Mesenchymal Stem Cells Do Not Suppress Lymphoblastic Leukemic Cell Line Proliferation

Background: Several studies have demonstrated the immunosuppresive effects of mes-enchymal stem cells (MSCs) in allogeneic or mitogenic interactions. Cell-cell contact inhibition and secretion of suppressive soluble factors have been suggested in this re-gard. Objective: To investigate if adipose derived MSCs could inhibit Jurkat lym-phoblastic leukemia T cell proliferation during coculture. Methods: Adherent cells with the ability of cellular growth were isolated from normal adipose tissues. Initial charac-terization of growing cells by flow cytometry suggested their mesenchymal stem cell characteristics. Cells were maintained in culture and used during third to fifth culture passages. Jurkat or allogeneic peripheral blood mononuclear cells (PBMCs) were la-beled with carboxy fluorescein diacetate succinimidyl ester and cocultured with increas-ing doses of MSCs or MSC culture supernatant. Proliferation of PBMCs or Jurkat cells under these conditions was assessed by flow cytometry after 2 and 3 days of coculture, respectively. Results: Results showed the expression of CD105, CD166 and CD44, and the absence of CD45, CD34 and CD14 on the surface of MSC like cells. Moreover, ini-tial differentiation studies showed the potential of cell differentiation into hepatocytes. Comparison of Jurkat cell proliferation in the presence and absence of MSCs showed no significant difference, with 70% of cells displaying signs of at least one cell division. Similarly, the highest concentration of MSC culture supernatant (50% vol/vol) had no significant effect on Jurkat cell proliferation (p>0.6). The same MSC lots significantly suppressed the allogeneic PHA activated PBMCs under similar culture conditions. Conclusion: Using Jurkat cells as a model of leukemia T cells, our results indicated an uncertainty about the suppressive effect of MSCs and their inhibitory metabolites on tumor or leukemia cell proliferation. Additional systematic studies with MSCs of differ-ent sources are needed to fully characterize the immunological properties of MSCs be-fore planning clinical applications.