IFNGamma Priming Protects Fetal and Embryonic MSC from NK Cell-Mediated Killing and Improves their Immunosuppressive Properties: Role of Activating and Inhibitory Receptors

Abstract

The enhancement of Mesenchymal Stem Cells (MSC) immunosuppressing function can favour the engraftment of MSC employed in tissue repair. IFN-γ is a pro-inflammatory cytokine, which induces tolerogenic molecules in bone marrow (BM) MSC. We have investigated the interaction of IFN-γ primed MSC from fetal (FL-MSC) and embryonic (ES-MSC) origin with natural killer (NK) cells. IFN-γ -primed FL-/ES-MSC were less susceptible to NK cell-mediated killing, where a major role was played by the IFN-γ-induced up-regulation of HLA-ABC and HLA-E. Monoclonal antibody-mediated blocking of CD94/NKG2A on NK cells increased killing of IFN-γ-primed MSC, suggesting a role of this NK cell inhibitory receptor in MSC protection. NKG2D ligands (such as MICA), LFA-1 and ICAM1 expressed on MSC were also involved in NK cell-mediated killing of un-primed, but not of IFN-γ-primed, FL-/ES-MSC. Importantly, NK cells from IFN-γ-primed FL-/ES-MSC-NK cell co-cultures displayed a reduced intracellular free calcium increase, pERK activation, degranulation, cytolysis and IFN-γ production upon interaction with the NK sensitive target cell K562 compared to NK cells from un-primed FL/ES-MSC-NK cell co-cultures. Finally, PGE-2, increased during NK/MSC co-cultures, appeared to be a key soluble factor responsible for FL-/ES-MSC-mediated immunosuppressive effect. These results suggest that surface molecules such as MICA, HLA-E and ICAM1 can play a role in recognizing un-primed FL/ES-MSC but not IFN-γ-primed MSC where HLA-I is a key molecule for NK cellmediated recognition. Further, the strong immunosuppressive effect of IFN-γ-primed FL-/ES-MSC on NK cells could be exploited in cellular therapy protocols.

Mesenchymal stem cells and natural killer cells interaction mechanisms and potential clinical applications

“…However, the researchers showed that MSCs were protected from lysis by NK cells by increasing IFN-γ during inflammatory responses. Spagiari et al [ 57 ] in a study on BM-MSC, and Giuliani et al [ 95 ] in a study on fetal-MSC (FL-MSC) and embryonic-MSC (ES-MSC), investigated the effect of IFN-γ on the protection of MSC against NK cells. They showed that IFN-γ increased HLA class I and HLA-E molecules expression in MSCs and decreased lysis of MSCs by NK cells.…”

Strategies to enhance immunomodulatory properties and reduce heterogeneity in mesenchymal stromal cells during ex vivo expansion

“…These immune cells are typically activated using antibodies, inflammatory cytokines or lipopolysaccharides, followed by coculture of the immune cells with MSCs, then analysis of immune cell proliferation, function and activity. Priming of MSCs with cytokines such as IFNg and TNFa improves the ability of MSCs to suppress T cell proliferation and activation [209], B cell proliferation [209] and NK cellÀmediated cytotoxicity [214] in co-culture assays. Such techniques involving specific immune cell populations, combined with the appropriate stimulus to both activate immune cells and prime the immunomodulatory capability of MSCs, represent a physiologically relevant assay to characterize the functional potency of MSCs.…”