High Concentrations of TNF-α Induce Cell Death during Interactions between Human Umbilical Cord Mesenchymal Stem Cells and Peripheral Blood Mononuclear Cells

Human umbilical cord mesenchymal stromal cells (hUC-MSCs) are currently being used as novel therapeutic agents in numerous clinical trials. Previous works have shown that hUC-MSCs possess profound immunomodulatory capacities through IL-1 stimulation produced by peripheral blood mononuclear cells (PBMCs), their main cellular partner in most pathophysiological and therapeutic situations. The present study was designed to explore the role of TNF-α in these interactions. In these experiments, we demonstrated that TNF-α originated from PBMCs under the influence of IL-1. We also showed that TNF-α acted differently depending upon the concentrations reached. At low concentrations it clearly contributed to IL-6 and monocyte chemotactic protein 1 (MCP-1) production. At high concentrations, used alone or in association with the TNF-related apoptosis-inducing ligand, TNF-α also stimulated hUC-MSC IL-6 but, more intensely, MCP-1 production. This stimulation was associated but independent of apoptosis induction in a process involving Inhibitor of Apoptosis Proteins. Interferon gamma (IFN-γ), tested to stimulate PBMC and tissue activation, amplified IL-6 and MCP-1 production and cell death by, apparently, a different process involving necrosis. Our findings bring new insights into the complex interactions between hUC-MSCs and PBMCs, involving cytokines, chemokines and cell death, and are of fundamental importance for tissue homeostasis.