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Mesenchymal stem cells (MSC) are multipotent cells present in a variety of tissues during human development and in adults mainly in bone marrow. Mesenchymal stem cells may be isolated and expanded in vitro and they are capable to differentiate into a variety of tissues, including bone, cartilage, muscle and adipose tissue. In this review we briefly analyze the main biological features of MSC with particular attention to their interaction with hemopoietic system and to their differentiative properties. Finally, we focus on the main MSC applications both in the fields of genetic and tissue engineering.

Objective: Adhesion mechanisms play a central role in the recruitment of leukocytes which characteristically infiltrate rheumatoid synovium. Therefore, we adapted an animal model, in which human rheumatoid synovium was transplanted into severe combined immunodeficient (SCID) mice, to study the effects of Tumor Necrosis Factor-alpha (TNF-alpha) in modulatine leukocyte migration and to investigate the chemotactic potential of Stromal Derived Factor-1 alpha (SDF-1 alpha)., Materials and Methods: Human synovium samples, obtained from patients undergoing joint replacement, were divided into two parts. One was analysed by immunohistology and the other was implanted subcutaneously into SCID mice under general anaesthesia. Four weeks post-transplantation, grafts were injected with optimal dose of SDF-1, TNF-alpha or saline (negative control). At the same time, animals were injected iv with fluorescently labelled cells. 48 hours later mice were sacrificed and grafts removed for cryo-hystology. The number of cells migrating to the grafts was determined by UV-microscopy and the results expressed as cells per high power field., Results and Conclusions: In these studies we provide the evidence that: 1) the animal model, in which human tissues are grafted into SCID mice, can be used to study cell migration under controlled experimental conditions; 2) direct intragraft injection of TNF-alpha increases lymphocytes migration and up-regulates the expression of human adhesion molecules (CAMs) and 3) SDF-1 alphainjected intragraft increases the migration of the pro-myelo-monocytic U937 cells to synovial transplants, even more efficiently than TNF-alpha, but without modifications of CAMs' expression.

As reproducible models for examining human early B-cell progenitors (BCPs) are poorly developed, the cells and molecules regulating their growth and differentiation are still incompletely characterized. We used a recently published short term culture system, using immunomagnetic beads and negative selection, in order to isolate an early BCPs enriched population from human fetal tissues that support further studies on B cell proliferation or differentiation events. This purified population was incubated with or without human recombinant Interleukin-4 (rIL4), and its capability to proliferate and differentiate was followed. We found that rIL4 did not induce either proliferation or differentiation of purified human BCPs. Furthermore in the presence of stromal cells (CD13+) it was able to enhance cy mu + cells and to induce the expression of surface Ig (sIg), surface CD22 on in vitro TdT + CD19 + CD10 + sIg-fetal liver cells. Human recombinant interleukin-7 (rIL-7) promoted the proliferation and the clonal growth of Tdt + CD19 + CD10 + fetal BCPs, confirming its critical role at early stages of human B lymphopoiesis. Furthermore rIL7 also induced growth of CFU-GM when unseparated fetal tissues or myeloid/monocytic contaminated BCPs were used as a target populations, probably by indirect mechanism. Transforming growth factor -beta (TGF-beta 1) partially inhibited the stromal cell-dependent rIL4 induced differentiation and rIL7 clonal growth and proliferation of fetal BCPs. Our study contributes to elucidate the growth factor requirements that characterize normal human B-cell ontogeny, suggesting another mechanism for the linkage between lymphopoiesis and myeloid/macrophagic micro-environment. The in vivo implications of this study are discussed.

The present work studies the possibility of inducing an alteration in the erythropoietic switchover from primitive to definitive red cells in the chicken embryo by means of Cytoarabine (Ara C). To this purpose two different concentrations of Ara C were injected into fertilized chicken eggs after 94 hours of incubation. Optical microscopy was used in the morphological analysis of the blood smears taken from treated and control embryos on the 7th and 8th day of incubation (state 30 and 33 in the Lillie Table). 1) Injection of Ara C 4.1 x 10(-5) M did not induce any significant differences in the hematological picture between treated embryos and the controls. 2) Injection of Ara C 4.1 x 10(-4) M revealed a delay in the erythropoietic switchover both at the 7th and 8th day of incubation. In fact, the peripheral blood of the treated embryos showed that in the treated embryos there was a more than 24 hour delay in erythropoietic maturation. This is indicated by an unusually high number of 1st generation erythrocytes in the peripheral blood. Moreover, the 2nd generation red cells are at a lower stage of cell differentiation than the controls.

Thiosemicarbazones are a wide group of organic derivatives whose biological activities are a function of the parent aldehyde or ketone and of the coordination metal type. Some thiosemicarbazones possess a broad spectrum of potentially useful chemotherapeutic properties (antitumor, antibacterial, antiviral, antimalarial). The present study reports the biological effects of pyridoxal thiosemicarbazone, H2L, and relative complexes with copper, [(Cu(HL)(OH2))2]++ and with cobalt, [Co(III)(L)(HL)] on the differentiation of Friend erythroleukemia cells (FLC). They are murine proerythroblasts chronically infected by a producing Friend leukemia virus complex; their exposure to dimethylsulfoxide (Me2SO) or other chemical agents induces these cells to terminal erythroid differentiation, therefore these cells represent a good model of differentiation in vitro. Here we describe induction differentiation experiment of pyridoxal thiosemicarbazone and relative complexes of copper and cobalt on FLC performed with concentrations of 50 ug/ml (ligand), 2 ug/ml (complexes). These have little effects on cell proliferation at doses used in these experiments. Higher doses have evident cytotoxic effects. The treatment with the copper complex induces a moderate differentiation of FLC and enhances effects on erythroid differentiation of Me2SO-induced FLC. On the contrary H2L and [Co(III)(L)(HL)] haven't inducing effects or enhancing effects on Me2SO-induced FLC hemopoietic differentiation. In conclusion, the present study shows that copper complexes of pyridoxal thiosemicarbazone exert action of inducing agent and are able to enhance Me2SO-induced FLC hemopoietic differentiation.

After defining chemoprevention a description is given of the phases of differentiation in normal epithelial cells and the features of proliferation in neoplasias developing in this epithelium. The latest studies on carcinogenesis indicate various types of prevention with which one can alter this transformation process. Epidemiological studies have shown that subjects with low serum levels of Vit-A or Beta carotenoids are at high risk of developing epithelial cancer. Three main categories of agents inducing cell transformation are described: a) physiological induction agents; b) non physiological induction agents; c) cytotoxic drugs. In regard to clinical use, some studies have focussed on the importance of Vit-A in chemoprevention of risk conditions (pre-cancerous lesions) and in prevention of cancer recurrence. The authors point out the increasing interest in the use of retinoids in the chemoprevention of head and neck cancer and report some personal clinical experience.

Six-day limb skin from a chick embryo was cultured in vitro for seven days in a complete medium either supplemented or not with histones. At the end of the incubation period, the chick embryo skin cultured in the absence of histones was found to undergo keratinization, the converse being true for the limbs cultured in the presence of histones. In the latter, when H3-leucine and C14-cystine were added to the medium, a sharp decrease in the labeled amino acid incorporation was found.

Epithelial-mesodermal tissue interactions have been shown to be required for normal cytodifferentiation of chick embryo skin. Six-day limb skin does not develop in a protein free chemically defined medium, but keratinization has been observed in medium containing chicken serum. In the present study the authors show that the addition of human serum may stimulate the in vitro differentiation of explants of six-day chick embryo skin. Human serum is able to support skin keratinization and this finding has been confirmed by histological and histochemical criteria. Synthesis of proteins in tissue cultures supplemented with human serum has been studied by use of labeled amino acids such as H3-Leucine and C14-Cystine. These incorporation studies show the existence of macromolecular factors in human serum which may be responsible for the observed skin differentiation.

The specific insulin binding activity of human promyelocitic HL 60 cell line during the myeloid and macrophagic differentiation induced by chemical compounds was investigated. Dimethyl sulfoxide (DMSO) and retinoic acid myeloid induced differentiation in HHL 60 cells was accompanied by a marked decrease of insulin receptors. In K 562 cell line, where DMS O has no effect on differentiation, the number of insulin receptors was only slightly affected. 12-0-tetradodecanoil phorbol 13-acetate (TPA) induced macrophagic differentiation of HL 60 cell line was also accompanied by a decrease of insulin binding activity. Our results support the hypothesis that during the process of terminal differentiation a decrease of insulin receptors occurs.

It has been recently shown that 1,25(OH)2D3 induces differentiation and inhibits the proliferation of normal and leukemic cells in vitro. A review of the literature and the preliminary clinical applications of this vitamin in hematology are reported.

The fibrinolytic activity of human acute leukemia HL 60 and K 562 cells was studied by the (I25)I-fibrin plate method. The treatment of this cell lines with chemical inducers of differentiation such as Dimethyl sulfoxide (DMSO), 12-0-tetradodecanoilphorbol 13-acetate (TPA), and retinoic acid was found in some instance to affect such fibrinolytic activity. Increased activity was found during the myeloid differentiation induced by retinoic acid of HL 60, while the DMSO, another inducer of myeloid differentiation, and TPA, an inducer of macrophagic differentiation, both produced a decreased of the lytic activity. In the treatment with retinoic acid of th K 562 cells, which do not differentiate by such compound, we failed to show an increase of the fibrinolytic activity. Our data suggest that changes of the fibrinolytic activity of HL 60 are related to the process of differentiation.

The amount of vital cells recovered, their morphology (studied by SEM) and some of their biochemical aspects concerning the differentiation processes (aerobic glycolysis, cell production of cAMP and CEA) were investigated in a strain of H4 hepatoma cultured for 8 days in the presence of 5 microM retinol (R) or retinoic Acid (RA). Vital cell recovery is slightly reduced either by R or RA treatment. Flattening of the cell shape and reduction of the plasma membrane prolongations and of intercellular bonds are observed in the R-treated cells but to a greater extent in those treated with RA. Aerobic glycolysis is decreased in the R-treated cells but increased in those treated with RA. Such events could be related to the regressive processes observed in the RA-treated cells. cAMP cell content is increased to a greater extent in the R-treated cells than in those treated with RA. CEA cell content is greatly decreased in the RA-treated cells but only slightly in those treated with R. Therefore, the treatment of HA hepatoma cells with 5 microM R or RA, while reducing cell growth only slightly, does not cause evident and unequivocal morphological and biochemical events related to cell redifferentiation.

Inositol phospholipid turnover is part of a signal transduction mechanism which mobilize intracellular calcium and activate a calcium- and phospholipid-dependent protein kinase, protein kinase C. Phosphatidylinositol turnover has recently been implicated in the regulation of cell proliferation and transformation. Its role in differentiation has now been investigated using LAN-1 cells, a human neuroblastoma cell line which can be induced to differentiate along the neuronal pathway by RA. Treatment of LAN-1 cells with RA was followed by a rapid decrease of inositol phospholipid metabolism, as determined by isotopic methodology employing myo-[1,2-3H] inositol or [1(3)-3H] glycerol. Analysis of labelled phosphatidylinositol metabolites from prelabelled cells indicated a rapid decrease of inositol (1,4,5)trisphosphate and (1,2)diacylglycerol within 1 min. of induction of LAN-1 cell differentiation. These findings suggest that inositol phospholipid-derived metabolites (i.e. diacylglycerol and inositol trisphosphate) may be part of the mechanism by which certain RA signals are transduced, playing a key role in control of neuroblastoma cell differentiation.

Friend leukemia cells (FLC) induced to erythroid differentiation by 5 mM hexamethylenebisacetamide (HMBA) are suitable for studies focused on the expression of different genes involved in the same differentiative program. In our studies FL cells have been cultured in alpha-medium (Gibco), 10% fetal calf serum (FCS, Flow Laboratories). Erythroid differentiation has been analysed by benzidine staining of the cells and globin synthesis by pulse-labelling the cells with 3H-leucine (New England Nuclear) and electrophoresis of newly-synthesized proteins on polyacrylamide gels. Hemoglobin production was determined by cellulose acetate gel electrophoresis. Our results demonstrate that heme synthesis is suppressed by the iron-chelator desferrioxamine. In addition "commitment" to erythroid differentiation and transcription and translation of globin mRNAs occur in HMBA-treated FLC in the absence of heme accumulation.

In the present study the authors have carried out further researches on the differentiation of six day limb skin from chick embryo cultured "in vitro" in a complete medium supplemented with histones. When histones were added to the medium in the first two days "in vitro", epidermal keratinization was not observed. However the addition of histones after four days "in vitro" did not interfere with epidermal differentiation.