Mesenchymal stem versus stromal cells: International Society for Cell & Gene Therapy (ISCT®) Mesenchymal Stromal Cell committee position statement on nomenclature.

The International Society for Cell & Gene Therapy (ISCT®) Mesenchymal Stromal Cell (ISCT MSC) committee offers a position statement to clarify the nomenclature of mesenchymal stromal cells (MSCs). The ISCT MSC committee continues to support the use of the acronym "MSCs" but recommends this be (i) supplemented by tissue-source origin of the cells, which would highlight tissue-specific properties; (ii) intended as MSCs unless rigorous evidence for stemness exists that can be supported by both in vitro and in vivo data; and (iii) associated with robust matrix of functional assays to demonstrate MSC properties, which are not generically defined but informed by the intended therapeutic mode of actions.

Quantifying levels of transplanted murine and human mesenchymal stem cells in vivo by real-time PCR.

BACKGROUND: Previously, we demonstrated that murine mesenchymal stem cells (MSCs) injected intracranially into mice expand throughout the central nervous system (CNS). This paper describes real-time PCR (RT-PCR) assays that enables accurate quantification of transplanted cells in vivo. METHODS: RT-PCR assays that amplify sequences in the mouse Y chromosome or human Alu repeats were developed and used to quantify the number of male, murine, or human MSCs in the CNS at various times after intracranial injection into neonatal mice, or in various organs of adult mice after i.p. injection of cells into 3 day-old embryos. RESULTS: In the CNS, levels of male mouse DNA in female transplant recipients increased on average 30-fold between 3 and 60 days post-injection but then was unchanged at 140 days post-transplant (P = 0.107). Male DNA accounted for up to 0.309% of the total DNA content of the brain, representing maximally 600000 donor cells. Human DNA was detected in the CNS up to 300 days post-transplant, but levels never exceeded 7.63 x 10 (-4) % of the total brain content. After in utero transplantation, human DNA levels ranged from 0.36 x 10(-5) % to 2.14 x 10 (-5) % of the total DNA content of liver, kidney and spleen. significantly higher levels were found in heart (P = 0.06), femur and brain (P = 0.0025). DISCUSSION: RT-PCR assays were developed to quantify levels of male, murine and human cells in vivo following sex-mismatched or xeno-transplants. Due to their accuracy, precision, and sensitivity, these assays provide a versatile alternative to measuring stem-cell engraftment in vivo.

MicroSAGE analysis of 2,353 expressed genes in a single cell-derived colony of undifferentiated human mesenchymal stem cells reveals mRNAs of multiple cell lineages.

Mesenchymal stem cells (MSCs) isolated from the bone marrow of adult organisms are capable of differentiating into adipocytes, chondrocytes, myoblasts, osteoblasts, and hematopoiesis-supporting stroma. We recently demonstrated that MSCs also adopt glial cell fates when transplanted into the developing central nervous system and hence can produce tissue elements derived from a separate embryonic layer. Despite these remarkable properties, it has been difficult to establish specific criteria to characterize MSCs. Using a modified protocol for micro-serial analysis of gene expression, we cataloged 2,353 unique genes expressed by a single cell-derived colony of undifferentiated human MSCs. This analysis revealed that the MSC colony simultaneously expressed transcripts characteristic of various mesenchymal cell lineages including chondrocytes, myoblasts, osteoblasts, and hematopoiesis-supporting stroma. Therefore, the profile of expressed transcripts reflects the developmental potential of the cells. Additionally, the MSC colony expressed mRNAs characteristic of endothelial, epithelial and neuronal cell lineages, a combination that provides a unique molecular signature for the cells. Other expressed transcripts included various products involved in wound repair as well as several neurotrophic factors. A total of 268 novel transcripts were also identified, one of which is the most abundantly expressed mRNA in MSCs. This study represents the first extensive gene expression analysis of MSCs and as such reveals new insight into the biology, ontogeny, and in vivo function of the cells.

Pathogenesis of HIV-1 infection within bone marrow cells.

Mononuclear phagocytic cells and CD4+ T lymphocytes represent the major targets for infection by HIV-1 in vivo. The most severe pathogenic features associated with HIV-1 infection can be attributed to malfunction or premature death of these cells that are of hematopoietic origin. Patients with acquired immunodeficiency syndrome (AIDS), suffer from many hematologic disorders, particularly those persons with long-term infection of HIV-1. These disorders include anemia, lymphocytopenia, thrombocytopenia and neutropenia. The mechanisms that lead to the induction of these disorders are multi-factorial. However, sufficient evidence has accumulated which suggests that HIV-1 infection of cells within the microenvironment of the bone marrow can lead to the induction of hematopoietic deficits. Most studies indicate that marrow-derived hematopoietic stem cells cannot be infected by HIV-1 until they undergo modest differentiation in order to express the appropriate receptors to enable virus entry and subsequent replication. Some cells within the mixed environment of the marrow stroma appear to support HIV-1 replication however. These cells include marrow microvascular endothelial cells, sometimes referred to as blanket cells, stromal fibroblasts, as well as mononuclear phagocytes. Our recent experiments suggest that the HIV-1 accessory protein, Vpr, plays some role in the activation of marrow-derived mononuclear phagocytes which appears to result in premature phagocytosis of non-adherent marrow cells present in the in vitro cultures. This phenomenon could account, in part, for the induction of cytopenias that are typical of individuals infected by HIV-1.

Potential use of stem cells from bone marrow to repair the extracellular matrix and the central nervous system.

A subset of stem-like cells from bone marrow that are referred to as marrow stromal cells (MSCs) have been shown to be capable of differentiating into osteoblasts, chondrocytes, adipocytes, myocytes, astrocytes and perhaps neurons. Recently, conditions have been developed where human MSCs can be expanded almost without limit in culture without apparently losing their multipotentiality for differentiation. The cells appear to be potentially useful for the repair of extracellular matrix and the central nervous system.

Propagation and senescence of human marrow stromal cells in culture: a simple colony-forming assay identifies samples with the greatest potential to propagate and differentiate.

Marrow stromal cells (MSCs) were isolated from bone marrow obtained by aspirates of the iliac crest of normal volunteers. The cells were isolated by their adherence to plastic and then passed in culture. Some of the samples expanded through over 15 cell doublings from the time frozen stocks were prepared. Others ceased replicating after about four cell doublings. The replicative potential of the cells in culture was best predicted by a simple colony-forming assay in which samples from early passages were plated at low densities of about 10 cells per cm2. Samples with high colony-forming efficiency exhibited the greatest replicative potential. The colonies obtained by plating early passage cells at low density varied in size and morphology. The large colonies readily differentiated into osteoblasts and adipocytes when incubated in the appropriate medium. As samples were expanded in culture and approached senescence, they retained their ability to differentiate into osteoblasts. However, the cells failed to differentiate into adipocytes. The loss of multipotentiality following serial passage in culture may have important implications for the use of expanded MSCs for cell and gene therapy.

Donor variation in the growth properties and osteogenic potential of human marrow stromal cells.

Human marrow stromal cells (MSCs) were isolated from posterior illiac crest marrow aspirates obtained from 17 healthy donors, ages 19-45 years, with no apparent physical disability. First passage hMSCs exhibited growth rates in vitro that varied up to 12-fold between donors. No correlation between growth rate and the age or gender of the donor was evident (P

Marrow stromal cells migrate throughout forebrain and cerebellum, and they differentiate into astrocytes after injection into neonatal mouse brains.

Stem cells are a valuable resource for treating disease, but limited access to stem cells from tissues such as brain restricts their utility. Here, we injected marrow stromal cells (MSCs) into the lateral ventricle of neonatal mice and asked whether these multipotential mesenchymal progenitors from bone marrow can adopt neural cell fates when exposed to the brain microenvironment. By 12 days postinjection, MSCs migrated throughout the forebrain and cerebellum without disruption to the host brain architecture. Some MSCs within the striatum and the molecular layer of the hippocampus expressed glial fibrillary acidic protein and, therefore, differentiated into mature astrocytes. MSCs also populated neuron rich regions including the Islands of Calleja, the olfactory bulb, and the internal granular layer of the cerebellum. A large number of MSCs also were found within the external granular layer of the cerebellum. In addition, neurofilament positive donor cells were found within the reticular formation of the brain stem, suggesting that MSCs also may have differentiated into neurons. Therefore, MSCs are capable of producing differentiated progeny of a different dermal origin after implantation into neonatal mouse brains. These results suggest that MSCs are potentially useful as vectors for treating a variety of central nervous system disorders.

Enhanced in situ detection of beta-glucuronidase activity in murine tissue.

We outline here a protocol for high-resolution in situ localization of beta-glucuronidase in murine tissues processed in glycol methacrylate (GMA). Murine tissues were first stained with 5-bromo-4-chloro-3-indolyl-beta-d-glucuronic acid (x-gluc), followed by histological processing in GMA. Retention of the blue indigo reaction product after overnight incubations in x-gluc allowed high-resolution localization of beta-glucuronidase activity by brightfield microscopy. When illuminated under darkfield, the x-gluc signal was enhanced, permitting detection even in cells with low-level enzyme activity. This technique offers for the first time a more sensitive enzyme histochemical method of detecting beta-glucuronidase activity in animal tissues and also the opportunity to examine expression at high magni-fication.

Plastic adherent stromal cells from the bone marrow of commonly used strains of inbred mice: variations in yield, growth, and differentiation.

Bone marrow stroma contains a unique cell population, referred to as marrow stromal cells (MSCs), capable of differentiating along multiple mesenchymal cell lineages. A standard liquid culture system has been developed to isolate MSCs from whole marrow by their adherence to plastic wherein the cells grow as clonal populations derived from a single precursor termed the colony-forming-unit fibroblast (CFU-F). Using this liquid culture system, we demonstrate that the relative abundance of MSCs in the bone marrow of five commonly used inbred strains of mice varies as much as 10-fold, and that the cells also exhibit markedly disparate levels of alkaline phosphatase expression, an early marker of osteoblast differentiation. For each strain examined, the method of isolating MSCs by plastic adherence yields a heterogeneous cell population. These plastic adherent cells also exhibit widely varying growth kinetics between the different strains. Importantly, of three inbred strains commonly used to prepare transgenic mice that we examined, only cells derived from FVB/N marrow readily expand in culture. Further analysis of cultures derived from FVB/N marrow showed that most plastic adherent cells express CD11b and CD45, epitopes of lymphohematopoietic cells. The later consists of both pre-B-cell progenitors, granulocytic and monocytic precursors, and macrophages. However, a subpopulation of the MSCs appear to represent bona fide mesenchymal progenitors, as cells can be induced to differentiate into osteoblasts and adipocytes after exposure to dexamethasone and into myoblasts after exposure to amphotericin B. Our results point to significant strain differences in the properties of MSCs and indicate that standard methods cannot be applied to murine bone marrow to isolate relatively pure populations of MSCs.

A 1,064 bp fragment from the promoter region of the Col11a2 gene drives lacZ expression not only in cartilage but also in osteoblasts adjacent to regions undergoing both endochondral and intramembranous ossification in mouse embryos.

We isolated a 1,064 bp promoter fragment that extended from the 3'-end of the adjacent gene for retinoic X receptor-beta to beyond the most clearly defined start site of the mouse Col11a2 gene. The fragment was then joined to a beta-galactosidase gene and used to prepare transgenic mice. Three independent lines of transgenic mice were generated. The reporter beta-galactosidase gene was expressed in essentially all cartilaginous tissues in 15.5-day-old mouse embryos. In addition, the construct was expressed in osteoprogenitors within developing periosteum and in osteoblasts within mineralized bone. This pattern of expression was evident during both endochondral and intramembranous bone formation. Therefore, the results suggest that 1,064 bp promoter fragment can drive tissue-specific expression of the Col11a2 gene.

Chromosomal integration dependent induction of junB by growth factors requires multiple flanking evolutionarily conserved sequences.

The junB locus contains nine flanking evolutionarily conserved sequences (FECS) that share 72% to 91% sequence identity between human and mouse. These FECS encompass the same regions of flanking DNA necessary for maximal mitogenic induction of junB. Most of the cis elements reported to date that affect junB regulation also reside within FECS. These observations suggest that the persistence of FECS through evolution reflects a necessary role in junB transcriptional regulation. In this report, we identify specific regulatory cis elements within junB FECS II and III and provide a quantitative analysis of the contribution made by these sequences to junB induction. These cis elements include a Serum Response Element (SRE), two Ets sites previously unrecognized as contributing to junB expression, and two novel Ets-linked motifs (ELMs). In general, mutating any single element significantly impairs junB induction. Moreover, the same mutations alter the structure of junB 5' flanking DNA within chromatin. Collectively, these results suggest that multiple proteins bound within FECS confederate to form a functional promoter complex, the activity of which is dependent upon a specific chromatin architecture.

Complex genetic organization of junB: multiple blocks of flanking evolutionarily conserved sequence at the murine and human junB loci.

A comparison of the murine and human junB loci reveals nine regions of distal 5'- and 3'-flanking DNA that exhibit greater than 72% sequence identity. A large fraction (over 50%) of the junB locus is contained in these flanking evolutionarily conserved sequences (FECS), which may be required for effecting the proper transcriptional regulation of this gene. Comparative sequence analyses involving kilobases of distal flanking DNAs have been performed for only a small number of vertebrate genes. The available data and the results presented here suggest that FECS may emerge as common yet important functional components of genes, a hypothesis with significant implications for characterizing genes involved in human disease.

Analysis of the hormone-dependent regulation of a JunD-estrogen receptor chimera.

The modular ligand-binding domains of steroid receptors have been widely used to generate protein chimeras that are ligand dependent for activity. In a similar manner, we generated a series of conditionally active JunD and c-Fos proteins by fusing their carboxyl (COOH)-terminal ends with a COOH-terminal fragment of the human estrogen receptor (ER) that contains the ligand-binding domain. JunD-ER (DER) and Fos-ER (FER) chimeras with an intact leucine zipper and basic region exhibit hormone-dependent activation of activator protein-1-directed transcription in transient expression assays. One of these fusions, DER, has been examined in detail to determine its mechanism of action. Results from immunoprecipitation experiments with extracts from DER and Fos transfected cells demonstrate that Fos and DER readily form heterodimer complexes. Surprisingly, the formation of Fos:DER heterodimers, and possibly DER homodimers, is estrogen-independent. However, gel shift assays clearly demonstrate that DNA binding to AP1 sites by Fos:DER heterodimers or DER homodimers is estrogen-dependent. Moreover, in the absence of estrogen, the DER protein is an effective inhibitor of Fos-mediated transactivation, and this effect is reversed by the presence of estrogen. Our results indicate that the DER protein is a direct, hormone-reversible inhibitor of Fos and that estrogen controls the conditional positive or dominant negative activities of DER at the level of DNA binding to AP1 sites. Accordingly, clonally derived fibroblast cell lines that stably express the DER protein exhibit reduced entry into the S phase of the cell cycle when quiescent cells are serum stimulated in the absence of estrogen. This is in contrast to the estrogen-treated controls. These results support the hypothesis that AP1 is important for cell cycle progression and provide a unique approach for examining the role of AP1 in this process.

Quantitative analysis of the contribution made by 5'-flanking and 3'-flanking sequences to the transcriptional regulation of junB by growth factors.

We have identified four DNAase I-hypersensitive regions (DHRs) at the junB locus. DHR1 is located between sequences -100 and +250, DHR2 is centered at -1000, DHR3 at -1650, and DHR4 at +2040 relative to the junB transcriptional start site. Sequence analysis of these DHRs revealed two serum response elements at -1452 and +2091, two cyclic AMP response elements at +2071 and +2116, and a 12-O-tetradecanoylphorbol-13-acetate (TPA) response element at -949. To study the contribution made by these cis-elements to junB transcriptional regulation, we stably transfected a recombinant mouse junB gene (JBSV4) containing the intact junB coding sequences, 6.3 kb of 5'-flanking DNA, and 2.0 kb of 3'-flanking DNA into Rat1A cells. The pattern of DHRs identified at the mouse junB locus was re-established at the JBSV4 locus. By directly comparing JBSV4 and rat junB mRNA levels, we found that these genes were induced to equivalent levels by serum, TPA, cyclic AMP, platelet-derived growth factor, epidermal growth factor, and basic fibroblastic growth factor. These results established that JBSV4 resides in a physical environment within chromatin that closely mimics that of the junB locus, and contains the necessary sequence information to recapitulate the transcriptional regulation of junB. By analysing a series of recombinant mouse junB genes containing deletion mutations in 5'-flanking and 3'-flanking sequences, we provide a quantitative assessment of the contribution these sequences make to junB induction by different regulatory agents.

Induction of a light-inducible gene in Arthrobacter sp. by exposure of cells to chelating agents and pH 5.

Transcription of a light-inducible gene in the prokaryote Arthrobacter sp. is induced in the dark when cells are incubated with chelating agents or in medium at pH 5. However, repletion of metal ions such as Ca2+, Mn2+ or Zn2+ or an increase in pH is required for accumulation of the gene product, an Mr 21,000 polypeptide. But such changes in condition restore repression of the gene, and the decay in the rate of synthesis of the polypeptide follows the same time-course as when photodynamically induced cells are transferred to the dark. These results are consistent with regulation of expression of this gene at transcriptional and posttranscriptional steps by mechanisms that involve metal-protein complexes.

Synthesis and antitumor activities of unsymmetrically substituted 1,4-bis[(aminoalkyl)amino]anthracene-9,10-diones and related systems.

A number of unsymmetrically substituted 1,4-bis[(aminoalkyl)amino]anthracene-9,10-diones have been synthesized and evaluated for their antitumor activity against L1210 in vitro and in vivo. The high activity of several compounds observed in vitro was not paralleled by comparable activity in vivo. The activities of the substituted 1,4-bis[(aminoalkyl)amino]anthracene-9,10-diones as inhibitors of cell growth were generally much higher than those of the related 1-[(aminoalkyl)amino]-4-methoxyanthracene-9,10-diones, and this correlated with the relative abilities of compounds of the two types to interact with calf thymus DNA.