Cytotoxicity of 111In-oxine on mesenchymal stem cells: a time-dependent adverse effect

Biodistribution of 89Zr-oxine-labeled human bone marrow-derived mesenchymal stem cells by micro-PET/computed tomography imaging in Sprague-Dawley rats

PURPOSE

To develop a method for labeling human bone marrow mesenchymal stem cells (hMSCs) with 89Zr-oxine to characterize the biodistribution characteristics of hMSCs in normal Sprague-Dawley (SD) rats in real-time by micro-PET-computed tomography (micro-PET/CT) imaging.

METHODS

89Zr-oxine complex was synthesized from 89Zr-oxalate and 8-hydroxyquinoline (oxine). After hMSCs were labeled with the 89Zr-oxine complex, the radioactivity retention, viability, proliferation, apoptosis, differentiation, morphology, and phenotype of labeled cells were assessed. The biodistribution of 89Zr-oxine-labeled hMSCs in SD rats was tracked in real-time by micro-PET/CT imaging.

RESULTS

The cell labeling efficiency was 52.6 ± 0.01%, and 89Zr-oxine was stably retained in cells (66.7 ± 0.9% retention on 7 days after labeling). Compared with the unlabeled hMSCs, 89Zr-oxine labeling did not affect the biological characteristics of cells. Following intravenous administration in SD rats, labeled hMSCs mainly accumulated in the liver (7.35 ± 1.41% ID/g 10 days after labeling, n = 6) and spleen (8.48 ± 1.20% ID/g 10 days after labeling, n = 6), whereas intravenously injected 89Zr-oxalate mainly accumulated in the bone (4.47 ± 0.35% ID/g 10 days after labeling, n = 3).

CONCLUSION

89Zr-oxine labeling and micro-PET/CT imaging provide a useful and non-invasive method of assessing the biodistribution of cell therapy products in SD rats. The platform provides a foundation for us to further understand the mechanism of action and migration dynamics of cell therapy products.

Direct Cell Radiolabeling for in Vivo Cell Tracking with PET and SPECT Imaging

The arrival of cell-based therapies is a revolution in medicine. However, its safe clinical application in a rational manner depends on reliable, clinically applicable methods for determining the fate and trafficking of therapeutic cells in vivo using medical imaging techniques─known as in vivo cell tracking. Radionuclide imaging using single photon emission computed tomography (SPECT) or positron emission tomography (PET) has several advantages over other imaging modalities for cell tracking because of its high sensitivity (requiring low amounts of probe per cell for imaging) and whole-body quantitative imaging capability using clinically available scanners. For cell tracking with radionuclides, ex vivo direct cell radiolabeling, that is, radiolabeling cells before their administration, is the simplest and most robust method, allowing labeling of any cell type without the need for genetic modification. This Review covers the development and application of direct cell radiolabeling probes utilizing a variety of chemical approaches: organic and inorganic/coordination (radio)chemistry, nanomaterials, and biochemistry. We describe the key early developments and the most recent advances in the field, identifying advantages and disadvantages of the different approaches and informing future development and choice of methods for clinical and preclinical application.

Optimisation of the Synthesis and Cell Labelling Conditions for [89Zr]Zr-oxine and [89Zr]Zr-DFO-NCS: a Direct In Vitro Comparison in Cell Types with Distinct Therapeutic Applications

BACKGROUND

There is a need to better characterise cell-based therapies in preclinical models to help facilitate their translation to humans. Long-term high-resolution tracking of the cells in vivo is often impossible due to unreliable methods. Radiolabelling of cells has the advantage of being able to reveal cellular kinetics in vivo over time. This study aimed to optimise the synthesis of the radiotracers [89Zr]Zr-oxine (8-hydroxyquinoline) and [89Zr]Zr-DFO-NCS (p-SCN-Bn-Deferoxamine) and to perform a direct comparison of the cell labelling efficiency using these radiotracers.

PROCEDURES

Several parameters, such as buffers, pH, labelling time and temperature, were investigated to optimise the synthesis of [89Zr]Zr-oxine and [89Zr]Zr-DFO-NCS in order to reach a radiochemical conversion (RCC) of >95 % without purification. Radio-instant thin-layer chromatography (iTLC) and radio high-performance liquid chromatography (radio-HPLC) were used to determine the RCC. Cells were labelled with [89Zr]Zr-oxine or [89Zr]Zr-DFO-NCS. The cellular retention of 89Zr and the labelling impact was determined by analysing the cellular functions, such as viability, proliferation, phagocytotic ability and phenotypic immunostaining.

RESULTS

The optimised synthesis of [89Zr]Zr-oxine and [89Zr]Zr-DFO-NCS resulted in straightforward protocols not requiring additional purification. [89Zr]Zr-oxine and [89Zr]Zr-DFO-NCS were synthesised with an average RCC of 98.4 % (n = 16) and 98.0 % (n = 13), respectively. Cell labelling efficiencies were 63.9 % (n = 35) and 70.2 % (n = 30), respectively. 89Zr labelling neither significantly affected the cell viability (cell viability loss was in the range of 1-8 % compared to its corresponding non-labelled cells, P value > 0.05) nor the cells' proliferation rate. The phenotype of human decidual stromal cells (hDSC) and phagocytic function of rat bone-marrow-derived macrophages (rMac) was somewhat affected by radiolabelling.

CONCLUSIONS

Our study demonstrates that [89Zr]Zr-oxine and [89Zr]Zr-DFO-NCS are equally effective in cell labelling. However, [89Zr]Zr-oxine was superior to [89Zr]Zr-DFO-NCS with regard to long-term stability, cellular retention, minimal variation between cell types and cell labelling efficiency.

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.

Noninvasive in vivo cell tracking using molecular imaging: A useful tool for developing mesenchymal stem cell-based cancer treatment

Mounting evidence has emphasized the potential of cell therapies in treating various diseases by restoring damaged tissues or replacing defective cells in the body. Cell therapies have become a strong therapeutic modality by applying noninvasive in vivo molecular imaging for examining complex cellular processes, understanding pathophysiological mechanisms of diseases, and evaluating the kinetics/dynamics of cell therapies. In particular, mesenchymal stem cells (MSCs) have shown promise in recent years as drug carriers for cancer treatment. They can also be labeled with different probes and tracked in vivo to assess the in vivo effect of administered cells, and to optimize therapy. The exact role of MSCs in oncologic diseases is not clear as MSCs have been shown to be involved in tumor progression and inhibition, and the exact interactions between MSCs and specific cancer microenvironments are not clear. In this review, a multitude of labeling approaches, imaging modalities, and the merits/demerits of each strategy are outlined. In addition, specific examples of the use of MSCs and in vivo imaging in cancer therapy are provided. Finally, present limitations and future outlooks in terms of the translation of different imaging approaches in clinics are discussed.

Multi-modal imaging probe for assessing the efficiency of stem cell delivery to orthotopic breast tumours

Stem cells have been utilised as anti-cancer agents due to their ability to home to and integrate within tumours. Methods to augment stem cell homing to tumours are being investigated with the goal of enhancing treatment efficacy. However, it is currently not possible to evaluate both cell localisation and cell viability after engraftment, hindering optimisation of therapy. In this study, luciferase-expressing human adipocyte-derived stem cells (ADSCs) were incubated with Indium-111 radiolabelled iron oxide nanoparticles to produce cells with tri-modal imaging capabilities. ADSCs were administered intravenously (IV) or intracardially (IC) to mice bearing orthotopic breast tumours. Cell fate was monitored using bioluminescence imaging (BLI) as a measure of cell viability, magnetic resonance imaging (MRI) for cell localisation and single photon emission computer tomography (SPECT) for cell quantification. Serial monitoring with multi-modal imaging showed the presence of viable ADSCs within tumours as early as 1-hour post IC injection and the percentage of ADSCs within tumours to be 2-fold higher after IC than IV. Finally, histological analysis was used to validate engraftment of ADSC within tumour tissue. These findings demonstrate that multi-modal imaging can be used to evaluate the efficiency of stem cell delivery to tumours and that IC cell administration is more effective for tumour targeting.

In vivo stem cell tracking using scintigraphy in a canine model of DMD

One of the main challenges in cell therapy for muscle diseases is to efficiently target the muscle. To address this issue and achieve better understanding of in vivo cell fate, we evaluated the relevance of a non-invasive cell tracking method in the Golden Retriever Muscular Dystrophy (GRMD) model, a well-recognised model of Duchenne Muscular Dystrophy (DMD). Mesoangioblasts were directly labelled with ¹¹¹In-oxine, and injected through one of the femoral arteries. The scintigraphy images obtained provided the first quantitative mapping of the immediate biodistribution of mesoangioblasts in a large animal model of DMD. The results revealed that cells were trapped by the first capillary filters: the injected limb and the lung. During the days following injection, radioactivity was redistributed to the liver. In vitro studies, performed with the same cells prepared for injecting the animal, revealed prominent cell death and ¹¹¹In release. In vivo, cell death resulted in ¹¹¹In release into the vasculature that was taken up by the liver, resulting in a non-specific and non-cell-bound radioactive signal. Indirect labelling methods would be an attractive alternative to track cells on the mid- and long-term.

In Vivo Tracking of Adoptively Transferred Natural Killer Cells in Rhesus Macaques Using 89Zirconium-Oxine Cell Labeling and PET Imaging

PURPOSE

Trials of adoptive natural killer (NK)-cell immunotherapy for hematologic malignancies have thus far shown only marginal effects, despite the potent in vitro antitumor activity of these cells. Homing of infused cells to tumor microenvironments is critical for efficacy, but has not been well characterized. We established a novel method to track and quantify the distribution of adoptively transferred NK cells using rhesus macaques (RM) as a clinically relevant preclinical model.

EXPERIMENTAL DESIGN

RM NK cells were expanded ex vivo for 14-21 days, labeled with 89Zr-oxine complex, and assessed for phenotype, function, and survival. Trafficking of 89Zr-labeled ex vivo-expanded NK cells infused into RMs was monitored and quantitated by serial positron emission tomography (PET)/CT (n = 3, 2.05 ± 0.72 MBq, 23.5 ± 2.0 × 106 NK cells/kg) and compared with that of 89Zr-labeled nonexpanded NK cells, apoptotic NK cells, and hematopoietic stem and progenitor cells (HSPC).

RESULTS

NK cells retained sufficient levels of 89Zr for accurate in vivo tracking for 7 days. 89Zr labeling did not alter cellular phenotype, viability, or function. PET/CT showed NK cells initially localized in the lungs, followed by their migration to the liver, spleen, and, at low levels, bone marrow. One day following transfer, only 3.4% of infused NK cells localized to the BM versus 22.1% of HSPCs. No clinical side effects were observed, and dosimetry analysis indicated low organ radioexposures of 6.24 mSv/MBq (spleen) or lower.

CONCLUSIONS

These data support translation of this technique to humans to track the distribution of adoptively infused cells and to develop novel techniques to improve immune cell homing to tumor microenvironments.

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

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

Computational cell analysis for label-free detection of cell properties in a microfluidic laminar flow

Although a flow cytometer, being one of the most popular research and clinical tools for biomedicine, can analyze cells based on the cell size, internal structures such as granularity, and molecular markers, it provides little information about the physical properties of cells such as cell stiffness and physical interactions between the cell membrane and fluid. In this paper, we propose a computational cell analysis technique using cells' different equilibrium positions in a laminar flow. This method utilizes a spatial coding technique to acquire the spatial position of the cell in a microfluidic channel and then uses mathematical algorithms to calculate the ratio of cell mixtures. Most uniquely, the invented computational cell analysis technique can unequivocally detect the subpopulation of each cell type without labeling even when the cell type shows a substantial overlap in the distribution plot with other cell types, a scenario limiting the use of conventional flow cytometers and machine learning techniques. To prove this concept, we have applied the computation method to distinguish live and fixed cancer cells without labeling, count neutrophils from human blood, and distinguish drug treated cells from untreated cells. Our work paves the way for using computation algorithms and fluidic dynamic properties for cell classification, a label-free method that can potentially classify over 200 types of human cells. Being a highly cost-effective cell analysis method complementary to flow cytometers, our method can offer orthogonal tests in companion with flow cytometers to provide crucial information for biomedical samples.

Preclinical imaging methods for assessing the safety and efficacy of regenerative medicine therapies

Regenerative medicine therapies hold enormous potential for a variety of currently incurable conditions with high unmet clinical need. Most progress in this field to date has been achieved with cell-based regenerative medicine therapies, with over a thousand clinical trials performed up to 2015. However, lack of adequate safety and efficacy data is currently limiting wider uptake of these therapies. To facilitate clinical translation, non-invasive in vivo imaging technologies that enable careful evaluation and characterisation of the administered cells and their effects on host tissues are critically required to evaluate their safety and efficacy in relevant preclinical models. This article reviews the most common imaging technologies available and how they can be applied to regenerative medicine research. We cover details of how each technology works, which cell labels are most appropriate for different applications, and the value of multi-modal imaging approaches to gain a comprehensive understanding of the responses to cell therapy in vivo.

Bone Marrow Cell Trafficking Analyzed by 89Zr-oxine Positron Emission Tomography in a Murine Transplantation Model

Purpose: The success of hematopoietic stem cell transplantation (HSCT) depends on donor cell homing to the bone marrow. However, there is no reliable method of noninvasively monitoring the kinetics and distribution of transferred cells. Using zirconium-89 (89Zr)-oxine cell labeling combined with PET imaging, we sought to visualize and quantify donor cell homing in a mouse bone marrow transplantation model.Experimental Design: The effect of 89Zr-oxine labeling on bone marrow cell viability and differentiation was evaluated in vitro89Zr-labeled bone marrow cells (2 × 107 cells, 16.6 kBq/106 cells) were transferred intravenously, and serial microPET images were obtained (n = 5). The effect of a CXCR4 inhibitor, plerixafor (5 mg/kg) and G-CSF (2.5 μg) on bone marrow homing and mobilization were examined (n = 4). Engraftment of the transferred 89Zr-labeled cells was evaluated (n = 3).Results:89Zr-oxine-labeled bone marrow cells showed delayed proliferation, but differentiated normally. Transferred bone marrow cells rapidly migrated to the bone marrow, spleen, and liver (n = 5). Approximately 36% of donor cells homed to the bone marrow within 4 hours, irrespective of prior bone marrow ablation. Inhibition of CXCR4 by plerixafor alone or with G-CSF significantly blocked the bone marrow homing (P < 0.0001, vs. nontreated, at 2 hours), confirming a crucial role of the CXCR4-CXCL12 system. Mobilization of approximately 0.64% of pretransplanted bone marrow cells induced a 3.8-fold increase of circulating bone marrow cells. 89Zr-labeled donor cells engrafted as well as nonlabeled cells.Conclusions:89Zr-oxine PET imaging reveals rapid bone marrow homing of transferred bone marrow cells without impairment of their stem cell functions, and thus, could provide useful information for optimizing HSCT. Clin Cancer Res; 23(11); 2759-68. ©2016 AACR.

Production and Clinical Applications of Radiopharmaceuticals and Medical Radioisotopes in Iran

During past 3 decades, nuclear medicine has flourished as vibrant and independent medical specialty in Iran. Since that time, more than 200 nuclear physicians have been trained and now practicing in nearly 158 centers throughout the country. In the same period, Tc-99m generators and variety of cold kits for conventional nuclear medicine were locally produced for the first time. Local production has continued to mature in robust manner while fulfilling international standards. To meet the ever-growing demand at the national level and with international achievements in mind, work for production of other Tc-99m-based peptides such as ubiquicidin, bombesin, octreotide, and more recently a kit formulation for Tc-99m TRODAT-1 for clinical use was introduced. Other than the Tehran Research Reactor, the oldest facility active in production of medical radioisotopes, there is one commercial and three hospital-based cyclotrons currently operational in the country. I-131 has been one of the oldest radioisotope produced in Iran and traditionally used for treatment of thyrotoxicosis and differentiated thyroid carcinoma. Since 2009, (131)I-meta-iodobenzylguanidine has been locally available for diagnostic applications. Gallium-67 citrate, thallium-201 thallous chloride, and Indium-111 in the form of DTPA and Oxine are among the early cyclotron-produced tracers available in Iran for about 2 decades. Rb-81/Kr-81m generator has been available for pulmonary ventilation studies since 1996. Experimental production of PET radiopharmaceuticals began in 1998. This work has culminated with development and optimization of the high-scale production line of (18)F-FDG shortly after installation of PET/CT scanner in 2012. In the field of therapy, other than the use of old timers such as I-131 and different forms of P-32, there has been quite a significant advancement in production and application of therapeutic radiopharmaceuticals in recent years. Application of (131)I-meta-iodobenzylguanidine for treatment of neuroblastoma, pheochromocytoma, and other neuroendocrine tumors has been steadily increasing in major academic university hospitals. Also (153)Sm-EDTMP, (177)Lu-EDTMP, (90)Y-citrate, (90)Y-hydroxyapatite colloid, (188/186)Re-sulfur colloid, and (188/186)Re-HEDP have been locally developed and now routinely available for bone pain palliation and radiosynovectomy. Cu-64 has been available to the nuclear medicine community for some time. With recent reports in diagnostic and therapeutic applications of this agent especially in the field of oncology, we anticipate an expansion in production and availability. The initiation of the production line for gallium-68 generator is one of the latest exciting developments. We are proud that Iran would be joining the club of few nations with production lines for this type of generator. There are also quite a number of SPECT and PET tracers at research and preclinical stage of development preliminarily introduced for possible future clinical applications. Availability of fluorine-18 tracers and gallium-68 generators would no doubt allow rapid dissemination of PET/CT practices in various parts of our large country even far from a cyclotron facility. Also, local production and availability of therapeutic radiopharmaceuticals are going to open exciting horizons in the field of nuclear medicine therapy. Given the available manpower, local infrastructure of SPECT imaging, and rapidly growing population, the production of Tc-99m generators and cold kit would continue to flourish in Iran.

In Vivo Tracking of Cell Therapies for Cardiac Diseases with Nuclear Medicine

Even though heart diseases are amongst the main causes of mortality and morbidity in the world, existing treatments are limited in restoring cardiac lesions. Cell transplantations, originally developed for the treatment of hematologic ailments, are presently being explored in preclinical and clinical trials for cardiac diseases. Nonetheless, little is known about the possible efficacy and mechanisms for these therapies and they are the center of continuous investigation. In this scenario, noninvasive imaging techniques lead to greater comprehension of cell therapies. Radiopharmaceutical cell labeling, firstly developed to track leukocytes, has been used successfully to evaluate the migration of cell therapies for myocardial diseases. A substantial rise in the amount of reports employing this methodology has taken place in the previous years. We will review the diverse radiopharmaceuticals, imaging modalities, and results of experimental and clinical studies published until now. Also, we report on current limitations and potential advances of radiopharmaceutical labeling for cell therapies in cardiac diseases.

Cell tracking technologies for acute ischemic brain injury

Stem cell therapy has showed considerable potential in the treatment of stroke over the last decade. In order that these therapies may be optimized, the relative benefits of growth factor release, immunomodulation, and direct tissue replacement by therapeutic stem cells are widely under investigation. Fundamental to the progress of this research are effective imaging techniques that enable cell tracking in vivo. Direct analysis of the benefit of cell therapy includes the study of cell migration, localization, division and/or differentiation, and survival. This review explores the various imaging tools currently used in clinics and laboratories, addressing image resolution, long-term cell monitoring, imaging agents/isotopes, as well as safety and costs associated with each technique. Finally, burgeoning tracking techniques are discussed, with emphasis on multimodal imaging.

In vivo tracking of human placenta derived mesenchymal stem cells in nude mice via ¹⁴C-TdR labeling

Background

In order to shed light on the regenerative mechanism of mesenchymal stem cells (MSCs) in vivo, the bio-distribution profile of implanted cells using a stable and long-term tracking method is needed. We herein investigated the bio-distribution of human placental deciduas basalis derived MSCs (termed as PDB-MSCs) in nude mice after intravenous injection by carbon radioisotope labeling thymidine (¹⁴C-TdR), which is able to incorporate into new DNA strands during cell replication.

Results

The proliferation rate and radioactive emission of human PDB-MSCs after labeled with different concentrations of ¹⁴C-TdR were measured. PDB-MSCs labeled with 1 μCi possessed high radioactivity, and the biological characteristics (i.e. morphology, colony forming ability, differentiation capabilities, karyotype and cell cycle) showed no significant changes after labeling. Thus, 1 μCi was the optimal concentration in this experimental design. In nude mice, 1 × 10⁶¹⁴C-TdR-labeled PDB-MSCs were injected intravenously and the organs were collected at days 1, 2, 3, 5, 30 and 180 after injection, respectively. Radiolabeled PDB-MSCs were found mainly in the lung, liver, spleen, stomach and left femur of the recipient nude mice at the whole observation period.

Conclusions

This work provided solid evidence that ¹⁴C-TdR labeling did not alter the biological characteristics of human placental MSCs, and that this labeling method has potential to decrease the signal from non-infused or dead cells for cell tracking. Therefore, this labeling technique can be utilized to quantify the infused cells after long-term follow-up in pre-clinical studies.

Combination of single-photon emission computed tomography and magnetic resonance imaging to track 111in-oxine-labeled human mesenchymal stem cells in neuroblastoma-bearing mice

Homing is an inherent, complex, multistep process performed by cells such as human bone marrow mesenchymal stem cells (hMSCs) to travel from a distant location to inflamed or damaged tissue and tumors. This ability of hMSCs has been exploited as a tumor-targeting strategy in cell-based cancer therapy. The purpose of this study was to investigate the applicability of 111In-oxine for tracking hMSCs in vivo by combining single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI). 111In-labeled hMSCs (106 cells) were infused intraperitoneally in neuroblastoma-bearing mice, whereas a control group received a dose of free 111In-oxine. SPECT and MRI studies were performed 24 and 48 hours afterwards. Initially, the images showed similar activity in the abdomen in both controls and hMSC-injected animals. In general, abdominal activity decreases at 48 hours. hMSC-injected animals showed increased uptake in the tumor area at 48 hours, whereas the control group showed a low level of activity at 24 hours, which decreased at 48 hours. In conclusion, tracking 111In-labeled hMSCs combining SPECT and MRI is feasible and may be transferable to clinical research. The multimodal combination is essential to ensure appropriate interpretation of the images.

Seeing stem cells at work in vivo

Stem cell based-therapies are novel therapeutic strategies that hold key for developing new treatments for diseases conditions with very few or no cures. Although there has been an increase in the number of clinical trials involving stem cell-based therapies in the last few years, the long-term risks and benefits of these therapies are still unknown. Detailed in vivo studies are needed to monitor the fate of transplanted cells, including their distribution, differentiation, and longevity over time. Advancements in non-invasive cellular imaging techniques to track engrafted cells in real-time present a powerful tool for determining the efficacy of stem cell-based therapies. In this review, we describe the latest approaches to stem cell labeling and tracking using different imaging modalities.

Radiopharmaceutical stem cell tracking for neurological diseases

Although neurological ailments continue to be some of the main causes of disease burden in the world, current therapies such as pharmacological agents have limited potential in the restoration of neural functions. Cell therapies, firstly applied to treat different hematological diseases, are now being investigated in preclinical and clinical studies for neurological illnesses. However, the potential applications and mechanisms for such treatments are still poorly comprehended and are the focus of permanent research. In this setting, noninvasive in vivo imaging allows better understanding of several aspects of stem cell therapies. Amongst the various methods available, radioisotope cell labeling has become one of the most promising since it permits tracking of cells after injection by different routes to investigate their biodistribution. A significant increase in the number of studies utilizing this method has occurred in the last years. Here, we review the different radiopharmaceuticals, imaging techniques, and findings of the preclinical and clinical reports published up to now. Moreover, we discuss the limitations and future applications of radioisotope cell labeling in the field of cell transplantation for neurological diseases.

Molecular imaging: the key to advancing cardiac stem cell therapy

Cardiac stem cell therapy continues to hold promise for the treatment of ischemic heart disease despite the fact that early promising pre-clinical findings have yet to be translated into consistent clinical success. The latest human studies have collectively identified a pressing need to better understand stem cell behavior in humans and called for more incorporation of noninvasive imaging techniques into the design and evaluation of human stem cell therapy trials. This review discusses the various molecular imaging techniques validated to date for studying stem cells in living subjects, with a particular emphasis on their utilities in assessing the acute retention and the long-term survival of transplanted stem cells. These imaging techniques will be essential for advancing cardiac stem cell therapy by providing the means to both guide ongoing optimization and predict treatment response in humans.

99mTc-thymine scintigraphy may be a promising method in the diagnosis of breast cancer

OBJECTIVE

Mammography has been established as the gold standard for the detection of breast cancer, and imaging techniques such as ultrasonography, magnetic resonance imaging, scintigraphy and positron emission tomography may be useful to improve its sensitivity and specificity. The objective of this study with breast scintigraphy was to evaluate the uptake of 99mTc-thymine in mammary lesions.

METHODS

A total of 45 patients were included in this study. Thirty-three patients (73%) were subjected to surgery or percutaneous biopsy, providing histopathological data. The other 12 patients who remained under surveillance received clinical examinations and biannual mammography with a normal follow-up of at least three years, the data from which were used for comparison with the scintimammography results.

RESULTS

The majority of patients (64.4%) had clinically impalpable lesions with a mammogram diagnosis of microcalcifications, impalpable nodules, or focal asymmetry. Of the studied lesions, 87% were smaller or equal to 20 mm in diameter, and 22% had malignant histopathological findings. Scintigraphy with 99mTc-thymine had a sensitivity of 70%, a specificity of 85.7%, positive and negative predictive values of 58.3% and 90.9%, respectively, and an accuracy of 82.2%.

CONCLUSIONS

The results of this study are consistent with those previously reported by other authors. The good specificity and high negative predictive value of this technique and the absence of uptake in the heart indicate that it may be a promising complementary method in clinical practice and that it may contribute to reducing unnecessary benign biopsies.

Tracking of In-111-labeled human umbilical tissue-derived cells (hUTC) in a rat model of cerebral ischemia using SPECT imaging

BACKGROUND

In order to increase understanding of how infused cells work, it becomes important to track their initial movement, localization, and engraftment efficiency following transplantation. However, the available in vivo cell tracking techniques are suboptimal. The study objective was to determine the biodistribution of intravenously administered Indium-111 (In-111) oxine labeled human umbilical tissue-derived cells (hUTC) in a rat model of transient middle cerebral occlusion (tMCAo) using single photon emission computed tomography (SPECT).

METHODS

Rats received 3 million In-111 labeled hUTC (i.v.) 48 hrs after tMCAo. Following the administration of either hUTC or equivalent dose of In-111-oxine (18.5 MBq), animals underwent SPECT imaging on days 0, 1, and 3. Radioactivity in various organs as well as in the stroke area and contralateral hemisphere was determined, decay corrected and normalized to the total (whole body including head) radioactivity on day 0. Immunohistochemical analysis was also performed to confirm the beneficial effects of hUTC on vascular and synaptic density, and apoptosis.

RESULTS

Most of the radioactivity (43.36±23.07% on day 0) trafficked to the lungs immediately following IV administration of In-111 labeled hUTC (day 0) and decreased drastically to 8.81±7.75 and 4.01±4.52% on days 1 and 3 post-injection, respectively. In contrast, radioactivity measured in the lung of animals that received In-111-oxine alone remained relatively unchanged from day 0 to day 1 (18.38±5.45% at day 0 to 12.59±5.94%) and decreased to 8.34±4.25% on day 3. Significantly higher radioactivity was observed in stroke areas of animals that received In-111 labeled hUTC indicating the presence of cells at the site of injury representing approximately 1% of total administered dose. In addition, there was significant increase in vascular and synaptophysin immunoreactivity in stroke areas of rats that received In-111 labeled hUTC.

CONCLUSIONS

The present studies showed the tracking of In-111 labeled hUTC to the sites of stroke in a rat model of tMCAo using SPECT. Animals treated with In-111 labeled hUTC showed histological improvements, with higher vascular and synaptic densities observed in the ischemic boundary zone (IBZ).

(111)Indium-oxine labelling for evaluating the homing process of autologous osteoblasts implanted percutaneously in atrophic nonunion fractures

PURPOSE

The aim of the study was to control the in vivo localisation of implanted cells in cell-based therapies. Labelling cells with (111)indium-oxine is one of the most interesting methods proposed. We evaluated this method in the setting of autologous osteoblast implantation in nonunion fractures.

METHODS

An in vitro study of osteoblasts was conducted after (111)indium-oxine labelling. Radioactivity retention and viability, proliferation and the ability to produce alkaline phosphatase were evaluated in a seven-day culture. In vivo labelling of implanted osteoblastic cells was conducted during a therapeutic trial of atrophic nonunion fractures, with the leakage outside the nonunion site and local uptake evolution at four, 24 and 48 hour being studied.

RESULTS

The mean labelling efficiency for osteoprogenitors was 78.8 ± 4.6 %. The intracellular retention was 89.4 ± 2.1 % at three hours and 67.3 ± 4.7 % at 18 hours. The viability assessed at three hours was 93.7 ± 0.6 %. After seven days of culture, morphology and alkaline phosphatase staining were similar for both labelled and unlabelled control cells, although the proliferation rate was decreased in the labelled cells. Some local intraosseous leakage was observed in four of 17 cases. All patients showed uptake at the injection site, with four having no other uptake. Four patients showed additional uptake in the bladder, liver and spleen, while 11 patients had additional uptake in the lungs in addition to the bladder, liver and spleen. The activity ratios (injection site/body) were 48 ± 28 % at four hours, 40 ± 25 % at 24 hours and 35 ± 25 % at 48 hours. After correcting for decay, the activity within the injection site was 82 ± 15 % at 24 hours and 69 ± 11 % at 48 hours compared with the activity measured at four hours. No relationship was found between uptake and radiological bone repair.

CONCLUSIONS

The (111)indium-oxine labelling appears to be a good method for monitoring the behaviour of the osteoblastic cells after their implantation in atrophic nonunion fractures.

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

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

Intra-arterial infusion of human bone marrow-derived mesenchymal stem cells results in transient localization in the brain after cerebral ischemia in rats

Cell therapies from various sources have been under intense research in stroke. Efficient homing of the cells to the injured brain without complications is necessary to realize the therapeutic potential of cell therapy. Intra-arterial (IA) infusion of cells bypasses the filtering organs and directs the cells to the target area more efficiently. Here we studied the biodistribution of human bone marrow-derived mesenchymal stromal/stem cells (BMMSCs) after a direct infusion into the external carotid artery (ECA) in rats. Cells, which were cultured without animal-derived agents and also treated with a proteolytic enzyme to transiently modify cell surface adhesion proteins, were infused 24 h after transient middle cerebral artery occlusion (MCAO). SPECT imaging was used immediately after cell infusion and 24 h thereafter to track (111)In-oxine-labeled BMMSC in sham-operated and MCAO rats. IA infusion of BMMSCs in rats resulted in immediate cell entrapment in the brain, but the majority of the signal disappeared during the next 24 h and relocated to the internal organs. In MCAO rats, radioactivity counts 24 h after infusion were higher in the ischemic hemisphere compared to the contralateral hemisphere. Our results showed that IA infusion through ECA is a safe and efficient administration route for BMMSCs resulting in a transient localization of cells in the rat brain.

In vivo imaging of therapy-induced anti-cancer immune responses in humans

Immunotherapy aims to re-engage and revitalize the immune system in the fight against cancer. Research over the past decades has shown that the relationship between the immune system and human cancer is complex, highly dynamic, and variable between individuals. Considering the complexity, enormous effort and costs involved in optimizing immunotherapeutic approaches, clinically applicable tools to monitor therapy-induced immune responses in vivo are most warranted. However, the development of such tools is complicated by the fact that a developing immune response encompasses several body compartments, e.g., peripheral tissues, lymph nodes, lymphatic and vascular systems, as well as the tumor site itself. Moreover, the cells that comprise the immune system are not static but constantly circulate through the vascular and lymphatic system. Molecular imaging is considered the favorite candidate to fulfill this task. The progress in imaging technologies and modalities has provided a versatile toolbox to address these issues. This review focuses on the detection of therapy-induced anticancer immune responses in vivo and provides a comprehensive overview of clinically available imaging techniques as well as perspectives on future developments. In the discussion, we will focus on issues that specifically relate to imaging of the immune system and we will discuss the strengths and limitations of the current clinical imaging techniques. The last section provides future directions that we envision to be crucial for further development.

Umbilical cord blood mononuclear cell transplantation for neonatal hypoxic-ischemic encephalopathy

Despite recent advances in the treatment of neonatal hypoxic-ischemic encephalopathy (HIE) using therapeutic hypothermia, at least 30% of the cooled infants will die or have moderate/severe neurological disability. Umbilical cord blood cells (UCBCs), which are readily available at birth, have been shown to reduce sensorimotor and/or cognitive impairments in several models of brain damage, representing a promising option for the treatment of neurological diseases. In this review, we discuss recent preclinical studies that assessed the effects of UCBC transplantation in the Rice-Vannucci animal model of HIE. We also review the possible cell types and mechanisms involved in the therapeutic effect of UCBC transplantation, including neuroprotection, immunomodulation, and stimulation of neural plasticity and regeneration. In addition, we discuss how neuroimaging methods, such as bioluminescence imaging, nuclear-medicine imaging, or magnetic resonance imaging, could be used to evaluate the biodistribution of UCBCs in both preclinical and clinical studies.

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.

A multimodality reporter gene for monitoring transplanted stem cells

INTRODUCTION

The aim of this study is to explore the feasibility of a triple-fused reporter gene, termed TGF [herpes simplex virus type 1 thymidine kinase (HSV1-tk), enhanced green fluorescent protein (eGFP) and firefly luciferase (Fluc)], to monitor stem cells using multimodality molecular imaging.

METHODS

A recombinant adenovirus vector carrying the triple-fused reporter gene (Ad5-TGF) was constructed. Bone marrow mesenchymal stem cells (BMSCs) were transfected with different virus titers of Ad5-TGF [multiplicities of infection (MOIs) were 0, 50, 100, 150, 200 and 250]. The mRNA and protein expressions of HSV1-tk, eGFP and Fluc in the transfected BMSCs were evaluated using polymerase chain reaction and Western blot. After the transfection of the BMSCs with different virus titers of Ad5-TGF (MOIs were 25, 50, 75, 100 and 125), their uptake rates of (131)I-FIAU were measured. Whole-body fluorescence, bioluminescence and micro-positron emission tomography (PET) images were acquired 1 day after the transfected BMSCs were injected into the left forelimb of rats.

RESULTS

After the transfection with different titers of Ad5-TGF, the positive transfection rate reached a peak (70%) when the MOI was 100. HSV1-tk, eGFP and Fluc mRNA and protein were detected in the Ad5-TGF-transfected BMSCs, which implies their successful transfection and expression. The BMSCs uptake of (131)I-FIAU increased with the adenovirus titer and incubation time and reached a plateau (approximately 5.3%) after 3 h. Strong signals were observed in the injected left forearms in the fluorescence, bioluminescence and micro-PET images.

CONCLUSIONS

A triple-fused reporter gene, TGF, can be used as a multifunctional molecular probe for multimodality imaging.

Emerging roles for integrated imaging modalities in cardiovascular cell-based therapeutics: a clinical perspective

Despite preclinical promise, the progress of cell-based therapy to clinical cardiovascular practice has been slowed by several challenges and uncertainties that have been highlighted by the conflicting results of human trials. Most telling has been the revelation that current strategies fall short of achieving sufficient retention and engraftment of cells to meet the ambitious objective of myocardial regeneration. This has sparked novel research into the refinement of cell biology and delivery to overcome these shortcomings. Within this context, molecular imaging has emerged as a valuable tool for providing noninvasive surveillance of cell fate in vivo. Direct and indirect labelling of cells can be coupled with clinically relevant imaging modalities, such as radionuclide single photon emission computed tomography and positron emission tomography, and magnetic resonance imaging, to assess their short- and long-term distributions, along with their viability, proliferation and functional interaction with the host myocardium. This review details the strengths and limitations of the different cell labelling and imaging techniques and their potential application to the clinical realm. We also consider the broader, multifaceted utility of imaging throughout the cell therapy process, providing a discussion of its considerable value during cell delivery and its importance during the evaluation of cardiac outcomes in clinical studies.

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.

Cell tracking in cardiac repair: what to image and how to image

Stem cell therapies hold the great promise and interest for cardiac regeneration among scientists, clinicians and patients. However, advancement and distillation of a standard treatment regimen are not yet finalised. Into this breach step recent developments in the imaging biosciences. Thus far, these technical and protocol refinements have played a critical role not only in the evaluation of the recovery of cardiac function but also in providing important insights into the mechanism of action of stem cells. Molecular imaging, in its many forms, has rapidly become a necessary tool for the validation and optimisation of stem cell engrafting strategies in preclinical studies. These include a suite of radionuclide, magnetic resonance and optical imaging strategies to evaluate non-invasively the fate of transplanted cells. In this review, we highlight the state-of-the-art of the various imaging techniques for cardiac stem cell presenting the strengths and limitations of each approach, with a particular focus on clinical applicability.

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.

In vivo imaging of immune cell trafficking in cancer

Tumour establishment, progression and regression can be studied in vivo using an array of imaging techniques ranging from MRI to nuclear-based and optical techniques that highlight the intrinsic behaviour of different cell populations in the physiological context. Clinical in vivo imaging techniques and preclinical specific approaches have been used to study, both at the macroscopic and microscopic level, tumour cells, their proliferation, metastasisation, death and interaction with the environment and with the immune system. Fluorescent, radioactive or paramagnetic markers were used in direct protocols to label the specific cell population and reporter genes were used for genetic, indirect labelling protocols to track the fate of a given cell subpopulation in vivo. Different protocols have been proposed to in vivo study the interaction between immune cells and tumours by different imaging techniques (intravital and whole-body imaging). In particular in this review we report several examples dealing with dendritic cells, T lymphocytes and macrophages specifically labelled for different imaging procedures both for the study of their physiological function and in the context of anti-neoplastic immunotherapies in the attempt to exploit imaging-derived information to improve and optimise anti-neoplastic immune-based treatments.

Stem cell labeling for noninvasive delivery and tracking in cardiovascular regenerative therapy

Clinical and basic scientific studies of stem cell-based therapies have shown promising results for cardiovascular diseases. Despite a rapid transition from animal studies to clinical trials, the mechanisms by which stem cells improve heart function are yet to be fully elucidated. To optimize cell therapies in patients will require a noninvasive means to evaluate cell survival, biodistribution and fate in the same subject over time. Cell labeling offers the ability to image distinct cell lineages in vivo and investigate the efficacy of these therapies using standard noninvasive imaging techniques. In this article, we will discuss the most promising cell labeling techniques for translation to clinical cardiovascular applications.

Serial in vivo imaging of the porcine heart after percutaneous, intramyocardially injected 111In-labeled human mesenchymal stromal cells

This pilot trial aimed to investigate the utilization of (111)In-labeling of mesenchymal stromal cells (MSC) for in vivo tracking after intramyocardial transplantation in a xenotransplantation model with gender mismatched cells. Human male MSC were expanded ex vivo and labeled with (111)In-tropolone. Ten female pigs were included. The labeled cells were transplanted intramyocardially using a percutaneous injection system. The (111)In activity was determined using gamma camera imaging. Excised hearts were analyzed by fluorescence in situ hybridization (FISH) and microscopy. Gamma camera imaging revealed focal cardiac (111)In accumulations up to 6 days after injection (N = 4). No MSC could be identified with FISH, and microscopy identified widespread acute inflammation. Focal (111)In accumulation, inflammation but no human MSC were similarly seen in pigs (N = 2) after immunosuppression. A comparable retention of (111)In activity was observed after intramyocardial injection of (111)In-tropolone (without cells) (N = 2), but without sign of myocardial inflammation. Injection of labeled non-viable cells (N = 1) also led to high focal (111)In activity up to 6 days after intramyocardial injection. As a positive control of the FISH method, we identified labeled cells both in culture and immediately after cell injection in one pig. This pilot trial suggests that after intramyocardial injection (111)In stays in the myocardium despite possible disappearance of labeled cells. This questions the clinical use of (111)In-labeled cells for tracking. The results further suggest that xenografting of human MSC into porcine hearts leads to inflammation contradicting previous studies implying a special immunoprivileged status for MSC.