Dynamic imaging of allogeneic mesenchymal stem cells trafficking to myocardial infarction

Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion

Mesenchymal stem cells (MSC) are under investigation as a therapy for a variety of disorders. Although animal models show long term regenerative and immunomodulatory effects of MSC, the fate of MSC after infusion remains to be elucidated. In the present study the localization and viability of MSC was examined by isolation and re-culture of intravenously infused MSC. C57BL/6 MSC (500,000) constitutively expressing DsRed-fluorescent protein and radioactively labeled with Cr-51 were infused via the tail vein in wild-type C57BL/6 mice. After 5 min, 1, 24, or 72 h, mice were sacrificed and blood, lungs, liver, spleen, kidneys, and bone marrow removed. One hour after MSC infusion the majority of Cr-51 was found in the lungs, whereas after 24 h Cr-51 was mainly found in the liver. Tissue cultures demonstrated that viable donor MSC were present in the lungs up to 24 h after infusion, after which they disappeared. No viable MSC were found in the other organs examined at any time. The induction of ischemia-reperfusion injury in the liver did not trigger the migration of viable MSC to the liver. These results demonstrate that MSC are short-lived after i.v. infusion and that viable MSC do not pass the lungs. Cell debris may be transported to the liver. Long term immunomodulatory and regenerative effects of infused MSC must therefore be mediated via other cell types.

Cell tracking and the development of cell-based therapies: a view from the Cardiovascular Cell Therapy Research Network

Cell-based therapies are being developed for myocardial infarction (MI) and its consequences (e.g., heart failure) as well as refractory angina and critical limb ischemia. The promising results obtained in preclinical studies led to the translation of this strategy to clinical studies. To date, the initial results have been mixed: some studies showed benefit, whereas in others, no benefit was observed. There is a growing consensus among the scientific community that a better understanding of the fate of transplanted cells (e.g., cell homing and viability over time) will be critical for the long-term success of these strategies and that future studies should include an assessment of cell homing, engraftment, and fate as an integral part of the trial design. In this review, different imaging methods and technologies are discussed within the framework of the physiological answers that the imaging strategies can provide, with a special focus on the inherent regulatory issues.

A novel suture-based method for efficient transplantation of stem cells

Advances in regenerative medicine have improved the potential of using cellular therapy for treating several diseases. However, the effectiveness of new cellular therapies is largely limited by low cell engraftment and inadequate localization. To improve on these limitations, we developed a novel delivery mechanism using cell-seeded biological sutures. We demonstrate the ability of cell-seeded biological sutures to efficiently implant human mesenchymal stem cells (hMSCs) to specific regions within the beating heart; a tissue known to have low cell retention and engraftment shortly after delivery. Cell-seeded biological sutures were developed by bundling discrete microthreads extruded from extracellular matrix proteins, attaching a surgical needle to the bundle and seeding the bundle with hMSCs. During cell preparation, hMSCs were loaded with quantum dot nanoparticles for cell tracking within the myocardium. Each biological suture contained an average of 5903 ± 1966 hMSCs/cm suture length. Delivery efficiency was evaluated by comparing cell-seeded biological suture implantation with intramyocardial (IM) cell injections (10,000 hMSCs in 35 μL) into the left ventricle of normal, noninfarcted rat hearts after 1 h. Delivery efficiency of hMSCs by biological sutures (63.6 ± 10.6%) was significantly higher than IM injection (11.8 ± 6.2%; p < 0.05). Cell-tracking analysis indicated suture-delivered hMSCs were found throughout the thickness of the ventricular myocardium: along the entire length of the biological suture track, localizing closely with native myocardium. These results suggest cell-seeded biological sutures can deliver cells to the heart more efficiently than conventional methods, demonstrating an effective delivery method for implanting cells in soft tissue.

Use of MR cell tracking to evaluate targeting of glial precursor cells to inflammatory tissue by exploiting the very late antigen-4 docking receptor

PURPOSE

To determine if glial precursor cells can be targeted to inflamed brain through overexpression of very late antigen-4 (VLA-4) and whether this docking process can be monitored with magnetic resonance (MR) cell tracking after intraarterial injection.

MATERIALS AND METHODS

All experimental procedures were performed between August 2010 and February 2012 and were approved by the institutional animal care and use committee. Human glial precursor cells (hGPs) were transfected with VLA-4 and labeled with superparamagnetic iron oxide that contained rhodamine. A microfluidic adhesion assay was used for assessing VLA-4 receptor-mediated cell docking in vitro. A rat model of global lipopolysaccharide (LPS)-mediated brain inflammation was used to induce global vascular cell adhesion molecule-1 (VCAM-1) expression. hGPs were infused into the carotid artery in four animal cohorts (consisting of three rats each): rats that received VLA-4-naive hGPs but did not receive LPS, rats that received VLA-4-expressing hGPs but not LPS, rats that received VLA-4-naive hGPs and LPS, and rats that received VLA-4-expressing hGPs and LPS. MR imaging was performed at 9.4 T before and 1, 10, 20, and 30 minutes after injection. Brain tissue was processed for histologic examination. Quantification of low-signal-intensity pixels was performed with pixel-by-pixel analysis for MR images obtained before and after cell injection.

RESULTS

With use of the microfluidic adhesion assay, cell binding to activated brain endothelium significantly increased compared with VLA-4-naive control cells (71.5 cells per field of view±11.7 vs 36.4 cells per field of view±3.3, respectively; P<.05). Real-time quantitative in vivo MR cell tracking revealed that VLA-4-expressing cells docked exclusively within the vascular bed of the ipsilateral carotid artery and that VLA-4-expressing cells exhibited significantly enhanced homing as compared with VLA-4-naive cells (1448 significant pixels±366.5 vs 113.3 significant pixels±19.88, respectively; P<.05). Furthermore, MR cell tracking was crucial for correct cell delivery and proper ligation of specific arteries.

CONCLUSION

Targeted intraarterial delivery and homing of VLA-4-expressing hGPs to inflamed endothelium is feasible and can be monitored in real time by using MR imaging in a quantitative, dynamic manner.

A novel strategy to enhance mesenchymal stem cell migration capacity and promote tissue repair in an injury specific fashion

Mesenchymal stem cells (MSCs) of bone marrow origin appear to be an attractive candidate for cell-based therapies. However, the major barrier to the effective implementation of MSC-based therapies is the lack of specific homing of exogenously infused cells and overall the inability to drive them to the diseased or damaged tissue. In order to circumvent these limitations, we developed a preconditioning strategy to optimize MSC migration efficiency and potentiate their beneficial effect at the site of injury. Initially, we screened different molecules by using an in vitro injury-migration setting, and subsequently, we evaluated the effectiveness of the different strategies in mice with acute kidney injury (AKI). Our results showed that preconditioning of MSCs with IGF-1 before infusion improved cell migration capacity and restored normal renal function after AKI. The present study demonstrates that promoting migration of MSCs could increase their therapeutic potential and indicates a new therapeutic paradigm for organ repair.

Mesenchymal Stem Cells Home to Sites of Injury and Inflammation

BACKGROUND

Mesenchymal stem cells (MSCs) have shown significant therapeutic potential in preclinical animal models of wound healing. However, the translation of MSC-based therapeutics to clinical practice has been delayed by questions including the mechanisms of MSC homing, engraftment, and ultimate function.

THE PROBLEM

Experimental models of MSC-based wound therapies often involve intravenous injection of cells followed by sacrifice of animals at various time points and detection of MSCs in wounds by histological methods. However, this methodology is limited by its sampling of only specific tissue at a single time point and provides no information about how exogenously transplanted MSCs home to the wound environment.

BASIC/CLINICAL SCIENCE ADVANCES

Most systemically injected MSCs initially become entrapped within the lungs before migrating out to the liver and spleen in the normal state. When an injury is present, after the initial lung entrapment, MSCs migrate in response to inflammatory mediators and home to sites of wounding.

CLINICAL CARE RELEVANCE

As MSC-based wound therapies continue to advance toward clinical trials, the availability of noninvasive methods to track cells after injection into patients affords the opportunity to monitor stem cell behavior post-transplantation.

CONCLUSION

MSCs have demonstrated great promise as an emerging therapeutic for wound management. However, further preclinical studies will be needed to elucidate the reparative mechanisms of these cells and to determine how to optimize their regenerative potential.

Stem cells as a tool for breast imaging

Stem cells are a scientific field of interest due to their therapeutic potential. There are different groups, depending on the differentiation state. We can find lonely stem cells, but generally they distribute in niches. Stem cells don't survive forever. They are affected for senescence. Cancer stem cells are best defined functionally, as a subpopulation of tumor cells that can enrich for tumorigenic property and can regenerate heterogeneity of the original tumor. Circulating tumor cells are cells that have detached from a primary tumor and circulate in the bloodstream. They may constitute seeds for subsequent growth of additional tumors (metastasis) in different tissues. Advances in molecular imaging have allowed a deeper understanding of the in vivo behavior of stem cells and have proven to be indispensable in preclinical and clinical studies. One of the first imaging modalities for monitoring pluripotent stem cells in vivo, magnetic resonance imaging (MRI) offers high spatial and temporal resolution to obtain detailed morphological and functional information. Advantages of radioscintigraphic techniques include their picomolar sensitivity, good tissue penetration, and translation to clinical applications. Radionuclide imaging is the sole direct labeling technique used thus far in human studies, involving both autologous bone marrow derived and peripheral stem cells.

The role of chemokines in mesenchymal stem cell homing to myocardium

A growing body of preclinical evidence suggests that mesenchymal stem cells (MSCs) are effective for the structural and functional recovery of the infracted heart. Accordingly, clinical trials are underway to determine the benefit of MSC-based therapies. While systemic administration of MSCs is an attractive strategy, and is the route currently used for the administration of MSCs in clinical studies for myocardial infarction, the majority of infused cells do not appear to localize to infracted myocardium in animal studies. Recently, important progress has been made in identifying chemokine receptors critical for the migration and homing of MSCs. Here, we review recent literature regarding mechanisms of MSC homing and recruitment to the ischemic myocardium, and discuss potential influences of low engraftment rates of systemically administered MSCs to the infracted heart tissue on the effects of MSC-based therapies on myocardial infarction.

Journey of mesenchymal stem cells for homing: strategies to enhance efficacy and safety of stem cell therapy

Human mesenchymal stem cells (MSCs) communicate with other cells in the human body and appear to "home" to areas of injury in response to signals of cellular damage, known as homing signals. This review of the state of current research on homing of MSCs suggests that favorable cellular conditions and the in vivo environment facilitate and are required for the migration of MSCs to the site of insult or injury in vivo. We review the current understanding of MSC migration and discuss strategies for enhancing both the environmental and cellular conditions that give rise to effective homing of MSCs. This may allow MSCs to quickly find and migrate to injured tissues, where they may best exert clinical benefits resulting from improved homing and the presence of increased numbers of MSCs.

Cell delivery routes for stem cell therapy to the heart: current and future approaches

An important factor to determine the success of stem cell therapy to the heart is the choice of cell delivery route. This will affect the fate of donor cells and subsequently influence the outcome of treatment; however, there is currently no optimum cell delivery route appropriate for every disease condition or every donor cell type. This review summarises currently available approaches for administering cells to the heart, with a particular focus on cell retention/survival and the therapeutic benefits seen in preclinical and clinical studies. Two major approaches are intracoronary and intramyocardial injection, which have been widely used for the delivery of various types of cells. Although there are advantages to both approaches, donor cell retention and survival are poor using these methods, potentially limiting therapeutic effects. Various attempts to improve current approaches, along with the development of emerging new approaches, are also described and discussed in this review.

Nonclinical safety strategies for stem cell therapies

Recent breakthroughs in stem cell biology, especially the development of the induced pluripotent stem cell techniques, have generated tremendous enthusiasm and efforts to explore the therapeutic potential of stem cells in regenerative medicine. Stem cell therapies are being considered for the treatment of degenerative diseases, inflammatory conditions, cancer and repair of damaged tissue. The safety of a stem cell therapy depends on many factors including the type of cell therapy, the differentiation status and proliferation capacity of the cells, the route of administration, the intended clinical location, long term survival of the product and/or engraftment, the need for repeated administration, the disease to be treated and the age of the population. Understanding the product profile of the intended therapy is crucial to the development of the nonclinical safety study design.

On the interactions between mesenchymal stem cells and regulatory T cells for immunomodulation in transplantation

Experimental studies have established the use of mesenchymal stem cells (MSC) as a candidate immunosuppressive therapy. MSC exert their immunomodulatory function through the inhibition of CD4⁺ and CD8⁺ T cell proliferation. It is unknown whether MSC impair the immunosuppressive function of regulatory T cells (Treg). In vitro and in vivo studies suggest that MSC mediate their immunomodulatory effects through the induction of Treg. In this review we will focus on the interactions between MSC and Treg, and evaluate the consequences of these cellular interplays for prospective MSC immunotherapy in organ transplantation.

Role of molecular imaging in stem cell therapy for myocardial restoration

During the past two decades, stem cells have created enthusiasm as a regenerative therapy for ischemic heart disease. Transplantation of bone marrow stem cells, skeletal myoblasts, and endothelial progenitor cells has shown to improve myocardial function after infarction. Recently, attention has focused on the potential use of embryonic stem cells and induced pluripotent stem cells because they possess the capacity to differentiate into various cell types, including cardiac and endothelial cells. Clinical trials have shown positive effects on the functional recovery of heart after myocardial infarction and have answered questions on timing, dosage, and cell delivery route of stem cells such as those derived from bone marrow. Despite the current advances in stem cell research, one main hurdle remains the lack of reliable information about the fate of cell engraftment, survival, and proliferation after transplantation. This review discusses the different cell types used in cardiac cell therapy as well as molecular imaging modalities relevant to survival issues.

Towards whole-body imaging at the single cell level using ultra-sensitive stem cell labeling with oligo-arginine modified upconversion nanoparticles

Mesenchymal stem cells (MSCs) have shown great potential in regenerative medicine. Sensitive and reliable methods for stem cell labeling and in vivo tracking are thus of great importance. Herein, we report the use of upconversion nanoparticles (UCNPs) as an exogenous contrast agent to track mouse MSCs (mMSCs) in vivo. To improve the labeling efficiency, oligo-arginine is conjugated to polyethylene glycol (PEG) coated UCNPs to enhance the nanoparticles uptake by mMSCs. Systematic in vitro tests reveal that the proliferation and differentiation of mMSCs are not notably affected by UCNP-labeling, suggesting that the labeled cells are able to maintain their stem cell potency. No apparent exocytosis is found in our in vitro labeling experiment by using a transwell culture system over a course of 10 days, indicating the potential capability of using our UCNP-labeling method for long-term stem cell tracking. To demonstrate the tracking sensitivity of our stem cell labeling approach, UCNP-labeled mMSCs are subcutaneously transplanted into mice and imaged using an in vivo upconversion luminescence (UCL) imaging system. As few as ~10 cells labeled with UCNPs are detected in vivo, evidencing a remarkable improvement in detection sensitivity of our UCNP-labeled hMSCs compared with other stem cell labeling techniques using conventional exogenous agents. We further track UCNP-labeled mMSCs after intravenous injection, and observe the translocation of mMSCs from lung where they initially accumulate, to liver, a phenomenon consistent to previous reports. Our results highlight the promise of using UCNPs as a new type of ultra-sensitive probes for labeling and in vivo tracking of stem cells at nearly the single cell level.

Magnetic resonance imaging and fluorescence labeling of clinical-grade mesenchymal stem cells without impacting their phenotype: study in a rat model of stroke

Human mesenchymal stem cells (hMSCs) have strong potential for cell therapy after stroke. Tracking stem cells in vivo following a graft can provide insight into many issues regarding optimal route and/or dosing. hMSCs were labeled for magnetic resonance imaging (MRI) and histology with micrometer-sized superparamagnetic iron oxides (M-SPIOs) that contained a fluorophore. We assessed whether M-SPIO labeling obtained without the use of a transfection agent induced any cell damage in clinical-grade hMSCs and whether it may be useful for in vivo MRI studies after stroke. M-SPIOs provided efficient intracellular hMSC labeling and did not modify cell viability, phenotype, or in vitro differentiation capacity. Following grafting in a rat model of stroke, labeled hMSCs could be detected using both in vivo MRI and fluorescent microscopy until 4 weeks following transplantation. However, whereas good label stability and unaffected hMSC viability were observed in vitro, grafted hMSCs may die and release iron particles in vivo.

Molecular imaging of stem cells: tracking survival, biodistribution, tumorigenicity, and immunogenicity

Being able to self-renew and differentiate into virtually all cell types, both human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) have exciting therapeutic implications for myocardial infarction, neurodegenerative disease, diabetes, and other disorders involving irreversible cell loss. However, stem cell biology remains incompletely understood despite significant advances in the field. Inefficient stem cell differentiation, difficulty in verifying successful delivery to the target organ, and problems with engraftment all hamper the transition from laboratory animal studies to human clinical trials. Although traditional histopathological techniques have been the primary approach for ex vivo analysis of stem cell behavior, these postmortem examinations are unable to further elucidate the underlying mechanisms in real time and in vivo. Fortunately, the advent of molecular imaging has led to unprecedented progress in understanding the fundamental behavior of stem cells, including their survival, biodistribution, immunogenicity, and tumorigenicity in the targeted tissues of interest. This review summarizes various molecular imaging technologies and how they have advanced the current understanding of stem cell survival, biodistribution, immunogenicity, and tumorigenicity.

Impact of indium-111 oxine labelling on viability of human mesenchymal stem cells in vitro, and 3D cell-tracking using SPECT/CT in vivo

PURPOSE

This study investigates the effects of (111)In-oxine incorporation on human mesenchymal stem cells' (hMSC) biology and viability, and the applicability of (111)In-oxine for single-photon emission computed tomography/X-ray computed tomography (SPECT/CT) monitoring of hMSC in vivo.

PROCEDURES

HMSC were labelled with 10 Bq/cell. Cellular retention of radioactivity, cell survival, and migration were evaluated over 48 h. Metabolic activity was assessed over 14 days and the hMSC's stem cell character was evaluated. Serial SPECT/CT was performed after intra-osseous injection to athymic rats over 48 h.

RESULTS

Labelling efficiency was 25%, with 61% of incorporated (111)In remaining in the hMSC at 48 h. The radiolabelling was without effect on cell viability, stem cell character, and plasticity, whereas metabolic activity and migration were significantly reduced. Grafted cells could be imaged in situ with SPECT/CT.

CONCLUSIONS

(111)In-oxine labelling moderately impaired hMSC's functional integrity while preserving their stem cell character. Combined SPECT/CT imaging of (111)In-oxine-labelled hMSC opens the possibility for non-invasive sequential monitoring of therapeutic stem cells.

Mechanisms of dendritic cell trafficking across the blood-brain barrier

Although the central nervous system (CNS) is considered to be an immunoprivileged site, it is susceptible to a host of autoimmune as well as neuroinflammatory disorders owing to recruitment of immune cells across the blood-brain barrier into perivascular and parenchymal spaces. Dendritic cells (DCs), which are involved in both primary and secondary immune responses, are the most potent immune cells in terms of antigen uptake and processing as well as presentation to T cells. In light of the emerging importance of DC traficking into the CNS, these cells represent good candidates for targeted immunotherapy against various neuroinflammatory diseases. This review focuses on potential physiological events and receptor interactions between DCs and the microvascular endothelial cells of the brain as they transmigrate into the CNS during degeneration and injury. A clear understanding of the underlying mechanisms involved in DC migration may advance the development of new therapies that manipulate these mechanistic properties via pharmacologic intervention. Furthermore, therapeutic validation should be in concurrence with the molecular imaging techniques that can detect migration of these cells in vivo. Since the use of noninvasive methods to image migration of DCs into CNS has barely been explored, we highlighted potential molecular imaging techniques to achieve this goal. Overall, information provided will bring this important leukocyte population to the forefront as key players in the immune cascade in the light of the emerging contribution of DCs to CNS health and disease.

Value of MR contrast media in image-guided body interventions

In the past few years, there have been multiple advances in magnetic resonance (MR) instrumentation, in vivo devices, real-time imaging sequences and interventional procedures with new therapies. More recently, interventionists have started to use minimally invasive image-guided procedures and local therapies, which reduce the pain from conventional surgery and increase drug effectiveness, respectively. Local therapy also reduces the systemic dose and eliminates the toxic side effects of some drugs to other organs. The success of MR-guided procedures depends on visualization of the targets in 3D and precise deployment of ablation catheters, local therapies and devices. MR contrast media provide a wealth of tissue contrast and allows 3D and 4D image acquisitions. After the development of fast imaging sequences, the clinical applications of MR contrast media have been substantially expanded to include pre- during- and post-interventions. Prior to intervention, MR contrast media have the potential to localize and delineate pathologic tissues of vital organs, such as the brain, heart, breast, kidney, prostate, liver and uterus. They also offer other options such as labeling therapeutic agents or cells. During intervention, these agents have the capability to map blood vessels and enhance the contrast between the endovascular guidewire/catheters/devices, blood and tissues as well as direct therapies to the target. Furthermore, labeling therapeutic agents or cells aids in visualizing their delivery sites and tracking their tissue distribution. After intervention, MR contrast media have been used for assessing the efficacy of ablation and therapies. It should be noted that most image-guided procedures are under preclinical research and development. It can be concluded that MR contrast media have great value in preclinical and some clinical interventional procedures. Future applications of MR contrast media in image-guided procedures depend on their safety, tolerability, tissue specificity and effectiveness in demonstrating success of the interventions and therapies.

MR fluoroscopy in vascular and cardiac interventions (review)

Vascular and cardiac disease remains a leading cause of morbidity and mortality in developed and emerging countries. Vascular and cardiac interventions require extensive fluoroscopic guidance to navigate endovascular catheters. X-ray fluoroscopy is considered the current modality for real time imaging. It provides excellent spatial and temporal resolution, but is limited by exposure of patients and staff to ionizing radiation, poor soft tissue characterization and lack of quantitative physiologic information. MR fluoroscopy has been introduced with substantial progress during the last decade. Clinical and experimental studies performed under MR fluoroscopy have indicated the suitability of this modality for: delivery of ASD closure, aortic valves, and endovascular stents (aortic, carotid, iliac, renal arteries, inferior vena cava). It aids in performing ablation, creation of hepatic shunts and local delivery of therapies. Development of more MR compatible equipment and devices will widen the applications of MR-guided procedures. At post-intervention, MR imaging aids in assessing the efficacy of therapies, success of interventions. It also provides information on vascular flow and cardiac morphology, function, perfusion and viability. MR fluoroscopy has the potential to form the basis for minimally invasive image-guided surgeries that offer improved patient management and cost effectiveness.

Mesenchymal bone marrow cell therapy in a mouse model of chagas disease. Where do the cells go?

BACKGROUND

Chagas disease, resulting from infection with the parasite Trypanosoma cruzi (T. cruzi), is a major cause of cardiomyopathy in Latin America. Drug therapy for acute and chronic disease is limited. Stem cell therapy with bone marrow mesenchymal cells (MSCs) has emerged as a novel therapeutic option for cell death-related heart diseases, but efficacy of MSC has not been tested in Chagas disease.

METHODS AND RESULTS

We now report the use of cell-tracking strategies with nanoparticle labeled MSC to investigate migration of transplanted MSC in a murine model of Chagas disease, and correlate MSC biodistribution with glucose metabolism and morphology of heart in chagasic mice by small animal positron emission tomography (microPET). Mice were infected intraperitoneally with trypomastigotes of the Brazil strain of T. cruzi and treated by tail vein injection with MSC one month after infection. MSCs were labeled with near infrared fluorescent nanoparticles and tracked by an in vivo imaging system (IVIS). Our IVIS results two days after transplant revealed that a small, but significant, number of cells migrated to chagasic hearts when compared with control animals, whereas the vast majority of labeled MSC migrated to liver, lungs and spleen. Additionally, the microPET technique demonstrated that therapy with MSC reduced right ventricular dilation, a phenotype of the chagasic mouse model.

CONCLUSIONS

We conclude that the beneficial effects of MSC therapy in chagasic mice arise from an indirect action of the cells in the heart rather than a direct action due to incorporation of large numbers of transplanted MSC into working myocardium.

Potential clinical applications of adult human mesenchymal stem cell (Prochymal®) therapy

In vitro, in vivo animal, and human clinical data show a broad field of application for mesenchymal stem cells (MSCs). There is overwhelming evidence of the usefulness of MSCs in regenerative medicine, tissue engineering, and immune therapy. At present, there are a significant number of clinical trials exploring the use of MSCs for the treatment of various diseases, including myocardial infarction and stroke, in which oxygen suppression causes widespread cell death, and others with clear involvement of the immune system, such as graft-versus-host disease, Crohn’s disease, and diabetes. With no less impact, MSCs have been used as cell therapy to treat defects in bone and cartilage and to help in wound healing, or in combination with biomaterials in tissue engineering development. Among the MSCs, allogeneic MSCs have been associated with a regenerative capacity due to their unique immune modulatory properties. Their immunosuppressive capability without evidence of immunosuppressive toxicity at a global level define their application in the treatment of diseases with a pathogenesis involving uncontrolled activity of the immune system. Until now, the limitation in the number of totally characterized autologous MSCs available represents a major obstacle to their use for adult stem cell therapy. The use of premanufactured allogeneic MSCs from controlled donors under optimal conditions and their application in highly standardized clinical trials would lead to a better understanding of their real applications and reduce the time to clinical translation.

Imaging: guiding the clinical translation of cardiac stem cell therapy

Stem cells have been touted as the holy grail of medical therapy, with promises to regenerate cardiac tissue, but it appears the jury is still out on this novel therapy. Using advanced imaging technology, scientists have discovered that these cells do not survive nor engraft long-term. In addition, only marginal benefit has been observed in large-animal studies and human trials. However, all is not lost. Further application of advanced imaging technology will help scientists unravel the mysteries of stem cell therapy and address the clinical hurdles facing its routine implementation. In this review, we will discuss how advanced imaging technology will help investigators better define the optimal delivery method, improve survival and engraftment, and evaluate efficacy and safety. Insights gained from this review may direct the development of future preclinical investigations and clinical trials.

In vivo MRI tracking of cell invasion and migration in a rat glioma model

PURPOSE

Malignant brain tumors are characterized by extensive infiltration into the normal brain tissue. Tumor migration is a complicated process which results from the interplay of a number of mechanisms, and the extent to which anatomic structure determined the migration pattern has not been extensively addressed. In the present study, we labeled C6 glioma cells with iron oxide nanoparticles and monitored the fate of the cells in vivo with magnetic resonance imaging (MRI).

PROCEDURES

C6 glioma cells were labeled with ferumoxide-poly-L-lysine complexes and their migration in the brains of rats tracked by T2-weighted MRI. The same amount of iron-laden cells were implanted into the caudate nucleus (CN) and at the vicinity of anterior commissure (AC), respectively, and MRI was performed during the course of 20-day monitoring period to track tumor growth and migration.

RESULTS

A clear tendency of tumor migration along the white matter fiber tracts was observed in the AC group, which is consistent with the previous reports; by contrast, tumor expanded to but remained confined within the boundary of right hemisphere in the CN group.

CONCLUSION

We successfully demonstrated the ability of MRI to investigate the impact of anatomical structure on the glioma migration pathway in vivo.

Concise review: Mesenchymal stem cell tumor-homing: detection methods in disease model systems

Despite the decline in U.S. cancer incidence and mortality rates, cancer remains the number one cause of death for people under the age of 85 and one in four people in the U.S. will die of cancer, mainly because of metastasis. Recently, interest in mesenchymal stem cell (MSC) tumor-homing has led to inquires into: (a) why MSCs home to tumors, (b) what the inherent protumor and antitumor consequences are, and (c) how to best capitalize on MSC tumor-homing for cell-based diagnostics and therapy. Here, these questions are reviewed and method for addressing them using animal models and tracking methodologies (or, synonymously, detection methodologies) are discussed. First, MSCs in a regenerative and tumor-homing context are reviewed, followed by MSC delivery and genetic labeling methods for tissue model systems. Finally, the use of the nonoptical methods, magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography, along with optical methods, fluorescence imaging and bioluminescent imaging, are reviewed related to tracking MSCs within disease model settings. The benefits and drawbacks of each detection method in animal models is reviewed along with the utility of each for therapeutic use.

Tracking stem cells for cardiovascular applications in vivo: focus on imaging techniques

Despite rapid translation of stem cell therapy into clinical practice, the treatment of cardiovascular disease using embryonic stem cells, adult stem and progenitor cells or induced pluripotent stem cells has not yielded satisfactory results to date. Noninvasive stem cell imaging techniques could provide greater insight into not only the therapeutic benefit, but also the fundamental mechanisms underlying stem cell fate, migration, survival and engraftment in vivo. This information could also assist in the appropriate choice of stem cell type(s), delivery routes and dosing regimes in clinical cardiovascular stem cell trials. Multiple imaging modalities, such as MRI, PET, SPECT and CT, have emerged, offering the ability to localize, monitor and track stem cells in vivo. This article discusses stem cell labeling approaches and highlights the latest cardiac stem cell imaging techniques that may help clinicians, research scientists or other healthcare professionals select the best cellular therapeutics for cardiovascular disease management.

Targeted probes for cardiovascular MRI

Molecular MRI plays an important role in studying molecular and cellular processes associated with heart disease. Targeted probes that recognize important biomarkers of atherosclerosis, apoptosis, necrosis, angiogenesis, thrombosis and inflammation have been developed. This review discusses the properties of chemically different contrast agents including iron oxide nanoparticles, gadolinium-based nanoparticles or micelles, discrete peptide conjugates and activatable probes. Numerous examples of contrast agents based on these approaches have been used in preclinical MRI of cardiovascular diseases. Clinical applications are still under investigation for some selected agents with highly promising initial results. Molecular MRI shows great potential for the detection and characterization of a wide range of cardiovascular diseases, as well as for monitoring response to therapy.

In vivo tracking of 111In-oxine labeled mesenchymal stem cells following infusion in patients with advanced cirrhosis

BACKGROUND

Several animal and few human studies suggest the beneficial role of bone marrow mesenchymal stem cells (MSCs) in liver cirrhosis. However, little is known about the fate of MSCs after infusion in cirrhotic patients. We evaluated stem cell biodistribution after peripheral infusion of MSCs in four cirrhotic patients.

METHODS

After three passages of MSCs, the patients received a total of 250-400×10(6) cells, of which only 50% of the cells were labeled. Specific activities of 0.21-0.67 MBq/10(6) cells were maintained for the injected labeled MSCs. Planar whole-body acquisitions (anterior/posterior projections) were acquired immediately following infusion as well as at 2 h, 4 h, 6 h, 24 h, 48 h, 7th and 10th days after cell infusion.

RESULTS

After intravenous infusion, the radioactivity was first observed to accumulate in the lungs. During the following hours to days, the radioactivity gradually increased in the liver and spleen, with spleen uptake exceeding that in the liver in all patients. Region-of-interest analysis showed that the percentage of cells homing to the liver (following decay and background corrections and geometric mean calculation) increased from 0.0%-2.8% at immediately post-infusion images to 13.0-17.4% in 10th-day post-infusion. Similarly, the residual activities in the spleen increased from 2.0%-10.2% at immediately post-infusion images to 30.1%-42.2% in 10th-day post-infusion. During the same period, the residual activities in the lungs decreased from 27.0-33.5% to 2.0-5.4%.

CONCLUSION

The infusion of MSCs labeled with (111)In-oxine through a peripheral vein is safe in cirrhosis. Cell labeling with (111)In-oxine is a suitable method for tracking MSC distribution after infusion.

Polyamidoamine dendrimer-conjugated quantum dots for efficient labeling of primary cultured mesenchymal stem cells

Monitoring of cells in vivo after transplantation could supply important information for determining the efficacy of stem cell therapy. The use of quantum dots (QDs) has several advantages for in vivo imaging, such as remarkable resistance to photo bleaching, high fluorescence efficiency, and size-tunable emission. After they are taken up by cells via endocytosis, QDs lose their fluorescence intensity in endosomes/lysosomes at low pH because the intensity cannot survive under acidic conditions. Moreover, the amount of QD uptake by mesenchymal stem cells (MSCs) is extremely small. Therefore, for effective labeling of MSCs and long observation of MSCs labeled by QDs in vivo, it is essential both to increase cellular uptake of QDs and to promote endosomal escape into the cytosol. The polyamidoamine (PAMAM) dendrimer had plenty of cationic charge, which promoted cellular uptake though electrostatic interactions, and a "buffering capacity," which enhanced endosomal escape into the cytosol. In this study, QDs were modified with PAMAM dendrimer for the efficient labeling of MSCs by QDs. The uptake efficiency and cytosolic distribution of QDs in primary cultured MSCs were increased by the modification of the PAMAM dendrimer. The fluorescence intensity in MSCs labeled by PAMAM dendrimer-conjugated QDs lasted for a longer time in harvested culture plates or in cell-transplanted mice than that in MSCs labeled by non-conjugated QDs.

In vivo imaging and monitoring of transplanted stem cells: clinical applications

Regenerative medicine using stem cells has appeared as a potential therapeutic alternative for coronary artery disease, and stem cell clinical studies are currently on their way. However, initial results of these studies have provided mixed information, in part because of the inability to correlate organ functional information with the presence/absence of transplanted stem cells. Recent advances in molecular biology and imaging have allowed the successful noninvasive monitoring of transplanted stem cells in the living subject. In this article, different imaging strategies (direct labeling, indirect labeling with reporter genes) to study the viability and biology of stem cells are discussed. In addition, the limitations of each approach and imaging modality (eg, single photon emission computed tomography, positron emission tomography, and MRI) and their requirements for clinical use are addressed. Use of these strategies will be critical as the different regenerative therapies are being tested for clinical use.

In vivo biodistribution of stem cells using molecular nuclear medicine imaging

Studies on stem cell are rapidly developing since these cells have great therapeutic potential for numerous diseases and has generated much promise as well as confusion due to contradictory results. Major questions in this research field have been raised as to how and in which numbers stem cells home to target tissues after administration, whether the cells engraft and differentiate, and what their long-term fate is. To answer these questions, reliable in vivo tracking techniques are essential. In vivo molecular imaging techniques using magnetic resonance imaging, bioluminescence, and scintigraphy have been applied for this purpose in experimental studies. The aim of this review is to discuss various radiolabeling techniques for early stem cell tracking, the need for validation of viability and performance of the cells after labeling, and the routes of administration in experimental animal models. In addition, we evaluate current problems and directions related to stem cell tracking using radiolabels, including a possible role for their clinical implementation.

Intra-arterial injection of neural stem cells using a microneedle technique does not cause microembolic strokes

Intra-arterial (IA) injection represents an experimental avenue for minimally invasive delivery of stem cells to the injured brain. It has however been reported that IA injection of stem cells carries the risk of reduction in cerebral blood flow (CBF) and microstrokes. Here we evaluate the safety of IA neural progenitor cell (NPC) delivery to the brain. Cerebral blood flow of rats was monitored during IA injection of single cell suspensions of NPCs after stroke. Animals received 1 × 10(6) NPCs either injected via a microneedle (microneedle group) into the patent common carotid artery (CCA) or via a catheter into the proximally ligated CCA (catheter group). Controls included saline-only injections and cell injections into non-stroked sham animals. Cerebral blood flow in the microneedle group remained at baseline, whereas in the catheter group a persistent (15 minutes) decrease to 78% of baseline occurred (P<0.001). In non-stroked controls, NPCs injected via the catheter method resulted in higher levels of Iba-1-positive inflammatory cells (P=0.003), higher numbers of degenerating neurons as seen in Fluoro-Jade C staining (P<0.0001) and ischemic changes on diffusion weighted imaging. With an appropriate technique, reduction in CBF and microstrokes do not occur with IA transplantation of NPCs.

Quantitative T2* imaging of metastatic human breast cancer to brain in the nude rat at 3 T

This study uses quantitative T(2)* imaging to track ferumoxides--protamine sulfate (FEPro)-labeled MDA-MB-231BR-Luc (231BRL) human breast cancer cells that metastasize to the nude rat brain. Four cohorts of nude rats were injected intracardially with FEPro-labeled, unlabeled or tumor necrosis factor-related apoptosis-inducing ligand(TRAIL)-treated (to induce apoptosis) 231BRL cells, or saline, in order to develop metastatic breast cancer in the brain. The heads of the rats were imaged serially over 3-4 weeks using gradient multi-echo and turbo spin-echo pulse sequences at 3 T with a solenoid receive-only 4-cm-diameter coil. Quantitative T(2)* maps of the whole brain were obtained by the application of single-exponential fitting to the signal intensity of T(2)* images, and the distribution of T(2)* values in brain voxels was calculated. MRI findings were correlated with Prussian blue staining and immunohistochemical staining for iron in breast cancer and macrophages. Quantitative analysis of T(2)* from brain voxels demonstrated a significant shift to lower values following the intracardiac injection of FEPro-labeled 231BRL cells, relative to animals receiving unlabeled cells, apoptotic cells or saline. Quartile analysis based on the T(2)* distribution obtained from brain voxels demonstrated significant differences (p < 0.0083) in the number of voxels with T(2)* values in the ranges 10-35  ms (Q1), 36-60  ms (Q2) and 61-86  ms (Q3) from 1 day to 3 weeks post-infusion of labeled 231BRL cells, compared with baseline scans. There were no significant differences in the distribution of T(2)* obtained from serial MRI in rats receiving unlabeled or TRAIL-treated cells or saline. Histologic analysis demonstrated isolated Prussian blue-positive breast cancer cells scattered in the brains of rats receiving labeled cells, relative to animals receiving unlabeled or apoptotic cells. Quantitative T(2)* analysis of FEPro-labeled metastasized cancer cells was possible even after the hypointense voxels were no longer visible on T(2)*-weighted images.

Design and characterization of a polymeric MRI contrast agent based on PVA for in vivo living-cell tracking

A novel water-soluble MRI contrast agent for in vivo living cell tracking was developed. Unlike the conventional in vivo cell tracking system based on superparamagnetic iron oxide beads, the newly developed contrast agent is eliminated from the body when the contrast agent exits the cells upon cell death, which makes living cell tracking possible. The contrast agent is composed of gadolinium chelates (Gd-DOTA) and a water-soluble carrier, poly(vinyl alcohol) (PVA), which is known to interact with cells and tissues very weakly. Since the Gd-PVA was not taken up by cells spontaneously, the electroporation method was used for cell labeling. The delivered Gd-PVA was localized only in the cytosolic compartment of growing cells with low cytotoxicity and did not leak out of the living cells for long periods of time. This stability may be due to the weak cell-membrane affinity of Gd-PVA, and did not affect cell proliferation at all. After cell labeling, signal enhancement of cells was observed in vitro and in vivo. These results indicate that Gd-PVA can visualize only the living cells in vivo for a long period of time, even in areas deep within large animal bodies.

Fibrin microthreads support mesenchymal stem cell growth while maintaining differentiation potential

We developed a method to produce discrete fibrin microthreads, which can be seeded with human mesenchymal stem cells (hMSCs) and used as a suture to enhance the efficiency and localization of cell delivery. To assess the efficacy of fibrin microthreads to support hMSC attachment, proliferation, and survival, microthreads (100 μm diameter per microthread) were bundled together, seeded with 50,000 hMSCs for 2 h, and cultured for 5 days. Cell density on microthread bundles increased over time in culture to a maximum average density of 731 ± 101 cells/mm(2) after 5 days. A LIVE/DEAD assay confirmed that the cells were viable, and Ki-67 staining verified hMSC proliferation. In addition, functional differentiation assays demonstrated that hMSCs cultured on microthreads retained their ability to differentiate into adipocytes and osteocytes. The results of this study demonstrate that fibrin microthreads support hMSC viability and proliferation, while maintaining their multipotency. We anticipate that these cell-seeded fibrin microthreads will serve as a platform technology to improve localized delivery and engraftment of viable cells to damaged tissue.

Homing pathways of mesenchymal stromal cells (MSCs) and their role in clinical applications

Mesenchymal stromal cells (MSCs) have come into focus for an increasing number of cellular therapies. Since most clinical protocols use intravenous application of MSCs, it has become important to understand their trafficking in the bloodstream. Moreover, since relatively little is known where the transplanted MSCs might locate, a better understanding of involved homing mechanisms will likely shed light on how MSCs exert their therapeutic effects. This review focuses on the current knowledge of homing pathways of transplanted MSCs. We describe regulatory signalling molecules and receptors involved. An outlook is given on significance of these findings for the future use of MSCs as a cellular therapeutic.

Therapeutic efficacy of intranasally delivered mesenchymal stem cells in a rat model of Parkinson disease

Safe and effective cell delivery remains one of the main challenges in cell-based therapy of neurodegenerative disorders. Graft survival, sufficient enrichment of therapeutic cells in the brain, and avoidance of their distribution throughout the peripheral organs are greatly influenced by the method of delivery. Here we demonstrate for the first time noninvasive intranasal (IN) delivery of mesenchymal stem cells (MSCs) to the brains of unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats. IN application (INA) of MSCs resulted in the appearance of cells in the olfactory bulb, cortex, hippocampus, striatum, cerebellum, brainstem, and spinal cord. Out of 1 × 10⁶ MSCs applied intranasally, 24% survived for at least 4.5 months in the brains of 6-OHDA rats as assessed by quantification of enhanced green fluorescent protein (EGFP) DNA. Quantification of proliferating cell nuclear antigen-positive EGFP-MSCs showed that 3% of applied MSCs were proliferative 4.5 months after application. INA of MSCs increased the tyrosine hydroxylase level in the lesioned ipsilateral striatum and substantia nigra, and completely eliminated the 6-OHDA-induced increase in terminal deoxynucleotidyl transferase (TdT)-mediated 2'-deoxyuridine, 5'-triphosphate (dUTP)-biotin nick end labeling (TUNEL) staining of these areas. INA of EGFP-labeled MSCs prevented any decrease in the dopamine level in the lesioned hemisphere, whereas the lesioned side of the control animals revealed significantly lower levels of dopamine 4.5 months after 6-OHDA treatment. Behavioral analyses revealed significant and substantial improvement of motor function of the Parkinsonian forepaw to up to 68% of the normal value 40-110 days after INA of 1 × 10⁶ cells. MSC-INA decreased the concentrations of inflammatory cytokines-interleukin-1β (IL-1β), IL-2, -6, -12, tumor necrosis factor (TNF), interferon-γ (IFN-γ, and granulocyte-macrophage colony-stimulating factor (GM-CSF)-in the lesioned side to their levels in the intact hemisphere. IN administration provides a highly promising noninvasive alternative to the traumatic surgical procedure of transplantation and allows targeted delivery of cells to the brain with the option of chronic application.