Mesenchymal stem cells inhibit dendritic cell differentiation and function by preventing entry into the cell cycle.
BACKGROUND
Mesenchymal stem cells (MSCs) play a crucial role in hematopoietic development and have been shown to exert a powerful immunosuppressive effect. In this study, we investigated the effect of bone marrow MSC on the differentiation and function of peripheral blood monocytes into dendritic cells (DCs).


METHODS
Human MSCs, generated from normal bone marrow, were added to peripheral blood monocytes stimulated in vitro with granulocyte-macrophage colony stimulating factor and interleukin-4 to become DCs. Monocytes were then examined for the expression of markers characteristic of DCs and their ability to stimulate allogeneic T cells. In addition, the effect of MSCs on the cell cycle of monocyte-derived DCs and the expression of various cell cycle proteins were analyzed by cytometric analysis and Western blotting with specific antibodies.


RESULTS
MSCs blocked the differentiation of monocytes into DCs and impaired their antigen-presenting ability. This resulted from a block of monocytes from entering the G1 phase of the cell cycle with a progressive number of cells accumulating in the G0 phase. Cyclin D2 was downregulated. However, differently from what was observed in T-cells stimulated in the presence of MSCs, the expression of p27 was found decreased, suggesting the involvement of similar but not identical pathways.


CONCLUSIONS
We conclude that MSCs impair monocyte differentiation and function by interfering with the cell cycle. These findings imply that MSC-induced immunosuppression might be a side product of a more general antiproliferative effect.
Ramasamy
Rajesh
R
Department of Immunology, Imperial College Faculty of Medicine, London, U.K.
Fazekasova
Henrietta
H
Lam
Eric W-F
EW
Soeiro
Inês
I
Lombardi
Giovanna
G
Dazzi
Francesco
F
D015703:Antigens, CD / Q000032:analysis; D001854:Bone Marrow Cells / Q000166:cytology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002453:Cell Cycle / Q000502:physiology*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D056742:Cyclin D2; D016213:Cyclins / Q000235:genetics; D003713:Dendritic Cells / Q000166:cytology* / Q000502:physiology*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D016130:Immunophenotyping; D015847:Interleukin-4 / Q000494:pharmacology; D008213:Lymphocyte Activation; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000502:physiology*; D009000:Monocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology / Q000502:physiology
D015703:Antigens, CD; C080336:CCND2 protein, human; D056742:Cyclin D2; D016213:Cyclins; D015847:Interleukin-4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor