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CONCISE REVIEW |
a Dipartimento di Medicina Sperimentale e Patologia, Universita' La Sapienza, Roma, Italy;
b Dipartimento di Medicina Sperimentale, Universita' dell'Aquila, L'Aquila, Italy;
c Craniofacial and Skeletal Diseases Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland, USA
Key Words. Marrow stromal stem cells • Microvasculature • Pericytes • Transplantation • Skeleton • Stem cells • Plasticity • Gene therapy • Somatic cell therapy
Correspondence:
Paolo Bianco, M.D., Dipartimento di Medicina Sperimentale e Patologia, Universita' La Sapienza, Viale Regina Elena 324, 00161 Roma, Italy. Telephone: 39-06-444-1049; Fax: 39-06-494-0896; e-mail: p.bianco{at}flashnet.it
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ABSTRACT |
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 Top Abstract IntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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INTRODUCTION |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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The increasing recognition of the properties of marrow stromal cells has spawned a major switch in our perception of their nature, and ramifications of their potential therapeutic application have been envisioned and implemented. Yet, several aspects of marrow stromal cell biology remain in question and unsettled throughout this evolution both in general perspective and in detail, and have gained further appeal and interest along the way. These include the identity, nature, developmental origin and in vivo function of marrow stromal cells, and their amenability to ex vivo manipulation and in vivo use for therapy. Just as with other current members of the growing list of somatic stem cells, imagination is required to put a finger on the seemingly unlikely properties of marrow stromal cells, many of which directly confront established dogmas or premature inferences made from other more extensively studied stem cell systems.
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COLONY FORMING UNIT-FIBROBLAST (CFU-F) AND THEIR PROGENY |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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The ratio of CFU-F in nucleated marrow cells, as determined by the colony-forming efficiency (CFE) assay [4], is highly dependent on the culture conditions, and there is a great deal of variability in the requirements from one animal species to another. In rodents, irradiated marrow feeder cells are absolutely required in addition to selected lots of serum in order to obtain the maximum number of assayable CFU-F (100% CFE), whereas CFE is feeder cell-independent in humans [5]. The mitogenic factors that are required to stimulate the proliferation of CFU-F are not completely known at this time, but do at least include platelet-derived growth factor (PDGF), epidermal growth factor (EGF), basic fibroblast growth factor, transforming growth factor-ß, and insulin-like growth factor-1 [6, 7]. Under optimal conditions, multi-colony-derived strains (where all colonies are combined by trypsinization) can undergo over 25 passages in vitro (more than 50 cell doublings), demonstrating a high capacity for self-replication. Therefore, billions of BMSCs can be generated from a limited amount of starting material, such as 1 ml of a bone marrow aspirate. Thus, the in vitro definition of BMSCs is that they are rapidly adherent and clonogenic, and capable of extended proliferation.
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HETEROGENEITY OF THE BMSC POPULATION |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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Upon transplantation into a host animal, multi-colony-derived strains form an ectopic ossicle, complete with a reticular stroma supportive of myelopoiesis and adipocytes, and occasionally, cartilage [8, 11]. When single colony-derived BMSC strains (isolated using cloning cylinders) are transplanted, a proportion of them have the ability to completely regenerate a bone/marrow organ in which bone cells, myelosupportive stroma, and adipocytes are clonal and of donor origin, whereas hematopoiesis and the vasculature are of recipient origin [7] (Fig. 1
). These results define the "stem" cell nature of the original CFU-F from which the clonal strain was derived. However, they also confirm that not all of the clonogenic cells (those cells able to proliferate to form a colony) are in fact multipotent stem cells. It must also be noted that it is the behavior of clonal strains upon transplantation, and not their in vitro phenotype, that provides the most reliable information on the actual differentiation potential of individual clones. Expression of osteogenic, chondrogenic, or adipogenic phenotypic markers in culture (detected either by mRNA expression or histochemical techniques), and even the production of mineralized matrix, does not reflect the degree of pluripotency of a selected clone in vivo [12]. Therefore, the identification of "stem" cells among stromal cells is only done a posteriori and only by using the appropriate assay. In this respect, chondrogenesis requires an additional comment. It is seldom observed in open transplantation assays, whereas it is commonly seen in closed systems such as diffusion chambers [11], or in micromass cultures of stromal cells in vitro [13], where locally low oxygen tensions, per se, permissive for chondrogenesis, are attained [14]. Thus, the conditions for transplantation or even in vitro assays are critical determinants of the range of differentiation characteristics that can be assessed.
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), a finding of potentially high significance (see below).
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-smooth muscle actin (-SMA) and some characteristics of endothelial cells such as endoglin and MUC-18. It has been claimed that the true "mesenchymal stem cell" can be isolated using rather standard procedures, and characterized using a long list of indeterminate markers [23]. However, in spite of this putative "purification" and extensive characterization, the resulting population was no more "pure" than multi-colony-derived strains isolated by simple, short-term adherence to plastic; the resulting clones displayed varying degrees of multipotentiality. Furthermore, the pattern of expressed markers in even clonal strains that are able to completely regenerate a bone/marrow organ in vivo is not identical, and changes as a function of time in culture. These results indicate that identifying the "phenotypic fingerprint" of a stromal stem cell may well be like shooting at a moving target, in that they seem to be constantly changing in response to their microenvironment, both in vitro and in vivo. |
POST-NATAL MARROW STROMAL CELLS AS CELLS OF THE VASCULAR WALL |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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, C, D, F, G) and -SMA (Fig. 3E), both of which are useful markers for their visualization in tissue sections. In the venous portion, cells residing on the abluminal side of the endothelium display a "reticular" morphology, with long processes emanating from the sinus wall into the adjacent hematopoietic cords where they establish close cell-cell contacts, that convey microenvironmental cues to maturing blood cells. These particular adventitial reticular cells express ALP (Fig. 3G) but not -SMA under normal steady-state conditions (Fig. 3H). In spite of this, but in view of their specific position along with the known diversity of pericytes in different sites, organs and tissues [28], reticular cells can be seen as bona fide specialized pericytes of venous sinusoids in the marrow. Hence, phenotypic properties of marrow pericytes vary along the different sections of the marrow microvascular network (arterial/capillary versus post-capillary venous sinusoids). In addition, adventitial reticular cells of venous sinusoids can accumulate lipid and convert to adipocytes, and they do so mainly under two circumstances: A) during growth of an individual skeletal segment when the expansion of the total marrow cavity makes available space in excess of what is required by hematopoietic cells, or B) independent of growth, when there is an abnormal or age-related numerical reduction of hematopoietic cells thereby making space redundant [29-31].
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Given the similar location of pericytes and stromal cells, the significance of -SMA expression, a marker of smooth muscle cells, in marrow stromal cells takes on new meaning, although its expression is variable, both in vitro and in vivo. -SMA expression is commonly observed in nonclonal, and some clonal cultures of marrow stromal cells [33], where it appears to be related to phases of active cell growth [34], and may reflect a myoid differentiation event, at least in vitro [35]. However, the phenotype of -SMA-expressing stromal cells in culture resembles that of pericytes and subintimal myoid cells rather than that of true smooth muscle cells [35]. In the steady-state normal bone marrow, -SMA expressing stromal cells other than those forming the pericyte/smooth muscle coats of arteries and capillaries are not seen. In contrast, -SMA+ stromal cells not associated with the vasculature are commonly observed in the fetal bone marrow [36, 37], that physically grows together with the bone encasing it. -SMA+ marrow stromal cells are likewise seen in conjunction with a host of hematological diseases [37], and in some bone diseases, such as hyperparathyroidism [37] and fibrous dysplasia (FD) of bone (Riminucci and Bianco, unpublished results). In some of these conditions, these cells have been interpreted as myofibroblasts [34, 37]. More interestingly, at least some of these conditions also feature an increased vascularity, possibly related to angiogenesis [38], and an increased number of CFU-F, quantitated as discussed above (Bianco, Kuznetsov, Robey, unpublished results). Taken together, these observations seem to indicate that -SMA expression in extravascular marrow stromal cells (other than arterial/ capillary pericytes) is related to growth or regeneration events in the marrow environment, which is in turn associated with angiogenesis.
Angiogenesis in all tissues involves the coordinated growth of endothelial cells and pericytes. Nascent endothelial tubes produce EGF and PDGF-B, which stimulate the growth and migration of pericytes away from the subintimal myoid cell layer of the vascular section. A precise ligand-receptor expression loop of PDGF-B produced by endothelial cells and expression of the cognate receptor on pericytes regulates the formation of a pericyte coating and its occurrence in physical continuity with the nascent vascular network [39]. Interestingly, PDGF-receptor beta and EGF receptor are two of the most abundant tyrosine kinase growth factor receptors in BMSCs, and PDGF-B and EGF have been found to stimulate proliferation of BMSCs [6, 40], indicating a physiological similarity between pericytes and BMSCs.
In bone, as in any other organ, angiogenesis is normally restricted to phases of developmentally programmed tissue growth, but may reappear in tissue repair and regeneration or proliferative/neoplastic diseases. During normal bone growth, endothelial cell growth, pericyte coverage, and bone formation by newly generated bone-forming cells occur in a precise spatial and temporal sequence, best visualized in metaphyseal growth plates. Growing endothelial tubes devoid of pericytes occupy the foremost 200 microns of the developing metaphysis [41]. Actively dividing abluminal pericytes and bone-forming osteoblasts are next in line. Progression of endochondral bone formation is dependent on efficient angiogenesis, and is blocked if angiogenesis is blocked, as illustrated by both experimental and pathological conditions. Experimentally, inhibition of VEGF signaling initiated by chondrocytes with blocking antibodies to the cognate receptor on growing blood vessels in the metaphysis results in a blockade not only of bone growth, but also of the related activities in the adjacent cartilage growth plates [42]. A remarkably similar event occurs naturally in rickets, and can be mimicked by microsurgical ablation of the metaphyseal vasculature [41].
Taking into account the similarities in their physical relationship to the vasculature, the cellular response to growth factors, and expression of similar markers lead one to suspect that marrow pericytes and marrow stromal cells are the same entity. Pericytes are perhaps one of the most elusive cell types in the body, and their significance as potential progenitor cells has been repeatedly surmised or postulated [28, 43-46]. Elegant as much as unconventional, experimental proof of their ability to generate cartilage and bone in vivo, for example, has been given in the past [47, 48]. Likewise, it has been shown that retinal pericytes form cartilage and bone (and express Stro-1) in vitro [49]. But, there has been little definitive understanding of the origin of this elusive cell type. Current evidence suggests that there is most likely more than one source of pericytes throughout development and growth. First, during development, pericytes may be recruited during angiogenesis or vasculogenesis from neighboring resident mesenchymal cells [50]. Secondly, as recently shown, pericytes may arise directly from endothelial cells or their progenitors [51, 52]. Third, they can be generated during angiogenesis, either pre- or post-natally, through replication, migration and differentiation of other pericytes downstream of the growing vascular bud [32, 39, 53, 54]. With regards to bone marrow, this implies that marrow pericytes might also be heterogeneous in their mode of development and origin. Some may be recruited during blood vessel formation from resident, preexisting osteogenic cells; others may originate from endothelial cells; still others may grow from preexisting pericytes during vascular growth. Interestingly, it would be predicted from this model that a hierarchy of marrow stromal/progenitor cells exists. Some would be osteogenic in nature, while others would not. If so, one would expect to find multipotent cells with markers of osteogenic commitment, and multipotent cells with endothelial/pericytic markers. With respect to the phenotypic characterization of clonal stromal cells, evidence supporting a dual origin is indeed available.
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ORTHODOX PLASTICITY OF MARROW STROMAL CELLS |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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There is a real physiological need for plasticity of connective tissue cells, namely the need to adapt different tissues that reside next to one another during organ growth, for example [30, 61], and it is likely that nature has evolved mechanisms for maintaining plasticity which remain to be fully elucidated. One example may be the key transcription factor controlling osteogenic commitment, cbfa1 [62, 63], which is commonly if not constitutively expressed in stromal cells derived in culture from the post-natal marrow [12], and maintained during differentiation towards other "cell types" such as adipocytes. This is perhaps the most stringent proof that a cell "committed" to osteogenesis (as demonstrated by expression of the key gene of commitment) may still enter other pathways of differentiation that were thought to be alternative ones [61]. Whether one can isolate a multipotent cbfa1-negative (non-osteogenically committed) stromal cell is at present unclear. However, freshly isolated stromal cells sorted as Stro-1bright have been shown to be cbfa1-negative by reverse transcriptase-polymerase chain reaction (Gronthos and Simmons, unpublished results). Interestingly, these cells also exhibit several endothelial markers, although never a true endothelial phenotype [21, 22].
The fact that chondrocytes, osteoblasts, reticular cells, and adipocytes come from a single precursor cell carrying a marker of osteogenic commitment is consistent with the fact that all of these cell types are members of the same organ, even though of different tissues. A single skeletal segment contains all of these cell types either at different stages of its own organogenesis or simultaneously. Although heretical to some and novel to others, even the notion that each of these cell phenotypes can switch to another within the same family under specific circumstances is consistent with the development and maintenance of the organ from which they were derived. This kind of plasticity is thus "orthodox," meaning that it remains within the context of the organ system.
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UNORTHODOX PLASTICITY OF MARROW STROMAL CELLS |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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Consequently, the first key question is—where do the multipotent cells of post-natal organisms come from? All answers at this time are hypothetical at best. However, if marrow stromal cells are indeed members of a diffuse system of post-natal multipotent stem cells and they are at the same time vascular/pericytic in nature/origin, then a natural corollary would read that perhaps the microvasculature is a repository of multipotent cells in many, if not all, tissues [70]—a hypothesis that is currently being tested.
A second question is that if multipotent cells are everywhere, or almost everywhere, then what are the mechanisms by which differentiated cells keep their multipotency from making every organ a teratoma? Phrased in another way, adult tissues must retain some kind of organizing ability previously thought of as specific to embryonic organizers. If indeed cells in the bone marrow are able to become muscle or liver or brain, then there must be mechanisms ensuring that there is no liver or brain or muscle in the marrow. Hence, signals for maintenance of a tissue's "self" must exist and be accomplished by differentiated cells. (That is, of course, if stem cells are not "differentiated" cells themselves).
A third question is—how much of the "stemness" (self-renewal and multipotency) observed in experimental systems is inherent to the cells that we manipulate, and how much is due to the manipulation? Are we discovering unknown and unexpected cells, or rather unknown and unexpected effects of manipulation of cells in culture? To what extent do cell culture conditions mimic the effects of an enucleated oocyte cytoplasm, which permits a somatic cell nucleus to generate an organism such as Dolly, the cloned sheep? For sure, a new definition of what a stem cell is—a timely, and biotechnologically correct, one—should incorporate the conditions under which phenomena are recorded, rather than guessing from ex vivo performance what the true in vivo properties are. This exercise also has important implications for understanding where and when stem cells come into action in physiology. Even for the mother of all stem cells, the ES cell, self-renewal and multipotency are limited to specific times and events in vivo, and are much less limited ex vivo. Are similar constraints operating for other stem cells? Marrow stromal stem cells for example, can be expanded extensively in culture, but the majority of them likely never divide in vivo once skeletal growth has ceased (except the few that participate in bone turnover, and perhaps in response to injury or disease). What physiological mechanism calls for resumption of a "stem cell behavior" in vivo in the skeleton and other systems?
All of these questions are important not only for philosophical or esoteric reasons, but also for applicative purposes. Knowing even a few of the answers will undoubtedly enable biotechnology to better harness the magical properties of stem cells for clinical applications.
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TRANSPLANTATION AND TRANSPLANTABILITY OF MARROW STROMAL CELLS |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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Local transplantation of marrow stromal cells for therapeutic applications permits the efficient reconstruction of bone defects larger than those that would spontaneously heal (critical size). A number of preclinical studies in animal models have convincingly shown the feasibility of marrow stromal cell grafts for orthopedic purposes [71-77], even though extensive work lies ahead in order to optimize the procedures, even in their simplest applications. For example, the ideal ex vivo expansion conditions have yet to be determined, or the composition and structure of the ideal carrier, or the numbers of cells that are required for regeneration of a volume of bone.
In addition to utilizing ex vivo-expanded BMSCs for regeneration of bone and associated tissues, evidence of the unorthodox plasticity of marrow stromal cells has suggested their potential use for unorthodox transplantation; that is, for example, to regenerate neural cells or deliver required gene products at unorthodox sites such as the central nervous system (CNS) [78]. This could simplify an approach to cell therapy of the nervous system by eliminating the need for harvesting autologous human neural stem cells, an admittedly difficult procedure, although it is currently believed that heterologous cells may be used for the CNS, given the immune tolerance of the brain. Moreover, if indeed marrow stromal cells represent just a special case of post-natal multipotent stem cells, there is little doubt that they represent one of the most accessible sources of such cells for therapeutic use. The ease with which they are harvested (a simple marrow aspirate), and the simplicity of the procedures required for their culture and expansion in vitro may make them ideal candidates. For applicative purposes, understanding the actual differentiation spectrum of stromal stem cells requires further investigation. Besides neural cells, cardiomyocytes have been reported to represent another possible target of stromal cell manipulation and transplantation [79]. It also remains to be determined whether the myogenic progenitors found in the marrow [64] are indeed stromal (as some recent data would suggest, [80]) or non-stromal in nature [81], or both.
Given their residency in the marrow, and the prevailing view that marrow stromal cells fit into the hematopoietic paradigm, it was unavoidable that systemic transplantation of marrow stromal cells would be attempted [82] in order to cure more generalized skeletal diseases based on the successes of hematopoietic reconstitution by BMT. Yet major uncertainties remain in this area. Undoubtedly, the marrow stromal cell is the entity responsible for conveying genetic alterations into diseases of the skeleton. This is illustrated very well by the ability of these cells to recapitulate natural or targeted genetic abnormalities into abnormal bone formation in animal transplantation assays [83-85]. As such, they also represent a potential repository for therapy to alleviate bone disease. However, a significant rationale for the ability of stromal cells to colonize the skeleton once infused into the circulation is still missing.
The stroma is not transplanted along with hematopoiesis in standard BMT performed for hematological or oncological purposes [86-88]. Infusion of larger numbers of stromal cells than those present in cell preparations used for hematological BMT should be investigated further, as it might result, in principle, in limited engraftment. Stringent criteria must be adopted when assessing successful engraftment of systemically infused stromal cells [61]. The detection of reporter genes in tissue extracts or the isolation in culture of cells of donor origin does not prove cell engraftment; it proves cell survival. In this respect, it should be noted that even intra-arterial infusion of marrow stromal cells in a mouse limb may result in virtually no engraftment, even though abundant cells of donor origin are found impacted within the marrow microvascular network. Of note, these nonengrafted cells would routinely be described as "engrafted" by the use of any reporter gene or ex vivo culture procedure. Less than stringent definitions of stromal cells (for example, their identification by generic or nonspecific markers) must be avoided when attempting their detection in the recipient's marrow. Clear-cut evidence for the sustained integration in the target tissue of differentiated cells of donor origin must be provided. This is rarely the case in current studies claiming engraftment of marrow stromal cells to the skeleton. Some evidence for a limited engraftment of skeletal progenitors following systemic infusion has, however, been obtained in animal models [89, 90]. These data match similar evidence for the possible delivery of marrow-derived myogenic progenitors to muscle via the systemic circulation [64]. It should be kept in mind that both skeletal and muscle tissues are normally formed during development and growth by extravascular cells that exploit migratory processes not involving the circulation. Is there an independent circulatory route for delivery of progenitors to solid phase tissues, and if so, are there physiologically circulating mesodermal progenitors? From where would these cells originate, both in development and post-natal organisms, and how would they negotiate the vessel wall? Addressing these questions is mandatory and requires extensive preclinical work.
Even once these issues are addressed, kinetic considerations regarding skeletal growth and turnover represent another major hurdle that must be overcome in order to cure systemic skeletal diseases via systemic infusion of skeletal progenitors. Yet there is broad opportunity for the treatment of single clinical episodes within the context of skeletal disease. While curing osteogenesis imperfecta by replacing the entire population of mutated skeletal progenitors with normal ones may remain an unattainable goal, individual fractures or deformity in osteogenesis imperfecta or FD of bone could be successfully treated with ex vivo "repaired" stromal cells, for example. Towards this end, future work must focus on the feasibility of transducing or otherwise genetically correcting autologous mutated osteoprogenitors ex vivo, and studies are beginning to move in this direction.
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GENE TRANSFER AND THERAPY UTILIZING BMSCS |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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Depending on the situation, there are several approaches that can be envisioned. If a short-lived effect is the goal, such as in speeding up bone regeneration, transient transduction would be the desired outcome, utilizing methods such as electroporation, chemical methods including calcium phosphate precipitation and lipofection, and plasmids and viral constructs such as adenovirus. Transducing BMSCs with adenoviral constructs containing BMP-2 has demonstrated at least partial efficacy of this approach in hastening bone regeneration in animal models [75, 91, 92]. Adenoviral techniques are attractive due to the lack of toxicity; however, the level at which BMSCs are transfected is variable, and problematic. It has been reported that normal, non-transformed BMSCs require 10x more infective agent than other cell types [93], which is often associated with cellular toxicity. Clearly, further optimization is needed for full implementation of this approach.
For treatment of recessive diseases in which a biological activity is either missing or diminished, long-lasting or permanent transduction is required, and has depended on the use of adeno-associated viruses, retroviruses, lentiviruses (a subclass of retrovirus), and more recently, adeno-retroviral chimeras [94]. These viruses are able to accommodate large constructs of DNA (up to 8 kb), and while retroviruses require active proliferation for efficient transfection, lentiviruses do not. Exogenous biological activity in BMSCs by transduction with retroviral constructs directing the synthesis of reporter molecules, interleukin 3, CD-2, Factor VIII, or the enzymes that synthesize L-DOPA has been reported [78, 95-102]. However, these studies also highlight some of the hurdles that must be overcome before this technology will become practical. The first hurdle is optimization of ex vivo transfection. It has been reported that lengthy ex vivo expansion (3-4 weeks) to increase cell numbers reduces transfectability of BMSCs, whereas short-term culture (10-12 days) does not [98]. Furthermore, high levels of transduction may require multiple rounds of transfection [95, 101]. The second hurdle relates to the durability of the desired gene expression. No reported study has extended beyond 4 months post-transplantation of transduced cells [99] (Gronthos, unpublished results), and in most instances, it has been reported that expression decreases with time [96], due to promoter inactivation [102] and/or loss of transduced cells (Mankani and Robey, unpublished results). While promising, these results point to the need for careful consideration of the ex vivo methods, choice of promoter to drive the desired biological activity, and assessment of the ability of the transduced BMSCs to retain their ability to self-maintain upon in vivo transplantation. It must also be pointed out that using retrovirally transduced BMSCs for this type of application, providing a missing or decreased biological activity, does not necessarily require that they truly engraft, as defined above. They may be able to perform this function by remaining resident without actually physically incorporating and functioning within a connective tissue. In this case, they can be envisioned as forming an in vivo biological mini-pump as a means of introducing a required factor, as opposed to standard means of oral or systemic administration.
Use of transduced BMSCs for the treatment of a dominant negative disease, in which there is actual expression of misfunctioning or inappropriate biological activity, is far more problematic, independent of whether we are able to deliver BMSCs systemically or orthotopically. In this case, an activity must be silenced such that it does not interfere with any normal activity that is present, or reintroduced by any other means. The most direct approach would be the application of homologous recombination, as applied to ES cells and generation of transgenic animals. The almost vanishing low rate of homologous recombination in current methodology, coupled with issues of the identification, separation, and expansion of such recombinants does not make this seem feasible in the near future. However, new techniques for increasing the rate of homologous recombinations are under development [103] which may make this approach more feasible. Another approach to gene therapy is based on the processes whereby mismatches in DNA heteroduplexes that arise sporadically during normal cell activity are automatically corrected. Genetic mutations could be targeted by introducing exogenous DNA with the desired sequence (either short DNA oligonucleotides or chimeric RNA/DNA oligonucleotides) which binds to homologous sequences in the genome forming a heteroduplex that is then rectified by a number of naturally occurring repair processes [104]. A third option exists using a specially constructed oligonucleotide that binds to the gene in question to form a triple helical structure, thereby disallowing gene transcription [105].
While it would be highly desirable to correct a genetic disease at the genomic level, mRNA represents another very significant target, and perhaps a more accessible one, to silence the activity of a dominant negative gene. Methods for inhibiting mRNA translation and/or increasing its degradation have been employed through the use of protein decoys to prevent association of a particular mRNA to the biosynthetic machinery and antisense sequences (either oligonucleotides or full-length sequences). Double-stranded RNA also induces rapid degradation of mRNA (termed RNA interference, RNAi) by a process that is not well understood [105]. However, eliminating mRNAs transcribed from a mutant allele with short or single-base mutations by these approaches would most likely not maintain mRNA from a normal allele. For this reason, hammerhead and hairpin ribozymes represent yet another alternative, based on their ability to bind to very specific sequences, and to cleave them and inactivate them from subsequent translation. Consequently, incorporating a mutant sequence, even one that transcribes a single base mutation, can direct a hammerhead or hairpin ribozyme to inactivate a very specific mRNA. This approach is currently being probed for its possible use in the treatment of osteogenesis imperfecta [106]. Taking this technology one step further, DNAzymes that mimic the enzymatic activity of ribozymes, which would be far more stable than ribozymes, are also being developed. Regardless of whether genomic or cytoplasmic sequences are the target of gene therapy, the efficacy of all of these new technologies will depend on: A) the efficiency at which the reagents are incorporated into BMSCs in the ex vivo environment; B) the selection of specific targets, and C) the maintenance of the ability of BMSCs to function appropriately in vitro.
In conclusion, the isolation of post-natal stem cells from a variety of tissues along with discovery of their unexpected capabilities has provided us with a new conceptual framework in which to both view them and use them. However, even with this new perspective, there is much to be done to better understand them: their origins, their relationships to one another, their ability to differentiate or re-differentiate, their physiological role during development, growth, and maturity, and in disease. These types of studies will most certainly require a great deal of interdisciplinary crosstalk between investigators in the areas of natal and post-natal development, and in different organ systems. Clearly, as these studies progress, open mindedness will be needed to better understand the nature of this exciting family of cells, as well as to better understand the full utilization of stem cells with or without genetic manipulation. Much to be learned. Much to be gained.
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ACKNOWLEDGMENTS |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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References |
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TopAbstractIntroductionColony Forming Unit-Fibroblast...Heterogeneity of the BMSC...Post-Natal Marrow Stromal Cells...Orthodox Plasticity of Marrow...Unorthodox Plasticity of Marrow...Transplantation and...Gene Transfer and Therapy...References |
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H. Miraoui, K. Oudina, H. Petite, Y. Tanimoto, K. Moriyama, and P. J. Marie Fibroblast Growth Factor Receptor 2 Promotes Osteogenic Differentiation in Mesenchymal Cells via ERK1/2 and Protein Kinase C Signaling J. Biol. Chem., February 20, 2009; 284(8): 4897 - 4904. [Abstract] [Full Text] [PDF]
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P. J. Psaltis, A. C.W. Zannettino, S. G. Worthley, and S. Gronthos Concise Review: Mesenchymal Stromal Cells: Potential for Cardiovascular Repair Stem Cells, September 1, 2008; 26(9): 2201 - 2210. [Abstract] [Full Text] [PDF]
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N. Kaltz, A. Funari, S. Hippauf, B. Delorme, D. Noel, M. Riminucci, V. R. Jacobs, T. Haupl, C. Jorgensen, P. Charbord, et al. In Vivo Osteoprogenitor Potency of Human Stromal Cells from Different Tissues Does Not Correlate with Expression of POU5F1 or Its Pseudogenes Stem Cells, September 1, 2008; 26(9): 2419 - 2424. [Abstract] [Full Text] [PDF]
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M. Morigi, M. Introna, B. Imberti, D. Corna, M. Abbate, C. Rota, D. Rottoli, A. Benigni, N. Perico, C. Zoja, et al. Human Bone Marrow Mesenchymal Stem Cells Accelerate Recovery of Acute Renal Injury and Prolong Survival in Mice Stem Cells, August 1, 2008; 26(8): 2075 - 2082. [Abstract] [Full Text] [PDF]
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G. Forte, F. Carotenuto, F. Pagliari, S. Pagliari, P. Cossa, R. Fiaccavento, A. Ahluwalia, G. Vozzi, B. Vinci, A. Serafino, et al. Criticality of the Biological and Physical Stimuli Array Inducing Resident Cardiac Stem Cell Determination Stem Cells, August 1, 2008; 26(8): 2093 - 2103. [Abstract] [Full Text] [PDF]
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Z. Belaid-Choucair, Y. Lepelletier, G. Poncin, A. Thiry, C. Humblet, M. Maachi, A. Beaulieu, E. Schneider, A. Briquet, P. Mineur, et al. Human Bone Marrow Adipocytes Block Granulopoiesis Through Neuropilin-1-Induced Granulocyte Colony-Stimulating Factor Inhibition Stem Cells, June 1, 2008; 26(6): 1556 - 1564. [Abstract] [Full Text] [PDF]
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 K.E. Schwab, P. Hutchinson, and C.E. Gargett Identification of surface markers for prospective isolation of human endometrial stromal colony-forming cells Hum. Reprod., April 1, 2008; 23(4): 934 - 943. [Abstract] [Full Text] [PDF]
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S. Ramanadham, K. E. Yarasheski, M. J. Silva, M. Wohltmann, D. V. Novack, B. Christiansen, X. Tu, S. Zhang, X. Lei, and J. Turk Age-Related Changes in Bone Morphology Are Accelerated in Group VIA Phospholipase A2 (iPLA2{beta})-Null Mice Am. J. Pathol., April 1, 2008; 172(4): 868 - 881. [Abstract] [Full Text] [PDF]
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A. M. Sonabend, I. V. Ulasov, M. A. Tyler, A. A. Rivera, J. M. Mathis, and M. S. Lesniak Mesenchymal Stem Cells Effectively Deliver an Oncolytic Adenovirus to Intracranial Glioma Stem Cells, March 1, 2008; 26(3): 831 - 841. [Abstract] [Full Text] [PDF]
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D Mrugala, C Bony, N Neves, L Caillot, S Fabre, D Moukoko, C Jorgensen, and D Noel Phenotypic and functional characterisation of ovine mesenchymal stem cells: application to a cartilage defect model Ann Rheum Dis, March 1, 2008; 67(3): 288 - 295. [Abstract] [Full Text] [PDF]
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U. Lakshmipathy and R. P. Hart Concise Review: MicroRNA Expression in Multipotent Mesenchymal Stromal Cells Stem Cells, February 1, 2008; 26(2): 356 - 363. [Abstract] [Full Text] [PDF]
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Z. Zhao, Z. Wang, C. Ge, P. Krebsbach, and R.T. Franceschi Healing Cranial Defects with AdRunx2-transduced Marrow Stromal Cells Journal of Dental Research, December 1, 2007; 86(12): 1207 - 1211. [Abstract] [Full Text] [PDF]
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S. J. Greco, K. Liu, and P. Rameshwar Functional Similarities Among Genes Regulated by Oct4 in Human Mesenchymal and Embryonic Stem Cells Stem Cells, December 1, 2007; 25(12): 3143 - 3154. [Abstract] [Full Text] [PDF]
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K.E. Schwab and C.E. Gargett Co-expression of two perivascular cell markers isolates mesenchymal stem-like cells from human endometrium Hum. Reprod., November 1, 2007; 22(11): 2903 - 2911. [Abstract] [Full Text] [PDF]
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K. A. Trzaska, E. V. Kuzhikandathil, and P. Rameshwar Specification of a Dopaminergic Phenotype from Adult Human Mesenchymal Stem Cells Stem Cells, November 1, 2007; 25(11): 2797 - 2808. [Abstract] [Full Text] [PDF]
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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, November 1, 2007; 25(11): 2896 - 2902. [Abstract] [Full Text] [PDF]
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S. J. Greco, S. V. Smirnov, R. G. Murthy, and P. Rameshwar Synergy between the RE-1 Silencer of Transcription and NF{kappa}B in the Repression of the Neurotransmitter Gene TAC1 in Human Mesenchymal Stem Cells J. Biol. Chem., October 12, 2007; 282(41): 30039 - 30050. [Abstract] [Full Text] [PDF]
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M.-S. Tsai, S.-M. Hwang, K.-D. Chen, Y.-S. Lee, L.-W. Hsu, Y.-J. Chang, C.-N. Wang, H.-H. Peng, Y.-L. Chang, A.-S. Chao, et al. Functional Network Analysis of the Transcriptomes of Mesenchymal Stem Cells Derived from Amniotic Fluid, Amniotic Membrane, Cord Blood, and Bone Marrow Stem Cells, October 1, 2007; 25(10): 2511 - 2523. [Abstract] [Full Text] [PDF]
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S. J. Greco and P. Rameshwar Enhancing Effect of IL-1{alpha} on Neurogenesis from Adult Human Mesenchymal Stem Cells: Implication for Inflammatory Mediators in Regenerative Medicine J. Immunol., September 1, 2007; 179(5): 3342 - 3350. [Abstract] [Full Text] [PDF]
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 R. A. Cahill, D. Wenkert, S. A. Perlman, A. Steele, S. P. Coburn, W. H. McAlister, S. Mumm, and M. P. Whyte Infantile Hypophosphatasia: Transplantation Therapy Trial Using Bone Fragments and Cultured Osteoblasts J. Clin. Endocrinol. Metab., August 1, 2007; 92(8): 2923 - 2930. [Abstract] [Full Text] [PDF]
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M. Shi, J. Li, L. Liao, B. Chen, B. Li, L. Chen, H. Jia, and R. C. Zhao Regulation of CXCR4 expression in human mesenchymal stem cells by cytokine treatment: role in homing efficiency in NOD/SCID mice Haematologica, July 1, 2007; 92(7): 897 - 904. [Abstract] [Full Text] [PDF]
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S. A. Kuznetsov, M. H. Mankani, A. I. Leet, N. Ziran, S. Gronthos, and P. G. Robey Circulating Connective Tissue Precursors: Extreme Rarity in Humans and Chondrogenic Potential in Guinea Pigs Stem Cells, July 1, 2007; 25(7): 1830 - 1839. [Abstract] [Full Text] [PDF]
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N. Meissner, M. Rutkowski, A. L. Harmsen, S. Han, and A. G. Harmsen Type I Interferon Signaling and B Cells Maintain Hemopoiesis during Pneumocystis Infection of the Lung J. Immunol., May 15, 2007; 178(10): 6604 - 6615. [Abstract] [Full Text] [PDF]
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D. Fang, B.-M. Seo, Y. Liu, W. Sonoyama, T. Yamaza, C. Zhang, S. Wang, and S. Shi Transplantation of Mesenchymal Stem Cells Is an Optimal Approach for Plastic Surgery Stem Cells, April 1, 2007; 25(4): 1021 - 1028. [Abstract] [Full Text] [PDF]
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 T. J. Bivalacqua, W. Deng, M. Kendirci, M. F. Usta, C. Robinson, B. K. Taylor, S. N. Murthy, H. C. Champion, W. J. G. Hellstrom, and P. J. Kadowitz Mesenchymal stem cells alone or ex vivo gene modified with endothelial nitric oxide synthase reverse age-associated erectile dysfunction Am J Physiol Heart Circ Physiol, March 1, 2007; 292(3): H1278 - H1290. [Abstract] [Full Text] [PDF]
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D. Falconi, K. Oizumi, and J. E. Aubin Leukemia Inhibitory Factor Influences the Fate Choice of Mesenchymal Progenitor Cells Stem Cells, February 1, 2007; 25(2): 305 - 312. [Abstract] [Full Text] [PDF]
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F. Anjos-Afonso and D. Bonnet Nonhematopoietic/endothelial SSEA-1+ cells define the most primitive progenitors in the adult murine bone marrow mesenchymal compartment Blood, February 1, 2007; 109(3): 1298 - 1306. [Abstract] [Full Text] [PDF]
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Q. He, C. Wan, and G. Li Concise Review: Multipotent Mesenchymal Stromal Cells in Blood Stem Cells, January 1, 2007; 25(1): 69 - 77. [Abstract] [Full Text] [PDF]
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A. L. Moharita, M. Taborga, K. E. Corcoran, M. Bryan, P. S. Patel, and P. Rameshwar SDF-1{alpha} regulation in breast cancer cells contacting bone marrow stroma is critical for normal hematopoiesis Blood, November 15, 2006; 108(10): 3245 - 3252. [Abstract] [Full Text] [PDF]
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G. Y. Rochefort, B. Delorme, A. Lopez, O. Herault, P. Bonnet, P. Charbord, V. Eder, and J. Domenech Multipotential Mesenchymal Stem Cells Are Mobilized into Peripheral Blood by Hypoxia Stem Cells, October 1, 2006; 24(10): 2202 - 2208. [Abstract] [Full Text] [PDF]
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X. Wang, F. Li, and C. Niyibizi Progenitors Systemically Transplanted into Neonatal Mice Localize to Areas of Active Bone Formation In Vivo: Implications of Cell Therapy for Skeletal Diseases Stem Cells, August 1, 2006; 24(8): 1869 - 1878. [Abstract] [Full Text] [PDF]
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D. Kim, S. W. Cho, S. J. Her, J. Y. Yang, S. W. Kim, S. Y. Kim, and C. S. Shin Retrovirus-Mediated Gene Transfer of Receptor Activator of Nuclear Factor-{kappa}B-Fc Prevents Bone Loss in Ovariectomized Mice Stem Cells, July 1, 2006; 24(7): 1798 - 1805. [Abstract] [Full Text] [PDF]
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M. Sudres, F. Norol, A. Trenado, S. Gregoire, F. Charlotte, B. Levacher, J.-J. Lataillade, P. Bourin, X. Holy, J.-P. Vernant, et al. Bone Marrow Mesenchymal Stem Cells Suppress Lymphocyte Proliferation In Vitro but Fail to Prevent Graft-versus-Host Disease in Mice. J. Immunol., June 15, 2006; 176(12): 7761 - 7767. [Abstract] [Full Text] [PDF]
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J. L. Chan, K. C. Tang, A. P. Patel, L. M. Bonilla, N. Pierobon, N. M. Ponzio, and P. Rameshwar Antigen-presenting property of mesenchymal stem cells occurs during a narrow window at low levels of interferon-{gamma} Blood, June 15, 2006; 107(12): 4817 - 4824. [Abstract] [Full Text] [PDF]
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R. Ebert, M. Ulmer, S. Zeck, J. Meissner-Weigl, D. Schneider, H. Stopper, N. Schupp, M. Kassem, and F. Jakob Selenium Supplementation Restores the Antioxidative Capacity and Prevents Cell Damage in Bone Marrow Stromal Cells In Vitro Stem Cells, May 1, 2006; 24(5): 1226 - 1235. [Abstract] [Full Text] [PDF]
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S.-H. Mirmalek-Sani, R. S. Tare, S. M. Morgan, H. I. Roach, D. I. Wilson, N. A. Hanley, and R. O.C. Oreffo Characterization and Multipotentiality of Human Fetal Femur-Derived Cells: Implications for Skeletal Tissue Regeneration Stem Cells, April 1, 2006; 24(4): 1042 - 1053. [Abstract] [Full Text] [PDF]
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K. Tamama, V. H. Fan, L. G. Griffith, H. C. Blair, and A. Wells Epidermal Growth Factor as a Candidate for Ex Vivo Expansion of Bone Marrow-Derived Mesenchymal Stem Cells Stem Cells, March 1, 2006; 24(3): 686 - 695. [Abstract] [Full Text] [PDF]
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F. Mannello, G. A.M. Tonti, G. P. Bagnara, and S. Papa Role and Function of Matrix Metalloproteinases in the Differentiation and Biological Characterization of Mesenchymal Stem Cells Stem Cells, March 1, 2006; 24(3): 475 - 481. [Abstract] [Full Text] [PDF]
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G. Forte, M. Minieri, P. Cossa, D. Antenucci, M. Sala, V. Gnocchi, R. Fiaccavento, F. Carotenuto, P. De Vito, P. M. Baldini, et al. Hepatocyte Growth Factor Effects on Mesenchymal Stem Cells: Proliferation, Migration, and Differentiation Stem Cells, January 1, 2006; 24(1): 23 - 33. [Abstract] [Full Text] [PDF]
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M. Reyes, S. Li, J. Foraker, E. Kimura, and J. S. Chamberlain Donor origin of multipotent adult progenitor cells in radiation chimeras Blood, November 15, 2005; 106(10): 3646 - 3649. [Abstract] [Full Text] [PDF]
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T. Tondreau, N. Meuleman, A. Delforge, M. Dejeneffe, R. Leroy, M. Massy, C. Mortier, D. Bron, and L. Lagneaux Mesenchymal Stem Cells Derived from CD133-Positive Cells in Mobilized Peripheral Blood and Cord Blood: Proliferation, Oct4 Expression, and Plasticity Stem Cells, September 1, 2005; 23(8): 1105 - 1112. [Abstract] [Full Text] [PDF]
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A. Braccini, D. Wendt, C. Jaquiery, M. Jakob, M. Heberer, L. Kenins, A. Wodnar-Filipowicz, R. Quarto, and I. Martin Three-Dimensional Perfusion Culture of Human Bone Marrow Cells and Generation of Osteoinductive Grafts Stem Cells, September 1, 2005; 23(8): 1066 - 1072. [Abstract] [Full Text] [PDF]
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L. Wang, S. Clutter, J. Benincosa, J. Fortney, and L. F. Gibson Activation of Transforming Growth Factor-{beta}1/p38/Smad3 Signaling in Stromal Cells Requires Reactive Oxygen Species-Mediated MMP-2 Activity During Bone Marrow Damage Stem Cells, September 1, 2005; 23(8): 1122 - 1134. [Abstract] [Full Text] [PDF]
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Y. Bi, C. H. Stuelten, T. Kilts, S. Wadhwa, R. V. Iozzo, P. G. Robey, X.-D. Chen, and M. F. Young Extracellular Matrix Proteoglycans Control the Fate of Bone Marrow Stromal Cells J. Biol. Chem., August 26, 2005; 280(34): 30481 - 30489. [Abstract] [Full Text] [PDF]
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A. Kortesidis, A. Zannettino, S. Isenmann, S. Shi, T. Lapidot, and S. Gronthos Stromal-derived factor-1 promotes the growth, survival, and development of human bone marrow stromal stem cells Blood, May 15, 2005; 105(10): 3793 - 3801. [Abstract] [Full Text] [PDF]
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A. Nakamizo, F. Marini, T. Amano, A. Khan, M. Studeny, J. Gumin, J. Chen, S. Hentschel, G. Vecil, J. Dembinski, et al. Human Bone Marrow-Derived Mesenchymal Stem Cells in the Treatment of Gliomas Cancer Res., April 15, 2005; 65(8): 3307 - 3318. [Abstract] [Full Text] [PDF]
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P. Terness, J.-J. Chuang, T. Bauer, L. Jiga, and G. Opelz Regulation of human auto- and alloreactive T cells by indoleamine 2,3-dioxygenase (IDO)-producing dendritic cells: too much ado about IDO? Blood, March 15, 2005; 105(6): 2480 - 2486. [Abstract] [Full Text] [PDF]
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K. J. Cho, K. A. Trzaska, S. J. Greco, J. McArdle, F. S. Wang, J.-H. Ye, and P. Rameshwar Neurons Derived From Human Mesenchymal Stem Cells Show Synaptic Transmission and Can Be Induced to Produce the Neurotransmitter Substance P by Interleukin-1{alpha} Stem Cells, March 1, 2005; 23(3): 383 - 391. [Abstract] [Full Text] [PDF]
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W. Deng, T. J. Bivalacqua, N. N. Chattergoon, J. R. Jeter Jr., and P. J. Kadowitz Engineering Ex Vivo-Expanded Marrow Stromal Cells to Secrete Calcitonin Gene-Related Peptide Using Adenoviral Vector Stem Cells, December 1, 2004; 22(7): 1279 - 1291. [Abstract] [Full Text] [PDF]
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S. Masson, D. J. Harrison, J. N. Plevris, and P. N. Newsome Potential of Hematopoietic Stem Cell Therapy in Hepatology: A Critical Review Stem Cells, November 1, 2004; 22(6): 897 - 907. [Abstract] [Full Text] [PDF]
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F. Anjos-Afonso, E. K. Siapati, and D. Bonnet In vivo contribution of murine mesenchymal stem cells into multiple cell-types under minimal damage conditions J. Cell Sci., November 1, 2004; 117(23): 5655 - 5664. [Abstract] [Full Text] [PDF]
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Y. Sakaguchi, I. Sekiya, K. Yagishita, S. Ichinose, K. Shinomiya, and T. Muneta Suspended cells from trabecular bone by collagenase digestion become virtually identical to mesenchymal stem cells obtained from marrow aspirates Blood, November 1, 2004; 104(9): 2728 - 2735. [Abstract] [Full Text] [PDF]
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S. L. Etheridge, G. J. Spencer, D. J. Heath, and P. G. Genever Expression Profiling and Functional Analysis of Wnt Signaling Mechanisms in Mesenchymal Stem Cells Stem Cells, September 1, 2004; 22(5): 849 - 860. [Abstract] [Full Text] [PDF]
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M. Morigi, B. Imberti, C. Zoja, D. Corna, S. Tomasoni, M. Abbate, D. Rottoli, S. Angioletti, A. Benigni, N. Perico, et al. Mesenchymal Stem Cells Are Renotropic, Helping to Repair the Kidney and Improve Function in Acute Renal Failure J. Am. Soc. Nephrol., July 1, 2004; 15(7): 1794 - 1804. [Abstract] [Full Text] [PDF]
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R. Meisel, A. Zibert, M. Laryea, U. Gobel, W. Daubener, and D. Dilloo Human bone marrow stromal cells inhibit allogeneic T-cell responses by indoleamine 2,3-dioxygenase-mediated tryptophan degradation Blood, June 15, 2004; 103(12): 4619 - 4621. [Abstract] [Full Text] [PDF]
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M. Bensidhoum, A. Chapel, S. Francois, C. Demarquay, C. Mazurier, L. Fouillard, S. Bouchet, J. M. Bertho, P. Gourmelon, J. Aigueperse, et al. Homing of in vitro expanded Stro-1- or Stro-1+ human mesenchymal stem cells into the NOD/SCID mouse and their role in supporting human CD34 cell engraftment Blood, May 1, 2004; 103(9): 3313 - 3319. [Abstract] [Full Text] [PDF]
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P. A. Dreyfus, F. Chretien, B. Chazaud, Y. Kirova, P. Caramelle, L. Garcia, G. Butler-Browne, and R. K. Gherardi Adult Bone Marrow-Derived Stem Cells in Muscle Connective Tissue and Satellite Cell Niches Am. J. Pathol., March 1, 2004; 164(3): 773 - 779. [Abstract] [Full Text] [PDF]
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 X.-Y. Zhang, V. F. La Russa, and J. Reiser Transduction of Bone-Marrow-Derived Mesenchymal Stem Cells by Using Lentivirus Vectors Pseudotyped with Modified RD114 Envelope Glycoproteins J. Virol., February 1, 2004; 78(3): 1219 - 1229. [Abstract] [Full Text] [PDF]
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 K. G. Sylvester and M. T. Longaker Stem Cells: Review and Update Arch Surg, January 1, 2004; 139(1): 93 - 99. [Abstract] [Full Text] [PDF]
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 S. O. Rzonca, L. J. Suva, D. Gaddy, D. C. Montague, and B. Lecka-Czernik Bone Is a Target for the Antidiabetic Compound Rosiglitazone Endocrinology, January 1, 2004; 145(1): 401 - 406. [Abstract] [Full Text] [PDF]
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S. Batouli, M. Miura, J. Brahim, T.W. Tsutsui, L.W. Fisher, S. Gronthos, P. G. Robey, and S. Shi Comparison of Stem-cell-mediated Osteogenesis and Dentinogenesis Journal of Dental Research, December 1, 2003; 82(12): 976 - 981. [Abstract] [Full Text] [PDF]
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 R. Gorlick, P. Anderson, I. Andrulis, C. Arndt, G. P. Beardsley, M. Bernstein, J. Bridge, N.-K. Cheung, J. S. Dome, D. Ebb, et al. Biology of Childhood Osteogenic Sarcoma and Potential Targets for Therapeutic Development: Meeting Summary Clin. Cancer Res., November 15, 2003; 9(15): 5442 - 5453. [Abstract] [Full Text] [PDF]
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 M. Kuwana, Y. Okazaki, H. Kodama, K. Izumi, H. Yasuoka, Y. Ogawa, Y. Kawakami, and Y. Ikeda Human circulating CD14+ monocytes as a source of progenitors that exhibit mesenchymal cell differentiation J. Leukoc. Biol., November 1, 2003; 74(5): 833 - 845. [Abstract] [Full Text] [PDF]
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W. A. Silva Jr., D. T. Covas, R. A. Panepucci, R. Proto-Siqueira, J. L.C. Siufi, D. L. Zanette, A. R.D. Santos, and M. A. Zago The Profile of Gene Expression of Human Marrow Mesenchymal Stem Cells Stem Cells, November 1, 2003; 21(6): 661 - 669. [Abstract] [Full Text] [PDF]
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 W. Deng, T. J. Bivalacqua, N. N. Chattergoon, A. L. Hyman, J. R. Jeter Jr., and P. J. Kadowitz Adenoviral gene transfer of eNOS: high-level expression in ex vivo expanded marrow stromal cells Am J Physiol Cell Physiol, November 1, 2003; 285(5): C1322 - C1329. [Abstract] [Full Text] [PDF]
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J. A. Potian, H. Aviv, N. M. Ponzio, J. S. Harrison, and P. Rameshwar Veto-Like Activity of Mesenchymal Stem Cells: Functional Discrimination Between Cellular Responses to Alloantigens and Recall Antigens J. Immunol., October 1, 2003; 171(7): 3426 - 3434. [Abstract] [Full Text] [PDF]
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S. Davani, A. Marandin, N. Mersin, B. Royer, B. Kantelip, P. Herve, J.-P. Etievent, and J.-P. Kantelip Mesenchymal Progenitor Cells Differentiate into an Endothelial Phenotype, Enhance Vascular Density, and Improve Heart Function in a Rat Cellular Cardiomyoplasty Model Circulation, September 9, 2003; 108(90101): II-253 - 258. [Abstract] [Full Text] [PDF]
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S. Sun, Z. Guo, X. Xiao, B. Liu, X. Liu, P.-H. Tang, and N. Mao Isolation of Mouse Marrow Mesenchymal Progenitors by a Novel and Reliable Method Stem Cells, September 1, 2003; 21(5): 527 - 535. [Abstract] [Full Text] [PDF]
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R. Cancedda, G. Bianchi, A. Derubeis, and R. Quarto Cell Therapy for Bone Disease: A Review of Current Status Stem Cells, September 1, 2003; 21(5): 610 - 619. [Abstract] [Full Text] [PDF]
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 N. Rosenthal Prometheus's Vulture and the Stem-Cell Promise N. Engl. J. Med., July 17, 2003; 349(3): 267 - 274. [Full Text] [PDF]
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 G. Collett, A. Wood, M. Y. Alexander, B. C. Varnum, R. P. Boot-Handford, V. Ohanian, J. Ohanian, Y.-W. Fridell, and A. E. Canfield Receptor Tyrosine Kinase Axl Modulates the Osteogenic Differentiation of Pericytes Circ. Res., May 30, 2003; 92(10): 1123 - 1129. [Abstract] [Full Text] [PDF]
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S. Gronthos, A. C. W. Zannettino, S. J. Hay, S. Shi, S. E. Graves, A. Kortesidis, and P. J. Simmons Molecular and cellular characterisation of highly purified stromal stem cells derived from human bone marrow J. Cell Sci., May 1, 2003; 116(9): 1827 - 1835. [Abstract] [Full Text] [PDF]
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J. Chagraoui, A. Lepage-Noll, A. Anjo, G. Uzan, and P. Charbord Fetal liver stroma consists of cells in epithelial-to-mesenchymal transition Blood, April 15, 2003; 101(8): 2973 - 2982. [Abstract] [Full Text] [PDF]
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S. M. Devine, C. Cobbs, M. Jennings, A. Bartholomew, and R. Hoffman Mesenchymal stem cells distribute to a wide range of tissues following systemic infusion into nonhuman primates Blood, April 15, 2003; 101(8): 2999 - 3001. [Abstract] [Full Text] [PDF]
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