Current Status and Perspectives of Human Mesenchymal Stem Cell TherapyView this Special Issue
Review Article | Open Access
Ross E. B. Fitzsimmons, Matthew S. Mazurek, Agnes Soos, Craig A. Simmons, "Mesenchymal Stromal/Stem Cells in Regenerative Medicine and Tissue Engineering", Stem Cells International, vol. 2018, Article ID 8031718, 16 pages, 2018. https://doi.org/10.1155/2018/8031718
Mesenchymal Stromal/Stem Cells in Regenerative Medicine and Tissue Engineering
As a result of over five decades of investigation, mesenchymal stromal/stem cells (MSCs) have emerged as a versatile and frequently utilized cell source in the fields of regenerative medicine and tissue engineering. In this review, we summarize the history of MSC research from the initial discovery of their multipotency to the more recent recognition of their perivascular identity in vivo and their extraordinary capacity for immunomodulation and angiogenic signaling. As well, we discuss long-standing questions regarding their developmental origins and their capacity for differentiation toward a range of cell lineages. We also highlight important considerations and potential risks involved with their isolation, ex vivo expansion, and clinical use. Overall, this review aims to serve as an overview of the breadth of research that has demonstrated the utility of MSCs in a wide range of clinical contexts and continues to unravel the mechanisms by which these cells exert their therapeutic effects.
By merit of their regenerative secretome and their capacity for differentiation toward multiple mesenchymal lineages, the fibroblastic cell type termed mesenchymal stromal/stem cells (MSCs) shows promise for a wide range of tissue engineering and regenerative medicine applications (Figure 1). As a result of their therapeutic versatility and the multitude of promising clinical results thus far, MSCs are poised to become an increasingly significant cell source for regenerative therapies as medicine evolves to focus on personalized and cell-based therapeutics. Given their emerging importance, this review aims to provide an overview of historical and ongoing work aimed at understanding and better utilizing these cells for therapeutic purposes.
2. Initial Discoveries and the Evolving Definition of “MSC”
The initial discovery of MSCs is attributed to Friedenstein et al. who discovered a fibroblastic cell type derived from mouse and guinea pig bone marrow that could produce clonal colonies capable of generating bone and reticular tissue when heterotopically transplanted [1, 2]. The subsequent discovery that colonies of this cell type can generate cartilage and adipose tissue, in addition to bone, gave rise to the descriptor mesenchymal stem cells, as originally coined by Arnold Caplan . Finally, Pittenger et al. established that human bone marrow also contains a subpopulation of stromal cells that are genuinely multipotent stem cells by demonstrating single colonies have trilineage mesenchymal potential .
Over time, the acronym MSC has come to take on multiple meanings including, mesenchymal stem cell, mesenchymal stromal cell, and multipotent stromal cell. To help clarify this, the International Society for Cellular Therapy (ISCT) has officially defined MSCs as multipotent mesenchymal stromal cells and suggests this to mean the plastic-adherent fraction from stromal tissues, while reserving the term mesenchymal stem cells to mean the subpopulation that actually has the two cardinal stem cell properties (i.e., self-renewal and the capacity to differentiate down multiple lineages) . Furthermore, ISCT has also defined MSCs as meeting several criteria including (i) being plastic adherent, (ii) having osteogenic, adipogenic, and chondrogenic trilineage differentiation potential, (iii) and being positive (>95%) and negative (<2%) for a panel of cell surface antigens. Positive markers for human MSCs include CD73 (also present on lymphocytes, endothelial cells, smooth muscle cells, and fibroblasts), CD90 (also present on hematopoietic stem cells, lymphocytes, endothelial cells, neurons, and fibroblasts), and CD105 (also found on endothelial cells, monocytes, hematopoietic progenitors, and fibroblasts) . Negative markers include CD34 (present on hematopoietic progenitors and endothelial cells), CD45 (a pan-leukocyte marker), CD14 or CD11b (present on monocytes and macrophages), CD79-α or CD19 (present on B cells), and HLA-DR unless stimulated with IFN-γ (present on macrophages, B cells, and dendritic cells) . It should be noted, however, that the validity of CD34 as a negative marker has recently been called into question and may require reexamination [6, 7].
As these elaborate inclusionary and exclusionary criteria highlight, no single MSC-specific epitope has been discovered, unlike for some other stem cell populations (e.g., LGR5, which labels resident stem cells in hair follicles and intestinal crypts) [8, 9]. However, some markers may be used to enrich for the stem cell population, including Stro-1, CD146, CD106, CD271, MSCA-1, and others (Table 1) [6, 10–13]. This unfortunate lack of a single definitive marker continues to confound the interpretation of a broad range of studies given that sorting out the canonical MSC population from the adherent fraction is rarely done, leading to the perennial question of which subpopulation in the adherent stromal fraction is actually eliciting the observed effects. This lack of a definitive MSC marker has also contributed to the challenge of delineating the exact in vivo location, function, and developmental origin of MSCs.
Bolded text indicates markers recommended by the International Society for Cellular Therapy (ISCT) for minimally defining human multipotent mesenchymal stromal cells by positive and negative selection.
3. MSC Adult Anatomical Location
In the bone marrow, where MSCs were first discovered, MSCs have been reported to typically localize near the sinusoidal endothelium in close association with the resident hematopoietic stem cells (HSCs) [14, 15]. In addition to serving as osteogenic progenitors, such MSCs have been shown to play an important role in regulating HSC function by maintaining the HSC niche and by secreting trophic factors such as angiopoietin 1 (Ang1), stem cell factor (SCF), and CXC ligand 12 (CXCL12) . Beyond the bone marrow, MSC/MSC-like populations have also been found in many adult tissues (e.g., skin, pancreas, heart, brain, lung, kidney, adipose tissue, cartilage, and tendon) [16–19]. Such a broad anatomical distribution would suggest a common and ubiquitous MSC niche exists throughout the body. Indeed, evidence suggests that many MSC populations are specifically located near blood vessels and are in fact a subpopulation of pericytes that reside on capillaries and venules . Supporting observations include the fact that pericytes and MSCs express similar surface antigens, and that cells in perivascular positions were found to express MSC markers in human bone marrow and dental pulp [16, 21]. Perhaps most definitively, Crisan et al. found that cells positive for NG2, CD146, and PDGFR-β specifically stained pericytes in multiple human tissues, and when cells with these markers were isolated, they were shown to have trilineage potential in vitro and were osteogenic once transplanted in vivo . The converse, that all pericytes are MSCs, is not thought to be the case .
In addition to being abluminal to microvessels, it should be noted that a Gli1+ MSC-like population has also been found to reside within the adventitia of larger vessels in mice. The Gli1+ population exhibits trilineage differentiation in vitro and is thought to play a role in arterial calcification in vivo [23–25]. Similarly, a MSC population with a CD34+ CD31− CD146− CD45− phenotype has been discovered to reside within the adventitia of human arteries and veins suggesting that not all perivascular MSCs are pericyte-like cells in humans . Furthermore, a MSC population has also been isolated from the perivascular tissue of umbilical cords (human umbilical cord perivascular cells (HUCPVCs)) which shows promise for tissue engineering applications given the cells’ noninvasive extraction and their relatively high abundance and proliferative capacity, compared to bone marrow-derived MSCs [26–28].
Finally, despite the prevalent view that MSCs reside in perivascular niches, some MSC populations may reside in avascular regions as well. For example, a lineage tracing study focused on murine tooth repair demonstrated that while some odontoblasts descend from cells expressing the pericyte marker, NG2, the majority of odontoblasts did not, suggestive of a nonpericyte origin (or at least not from NG2-positive pericytes) . Additionally, MSCs have been isolated from tissues that are typically avascular, including human synovial tissue [30–32] and porcine aortic valve . However, there are fenestrated capillaries localized near the synovial surface , and diseased sclerotic and stenotic valves can be partially vascularized [35, 36], raising the possibility of MSCs trafficking from one anatomical location to another (e.g., synovium-associated vasculature to avascular cartilage) and innate differences in the local presence or absence of perivascular MSCs. Future work focused on these questions will have important implications for understanding disease progression and potential regenerative avenues.
4. MSC Developmental Origins
Presently, there are considered to be multiple developmental origins of MSCs. Unsurprisingly, given their mesenchymal differentiation potential, certain subsets of MSCs are derived from mesodermal precursors, such as lateral plate mesoderm- (LPM-) derived mesoangioblast cells from the embryonic dorsal aorta [37, 38]. Support for this comes from the observation that mesoangioblast cells isolated from the mouse dorsal aorta and then grafted into chick embryos incorporated into several mesodermal tissues (bone, cartilage, muscle, and blood) .
Other reports suggest MSCs partly descend from a subpopulation of neural crest cells, with the remaining MSCs descending from unknown origins. Support for this comes from the observation that a population of murine Sox1+ trunk neuroepithelial cells could undergo clonogenic expansion and maintain adipogenic, chondrogenic, and osteogenic differentiation in vitro . This neural crest origin may help explain why MSCs have neural differentiation potential and why human bone marrow-derived MSCs can be enriched for using antibodies against nerve growth factor receptor [12, 38]. Given their lineage tracing results, the authors claimed that neural crest-derived MSCs are the earliest MSCs to arise in the embryo, but they did note that other MSCs must also arise later on in development as not all MSCs detected were found to be of a neural crest origin. Corroborating this, a lineage tracing study using the promoter from Protein-0, a neural crest-associated marker, found that only a portion of bone marrow-derived MSCs were labeled in adult mice, suggestive of both a neural crest and nonneural crest origin .
It is possible that the indefinite nonneural crest source of MSCs observed in these studies may be mesoangioblasts or another mesoderm-derived cell type. It has also been suggested that data indicative of a mesoangioblast origin may alternatively be explained by simply “contamination” of neural crest cells as the neural tube is close to dorsal aorta at day 9.5 . With regard to human MSC origins, similar dual mesoderm and neural crest origins may also exist given that human iPSCs differentiated toward these two lineages can both give rise to MSC-like cells [42, 43]. Further study will be required to resolve these issues and to elucidate if any lasting functional dissimilarities exist between MSC subpopulations that arise from differing time periods and locations during development.
5. MSC Expansion in Culture
Once isolated from their respective in vivo locations, human MSC populations can be expanded up to several hundredfold while maintaining their multipotency and capacity to form fibroblastic colony-forming units (CFU-F) provided the cells are seeded at a satisfactorily low seeding density (~10–100 cell/cm2) . When cultured at low clonal density, MSCs take on a highly proliferative phenotype and maintain their trilineage potential; such cells have become commonly referred to as RS-MSCs (rapidly self-renewing MSCs). This proliferative phase is thought to be dependent on Dickkopf-related protein 1 (Dkk-1) autocrine signaling which inhibits Wnt signaling that would otherwise promote differentiation . Favorable for minimizing risk to patients, in vitro proliferation of human MSCs exhibits a relatively low frequency of oncogenic transformation (<10−9) [46–48]. This is in stark contrast with murine MSCs which frequently gain chromosomal defects in vitro and often produce fibrosarcomas when injected back into mice .
With time, sparsely plated human MSCs create colonies with distinct in vitro niches with the inner cells expressing differentiation markers and the outer cells exhibiting a more RS-MSC phenotype with high motility and proliferation [50, 51]. Yet, when replated, both inner and outer regions create colonies similar to the original, implying differentiation of the inner colony is reversible to some extent . If MSCs are seeded at a higher density (~1000 cell/cm2) and/or are cultured to confluence, RS-MSCs will decrease and SR-MSCs (slowly replicating MSCs) will increase over time, while both the CFU-F and proportion of multipotent cells will gradually decline [44, 51]. This dynamic nature during culture underlines the importance of properly maintaining MSC cultures to ensure maximum self-renewal and the maintenance of differentiation potential for downstream applications.
6. MSC Differentiation Potential
As mentioned earlier, by definition, MSCs have trilineage potential with the capacity to undergo osteogenesis, adipogenesis, and chondrogenesis contingent on their exposure to the particular soluble factors in their microenvironment. Differentiation protocols for driving differentiation toward these lineages have been routinely utilized and extensively optimized [52, 53]. For example, osteogenesis typically involves the use of dexamethasone, β-glycerolphosphate, and ascorbic acid. Adipogenesis protocols also utilize dexamethasone, in addition to isobutylmethylxanthine and indomethacin. Chondrogenesis protocols, on the other hand, typically utilize dexamethasone, ascorbic acid, sodium pyruvate, TGF-β1, and a combination of insulin-transferrin-selenium (ITS). However, variations of the components and their concentrations exist and the optimal formulations may depend on the subpopulation of MSC used and the ultimate therapeutic goal. MSCs predifferentiated toward these three lineages have been investigated extensively in the context of tissue engineering wherein cells are implanted at the site of desired repair or replacement, often along with a scaffold (Figure 1) [54–58].
Beyond the standard trilineage potential of MSCs, differentiation has also been observed toward other cell types, such as tenocytes, skeletal myocytes, cardiomyocytes, smooth muscle cells, and even neurons [59–61]. However, some of these claims have courted a degree of skepticism in regard to the frequency of differentiation and the functionality of the terminal cells produced, especially for nonmesenchymal and nonmesodermal cell types. For example, while MSCs have been shown to differentiate into neuron-like cells, the functionality of rat MSC-derived neurons has been called into question in terms of their capacity to generate normal action potentials [62, 63]. Similarly, human MSCs have also been reported to differentiate into endothelial-like cells; however, such cells have lower expression of endothelial markers compared to mature endothelial cells . Further study into the differentiation frequency and normal functioning of MSC-derived terminally differentiated cells will be necessary, in addition to determining if different MSC populations are better suited to differentiate into some cell types than others. With regard to the latter, a recent study comparing human CD146+/CD34−/CD45− MSCs isolated from different anatomical locations (bone marrow, periosteum, and skeletal muscle) revealed that each subpopulation differed considerably in their transcriptomic signature and in vivo differentiation potential, hence suggesting that MSCs are not a uniform population throughout the body . Moreover, MSC heterogeneity may not only exist between tissue types but also within individual tissues. For example, locationally and transcriptionally distinct subpopulations of CD34+/CD146− “adventitial MSCs” and CD34−/CD146+ “pericyte-like MSCs” have been found to reside in human adipose tissue, a commonly used cell source for regenerative medicine . Similar findings have also been noted in horses and canines, suggesting these dual perivascular subpopulations are conserved in mammals [67, 68]. Interestingly, both equine and human adipose-derived CD34−/CD146+ MSCs display greater angiogenicity compared to CD34+/CD146− MSCs indicative of a relatively conserved functional phenotype as well, possibly due to their pericyte-like differentiation state [67, 69]. Heterogeneity among MSCs may also have important implications for treating disease resulting from inappropriate differentiation and proliferation. Of note, subsets of PDGFRβ+ and/or PDGFRα+ MSC-like progenitor cells with fibro-adipogenic potential have been found to be present in multiple tissues (e.g., tendon, myocardium, and skeletal muscle) and may prove to be useful targets for reducing fibrotic damage after injury [70, 71]. Further investigation into MSC heterogeneity will be required to resolve if such differences are solely a result of innate differences arising from different developmental origins or if differing local microenvironments also play a role.
Unlike some other stem cell populations (e.g., hematopoietic stem cells), which have a well-established and relatively straight-forward unidirectional differentiation hierarchy, the hierarchy of MSC differentiation is currently poorly defined. To date, one of the MSC-like populations that have been most vigorously investigated in terms of hierarchy are human umbilical cord-perivascular cells (HUCPVCs). Such cells have been found to differentiate from quintipotential stem cells (with osteogenic, adipogenic, chondrogenic, myogenic, and fibrogenic potential) to a restricted fibroblast-state in a deterministic manner with a predictable order of loss in potency . Whether this is true for all or some MSC populations remains to be examined, but this study should serve as a useful template for future investigation. As well, computational approaches that cluster cells according to differentially expressed genes may also help clarify the hierarchy of MSC subpopulations and their progeny cells  and may serve as a guide for future lineage tracing studies. That said, transdifferentiation toward nonmesodermal lineages and bidirectional phenotype switching between different mesenchymal cell types (e.g., transitions between fibroblasts and myofibroblasts or between synthetic and contractile smooth muscle cells) may further complicate any MSC hierarchical differentiation model established . Regardless of any specific hierarchy and the potential for phenotypic plasticity, it should be emphasized that ultimately, the microenvironment dictates MSC behaviour, in terms of both their differentiation and their interaction with other cell types.
7. MSC Immunomodulatory Paracrine Signaling
Recently, a paradigm shift has occurred in the understanding of the therapeutic effects of MSCs. Despite the differentiation potential these cells exhibit and contrary to initial assumptions, in many therapeutic contexts, MSCs exert their healing effects not through engraftment and differentiation but rather through paracrine signaling and communication through cell-cell contacts [51, 74]. The significance of this paradigm change is reflected in the recent recommendation to rebrand MSCs as medicinal signaling cells by Arnold Caplan, who had originally coined the term mesenchymal stem cells . Notable examples of MSC paracrine/juxtacrine-mediated treatments currently in preclinical and clinical development include injections into the myocardium after infarction, treatments for graft versus host disease (GvHD), and therapies for autoimmunity disorders (such as Crohn’s disease and type I diabetes) [76–79]. Given these successes, it is becoming increasing clear that the MSC secretome has broadly beneficial effects that can be exploited for a wide range of therapeutic applications.
The MSC secretome contains a large range of molecules that are beneficial for tissue repair, including ligands that promote the proliferation and differentiation of other stem/progenitor cells, chemoattraction, antifibrosis, antiapoptosis, angiogenesis, and immunomodulation . Currently, perhaps the most impactful of these properties from a clinical perspective is their capacity for immunomodulation, which has motivated the development of intravenous injections of MSCs, such as Osiris Therapeutics’ Prochymal®, which is approved for GvHD in Canada and currently in clinical trials for several autoimmune disorders in Canada and the USA. This immunomodulatory capacity has been partly attributed to the ability of MSCs to inhibit effector T-cell activation and proliferation, both directly through various cytokines and indirectly through modulating the activity of regulatory T-cells [81, 82]. MSCs have also been described as modulating the behaviors of natural killer cells, dendritic cells, B-cells, neutrophils, and monocytes/macrophages through the actions of a number of molecules, including prostaglandin E2 (PGE2), indoleamine 2,3-dioxygenase (IDO), nitric oxide (NO), interleukin-10 (IL-10), and many others [8, 80]. Notably in the context of localized tissue repair, MSCs have been implicated in promoting alternative activation of macrophages toward a regenerative and proangiogenic M2 phenotype, as opposed to a classical proinflammatory M1 phenotype [83–86]. Consequently, given the many roles MSCs play in therapeutic immunomodulation and regeneration, it is becoming increasingly acknowledged that one of the main roles of adult MSCs in vivo may be to coordinate healing responses and to help prevent autoimmunity after injury [8, 74, 80].
Lastly, it should be noted that MSCs are not solely anti-inflammatory. Under certain conditions, MSCs can elicit an inflammatory response by presenting antigens to induce CD8+ T-cell responses, and increasing expression of MHCDII and presenting antigens to CD4+ T-cells [87–89]. The “switch” between eliciting an inflammatory or anti-inflammatory response generally seems to be whether the activating signals are associated with infections or tissue injury, respectively .
8. MSC Angiogenic Paracrine Signaling
In addition to being proangiogenic by promoting a regenerative microenvironment via immunomodulation, MSCs also directly secrete angiogenic factors that affect endothelial cell survival, proliferation, and migration. Such factors include key growth factors critical for initial vessel formation and subsequent stabilization, such as VEGF, FGF2, SDF1, ANG1, MCP-1, HGF, and many others [91, 92]. Beyond these classical angiogenic growth factors, MSCs also secrete microvesicles (>200 μm) and exosomes (~50–200 μm) that can carry both growth factors and miRNAs and have been demonstrated to have proangiogenic activities both in vitro and in vivo . Such extracellular vesicles have been shown to enhance angiogenesis and healing in a number of contexts, including murine and rat models of burn injury, cutaneous wounds, myocardial infarction, and limb ischemia [94–99]. Recent proteomic analysis has found human MSC-derived exosomes contain a number of proteins associated with angiogenesis that were upregulated when MSCs were exposed to ischemic-like conditions, including PDGF, EGF, FGF, and NF-κB pathway-affiliated proteins .
Similarly, recent qPCR screening of exosomes derived from murine MSC-like cells revealed they contain a number of known proangiogenic microRNAs, several of which were found to be preferentially internalized by endothelial cells, including miR-424, miR-30c, miR-30b, and let-7f . Relatedly, miR-210 has also been implicated in the therapeutic effect of MSC-derived extracellular vesicles in a mouse model of cardiac infarction, as siRNA knockdown reduced the angiogenic effect of the vesicles . Delineating which specific MSC-derived exosomal miRNAs are responsible for particular aspects of angiogenesis is an ongoing area of research. Recently, for example, exosomal miRNA-125a from human adipose-derived MSCs has been implicated in enhancing angiogenesis specifically by promoting tip cell formation through the inhibition of delta-like 4 (DLL4) . Ultimately, however, as is the case with angiogenic growth factors, multiple miRNAs may have to work in concert to achieve maximal effects and interrogating which subsets are critical for different stages of angiogenesis will require further inquiry.
9. Direct Cellular Involvement of MSCs in Angiogenesis
In addition to their interaction via various paracrine routes, MSCs also participate in direct cell-cell contact with endothelial cells. When cocultured on or embedded within hydrogels (e.g., fibrin or Matrigel), endothelial cells form capillary-like structures on which MSCs may adhere and assume an abluminal position akin to their perivascular position in vivo . This maintained mural cell behavior after culture may be exploited for microvascular tissue engineering as it has beneficial effects for the nascent endothelial tubules. For example, the permeability of these in vitro structures is decreased in the presence of MSCs relative to simply coculturing endothelial cells with fibroblasts potentially due to tighter cell-cell junctions and VE-cadherin expression . This effect may also be attributed to increased basement membrane formation, as extensive studies of pericyte-endothelial cell cocultures have demonstrated that both the expression and deposition of basement membrane proteins is upregulated through cell-cell contact in vitro [106, 107]. However, any specific effects of MSCs on basement membrane formation and its composition, compared to non-multipotent pericytes, has yet to be elucidated.
Under in vivo contexts, MSCs can also assume a perivascular cell phenotype and have beneficial effects on vessel stability and permeability. For example, when collagen-fibronectin gels containing EGFP-labeled human MSCs and HUVEC (human umbilical vein endothelial cells) were implanted in cranial windows of SCID mice, implants with MSCs resulted in a higher vessel density compared to HUVEC-only implants, and EGFP colocalized with staining for the smooth muscle cell- (SMC-) related markers, αSMA and SM22α . Similarly, when embedded within submillimeter collagen rods coated with endothelial cells and then implanted in an omental pouch within rats, GFP-labeled rat MSCs were found to migrate out of the modules and began to associate with blood vessels and express αSMA at day 7 postimplantation, while at day 21, all GFP+ MSCs were found to be in a perivascular position . Strikingly, when examined by microCT after Microfil® injection, including MSCs within the implant created vasculature with reduced leakiness compared to endothelial cell-only controls which exhibited a leaky core.
Similarly, after subcutaneous injection of HUVEC and fibrin hydrogel into SCID mice, HUVEC-derived vessels formed after 7 and 14 days showed decreased permeability to 70 kDa dextran in conditions including human adipose and bone marrow-derived MSCs, compared to lung fibroblasts or endothelial cells alone . Correspondingly, with this improved barrier function, only implants with ASCs and BMSCs contained vessels with abluminal calponin staining, suggestive of SMC differentiation of the implanted stromal cells. Collectively, it is clear that not only is the presence of a mesenchymal cell type advantageous for vessel formation and stabilization, but the identity of the mesenchymal cell type and its propensity to take on an abluminal position and perivascular cell phenotype has an impact on the functionality of the resulting vessels.
10. Clinical Considerations for Using Bone or Adipose MSC Sources
As noted previously, MSCs can be isolated from many different human tissues; however, the most common adult sources for clinical use are bone marrow and adipose tissue. This is due to a number of reasons, including the total cell numbers that can be harvested, the frequency of the cells of interest, and the relatively small procedural risk associated with obtaining cells from these locations compared to other anatomical locations. As well, in the case of adipose tissue removal, if the procedure is being carried out for other purposes (e.g., elective cosmetic surgery), there is no additional risk associated with the harvesting of progenitor cells which would otherwise be discarded.
In the case of bone marrow aspirate, the procedure is generally carried out at the bedside using a local anesthetic (e.g., lidocaine) with the posterior superior iliac spine being the preferred collection site owing to its relative ease of access . After sterilization of the overlying skin, a fine gauge trocar is used to gain access to the marrow space, which then permits the subsequent aspiration of marrow by syringe . For the purposes of stem cell harvesting, it is possible to harvest as much as 20 mL of marrow from a single aspirate site .
Bone marrow sampling is generally considered to be safe but can frequently result in pain during and after the procedure . Preventative measures, such as first ensuring that the periosteum is adequately anesthetized, can be used to reduce the pain to acceptable levels . Other adverse events during bone marrow sampling are rare, with an estimated event rate of 5/10,000 and a fatality rate of 1-2/100,000 . In a 2013 survey conducted by the British Society of Haematology, out of a total of 19,259 bone marrow aspirates with or without trephine biopsies, clinically significant hemorrhage occurred in only 11 patients, while infections were seen in just two . The risk of bleeding can be mitigated through careful patient selection and correction of underlying coagulopathies if necessary. When bleeding does occur, it is usually mild and can often be controlled by the manual application of pressure to the site . In the event of more significant bleeding, arterial embolization has been demonstrated to be an effective hemostatic therapy . The risk of infection can be mitigated by first ensuring an absence of any overlying skin or soft tissue infection or presence of osteomyelitis. In suspected occurrences of infectious complications, topical antimicrobials are generally considered to be adequate in most cases.
In contrast to bone marrow aspirate, adipose tissue—in the form of liquid fat from liposuction or solid fat from abdominoplasty—is obtained under general anesthetic with a greater risk of procedural morbidity and mortality . In the case of liposuction, the targeted fat is removed via aspiration after injection of a sterile saline solution containing epinephrine and a topical anesthetic . The process may be facilitated by the liquefaction of fat using ultrasound- or laser-assisted liposuction . Conversely, abdominoplasty involves the surgical excision of excess solid adipose tissue and dermis.
Common adverse events for liposuction include postoperative nausea and vomiting, local nerve damage and paresthesias, intra- and postprocedural bleeding and hematomas, persistent edema, surgical wound infection, skin necrosis, and unplanned hospitalization or increased length of stay . The risk of fatality of liposuction is conservatively estimated to be 1/5000 with deaths being attributable to pulmonary embolism, visceral perforation, cardiorespiratory complications associated with anesthesia, and hemorrhage (in order of decreasing frequency) . Abdominoplasty is a more invasive procedure with higher rates of surgical complications, including wound dehiscence and necrosis, infection, and a fatality rate approaching 1/600 .
Given the relatively unfavorable risk profile associated with surgical collection of adipose tissue, the harvesting of adipose-derived MSCs is ideal for patients who are already planning on undergoing such a procedure. Otherwise, bone marrow aspirate remains a preferred option as it can permit the ad hoc collection of MSCs at a lower risk of morbidity and mortality. However, such clinical risks must be weighed against certain practical requirements as well.
In addition to considering the risks associated with the different anatomical sites and any contraindications specific to a certain patient, the preference for one tissue source over the other may also be affected by the number of desired cells that can be collected from a certain source and the quantity of cells requisite for a particular application. As summarized by Murphy et al., in the case of a bone marrow aspirate, approximately 109–664 CFU-F/mL can be obtained at a frequency of 10–83 CFU-F/106 nucleated cells . In contrast, lipoaspirate typically yields far more cells of interest per milliliter of tissue, with 2058–9650 CFU-F/mL at a frequency of 205–51,000 CFU-F/106 nucleated cells . Hence, if the quantity of cells that can be obtained via bone marrow aspirate are insufficient for a particular autologous application, relying on an adipose cell source instead may be a sensible option. This is especially true in situations where ex vivo culture must be limited to preserve a desired cellular phenotype or when culture is not utilized at all (i.e., immediate autologous use of the stromal vascular fraction (SVF) after harvesting).
Beyond differences in the quantity of cells obtainable from either bone or adipose tissues, innate differences in differentiation ability between cell types may also affect the preference of one MSC population over the other for a particular application. Unsurprisingly, given their developmental and anatomical origins, adipose-derived MSCs have been demonstrated to have an increased capacity for in vitro adipogenic differentiation by Oil Red O staining, possibly due to their relatively higher expression of the adipogenesis-regulating transcription factor, PPAR-γ, after exposure to adipogenic stimuli [121, 122]. Similarly, bone marrow-derived MSCs have been demonstrated to have an increased capacity for osteogenic differentiation over MSCs derived from adipose tissue via alizarin red staining [121, 122]. This may be partly attributable to their higher expression of the key osteogenic transcription factor, Runx2, during osteogenic differentiation . Moreover, bone marrow-derived MSCs have also been shown to have a higher capacity for chondrogenic differentiation (by alcian blue staining and collagen II expression), as may be expected considering the close relationship between chondrogenesis and osteogenesis in the generation of osseous tissues [121–123]. It should be noted, however, that some conflicting reports to these general findings also exist and suggest that whether adipose or bone-derived MSCs have the higher capacity to differentiate toward a particular lineage may depend on the characteristics of the patient (e.g., sex, age, and disease state), the isolation protocol, and the differentiation conditions .
Other notable functional differences between the two cell types have been documented. For example, in a comparison of the immunomodulatory capacity of adipose and bone marrow-derived MSCs isolated from the same donor, Valencia et al. found that MSCs from bone marrow had a higher capacity to inhibit natural killer cytotoxic activity, whereas adipose-derived MSCs had a higher capacity to inhibit dendritic cell differentiation . Corroborating this, other reports have also described similar findings regarding these differential effects on natural killer cells and dendritic cell differentiation [125, 126]. Similarly, differences in growth factor expression between the two cell types have also been noted and may influence which cell type to use in clinical applications where MSCs are intended to provide trophic support. For example, bone marrow-derived MSCs have been shown to produce significantly more HGF compared to adipose-derived MSCs, which may be an important consideration for regenerative therapies involving the liver . Overall, the choice of bone or adipose sources is complex and is influenced by factors specific to the application and the patient. As the use of MSCs becomes increasingly common, the optimal choice of cell source for specific clinical circumstances will likely become clearer.
11. iPSC Sources and Epigenetic Reprogramming of MSCs
Despite the clinical promise of MSCs in allogeneic applications (or the use of HLA-matched donor cells), some therapies may necessitate an autologous approach, such as long-term implantation of MSC-derived engineered tissues. However, this presents a significant challenge in cases where the desired cell type cannot be obtained in sufficient numbers to be clinically useful. This may occur in the case of needing to engineer particularly large replacement tissues, as MSCs have limited expansion capability in culture, partly due to their low to absent expression of telomerase [127, 128]. As well, this may occur when patients have insufficient MSCs of adequate quality due to age or disease. With regard to aging, CFU-F frequency within the bone marrow generally declines with age, and the capacity of the remaining MSCs to withstand oxidative stress appears to also decline along with their function and therapeutic efficacy [129–131]. Such functional changes may be the result of progressively shortening telomeres, accumulated molecular damage, and stochastic genetic and epigenetic changes over time [132–136]. Such age-associated epigenetic dysregulation may also contribute to alterations in the differentiation potential and heterogeneity of MSCs [137, 138]. In addition to age-induced functional decline, conditions such as type 2 diabetes and metabolic syndrome may similarly limit the therapeutic potential of MSCs for autologous use due to increased oxidative stress, mitochondrial dysfunction, and increased senescence .
One potential solution to address this issue is iPSC (induced pluripotent stem cell) technology in which somatic cells from a patient are first reprogrammed to a pluripotent state, usually by the overexpression of transcription factors (e.g., KLF4, c-MYC, OCT4, and SOX2) [140, 141]. Favorably, such cells can then be expanded in vitro extensively prior to differentiation, partly due to their expression of telomerase. Also favorably, especially for cells harvested from aged patients, once harvested cells are differentiated into the desired cell type after having been in a transient pluripotent state results in longer telomeres compared to the starting donor cell along with a “rejuvenated” epigenetic landscape with reduced aging-associated epigenetic marks and increased resistance to oxidative stress [142, 143].
Multiple studies have explored methods for differentiating MSC-like cells from iPSCs [143–149]. These reports have described iPSC-MSCs as being largely comparable to mature MSCs in terms of trilineage potential, immunomodulation, and trophic support. However, some minor differences have also been noted, such as differences in adipose differentiation, T-cell regulation, sensitivity to NK cells, and their expression levels of certain genes (e.g., interleukin-1 and TGFβ receptors) [143, 150–153]. Interestingly, a recent study by Chin et al. reported that differentiation of human pluripotent stem cells into MSCs results in two distinct subpopulations with different trophic phenotypes . One subpopulation with higher expression of CD146 and CD73 could maintain HSCs (hematopoietic stem cells) ex vivo and expressed HSC niche-related genes, while a second subpopulation with lower expression of CD146 and CD73 displayed poor maintenance of HSCs. Such in vitro findings using iPSCs are intriguingly reminiscent of in vivo MSC heterogeneity and may not only help provide a source of MSCs for clinical use but may also help elucidate the developmental origins of different MSC subpopulations.
While iPSCs are a promising source of MSCs, they do carry the risk of malignant transformation during culture and teratoma formation after transplantation due to residual pluripotent cells . Alternative means for returning aged or diseased MSCs to a more therapeutically effective state without relying on a transient pluripotent stage may also exist. One option may consist of using the pluripotency genes used for creating iPSCs but for a shorter duration in order to elicit partial reprogramming and reverse age-associated epigenetic marks but not loss of cellular identity. Such an approach yielded impressive results in mice in terms of improving recovery from metabolic disease and increasing muscle regeneration after transient in vivo overexpression . It remains to be seen, however, if this approach has a beneficial effect on MSCs as well. Future work will need to focus on determining the optimal dosing regimen for human cells and examining if this method is useful for the ex vivo rejuvenation of human MSCs.
Alternatives for rejuvenating cells that do not rely on pluripotency genes at all also exist, which may be preferable for further mitigating tumorigenic risks. One option may be to alter the levels of beneficial or detrimental miRNAs within cultured MSCs prior to transplantation. For example, Okada et al. unveiled that miR-195 plays a key role in inducing senescence in murine bone marrow-derived MSCs by inhibiting the expression of telomerase . When the authors inhibited miR-195, telomere lengths and cellular proliferation were increased compared to control cells. Most importantly though, using a mouse model of acute myocardial infarction, the authors demonstrated that when transplanted the rejuvenated cells resulted in reduced infarct size and improved left-ventricle function.
Conversely, upregulation of certain molecules, such as miR-543 and miR-590-3p may also be useful in preventing senescence given their inhibitory roles in senescence onset in MSCs . Upregulation of SIRT1, a NAD+-dependent deacetylase, has also been shown to prevent MSC senescence possibly through increasing telomerase activity and reducing DNA damage . Strikingly, overexpression of telomerase and myocardin in aged murine MSCs resulted in improved therapeutic efficacy when used in a model of hindlimb ischemia, in terms of stimulating arteriogenesis and increasing blood flow . Regardless of whether particular factors are upregulated or downregulated, it should be stressed that any approach that alters regulators of senescence, telomere length, and/or pluripotency will require extensive investigation in order to ensure that rejuvenation of MSCs does not come at the cost of increasing tumorigenesis.
12. Clinical Risks and Challenges
As of May 2018, there are currently 82 active and recruiting trials involving “mesenchymal stem cells” listed by ClinicalTrials.gov in the United States alone, in addition to 44 already completed studies; moreover, there are also 27 active/recruiting trials involving “mesenchymal stromal cells” with 9 already completed. Of these ongoing studies, the majority are currently in phase 1 followed by phase 2 trials. Given these appreciable number of trials and their early stages, it will be crucial to discern if any patterns of adverse effects can be detected among MSC clinical trials in order to develop effective solutions to these issues. The risks involved in these trials are partly dependent on the route of administration of MSCs (Figure 1).
In terms of risks involving the systemic infusion of MSCs, Lalu et al. conducted a meta-analysis of clinical trials with both autologous and allogeneic MSCs and concluded that this route of administration appears generally safe as their analysis did not find any significant association between MSC infusion and acute toxicity, infection, organ system complications, malignancy, or death . There was, however, a significant association with transient fever in some patients. Other studies have also identified chill, infection, and liver damage as potential adverse effects of systemic administration [161, 162]. Lalu et al. also commented on the frequent absence of reporting follow-up duration for long-term adverse events in the studies they examined and noted that it is critical that future studies investigate both short-term and long-term adverse events given that experimental cell-based therapies may have serious long-term consequences (e.g., immunological complications, causing/enhancing neoplastic growth). Favorably for risk mitigation, however, there is evidence to suggest that MSCs that are infused systemically generally do not persist over the long-term . Also favorably, of the 13 studies examined by Lalu et al. that used unmatched allogeneic MSCs, none reported acute infusional toxicity. Such findings bode well for systemically administered therapies requiring large quantities of cells that cannot be acquired from a single patient and for cases in which a patient’s own MSCs may be functionally inadequate and/or inaccessible due to underlying disease.
Regardless, while MSCs themselves appear generally safe for systemic infusion, biological and chemical components associated with the ex vivo culture and storage of MSCs, such as fetal bovine serum (FBS) and dimethylsulfoxide (DMSO) may introduce risks in the clinical use of MSCs. Such components warrant caution due to the possibility of infectious contamination, immunogenicity, and/or infusional toxicity [164, 165]. With regard to zoonotic concerns regarding FBS, such risks may be addressed through the use of human platelet lysate in place of FBS for supporting the ex vivo growth of MSCs [164, 166].
Risks and their associated challenges regarding more experimental interventions involving the local injection of MSCs and implantation of engineered tissues are currently less well defined compared to the more commonly used systemic administration route. Currently, challenges associated with these approaches often relate to first establishing clinically significant efficacy in order to justify these more invasive procedures. Some key challenges for local injections include maintaining cell viability, increasing MSC permanence after injection, and optimizing delivery to a specific location [161, 167, 168]. In regard to this, rapidly gelling injectable hydrogels have shown promise in targeting MSCs to specific anatomical locations and in maintaining their viability after injection to prolong therapeutic function . Currently, investigations into generating engineered tissues are primarily focused on ensuring comparable function to native tissues (or at least, similar enough to be therapeutically useful). Key challenges include optimizing the differentiation process, developing effective scaffold materials, and ensuring sufficient maturation of the nascent tissues through chemical and mechanical cues [73, 170, 171]. As well, depending on the tissue type and its dimensions, the issue of vascularization either pre- or postimplantation must also be addressed in order to preserve function and to avoid ischemia-induced inflammation. As discussed previously in this review, MSCs themselves may be of use in this regard given their proangiogenic signaling and native perivascular phenotype. Ostensibly, some engineered tissues may be optimally composed of MSC-derived terminally differentiated cells along with angiogenic undifferentiated MSCs, in order to fully take advantage of both their differentiation and angiogenic capabilities.
13. Concluding Remarks
Efforts into understanding and exploiting MSCs for therapeutic use have garnered a multifaceted view into the capabilities of these cells, albeit sometimes in a nonlinear and even serendipitous manner. Contrary to many other clinical successes for drugs and cell therapies alike, where a comprehensive understanding of the therapeutic mechanism(s) is first established before being employed clinically, MSCs have had remarkable successes despite a limited understanding of their in vivo function under normal physiological conditions. To further improve and build on these early successes, future work will need to be directed toward understanding the more nuanced aspects of these cells. As alluded to earlier, this will partly involve developing an improved understanding of the differences between MSCs found in different anatomical locations and the heterogeneity that exists within these subpopulations, in addition to performing rigorous investigation into the functional differences between cells differentiated from MSCs and native terminal cells. By building on the body of MSC research that has been produced thus far, potential risks in downstream clinical applications can be mitigated and the therapeutic potential of MSCs may be further expanded upon to benefit patients in a wide range of clinical settings.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
This work was financially supported by Canadian Institutes of Health Research (CIHR) operating grants MOP-102721, RMF-111624, and MOP-130481. Ross E.B. Fitzsimmons was financially supported by a CIHR Banting and Best Doctoral Scholarship.
- A. J. Friedenstein, I. I. Piatetzky-Shapiro, and K. V. Petrakova, “Osteogenesis in transplants of bone marrow cells,” Development, vol. 16, no. 3, pp. 381–390, 1966.
- A. J. Friedenstein, R. K. Chailakhjan, and K. S. Lalykina, “The development of fibroblast colonies in monolayer cultures of guinea-pig bone marrow and spleen cells,” Cell Proliferation, vol. 3, no. 4, pp. 393–403, 1970.
- A. I. Caplan, “Mesenchymal stem cells,” Journal of Orthopaedic Research, vol. 9, no. 5, pp. 641–650, 1991.
- M. F. Pittenger, A. M. Mackay, S. C. Beck et al., “Multilineage potential of adult human mesenchymal stem cells,” Science, vol. 284, no. 5411, pp. 143–147, 1999.
- M. Dominici, K. le Blanc, I. Mueller et al., “Minimal criteria for defining multipotent mesenchymal stromal cells. The International Society for Cellular Therapy position statement,” Cytotherapy, vol. 8, no. 4, pp. 315–317, 2006.
- C.-S. Lin, Z.-C. Xin, J. Dai, and T. F. Lue, “Commonly used mesenchymal stem cell markers and tracking labels: limitations and challenges,” Histology and Histopathology, vol. 28, no. 9, pp. 1109–1116, 2013.
- M. Corselli, C.-W. Chen, B. Sun, S. Yap, J. P. Rubin, and B. Peault, “The tunica adventitia of human arteries and veins as a source of mesenchymal stem cells,” Stem Cells and Development, vol. 21, no. 8, pp. 1299–1308, 2012.
- A. J. Nauta and W. E. Fibbe, “Immunomodulatory properties of mesenchymal stromal cells,” Blood, vol. 110, no. 10, pp. 3499–3506, 2007.
- N. Barker and H. Clevers, “Leucine-rich repeat-containing G-protein-coupled receptors as markers of adult stem cells,” Gastroenterology, vol. 138, no. 5, pp. 1681–1696, 2010.
- B. Sacchetti, A. Funari, S. Michienzi et al., “Self-renewing osteoprogenitors in bone marrow sinusoids can organize a hematopoietic microenvironment,” Cell, vol. 131, no. 2, pp. 324–336, 2007.
- S. Gronthos, A. C. W. Zannettino, S. J. Hay et al., “Molecular and cellular characterisation of highly purified stromal stem cells derived from human bone marrow,” Journal of Cell Science, vol. 116, no. 9, pp. 1827–1835, 2003.
- N. Quirici, D. Soligo, P. Bossolasco, F. Servida, C. Lumini, and G. L. Deliliers, “Isolation of bone marrow mesenchymal stem cells by anti-nerve growth factor receptor antibodies,” Experimental Hematology, vol. 30, no. 7, pp. 783–791, 2002.
- M. Sobiesiak, K. Sivasubramaniyan, C. Hermann et al., “The mesenchymal stem cell antigen MSCA-1 is identical to tissue non-specific alkaline phosphatase,” Stem Cells and Development, vol. 19, no. 5, pp. 669–677, 2010.
- S. J. Morrison and D. T. Scadden, “The bone marrow niche for haematopoietic stem cells,” Nature, vol. 505, no. 7483, pp. 327–334, 2014.
- B. A. Anthony and D. C. Link, “Regulation of hematopoietic stem cells by bone marrow stromal cells,” Trends in Immunology, vol. 35, no. 1, pp. 32–37, 2014.
- C. Nombela-Arrieta, J. Ritz, and L. E. Silberstein, “The elusive nature and function of mesenchymal stem cells,” Nature Reviews Molecular Cell Biology, vol. 12, no. 2, pp. 126–131, 2011.
- N. Beyer Nardi and L. da Silva Meirelles, “Mesenchymal stem cells: isolation, in vitro expansion and characterization,” in Stem Cells. Handbook of Experimental Pharmacology, vol 174, A. M. Wobus and K. R. Boheler, Eds., pp. 249–282, Springer, Berlin, Heidelberg, 2006.
- W. C. W. Chen, J. E. Baily, M. Corselli et al., “Human myocardial pericytes: multipotent mesodermal precursors exhibiting cardiac specificity,” Stem Cells, vol. 33, no. 2, pp. 557–573, 2015.
- A. Stefanska, C. Kenyon, H. C. Christian et al., “Human kidney pericytes produce renin,” Kidney International, vol. 90, no. 6, pp. 1251–1261, 2016.
- A. I. Caplan, “All MSCs are pericytes?” Cell Stem Cell, vol. 3, no. 3, pp. 229-230, 2008.
- S. Shi and S. Gronthos, “Perivascular niche of postnatal mesenchymal stem cells in human bone marrow and dental pulp,” Journal of Bone and Mineral Research, vol. 18, no. 4, pp. 696–704, 2003.
- M. Crisan, S. Yap, L. Casteilla et al., “A perivascular origin for mesenchymal stem cells in multiple human organs,” Cell Stem Cell, vol. 3, no. 3, pp. 301–313, 2008.
- R. Kramann, R. K. Schneider, D. P. DiRocco et al., “Perivascular Gli1+ progenitors are key contributors to injury-induced organ fibrosis,” Cell Stem Cell, vol. 16, no. 1, pp. 51–66, 2015.
- R. Kramann, C. Goettsch, J. Wongboonsin et al., “Adventitial MSC-like cells are progenitors of vascular smooth muscle cells and drive vascular calcification in chronic kidney disease,” Cell Stem Cell, vol. 19, no. 5, pp. 628–642, 2016.
- A. H. Baker and B. Peault, “A Gli(1) ttering role for perivascular stem cells in blood vessel remodeling,” Cell Stem Cell, vol. 19, no. 5, pp. 563–565, 2016.
- R. Sarugaser, D. Lickorish, D. Baksh, M. M. Hosseini, and J. E. Davies, “Human umbilical cord perivascular (HUCPV) cells: a source of mesenchymal progenitors,” Stem Cells, vol. 23, no. 2, pp. 220–229, 2005.
- J. Ennis, C. Götherström, K. Le Blanc, and J. E. Davies, “In vitro immunologic properties of human umbilical cord perivascular cells,” Cytotherapy, vol. 10, no. 2, pp. 174–181, 2008.
- N. Zebardast, D. Lickorish, and J. E. Davies, “Human umbilical cord perivascular cells (HUCPVC): a mesenchymal cell source for dermal wound healing,” Organogenesis, vol. 6, no. 4, pp. 197–203, 2010.
- J. Feng, A. Mantesso, C. De Bari, A. Nishiyama, and P. T. Sharpe, “Dual origin of mesenchymal stem cells contributing to organ growth and repair,” Proceedings of the National Academy of Sciences, vol. 108, no. 16, pp. 6503–6508, 2011.
- Y. Sakaguchi, I. Sekiya, K. Yagishita, and T. Muneta, “Comparison of human stem cells derived from various mesenchymal tissues: superiority of synovium as a cell source,” Arthritis & Rheumatology, vol. 52, no. 8, pp. 2521–2529, 2005.
- A. Nimura, T. Muneta, H. Koga et al., “Increased proliferation of human synovial mesenchymal stem cells with autologous human serum: comparisons with bone marrow mesenchymal stem cells and with fetal bovine serum,” Arthritis & Rheumatology, vol. 58, no. 2, pp. 501–510, 2008.
- Y. Ogata, Y. Mabuchi, M. Yoshida et al., “Purified human synovium mesenchymal stem cells as a good resource for cartilage regeneration,” PLoS One, vol. 10, no. 6, article e0129096, 2015.
- J.-H. Chen, C. Y. Y. Yip, E. D. Sone, and C. A. Simmons, “Identification and characterization of aortic valve mesenchymal progenitor cells with robust osteogenic calcification potential,” The American Journal of Pathology, vol. 174, no. 3, pp. 1109–1119, 2009.
- J. R. Levick, “Microvascular architecture and exchange in synovial joints,” Microcirculation, vol. 2, no. 3, pp. 217–233, 1995.
- K. L. Weind, C. G. Ellis, and D. R. Boughner, “The aortic valve blood supply,” The Journal of Heart Valve Disease, vol. 9, pp. 1–7, 2000.
- Y. Soini, T. Salo, and J. Satta, “Angiogenesis is involved in the pathogenesis of nonrheumatic aortic valve stenosis,” Human Pathology, vol. 34, no. 8, pp. 756–763, 2003.
- G. Sheng, “The developmental basis of mesenchymal stem/stromal cells (MSCs),” BMC Developmental Biology, vol. 15, no. 1, pp. 44–48, 2015.
- L. da Silva Meirelles, A. I. Caplan, and N. B. Nardi, “In search of the in vivo identity of mesenchymal stem cells,” Stem Cells, vol. 26, no. 9, pp. 2287–2299, 2008.
- M. G. Minasi, M. Riminucci, L. de Angelis et al., “The meso-angioblast: a multipotent, self-renewing cell that originates from the dorsal aorta and differentiates into most mesodermal tissues,” Development, vol. 129, no. 11, pp. 2773–2783, 2002.
- Y. Takashima, T. Era, K. Nakao et al., “Neuroepithelial cells supply an initial transient wave of MSC differentiation,” Cell, vol. 129, no. 7, pp. 1377–1388, 2007.
- S. Morikawa, Y. Mabuchi, K. Niibe et al., “Development of mesenchymal stem cells partially originate from the neural crest,” Biochemical and Biophysical Research Communications, vol. 379, no. 4, pp. 1114–1119, 2009.
- M. A. Vodyanik, J. Yu, X. Zhang et al., “A mesoderm-derived precursor for mesenchymal stem and endothelial cells,” Cell Stem Cell, vol. 7, no. 6, pp. 718–729, 2010.
- R. Chijimatsu, M. Ikeya, Y. Yasui et al., “Characterization of mesenchymal stem cell-like cells derived from human iPSCs via neural crest development and their application for osteochondral repair,” Stem Cells International, vol. 2017, Article ID 1960965, 18 pages, 2017.
- I. Sekiya, B. L. Larson, J. R. Smith, R. Pochampally, J.-G. Cui, and D. J. Prockop, “Expansion of human adult stem cells from bone marrow stroma: conditions that maximize the yields of early progenitors and evaluate their quality,” Stem Cells, vol. 20, no. 6, pp. 530–541, 2002.
- C. A. Gregory, H. Singh, A. S. Perry, and D. J. Prockop, “The Wnt signaling inhibitor dickkopf-1 is required for reentry into the cell cycle of human adult stem cells from bone marrow,” Journal of Biological Chemistry, vol. 278, no. 30, pp. 28067–28078, 2003.
- M. E. Bernardo, N. Zaffaroni, F. Novara et al., “Human bone marrow derived mesenchymal stem cells do not undergo transformation after long-term in vitro culture and do not exhibit telomere maintenance mechanisms,” Cancer Research, vol. 67, no. 19, pp. 9142–9149, 2007.
- D. J. Prockop, M. Brenner, W. E. Fibbe et al., “Defining the risks of mesenchymal stromal cell therapy,” Cytotherapy, vol. 12, no. 5, pp. 576–578, 2010.
- A. Conforti, N. Starc, S. Biagini et al., “Resistance to neoplastic transformation of ex-vivo expanded human mesenchymal stromal cells after exposure to supramaximal physical and chemical stress,” Oncotarget, vol. 7, no. 47, pp. 77416–77429, 2016.
- M. Miura, Y. Miura, H. M. Padilla-Nash et al., “Accumulated chromosomal instability in murine bone marrow mesenchymal stem cells leads to malignant transformation,” Stem Cells, vol. 24, no. 4, pp. 1095–1103, 2006.
- C. A. Gregory, J. Ylostalo, and D. J. Prockop, “Adult bone marrow stem/progenitor cells (MSCs) are preconditioned by microenvironmental “niches” in culture: a two-stage hypothesis for regulation of MSC fate,” Science's STKE, vol. 2005, no. 294, article pe37, 2005.
- D. J. Prockop, “Repair of tissues by adult stem/progenitor cells (MSCs): controversies, myths, and changing paradigms,” Molecular Therapy, vol. 17, no. 6, pp. 939–946, 2009.
- M. C. Ciuffreda, G. Malpasso, P. Musarò, V. Turco, and M. Gnecchi, “Protocols for in vitro differentiation of human mesenchymal stem cells into osteogenic, chondrogenic and adipogenic lineages,” in Mesenchymal Stem Cells. Methods in Molecular Biology, vol 1416, M. Gnecchi, Ed., pp. 149–158, Humana Press, New York, NY, USA, 2016.
- C. Vater, P. Kasten, and M. Stiehler, “Culture media for the differentiation of mesenchymal stromal cells,” Acta Biomaterialia, vol. 7, no. 2, pp. 463–477, 2011.
- S. Bose, M. Roy, and A. Bandyopadhyay, “Recent advances in bone tissue engineering scaffolds,” Trends in Biotechnology, vol. 30, no. 10, pp. 546–554, 2012.
- A. R. Amini, C. T. Laurencin, and S. P. Nukavarapu, “Bone tissue engineering: recent advances and challenges,” Critical Reviews™ in Biomedical Engineering, vol. 40, no. 5, pp. 363–408, 2012.
- E. A. Makris, A. H. Gomoll, K. N. Malizos, J. C. Hu, and K. A. Athanasiou, “Repair and tissue engineering techniques for articular cartilage,” Nature Reviews Rheumatology, vol. 11, no. 1, pp. 21–34, 2015.
- L. Zhang, J. Hu, and K. A. Athanasiou, “The role of tissue engineering in articular cartilage repair and regeneration,” Critical Reviews™ in Biomedical Engineering, vol. 37, no. 1-2, pp. 1–57, 2009.
- J. H. Choi, J. M. Gimble, K. Lee et al., “Adipose tissue engineering for soft tissue regeneration,” Tissue Engineering Part B: Reviews, vol. 16, no. 4, pp. 413–426, 2010.
- D. W. Youngstrom, J. E. LaDow, and J. G. Barrett, “Tenogenesis of bone marrow-, adipose-, and tendon-derived stem cells in a dynamic bioreactor,” Connective Tissue Research, vol. 57, no. 6, pp. 454–465, 2016.
- D. Galli, M. Vitale, and M. Vaccarezza, “Bone marrow-derived mesenchymal cell differentiation toward myogenic lineages: facts and perspectives,” BioMed Research International, vol. 2014, Article ID 762695, 6 pages, 2014.
- V. M. Tatard, G. D'Ippolito, S. Diabira et al., “Neurotrophin-directed differentiation of human adult marrow stromal cells to dopaminergic-like neurons,” Bone, vol. 40, no. 2, pp. 360–373, 2007.
- S. Wislet-Gendebien, G. Hans, P. Leprince, J.-M. Rigo, G. Moonen, and B. Rogister, “Plasticity of cultured mesenchymal stem cells: switch from nestin-positive to excitable neuron-like phenotype,” Stem Cells, vol. 23, no. 3, pp. 392–402, 2005.
- D. G. Phinney and D. J. Prockop, “Concise review: mesenchymal stem/multipotent stromal cells: the state of transdifferentiation and modes of tissue repair-current views,” Stem Cells, vol. 25, no. 11, pp. 2896–2902, 2007.
- A.-C. Volz, B. Huber, and P. J. Kluger, “Adipose-derived stem cell differentiation as a basic tool for vascularized adipose tissue engineering,” Differentiation, vol. 92, no. 1-2, pp. 52–64, 2016.
- B. Sacchetti, A. Funari, C. Remoli et al., “No identical “mesenchymal stem cells” at different times and sites: human committed progenitors of distinct origin and differentiation potential are incorporated as adventitial cells in microvessels,” Stem Cell Reports, vol. 6, no. 6, pp. 897–913, 2016.
- W. R. Hardy, N. I. Moldovan, L. Moldovan et al., “Transcriptional networks in single perivascular cells sorted from human adipose tissue reveal a hierarchy of mesenchymal stem cells,” Stem Cells, vol. 35, no. 5, pp. 1273–1289, 2017.
- C. L. Esteves, T. A. Sheldrake, S. P. Mesquita et al., “Isolation and characterization of equine native MSC populations,” Stem Cell Research and Therapy, vol. 8, no. 1, p. 80, 2017.
- A. W. James, X. Zhang, M. Crisan et al., “Isolation and characterization of canine perivascular stem/stromal cells for bone tissue engineering,” PLoS One, vol. 12, no. 5, pp. e0177308–e0177316, 2017.
- N. E. Lee, S. J. Kim, S.-J. Yang et al., “Comparative characterization of mesenchymal stromal cells from multiple abdominal adipose tissues and enrichment of angiogenic ability via CD146 molecule,” Cytotherapy, vol. 19, no. 2, pp. 170–180, 2017.
- A. R. Jensen, B. V. Kelley, G. M. Mosich et al., “Neer Award 2018: platelet-derived growth factor receptor α co-expression typifies a subset of platelet-derived growth factor receptor β–positive progenitor cells that contribute to fatty degeneration and fibrosis of the murine rotator cuff,” Journal of Shoulder and Elbow Surgery, vol. 27, no. 7, pp. 1149–1161, 2018.
- I. R. Murray, Z. N. Gonzalez, J. Baily et al., “αv integrins on mesenchymal cells regulate skeletal and cardiac muscle fibrosis,” Nature Communications, vol. 8, no. 1, p. 1118, 2017.
- R. Sarugaser, L. Hanoun, A. Keating, W. L. Stanford, and J. E. Davies, “Human mesenchymal stem cells self-renew and differentiate according to a deterministic hierarchy,” PLoS One, vol. 4, no. 8, article e6498, 2009.
- A. I. Caplan, “Adult mesenchymal stem cells for tissue engineering versus regenerative medicine,” Journal of Cellular Physiology, vol. 213, no. 2, pp. 341–347, 2007.
- A. I. Caplan and D. Correa, “The MSC: an injury drugstore,” Cell Stem Cell, vol. 9, no. 1, pp. 11–15, 2011.
- A. I. Caplan, “Mesenchymal stem cells: time to change the name!,” Stem Cells Translational Medicine, vol. 6, no. 6, pp. 1445–1451, 2017.
- M. Cai, R. Shen, L. Song et al., “Bone marrow mesenchymal stem cells (BM-MSCs) improve heart function in swine myocardial infarction model through paracrine effects,” Scientific Reports, vol. 6, no. 1, pp. 1–12, 2016.
- B. Amorin, A. P. Alegretti, V. Valim et al., “Mesenchymal stem cell therapy and acute graft-versus-host disease: a review,” Human Cell, vol. 27, no. 4, pp. 137–150, 2014.
- J. Dalal, K. Gandy, and J. Domen, “Role of mesenchymal stem cell therapy in Crohn’s disease,” Pediatric Research, vol. 71, no. 4–2, pp. 445–451, 2012.
- J. Katuchova, D. Harvanova, T. Spakova et al., “Mesenchymal stem cells in the treatment of type 1 diabetes mellitus,” Endocrine Pathology, vol. 26, no. 2, pp. 95–103, 2015.
- N. G. Singer and A. I. Caplan, “Mesenchymal stem cells: mechanisms of inflammation,” Annual Review of Pathology: Mechanisms of Disease, vol. 6, no. 1, pp. 457–478, 2011.
- M. M. Duffy, T. Ritter, R. Ceredig, and M. D. Griffin, “Mesenchymal stem cell effects on T-cell effector pathways,” Stem Cell Research & Therapy, vol. 2, no. 4, p. 34, 2011.
- R. Haddad and F. Saldanha-Araujo, “Mechanisms of T-cell immunosuppression by mesenchymal stromal cells: what do we know so far?” BioMed Research International, vol. 2014, Article ID 216806, 14 pages, 2014.
- E. Eggenhofer and M. J. Hoogduijn, “Mesenchymal stem cell-educated macrophages,” Transplantation Research, vol. 1, no. 1, p. 12, 2012.
- A. Mantovani, S. K. Biswas, M. R. Galdiero, A. Sica, and M. Locati, “Macrophage plasticity and polarization in tissue repair and remodelling,” The Journal of Pathology, vol. 229, no. 2, pp. 176–185, 2013.
- M. E. Bernardo and W. E. Fibbe, “Mesenchymal stromal cells: sensors and switchers of inflammation,” Cell Stem Cell, vol. 13, no. 4, pp. 392–402, 2013.
- E. Chung and Y. Son, “Crosstalk between mesenchymal stem cells and macrophages in tissue repair,” Tissue Engineering and Regenerative Medicine, vol. 11, no. 6, pp. 431–438, 2014.
- W. K. Chan, A. S.-Y. Lau, J. C.-B. Li, H. K.-W. Law, Y. L. Lau, and G. C.-F. Chan, “MHC expression kinetics and immunogenicity of mesenchymal stromal cells after short-term IFN-γ challenge,” Experimental Hematology, vol. 36, no. 11, pp. 1545–1555, 2008.
- M. François, R. Romieu-Mourez, S. Stock-Martineau, M.-N. Boivin, J. L. Bramson, and J. Galipeau, “Mesenchymal stromal cells cross-present soluble exogenous antigens as part of their antigen-presenting cell properties,” Blood, vol. 114, no. 13, pp. 2632–2638, 2009.
- J. L. Chan, K. C. Tang, A. P. Patel et al., “Antigen-presenting property of mesenchymal stem cells occurs during a narrow window at low levels of interferon-γ,” Blood, vol. 107, no. 12, pp. 4817–4824, 2006.
- M. Strioga, S. Viswanathan, A. Darinskas, O. Slaby, and J. Michalek, “Same or not the same? Comparison of adipose tissue-derived versus bone marrow-derived mesenchymal stem and stromal cells,” Stem Cells and Development, vol. 21, no. 14, pp. 2724–2752, 2012.
- S. M. Nassiri and R. Rahbarghazi, “Interactions of mesenchymal stem cells with endothelial cells,” Stem Cells and Development, vol. 23, no. 4, pp. 319–332, 2014.
- H. Tao, Z. Han, Z. C. Han, and Z. Li, “Proangiogenic features of mesenchymal stem cells and their therapeutic applications,” Stem Cells International, vol. 2016, Article ID 1314709, 11 pages, 2016.
- D. G. Phinney and M. F. Pittenger, “Concise review: MSC-derived exosomes for cell-free therapy,” Stem Cells, vol. 35, no. 4, pp. 851–858, 2017.
- A. Shabbir, A. Cox, L. Rodriguez-Menocal, M. Salgado, and E. V. Badiavas, “Mesenchymal stem cell exosomes induce proliferation and migration of normal and chronic wound fibroblasts, and enhance angiogenesis in vitro,” Stem Cells and Development, vol. 24, no. 14, pp. 1635–1647, 2015.
- B. Zhang, X. Wu, X. Zhang et al., “Human umbilical cord mesenchymal stem cell exosomes enhance angiogenesis through the Wnt4/β-catenin pathway,” Stem Cells Translational Medicine, vol. 4, no. 5, pp. 513–522, 2015.
- S. Bian, L. Zhang, L. Duan, X. Wang, Y. Min, and H. Yu, “Extracellular vesicles derived from human bone marrow mesenchymal stem cells promote angiogenesis in a rat myocardial infarction model,” Journal of Molecular Medicine, vol. 92, no. 4, pp. 387–397, 2014.
- X. Teng, L. Chen, W. Chen, J. Yang, Z. Yang, and Z. Shen, “Mesenchymal stem cell-derived exosomes improve the microenvironment of infarcted myocardium contributing to angiogenesis and anti-inflammation,” Cellular Physiology and Biochemistry, vol. 37, no. 6, pp. 2415–2424, 2015.
- J. Zhang, J. Guan, X. Niu et al., “Exosomes released from human induced pluripotent stem cells-derived MSCs facilitate cutaneous wound healing by promoting collagen synthesis and angiogenesis,” Journal of Translational Medicine, vol. 13, no. 1, p. 49, 2015.
- G.-W. Hu, Q. Li, X. Niu et al., “Exosomes secreted by human-induced pluripotent stem cell-derived mesenchymal stem cells attenuate limb ischemia by promoting angiogenesis in mice,” Stem Cell Research & Therapy, vol. 6, no. 1, p. 10, 2015.
- J. D. Anderson, H. J. Johansson, C. S. Graham et al., “Comprehensive proteomic analysis of mesenchymal stem cell exosomes reveals modulation of angiogenesis via nuclear factor-kappaB signaling,” Stem Cells, vol. 34, no. 3, pp. 601–613, 2016.
- M. Gong, B. Yu, J. Wang et al., “Mesenchymal stem cells release exosomes that transfer miRNAs to endothelial cells and promote angiogenesis,” Oncotarget, vol. 8, no. 28, pp. 45200–45212, 2017.
- N. Wang, C. Chen, D. Yang et al., “Mesenchymal stem cells-derived extracellular vesicles, via miR-210, improve infarcted cardiac function by promotion of angiogenesis,” Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, vol. 1863, no. 8, pp. 2085–2092, 2017.
- X. Liang, L. Zhang, S. Wang, Q. Han, and R. C. Zhao, “Exosomes secreted by mesenchymal stem cells promote endothelial cell angiogenesis by transferring miR-125a,” Journal of Cell Science, vol. 129, no. 11, pp. 2182–2189, 2016.
- R. R. Rao, A. W. Peterson, J. Ceccarelli, A. J. Putnam, and J. P. Stegemann, “Matrix composition regulates three-dimensional network formation by endothelial cells and mesenchymal stem cells in collagen/fibrin materials,” Angiogenesis, vol. 15, no. 2, pp. 253–264, 2012.
- S. J. Grainger and A. J. Putnam, “Assessing the permeability of engineered capillary networks in a 3D culture,” PLoS One, vol. 6, no. 7, article e22086, 2011.
- A. N. Stratman, W. B. Saunders, A. Sacharidou et al., “Endothelial cell lumen and vascular guidance tunnel formation requires MT1-MMP-dependent proteolysis in 3-dimensional collagen matrices,” Blood, vol. 114, no. 2, pp. 237–247, 2009.
- A. N. Stratman and G. E. Davis, “Endothelial cell-pericyte interactions stimulate basement membrane matrix assembly: influence on vascular tube remodeling, maturation, and stabilization,” Microscopy and Microanalysis, vol. 18, no. 01, pp. 68–80, 2012.
- P. Au, J. Tam, D. Fukumura, and R. K. Jain, “Bone marrow-derived mesenchymal stem cells facilitate engineering of long-lasting functional vasculature,” Blood, vol. 111, no. 9, pp. 4551–4558, 2008.
- M. D. Chamberlain, R. Gupta, and M. V. Sefton, “Bone marrow-derived mesenchymal stromal cells enhance chimeric vessel development driven by endothelial cell-coated microtissues,” Tissue Engineering Part A, vol. 18, no. 3-4, pp. 285–294, 2012.
- S. J. Grainger, B. Carrion, J. Ceccarelli, and A. J. Putnam, “Stromal cell identity influences the in vivo functionality of engineered capillary networks formed by co-delivery of endothelial cells and stromal cells,” Tissue Engineering Part A, vol. 19, no. 9-10, pp. 1209–1222, 2013.
- S. Malempati, S. Joshi, S. Lai, D. A. V. Braner, and K. Tegtmeyer, “Videos in clinical medicine. Bone marrow aspiration and biopsy,” The New England Journal of Medicine, vol. 361, no. 15, article e28, 2009.
- E. M. Fennema, A. J. S. Renard, A. Leusink, C. A. van Blitterswijk, and J. de Boer, “The effect of bone marrow aspiration strategy on the yield and quality of human mesenchymal stem cells,” Acta Orthopaedica, vol. 80, no. 5, pp. 618–621, 2009.
- N. Hjortholm, E. Jaddini, K. Hałaburda, and E. Snarski, “Strategies of pain reduction during the bone marrow biopsy,” Annals of Hematology, vol. 92, no. 2, pp. 145–149, 2013.
- B. J. Bain, “Bone marrow biopsy morbidity and mortality,” British Journal of Haematology, vol. 121, no. 6, pp. 949–951, 2003.
- B. J. Bain, “Morbidity associated with bone marrow aspiration and trephine biopsy - a review of UK data for 2004,” Haematologica, vol. 91, no. 9, pp. 1293-1294, 2006.
- J. P. Hunstad and M. E. Aitken, “Liposuction: techniques and guidelines,” Clinics in Plastic Surgery, vol. 33, no. 1, pp. 13–25, 2006.
- R. A. Yoho, J. J. Romaine, and D. O'Neil, “Review of the liposuction, abdominoplasty, and face-lift mortality and morbidity risk literature,” Dermatologic Surgery., vol. 31, no. 7, pp. 733–743, 2005.
- F. M. Grazer and R. H. de Jong, “Fatal outcomes from liposuction: census survey of cosmetic surgeons,” Plastic and Reconstructive Surgery, vol. 105, no. 1, pp. 436–446, 2000.
- M. Chaouat, P. Levan, B. Lalanne, T. Buisson, P. Nicolau, and M. Mimoun, “Abdominal dermolipectomies: early postoperative complications and long-term unfavorable results,” Plastic and Reconstructive Surgery, vol. 106, no. 7, pp. 1614–1618, 2000.
- M. B. Murphy, K. Moncivais, and A. I. Caplan, “Mesenchymal stem cells: environmentally responsive therapeutics for regenerative medicine,” Experimental & Molecular Medicine, vol. 45, no. 11, article e54, 2013.
- T. M. Liu, M. Martina, D. W. Hutmacher, J. H. P. Hui, E. H. Lee, and B. Lim, “Identification of common pathways mediating differentiation of bone marrow- and adipose tissue-derived human mesenchymal stem cells into three mesenchymal lineages,” Stem Cells, vol. 25, no. 3, pp. 750–760, 2007.
- C.-Y. Li, X.-Y. Wu, J.-B. Tong et al., “Comparative analysis of human mesenchymal stem cells from bone marrow and adipose tissue under xeno-free conditions for cell therapy,” Stem Cell Research & Therapy, vol. 6, no. 1, p. 55, 2015.
- Y. Jing, J. Jing, L. Ye et al., “Chondrogenesis and osteogenesis are one continuous developmental and lineage defined biological process,” Scientific Reports, vol. 7, no. 1, p. 10020, 2017.
- J. Valencia, B. Blanco, R. Yáñez et al., “Comparative analysis of the immunomodulatory capacities of human bone marrow- and adipose tissue-derived mesenchymal stromal cells from the same donor,” Cytotherapy, vol. 18, no. 10, pp. 1297–1311, 2016.
- B. Blanco, M. C. Herrero-Sánchez, C. Rodríguez-Serrano et al., “Immunomodulatory effects of bone marrow versus adipose tissue-derived mesenchymal stromal cells on NK cells: implications in the transplantation setting,” European Journal of Haematology, vol. 97, no. 6, pp. 528–537, 2016.
- E. Ivanova-Todorova, I. Bochev, M. Mourdjeva et al., “Adipose tissue-derived mesenchymal stem cells are more potent suppressors of dendritic cells differentiation compared to bone marrow-derived mesenchymal stem cells,” Immunology Letters, vol. 126, no. 1-2, pp. 37–42, 2009.
- S. Zimmermann, M. Voss, S. Kaiser, U. Kapp, C. F. Waller, and U. M. Martens, “Lack of telomerase activity in human mesenchymal stem cells,” Leukemia, vol. 17, no. 6, pp. 1146–1149, 2003.
- N. Serakinci, J. Graakjaer, and S. Kolvraa, “Telomere stability and telomerase in mesenchymal stem cells,” Biochimie, vol. 90, no. 1, pp. 33–40, 2008.
- A. Stolzing, E. Jones, D. McGonagle, and A. Scutt, “Age-related changes in human bone marrow-derived mesenchymal stem cells: consequences for cell therapies,” Mechanisms of Ageing and Development, vol. 129, no. 3, pp. 163–173, 2008.
- G. Kasper, L. Mao, S. Geissler et al., “Insights into mesenchymal stem cell aging: involvement of antioxidant defense and actin cytoskeleton,” Stem Cells, vol. 27, no. 6, pp. 1288–1297, 2009.
- P. Ganguly, J. J. El-Jawhari, P. V. Giannoudis, A. N. Burska, F. Ponchel, and E. A. Jones, “Age-related changes in bone marrow mesenchymal stromal cells: a potential impact on osteoporosis and osteoarthritis development,” Cell Transplantation, vol. 26, no. 9, pp. 1520–1529, 2017.
- Y. Li, Q. Wu, Y. Wang, L. Li, H. Bu, and J. Bao, “Senescence of mesenchymal stem cells (review),” International Journal of Molecular Medicine, vol. 39, no. 4, pp. 775–782, 2017.
- B. R. Stab, L. Martinez, A. Grismaldo et al., “Mitochondrial functional changes characterization in young and senescent human adipose derived MSCs,” Frontiers in Aging Neuroscience, vol. 8, p. 299, 2016.
- M. J. Peffers, J. Collins, Y. Fang et al., “Age-related changes in mesenchymal stem cells identified using a multi-omics approach,” European Cell and Materials, vol. 31, pp. 136–159, 2016.
- E. G. Toraño, G. F. Bayón, Á. del Real et al., “Age-associated hydroxymethylation in human bone-marrow mesenchymal stem cells,” Journal of Translational Medicine, vol. 14, no. 1, p. 207, 2016.
- J. Franzen, W. Wagner, and E. Fernandez-Rebollo, “Epigenetic modifications upon senescence of mesenchymal stem cells,” Current Stem Cell Reports, vol. 2, no. 3, pp. 248–254, 2016.
- Z. Li, C. Liu, Z. Xie et al., “Epigenetic dysregulation in mesenchymal stem cell aging and spontaneous differentiation,” PLoS One, vol. 6, no. 6, article e20526, 2011.
- Z. Hamidouche, K. Rother, J. Przybilla et al., “Bistable epigenetic states explain age-dependent decline in mesenchymal stem cell heterogeneity,” Stem Cells, vol. 35, no. 3, pp. 694–704, 2017.
- K. Kornicka, J. Houston, and K. Marycz, “Dysfunction of mesenchymal stem cells isolated from metabolic syndrome and type 2 diabetic patients as result of oxidative stress and autophagy may limit their potential therapeutic use,” Stem Cell Reviews and Reports, vol. 14, no. 3, pp. 337–345, 2018.
- K. Takahashi and S. Yamanaka, “Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors,” Cell, vol. 126, no. 4, pp. 663–676, 2006.
- K. Takahashi, K. Tanabe, M. Ohnuki et al., “Induction of pluripotent stem cells from adult human fibroblasts by defined factors,” Cell, vol. 131, no. 5, pp. 861–872, 2007.
- L. Lapasset, O. Milhavet, A. Prieur et al., “Rejuvenating senescent and centenarian human cells by reprogramming through the pluripotent state,” Genes & Development, vol. 25, no. 21, pp. 2248–2253, 2011.
- J. Frobel, H. Hemeda, M. Lenz et al., “Epigenetic rejuvenation of mesenchymal stromal cells derived from induced pluripotent stem cells,” Stem Cell Reports, vol. 3, no. 3, pp. 414–422, 2014.
- L. G. Villa-Diaz, S. E. Brown, Y. Liu et al., “Derivation of mesenchymal stem cells from human induced pluripotent stem cells cultured on synthetic substrates,” Stem Cells, vol. 30, no. 6, pp. 1174–1181, 2012.
- L. Zou, Y. Luo, M. Chen et al., “A simple method for deriving functional MSCs and applied for osteogenesis in 3D scaffolds,” Scientific Reports, vol. 3, no. 1, article 2243, 2013.
- K. Hynes, D. Menicanin, K. Mrozik, S. Gronthos, and P. M. Bartold, “Generation of functional mesenchymal stem cells from different induced pluripotent stem cell lines,” Stem Cells and Development, vol. 23, no. 10, pp. 1084–1096, 2014.
- M. Moslem, I. Eberle, I. Weber, R. Henschler, and T. Cantz, “Mesenchymal stem/stromal cells derived from induced pluripotent stem cells support CD34pos hematopoietic stem cell propagation and suppress inflammatory reaction,” Stem Cells International, vol. 2015, Article ID 843058, 14 pages, 2015.
- K. Hynes, D. Menicanin, S. Gronthos, and M. P. Bartold, “Differentiation of iPSC to mesenchymal stem-like cells and their characterization,” in Induced Pluripotent Stem (iPS) Cells. Methods in Molecular Biology, vol 1357, K. Turksen and A. Nagy, Eds., Humana Press, New York, NY, USA.
- C. J. Chin, S. Li, M. Corselli et al., “Transcriptionally and functionally distinct mesenchymal subpopulations are generated from human pluripotent stem cells,” Stem Cell Reports, vol. 10, no. 2, pp. 436–446, 2018.
- R. Kang, Y. Zhou, S. Tan et al., “Mesenchymal stem cells derived from human induced pluripotent stem cells retain adequate osteogenicity and chondrogenicity but less adipogenicity,” Stem Cell Research & Therapy, vol. 6, no. 1, p. 144, 2015.
- S. Diederichs and R. S. Tuan, “Functional comparison of human-induced pluripotent stem cell-derived mesenchymal cells and bone marrow-derived mesenchymal stromal cells from the same donor,” Stem Cells and Development, vol. 23, no. 14, pp. 1594–1610, 2014.
- M. Giuliani, N. Oudrhiri, Z. M. Noman et al., “Human mesenchymal stem cells derived from induced pluripotent stem cells down-regulate NK-cell cytolytic machinery,” Blood, vol. 118, no. 12, pp. 3254–3262, 2011.
- Q. Zhao, C. A. Gregory, R. H. Lee et al., “MSCs derived from iPSCs with a modified protocol are tumor-tropic but have much less potential to promote tumors than bone marrow MSCs,” Proceedings of the National Academy of Sciences of the United States of America, vol. 112, no. 2, pp. 530–535, 2015.
- A. S. Lee, C. Tang, M. S. Rao, I. L. Weissman, and J. C. Wu, “Tumorigenicity as a clinical hurdle for pluripotent stem cell therapies,” Nature Medicine, vol. 19, no. 8, pp. 998–1004, 2013.
- A. Ocampo, P. Reddy, P. Martinez-Redondo et al., “In vivo amelioration of age-associated hallmarks by partial reprogramming,” Cell, vol. 167, no. 7, pp. 1719–1733.e12, 2016.
- M. Okada, H. W. Kim, K. Matsu-ura, Y.-G. Wang, M. Xu, and M. Ashraf, “Abrogation of age-induced microRNA-195 rejuvenates the senescent mesenchymal stem cells by reactivating telomerase,” Stem Cells, vol. 34, no. 1, pp. 148–159, 2016.
- S. Lee, K.-R. Yu, Y.-S. Ryu et al., “miR-543 and miR-590-3p regulate human mesenchymal stem cell aging via direct targeting of AIMP3/p18,” Age, vol. 36, no. 6, article 9724, 2014.
- H. Chen, X. Liu, W. Zhu et al., “SIRT1 ameliorates age-related senescence of mesenchymal stem cells via modulating telomere shelterin,” Frontiers in Aging Neuroscience, vol. 6, p. 103, 2014.
- R. Madonna, D. A. Taylor, Y. J. Geng et al., “Transplantation of mesenchymal cells rejuvenated by the overexpression of telomerase and myocardin promotes revascularization and tissue repair in a murine model of hindlimb ischemia,” Circulation Research, vol. 113, no. 7, pp. 902–914, 2013.
- M. M. Lalu, L. McIntyre, C. Pugliese et al., “Safety of cell therapy with mesenchymal stromal cells (SafeCell): a systematic review and meta-analysis of clinical trials,” PLoS One, vol. 7, no. 10, pp. e47559–e47521, 2012.
- G. Ren, X. Chen, F. Dong et al., “Concise review: mesenchymal stem cells and translational medicine: emerging issues,” Stem Cells Translational Medicine, vol. 1, no. 1, pp. 51–58, 2012.
- L. von Bahr, B. Sundberg, L. Lönnies et al., “Long-term complications, immunologic effects, and role of passage for outcome in mesenchymal stromal cell therapy,” Biology of Blood and Marrow Transplantation, vol. 18, no. 4, pp. 557–564, 2012.
- E. Eggenhofer, V. Benseler, A. Kroemer et al., “Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion,” Frontiers in Immunology, vol. 3, p. 297, 2012.
- H. Hemeda, B. Giebel, and W. Wagner, “Evaluation of human platelet lysate versus fetal bovine serum for culture of mesenchymal stromal cells,” Cytotherapy, vol. 16, no. 2, pp. 170–180, 2014.
- M. Duijvestein, A. C. W. Vos, H. Roelofs et al., “Autologous bone marrow-derived mesenchymal stromal cell treatment for refractory luminal Crohn's disease: results of a phase I study,” Gut, vol. 59, no. 12, pp. 1662–1669, 2010.
- E. Fernandez-Rebollo, B. Mentrup, R. Ebert et al., “Human platelet lysate versus fetal calf serum: these supplements do not select for different mesenchymal stromal cells,” Scientific Reports, vol. 7, no. 1, p. 5132, 2017.
- T. J. Kean, P. Lin, A. I. Caplan, and J. E. Dennis, “MSCs: delivery routes and engraftment, cell-targeting strategies, and immune modulation,” Stem Cells International, vol. 2013, Article ID 732742, 13 pages, 2013.
- S. T. Ji, H. Kim, J. Yun, J. S. Chung, and S.-M. Kwon, “Promising therapeutic strategies for mesenchymal stem cell-based cardiovascular regeneration: from cell priming to tissue engineering,” Stem Cells International, vol. 2017, Article ID 3945403, 13 pages, 2017.
- L. M. Marquardt and S. C. Heilshorn, “Design of injectable materials to improve stem cell transplantation,” Current Stem Cell Reports, vol. 2, no. 3, pp. 207–220, 2016.
- S. Hanson, R. N. D'Souza, and P. Hematti, “Biomaterial-mesenchymal stem cell constructs for immunomodulation in composite tissue engineering,” Tissue Engineering Part A, vol. 20, no. 15-16, pp. 2162–2168, 2014.
- A. B. Castillo and C. R. Jacobs, “Mesenchymal stem cell mechanobiology,” Current Osteoporosis Reports, vol. 8, no. 2, pp. 98–104, 2010.
- A. Schäffler and C. Büchler, “Concise review: adipose tissue-derived stromal cells—basic and clinical implications for novel cell-based therapies,” Stem Cells, vol. 25, no. 4, pp. 818–827, 2007.
- H.-J. Bühring, V. L. Battula, S. Treml, B. Schewe, L. Kanz, and W. Vogel, “Novel markers for the prospective isolation of human MSC,” Annals of the New York Academy of Sciences, vol. 1106, no. 1, pp. 262–271, 2007.
- C. Muñiz, C. Teodosio, A. Mayado et al., “Ex vivo identification and characterization of a population of CD13high CD105+ CD45− mesenchymal stem cells in human bone marrow,” Stem Cell Research & Therapy, vol. 6, no. 1, p. 169, 2015.
- O. G. Davies, P. R. Cooper, R. M. Shelton, A. J. Smith, and B. A. Scheven, “Isolation of adipose and bone marrow mesenchymal stem cells using CD29 and CD90 modifies their capacity for osteogenic and adipogenic differentiation,” Journal of Tissue Engineering, vol. 6, 10 pages, 2015.
- H. Zhu, N. Mitsuhashi, A. Klein et al., “The role of the hyaluronan receptor CD44 in mesenchymal stem cell migration in the extracellular matrix,” Stem Cells, vol. 24, no. 4, pp. 928–935, 2006.
- K.-R. Yu, S.-R. Yang, J.-W. Jung et al., “CD49f enhances multipotency and maintains stemness through the direct regulation of OCT4 and SOX2,” Stem Cells, vol. 30, no. 5, pp. 876–887, 2012.
- E. G. Suto, Y. Mabuchi, N. Suzuki et al., “Prospectively isolated mesenchymal stem/stromal cells are enriched in the CD73+ population and exhibit efficacy after transplantation,” Scientific Reports, vol. 7, no. 1, p. 4838, 2017.
- P. A. Zuk, M. Zhu, P. Ashjian et al., “Human adipose tissue is a source of multipotent stem cells,” Molecular Biology of the Cell, vol. 13, no. 12, pp. 4279–4295, 2002.
- S. Halfon, N. Abramov, B. Grinblat, and I. Ginis, “Markers distinguishing mesenchymal stem cells from fibroblasts are downregulated with passaging,” Stem Cells and Development, vol. 20, no. 1, pp. 53–66, 2011.
- B. Delorme, J. Ringe, N. Gallay et al., “Specific plasma membrane protein phenotype of culture-amplified and native human bone marrow mesenchymal stem cells,” Blood, vol. 111, no. 5, pp. 2631–2635, 2008.
- S. F. H. de Witte, M. Franquesa, C. C. Baan, and M. J. Hoogduijn, “Toward development of iMesenchymal stem cells for immunomodulatory therapy,” Frontiers in Immunology, vol. 6, p. 648, 2016.
- C. Martinez, T. J. Hofmann, R. Marino, M. Dominici, and E. M. Horwitz, “Human bone marrow mesenchymal stromal cells express the neural ganglioside GD2: a novel surface marker for the identification of MSCs,” Blood, vol. 109, no. 10, pp. 4245–4248, 2007.
- P. A. Oktar, S. Yildirim, D. Balci, and A. Can, “Continual expression throughout the cell cycle and downregulation upon adipogenic differentiation makes nucleostemin a vital human MSC proliferation marker,” Stem Cell Reviews and Reports, vol. 7, no. 2, pp. 413–424, 2011.
- S. Fitter, S. Gronthos, S. S. Ooi, and A. C. W. Zannettino, “The mesenchymal precursor cell marker antibody STRO-1 binds to cell surface heat shock cognate 70,” Stem Cells, vol. 35, no. 4, pp. 940–951, 2017.
- S. Gronthos, R. McCarty, K. Mrozik et al., “Heat shock protein-90 beta is expressed at the surface of multipotential mesenchymal precursor cells: generation of a novel monoclonal antibody, STRO-4, with specificity for mesenchymal precursor cells from human and ovine tissues,” Stem Cells and Development, vol. 18, no. 9, pp. 1253–1262, 2009.
- E. J. Gang, D. Bosnakovski, C. A. Figueiredo, J. W. Visser, and R. C. R. Perlingeiro, “SSEA-4 identifies mesenchymal stem cells from bone marrow,” Blood, vol. 109, no. 4, pp. 1743–1751, 2007.
- K. Sivasubramaniyan, A. Harichandan, S. Schumann et al., “Prospective isolation of mesenchymal stem cells from human bone marrow using novel antibodies directed against sushi domain containing 2,” Stem Cells and Development, vol. 22, no. 13, pp. 1944–1954, 2013.
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