Abstract
Background aims. Multipotent mesenchymal stromal cells, also known as mesenchymal stem cells (MSC), can be isolated from adult and fetal tissues. Recently, there has been considerable interest in MSC because they have features favorable for transplantation, namely their multipotency and non-immunogenic properties. Methods. We analyzed how human MSC derived from first-trimester fetal liver and adult bone marrow interact with naive and activated innate natural killer (NK) cells. NK cell function was studied by measuring killing of MSC, as well as degranulation (CD107a) induced by MSC. To assess the importance of NK cell killing, expression of surface epitopes was analyzed by flow cytometry on MSC before and after stimulation with interferon (IFN)γ. Results. Fetal and adult MSC express several ligands to activating NK cell receptors as well as low levels of HLA class I, with large inter-individual variation. Naive peripheral blood NK cells did not lyse fetal or adult MSC, whereas interleukin (IL)2 activated allogeneic as well as autologous NK cells did. Pre-incubation of MSC with IFN-γ increased their levels of HLA class I, protecting them from NK cell recognition. Fetal and adult MSC were preferably killed via the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL) pathways, respectively. Blocking NKG2D reduced NK cell degranulation in both fetal and adult MSC. Conclusions. Fetal and adult MSC differ in their interactions with NK cells. Both fetal and adult MSC are susceptible to lysis by activated NK cells, which may have implications for the use of MSC in cell therapy.
Acknowledgements
This study was supported by grants from the Swedish Society for Medical Research, Magnus Bergvall foundation, Swedish Cancer Society (08 0502), Children's Cancer Foundation (08/071), Swedish Research Council (K2006–32X-14716-04-1, K2008–64X-20742-01-3, K2008-64P-15457-04-3), Tobias Foundation, Cancer Society in Stockholm, Swedish Society of Medicine, Sven and Ebba-Christina Hagbergs Foundation, Stockholm County Council, Karolinska Institutet and National Institutes of Health.
Disclosure of interest: The authors report no potential conflicts of interest. This paper represents original work and has not been submitted for publication elsewhere.