Growth and repair of skeletal muscle are normally mediated by the satellite cells that surround muscle fibers. In regenerating muscle, however, the number of myogenic precursors exceeds that of resident satellite cells, implying migration or recruitment of undifferentiated progenitors from other sources. Transplantation of genetically marked bone marrow into immunodeficient mice revealed that marrow-derived cells migrate into areas of induced muscle degeneration, undergo myogenic differentiation, and participate in the regeneration of the damaged fibers. Genetically modified, marrow-derived myogenic progenitors could potentially be used to target therapeutic genes to muscle tissue, providing an alternative strategy for treatment of muscular dystrophies.

In allogeneic bone marrow transplantation (allo-BMT), donor lymphocytes play a central therapeutic role in both graft-versus-leukemia (GvL) and immune reconstitution. However, their use is limited by the risk of severe graft-versus-host disease (GvHD). Eight patients who relapsed or developed Epstein-Barr virus-induced lymphoma after T cell-depleted BMT were then treated with donor lymphocytes transduced with the herpes simplex virus thymidine kinase (HSV-TK) suicide gene. The transduced lymphocytes survived for up to 12 months, resulting in antitumor activity in five patients. Three patients developed GvHD, which could be effectively controlled by ganciclovir-induced elimination of the transduced cells. These data show that genetic manipulation of donor lymphocytes may increase the efficacy and safety of allo-BMT and expand its application to a larger number of patients.

IntroductionBone marrow (BM) is a complex tissue containing hematopoietic progenitor cells and a connective-tissue network of stromal cells. Marrow stroma includes a subpopulation of undifferentiated cells that are capable of becoming one of a number of phenotypes, including bone and cartilage, tendon, muscle, fat, and marrow stromal connective tissue that supports hematopoietic cell differentiation. 1,2 These cells are referred to as mesenchymal stem cells (MSCs), since they are known to have capacity of proliferation and differentiation into the mesenchymal lineage. Due to their potential for differentiation into different tissues, MSCs have emerged as a promising tool for clinical applications such as tissue engineering and cell and gene therapy. [3][4][5] Several reports underline the ability of MSCs to migrate. [6][7][8][9][10][11][12][13] MSCs are thought to migrate in the bloodstream to seed new sites of hematopoiesis and to various tissues during embryonic and fetal development. 14,15 MSCs are present in large numbers in human blood from at least 7 weeks' gestation and they persist until approximately 12 weeks' gestation. 14 Although circulating MSCs decrease after 12 weeks, there is evidence that a very lowfrequency population of circulating multipotent nonhematopoietic cells resembling the classical MSCs persist through to adult life. [16][17][18] MSCs migrate efficiently to hematopoietic tissues (BM and spleen) after transplantation in some experimental animal models, 19,20 whereas reports of BM homing in humans are inconsistent. [21][22][23][24][25][26] Of particular interest for tissue remodeling, intravenous delivery of MSCs results in their specific migration to a site of injury. [6][7][8]10,27 This ability of implanted MSCs to seek out the site of tissue damage has been demonstrated in bone or cartilage fracture, 28 myocardial infarction, 8,29 and ischemic cerebral injury. 6,10,11 Because MSCs have been shown to give rise to many tissues (such as bone, cartilage, fat, endothelia, muscle, brain, and pancreatic islet cells 30,31 ), migrating MSCs may represent a source of pluripotent cells that are constantly available for the repair of damaged organs. The mechanisms that guide homing of implanted cells are unclear. In this study, we examined the role of chemokines and their receptors in the migration of human MSCs. Moreover the interaction between human pancreatic islets and MSCs was investigated as a model of tissue cross talk. Material and methods Human bone marrow mesenchymal stem cell cultureHuman bone marrow mesenchymal stem cells (BM-MSCs) were obtained from Cambrex (Baltimore, MD). There were 3 different batches used for the study. Before use, the cells were analyzed for morphology, marker For personal use only. on May 11, 2018. by guest www.bloodjournal.org From expression, and osteogenic differentiation. All batches used had a fibroblastlike morphology in culture, were homogeneously CD73 ϩ , CD105 ϩ , HLA I ϩ , ␣V␤3 ϩ , ␣V␤5 ϩ , CD34 Ϫ , CD45 Ϫ , CD117 Ϫ , CD31 Ϫ , HLAII Ϫ , CD18 Ϫ , CD80...

Adenosine deaminase (ADA) deficiency results in severe combined immunodeficiency, the first genetic disorder treated by gene therapy. Two different retroviral vectors were used to transfer ex vivo the human ADA minigene into bone marrow cells and peripheral blood lymphocytes from two patients undergoing exogenous enzyme replacement therapy. After 2 years of treatment, long-term survival of T and B lymphocytes, marrow cells, and granulocytes expressing the transferred ADA gene was demonstrated and resulted in normalization of the immune repertoire and restoration of cellular and humoral immunity. After discontinuation of treatment, T lymphocytes, derived from transduced peripheral blood lymphocytes, were progressively replaced by marrow-derived T cells in both patients. These results indicate successful gene transfer into long-lasting progenitor cells, producing a functional multilineage progeny.

It has recently been shown that mononuclear cells from murine skeletal muscle contain the potential to repopulate all major peripheral blood lineages in lethally irradiated mice, but the origin of this activity is unknown. We have fractionated muscle cells on the basis of hematopoietic markers to show that the active population exclusively expresses the hematopoietic stem cell antigens Sca-1 and CD45. Muscle cells obtained from 6-to 8-week-old C57BL͞6-CD45.1 mice and enriched for cells expressing Sca-1 and CD45 were able to generate hematopoietic but not myogenic colonies in vitro and repopulated multiple hematopoietic lineages of lethally irradiated C57BL͞6-CD45.2 mice. These data show that muscle-derived hematopoietic stem cells are likely derived from the hematopoietic system and are a result not of transdifferentiation of myogenic stem cells but instead of the presence of substantial numbers of hematopoietic stem cells in the muscle. Although CD45-negative cells were highly myogenic in vitro and in vivo, CD45-positive muscle-derived cells displayed only very limited myogenic activity and only in vivo.S tem cells are defined by their ability to self renew and differentiate into the cell types of their derivative tissue. Traditionally, it has been assumed that a stem cell derived from adult tissues can give rise only to progeny specific to that tissue type. However, this dogma has been challenged recently by a series of studies that suggest that adult tissue-derived stem cells may have the potential to differentiate into disparate cell types. For example, purified hematopoietic stem cells (HSCs), derived from whole bone marrow (WBM), have been shown to contribute to regenerating skeletal muscle (1), cardiac muscle (2), liver (3), and multiple epithelial tissues (4). In addition, stem cells from other tissues have also been proposed to differentiate outside their tissue of origin (5, 6). Although these studies have provoked new critical thinking about stem cell differentiation capacity, definitive proof of transdifferentiation remains to be established at a clonal level.Two recent studies focused on the ability of muscle-derived cells to repopulate WBM in lethally irradiated mice. Gussoni et al. (1) reported that muscle cells fractionated on the basis of their efflux of Hoechst dye could rescue lethally irradiated recipients. Similarly, Jackson et al. (7) reported that unfractionated mononuclear muscle cells could repopulate all major blood lineages of lethally irradiated mice up to 12 weeks after transplant. In addition, when bone marrow from engrafted animals was transplanted into secondary recipients, their peripheral blood was also repopulated with muscle-derived cells, demonstrating the important property of self renewal (7).Satellite cells are a potent myogenic stem cell population that resides in the muscle and are responsible for postnatal muscle regeneration and growth (8, 9). We proposed that satellite cells accounted for muscle-derived hematopoietic activity via transdifferentiation when introduced...

SummaryGenerating human skeletal muscle models is instrumental for investigating muscle pathology and therapy. Here, we report the generation of three-dimensional (3D) artificial skeletal muscle tissue from human pluripotent stem cells, including induced pluripotent stem cells (iPSCs) from patients with Duchenne, limb-girdle, and congenital muscular dystrophies. 3D skeletal myogenic differentiation of pluripotent cells was induced within hydrogels under tension to provide myofiber alignment. Artificial muscles recapitulated characteristics of human skeletal muscle tissue and could be implanted into immunodeficient mice. Pathological cellular hallmarks of incurable forms of severe muscular dystrophy could be modeled with high fidelity using this 3D platform. Finally, we show generation of fully human iPSC-derived, complex, multilineage muscle models containing key isogenic cellular constituents of skeletal muscle, including vascular endothelial cells, pericytes, and motor neurons. These results lay the foundation for a human skeletal muscle organoid-like platform for disease modeling, regenerative medicine, and therapy development.

No abstract

No abstract