Characterization and functionality of cell surface molecules on human mesenchymal stem cells.

We have characterized adhesion molecules on the surface of multipotential human mesenchymal stem cells (hMSCs) and identified molecules whose ligands are present on mature hematopoietic cells. Flow cytometric analysis of hMSCs identified the expression of integrins: alpha1, alpha2, alpha3, alpha5, alpha6, alphav, beta1, beta3, and beta4, in addition to ICAM-1, ICAM-2, VCAM-1, CD72, and LFA-3. Exposure of hMSCs to IL-1alpha, TNFalpha or IFNgamma up-modulated ICAM-1 surface expression, whereas only IFNgamma increased both HLA-class I and -class II molecules on the cell surface. Whole cell-binding assays between the hMSCs and hematopoietic cell lines showed that T lymphocytic lines bound hMSCs with higher affinity than lines of either B lymphocytes or those of myeloid lineage. Experiments using autologous T lymphocytes isolated from peripheral blood mononuclear cells showed that hMSCs exhibited increased affinity for activated T-lymphocytes compared to resting T cells by quantitative whole cell binding and rosetting assays. Flow cytometric analysis of rosetted cells demonstrated that both CD4+ and CD8+ cells bound to hMSCs. To determine the functional significance of these findings, we tested the ability of hMSCs to present antigen to T lymphocytes. hMSCs pulsed with tetanus toxoid stimulated proliferation and cytokine production (IL-4, IL-10, and IFNgamma) in a tetanus-toxoid-specific T cell line. Maximal cytokine production correlated with maximal antigen-dependent proliferation. These data demonstrate physiological outcome as a consequence of interactions between hMSCs and human hematopoietic lineage cells, suggesting a role for hMSCs in vivo to influence both hematopoietic and immune function(s).

Mesenchymal stem cells suppress lymphocyte proliferation in vitro and prolong skin graft survival in vivo.

OBJECTIVE: Mesenchymal stem cells (MSCs), multipotential cells that reside within the bone marrow, can be induced to differentiate into various components of the marrow microenvironment, such as bone, adipose, and stromal tissues. The bone marrow microenvironment is vital to the development, differentiation, and regulation of the lymphohematopoietic system. We hypothesized that the activities of MSCs in the bone marrow microenvironment might also include immunomodulatory effects on lymphocytes. METHODS: Baboon MSCs were tested in vitro for their ability to elicit a proliferative response from allogeneic lymphocytes, to inhibit an ongoing allogeneic response, and to inhibit a proliferative response to potent T-cell mitogens. In vivo effects were tested by intravenous administration of donor MSCs to MHC-mismatched recipient baboons prior to placement of autologous, donor, and third-party skin grafts. RESULTS: MSCs failed to elicit a proliferative response from allogeneic lymphocytes. MSCs added into a mixed lymphocyte reaction, either on day 0 or on day 3, or to mitogen-stimulated lymphocytes, led to a greater than 50% reduction in proliferative activity. This effect could be maximized by escalating the dose of MSCs and could be reduced with the addition of exogenous IL-2. In vivo administration of MSCs led to prolonged skin graft survival when compared to control animals: 11.3 +/- 0.3 vs 7 +/- 0. CONCLUSIONS: Baboon MSCs have been observed to alter lymphocyte reactivity to allogeneic target cells and tissues. These immunoregulatory features may prove useful in future applications of tissue regeneration and stem cell engineering.