Rapid hematopoietic recovery after coinfusion of autologous-blood stem cells and culture-expanded marrow mesenchymal stem cells in advanced breast cancer patients receiving high-dose chemotherapy.

PURPOSE: Multipotential mesenchymal stem cells (MSCs) are found in human bone marrow and are shown to secrete hematopoietic cytokines and support hematopoietic progenitors in vitro. We hypothesized that infusion of autologous MSCs after myeloablative therapy would facilitate engraftment by hematopoietic stem cells, and we investigated the feasibility, safety, and hematopoietic effects of culture-expanded MSCs in breast cancer patients receiving autologous peripheral-blood progenitor-cell (PBPC) infusion. PATIENTS AND METHODS: We developed an efficient method of isolating and culture-expanding a homogenous population of MSCs from a small marrow-aspirate sample obtained from 32 breast cancer patients. Twenty-eight patients were given high-dose chemotherapy and autologous PBPCs plus culture-expanded MSC infusion and daily granulocyte colony-stimulating factor. RESULTS: Human MSCs were successfully isolated from a mean +/- SD of 23.4 +/- 5.9 mL of bone marrow aspirate from all patients. Expansion cultures generated greater than 1 x 10(6) MSCs/kg for all patients over 20 to 50 days with a mean potential of 5.6 to 36.3 x 10(6) MSCs/kg after two to six passages, respectively. Twenty-eight patients were infused with 1 to 2.2 x 10(6) expanded autologous MSCs/kg intravenously over 15 minutes. There were no toxicities related to the infusion of MSCs. Clonogenic MSCs were detected in venous blood up to 1 hour after infusion in 13 of 21 patients (62%). Median time to achieve a neutrophil count greater than 500/microL and platelet count >/= 20,000/microL untransfused was 8 days (range, 6 to 11 days) and 8.5 days (range, 4 to 19 days), respectively. CONCLUSION: This report is the first describing infusion of autologous MSCs with therapeutic intent. We found that autologous MSC infusion at the time of PBPC transplantation is feasible and safe. The observed rapid hematopoietic recovery suggests that MSC infusion after myeloablative therapy may have a positive impact on hematopoiesis and should be tested in randomized trials.

LacZ and interleukin-3 expression in vivo after retroviral transduction of marrow-derived human osteogenic mesenchymal progenitors.

Human marrow-derived mesenchymal progenitor cells (hMPCs), which have the capacity for osteogenic and marrow stromal differentiation, were transduced with the myeloproliferative sarcoma virus (MPSV)-based retrovirus, vM5LacZ, that contains the LacZ and neo genes. Stable transduction and gene expression occurred in 18% of cells. After culture expansion and selection in G418, approximately 70% of neo(r) hMPCs co-expressed LacZ. G418-selected hMPC retain their osteogenic potential and form bone in vivo when seeded into porous calcium phosphate ceramic cubes implanted subcutaneously into SCID mice. LacZ expression was evident within osteoblasts and osteocytes in bone developing within the ceramics 6 and 9 weeks after implantation. Likewise, hMPCs transduced with human interleukin-3 (hIL-3) cDNA, adhered to ceramic cubes and implanted into SCID mice, formed bone and secreted detectable levels of hIL-3 into the systemic circulation for at least 12 weeks. These data indicate that genetically transduced, culture-expanded bone marrow-derived hMPCs retain a precursor phenotype and maintain similar levels of transgene expression during osteogenic lineage commitment and differentiation in vivo. Because MPCs have been shown to differentiate into bone, cartilage, and tendon, these cells may be a useful target for gene therapy.

Cell surface antigens on human marrow-derived mesenchymal cells are detected by monoclonal antibodies.

Human bone marrow has been shown to contain mesenchymal cells, which fabricate the connective tissue network of the marrow called the stroma. A subset of these marrow-derived mesenchymal cells can be isolated, expanded in culture, and then induced to differentiate into bone-producing osteoblasts and ultimately osteocytes when placed in the proper environment. At present, there are no methods for definitively identifying these cells in human marrow tissue or following their differentiation into osteogenic phenotypes. Therefore, we culture-expanded, marrow-derived mesenchymal cells from human donors and used these cells to immunize cells from human donors and used these cells to immunize mice whose spleens were used to generate hybridoma cell lines, which secrete antibodies to antigens on the cell surface of these culture-expanded mesenchymal cells. Hybridoma culture supernatants were successively screened against highly enriched samples of culture-expanded, marrow-derived mesenchymal cells in cryosections and live cell cultures to identify unique cell surface antigens. Positive clones were then screened against cell suspensions of whole and fractionated marrow to identify hybridomas whose supernatants were nonreactive with marrow hemopoietic cells. Three hybridoma cell lines, SH2, SH3, and SH4, were identified; these hybridomas secrete antibodies that recognize antigens on the cell surface of marrow-derived mesenchymal cells, but fail to react with marrow-derived hemopoietic cells. Additional tissue screening reveals unique tissue distributions for each of the recognized antigens, which suggests different antigen recognition for each antibody. However, all three antibodies fail to react with the cell surface of osteoblasts or osteocytes, suggesting that the antigens recognized by these antibodies are developmentally regulated and specific for primitive or early-stage cells of the osteogenic lineage.

Characterization of cells with osteogenic potential from human marrow.

Studies using animal tissue suggest that bone marrow contains cells with the potential to differentiate into cartilage and bone. We report the extension of these studies to include human marrow. Bone marrow from male and female donors of various ages was obtained either from the femoral head or as aspirates from the iliac crest, and introduced into culture. Culture-adherent cells were expanded, subcultured, and then tested for bone and cartilage differentiation potential utilizing two different in vivo assays in nude mice. One assay involved subcutaneous implantation of porous calcium phosphate ceramics loaded with cultured, marrow-derived, mesenchymal cells; the other involved peritoneal implantation of diffusion chambers, also inoculated with cultured, marrow-derived, mesenchymal cells. Histological evaluation showed bone formation in ceramics implanted with cultured, marrow-derived, mesenchymal cells originating from both the femoral head and the iliac crest. Immunocytochemical analysis indicates that the bone is derived from the implanted human cells and not from the cells of the rodent host. No cartilage was observed in any of these ceramic grafts. In contrast, aliquots from the same preparations of cultured, marrow-derived, mesenchymal cells failed to form bone or cartilage in diffusion chambers. These data suggest that human marrow contains cells with osteogenic potential, which can be enriched and expanded in culture. Our findings also suggest that subcutaneous implantation of these cells in porous calcium phosphate ceramics may be a more sensitive in vivo assay than diffusion chambers for measuring their osteogenic lineage potential.

Monoclonal antibodies reactive with human osteogenic cell surface antigens.

Monoclonal antibodies (McAbs) against the surface of osteoblastic cells have been used to characterize the osteogenic lineage. In view of the paucity of probes against the surface of normal human osteogenic cells, we sought to generate McAbs which could be used for both in vivo and in vitro studies. We raised a series of McAbs against early osteoblastic cell surface antigens by immunizing mice with human mesenchymal stem cells (MSCs) that had been directed into the osteogenic lineage in vitro. After screening against the surface of osteogenic cells at various stages of differentiation in vitro, as well as evaluating in situ reactivity with human fetal limbs, we isolated three hybridoma cell lines referred to as SB-10, SB-20, and SB-21. Immunocytochemical analyses during osteogenic differentiation demonstrate that SB-10 reacts with MSCs and osteoprogenitors, but no longer reacts with cells once alkaline phosphatase (APase) is expressed. Flow cytometry documents that SB-10 is expressed on the surface of all purified, culture-expanded human MSCs, thus providing further evidence that these cells are a homogeneous population. By contrast, SB-20 and SB-21 do not react with the progenitor cells in situ, but bind to a subset of the APase-positive osteoblasts. None of these antibodies stain terminally differentiated osteocytes in sections of developing bone. Furthermore, these McAbs were not observed to react in samples from chick, rat, rabbit, canine, or bovine bone, although selected extraskeletal human tissues were immunostained. In all cell and tissue specimens examined, SB-20 immunostaining is identical to that observed with SB-21. We have used these McAbs to refine our understanding of the discrete cellular transitions that constitute the osteogenic cell lineage. We suggest a refined model for understanding osteoblast differentiation that is based on the proposition that the sequential acquisition and loss of specific cell surface molecules can be used to define positions of individual cells within the osteogenic cell lineage.

Bone and cartilage formation in diffusion chambers by subcultured cells derived from the periosteum.

Periosteal cells were enzymatically isolated from the tibiae of young chicks, introduced into cell culture, allowed to reach confluence, and subcultured. The freshly isolated or subcultured cells were loaded into diffusion chambers and implanted into the peritoneal cavity of athymic mice to test their osteo-chondrogenic potential in a contained in vivo location. Freshly isolated periosteal cells formed both bone and cartilage tissue in such test chambers, but with a relatively low incidence. In contrast, cultured periosteal cells consistently gave rise to bone and cartilage even after 10 population doublings. With further passages of cells, the osteo-chondrogenic potential diminished substantially, until complete loss of expressivity at 16 population doublings or longer. Cultured muscle fibroblasts, when loaded into diffusion chambers under identical conditions to those of cultured periosteal cells, formed neither bone nor cartilage. These observations suggest that periosteal cells of young chicks contain subsets of progenitor cells or mesenchymal stem cells which possess the potential to differentiate into osteoblasts or chondrocytes, and this potential is retained after enzymatic isolation and for several population doublings in culture.

Ex vivo expansion and subsequent infusion of human bone marrow-derived stromal progenitor cells (mesenchymal progenitor cells): implications for therapeutic use.

We report a phase I trial to determine the feasibility of collection, ex vivo culture-expansion and intravneous infusion of human bone marrow-derived progenitor stromal cells (mesenchymal progenitor cells (MPCs)). Ten milliliter bone marrow samples were obtained from 23 patients with hematologic malignancies in complete remission. Bone marrow mononuclear cells were separated and adherent cells were culture-expanded in vitro for 4-7 weeks. Autologous MPCs were reinfused intravenously and a bone marrow examination repeated 2 weeks later for histologic assessment and in vitro hematopoietic cultures. Patient age ranged from 18 to 68 years and 12 subjects previously had undergone an autologous or syngeneic bone marrow transplant 4-52 months prior to collection of MPCs. A median of 364 x 10(6) nucleated bone marrow cells (range: 103 to 1004 x 10(6)) were used for ex vivo expansion. Median number of MPCs which were obtained after ex vivo culture expansion was 59.0 (range: 1.1 to 347 x 10(6)) representing a median cell doubling of 16,000-fold (13 doublings). Fifteen of 23 patients completed the ex vivo expansion and underwent MPC infusion. Time to infusion of MPCs after collection ranged from 28 to 49 days. Five patients in each of three groups were given 1, 10 and 50 x 10(6) MPCs. No adverse reactions were observed with the infusion of the MPCs. MPCs obtained from cancer patients can be collected, expanded in vitro and infused intravenously without toxicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Human mesenchymal stem cells support unrelated donor hematopoietic stem cells and suppress T-cell activation.

Bone marrow-derived mesenchymal stem cells (MSCs) are known to interact with hematopoietic stem cells (HSCs) and immune cells, and represent potential cellular therapy to enhance allogeneic hematopoietic engraftment and prevent graft-versus-host disease (GVHD). We investigated the role of human MSCs in NOD-SCID mice repopulation by unrelated human hematopoietic cells and studied the immune interactions between human MSCs and unrelated donor blood cells in vitro. When hematopoietic stem cell numbers were limited, human engraftment of NOD-SCID mice was observed only after coinfusion of unrelated human MSCs, but not with coinfusion of mouse mesenchymal cell line. Unrelated human MSCs did not elicit T-cell activation in vitro and suppressed T-cell activation by Tuberculin and unrelated allogeneic lymphocytes in a dose-dependent manner. Cell-free MSC culture supernatant, mouse stromal cells and human dermal fibroblasts did not elicit this effect. These preclinical data suggest that unrelated, human bone marrow-derived, culture-expanded MSCs may improve the outcome of allogeneic transplantation by promoting hematopoietic engraftment and limiting GVHD and their therapeutic potential should be tested in clinic.

Osteogenesis in marrow-derived mesenchymal cell porous ceramic composites transplanted subcutaneously: effect of fibronectin and laminin on cell retention and rate of osteogenic expression.

Cultured-expanded rat marrow-derived mesenchymal cells differentiate into osteoblasts when combined with a porous calcium phosphate delivery vehicle and subsequently implanted in vivo. In this study, the effects of ceramic pretreatment with the cell-binding proteins fibronectin and laminin on the osteogenic expression of marrow-derived mesenchymal cells were assessed by scanning electron microscopy, [3H]-thymidine-labeled cell quantitation, and histological evaluation of bone formation. Scanning electron microscopic observations showed that marrow-derived mesenchymal cells rapidly spread and attach to both fibronectin- or laminin-adsorbed ceramic surfaces but retain a rounded morphology on untreated ceramic surfaces. Quantitation of [3H]-thymidine labeled cells demonstrated that laminin and fibronectin preadsorbed ceramics retain approximately double the number of marrow-derived mesenchymal cells than do untreated ceramics harvested 1 wk postimplantation. Histological observations indicate that the amount of time required to first detect osteogenesis was shortened significantly by pretreatment of the ceramic with either fibronectin or laminin. Fibronectin- and laminin-coated ceramic composite samples were observed to contain bone within 2 wk postimplantation, while in untreated ceramic the earliest observation of bone was at 4 wk postimplantation. A comparison was made of the initial cell-loading, in vivo cell retention characteristics, and rate of osteogenesis initiation of marrow-derived mesenchymal cells on two types of ceramic with different pore structure and chemical composition, with and without preadsorption with fibronectin or laminin. "Biphasic" ceramics contain randomly distributed pores 200-400 microns in diameter, and "coral-based" ceramics have continuous pores of approximately 200 microns in diameter. Laminin or fibronectin preadsorption significantly increases the number of cells retained in all ceramic test groups by day 7 postimplantation. In addition, by day 7 postimplantation, the biphasic ceramics retain a significantly greater number of cells for all test groups than do coral-based ceramics. The biphasic ceramics consistently have more specimens positive for bone with the identical cell-loading conditions used throughout this study. These results indicate that the retention of cells within the ceramic is an important factor for optimization of marrow mesenchymal cell initiated bone formation. The retention of cells within ceramics is augmented by the adsorption of the cell-binding proteins laminin and fibronectin, but this effect varies depending on ceramic pore structure and/or chemical composition.

Growth kinetics, self-renewal, and the osteogenic potential of purified human mesenchymal stem cells during extensive subcultivation and following cryopreservation.

Recent studies have demonstrated the existence of a subset of cells in human bone marrow capable of differentiating along multiple mesenchymal lineages. Not only do these mesenchymal stem cells (MSCs) possess multilineage developmental potential, but they may be cultured ex vivo for many passages without overt expression of a differentiated phenotype. The goals of the current study were to determine the growth kinetics, self-renewing capacity and the osteogenic potential of purified MSCs during extensive subcultivation and following cryopreservation. Primary cultures of MSCs were established from normal iliac crest bone marrow aspirates, an aliquot was cryopreserved and thawed, and then both frozen and unfrozen populations were subcultivated in parallel for as many as 15 passages. Cells derived from each passage were assayed for their kinetics of growth and their osteogenic potential in response to an osteoinductive medium containing dexamethasone. Spindle-shaped human MSCs in primary culture exhibit a lag phase of growth, followed by a log phase, finally resulting in a growth plateau state. Passaged cultures proceed through the same stages, however, the rate of growth in log phase and the final number of cells after a fixed period in culture diminishes as a function of continued passaging. The average number of population doublings for marrow-derived adult human MSCs was determined to be 38 +/- 4, at which time the cells finally became very broad and flattened before degenerating. The osteogenic potential of cells was conserved throughout every passage as evidenced by the significant increase in APase activity and formation of mineralized nodular aggregates. Furthermore, the process of cryopreserving and thawing the cells had no effect on either their growth or osteogenic differentiation. Importantly, these studies demonstrate that replicative senescence of MSCs is not a state of terminal differentiation since these cells remain capable of progressing through the osteogenic lineage. The use of population doubling potential as a measure of biological age suggests that MSCs are intermediately between embryonic and adult tissues, and as such, may provide an in situ source for mesenchymal progenitor cells throughout an adult's lifetime.

Comparison of the cartilage proteoglycan core protein synthesized by chondrocytes of different ages.

Chondrocytes of different ages synthesize proteoglycans which have structural differences in both the chondroitin sulfate and keratan sulfate glycosaminoglycans. In order to ascertain whether age-dependent differences also occur in the core protein, the chick limb bud mesenchymal cell culture system was utilized to analyze newly synthesized proteoglycan core protein from undifferentiated mesenchymal cells (day 1 and 2), newly differentiated cartilage (day 4), mature cartilage (day 8), and senescent cartilage (day 16). The core protein synthesized at various times was identified by radiolabeling with [3H]leucine and [35S]sulfate immediately prior to extraction and purification. The sizes of the various core protein preparations were compared by electrophoresis on a 3% polyacrylamide gel after partial deglycosylation with chondroitinase AC and keratanase. The proteoglycans from day 4, 8, and 16 cultures each give rise to a single band of approximately 475,000 daltons. The proteoglycans from day 1 and 2 cultures also give rise to the 475,000 dalton band, but each contains several other components which produce a smear of high molecular weight material on the gel. The monomer proteoglycans were incubated with cyanogen bromide and the resultant peptides separated by electrophoresis on a 5-17.5% polyacrylamide gel. The peptide displays of core proteins synthesized on days 4, 8 and 16 are virtually identical in terms of the number and electrophoretic distribution of the core protein peptides. In contrast, proteoglycan core proteins from day 1 and day 2 cultures give rise to peptide displays which resemble those from older cultures in some respects but have distinct features as well. The absence of structural variation in the newly synthesized proteoglycan core proteins from cartilage of different ages suggests that the age-related changes in the structure of the intact proteoglycans result from differences in the glycosaminoglycan biosynthetic machinery rather than alterations in the acceptor molecule (i.e., the core protein).

Cytokine expression by human marrow-derived mesenchymal progenitor cells in vitro: effects of dexamethasone and IL-1 alpha.

We previously reported the purification, culture-expansion, and osteogenic differentiation potential of mesenchymal progenitor cells (MPCs) derived from human bone marrow. As a first step to establishing the phenotypic characteristics of MPCs, we reported on the identification of unique cell surface proteins which were detected with monoclonal antibodies. In this study, the phenotypic characterization of human marrow-derived MPCs is further established through the identification of a cytokine expression profile under standardized growth medium conditions and in the presence of regulators of the osteogenic and stromal cell lineages, dexamethasone and interleukin-1 alpha (IL-1 alpha), respectively. Constitutively expressed cytokines in this growth phase include G-CSF, SCF, LIF, M-CSF, IL-6, and IL-11, while GM-CSF, IL-3, TGF-beta 2 and OSM were not detected in the growth medium. Exposure of cells in growth medium to dexamethasone resulted in a decrease in the expression of LIF, IL-6, and IL-11. These cytokines have been reported to exert influence on the differentiation of cells derived from the bone marrow stroma through target cell receptors that utilize gp130-associated signal transduction pathways. Dexamethasone had no effect on the other cytokines expressed under growth medium conditions and was not observed to increase the expression of any of the cytokines measured in this study. In contrast, IL-1 alpha increased the expression of G-CSF, M-CSF, LIF, IL-6 and IL-11 and induced the expression of GM-CSF. IL-1 alpha had no effect on SCF expression and was not observed to decrease the production of any of the cytokines assayed. These data indicate that MPCs exhibit a distinct cytokine expression profile. We interpret this cytokine profile to suggest that MPCs serve specific supportive functions in the microenvironment of bone marrow. MPCs provide inductive and regulatory information which are consistent with the ability to support hematopoiesis, and also supply autocrine, paracrine, and juxtacrine factors that influence the cells of the marrow microenvironment itself. In addition, the cytokine profiles expressed by MPCs, in response to dexamethasone and IL-1 alpha, identify specific cytokines whose levels of expression change as MPCs differentiate or modulate their phenotype during osteogenic or stromagenic lineage entrance/progression.

Characterization of the core protein of the large chondroitin sulfate proteoglycan synthesized by chondrocytes in chick limb bud cell cultures.

The core protein of high buoyant density proteoglycans synthesized by chondrocytes in stage 24 chick limb bud mesenchymal cell cultures was cleaved with cyanogen bromide to produce 17 resolvable peptides on sodium dodecyl sulfate-polyacrylamide slab gels. Of these peptides, 10 appear to originate from the chondroitin sulfate-rich region, 2 appear to be derived from the keratan sulfate-rich region, and 5 seem to be derived from the hyaluronic acid-binding region. The peptides from the chondroitin sulfate-rich region are almost all large (200 to 64 kDa). In contrast, the peptides from the keratan sulfate-rich and hyaluronic acid-binding regions are relatively small (47 to 12 kDa). One peptide from the hyaluronic acid-binding region appears to contain mannose-rich N-linked oligosaccharides as inferred from its observed binding by concanavalin A. A different hyaluronic acid-binding region peptide and one of the keratan sulfate-rich peptides were shown to contain disulfide bonds and therefore may be involved in contributing to the tertiary structure of the hyaluronic acid-binding region. Based on these observations, a map of the chick chondrocyte proteoglycan core protein has been constructed.

The SH-3 and SH-4 antibodies recognize distinct epitopes on CD73 from human mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are pluripotent cells in the bone marrow that have the capacity to differentiate along a number of connective tissue lineages, including cartilage, bone, adipose tissue, and stroma. The SH-3 and SH-4 monoclonal antibodies recognize epitopes present on the surface of human MSCs. This study describes the isolation and characterization of the antigen that is recognized by these antibodies. A protein of molecular weight approximately 67 kDa was immunoprecipitated from a solubilized membrane preparation of human MSCs using the SH-3 antibody. Analysis of peptides derived from this protein by mass spectrometry and sequencing identified it as CD73 (ecto-5'-nucleotidase). The SH-4 antibody was also shown to react with purified bovine CD73 by immunoblotting, but the SH-3 antibody failed to react with the bovine protein. These results indicate that both SH-3 and SH-4 epitopes are present on CD73, but they are distinct. CD73, present in lymphoid tissue, plays a role in the activation of B-lymphocytes and in signal transduction in the hematopoietic compartment of bone marrow. The role that CD73 may play in bone marrow stromal interactions and in the differentiation of MSCs is discussed.

Osteogenic differentiation of purified, culture-expanded human mesenchymal stem cells in vitro.

Human bone marrow contains a population of cells capable of differentiating along multiple mesenchymal cell lineages. Recently, techniques for the purification and culture-expansion of these human marrow-derived Mesenchymal Stem Cells (MSCs) have been developed. The goals of the current study were to establish a reproducible system for the in vitro osteogenic differentiation of human MSCs, and to characterize the effect of changes in the microenvironment upon the process. MSCs derived from 2nd or 3rd passage were cultured for 16 days in various base media containing 1 to 1000 nM dexamethasone (Dex), 0.01 to 4 mM L-ascorbic acid-2-phosphate (AsAP) or 0.25 mM ascorbic acid, and 1 to 10 mM beta-glycerophosphate (beta GP). Optimal osteogenic differentiation, as determined by osteoblastic morphology, expression of alkaline phosphatase (APase), reactivity with anti-osteogenic cell surface monoclonal antibodies, modulation of osteocalcin mRNA production, and the formation of a mineralized extracellular matrix containing hydroxyapatite was achieved with DMEM base medium plus 100 nM Dex, 0.05 mM AsAP, and 10 mM beta GP. The formation of a continuously interconnected network of APase-positive cells and mineralized matrix supports the characterization of this progenitor population as homogeneous. While higher initial seeding densities did not affect cell number of APase activity, significantly more mineral was deposited in these cultures, suggesting that events which occur early in the differentiation process are linked to end-stage phenotypic expression. Furthermore, cultures allowed to concentrate their soluble products in the media produced more mineralized matrix, thereby implying a role for autocrine or paracrine factors synthesized by human MSCs undergoing osteoblastic lineage progression. This culture system is responsive to subtle manipulations including the basal nutrient medium, dose of physiologic supplements, cell seeding density, and volume of tissue culture medium. Cultured human MSCs provide a useful model for evaluating the multiple factors responsible for the step-wise progression of cells from undifferentiated precursors to secretory osteoblasts, and eventually terminally differentiated osteocytes.

Human bone marrow-derived mesenchymal (stromal) progenitor cells (MPCs) cannot be recovered from peripheral blood progenitor cell collections.

The purpose of this study was to compare the ability to collect human bone marrow-derived mesenchymal (stromal) progenitor cells (MPC) from bone marrow versus peripheral blood hematopoietic progenitor cell (PBPC) collections using in vitro and in vivo assays. Ten milliliter samples of PBPC collections mobilized from 11 patients undergoing autotransplants using chemotherapy followed by G-CSF 5-10 micrograms/kg were evaluated using in vitro and in vivo assays for hematopoietic progenitors and MPCs. Additionally, 10 ml samples of unstimulated bone marrow aspirates as well as PBPC collected after mobilization using G-CSF 10 micrograms/kg obtained from 3 normal, histocompatible allogeneic donors were analyzed for hematopoietic progenitors and MPCs. The MPCs were isolated and culture-expanded as adherent cells in vitro and subsequently tested for the capacity to differentiate into mesenchymal phenotypes in vivo using calcium hydroxyapatite porous ceramic cubes implanted s.c. in athymic mice. Demineralized sections of these cubes were analyzed histologically for the appearance of bone and cartilage. Seven autotransplant subjects with cancer received G-CSF after chemotherapy administration, whereas 4 cancer patients and all 3 normal donors received G-CSF alone as the mobilizing regimen. For the autologous PBPC collections and the normal marrow aspirations, median hematopoietic progenitor content was in the normal range for our institution. MPCs were detected in in vitro cultures and as bone-positive ceramic cubes in samples of all 3 allogeneic donor bone marrows but in none of the 14 autologous and 6 allogeneic PBPC collections. In conclusion, MPCs could not be recovered in PBPC collections obtained from either normal donors or patients who underwent PBPC collections after mobilization therapy but could be obtained routinely from bone marrow samples. Although the role of transplanted MPCs is an area of clinical investigation, this study points out a fundamental differences in the population of cells transplanted after collection from bone marrow versus peripheral blood.

Monoclonal antibody against adult marrow-derived mesenchymal stem cells recognizes developing vasculature in embryonic human skin.

We have described previously a monoclonal antibody (SH2) that specifically recognizes undifferentiated mesenchymal progenitor cells isolated from adult human bone marrow. These cells, which we operationally refer to as mesenchymal stem cells, have the capacity to differentiate and form distinct mesenchymal tissues such as bone and cartilage when the isolated cells are placed in the appropriate in vivo or in vitro environment. We report here the partial biochemical characterization of the antigen recognized by the SH2 antibody. Metabolically radiolabelled adult marrow-derived mesenchymal stem cells in culture were extracted and immunoprecipitated with the SH2 antibody. The purified antigen migrated as a single band of 90 kDa after sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed under reducing conditions. The SH2-immunoprecipitated protein exhibited a molecular weight band shift after removal of N-linked oligosaccharides. We investigated the expression of the SH2 antigen, along with the endothelial markers factor VIII-related antigen and Ulex europaeus I (UEA-I) lectin during specific developmental periods in human dermal embryogenesis and in the postnatal period through aged adults. Frozen sections of human embryonic, fetal, or postnatal skin ranging from 8 weeks estimated gestational age (EGA) through 84 years of age were immunostained or double immunolabelled with antibodies SH2, UEA-I, or factor VIII-related antigen followed by second antibodies with fluorescent markers. Positive cell surface reactivity with the SH2 antibody was seen in cells in the vascular plane in the earliest specimens (day 55 EGA) corresponding to the late cellular dermis period. During the period of the cellular to fibrous transition, in which the initiation of appendage development occurs, most SH2-reactive cells colocalized with vasculature markers UEA-I and factor VIII-related antigen, although there was a subset of cells recognized by SH2 antibody that did not colocalize with the endothelial markers. In contrast to the endothelial markers UEA-I and factor VIII-related antigen, in which the number of immunopositive cells became more prominent with age and maturation of the dermis, the frequency of cells that contained the SH2-reactive antigen diminished with age. The SH2 reactivity evident in embryonic, fetal, and early postnatal periods was not observed in human skin specimens taken from adults greater than 30 years old. These observations support the hypothesis that the SH2 antigen is a cell surface marker of developing microvasculature and may play a role in dermal embryogenesis and angiogenesis.

Mesenchymal stem cells inhibit and stimulate mixed lymphocyte cultures and mitogenic responses independently of the major histocompatibility complex.

We aimed to study the effects of mesenchymal stem cells (MSCs) on alloreactivity and effects of T-cell activation on human peripheral blood lymphocytes (PBLs) in vitro. MSCs were expanded from the bone marrow of healthy subjects. MSCs isolated from second to third passage were positive for CD166, CD105, CD44, CD29, SH-3 and SH-4, but negative for CD34 and CD45. MSCs cultured in osteogenic, adipogenic or chondrogenic media differentiated, respectively, into osteocytes, adipocytes or chondrocytes. MSC added to PBL cultures had various effects, ranging from slight inhibition to stimulation of DNA synthesis. The stimulation index (SI = (PBL + MSC)/PBL) varied between 0.2 and 7.3. The SI was not affected by the MSC dose or by the addition of allogeneic or autologous MSCs to the lymphocytes. Suppression of proliferative activity was observed in all experiments after the addition of 10,000-40,000 MSCs to mixed lymphocyte cultures (MLCs). Lymphocyte proliferation was 10-90%, compared with a control MLC run in parallel without MSCs. In contrast, the addition of fewer MSCs (10-1000 cells) led to a less consistent suppression or a marked lymphocyte proliferation in several experiments, ranging from 40 to 190% of the maximal lymphocyte proliferation in control MLCs. The ability to inhibit or stimulate T-cell alloresponses appeared to be independent of the major histocompatibility complex, as results were similar using 'third party' MSCs or MSCs that were autologous to the responder or stimulating PBLs. The strongest inhibitory effect was seen if MSCs were added at the beginning of the 6 day culture, and the effect declined if MSCs were added on day 3 or 5. Marked inhibitory effects of allogeneic and autologous MSCs (15,000) were also noted after mitogenic lymphocyte stimulation by phytohaemagglutinin (median lymphocyte proliferation of 30% of controls), Concanavalin A (56%) and protein A (65%). Little, if any, inhibition occurred after stimulation with pokeweed mitogen. Low numbers of MSCs (150 cells) were unable to inhibit mitogen-induced T-cell responses. MSCs have significant immune modulatory effects on MLCs and after mitogenic stimulation of PBL. High numbers of MSCs suppress alloreactive T cells, whereas very low numbers clearly stimulated lymphocyte proliferation in some experiments. The effect of a larger number of MSCs on MLCs seems more dependent on cell dose than histocompatibility and could result from an 'overload' of a stimulatory mechanism.

The monoclonal antibody SH-2, raised against human mesenchymal stem cells, recognizes an epitope on endoglin (CD105).

Mesenchymal stem cells are multipotent cells resident in the bone marrow throughout adulthood which have the capacity to differentiate into cartilage, bone, fat, muscle, and tendon. A number of monoclonal antibodies raised against human MSCs have been shown to react with surface antigens on these cells in vitro. A protein of molecular mass 92 kDa was immunoprecipitated using the SH-2 monoclonal antibody. This was purified and identified by peptide sequencing analysis and mass spectrometry as endoglin (CD105), the TGF-beta receptor III present on endothelial cells, syncytiotrophoblasts, macrophages, and connective tissue stromal cells. Endoglin on MSCs potentially plays a role in TGF-beta signalling in the control of chondrogenic differentiation of MSCs and also in mediating interactions between MSCs and haematopoietic cells in the bone marrow microenvironment.

In vitro differentiation of bone and hypertrophic cartilage from periosteal-derived cells.

Periosteal cells were enzymatically liberated from the tibiae of young chicks, introduced into cell culture, and allowed to reach confluence. The morphology of the cells gave the impression of a relatively homogeneous population of fibroblast-like cells. These cultured cells did not overtly express osteogenic or chondrogenic properties as judged by their morphology and the lack of reactivity with probes to phenotype-specific antigens of osteoblasts or chondrocytes. The cells were then replated at relatively high density and chronologically evaluated for the differentiation of bone and cartilage. These replated cells formed a multi-layer of fibroblast-like cells, the top portion of which eventually differentiated into bone tissue as evidenced by the presence of mineralization and immunocytochemical reactivity to bone Gla protein- and osteocyte-specific probes. Cells below this distinctive top layer differentiated into chondrocytes, which eventually further developed into hypertrophic chondrocytes as evidenced by their morphology and the presence of immunoreactive type X collagen in the matrix. Mineralization was also observed in the territorial matrix of these hypertrophic chondrocytes, when the culture was augmented with beta-glycerophosphate. Periosteal-derived cells replated at a lower density as controls did not show signs of osteochondrogenic differentiation. These observation suggest that periosteal-derived cells of young chicks contain mesenchymal cells which possess the potential to undergo terminal differentiation into osteogenic or chondrogenic phenotypes depending on local environmental or positional cues.