Assessment of the green florescence protein labeling method for tracking implanted mesenchymal stem cells

Harnessing the potential of hydrogels for advanced therapeutic applications: current achievements and future directions

The applications of hydrogels have expanded significantly due to their versatile, highly tunable properties and breakthroughs in biomaterial technologies. In this review, we cover the major achievements and the potential of hydrogels in therapeutic applications, focusing primarily on two areas: emerging cell-based therapies and promising non-cell therapeutic modalities. Within the context of cell therapy, we discuss the capacity of hydrogels to overcome the existing translational challenges faced by mainstream cell therapy paradigms, provide a detailed discussion on the advantages and principal design considerations of hydrogels for boosting the efficacy of cell therapy, as well as list specific examples of their applications in different disease scenarios. We then explore the potential of hydrogels in drug delivery, physical intervention therapies, and other non-cell therapeutic areas (e.g., bioadhesives, artificial tissues, and biosensors), emphasizing their utility beyond mere delivery vehicles. Additionally, we complement our discussion on the latest progress and challenges in the clinical application of hydrogels and outline future research directions, particularly in terms of integration with advanced biomanufacturing technologies. This review aims to present a comprehensive view and critical insights into the design and selection of hydrogels for both cell therapy and non-cell therapies, tailored to meet the therapeutic requirements of diverse diseases and situations.

Emerging point-of-care autologous cellular therapy using adipose-derived stromal vascular fraction for neurodegenerative diseases

Neurodegenerative disorders are characterized by the gradual decline and irreversible loss of cognitive functions and CNS structures. As therapeutic recourse stagnates, neurodegenerative diseases will cost over a trillion dollars by 2050. A dearth of preventive and regenerative measures to hinder regression and enhance recovery has forced patients to settle for traditional therapeutics designed to manage symptoms, leaving little hope for a cure. In the last decade, pre-clinical animal models and clinical investigations in humans have demonstrated the safety and promise of an emerging cellular product from subcutaneous fat. The adipose-derived stromal vascular fraction (SVF) is an early intervention and late-stage novel 'at point' of care cellular treatment, demonstrating improvements in clinical applications for Multiple Sclerosis, Alzheimer's disease, and Parkinson's disease. SVF is a heterogeneous fraction of cells forming a robust cellular ecosystem and serving as a novel and valuable source of point-of-care autologous cell therapy, providing an easy-to-access population that we hypothesize can mediate repair through 'bi-directional' communication in response to pathological cues. We provide the first comprehensive review of all pre-clinical and clinical findings available to date and highlight major challenges and future directions. There is a greater medical and economic urgency to innovate and develop novel cellular therapy solutions that enable the repair and regeneration of neuronal tissue that has undergone irreversible and permanent damage.

Human Adipose Mesenchymal Stromal/Stem Cells Improve Fat Transplantation Performance

The resorption rate of autologous fat transfer (AFT) is 40–60% of the implanted tissue, requiring new surgical strategies for tissue reconstruction. We previously demonstrated in a rabbit model that AFT may be empowered by adipose-derived mesenchymal stromal/stem cells (AD-MSCs), which improve graft persistence by exerting proangiogenic/anti-inflammatory effects. However, their fate after implantation requires more investigation. We report a xenograft model of adipose tissue engineering in which NOD/SCID mice underwent AFT with/without human autologous AD-MSCs and were monitored for 180 days (d). The effect of AD-MSCs on AFT grafting was also monitored by evaluating the expression of CD31 and F4/80 markers. Green fluorescent protein-positive AD-MSCs (AD-MSC-GFP) were detected in fibroblastoid cells 7 days after transplantation and in mature adipocytes at 60 days, indicating both persistence and differentiation of the implanted cells. This evidence also correlated with the persistence of a higher graft weight in AFT-AD-MSC compared to AFT alone treated mice. An observation up to 180 d revealed a lower resorption rate and reduced lipidic cyst formation in the AFT-AD-MSC group, suggesting a long-term action of AD-MSCs in support of AFT performance and an anti-inflammatory/proangiogenic activity. Together, these data indicate the protective role of adipose progenitors in autologous AFT tissue resorption.

Microglia-derived CCL2 has a prime role in neocortex neuroinflammation

Background

In myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), several areas of demyelination are detectable in mouse cerebral cortex, where neuroinflammation events are associated with scarce inflammatory infiltrates and blood–brain barrier (BBB) impairment. In this condition, the administration of mesenchymal stem cells (MSCs) controls neuroinflammation, attenuating astrogliosis and promoting the acquisition of stem cell traits by astrocytes. To contribute to the understanding of the mechanisms involved in the pathogenesis of EAE in gray matter and in the reverting effects of MSC treatment, the neocortex of EAE-affected mice was investigated by analyzing the cellular source(s) of chemokine CCL2, a molecule involved in immune cell recruitment and BBB-microvessel leakage.

Methods

The study was carried out by immunohistochemistry (IHC) and dual RNAscope IHC/in situ hybridization methods, using astrocyte, NG2-glia, macrophage/microglia, and microglia elective markers combined with CCL2.

Results

The results showed that in EAE-affected mice, hypertrophic microglia are the primary source of CCL2, surround the cortex neurons and the damaged BBB microvessels. In EAE-affected mice treated with MSCs, microgliosis appeared diminished very soon (6 h) after treatment, an observation that was long-lasting (tested after 10 days). This was associated with a reduced CCL2 expression and with apparently preserved/restored BBB features. In conclusion, the hallmark of EAE in the mouse neocortex is a condition of microgliosis characterized by high levels of CCL2 expression.

Conclusions

This finding supports relevant pathogenetic and clinical aspects of the human disease, while the demonstrated early control of neuroinflammation and BBB permeability exerted by treatment with MSCs may have important therapeutic implications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00365-5.

Tracking of human embryonic stem cell-derived mesenchymal stem cells in premature ovarian failure model mice

Premature ovarian failure (POF) is defined by amenorrhea, hypoestrogenism, elevated gonadotropin levels, and infertility. Chemotherapeutic agents are the most gonadotoxic agents that lead to POF. Although some previous studies have presented that mesenchymal stem cells (MSCs) transplantation could rescue the ovary function of POF animal models through the paracrine pathway, these mechanisms require further investigation. However, mechanisms of embryonic stem cell-derived MSCs (ES-MSCs) therapeutic effects on POF animal models have not been fully investigated yet. This study aimed to evaluate the migration and distribution of ES-MSCs in a model of chemotherapy-induced POF. Female mice received intraperitoneal injections of cyclophosphamide (Cy) to induce POF. Then, MSCs were labeled with green fluorescent protein (GFP) in vitro and injected intravenously into POF mice, and the distribution of MSCs was dynamically monitored at 1 week after transplantation. We harvested the lungs, liver, spleen, ovaries, heart, and kidneys 1 week after transplantation. The sections of these tissues were observed under the fluorescent microscope. More than 70% MSCs were successfully labeled with GFP at 72 h after labeling. MSCs were uniformly distributed in multiple organs and tissues including lungs, liver, spleen, ovaries, heart, and kidneys of POF mice. In mice, at 1week after intravenous transplantation, GFP labeled ES-MSCs were observed in the lungs, liver, spleen, ovaries, heart, and kidneys of POF mice, and the number of GFP labeled ES-MSCs in lungs, ovaries, and heart were higher than that in the spleen, kidneys, and liver. Our results revealed intravenously implanted ES-MSCs could migrate into the various tissues in chemotherapy-induced damaged POF mice.

Distribution of the CM-Dil-Labeled Human Umbilical Cord Vein Mesenchymal Stem Cells Migrated to the Cyclophosphamide-Injured Ovaries in C57BL/6 Mice

Background

Mesenchymal stem cells (MSCs) can be used to treat premature ovarian failure (POF). Different methods have already been applied to detect MSCs in tissues. This study aimed to investigate the quantitative distribution of CM-DiI-labeled human umbilical cord vein MSCs (hUCV-MSCs) in different regions of the ovarian tissue of the cyclophosphamide (CTX)-induced POF in mice.

Methods

Adult female C57BL/6 mice (n = 40) were divided into four groups: (1) Mice receiving PBS as control (Ctrl) group; (2) mice receiving hUCV-MSCs intravenously as Ctrl + hUCV-MSCs group; (3) mice receiving CTX intraperitoneally (i.p.) as CTX group; (4) mice receiving CM-DiI-labeled hUCV-MSCs after CTX injection as CTX + hUCV-MSCs group. Histological changes and CM-DiI-labeled hUCV-MSCs distribution were analyzed in the ovarian tissues. Quantitative real-time PCR was performed to detect human mitochondrial cytochrome b (MTCYB) gene in the ovarian tissues of the mice.

Results

The mean number of the fluorescent hUCV-MSCs was 20 ± 2.5 (57.1%) in the medulla, 11.3 ± 2.8 (32.2%) in the cortex, and 5.5 ± 1 (15%) in the germinal epithelium of the ovarian tissue (p < 0.05). Moreover, MTCYB gene was detected in the mice ovaries of the CTX + hUCV-MSCs group, but not in other groups.

Conclusion

Our findings suggest that the distribution of the transplanted hUCV-MSCs in different regions of the ovarian tissue is not equal, and it is greater in the medulla than the cortex and germinal epithelium. This is the first report of quantitative distribution of MSCs in different regions of ovarian tissue in the POF model.

Distribution of the CM-Dil-Labeled Human Umbilical Cord Vein Mesenchymal Stem Cells Migrated to the Cyclophosphamide-Injured Ovaries in C57BL/6 Mice

Background

Mesenchymal stem cells (MSCs) can be used to treat premature ovarian failure (POF). Different methods have already been applied to detect MSCs in tissues. This study aimed to investigate the quantitative distribution of CM-DiI-labeled human umbilical cord vein MSCs (hUCV-MSCs) in different regions of the ovarian tissue of the cyclophosphamide (CTX)-induced POF in mice.

Methods

Adult female C57BL/6 mice (n = 40) were divided into four groups: (1) Mice receiving PBS as control (Ctrl) group; (2) mice receiving hUCV-MSCs intravenously as Ctrl + hUCV-MSCs group; (3) mice receiving CTX intraperitoneally (i.p.) as CTX group; (4) mice receiving CM-DiI-labeled hUCV-MSCs after CTX injection as CTX + hUCV-MSCs group. Histological changes and CM-DiI-labeled hUCV-MSCs distribution were analyzed in the ovarian tissues. Quantitative real-time PCR was performed to detect human mitochondrial cytochrome b (MTCYB) gene in the ovarian tissues of the mice.

Results

The mean number of the fluorescent hUCV-MSCs was 20 ± 2.5 (57.1%) in the medulla, 11.3 ± 2.8 (32.2%) in the cortex, and 5.5 ± 1 (15%) in the germinal epithelium of the ovarian tissue (p < 0.05). Moreover, MTCYB gene was detected in the mice ovaries of the CTX + hUCV-MSCs group, but not in other groups.

Conclusion

Our findings suggest that the distribution of the transplanted hUCV-MSCs in different regions of the ovarian tissue is not equal, and it is greater in the medulla than the cortex and germinal epithelium. This is the first report of quantitative distribution of MSCs in different regions of ovarian tissue in the POF model.

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.

Mineralocorticoid receptor deficiency improves the therapeutic effects of mesenchymal stem cells for myocardial infarction via enhanced cell survival

The poor survival of stem cells seriously limits their therapeutic efficacy for myocardial infarction (MI). Mineralocorticoid receptor (MR) activation plays an important role in the pathogenesis of multiple cardiovascular diseases. Here, we examined whether MR silencing in bone marrow derived mesenchymal stem cells (MSCs) could improve MSCs’ survival and enhance their cardioprotective effects in MI. MSCs from male Sprague‐Dawley rats were transfected with adenoviral small interfering RNA to silence MR (siRNA‐MR). MR silencing decreased hypoxia‐induced MSCs’ apoptosis, as demonstrated by Annexin V/7‐AAD staining. The mechanisms contributing to the beneficial effects of MR depletion were associated with inhibiting intracellular reactive oxygen species production and increased Bcl‐2/Bax ratio. In vivo study, 1 × 10⁶ of MSCs with or without siRNA‐MR were injected into rat hearts immediately after MI. Depletion of MR could improve the MSCs’ survival significantly in infarcted myocardium, associated with more cardiac function improvement and smaller infarct size. Capillary density were also significantly higher in siRNA group with increased expression of vascular endothelial growth factor. Our study demonstrated that silencing MR promoted MSCs’ survival and repair efficacy in ischaemic hearts. MR might be a potential target for enhancing the efficacy of cell therapy in ischaemic heart disease.

Organic Nanoparticles with Aggregation-Induced Emission for Bone Marrow Stromal Cell Tracking in a Rat PTI Model

Stem-cell based therapy is an emerging therapeutic approach for ischemic stroke treatment. Bone marrow stromal cells (BMSCs) are in common use as a cell source for stem cell therapy and show promising therapeutic outcomes for stroke treatment. One challenge is to develop a reliable tracking strategy to monitor the fate of BMSCs and assess their therapeutic effects in order to improve the success rate of such treatment. Herein, TPEEP, a fluorogen with aggregation-induced emission characteristics and near-infrared emission are designed and synthesized and further fabricated into organic nanoparticles (NPs). The obtained NPs show high fluorescence quantum yield, low cytotoxicity with good physical and photostability, which display excellent tracking performance of BMSCs in vitro and in vivo. Using a rat photothrombotic ischemia model as an example, the NP-labeled BMSCs are able to migrate to the stroke lesion site to yield bright red fluorescence. Immunofluorescence staining shows that the NP labeling does not affect the normal function of BMSCs, proving their good biocompatibility in vivo. These merits make TPEEP NP a potential cell tracker to evaluate the fate of BMSCs in cell therapy.

Bone repair with skeletal stem cells: rationale, progress to date and clinical application

Bone marrow (BM) contains stem cells for both hematopoietic and nonhematopoietic lineages. Hematopoietic stem cells enable hematopoiesis to occur in a controlled manner in order to accurately compensate for the loss of short- as well as long-lived mature blood cells. The physiological role of nonhematopoietic BM stem cells, often referred to as multipotential stromal cells or skeletal stem cells (SSCs), is less understood. According to an authoritative current opinion, the main function of SSCs is to give rise to cartilage, bone, marrow fat and hematopoiesis-supportive stroma, in a specific sequence during embryonic and postnatal development. This review outlines recent advances in the understanding of origins and homeostatic functions of SSCs in vivo and highlights current and future SSC-based treatments for skeletal and joint disorders.

The current 'state of play' of regenerative medicine in horses: what the horse can tell the human

The horse is an attractive model for many human age-related degenerative diseases of the musculoskeletal system because it is a large animal species that both ages and exercises, and develops naturally occurring injuries with many similarities to the human counterpart. It therefore represents an ideal species to use as a 'proving ground' for new therapies, most notably regenerative medicine. Regenerative techniques using cell-based therapies for the treatment of equine musculoskeletal disease have been in use for over a decade. This review article provides a summary overview of the sources, current challenges and problems surrounding the use of stem cell and non-cell-based therapy in regenerative medicine in horses and is based on presentations from a recent Havemeyer symposium on equine regenerative medicine where speakers are selected from leading authorities in both equine and human regenerative medicine fields from 10 different countries.

Finding and tracing human MSC in 3D microenvironments with the photoconvertible protein Dendra2

Mesenchymal Stem/Stromal Cells (MSC) are a promising cell type for cell-based therapies - from tissue regeneration to treatment of autoimmune diseases - due to their capacity to migrate to damaged tissues, to differentiate in different lineages and to their immunomodulatory and paracrine properties. Here, a simple and reliable imaging technique was developed to study MSC dynamical behavior in natural and bioengineered 3D matrices. Human MSC were transfected to express a fluorescent photoswitchable protein, Dendra2, which was used to highlight and follow the same group of cells for more than seven days, even if removed from the microscope to the incubator. This strategy provided reliable tracking in 3D microenvironments with different properties, including the hydrogels Matrigel and alginate as well as chitosan porous scaffolds. Comparison of cells mobility within matrices with tuned physicochemical properties revealed that MSC embedded in Matrigel migrated 64% more with 5.2 mg protein/mL than with 9.6 mg/mL and that MSC embedded in RGD-alginate migrated 51% faster with 1% polymer concentration than in 2% RGD-alginate. This platform thus provides a straightforward approach to characterize MSC dynamics in 3D and has applications in the field of stem cell biology and for the development of biomaterials for tissue regeneration.

Analgesia for neuropathic pain by dorsal root ganglion transplantation of genetically engineered mesenchymal stem cells: initial results

Background

Cell-based therapy may hold promise for treatment of chronic pain. Mesenchymal stem cells (MSCs) are readily available and robust, and their secretion of therapeutic peptides can be enhanced by genetically engineering. We explored the analgesic potential of transplanting bone marrow-derived MSCs that have been transduced with lentivectors. To optimize efficacy and safety, primary sensory neurons were targeted by MSC injection into the dorsal root ganglia (DRGs).

Results

MSCs were transduced using lentivectors to express enhanced green fluorescent protein (EGFP) or to co-express the analgesic peptide glial cell line-derived neurotrophic factor (GDNF) and EGFP by a viral 2A bicistronic transgene cassette. Engineered MSCs were injected into the 4^th lumbar (L4) and L5 DRGs of adult allogeneic rats to evaluate survival in the DRGs. MSCs were detected by immunofluorescence staining up to 2–3 weeks after injection, distributed in the extracellular matrix space without disrupting satellite glial cell apposition to sensory neurons, suggesting well-tolerated integration of engrafted MSCs into DRG tissue. To examine their potential for inhibiting development of neuropathic pain, MSCs were injected into the L4 and L5 DRGs ipsilateral to a spinal nerve ligation injury. Animals injected with GDNF-engineered MSCs showed moderate but significant reduction in mechanical allodynia and hyperalgesia compared to controls implanted with MSCs expressing EGFP alone. We also observed diminished long-term survival of allografted MSCs at 3 weeks, and the development of a highly-proliferating population of MSCs in 12% of DRGs after transplantation.

Conclusions

These data indicate that genetically modified MSCs secreting analgesic peptides could potentially be developed as a novel DRG-targeted cell therapy for treating neuropathic pain. However, further work is needed to address the challenges of MSC survival and excess proliferation, possibly with trials of autologous MSCs, evaluation of clonally selected populations of MSCs, and investigation of regulation of MSC proliferation.

Modulation of nuclear factor-κB-mediated pro-inflammatory response is associated with exogenous administration of bone marrow-derived mesenchymal stem cells for treatment of experimental colitis

Mesenchymal stem cells (MSCs) inhibit the immune response in vitro and prevent the induction of disease in certain experimental models. As a result, MSC‑mediated therapy is a rapidly growing field of research. However, the efficacy of MSCs in the treatment of inflammatory bowel disease (IBD) has remained to be determined. In the present study, rats with 2,4,6‑trinitrobenzene sulfonic acid (TNBS)‑induced colitis were injected with prepared MSCs (1x106) into the tail vein. Two weeks following intravenous MSC administration, the concentration of tumor necrosis factor‑α (TNF‑α) in the serum was measured by an ELISA. The protein expression of nuclear factor‑κB (NF‑κBp65) in the colonic mucosa was assessed by western blot analysis. mRNA expression of TNF‑α and NF‑κBp65 was determined by reverse‑transcription quantitative polymerase chain reaction. MSCs were shown to exert an immunomodulatory effect on TNBS‑induced colitis and may be of use in the treatment of IBD. In addition, modulation of the NF‑κB‑mediated pro‑inflammatory response may contribute to the underlying mechanism by which MSCs ameliorate the clinical and histological changes associated with IBD.

Comparison of chloromethyl-dialkylcarbocyanine and green fluorescent protein for labeling human umbilical mesenchymal stem cells

To investigate the effectiveness of chloromethyl-dialkylcarbocyanine (CM-Dil) and green florescent protein (GFP) for tracking transplanted stem human umbilical cord-derived mesenchymal stem cells (hUC-MSCs), hUC-MSCs were labeled with CM-Dil or GFP and transplanted into guinea pigs with nasal mucosa radiation injury. In vitro and in vivo labeling efficiency was investigated by flow cytometry and fluorescence microscopy. Proliferation and multi-lineage differentiation potential of labeled hUC-MSCs were assessed via cell quantification and specific staining. In vitro CM-Dil and GFP labeling efficiency was 95 ± 12.2 and 90 ± 8 % at first passage, respectively. Labeled hUC-MSCs were detected by fluorescence microscopy 10 days (CM-Dil) or 20 days (GFP) after transplantation. Neither type of cell labeling affected the multi-differentiation potential but GFP labeling inhibited hUC-MSC proliferation due to virus toxicity. hUC-MSCs can be labeled with either CM-Dil or GFP with high efficiency without impacting multi-differentiation potential.

Immunogenicity of allogeneic mesenchymal stem cells transplanted via different routes in diabetic rats

Due to their hypoimmunogenicity and unique immunosuppressive properties, mesenchymal stem cells (MSCs) are considered one of the most promising adult stem cell types for cell therapy. Although many studies have shown that MSCs exert therapeutic effects on several acute and subacute conditions, their long-term effects are not confirmed in chronic diseases. Immunogenicity is a major limitation for cell replacement therapy, and it is not well understood in vivo. We evaluated the immunogenicity of allogeneic MSCs in vivo by transplanting MSCs into normal and diabetic rats via the tail vein or pancreas and found that MSCs exhibited low immunogenicity in normal recipients and even exerted some immunosuppressive effects in diabetic rats during the initial phase. However, during the later stage in the pancreas group, MSCs expressed insulin and MHC II, eliciting a strong immune response in the pancreas. Simultaneously, the peripheral blood mononuclear cells in the recipients in the pancreas group were activated, and alloantibodies developed in vivo. Conversely, in the tail vein group, MSCs remained immunoprivileged and displayed immunosuppressive effects in vivo. These data indicate that different transplanting routes and microenvironments can lead to divergent immunogenicity of MSCs.

Enhancing the migration ability of mesenchymal stromal cells by targeting the SDF-1/CXCR4 axis

Mesenchymal stromal cells (MSCs) are currently being investigated in numerous clinical trials of tissue repair and various immunological disorders based on their ability to secrete trophic factors and to modulate inflammatory responses. MSCs have been shown to migrate to sites of injury and inflammation in response to soluble mediators including the chemokine stromal cell-derived factor-(SDF-)1, but during in vitro culture expansion MSCs lose surface expression of key homing receptors particularly of the SDF-1 receptor, CXCR4. Here we review studies on enhancement of SDF-1-directed migration of MSCs with the premise that their improved recruitment could translate to therapeutic benefits. We describe our studies on approaches to increase the CXCR4 expression in in vitro-expanded cord blood-derived MSCs, namely, transfection, using the commercial liposomal reagent IBAfect, chemical treatment with the histone deacetylase inhibitor valproic acid, and exposure to recombinant complement component C1q. These methodologies will be presented in the context of other cell targeting and delivery strategies that exploit pathways involved in MSC migration. Taken together, these findings indicate that MSCs can be manipulated in vitro to enhance their in vivo recruitment and efficacy for tissue repair.

Nanoparticles based stem cell tracking in regenerative medicine

Stem cell therapies offer great potentials in the treatment for a wide range of diseases and conditions. With so many stem cell replacement therapies going through clinical trials currently, there is a great need to understand the mechanisms behind a successful therapy, and one of the critical points of discovering them is to track stem cell migration, proliferation and differentiation in vivo. To be of most use tracking methods should ideally be non-invasive, high resolution and allow tracking in three dimensions. Magnetic resonance imaging (MRI) is one of the ideal methods, but requires a suitable contrast agent to be loaded to the cells to be tracked, and one of the most wide-spread in stem cell tracking is a group of agents known as magnetic nanoparticles. This review will explore the current use of magnetic nanoparticles in developing and performing stem cell therapies, and will investigate their potential limitations and the future directions magnetic nanoparticle tracking is heading in.