Human mesenchymal stem cells require monocyte-mediated activation to suppress alloreactive T cells.

Human bone marrow-derived mesenchymal cells (MSCs) are precursors of nonhematopoietic mesenchymal cells of the bone marrow microenvironment. MSCs were shown to inhibit alloreactive T lymphocytes, but the mechanism and mediators of this effect are not fully understood. Here we describe a novel interaction between blood monocytes and bone marrow-derived, culture-expanded MSCs, which results in inhibition of T-lymphocyte activation.

Expansion of LTC-ICs and maintenance of p21 and BCL-2 expression in cord blood CD34(+)/CD38(-) early progenitors cultured over human MSCs as a feeder layer.

Allogeneic transplantation with umbilical cord blood (UCB) is limited in adult recipients by a low CD34(+) cell dose. Clinical trials incorporating cytokine-based UCB in vitro expansion have not demonstrated significant shortening of hematologic recovery despite substantial increases in CD34(+) cell dose, suggesting loss of stem cell function. To sustain stem cell function during cytokine-based in vitro expansion, a feeder layer of human mesenchymal stem cells (MSCs) was incorporated in an attempt to mimic the stem cell niche in the marrow microenvironment.