.

In Vivo MR Imaging of Dual MRI Reporter Genes and Deltex-1 Gene-modified Human Mesenchymal Stem Cells in the Treatment of Closed Penile Fracture

PURPOSE

The purpose of this study was to investigate the feasibility of dual magnetic resonance imaging (MRI) reporter genes, including ferritin heavy subunit (Fth) and transferrin receptor (TfR), which provide sufficient MRI contrast for in vivo MRI tracking, and the Deltex-1 (DTX1) gene, which promotes human mesenchymal stem cell (hMSC) differentiation to smooth muscle cells (SMCs), to treat closed penile fracture (CPF).

METHODS

Multi-gene co-expressing hMSCs were generated. The expression of mRNA and proteins was assessed, and the original biological properties of hMSCs were determined and compared. The intracellular uptake of iron was evaluated, and the ability to differentiate into SMCs was detected. Fifty rabbits with CPF were randomly transplanted with PBS, hMSCs, Fth-TfR-hMSCs, DTX1-hMSCs, and Fth-TfR-DTX1-hMSCs. In vivo MRI was performed to detect the distribution and migration of the grafted cells and healing progress of CPF, and the results were correlated with histology.

RESULTS

The mRNA and proteins of the multi-gene were highly expressed. The transgenes could not influence the original biological properties of hMSCs. The dual MRI reporter genes increased the iron accumulation capacity, and the DTX1 gene promoted hMSC differentiation into SMCs. The distribution and migration of the dual MRI reporter gene-modified hMSCs, and the healing state of CPF could be obviously detected by MRI and confirmed by histology.

CONCLUSION

The dual MRI reporter genes could provide sufficient MRI contrast, and the distribution and migration of MSCs could be detected in vivo. The DTX1 gene can promote MSC differentiation into SMCs for the treatment of CPF and effectively inhibit granulation tissue formation.

Static Magnetic Field (SMF) as a Regulator of Stem Cell Fate - New Perspectives in Regenerative Medicine Arising from an Underestimated Tool

Tissue engineering and stem cell-based therapies are one of the most rapidly developing fields in medical sciences. Therefore, much attention has been paid to the development of new drug-delivery systems characterized by low cytotoxicity, high efficiency and controlled release. One of the possible strategies to achieve these goals is the application of magnetic field and/or magnetic nanoparticles, which have been shown to exert a wide range of effects on cellular metabolism. Static magnetic field (SMF) has been commonly used in medicine as a tool to increase wound healing, bone regeneration and as a component of magnetic resonance technique. However, recent data shed light on deeper mechanism of SMF action on physiological properties of different cell populations, including stem cells. In the present review, we focused on SMF effects on stem cell biology and its possible application as a tool for controlled drug delivery. We also highlighted the perspectives, in which SMF can be used in future therapies in tissue engineering due to its easy application and a wide range of possible effects on cells and organisms.

Characterization of Magneto-Endosymbionts as MRI Cell Labeling and Tracking Agents

PURPOSE

Magneto-endosymbionts (MEs) show promise as living magnetic resonance imaging (MRI) contrast agents for in vivo cell tracking. Here we characterize the biomedical imaging properties of ME contrast agents, in vitro and in vivo.

PROCEDURES

By adapting and engineering magnetotactic bacteria to the intracellular niche, we are creating magneto-endosymbionts (MEs) that offer advantages relative to passive iron-based contrast agents (superparamagnetic iron oxides, SPIOs) for cell tracking. This work presents a biomedical imaging characterization of MEs including: MRI transverse relaxivity (r ₂) for MEs and ME-labeled cells (compared to a commercially available iron oxide nanoparticle); microscopic validation of labeling efficiency and subcellular locations; and in vivo imaging of a MDA-MB-231BR (231BR) human breast cancer cells in a mouse brain.

RESULTS

At 7T, r ₂ relaxivity of bare MEs was higher (250 s^-1 mM^-1) than that of conventional SPIO (178 s^-1 mM^-1). Optimized in vitro loading of MEs into 231BR cells yielded 1-4 pg iron/cell (compared to 5-10 pg iron/cell for conventional SPIO). r ₂ relaxivity dropped by a factor of ~3 upon loading into cells, and was on the same order of magnitude for ME-loaded cells compared to SPIO-loaded cells. In vivo, ME-labeled cells exhibited strong MR contrast, allowing as few as 100 cells to be detected in mice using an optimized 3D SPGR gradient-echo sequence.

CONCLUSIONS

Our results demonstrate the potential of magneto-endosymbionts as living MR contrast agents. They have r ₂ relaxivity values comparable to traditional iron oxide nanoparticle contrast agents, and provide strong MR contrast when loaded into cells and implanted in tissue.

Synthetic Cargo Internalization Receptor System for Nanoparticle Tracking of Individual Cell Populations by Fluorine Magnetic Resonance Imaging

Specific detection of target structures or cells lacking particular surface epitopes still poses a serious problem for all imaging modalities. Here, we demonstrate the capability of synthetic "cargo internalization receptors" (CIRs) for tracking of individual cell populations by ¹H/¹⁹F magnetic resonance imaging (MRI). To this end, a nanobody for green fluorescent protein (GFP) was used to engineer cell-surface-expressed CIRs which undergo rapid internalization after GFP binding. For ¹⁹F MR visibility, the GFP carrier was equipped with "contrast cargo", in that GFP was coupled to perfluorocarbon nanoemulsions (PFCs). To explore the suitability of different uptake mechanisms for this approach, CIRs were constructed by combination of the GFP nanobody and three different cytoplasmic tails that contained individual internalization motifs for endocytosis of the contrast cargo (CIR1-3). Exposure of CIR⁺ cells to GFP-PFCs resulted in highly specific binding and internalization as confirmed by fluorescence microscopy as well as flow cytometry and enabled visualization by ¹H/¹⁹F MRI. In particular, expression of CIR2/3 resulted in substantial incorporation of ¹⁹F cargo and readily enabled in vivo visualization of GFP-PFC recruitment to transplanted CIR⁺ cells by ¹H/¹⁹F MRI in mice. Competition experiments with blood immune cells revealed that CIR⁺ cells are predominantly loaded with GFP-PFCs even in the presence of cells with strong phagocytotic capacity. Importantly, binding and internalization of GFP-PFCs did not result in the activation of signaling cascades and therefore does not alter cell physiology. Overall, this approach represents a versatile in vivo imaging platform for tracking of individual cell populations by making use of cell-type-specific CIR⁺ mice.

Aggregation-Induced Emission Luminogens: Union Is Strength, Gathering Illuminates Healthcare

The rapid development of healthcare techniques encourages the emergence of new molecular imaging agents and modalities. Fluorescence imaging that enables precise monitoring and detection of biological processes/diseases is extensively investigated as this imaging technique has strengths in terms of high sensitivity, excellent temporal resolution, low cost, and good safety. Aggregation-induced emission luminogens (AIEgens) have recently emerged as a new class of emitters that possess several notable features, such as high brightness, large Stokes shift, marked photostability, good biocompatibility, and so on. So far, AIEgens are widely explored and exhibit superb performance in the area of biomedicine and life sciences. Herein, this review summarizes and discusses the recent investigations of AIEgens for in vivo diagnosis and therapy including long-term tracking, 3D angiography, multimodality imaging, disease theranostics, and activatable sensing. Collectively, these results reveal that AIEgens are of great promise for in vivo biomedical applications. It is hoped that this review will lead to new insights into the development of advanced healthcare materials.

Liposome-Indocyanine Green Nanoprobes for Optical Labeling and Tracking of Human Mesenchymal Stem Cells Post-Transplantation In Vivo

Direct labeling of human mesenchymal stem cells (hMSC) prior to transplantation provides a means to track cells after administration and it is a powerful tool for the assessment of new cell-based therapies. Biocompatible nanoprobes consisting of liposome-indocyanine green hybrid vesicles (liposome-ICG) are used to safely label hMSC. Labeled hMSC recapitulating a 3D cellular environment is transplanted as spheroids subcutaneously and intracranially in athymic nude mice. Cells emit a strong NIR signal used for tracking post-transplantation with the IVIS imaging system up to 2 weeks (subcutaneous) and 1 week (intracranial). The transplanted stem cells are imaged in situ after engraftment deep in the brain up to 1 week in living animals using optical imaging techniques and without the need to genetically modify the cells. This method is proposed for efficient, nontoxic direct cell labeling for the preclinical assessment of cell-based therapies and the design of clinical trials, and potentially for localization of the cell engraftment after transplantation into patients.

In Vivo Long-Term Tracking of Neural Stem Cells Transplanted into an Acute Ischemic Stroke model with Reporter Gene-Based Bimodal MR and Optical Imaging

Transplantation of neural stem cells (NSCs) is emerging as a new therapeutic approach for stroke. Real-time imaging of transplanted NSCs is essential for successful cell delivery, safety monitoring, tracking cell fate and function, and understanding the interactions of transplanted cells with the host environment. Magnetic resonance imaging (MRI) of magnetic nanoparticle-labeled cells has been the most widely used means to track stem cells in vivo. Nevertheless, it does not allow for the reliable discrimination between live and dead cells. Reporter gene-based MRI was considered as an alternative strategy to overcome this shortcoming. In this work, a class of lentiviral vector-encoding ferritin heavy chain (FTH) and enhanced green fluorescent protein (EGFP) was constructed to deliver reporter genes into NSCs. After these transgenic NSCs were transplanted into the contralateral hemisphere of rats with acute ischemic stroke, MRI and fluorescence imaging (FLI) were performed in vivo for tracking the fate of transplanted cells over a long period of 6 wk. The results demonstrated that the FTH and EGFP can be effectively and safely delivered to NSCs via the designed lentiviral vector. The distribution and migration of grafted stem cells could be monitored by bimodal MRI and FLI. FTH can be used as a robust MRI reporter for reliable reporting of the short-term viability of cell grafts, whereas its capacity for tracking the long-term viability of stem cells remains dependent on several confounding factors such as cell death and the concomitant reactive inflammation.

New imaging probes to track cell fate: reporter genes in stem cell research

Cell fate is a concept used to describe the differentiation and development of a cell in its organismal context over time. It is important in the field of regenerative medicine, where stem cell therapy holds much promise but is limited by our ability to assess its efficacy, which is mainly due to the inability to monitor what happens to the cells upon engraftment to the damaged tissue. Currently, several imaging modalities can be used to track cells in the clinical setting; however, they do not satisfy many of the criteria necessary to accurately assess several aspects of cell fate. In recent years, reporter genes have become a popular option for tracking transplanted cells, via various imaging modalities in small mammalian animal models. This review article examines the reporter gene strategies used in imaging modalities such as MRI, SPECT/PET, Optoacoustic and Bioluminescence Imaging. Strengths and limitations of the use of reporter genes in each modality are discussed.

Pre-Microporation Improves Outcome of Pancreatic Islet Labelling for Optical and 19F MR Imaging

Background

In vitro labelling of cells and small cell structures is a necessary step before in vivo monitoring of grafts. We modified and optimised a procedure for pancreatic islet labelling using bimodal positively charged poly(lactic-co-glycolic acid) nanoparticles with encapsulated perfluoro crown ethers and indocyanine green dye via microporation and compared the method with passive endocytosis.

Results

Pancreatic islets were microporated using two pulses at various voltages. We tested a standard procedure (poration in the presence of nanoparticles) and a modified protocol (pre-microporation in a buffer only, and subsequent islet incubation with nanoparticles on ice for 10 min).

We compared islet labelling by microporation with labelling by endocytosis, i.e. pancreatic islets were incubated for 24 h in a medium with suspended nanoparticles.

In order to verify the efficiency of the labelling procedures, we used ¹⁹F magnetic resonance imaging, optical fluorescence imaging and confocal microscopy.

The experiment confirmed that microporation, albeit fast and effective, is invasive and may cause substantial harm to islets. To achieve sufficient poration and to minimise the reduction of viability, the electric field should be set at 20 kV/m (two pulses, 20 ms each).

Poration in the presence of nanoparticles was found to be unsuitable for the nanoparticles used. The water suspension of nanoparticles (which served as a surfactant) was slightly foamy and microbubbles in the suspension were responsible for sparks causing the destruction of islets during poration. However, pre-microporation (poration of islets in a buffer only) followed by 10-min incubation with nanoparticles was safer.

Conclusions

For labelling of pancreatic islets using poly(lactic-co-glycolic acid) nanoparticles, the modified microporation procedure with low voltage was found to be safer than the standard microporation procedure. The modified procedure was fast, however, efficiency was lower compared to endocytosis.

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.

Use of Nanoparticle Contrast Agents for Cell Tracking with Computed Tomography

Efforts to develop novel cell-based therapies originated with the first bone marrow transplant on a leukemia patient in 1956. Preclinical and clinical examples of cell-based treatment strategies have shown promising results across many disciplines in medicine, with recent advances in immune cell therapies for cancer producing remarkable response rates, even in patients with multiple treatment failures. However, cell-based therapies suffer from inconsistent outcomes, motivating the search for tools that allow monitoring of cell delivery and behavior in vivo. Noninvasive cell imaging techniques, also known as cell tracking, have been developed to address this issue. These tools can allow real-time, quantitative, and long-term monitoring of transplanted cells in the recipient, providing insight on cell migration, distribution, viability, differentiation, and fate, all of which play crucial roles in treatment efficacy. Understanding these parameters allows the optimization of cell choice, delivery route, and dosage for therapy and advances cell-based therapy for specific clinical uses. To date, most cell tracking work has centered on imaging modalities such as MRI, radionuclide imaging, and optical imaging. However, X-ray computed tomography (CT) is an emerging method for cell tracking that has several strengths such as high spatial and temporal resolution, and excellent quantitative capabilities. The advantages of CT for cell tracking are enhanced by its wide availability and cost effectiveness, allowing CT to become one of the most popular clinical imaging modalities and a key asset in disease diagnosis. In this review, we will discuss recent advances in cell tracking methods using X-ray CT in various applications, in addition to predictions on how the field will progress.

Drugs in clinical development for the treatment of amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a fatal motor neuron progressive disorder for which no treatment exists to date. However, there are other investigational drugs and therapies currently under clinical development may offer hope in the near future. Areas covered: We have reviewed all the ALS ongoing clinical trials (until November 2016) and collected in Clinicaltrials.gov or EudraCT. We have described them in a comprehensive way and have grouped them in the following sections: biomarkers, biological therapies, cell therapy, drug repurposing and new drugs. Expert opinion: Despite multiple obstacles that explain the absence of effective drugs for the treatment of ALS, joint efforts among patient's associations, public and private sectors have fueled innovative research in this field, resulting in several compounds that are in the late stages of clinical trials. Drug repositioning is also playing an important role, having achieved the approval of some orphan drug applications, in late phases of clinical development. Endaravone has been recently approved in Japan and is pending in USA.

Micro-Computed Tomography Detection of Gold Nanoparticle-Labelled Mesenchymal Stem Cells in the Rat Subretinal Layer

Mesenchymal stem cells are widely used in many pre-clinical and clinical settings. Despite advances in molecular technology; the migration and homing activities of these cells in in vivo systems are not well understood. Labelling mesenchymal stem cells with gold nanoparticles has no cytotoxic effect and may offer suitable indications for stem cell tracking. Here, we report a simple protocol to label mesenchymal stem cells using 80 nm gold nanoparticles. Once the cells and particles were incubated together for 24 h, the labelled products were injected into the rat subretinal layer. Micro-computed tomography was then conducted on the 15th and 30th day post-injection to track the movement of these cells, as visualized by an area of hyperdensity from the coronal section images of the rat head. In addition, we confirmed the cellular uptake of the gold nanoparticles by the mesenchymal stem cells using transmission electron microscopy. As opposed to other methods, the current protocol provides a simple, less labour-intensive and more efficient labelling mechanism for real-time cell tracking. Finally, we discuss the potential manipulations of gold nanoparticles in stem cells for cell replacement and cancer therapy in ocular disorders or diseases.

Transplanted human glial-restricted progenitors can rescue the survival of dysmyelinated mice independent of the production of mature, compact myelin

The therapeutic effect of glial progenitor transplantation in diseases of dysmyelination is currently attributed to the formation of new myelin. Using magnetic resonance imaging (MRI), we show that the therapeutic outcome in dysmyelinated shiverer mice is dependent on the extent of cell migration but not the presence of mature and compact myelin. Human or mouse glial restricted progenitors (GRPs) were transplanted into rag2^-/- shiverer mouse neonates and followed for over one year. Mouse GRPs produced mature myelin as detected with multi-parametric MRI, but showed limited migration without extended animal lifespan. In sharp contrast, human GRPs migrated extensively and significantly increased animal survival, but production of mature myelin did not occur until 46weeks post-grafting. We conclude that human GRPs can extend the survival of transplanted shiverer mice prior to production of mature myelin, while mouse GRPs fail to extend animal survival despite the early presence of mature myelin. This paradox suggests that transplanted GRPs provide therapeutic benefits through biological processes other than the formation of mature myelin capable to foster rapid nerve conduction, challenging the current dogma of the primary role of myelination in regaining function of the central nervous system.

Effect of Gold Nanoparticle Size and Coating on Labeling Monocytes for CT Tracking

With advances in cell therapies, interest in cell tracking techniques to monitor the migration, localization, and viability of these cells continues to grow. X-ray computed tomography (CT) is a cornerstone of medical imaging but has been limited in cell tracking applications due to its low sensitivity toward contrast media. In this study, we investigate the role of size and surface functionality of gold nanoparticles for monocyte uptake to optimize the labeling of these cells for tracking in CT. We synthesized gold nanoparticles (AuNP) that range from 15 to 150 nm in diameter and examined several capping ligands, generating 44 distinct AuNP formulations. In vitro cytotoxicity and uptake experiments were performed with the RAW 264.7 monocyte cell line. The majority of formulations at each size were found to be biocompatible, with only certain 150 nm PEG functionalized particles reducing viability at high concentrations. High uptake of AuNP was found using small capping ligands with distal carboxylic acids (11-MUA and 16-MHA). Similar uptake values were found with intermediate sizes (50 and 75 nm) of AuNP when coated with 2000 MW poly(ethylene-glycol) carboxylic acid ligands (PCOOH). Low uptake values were observed with 15, 25, 100, and 150 nm PCOOH AuNP, revealing interplay between size and surface functionality. Transmission electron microscopy (TEM) and CT performed on cells revealed similar patterns of high gold uptake for 50 nm PCOOH and 75 nm PCOOH AuNP. These results demonstrate that highly negatively charged carboxylic acid coatings for AuNP provide the greatest internalization of AuNP in monocytes, with a complex dependency on size.

Serial in vivo imaging of transplanted allogeneic neural stem cell survival in a mouse model of amyotrophic lateral sclerosis

Neural stem cells (NSCs) are being investigated as a possible treatment for amyotrophic lateral sclerosis (ALS) through intraspinal transplantation, but no longitudinal imaging studies exist that describe the survival of engrafted cells over time. Allogeneic firefly luciferase-expressing murine NSCs (Luc⁺-NSCs) were transplanted bilaterally (100,000 cells/2μl) into the cervical spinal cord (C5) parenchyma of pre-symptomatic (63day-old) SOD1^G93A ALS mice (n=14) and wild-type age-matched littermates (n=14). Six control SOD1^G93A ALS mice were injected with saline. Mice were immunosuppressed using a combination of tacrolimus+sirolimus (1mg/kg each, i.p.) daily. Compared to saline-injected SOD1^G93A ALS control mice, a transient improvement (p<0.05) in motor performance (rotarod test) was observed after NSC transplantation only at the early disease stage (weeks 2 and 3 post-transplantation). Compared to day one post-transplantation, there was a significant decline in bioluminescent imaging (BLI) signal in SOD1^G93A ALS mice at the time of disease onset (71.7±17.9% at 4weeks post-transplantation, p<0.05), with a complete loss of BLI signal at endpoint (120day-old mice). In contrast, BLI signal intensity was observed in wild-type littermates throughout the entire study period, with only a 41.4±8.7% decline at the endpoint. In SOD1^G93A ALS mice, poor cell survival was accompanied by accumulation of mature macrophages and the presence of astrogliosis and microgliosis. We conclude that the disease progression adversely affects the survival of engrafted murine Luc⁺-NSCs in SOD1^G93A ALS mice as a result of the hostile ALS spinal cord microenvironment, further emphasizing the challenges that face successful cell therapy of ALS.

Stem Cells and Labeling for Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition that usually results in sudden and long-lasting locomotor and sensory neuron degeneration below the lesion site. During the last two decades, the search for new therapies has been revolutionized with the improved knowledge of stem cell (SC) biology. SCs therapy offers several attractive strategies for spinal cord repair. The transplantation of SCs promotes remyelination, neurite outgrowth and axonal elongation, and activates resident or transplanted progenitor cells across the lesion cavity. However, optimized growth and differentiation protocols along with reliable safety assays should be established prior to the clinical application of SCs. Additionally, the ideal method of SCs labeling for efficient cell tracking after SCI remains a challenging issue that requires further investigation. This review summarizes the current findings on the SCs-based therapeutic strategies, and compares different SCs labeling approaches for SCI.

Improved method to track and precisely count Schwann cells post-transplantation in a peripheral nerve injury model

BACKGROUND

To optimize survival evaluation of Schwann cells (SCs) in vivo, we tested fluorescent labeling of the nucleus as an improved method of tracking and counting the transplanted SCs at sciatic nerve injury sites in rodents. We also investigated if co-administering cells with the glial growth factor Neuregulin-1 β (NRG1β) improves in vivo survival.

NEW METHOD

We transduced SCs using a Lentiviral vector with a nuclear localization signal (NLS) fused with mCherry and transplanted them in the sciatic nerve of rat post-crush injury (bilateral) either in the presence or absence of NRG1β in the injectate media. For comparison, in a separate group of similar injury, GFP-labeled cells were transplanted. After 10 days, nerves were harvested and sections (14μm) were counterstained with Hoechst and imaged. Cells showing co-localization with Hoechst and GFP or mCherry were exhaustively counted and data analyzed.

RESULTS

Percentage cells counted in with- and without-NRG condition in both the groups were 0.83±0.13% and 0.06±0.04% (Group 1) & 2.83*±1.95% and 0.23*±0.29% (Group 2).

COMPARISON TO EXISTING METHOD

We are introducing fluorescent labeling of the nucleus as a reliable and efficient technique to perform survival assessments in Schwann cell based treatment studies in animal model. This method can overcome the challenges and limitations of the existing method that could result in underestimation of the therapeutic outcome.

CONCLUSIONS

Nucleus-restricted fluorescent labeling technique offer improved method of tracking as well as accurately counting transplanted SCs in vivo while NRG1β in the injectate media can improve survival.

Intraperitoneal injection (IP), Intravenous injection (IV) or anal injection (AI)? Best way for mesenchymal stem cells transplantation for colitis

Stem cell transplantation showed promising results in IBD management. However, the therapeutic impacts of cell delivery route that is critical for clinical translation are currently poorly understood. Here, three different MSCs delivery routes: intraperitoneal (IP), intravenous (IV), and anal injection (AI) were compared on DSS-induced colitic mice model. The overall therapeutic factors, MSCs migration and targeting as well as local immunomodulatory cytokines and FoxP3⁺ cells infiltration were analyzed. Colitis showed varying degrees of alleviation after three ways of MSCs transplantation, and the IP injection showed the highest survival rate of 87.5% and displayed the less weight loss and quick weight gain. The fecal occult blood test on the day 3 also showed nearly complete absence of occult blood in IP group. The fluorescence imaging disclosed higher intensity of engrafted cells in inflamed colon and the corresponding mesentery lymph nodes (MLNs) in IP and AI groups than the IV group. Real time-PCR and ELISA also demonstrate lower TNF-α and higher IL-10, TSG-6 levels in IP group. The immunohistochemistry indicated higher repair proliferation (Ki-67) and more FoxP3⁺ cells accumulation of IP group. IP showed better colitis recovery and might be the optimum MSCs delivery route for the treatment of DSS-induced colitis.