Labeling human mesenchymal stem cells with fluorescent contrast agents: the biological impact

Perovskites as Multiphoton Fluorescence Contrast Agents for In Vivo Imaging

Multiphoton fluorescence microscopy is a powerful tool for imaging and exploring biological tissue at subcellular spatial resolution while minimizing photobleaching and autofluorescence. For optimal performance in multiphoton microscopy, materials exhibiting a large multiphoton absorption cross section (σn) and fluorescence quantum yield are desired. Notably, perovskite nanocrystals (CsPbX3, PNCs) exhibit exceptionally large two-, three-, up to five photon absorption cross section (σ2 ∼ 106 GM, σ3 ∼ 10-73 cm6s2 photon-2, σ5 ∼ 10-136 cm10s4 photon-4), along with near unity fluorescence quantum yield, making them desirable for deep tissue applications. Here, we employed PNCs as contrast agents to image mesenchymal stromal cells in a living mouse. The PNCs were stabilized by encapsulating them in a SiO2 matrix (∼60-70 nm in diameter), offering versatility for subsequent surface modification to target specific biological entities for both diagnostic and therapeutic applications. Multiphoton imaging of PNCs offers substantial benefits for dynamic tracking of cells in deep tissue, such as in understanding immune cell migration and other biological processes in both healthy and diseased tissues.

Fluorescence-Based Mono- and Multimodal Imaging for In Vivo Tracking of Mesenchymal Stem Cells

The advancement of stem cell therapy has offered transformative therapeutic outcomes for a wide array of diseases over the past decades. Consequently, stem cell tracking has become significant in revealing the mechanisms of action and ensuring safe and effective treatments. Fluorescence stands out as a promising choice for stem cell tracking due to its myriad advantages, including high resolution, real-time monitoring, and multi-fluorescence detection. Furthermore, combining fluorescence with other tracking modalities-such as bioluminescence imaging (BLI), positron emission tomography (PET), photoacoustic (PA), computed tomography (CT), and magnetic resonance (MR)-can address the limitations of single fluorescence detection. This review initially introduces stem cell tracking using fluorescence imaging, detailing various labeling strategies such as green fluorescence protein (GFP) tagging, fluorescence dye labeling, and nanoparticle uptake. Subsequently, we present several combinations of strategies for efficient and precise detection.

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.

Rapid, label-free classification of tumor-reactive T cell killing with quantitative phase microscopy and machine learning

Quantitative phase microscopy (QPM) enables studies of living biological systems without exogenous labels. To increase the utility of QPM, machine-learning methods have been adapted to extract additional information from the quantitative phase data. Previous QPM approaches focused on fluid flow systems or time-lapse images that provide high throughput data for cells at single time points, or of time-lapse images that require delayed post-experiment analyses, respectively. To date, QPM studies have not imaged specific cells over time with rapid, concurrent analyses during image acquisition. In order to study biological phenomena or cellular interactions over time, efficient time-dependent methods that automatically and rapidly identify events of interest are desirable. Here, we present an approach that combines QPM and machine learning to identify tumor-reactive T cell killing of adherent cancer cells rapidly, which could be used for identifying and isolating novel T cells and/or their T cell receptors for studies in cancer immunotherapy. We demonstrate the utility of this method by machine learning model training and validation studies using one melanoma-cognate T cell receptor model system, followed by high classification accuracy in identifying T cell killing in an additional, independent melanoma-cognate T cell receptor model system. This general approach could be useful for studying additional biological systems under label-free conditions over extended periods of examination.

Using flow cytometry and multistage machine learning to discover label-free signatures of algal lipid accumulation

Most applications of flow cytometry or cell sorting rely on the conjugation of fluorescent dyes to specific biomarkers. However, labeled biomarkers are not always available, they can be costly, and they may disrupt natural cell behavior. Label-free quantification based upon machine learning approaches could help correct these issues, but label replacement strategies can be very difficult to discover when applied labels or other modifications in measurements inadvertently modify intrinsic cell properties. Here we demonstrate a new, but simple approach based upon feature selection and linear regression analyses to integrate statistical information collected from both labeled and unlabeled cell populations and to identify models for accurate label-free single-cell quantification. We verify the method’s accuracy to predict lipid content in algal cells (Picochlorum soloecismus) during a nitrogen starvation and lipid accumulation time course. Our general approach is expected to improve label-free single-cell analysis for other organisms or pathways, where biomarkers are inconvenient, expensive, or disruptive to downstream cellular processes.

Experimental Strategies of Mesenchymal Stem Cell Propagation: Adverse Events and Potential Risk of Functional Changes

Mesenchymal stem cells (MSCs) are attractive candidates for cell-based tissue repair approaches. Hundreds of clinical trials using MSCs have been completed and many others are still being investigated. For most therapeutic applications, MSC propagation in vitro is often required. However, ex vivo culture condition is not fully physiological and may affect biological properties of MSCs including their regenerative potential. Moreover, both cell cryopreservation and labelling procedure prior to infusion may have the negative impact on their expected effect in vivo. The incidence of MSC transformation during in vitro culture should be also taken into consideration before using cells in stem cell therapy. In our review, we focused on different aspects of MSC propagation that might influence their regenerative properties of MSC. We also discussed the influence of different factors that might abolish MSC proliferation and differentiation as well as potential impact of stem cell senescence and aging. Despite of many positive therapeutic effects of MSC therapy, one has to be conscious about potential cell changes that could appear during manufacturing of MSCs.

Nanobiosensing Platforms for Real-Time and Non-Invasive Monitoring of Stem Cell Pluripotency and Differentiation

Breakthroughs in the biomedical and regenerative therapy fields have led to the influential ability of stem cells to differentiate into specific types of cells that enable the replacement of injured tissues/organs in the human body. Non-destructive identification of stem cell differentiation is highly necessary to avoid losses of differentiated cells, because most of the techniques generally used as confirmation tools for the successful differentiation of stem cells can result in valuable cells becoming irrecoverable. Regarding this issue, recent studies reported that both Raman spectroscopy and electrochemical sensing possess excellent characteristics for monitoring the behavior of stem cells, including differentiation. In this review, we focus on numerous studies that have investigated the detection of stem cell pluripotency and differentiation in non-invasive and non-destructive manner, mainly by using the Raman and electrochemical methods. Through this review, we present information that could provide scientific or technical motivation to employ or further develop these two techniques for stem cell research and its application.

Characterization of the Tumor Microenvironment and Tumor-Stroma Interaction by Non-invasive Preclinical Imaging

Tumors are often characterized by hypoxia, vascular abnormalities, low extracellular pH, increased interstitial fluid pressure, altered choline-phospholipid metabolism, and aerobic glycolysis (Warburg effect). The impact of these tumor characteristics has been investigated extensively in the context of tumor development, progression, and treatment response, resulting in a number of non-invasive imaging biomarkers. More recent evidence suggests that cancer cells undergo metabolic reprograming, beyond aerobic glycolysis, in the course of tumor development and progression. The resulting altered metabolic content in tumors has the ability to affect cell signaling and block cellular differentiation. Additional emerging evidence reveals that the interaction between tumor and stroma cells can alter tumor metabolism (leading to metabolic reprograming) as well as tumor growth and vascular features. This review will summarize previous and current preclinical, non-invasive, multimodal imaging efforts to characterize the tumor microenvironment, including its stromal components and understand tumor-stroma interaction in cancer development, progression, and treatment response.

Deep Learning in Label-free Cell Classification

Label-free cell analysis is essential to personalized genomics, cancer diagnostics, and drug development as it avoids adverse effects of staining reagents on cellular viability and cell signaling. However, currently available label-free cell assays mostly rely only on a single feature and lack sufficient differentiation. Also, the sample size analyzed by these assays is limited due to their low throughput. Here, we integrate feature extraction and deep learning with high-throughput quantitative imaging enabled by photonic time stretch, achieving record high accuracy in label-free cell classification. Our system captures quantitative optical phase and intensity images and extracts multiple biophysical features of individual cells. These biophysical measurements form a hyperdimensional feature space in which supervised learning is performed for cell classification. We compare various learning algorithms including artificial neural network, support vector machine, logistic regression, and a novel deep learning pipeline, which adopts global optimization of receiver operating characteristics. As a validation of the enhanced sensitivity and specificity of our system, we show classification of white blood T-cells against colon cancer cells, as well as lipid accumulating algal strains for biofuel production. This system opens up a new path to data-driven phenotypic diagnosis and better understanding of the heterogeneous gene expressions in cells.

Magnetic resonance imaging of stem cell apoptosis in arthritic joints with a caspase activatable contrast agent

About 43 million individuals in the U.S. encounter cartilage injuries due to trauma or osteoarthritis, leading to joint pain and functional disability. Matrix-associated stem cell implants (MASI) represent a promising approach for repair of cartilage defects. However, limited survival of MASI creates a significant bottleneck for successful cartilage regeneration outcomes and functional reconstitution. We report an approach for noninvasive detection of stem cell apoptosis with magnetic resonance imaging (MRI), based on a caspase-3-sensitive nanoaggregation MRI probe (C-SNAM). C-SNAM self-assembles into nanoparticles after hydrolysis by caspase-3, leading to 90% amplification of (1)H MR signal and prolonged in vivo retention. Following intra-articular injection, C-SNAM causes significant MR signal enhancement in apoptotic MASI compared to viable MASI. Our results indicate that C-SNAM functions as an imaging probe for stem cell apoptosis in MASI. This concept could be applied to a broad range of cell transplants and target sites.

Effect of DiD Carbocyanine Dye Labeling on Immunoregulatory Function and Differentiation of Mice Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) have been used to treat a variety of degenerative disorders. Labeling of MSCs with an appropriate tracer is vital to demonstrate the in vivo engraftment and differentiation of transplanted MSCs. DiD is a lipophilic fluorescent dye with near infrared emission spectra that makes it suitable for in vivo tracing. Therefore, in the present study the consequences of DiD labeling on induction of oxidative stress and apoptosis as well as inhibition of biological functions of mesenchymal stem cells (MSCs) were investigated. DiD labeling did not provoke the production of ROS, induction of apoptosis, or inhibition of production of immunosuppressive factors (PGE2 and IL-10) by MSCs. In addition, there were no statistical differences between DiD-labeled and unlabeled MSCs in suppression of proliferation and cytokine production (IFN-γ and IL-17) by in vitro stimulated splenocytes or improvement of clinical score in EAE after in vivo administration. In addition, DiD labeling did not alter the differentiation capacity of MSCs. Taken together, DiD can be considered as a safe dye for in vivo tracking of MSCs.

Dose-response of superparamagnetic iron oxide labeling on mesenchymal stem cells chondrogenic differentiation: a multi-scale in vitro study

Aim

The aim of this work was the development of successful cell therapy techniques for cartilage engineering. This will depend on the ability to monitor non-invasively transplanted cells, especially mesenchymal stem cells (MSCs) that are promising candidates to regenerate damaged tissues.

Methods

MSCs were labeled with superparamagnetic iron oxide particles (SPIO). We examined the effects of long-term labeling, possible toxicological consequences and the possible influence of progressive concentrations of SPIO on chondrogenic differentiation capacity.

Results

No influence of various SPIO concentrations was noted on human bone marow MSC viability or proliferation. We demonstrated long-term (4 weeks) in vitro retention of SPIO by human bone marrow MSCs seeded in collagenic sponges under TGF-β1 chondrogenic conditions, detectable by Magnetic Resonance Imaging (MRI) and histology. Chondrogenic differentiation was demonstrated by molecular and histological analysis of labeled and unlabeled cells. Chondrogenic gene expression (COL2A2, ACAN, SOX9, COL10, COMP) was significantly altered in a dose-dependent manner in labeled cells, as were GAG and type II collagen staining. As expected, SPIO induced a dramatic decrease of MRI T2 values of sponges at 7T and 3T, even at low concentrations.

Conclusions

This study clearly demonstrates (1) long-term in vitro MSC traceability using SPIO and MRI and (2) a deleterious dose-dependence of SPIO on TGF-β1 driven chondrogenesis in collagen sponges. Low concentrations (12.5–25 µg Fe/mL) seem the best compromise to optimize both chondrogenesis and MRI labeling.

Protective effect and localization by optical imaging of human renal CD133+ progenitor cells in an acute kidney injury model

Recent approaches of regenerative medicine can offer a therapeutic option for patients undergoing acute kidney injury. In particular, mesenchymal stem cells were shown to ameliorate renal function and recovery after acute damage. We here evaluated the protective effect and localization of CD133⁺ renal progenitors from the human inner medulla in a model of glycerol‐induced acute tubular damage and we compared the results with those obtained with bone marrow‐derived mesenchymal stem cells. We found that CD133⁺ progenitor cells promoted the recovery of renal function, preventing tubular cell necrosis and stimulating resident cell proliferation and survival, similar to mesenchymal stem cells. In addition, by optical imaging analysis, CD133⁺ progenitor cells accumulated within the renal tissue, and a reduced entrapment in lung, spleen, and liver was observed. Mesenchymal stem cells were detectable at similar levels in the renal tissue, but a higher signal was present in extrarenal organs. Both cell types produced several cytokines/growth factors, suggesting that a combination of different mediators is involved in their biological action. These results indicate that human CD133⁺ progenitor cells are renotropic and able to improve renal regeneration in acute kidney injury.

In the present study, we found that administration of human CD133⁺ renal progenitors promoted renal repair after murine AKI, similar to mesenchymal stem cells. In addition, these cells showed a high renal localization evaluated by optical imaging analysis, and the production of renoprotective factors. Mesenchymal stem cells were detectable at similar levels in the renal tissue, but a higher signal was present in extrarenal organs.

Biodistribution of mesenchymal stem cell-derived extracellular vesicles in a model of acute kidney injury monitored by optical imaging

Mesenchymal stem cells (MSCs) contribute to the recovery of tissue injury, providing a paracrine support. Cell-derived extracellular vesicles (EVs), carrying membrane and cytoplasmatic constituents of the cell of origin, have been described as a fundamental mechanism of intercellular communication. We previously demonstrated that EVs derived from human MSCs accelerated recovery following acute kidney injury (AKI) in vivo. The aim of the present study was to investigate the biodistribution and the renal localization of EVs in AKI. For this purpose, two methods for EV labeling suitable for in vivo tracking with optical imaging (OI), were employed using near infrared (NIR) dye (DiD): i) labeled EVs were generated by MSCs pre-incubated with NIR dye and collected from cell supernatants; ii) purified EVs were directly labeled with NIR dye. EVs obtained with these two procedures were injected intravenously (i.v.) into mice with glycerol-induced AKI and into healthy mice to compare the efficacy of the two labeling methods for in vivo detection of EVs at the site of damage. We found that the labeled EVs accumulated specifically in the kidneys of the mice with AKI compared with the healthy controls. After 5 h, the EVs were detectable in whole body images and in dissected kidneys by OI with both types of labeling procedures. The directly labeled EVs showed a higher and brighter fluorescence compared with the labeled EVs produced by cells. The signal generated by the directly labeled EVs was maintained in time, but provided a higher background than that of the labeled EVs produced by cells. The comparison of the two methods indicated that the latter displayed a greater specificity for the injured kidney.

Silica nanoparticles for cell imaging and intracellular sensing

There is increasing interest in the use of nanoparticles (NPs) for biomedical applications. In particular, nanobiophotonic approaches using fluorescence offers the potential of high sensitivity and selectivity in applications such as cell imaging and intracellular sensing. In this review, we focus primarily on the use of fluorescent silica NPs for these applications and, in so doing, aim to enhance and complement the key recent review articles on these topics. We summarize the main synthetic approaches, namely the Stöber and microemulsion processes, and, in this context, we deal with issues in relation to both covalent and physical incorporation of different types of dyes in the particles. The important issue of NP functionalization for conjugation to biomolecules is discussed and strategies published in the recent literature are highlighted and evaluated. We cite recent examples of the use of fluorescent silica NPs for cell imaging in the areas of cancer, stem cell and infectious disease research, and we review the current literature on the use of silica NPs for intracellular sensing of oxygen, pH and ionic species. We include a short final section which seeks to identify the main challenges and obstacles in relation to the potential widespread use of these particles for in vivo diagnostics and therapeutics.

Intracellular aggregation of multimodal silica nanoparticles for ultrasound-guided stem cell implantation

The promises of cardiac stem cell therapy have yet to be fully realized, in part because of poor survival and engraftment efficacy of implanted cells. Cells die after implantation owing to ischemia, inflammation, immune response, as well as mis-injection or implantation into fibrotic tissue. Imaging tools can help implant cells in areas of the heart most receptive to stem cell therapy and monitor the efficacy of treatment by reporting the viability, location, and number of implanted stem cells. We describe a multimodal, silica-based nanoparticle that can be used for cell sorting (fluorescence), real-time guided cell implantation ultrasound, and high-resolution, long-term monitoring by magnetic resonance imaging (MRI). The nanoparticle agent increased the ultrasound and MRI contrast of labeled human mesenchymal stem cells (hMSCs) 700 and 200% versus unlabeled cells, respectively, and allowed cell imaging in animal models for 13 days after implantation. The agent had no significant impact on hMSC cell metabolic activity, proliferation, or pluripotency, and it increased the production of many paracrine factors implicated in cardiac repair. Electron microscopy and ultrasound imaging suggest that the mechanism of action is in vivo aggregation of the 300-nm silica nanoparticles into larger silica frameworks that amplify the ultrasound backscatter. The detection limit in cardiac tissue was 250,000 hMSCs via MRI and 70,000 via ultrasound. This ultrasound-guided cell delivery and multimodal optical/ultrasound/MRI intracardiac cell-tracking platform could improve cell therapy in the clinic by minimizing misdelivery or implantation into fibrotic tissue.

Ferumoxytol: a new, clinically applicable label for stem-cell tracking in arthritic joints with MRI

AIM

To develop a clinically applicable MRI technique for tracking stem cells in matrix-associated stem-cell implants, using the US FDA-approved iron supplement ferumoxytol.

MATERIALS & METHODS

Ferumoxytol-labeling of adipose-derived stem cells (ADSCs) was optimized in vitro. A total of 11 rats with osteochondral defects of both femurs were implanted with ferumoxytol- or ferumoxides-labeled or unlabeled ADSCs, and underwent MRI up to 4 weeks post matrix-associated stem-cell implant. The signal-to-noise ratio of different matrix-associated stem-cell implant was compared with t-tests and correlated with histopathology.

RESULTS

An incubation concentration of 500 µg iron/ml ferumoxytol and 10 µg/ml protamine sulfate led to significant cellular iron uptake, T2 signal effects and unimpaired ADSC viability. In vivo, ferumoxytol- and ferumoxides-labeled ADSCs demonstrated significantly lower signal-to-noise ratio values compared with unlabeled controls (p < 0.01). Histopathology confirmed engraftment of labeled ADSCs, with slow dilution of the iron label over time.

CONCLUSION

Ferumoxytol can be used for in vivo tracking of stem cells with MRI.

Human liver stem cells improve liver injury in a model of fulminant liver failure

Liver transplantation is currently the only effective therapy for fulminant liver failure, but its use is limited by the scarcity of organs for transplantation, high costs, and lifelong immunosuppression. Here we investigated whether human liver stem cells (HLSCs) protect from death in a lethal model of fulminant liver failure induced by intraperitoneal injection of D-galactosamine and lipopolysaccharide in SCID mice. We show that injection of HLSCs and of HLSC-conditioned medium (CM) significantly attenuates mouse mortality in this model. Histopathological analysis of liver tissue showed reduction of liver apoptosis and enhancement of liver regeneration. By optical imaging we observed a preferential localization of labeled HLSCs within the liver. HLSCs were detected by immunohistochemistry in large liver vessels (at 24 hours) and in the liver parenchyma (after day 3). Fluorescence in situ hybridization analysis with the human pan-centromeric probe showed that positive cells were cytokeratin-negative at 24 hours. Coexpression of cytokeratin and human chromosome was observed at 7 and, to a lesser extent, at 21 days. HLSC-derived CM mimicked the effect of HLSCs in vivo. Composition analysis of the HLSC-CM revealed the presence of growth factors and cytokines with liver regenerative properties. In vitro experiments showed that HLSC-CM protected human hepatocytes from apoptosis and enhanced their proliferation.

CONCLUSION

These data suggest that fulminant liver failure may potentially benefit from treatment with HLSCs or HLSC-CM.

Canine mesenchymal stem cells are effectively labeled with silica nanoparticles and unambiguously visualized in highly autofluorescent tissues

Background

Development of a method for long-term labeling of cells is critical to elucidate transplanted cell fate and migration as well as the contribution to tissue regeneration. Silica nanoparticles have been recently developed and demonstrated to be biocompatible with a high labeling capacity. Thus, our study was designed to assess the suitability of silica nanoparticles for labeling canine mesenchymal stem cells (MSCs) and the fluorescence afficiency in highly autofluorescent tissue.

Results

We examined the effect of silica nanoparticle labeling on stem cell morphology, viability and differentiation as compared with those of unlabeled control cells. After 4 h of incubation with silica nanoparticles, they were internalized by canine MSCs without a change in the morphology of cells compared with that of control cells. The viability and proliferation of MSCs labeled with silica nanoparticles were evaluated by a WST-1 assay and trypan blue exclusion. No effects on cell viability were observed, and the proliferation of canine MSCs was not inhibited during culture with silica nanoparticles. Furthermore, adipogenic and osteogenic differentiation of silica nanoparticle-labeled canine MSCs was at a similar level compared with that of unlabeled cells, indicating that silica nanoparticle labeling did not alter the differentiation capacity of canine MSCs. Silica nanoparticle-labeled canine MSCs were injected into the kidneys of BALB/c mice after celiotomy, and then the mice were sacrificed after 2 or 3 weeks. The localization of injected MSCs was closely examined in highly autofluorescent renal tissues. Histologically, canine MSCs were uniformly and completely labeled with silica nanoparticles, and were unambiguously imaged in histological sections.

Conclusions

The results of the current study showed that silica nanoparticles are useful as an effective labeling marker for MSCs, which can elucidate the distribution and fate of transplanted MSCs.

Cell motility of neural stem cells is reduced after SPIO-labeling, which is mitigated after exocytosis

MRI is used for tracking of superparamagnetic iron oxide (SPIO)-labeled neural stem cells. Studies have shown that long-term MR tracking of rapidly dividing cells underestimates their migration distance. Time-lapse microscopy of random cellular motility and cell division was performed to evaluate the effects of SPIO-labeling on neural stem cell migration. Labeled cells divided symmetrically and exhibited no changes in cell viability, proliferation, or apoptosis. However, SPIO-labeling resulted in decreased motility of neural stem cells as compared with unlabeled controls. When SPIO-labeled neural stem cells and human induced pluripotent stem cells were transplanted into mouse brain, rapid exocytosis of SPIO by live cells was observed as early as 48 h postengraftment, with SPIO-depleted cells showing the farthest migration distance. As label dilution is negligible at this early time point, we conclude that MRI underestimation of cell migration can also occur as a result of reduced cell motility, which appears to be mitigated following SPIO exocytosis.

Emerging therapeutic approaches for multipotent mesenchymal stromal cells

PURPOSE OF REVIEW

Multipotent mesenchymal stromal cells (MSCs) are rare cells resident in bone marrow and other organs capable of differentiating into mesodermal lineage tissues. MSCs possess immunomodulatory properties and have extensive capacity for ex-vivo expansion. Early clinical studies demonstrated safety and feasibility of infusing autologous MSCs and suggested a role in enhancing engraftment after hematopoietic cell transplant (HCT). Subsequent pilot studies using allogeneic MSCs showed safety but presented contradictory results regarding efficacy in treating graft-versus-host disease (GVHD).

RECENT FINDINGS

Larger, phase II allogeneic MSC infusion studies, including cells obtained from haploidentical and third-party donors, showed efficacy in GVHD treatment; however, recent randomized, placebo-controlled studies failed to corroborate these results. New investigations include MSC infusions in umbilical cord blood transplantation, MSC therapy for tissue regeneration/repair, harvest and use of MSCs from adipose tissue and cell-tracking/imaging studies using radionuclides, gene and fluorescent dye-labeled MSCs.

SUMMARY

MSCs remain the subject of intense investigation in HCT because of their differentiation potential and immunomodulatory properties. Whereas infusions of autologous, allogeneic and third-party donor MSCs are well tolerated, further research is needed to clarify the optimal methods for harvesting and expansion, optimal timing of administration and efficacy in the setting of HCT.

In vivo magnetic resonance imaging and optical imaging comparison of viable and nonviable mesenchymal stem cells with a bifunctional label

The purpose of this study was to compare viable and nonviable bilabeled mesenchymal stem cells (MSCs) in arthritic joints with magnetic resonance imaging (MRI) and optical imaging (OI). MSCs were labeled with ferucarbotran and DiD. MRI and OI of bilabeled cells were compared with controls. Six rats with arthritis received intra-articular injections of bilabeled viable MSCs into the right knee and nonviable MSCs into the left knee. Animals underwent MRI and OI preinjection and at 4, 24, 48, and 72 hours postinjection. The results were analyzed with a mixed random effects model and Fisher probability. Bilabeled MSCs showed increased MRI and OI signals compared to unlabeled controls (p < .0001). After intra-articular injection, bilabeled MSCs caused significant T2 and T2* effect on MRI and fluorescence on OI up to 72 hours postinjection (p < .05). There was no significant difference between viable and nonviable MSC signal in the knee joints; however, some of the viable cells migrated to an adjacent inflamed ankle joint (p < .05). Immunohistochemistry confirmed viable MSCs in right knee and ankle joints and nonviable MSCs in the left knee. Viable and nonviable cells could not be differentiated with MRI or OI signal intensity but were differentiated based on their ability to migrate in vivo.