Immunomodulatory activity of mesenchymal stem cells.

Mesenchymal stem cells (MSCs) were discovered as a rare population of non-hematopoietic stem cells that reside in the bone marrow and interact closely with hematopoietic stem cells to support their growth and differentiation. MSCs are multipotent cells that have the ability to differentiate into cells of the mesenchymal lineage including adipocytes, osteocytes and chondrocytes and they have been reported to home to areas of tissue injury and participate in tissue repair. More recently, MSCs have also been described to possess anti-inflammatory and immunomodulatory properties that can affect multiple arms of the immune system. MSCs have been shown to inhibit T and B cell proliferation, downregulate the lytic activity of cytotoxic T lymphocytes and NK cells, inhibit the maturation and antigen-presenting function of dendritic cells and modulate macrophage function through both contact-dependent and contact-independent mechanisms. The administration of MSCs in models of autoimmune disease such as collagen-induced arthritis, EAE and autoimmune diabetes has provided additional evidence for an immunoregulatory role of MSCs supporting their use in controlling autoimmunity. The administration of allogeneic MSCs as immunosuppressive agents represents a viable approach as they appear to be largely non-immunogenic and clinical trials with allogeneic MSCs are currently underway in graftversus- host disease, Crohn's disease and type I diabetes indications. The immunomodulatory properties, mechanism of action and potential clinical utility of MSCs are reviewed herein.

A changing time: the International Society for Cellular Therapy embraces its industry members.

The last decade has seen a dramatic rise in the development of new cellular therapeutics in a wide range of indications. There have been acceptable safety profiles reported in early studies using blood-derived and adherent stem cell products, but also an inconsistent efficacy record. Further expansion has been hindered in part by a lack of capital (both private and public) and delayed entry into the cell therapy space by large healthcare and pharmaceutical companies, those members of the industry most reliably able to initiate and maintain advanced-phase clinical trials. With recognition that the International Society for Cellular Therapy (ISCT) is uniquely positioned to serve the global translational regenerative medicine research community as a network hub for scientific standards and policy, the ISCT commissioned the establishment of an Industry Task Force (ITF) to address current and future roles for industry. The objectives of the ITF were to gather information and prioritize efforts for a new Commercialization Committee (CC) and to construct innovative platforms that would foster constructive and synergistic collaborations between industry and ISCT. Recommendations and conclusions of the ITF included that the new CC: (1) foster new relationships with therapeutic and stem cell societies, (2) foster educational workshops and forums to cross-educate and standardize practices, (3) create industry subcommittees to address priority initiatives, with clear benchmarks and global implementation, and (4) establish a framework for a greater industry community within ISCT, opening doors for industry to share the new vision for commercialization of cell therapy, emphasizing the regenerative medicine space.

CCAAT/Enhancer binding proteins repress the leukemic phenotype of acute myeloid leukemia.

CCAAT/enhancer binding proteins (C/EBPs) are a family of factors that regulate cell growth and differentiation. These factors, particularly C/EBPalpha and C/EBPepsilon, have important roles in normal myelopoiesis. In addition, loss of C/EBP activity appears to have a role in the pathogenesis of myeloid disorders including acute myeloid leukemia (AML). Acute promyelocytic leukemia (APL) is a subtype of AML in which a role for C/EBPs has been postulated. In almost all cases of APL, a promyelocytic leukemia-retinoic acid receptor alpha (PML-RARalpha) fusion protein is expressed as a result of a t(15;17)(q22;q12) chromosomal translocation. PML-RARalpha inhibits expression of C/EBPepsilon, whereas all-trans retinoic acid (tRA), a differentiating agent to which APL is particularly susceptible, induces C/EBPepsilon expression. PML-RARalpha may also inhibit C/EBPalpha activity. Thus, the effects of PML-RARalpha on C/EBPs may contribute to both the development of leukemia and the unique sensitivity of APL to tRA. We tested the hypothesis that increasing the activity of C/EBPs would revert the leukemic phenotype. C/EBPalpha and C/EBPepsilon were introduced into the FDC-P1 myeloid cell line and into leukemic cells from PML-RARA transgenic mice. C/EBP factors suppressed growth and induced partial differentiation in vitro. In vivo, enhanced expression of C/EBPs prolonged survival. By using a tamoxifen-responsive version of C/EBPepsilon, we observed that C/EBPepsilon could mimic the effect of tRA, driving neutrophilic differentiation in leukemic animals. Our results support the hypothesis that induction of C/EBP activity is a critical effect of tRA in APL. Furthermore, our findings suggest that targeted modulation of C/EBP activities could provide a new approach to therapy of AML.

Systematic analysis of reportedly distinct populations of multipotent bone marrow-derived stem cells reveals a lack of distinction.

Adult human bone marrow-derived stem cells, having the ability to differentiate into cells of multiple lineages, have been isolated and propagated by varied protocols, including positive (CD105(+))/negative (CD45(-)GlyA(-)) selection with immunomagnetic beads, or direct plating into selective culture media. Each substratum-adherent cell population was subjected to a systematic analysis of their cell surface markers and differentiation potential. In the initial stages of culture, each cell population proliferated slowly, reaching confluence in 10-14 days. Adherent cells proliferated at similar rates whether cultured in serum-free medium supplemented with basic fibroblast growth factor, medium containing 2% fetal bovine serum (FBS) supplemented with epidermal growth factor and platelet-derived growth factor, or medium containing 10% FBS alone. Cell surface marker analysis revealed that more than 95% of the cells were positive for CD105/endoglin, a putative mesenchymal stem cell marker, and negative for CD34, CD31, and CD133, markers of hematopoietic, endothelial, and neural stem cells, respectively, regardless of cell isolation and propagation method. CD44 expression was variable, apparently dependent on serum concentration. Functional similarity of the stem cell populations was also observed, with each different cell population expressing the cell type-specific markers beta-tubulin, type II collagen, and desmin, and demonstrating endothelial tube formation when cultured under conditions favoring neural, cartilage, muscle, and endothelial cell differentiation, respectively. On the basis of these data, adult human bone marrow-derived stem cells cultured in adherent monolayer are virtually indistinguishable, both physically and functionally, regardless of the method of isolation or proliferative expansion.