Clinical Tracking of Cell Transfer and Cell Transplantation: Trials and Tribulations

A review on recent advances in polymeric microneedle loading cells: Design strategies, fabrication technologies, transdermal application and challenges

Microneedle systems (MNs) loading living cells are a powerful platform to treat various previously incurable diseases in the era of precision medicine. Herein, an overview of recent advances in MN-based strategies for cell delivery is summarized, including material selection, design of morphological structures, and processing methods. We also systematically outlined the law of microstructural design relative to the structure-effective/function relationship in transdermal delivery or precision medicine and the design principles of cell microneedle (CMN). Furthermore, the representative works of precision treatments focusing on inflammatory skin diseases were tracked and discussed using CMN. Indeed, it highlights a practical path to solving the dilemma of cell therapy and raising the hope of precision medicine. However, there are still some challenges in developing CMN since they need multi-dimensional comprehensive properties, including mechanical properties, cell viability preservation, release, therapeutic effect, etc. The manuscript could provide insights into developing an innovative fit-to-purpose vehicle in cell therapy for interested researchers.

A perspective from the National Eye Institute Extracellular Vesicle Workshop: Gaps, needs, and opportunities for studies of extracellular vesicles in vision research

With an evolving understanding and new discoveries in extracellular vesicle (EV) biology and their implications in health and disease, the significant diagnostic and therapeutic potential of EVs for vision research has gained recognition. In 2021, the National Eye Institute (NEI) unveiled its Strategic Plan titled 'Vision for the Future (2021-2025),' which listed EV research as a priority within the domain of Regenerative Medicine, a pivotal area outlined in the Plan. In alignment with this prioritization, NEI organized a workshop inviting twenty experts from within and beyond the visual system. The workshop aimed to review current knowledge in EV research and explore gaps, needs and opportunities for EV research in the eye, including EV biology and applications of EVs in diagnosis, therapy and prognosis within the visual system. This perspective encapsulates the workshop's deliberations, highlighting the current landscape and potential implications of EV research in advancing eye health and addressing visual diseases.

A Comparison of the Sensitivity and Cellular Detection Capabilities of Magnetic Particle Imaging and Bioluminescence Imaging

BACKGROUND

Preclinical cell tracking is enhanced with a multimodal imaging approach. Bioluminescence imaging (BLI) is a highly sensitive optical modality that relies on engineering cells to constitutively express a luciferase gene. Magnetic particle imaging (MPI) is a newer imaging modality that directly detects superparamagnetic iron oxide (SPIO) particles used to label cells. Here, we compare BLI and MPI for imaging cells in vitro and in vivo.

METHODS

Mouse 4T1 breast carcinoma cells were transduced to express firefly luciferase, labeled with SPIO (ProMag), and imaged as cell samples after subcutaneous injection into mice.

RESULTS

For cell samples, the BLI and MPI signals were strongly correlated with cell number. Both modalities presented limitations for imaging cells in vivo. For BLI, weak signal penetration, signal attenuation, and scattering prevented the detection of cells for mice with hair and for cells far from the tissue surface. For MPI, background signals obscured the detection of low cell numbers due to the limited dynamic range, and cell numbers could not be accurately quantified from in vivo images.

CONCLUSIONS

It is important to understand the shortcomings of these imaging modalities to develop strategies to improve cellular detection sensitivity.

Roadmap on magnetic nanoparticles in nanomedicine

Magnetic nanoparticles (MNPs) represent a class of small particles typically with diameters ranging from 1 to 100 nanometers. These nanoparticles are composed of magnetic materials such as iron, cobalt, nickel, or their alloys. The nanoscale size of MNPs gives them unique physicochemical (physical and chemical) properties not found in their bulk counterparts. Their versatile nature and unique magnetic behavior make them valuable in a wide range of scientific, medical, and technological fields. Over the past decade, there has been a significant surge in MNP-based applications spanning biomedical uses, environmental remediation, data storage, energy storage, and catalysis. Given their magnetic nature and small size, MNPs can be manipulated and guided using external magnetic fields. This characteristic is harnessed in biomedical applications, where these nanoparticles can be directed to specific targets in the body for imaging, drug delivery, or hyperthermia treatment. Herein, this roadmap offers an overview of the current status, challenges, and advancements in various facets of MNPs. It covers magnetic properties, synthesis, functionalization, characterization, and biomedical applications such as sample enrichment, bioassays, imaging, hyperthermia, neuromodulation, tissue engineering, and drug/gene delivery. However, as MNPs are increasingly explored forin vivoapplications, concerns have emerged regarding their cytotoxicity, cellular uptake, and degradation, prompting attention from both researchers and clinicians. This roadmap aims to provide a comprehensive perspective on the evolving landscape of MNP research.

Cell therapy for neurological disorders

Cell therapies for neurological disorders are entering the clinic and present unique challenges and opportunities compared with conventional medicines. They have the potential to replace damaged nervous tissue and integrate into the brain or spinal cord to produce functional effects for the lifetime of the patient, which could revolutionize the way clinicians treat debilitating neurological disorders. The major challenge has been cell sourcing, which historically relied mainly on fetal brain tissue. This has largely been overcome with the advent of pluripotent stem cell technology and the ability to make almost any cell of the nervous system at scale. Furthermore, advances in gene editing now allow the generation of genetically modified cells that could perform better and evade the immune system. With all the remarkable new approaches to treat neurological disorders, we take a critical look at the state of current clinical trials and how challenges may be overcome with the evolving technology and innovation occurring in the stem cell field.

Cationic fluorinated micelles for cell labeling and 19F-MR imaging

Magnetic resonance imaging (MRI) relies on appropriate contrast agents, especially for visualizing transplanted cells within host tissue. In recent years, compounds containing fluorine-19 have gained significant attention as MRI probe, particularly in dual 1H/19F-MR imaging. However, various factors affecting probe sensitivity, such as fluorine content and the equivalency of fluorine atoms, must be considered. In this study, we synthesized fluorinated micelles with adjustable surface positive charge density and investigated their physicochemical properties and MRI efficacy in phantoms and labeled cells. While the micelles exhibited clear signals in 19F-MR spectra and imaging, the concentrations required for MRI visualization of labeled cells were relatively high, adversely affecting cell viability. Despite their favourable physicochemical properties, achieving higher labeling rates without compromising cell viability during labeling remains a challenge for potential in vivo applications.

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.

Application of Mesenchymal Stem Cells in Female Infertility Treatment: Protocols and Preliminary Results

Infertility is a global phenomenon that impacts people of both the male and the female sex; it is related to multiple factors affecting an individual's overall systemic health. Recently, investigators have been using mesenchymal stem cell (MSC) therapy for female-fertility-related disorders such as polycystic ovarian syndrome (PCOS), premature ovarian failure (POF), endometriosis, preeclampsia, and Asherman syndrome (AS). Studies have shown promising results, indicating that MSCs can enhance ovarian function and restore fertility for affected individuals. Due to their regenerative effects and their participation in several paracrine pathways, MSCs can improve the fertility outcome. However, their beneficial effects are dependent on the methodologies and materials used from isolation to reimplantation. In this review, we provide an overview of the protocols and methods used in applications of MSCs. Moreover, we summarize the findings of published preclinical studies on infertility treatments and discuss the multiple properties of these studies, depending on the isolation source of the MSCs used.

Comparison between USPIOs and SPIOs for Multimodal Imaging of Extracellular Vesicles Extracted from Adipose Tissue-Derived Adult Stem Cells

Adipose tissue-derived adult stem (ADAS) cells and extracellular vesicle (EV) therapy offer promising avenues for treating neurodegenerative diseases due to their accessibility and potential for autologous cell transplantation. However, the clinical application of ADAS cells or EVs is limited by the challenge of precisely identifying them in specific regions of interest. This study compares two superparamagnetic iron oxide nanoparticles, differing mainly in size, to determine their efficacy for allowing non-invasive ADAS tracking via MRI/MPI and indirect labeling of EVs. We compared a USPIO (about 5 nm) with an SPIO (Resovist®, about 70 nm). A physicochemical characterization of nanoparticles was conducted using DLS, TEM, MRI, and MPI. ADAS cells were labeled with the two nanoparticles, and their viability was assessed via MTT assay. MRI detected labeled cells, while TEM and Prussian Blue staining were employed to confirm cell uptake. The results revealed that Resovist® exhibited higher transversal relaxivity value than USPIO and, consequently, allows for detection with higher sensitivity by MRI. A 200 µgFe/mL concentration was identified as optimal for ADAS labeling. MPI detected only Resovist®. The findings suggest that Resovist® may offer enhanced detection of ADAS cells and EVs, making it suitable for multimodal imaging. Preliminary results obtained by extracting EVs from ADAS cells labeled with Resovist® indicate that EVs retain the nanoparticles, paving the way to an efficient and multimodal detection of EVs.

Application of cell transplantation in the treatment of neuropathic pain

Nerve injury can not only lead to sensory and motor dysfunction, but also be complicated with neuropathic pain (NPP), which brings great psychosomatic injury to patients. At present, there is no effective treatment for NPP. Based on the functional characteristics of cell transplantation in nerve regeneration and injury repair, cell therapy has been used in the exploratory treatment of NPP and has become a promising treatment of NPP. In this article, we discuss the current mainstream cell types for the treatment of NPP, including Schwann cells, olfactory ensheathing cells, neural stem cells and mesenchymal stem cells in the treatment of NPP. These bioactive cells transplanted into the host have pharmacological properties of decreasing pain threshold and relieving NPP by exerting nutritional support, neuroprotection, immune regulation, promoting axonal regeneration, and remyelination. Cell transplantation can also change the microenvironment around the nerve injury, which is conducive to the survival of neurons. It can effectively relieve pain by repairing the injured nerve and rebuilding the nerve function. At present, some preclinical and clinical studies have shown that some encouraging results have been achieved in NPP treatment based on cell transplantation. Therefore, we discussed the feasible strategy of cell transplantation as a treatment of NPP and the problems and challenges that need to be solved in the current application of cell transplantation in NPP therapy.

Safety and Biodistribution of an Autologous Bone Marrow-Derived Mononuclear Cell Infusion into Renal Arteries in Patients with Focal Segmental Glomerulosclerosis: A Phase 1 Study

Patients with focal segmental glomerulosclerosis (FSGS) who are refractory to drug treatment may present progressive loss of kidney function, leading to chronic kidney disease stage 5 under dialysis treatment. The safety of systemic administration of bone marrow-derived mononuclear cells (BMDMCs) has been shown in different preclinical models of kidney diseases. However, to date, no study has evaluated the safety and biodistribution of BMDMCs after infusion in renal arteries in patients with FSGS. We used a prospective, non-randomized, single-center longitudinal design to investigate this approach. Five patients with refractory FSGS and an estimated glomerular filtration rate (eGFR) between 20 and 40 ml/min/1.73 m2 underwent bone marrow aspiration and received an arterial infusion of autologous BMDMCs (5 × 107) for each kidney. In addition, BMDMCs labeled with technetium-99m (99mTc-BMDMCs) were used to assess the biodistribution by scintigraphy. All patients completed the 270-day follow-up protocol with no serious adverse events. A transient increase in creatinine was observed after the cell therapy, with improvement on day 30. 99mTc-BMDMCs were detected in both kidneys and counts were higher after 2 hr compared with 24 hr. The arterial infusion of BMDMCs in both kidneys of patients with FSGS was considered safe with stable eGFR at the end of follow-up. This trial is registered with NCT02693366.

Economic and Accessible Portable Homemade Magnetic Hyperthermia System: Influence of the Shape, Characteristics and Type of Nanoparticles in Its Effectiveness

Currently, one of the main causes of death in the world is cancer; therefore, it is urgent to obtain a precocious diagnosis, as well as boost research and development of new potential treatments, which should be more efficient and much less invasive for the patient. Magnetic hyperthermia (MH) is an emerging cancer therapy using nanoparticles, which has proved to be effective when combined with chemotherapy, radiotherapy and/or surgery, or even by itself, depending on the type and location of the tumor's cells. This article presents the results obtained by using a previously developed economic homemade hyperthermia device with different types of magnetite nanoparticles, with sizes ranging between 12 ± 5 and 36 ± 11 nm and presenting different shapes (spherical and cubic particles). These magnetic nanoparticles (MNPs) were synthesized by three different methods (co-precipitation, solvothermal and hydrothermal processes), with their final form being naked, or possessing different kinds of covering layers (polyethylene glycol (PEG) or citric acid (CA)). The parameters used to characterize the heating by magnetic hyperthermia, namely the Specific Absorption Rate (SAR) and the intrinsic loss power (ILP), have been obtained by two different methods. Among other results, these experiments allowed for the determination of which synthesized MNPs showed the best performance concerning hyperthermia. From the results, it may be concluded that, as expected, the shape of MNPs is an important factor, as well as the time that the MNPs can remain suspended in solution (which is directly related to the concentration and covering layer of the MNPs). The MNPs that gave the best results in terms of the SAR were the cubic particles covered with PEG, while in terms of total heating the spherical particles covered with citric acid proved to be better.

Use of Magnetotactic Bacteria as an MRI Contrast Agent for In Vivo Tracking of Adoptively Transferred Immune Cells

PURPOSE

In vivo immune cell tracking using MRI can be a valuable tool for studying the mechanisms underlying successful cancer therapies. Current cell labeling methods using superparamagnetic iron oxide (SPIO) lack the persistence to track the fate and location of transplanted cells long-term. Magnetospirillum magneticum is a commercially available, iron-producing bacterium that can be taken up by and live harmoniously within mammalian cells as magneto-endosymbionts (MEs). MEs have shown promise as labeling agents for in vivo stem and cancer cell tracking but have yet to be evaluated in immune cells. This pilot study examined ME labeling in myeloid-derived suppressor cells (MDSCs), cytotoxic T lymphocytes (CTLs), and dendritic cells (DCs) and its effects on cell purity, function, and MRI contrast.

PROCEDURES

MDSCs, CTLs, and DCs were incubated with MEs at various ME labeling ratios (MLR), and various biological metrics and iron uptake were assessed. For in vivo imaging, MDSCs were labeled overnight with either MEs or SPIO (Molday ION Rhodamine B) and injected into C3 tumor-bearing mice via tail vein injection 24 days post-implant and scanned daily with MRI for 1 week to assess cellular quantification.

RESULTS

Following incubations, MDSCs contained > 0.6 pg Fe/cell. CTLs achieved Fe loading of < 0.5 pg/cell, and DCs achieved Fe loading of ~ 1.4 pg/cell. The suppressive functionality of MDSCs at 1000 MLR was not affected by ME labeling but was affected at 2000 MLR. Markers of CTL dysfunction were not markedly affected by ME labeling nor were DC markers. In vivo data demonstrated that the MDSCs labeled with MEs generated sufficient contrast to be detectable using TurboSPI, similar to SPIO-labeled cells.

CONCLUSIONS

Cells can be labeled with sufficient numbers of MEs to be detectable with MRI without compromising cell viability. Care must be taken at higher concentrations of MEs, which may affect some cell types' functional activity and/or morphology. Immune cells with minimal phagocytic behavior have much lower iron content per cell after incubation with MEs vs SPIO; however, MEs can successfully be used as a contrast agent for phagocytic immune cells.

Omniparticle Contrast Agent for Multimodal Imaging: Synthesis and Characterization in an Animal Model

PURPOSE

Individual imaging modalities have certain advantages, but each suffers from drawbacks that other modalities may overcome. The goal of this study was to create a novel contrast agent suitable for various imaging modalities that after a single administration can bridge and strengthen the collaboration between the research fields as well as enrich the information obtained from any one modality.

PROCEDURES

The contrast agent platform is based on dextran-coated iron oxide nanoparticles (for MRI and MPI) and synthesized using a modified co-precipitation method, followed by a series of conjugation steps with a fluorophore (for fluorescence and photoacoustic imaging), thyroxine (for CT imaging), and chelators for radioisotope labeling (for PET imaging). The fully conjugated agent was then tested in vitro in cell uptake, viability, and phantom studies and in vivo in a model of intraductal injection and in a tumor model.

RESULTS

The agent was synthesized, characterized, and tested in vitro where it showed the ability to produce a signal on MRI/MPI/FL/PA/CT and PET images. Studies in cells showed the expected concentration-dependent uptake of the agent without noticeable toxicity. In vivo studies demonstrated localization of the agent to the ductal tree in mice after intraductal injection with different degrees of resolution, with CT being the best for this particular application. In a model of injected labeled tumor cells, the agent produced a signal with all modalities and showed persistence in tumor cells confirmed by histology.

CONCLUSIONS

A fully functional omniparticle contrast agent was synthesized and tested in vitro and in vivo in two animal models. Results shown here point to the generation of a potent signal in all modalities tested without detrimental toxicity. Future use of this agent includes its exploration in various models of human disease including image-guided diagnostic and therapeutic applications.

Magnetic Particle Imaging in Vascular Imaging, Immunotherapy, Cell Tracking, and Noninvasive Diagnosis

Magnetic particle imaging (MPI) is a new tracer-based imaging modality that is useful in diagnosing various pathophysiology related to the vascular system and for sensitive tracking of cytotherapies. MPI uses nonradioactive and easily assimilated nanometer-sized iron oxide particles as tracers. MPI images the nonlinear Langevin behavior of the iron oxide particles and has allowed for the sensitive detection of iron oxide-labeled therapeutic cells in the body. This review will provide an overview of MPI technology, the tracer, and its use in vascular imaging and cytotherapies using molecular targets.

Emerging immunomodulatory strategies for cell therapeutics

Cellular therapies are poised to transform the field of medicine by restoring dysfunctional tissues and treating various diseases in a dynamic manner not achievable by conventional pharmaceutics. Spanning various therapeutic areas inclusive of cancer, regenerative medicine, and immune disorders, cellular therapies comprise stem or non-stem cells derived from various sources. Despite numerous clinical approvals or trials underway, the host immune response presents a critical impediment to the widespread adoption and success of cellular therapies. Here, we review current research and clinical advances in immunomodulatory strategies to mitigate immune rejection or promote immune tolerance to cellular therapies. We discuss the potential of these immunomodulatory interventions to accelerate translation or maximize the prospects of improving therapeutic outcomes of cellular therapies for clinical success.

Dynamic MRI of the Mesenchymal Stem Cells Distribution during Intravenous Transplantation in a Rat Model of Ischemic Stroke

Systemic transplantation of mesenchymal stem cells (MSCs) is a promising approach for the treatment of ischemia-associated disorders, including stroke. However, exact mechanisms underlying its beneficial effects are still debated. In this respect, studies of the transplanted cells distribution and homing are indispensable. We proposed an MRI protocol which allowed us to estimate the dynamic distribution of single superparamagnetic iron oxide labeled MSCs in live ischemic rat brain during intravenous transplantation after the transient middle cerebral artery occlusion. Additionally, we evaluated therapeutic efficacy of cell therapy in this rat stroke model. According to the dynamic MRI data, limited numbers of MSCs accumulated diffusely in the brain vessels starting at the 7th minute from the onset of infusion, reached its maximum by 29 min, and gradually eliminated from cerebral circulation during 24 h. Despite low numbers of cells entering brain blood flow and their short-term engraftment, MSCs transplantation induced long lasting improvement of the neurological deficit, but without acceleration of the stroke volume reduction compared to the control animals during 14 post-transplantation days. Taken together, these findings indicate that MSCs convey their positive action by triggering certain paracrine mechanisms or cell-cell interactions or invoking direct long-lasting effects on brain vessels.

In Vivo Cellular Magnetic Imaging: Labeled vs. Unlabeled Cells

Superparamagnetic iron oxide (SPIO)-labeling of cells has been applied for magnetic resonance imaging (MRI) cell tracking for over 30 years, having resulted in a dozen or so clinical trials. SPIO nanoparticles are biodegradable and can be broken down into elemental iron, and hence the tolerance of cells to magnetic labeling has been overall high. Over the years, however, single reports have accumulated demonstrating that the proliferation, migration, adhesion and differentiation of magnetically labeled cells may differ from unlabeled cells, with inhibition of chondrocytic differentiation of labeled human mesenchymal stem cells (hMSCs) as a notable example. This historical perspective provides an overview of some of the drawbacks that can be encountered with magnetic labeling. Now that magnetic particle imaging (MPI) cell tracking is emerging as a new in vivo cellular imaging modality, there has been a renaissance in the formulation of SPIO nanoparticles this time optimized for MPI. Lessons learned from the occasional past pitfalls encountered with SPIO-labeling of cells for MRI may expedite possible future clinical translation of (combined) MRI/MPI cell tracking.

Intracellular accumulation and immunological response of NIR-II polymeric nanoparticles

Polymeric nanoparticles (NPs) are extremely promising for theranostic applications. However, their interest depends largely on their interactions with immune system, including the capacity to activate inflammation after their capture by macrophages. In the present study, we generated monodisperse poly(ethyl methacrylate) (PEMA) NPs loaded with hydrophobic photoluminescent gold nanoclusters (Au NCs) emitting in the NIR-II optical windows and studied their interaction in vitro with J774.1A macrophages. PEMA NPs showed an efficient time and dose dependent cellular uptake with up to 70 % of macrophages labelled in 24 h without detectable cell death. Interestingly, PEMA and Au-PEMA NPs induced an anti-inflammatory response and a strong down-regulation of nitric oxide level on lipopolysacharides (LPS) activated macrophages, but without influence on the levels of reactive oxygen species (ROS). These polymeric NPs may thus present a potential interest for the treatment of inflammatory diseases.

19F MRI-fluorescence imaging dual-modal cell tracking with partially fluorinated nanoemulsions

As a noninvasive “hot-spot” imaging technology, fluorine-19 magnetic resonance imaging (19F MRI) has been extensively used in cell tracking. However, the peculiar physicochemical properties of perfluorocarbons (PFCs), the most commonly used 19F MRI agents, sometimes cause low sensitivity, poor cell uptake, and misleading results. In this study, a partially fluorinated agent, perfluoro-tert-butyl benzyl ether, was used to formulate a 19F MRI-fluorescence imaging (FLI) dual-modal nanoemulsion for cell tracking. Compared with PFCs, the partially fluorinated agent showed considerably improved physicochemical properties, such as lower density, shorter longitudinal relaxation times, and higher solubility to fluorophores, while maintaining high 19F MRI sensitivity. After being formulated into stable, monodisperse, and paramagnetic Fe3+-promoted nanoemulsions, the partially fluorinated agent was used in 19F MRI-FLI dual imaging tracking of lung cancer A549 cells and macrophages in an inflammation mouse model.

Cell sorting microbeads as novel contrast agent for magnetic resonance imaging

The success of several cell-based therapies and prevalent use of magnetic resonance imaging (MRI) in the clinic has fueled the development of contrast agents for specific cell tracking applications. Safe and efficient labeling of non-phagocytic cell types such as T cells nonetheless remains challenging. We developed a one-stop shop approach where the T cell sorting agent also labels the cells which can subsequently be depicted using non-invasive MRI. We compared the MR signal effects of magnetic-assisted cell sorting microbeads (CD25) to the current preclinical gold standard, ferumoxytol. We investigated in vitro labeling efficiency of regulatory T cells (Tregs) with MRI and histopathologic confirmation. Thereafter, Tregs and T cells were labeled with CD25 microbeads in vitro and delivered via intravenous injection. Liver MRIs pre- and 24 h post-injection were performed to determine in vivo tracking feasibility. We show that CD25 microbeads exhibit T2 signal decay properties similar to other iron oxide contrast agents. CD25 microbeads are readily internalized by Tregs and can be detected by non-invasive MRI with dose dependent T2 signal suppression. Systemically injected labeled Tregs can be detected in the liver 24 h post-injection, contrary to T cell control. Our CD25 microbead-based labeling method is an effective tool for Treg tagging, yielding detectable MR signal change in cell phantoms and in vivo. This novel cellular tracking method will be key in tracking the fate of Tregs in inflammatory pathologies and solid organ transplantation.

Immunological response of polysaccharide nanogel-incorporating PEG hydrogels in an in vivo diabetic model

Cell-based therapies hold significant advantages in comparison with the traditional drug-based or injection-based treatments. However, for long-term functional cellular implants, immune acceptance must be established. To accomplish the acceptance of the implanted cells, various biomaterial systems have been studied. Nanogels have shown great potential for modulation of cellular microenvironments, acting as a physical barrier between the immune system and the implant. However, internalization of nano-scale materials by implanted cells is not desirable and is yet to be overcome. In this study, we incorporated acrylate modified cholesterol-bearing pullulan (CHPOA) nanogels into poly (ethylene glycol) diacrylate (PEGDA) hydrogels through covalent crosslinking, where we used visible light-induced photopolymerization. We characterized morphology and swelling properties of CHPOA incorporated PEG composite hydrogels using FE-SEM and gravimetric analysis. Also, we investigated the biocompatibility properties of composite hydrogels in vivo, where we used both healthy and diabetic mice. We induced diabetes in mice using a low dose streptozotocin (STZ) injections and implanted composite hydrogels in both diabetic and healthy mice through subcutaneous route. Immune cell infiltration of the retrieved tissue was examined through histological analysis, where we observed minimum immune response levels of 0-2 rareness, according to ISO standard of biological evaluation of medical devices. Our observation suggests that the composite hydrogel developed here can be used to introduce nanostructured domains into bulk hydrogels and that this system has potential to be used as immunologically acceptable composite material in cellular therapy without internalization of nanoparticles.

Imaging cellular immunotherapies and immune cell biomarkers: from preclinical studies to patients

Cellular immunotherapies have emerged as a successful therapeutic approach to fight a wide range of human diseases, including cancer. However, responses are limited to few patients and tumor types. An in-depth understanding of the complexity and dynamics of cellular immunotherapeutics, including what is behind their success and failure in a patient, the role of other immune cell types and molecular biomarkers in determining a response, is now paramount. As the cellular immunotherapy arsenal expands, whole-body non-invasive molecular imaging can shed a light on their in vivo fate and contribute to the reliable assessment of treatment outcome and prediction of therapeutic response. In this review, we outline the non-invasive strategies that can be tailored toward the molecular imaging of cellular immunotherapies and immune-related components, with a focus on those that have been extensively tested preclinically and are currently under clinical development or have already entered the clinical trial phase. We also provide a critical appraisal on the current role and consolidation of molecular imaging into clinical practice.

Cell Tracking by Magnetic Particle Imaging: Methodology for Labeling THP-1 Monocytes with Magnetic Nanoparticles for Cellular Imaging

Magnetic particle imaging (MPI) is a noninvasive tomographic imaging modality for the quantitative visualization of magnetic nanoparticles (MNPs) with high temporal and spatial resolution. The general capability of MPI for cell tracking (e.g., monitoring living cells labeled with MNPs) has successfully been shown. MNPs in cell culture media are often subjected to structural and magnetic changes. In addition to the deteriorating reproducibility, this also complicates the systematic study of the relationship between the MNP properties and their cellular uptake for MPI. Here, we present a method for the preparation of magnetically labeled THP-1 (Tamm-Horsfall Protein-1) monocytes that are used in MPI cell tracking. The method development was performed using two different MPI tracers, which exhibited electrostatic and steric stabilizations, respectively. In the first step, the interaction between the MNPs and cell culture media was investigated and adjusted to ensure high structural and magnetic stability. Furthermore, the influences of the incubation time, MNP concentration used for cellular uptake, and individual preparation steps (e.g., the washing of cells) were systematically investigated. Finally, the success of the developed loading method was demonstrated by the MPI measurements. The presented systematic investigation of the factors that influence the MNP loading of cells will help to develop a reliable and reproducible method for MPI monocyte tracking for the early detection of inflammation in the future.

Monoclonal antibody-mediated immunosuppression enables long-term survival of transplanted human neural stem cells in mouse brain

BACKGROUND

As the field of stem cell therapy advances, it is important to develop reliable methods to overcome host immune responses in animal models. This ensures survival of transplanted human stem cell grafts and enables predictive efficacy testing. Immunosuppressive drugs derived from clinical protocols are frequently used but are often inconsistent and associated with toxic side effects. Here, using a molecular imaging approach, we show that immunosuppression targeting costimulatory molecules CD4 and CD40L enables robust survival of human xenografts in mouse brain, as compared to conventional tacrolimus and mycophenolate mofetil.

METHODS

Human neural stem cells were modified to express green fluorescent protein and firefly luciferase. Cells were implanted in the fimbria fornix of the hippocampus and viability assessed by non-invasive bioluminescent imaging. Cell survival was assessed using traditional pharmacologic immunosuppression as compared to monoclonal antibodies directed against CD4 and CD40L. This paradigm was also implemented in a transgenic Alzheimer's disease mouse model.

RESULTS

Graft rejection occurs within 7 days in non-immunosuppressed mice and within 14 days in mice on a traditional regimen. The addition of dual monoclonal antibody immunosuppression extends graft survival past 7 weeks (p < .001) on initial studies. We confirm dual monoclonal antibody treatment is superior to either antibody alone (p < .001). Finally, we demonstrate robust xenograft survival at multiple cell doses up to 6 months in both C57BL/6J mice and a transgenic Alzheimer's disease model (p < .001). The dual monoclonal antibody protocol demonstrated no significant adverse effects, as determined by complete blood counts and toxicity screen.

CONCLUSIONS

This study demonstrates an effective immunosuppression protocol for preclinical testing of stem cell therapies. A transition towards antibody-based strategies may be advantageous by enabling stem cell survival in preclinical studies that could inform future clinical trials.

A novel glaucoma approach: Stem cell regeneration of the trabecular meshwork

Glaucoma is the leading cause of global irreversible blindness, necessitating research for new, more efficacious treatment options than currently exist. Trabecular meshwork (TM) cells play an important role in the maintenance and function of the aqueous outflow pathway, and studies have found that there is decreased cellularity of the TM in glaucoma. Regeneration of the TM with stem cells has been proposed as a novel therapeutic option by several reports over the last few decades. Stem cells have the capacity for self-renewal and the potential to differentiate into adult functional cells. Several types of stem cells have been investigated in ocular regenerative medicine: tissue specific stem cells, embryonic stem cells, induced pluripotent stem cells, and adult mesenchymal stem cells. These cells have been used in various glaucoma animal models and ex vivo models and have shown success in IOP homeostasis and TM cellularity restoration. They have also demonstrated stability without serious side effects for a significant period of time. Based on current knowledge of TM pathology in glaucoma and existing literature regarding stem cell regeneration of this tissue, we propose a human clinical study as the next step in understanding this potentially revolutionary treatment paradigm. The ability to protect and replace TM cells in glaucomatous eyes could change the field forever.

Enhanced detection of paramagnetic fluorine-19 magnetic resonance imaging agents using zero echo time sequence and compressed sensing

Fluorine-19 (19 F) magnetic resonance imaging (MRI) is an emerging technique offering specific detection of labeled cells in vivo. Lengthy acquisition times and modest signal-to-noise ratio (SNR) makes three-dimensional spin-density-weighted 19 F imaging challenging. Recent advances in tracer paramagnetic metallo-perfluorocarbon (MPFC) nanoemulsion probes have shown multifold SNR improvements due to an accelerated 19 F T1 relaxation rate and a commensurate gain in imaging speed and averages. However, 19 F T2 -reduction and increased linewidth limit the amount of metal additive in MPFC probes, thus constraining the ultimate SNR. To overcome these barriers, we describe a compressed sampling (CS) scheme, implemented using a "zero" echo time (ZTE) sequence, with data reconstructed via a sparsity-promoting algorithm. Our CS-ZTE scheme acquires k-space data using an undersampled spherical radial pattern and signal averaging. Image reconstruction employs off-the-shelf sparse solvers to solve a joint total variation and l 1 -norm regularized least square problem. To evaluate CS-ZTE, we performed simulations and acquired 19 F MRI data at 11.7 T in phantoms and mice receiving MPFC-labeled dendritic cells. For MPFC-labeled cells in vivo, we show SNR gains of ~6.3 × with 8-fold undersampling. We show that this enhancement is due to three mechanisms including undersampling and commensurate increase in signal averaging in a fixed scan time, denoising attributes from the CS algorithm, and paramagnetic reduction of T1 . Importantly, 19 F image intensity analyses yield accurate estimates of absolute quantification of 19 F spins. Overall, the CS-ZTE method using MPFC probes achieves ultrafast imaging, a substantial boost in detection sensitivity, accurate 19 F spin quantification, and minimal image artifacts.

Enzyme-mediated intratumoral self-assembly of nanotheranostics for enhanced imaging and tumor therapy

Enzyme-mediated intratumoral self-assembled (EMISA) nanotheranostics represent a new class of smart agents for combined imaging and therapy of cancer. Cancer cells overexpress various enzymes that are essential for high metabolism, fast proliferation, and tissue invasion and metastasis. By conjugating small molecules that contain an enzyme-specific cleavage site to appropriate chemical linkers, it is possible to induce self-assembly of nanostructures in tumor cells having the target enzyme. This approach of injecting small theranostic molecules that eventually become larger nanotheranostics in situ avoids some of the major limitations that are encountered when injecting larger, pre-assembled nanotheranostics. The advantage of EMISA nanotheranostics include the avoidance of nonspecific uptake and rapid clearance by phagocytic cells, increased cellular accumulation, reduced drug efflux and prolonged cellular exposure time, all of which lead to an amplified imaging signal and therapeutic efficacy. We review here the different approaches that can be used for preparing EMISA-based organic, inorganic, or organic/inorganic hybrid nanotheranostics based on noncovalent interactions and/or covalent bonding. Imaging examples are shown for fluorescence imaging, nuclear imaging, photoacoustic imaging, Raman imaging, computed tomography imaging, bioluminescent imaging, and magnetic resonance imaging. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Biology-Inspired Nanomaterials > Peptide-Based Structures.

In vivo tracking of unlabelled mesenchymal stromal cells by mannose-weighted chemical exchange saturation transfer MRI

The tracking of the in vivo biodistribution of transplanted human mesenchymal stromal cells (hMSCs) relies on reporter genes or on the addition of exogenous imaging agents. However, reporter genes and exogenous labels may require bespoke manufacturing and regulatory processes if used in cell therapies, and the labels may alter the cells' properties and are diluted on cellular division. Here we show that high-mannose N-linked glycans, which are abundantly expressed on the surface of hMSCs, can serve as a biomarker for the label-free tracking of transplanted hMSCs by mannose-weighted chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI). For live mice with luciferase-transfected hMSCs transplanted into their brains, post-mortem fluorescence staining with a mannose-specific lectin showed that increases in the CEST MRI signal, which correlated well with the bioluminescence intensity of viable hMSCs for 14 days, corresponded to the presence of mannose. In vitro, osteogenically differentiated hMSCs led to lower CEST MRI signal intensities owing to the concomitantly reduced expression of mannose. The label-free imaging of hMSCs may facilitate the development and testing of cell therapies.

Clinical magnetic hyperthermia requires integrated magnetic particle imaging

Magnetic nanomaterials that respond to clinical magnetic devices have significant potential as cancer nanotheranostics. The complexities of their physics, however, introduce challenges for these applications. Hyperthermia is a heat‐based cancer therapy that improves treatment outcomes and patient survival when controlled energy delivery is combined with accurate thermometry. To date, few technologies have achieved the needed evolution for the demands of the clinic. Magnetic fluid hyperthermia (MFH) offers this potential, but to be successful it requires particle‐imaging technology that provides real‐time thermometry. Presently, the only technology having the potential to meet these requirements is magnetic particle imaging (MPI), for which a proof‐of‐principle demonstration with MFH has been achieved. Successful clinical translation and adoption of integrated MPI/MFH technology will depend on successful resolution of the technological challenges discussed.

This article is categorized under:

Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease

Diagnostic Tools > In Vivo Nanodiagnostics and Imaging

Opportunities for Molecular Imaging in Multiple Sclerosis Management: Linking Probe to Treatment

Imaging has been a critical component of multiple sclerosis (MS) management for nearly 40 years. The visual information derived from structural MRI, that is, signs of blood-brain barrier disruption, inflammation and demyelination, and brain and spinal cord atrophy, are the primary metrics used to evaluate therapeutic efficacy in MS. The development of targeted imaging probes has expanded our ability to evaluate and monitor MS and its therapies at the molecular level. Most molecular imaging probes evaluated for MS applications are small molecules initially developed for PET, nearly half of which are derived from U.S. Food and Drug Administration-approved drugs and those currently undergoing clinical trials. Superparamagnetic and fluorinated particles have been used for tracking circulating immune cells (in situ labeling) and immunosuppressive or remyelinating therapeutic stem cells (ex vivo labeling) clinically using proton (hydrogen 1 [¹H]) and preclinically using fluorine 19 MRI. Translocator protein PET and ¹H MR spectroscopy have been demonstrated to complement imaging metrics from structural (gadolinium-enhanced) MRI in nine and six trials for MS disease-modifying therapies, respectively. Still, despite multiple demonstrations of the utility of molecular imaging probes to evaluate the target location and to elucidate the mechanisms of disease-modifying therapies for MS applications, their use has been sparse in both preclinical and clinical settings.

Nanotechnology-Assisted Cell Tracking

The usefulness of nanoparticles (NPs) in the diagnostic and/or therapeutic sector is derived from their aptitude for navigating intra- and extracellular barriers successfully and to be spatiotemporally targeted. In this context, the optimization of NP delivery platforms is technologically related to the exploitation of the mechanisms involved in the NP-cell interaction. This review provides a detailed overview of the available technologies focusing on cell-NP interaction/detection by describing their applications in the fields of cancer and regenerative medicine. Specifically, a literature survey has been performed to analyze the key nanocarrier-impacting elements, such as NP typology and functionalization, the ability to tune cell interaction mechanisms under in vitro and in vivo conditions by framing, and at the same time, the imaging devices supporting NP delivery assessment, and consideration of their specificity and sensitivity. Although the large amount of literature information on the designs and applications of cell membrane-coated NPs has reached the extent at which it could be considered a mature branch of nanomedicine ready to be translated to the clinic, the technology applied to the biomimetic functionalization strategy of the design of NPs for directing cell labelling and intracellular retention appears less advanced. These approaches, if properly scaled up, will present diverse biomedical applications and make a positive impact on human health.

Development and regulation of stem cell-based therapies in China

BACKGROUND

Clinical researches of stem cell-based therapies are highly active in China, while it was arduous to determine the most effective way of clinical translation of those advanced therapies.

METHODS

This article briefly introduced the regulatory framework development, the progress in stem cell clinical researches and clinical trials of commercially developed stem cell-based products, as well as the clinical review concerns of stem cell-based products in China.

MAIN FINDINGS

The current regulatory framework of stem cell clinical researches in China was launched in 2015, when regulatory authorities issued "Administrative Measures on Stem Cell Clinical Research" (AMSCCR) detailing the rules of stem cell clinical research. Thereafter, the rapidly growing stem cell clinical researches were rigorously managed and clinical use of stem cell therapy was halted. Meanwhile, commercially developed stem cell-based products are supervised by Drug Administration Law (DAL).

CONCLUSION

The regulatory framework of stem cell-based therapy in China has progressed in the last few decades, which is currently regulated according to AMSCCR and DAL. Well-designed and patient-focused clinical trial is required for commercially developed stem cell-based products, and definite clinical benefit evidence is crucial to obtain marketing authorization.

Visualizing CAR-T cell Immunotherapy Using 3 Tesla Fluorine-19 MRI

PURPOSE

Chimeric antigen receptor (CAR) T cell cancer immunotherapies have shown remarkable results in patients with hematological malignancies and represent the first approved genetically modified cellular therapies. However, not all blood cancer patients respond favorably, serious side effects have been reported, and the treatment of solid tumors has been a challenge. An imaging tool for visualizing the variety of CAR-T cell products in use and being explored could provide important patient-specific data on CAR-T cell location to inform on potential success or failure of treatment as well as off-target toxicities. Fluorine-19 (19F) magnetic resonance imaging (MRI) allows for the noninvasive detection of 19F perfluorocarbon (PFC) labeled cells. Our objective was to visualize PFC-labeled (PFC +) CAR-T cells in a mouse model of leukemia using clinical field strength (3 Tesla) 19F MRI and compare the cytotoxicity of PFC + versus unlabeled CAR-T cells.

PROCEDURES

NSG mice (n = 17) received subcutaneous injections of CD19 + human B cell leukemia cells (NALM6) expressing firefly luciferase in their left hind flank (1 × 106). Twenty-one days later, each mouse received an intratumoral injection of 10 × 106 PFC + CD19-targeted CAR-T cells (n = 6), unlabeled CD19-targeted CAR-T cells (n = 3), PFC + untransduced T cells (n = 5), or an equivalent volume of saline (n = 3). 19F MRI was performed on mice treated with PFC + CAR-T cells days 1, 3, and 7 post-treatment. Bioluminescence imaging (BLI) was performed on all mice days - 1, 5, 10, and 14 post-treatment to monitor tumor response.

RESULTS

PFC + CAR-T cells were successfully detected in tumors using 19F MRI on days 1, 3, and 7 post-injection. In vivo BLI data revealed that mice treated with PFC + or PFC - CAR-T cells had significantly lower tumor burden by day 14 compared to untreated mice and mice treated with PFC + untransduced T cells (p < 0.05). Importantly, mice treated with PFC + CAR-T cells showed equivalent cytotoxicity compared to mice receiving PFC - CAR-T cells.

CONCLUSIONS

Our studies demonstrate that clinical field strength 19F MRI can be used to visualize PFC + CAR-T cells for up to 7 days post-intratumoral injection. Importantly, PFC labeling did not significantly affect in vivo CAR-T cell cytotoxicity. These imaging tools may have broad applications for tracking emerging CAR-T cell therapies in preclinical models and may eventually be useful for the detection of CAR-T cells in patients where localized injection of CAR-T cells is being pursued.

Ferromagnetic Vortex Iron Oxide Nanorings Modified with Integrin β1 Antibody for Targeted MRI Tracking of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) have demonstrated great potential for tissue engineering and regenerative medicine applications. Noninvasive and real-term tracking of transplanted MSCs in vivo is crucial for studying the distribution and migration of MSCs, and their role in tissue injury repair. This study reports on the use of ferrimagnetic vortex iron oxide (FVIO) nanorings modified with anti-human integrin β1 for specific recognition and magnetic resonance imaging (MRI) tracking of human MSCs (hMSCs). Integrin β1 is highly expressed at all stem cell proliferation and differentiation stages. Therefore, the anti-integrin β1 antibody (Ab) introduced in FVIO targets integrin β1, thus enabling FVIO to target stem cells at any stage. This is unlike the traditional MRI-based monitoring of transplanted stem cells, which usually requires pre-labeling the stem cells with tracers before injection. Because of the ability to recognize hMSCs, the Ab-modified FVIO nanotracers (FVIO-Ab) have the advantage of not requiring pre-labeling before stem cell transplantation. Furthermore, the FVIO-Ab nanotracers have high T^*₂ contrast resulting from the unique magnetic properties of FVIO which can improve the MRI tracking efficiency of stem cells. This work may provide a new way for stem cell labeling and in vivo MRI tracking, thus reducing the risks associated with stem cell transplantation and promoting clinical translation.

In Vivo MRI Tracking of Tumor Vaccination and Antigen Presentation by Dendritic Cells

Cancer vaccination using tumor antigen-primed dendritic cells (DCs) was introduced in the clinic some 25 years ago, but the overall outcome has not lived up to initial expectations. In addition to the complexity of the immune response, there are many factors that determine the efficacy of DC therapy. These include accurate administration of DCs in the target tissue site without unwanted cell dispersion/backflow, sufficient numbers of tumor antigen-primed DCs homing to lymph nodes (LNs), and proper timing of immunoadjuvant administration. To address these uncertainties, proton (1H) and fluorine (19F) magnetic resonance imaging (MRI) tracking of ex vivo pre-labeled DCs can now be used to non-invasively determine the accuracy of therapeutic DC injection, initial DC dispersion, systemic DC distribution, and DC migration to and within LNs. Magnetovaccination is an alternative approach that tracks in vivo labeled DCs that simultaneously capture tumor antigen and MR contrast agent in situ, enabling an accurate quantification of antigen presentation to T cells in LNs. The ultimate clinical premise of MRI DC tracking would be to use changes in LN MRI signal as an early imaging biomarker to predict the efficacy of tumor vaccination and anti-tumor response long before treatment outcome becomes apparent, which may aid clinicians with interim treatment management.

Deep tissue localization and sensing using optical microcavity probes

Optical microcavities and microlasers were recently introduced as probes inside living cells and tissues. Their main advantages are spectrally narrow emission lines and high sensitivity to the environment. Despite numerous novel methods for optical imaging in strongly scattering biological tissues, imaging at single-cell resolution beyond the ballistic light transport regime remains very challenging. Here, we show that optical microcavity probes embedded inside cells enable three-dimensional localization and tracking of individual cells over extended time periods, as well as sensing of their environment, at depths well beyond the light transport length. This is achieved by utilizing unique spectral features of the whispering-gallery modes, which are unaffected by tissue scattering, absorption, and autofluorescence. In addition, microcavities can be functionalized for simultaneous sensing of various parameters, such as temperature or pH value, which extends their versatility beyond the capabilities of standard fluorescent labels.

Iron Oxide Nanoparticles in Mesenchymal Stem Cell Detection and Therapy

Mesenchymal stem cells (MSCs) exhibit regenerative and reparative properties. However, most MSC-related studies remain to be translated for regular clinical usage, partly due to challenges in pre-transplantation cell labelling and post-transplantation cell tracking. Amidst this, there are growing concerns over the toxicity of commonly used gadolinium-based contrast agents that mediate in-vivo cell detection via MRI. This urges to search for equally effective but less toxic alternatives that would facilitate and enhance MSC detection post-administration and provide therapeutic benefits in-vivo. MSCs labelled with iron oxide nanoparticles (IONPs) have shown promising results in-vitro and in-vivo. Thus, it would be useful to revisit these studies before inventing new labelling approaches. Aiming to inform regenerative medicine and augment clinical applications of IONP-labelled MSCs, this review collates and critically evaluates the utility of IONPs in enhancing MSC detection and therapeutics. It explains the rationale, principle, and advantages of labelling MSCs with IONPs, and describes IONP-induced intracellular alterations and consequent cellular manifestations. By exemplifying clinical pathologies, it examines contextual in-vitro, animal, and clinical studies that used IONP-labelled bone marrow-, umbilical cord-, adipose tissue- and dental pulp-derived MSCs. It compiles and discusses studies involving MSC-labelling of IONPs in combinations with carbohydrates (Venofer, ferumoxytol, dextran, glucosamine), non-carbohydrate polymers [poly(L-lysine), poly(lactide-co-glycolide), poly(L-lactide), polydopamine], elements (ruthenium, selenium, gold, zinc), compounds/stains (silica, polyethylene glycol, fluorophore, rhodamine B, DAPI, Prussian blue), DNA, Fibroblast growth Factor-2 and the drug doxorubicin. Furthermore, IONP-labelling of MSC exosomes is reviewed. Also, limitations of IONP-labelling are addressed and methods of tackling those challenges are suggested.

The sensitivity of magnetic particle imaging and fluorine-19 magnetic resonance imaging for cell tracking

Magnetic particle imaging (MPI) and fluorine-19 (19F) MRI produce images which allow for quantification of labeled cells. MPI is an emerging instrument for cell tracking, which is expected to have superior sensitivity compared to 19F MRI. Our objective is to assess the cellular sensitivity of MPI and 19F MRI for detection of mesenchymal stem cells (MSC) and breast cancer cells. Cells were labeled with ferucarbotran or perfluoropolyether, for imaging on a preclinical MPI system or 3 Tesla clinical MRI, respectively. Using the same imaging time, as few as 4000 MSC (76 ng iron) and 8000 breast cancer cells (74 ng iron) were reliably detected with MPI, and 256,000 MSC (9.01 × 1016 19F atoms) were detected with 19F MRI, with SNR > 5. MPI has the potential to be more sensitive than 19F MRI for cell tracking. In vivo sensitivity with MPI and 19F MRI was evaluated by imaging MSC that were administered by different routes. In vivo imaging revealed reduced sensitivity compared to ex vivo cell pellets of the same cell number. We attribute reduced MPI and 19F MRI cell detection in vivo to the effect of cell dispersion among other factors, which are described.

Non-invasive cell-tracking methods for adoptive T cell therapies

Adoptive T cell therapies (ACT) have demonstrated groundbreaking results in blood cancers and melanoma. Nevertheless, their significant cost, the occurrence of severe adverse events, and their poor performance in solid tumors are important hurdles hampering more widespread applicability. In vivo cell tracking allows instantaneous and non-invasive monitoring of the distribution, tumor homing, persistence, and redistribution to other organs of infused T cells in patients. Furthermore, cell tracking could aid in the clinical management of patients, allowing the detection of non-responders or severe adverse events at an early stage. This review provides a concise overview of the main principles and potential of cell tracking, followed by a discussion of the clinically relevant labeling strategies and their application in ACT.

The in vivo fate of tobacco mosaic virus nanoparticle theranostic agents modified by the addition of a polydopamine coat

Plant virus nanoparticles (VNPs) have multiple advantages over their synthetic counterparts including the cost-effective large-scale manufacturing of uniform particles that are easy to functionalize. Tobacco mosaic virus (TMV) is one of the most promising VNP scaffolds, reflecting its high aspect ratio and ability to carry and/or display multivalent therapeutic ligands and contrast agents. Here we investigated the circulation, protein corona, immunogenicity, and organ distribution/clearance of TMV particles internally co-labeled with cyanine 5 (Cy5) and chelated gadolinium (Gd) for dual tracking by fluorescence imaging and optical emission spectrometry, with or without an external coating of polydopamine (PDA) to confer photothermal and photoacoustic capabilities. The PDA-coated particles (Gd-Cy5-TMV-PDA) showed a shorter plasma circulation time and broader distribution to organs of the reticuloendothelial system (liver, lungs, and spleen) than uncoated Gd-Cy5-TMV particles (liver and spleen only). The Gd-Cy5-TMV-PDA particles were surrounded by 2-10-fold greater protein corona (containing mainly immunoglobulins) compared to Gd-Cy5-TMV particles. However, the enzyme-linked immunosorbent assay (ELISA) revealed that PDA-coated particles bind 2-fold lesser to anti-TMV antibodies elicited by particle injection than uncoated particles, suggesting that the PDA coat enables evasion from systemic antibody surveillance. Gd-Cy5-TMV-PDA particles were cleared from organs after 8 days compared to 5 days for the uncoated particles. The slower tissue clearance of the coated particles makes them ideal for theranostic applications by facilitating sustained local delivery in addition to multimodal imaging and photothermal capabilities. We have demonstrated the potential of PDA-coated proteinaceous nanoparticles for multiple biomedical applications.

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.

MRI-Based and Histologically Verified 3D Modeling of Spatial Distribution of Intra-Arterially Transplanted Cells in Rat Brain

Visualization of transplanted stem cells in the brain is an important issue in the study of the mechanisms of their therapeutic action. MRI allowing visualization of single transplanted cells previously labeled with superparamagnetic iron oxide particles is among the most informative methods of non-invasive intravital imaging. Verification of MRI data using pathomorphological examination at the microscopic level helps to avoid errors in data interpretation. However, making serial sections of the whole brain and searching for transplanted cells under the microscope is laborious and time-consuming. We have developed a method for 3D modeling of the distribution of transplanted cells in the brain allowing navigating through various brain structures and identifying the areas of accumulation of transplanted cells, which significantly increases the efficiency and reduces the time of histological examination.

Options for imaging cellular therapeutics in vivo: a multi-stakeholder perspective

Cell-based therapies have been making great advances toward clinical reality. Despite the increase in trial activity, few therapies have successfully navigated late-phase clinical trials and received market authorization. One possible explanation for this is that additional tools and technologies to enable their development have only recently become available. To support the safety evaluation of cell therapies, the Health and Environmental Sciences Institute Cell Therapy-Tracking, Circulation and Safety Committee, a multisector collaborative committee, polled the attendees of the 2017 International Society for Cell & Gene Therapy conference in London, UK, to understand the gaps and needs that cell therapy developers have encountered regarding safety evaluations in vivo. The goal of the survey was to collect information to inform stakeholders of areas of interest that can help ensure the safe use of cellular therapeutics in the clinic. This review is a response to the cellular imaging interests of those respondents. The authors offer a brief overview of available technologies and then highlight the areas of interest from the survey by describing how imaging technologies can meet those needs. The areas of interest include imaging of cells over time, sensitivity of imaging modalities, ability to quantify cells, imaging cellular survival and differentiation and safety concerns around adding imaging agents to cellular therapy protocols. The Health and Environmental Sciences Institute Cell Therapy-Tracking, Circulation and Safety Committee believes that the ability to understand therapeutic cell fate is vital for determining and understanding cell therapy efficacy and safety and offers this review to aid in those needs. An aim of this article is to share the available imaging technologies with the cell therapy community to demonstrate how these technologies can accomplish unmet needs throughout the translational process and strengthen the understanding of cellular therapeutics.

3D in vivo Magnetic Particle Imaging of Human Stem Cell-Derived Islet Organoid Transplantation Using a Machine Learning Algorithm

Stem cell-derived islet organoids constitute a promising treatment of type 1 diabetes. A major hurdle in the field is the lack of appropriate in vivo method to determine graft outcome. Here, we investigate the feasibility of in vivo tracking of transplanted stem cell-derived islet organoids using magnetic particle imaging (MPI) in a mouse model. Human induced pluripotent stem cells-L1 were differentiated to islet organoids and labeled with superparamagnetic iron oxide nanoparticles. The phantoms comprising of different numbers of labeled islet organoids were imaged using an MPI system. Labeled islet organoids were transplanted into NOD/scid mice under the left kidney capsule and were then scanned using 3D MPI at 1, 7, and 28 days post transplantation. Quantitative assessment of the islet organoids was performed using the K-means++ algorithm analysis of 3D MPI. The left kidney was collected and processed for immunofluorescence staining of C-peptide and dextran. Islet organoids expressed islet cell markers including insulin and glucagon. Image analysis of labeled islet organoids phantoms revealed a direct linear correlation between the iron content and the number of islet organoids. The K-means++ algorithm showed that during the course of the study the signal from labeled islet organoids under the left kidney capsule decreased. Immunofluorescence staining of the kidney sections showed the presence of islet organoid grafts as confirmed by double staining for dextran and C-peptide. This study demonstrates that MPI with machine learning algorithm analysis can monitor islet organoids grafts labeled with super-paramagnetic iron oxide nanoparticles and provide quantitative information of their presence in vivo.

pH-Triggered Aggregation of Gold Nanoparticles for Enhanced Labeling and Long-Term CT Imaging Tracking of Stem Cells in Pulmonary Fibrosis Treatment

Gold nanoparticles (AuNPs) pose a great challenge in the development of nanotracers that can self-adaptively alter their properties in response to certain cellular environments for long-term stem cell tracking. Herein, pH-sensitive Au nanotracers (CPP-PSD@Au) are fabricated by sequential coupling of AuNPs with sulfonamide-based polymer (PSD) and cell-penetrating peptide (CPP), which can be efficiently internalized by mesenchymal stem cells (MSCs) and undergo pH-induced self-assembly in endosomes, facilitating long-term computed tomography (CT) imaging tracking MSCs in a murine model of idiopathic pulmonary fibrosis (IPF). Using the CPP-PSD@Au, the transplanted MSCs for the first time can be monitored with CT imaging for up to 35 days after transplantation into the lung of IPF mice, clearly elucidating the migration process of MSCs in vivo. Moreover, we preliminarily explored the mechanism of the CPP-PSD@Au labeled MSCs in the alleviation of IPF, including recovery of alveolar integrity, decrease of collagen deposition, as well as down-regulation of relevant cytokine level. This work facilitates our understanding of the behavior and effect of MSCs in the therapy of IPF, thereby providing an important insight into the stem cell-based treatment of lung diseases.