Alterations of Multipotent Mesenchymal Stromal Cells Induced by Interaction with Allogeneic Lymphocytes In Vitro

Multipotent mesenchymal stromal cells (MSCs) are widely used for cell therapy. Treatment with interferon-γ (IFNγ) increases the immunomodulating properties of MSCs. When administered intravenously, MSCs interact with lymphocytes. It is impossible to follow the fate of MSCs in the recipient organism. The aim of this study was to investigate the properties of MSCs after their interaction with lymphocytes in vitro. Bone marrow MSCs were co-cultured for 4 days with activated and non-activated lymphocytes. A portion of the MSCs was pretreated with IFNγ. HLA-DR expression on the MSCs increased when these cells were co-cultured with lymphocytes and after they were treated with IFNγ. The activated lymphocytes induced significantly higher HLA-DR expression levels than did IFNγ treatment. IFNγ increased the viability of MSCs when these cells were co-cultured with lymphocytes. The immunomodulating properties of MSCs were amplified after IFNγ priming and co-cultivation with lymphocytes; therefore, this amplification was not dependent on the IFNγ source. IFNγ treatment and lymphocyte interactions induced increases in the relative expression levels (RELs) of ICAM1 and factors involved in immunomodulation in the MSCs. IFNγ stabilizes MSCs while maintaining their viability. The data suggest that MSCs obtained from the hematopoietic cells donor or autologous should be used for cell therapy

Local clonal analysis of the hematopoietic system shows that multiple small short-living clones maintain life-long hematopoiesis in reconstituted mice

We describe here a technique to study the clonal contribution of primitive stem cells that account for long-term hematopoiesis in the same mouse over a 14-month period. Specifically, irradiated recipient female mice were transplanted with retrovirally marked male hematopoietic progenitors. Bone marrow was then collected repeatedly from local sites from the same mice throughout a 14-month period and injected into secondary irradiated recipients for analysis of donor retrovirally marked day-11 colony-forming unit-spleen (CFU-S-11). We have tracked the temporal in vivo fate of 194 individual CFU-S-derived cell clones in 38 mice reconstituted with such retrovirally marked bone marrow cells. Our data show that long-term hematopoiesis is maintained by a large number of simultaneously functioning small, shortlived (1 to 3 months) clones that usually grow locally with little or no dispersion between different regions of the hematopoietic system. Furthermore, the clones that disappeared were never detected again. The data suggest that normal hematopoiesis is supported by the sequential recruitment of marrow repopulating cells into a differentiation mode.</jats:p

Clonal dynamics of native haematopoiesis

It is currently thought that life-long blood cell production is driven by the action of a small number of multipotent haematopoietic stem cells. Evidence supporting this view has been largely acquired through the use of functional assays involving transplantation. However, whether these mechanisms also govern native non-transplant haematopoiesis is entirely unclear. Here we have established a novel experimental model in mice where cells can be uniquely and genetically labelled in situ to address this question. Using this approach, we have performed longitudinal analyses of clonal dynamics in adult mice that reveal unprecedented features of native haematopoiesis. In contrast to what occurs following transplantation, steady-state blood production is maintained by the successive recruitment of thousands of clones, each with a minimal contribution to mature progeny. Our results demonstrate that a large number of long-lived progenitors, rather than classically defined haematopoietic stem cells, are the main drivers of steady-state haematopoiesis during most of adulthood. Our results also have implications for understanding the cellular origin of haematopoietic disease