The tumor immune response is not compromised by mesenchymal stromal cells in humanized mice

Therapeutic uses of mesenchymal stromal cells (MSCs) have emerged over the past decade. Yet, their effect on tumor growth remains highly debated, particularly in an immune competent environment. Here, we wanted to investigate the impact of human umbilical cord MSCs (hUC-MSCs) on tumor growth in humanized mice generated by the adoptive transfer of peripheral blood mononuclear cells (Hu-AT) or the co-transplantation of hematopoietic stem cells and human thymic tissue (Hu-BLT). Our results showed that the growth and immune rejection of engineered human tumors was not altered by the injection of hUC-MSCs in immune-deficient or humanized mice respectively. This was observed whether tumor cells were injected subcutaneously or intravenously and independently of the injection route of the hUC-MSCs. Moreover, only in Hu-BLT mice did hUC-MSCs have some effects on the tumor immune infiltrate, yet without altering tumor growth. These results demonstrate that hUC-MSCs do not promote tumor growth and neither do they prevent tumor infiltration and rejection by immune cells in humanized mice.