Improving the Therapeutic Ability of Mesenchymal Stem/Stromal Cells for the Treatment of Conditions Influenced by Immune Cells

Abstract

Mesenchymal stem/stromal cells (MSCs) have been initially described decades ago as fibroblastic precursors that could be isolated from the bone marrow and establish cultures of fibroblastic cells. These fibroblastic cells were shown tosupport hematopoiesis in vitro, which is a characteristic of stromal cells, and, later, to give rise to mature mesenchymal cells such as bone, cartilage, and fat cells when cultured under appropriate conditions. The proposition that a mesenchymal stem cell exists in postnatal bone marrow and other tissues asblood vessel-associated cells provided further momentum to research on these cells, as well as divergences on how to call them. The impetus of using MSCs to replace cells lost in various types of conditions eventually decreased, as the therapeutic benefits provided by these cells were found to be mostly due to the secretion of paracrine signaling molecules,which can be carried by extracellular vesicles. In the meantime, MSCs were found to modulate the behavior of immunecells by means of secretion of molecules that could, in different scenarios, inhibit the activation of T cells that promote adaptive immune responses. Subsequently, the effects of MSCs on other cells of the immune system were alsodescribed. Today, a number of clinical trials using MSCs to treat conditions influenced by immune cells are under way. While preclinical data indicates that MSCs have important immunomodulatory properties, further studies are still in progress to increase the knowledge on the differences regarding the action of MSCs on immune cells according to their tissue of origin, on how MSCs exert their effects on the different types of immune cells, and on ways to improve the outcome of conditions influenced by immune cells when treated using MSCS.