Prostaglandin E2 Plays a Key Role in the Immunosuppressive Properties of Adipose Tissue-Derived Mesenchymal Stromal Cells.

Abstract 3636

Poster Board III-572

Mesenchymal stromal cells (MSCs) are multipotential non-hematopoietic cells that can be obtained from several tissues. These cells have a limited immunogenicity, and their immunosuppressive properties have led to their use to treat graft-versus-host disease (GVHD) in patients undergoing allogeneic hematopoietic stem cells transplantation. In previous studies, we demonstrated that adipocyte tissue-derived MSCs (Ad-MSCs) suppress activated T cells proliferation and prevent GVHD in a haploidentical hematopoietic transplantation mouse model (Yañez, Stem Cells 2006). In the present study, we have investigated the mechanisms participating in the immunosuppressive properties of human Ad-MSCs. First, we confirmed that the addition of Ad-MSCs to activated T lymphocytes inhibited the production of pro-inflammatory cytokines (TNF-a, IFN-g, IL-6 and IL-12), and increased the secretion of the immunosuppressive IL-10. In these co-cultures, high levels of PGE2 were detected. The addition of indomethacin (IDM), an inhibitor of PGE2, restored the proliferation of activated T lymphocytes and increased the expression of genes related with proliferation. Furthermore, an increase in the expression of genes related with transcription factors and cytokines involved in the TH1/TH2 differentiation pathway of the activated T cells was detected. These results show that PGE2 plays a key role in the immunosuppressive effects of Ad-MSCs over activated T lymphocytes.

Although, strikingly, the blockade of PGE2 by IDM did not restore the pro-inflammatory cytokine secretion profile in the Ad-MSCs/activated T lymphocytes co-cultures, the increase in the expression of activation and differentiation-related genes suggests a restoration, at an early time, of the cytokine secretion of the activated T lymphocytes. Analyses at different time-points after the addition of IDM are being conducted to confirm this hypothesis.

When TGF-b was determined in these cultures, no changes were detected by the addition of Ad-MSCs to activated T lymphocytes cultures, showing that this factor does not account for the inhibitory effects of Ad-MSCs over activated T cells.

Next, we studied the impact of Ad-MSCs over the maturation of dendritic cells. We generated immature myeloid (m-DCs) and plasmocytoid (p-DCs) dendritic cells, and induced their maturation with LPS. We found that in co-culture with Ad-MSCs, dendritic cells remained in an immature state, shown by decreased CD83 and CD80 expression, and by a decreased secretion of TNF-β by myeloid-DCs (m-DCs), and an increased production of IL-10 by plasmocytoid-DCs (p-DCs). The blockade by IDM of the PGE2 present in the co-cultures resulted in the maturation of p-DCs, but not of m-DCs, that remained in an immature state. These results show that PGE2 accounts for the immunosuppressive effects of Ad-MSCs over the maturation of p-DCs, but not over the maturation of m-DCs. Finally, when TGF-b1 was studied, no changes in the very low values of TGF-b levels were detected in the supernatants of m-DCs and p-DCs co-cultured Ad-MSCs, showing that this factor does not play an important role in the effects of Ad-MSCs on the maturation of m-DCs and p-DCs.