Therapy-educated mesenchymal stem cells enrich for tumor initiating cells

Stromal cells residing in the tumor microenvironment contribute to the development of therapy resistance. Here we show that chemotherapy-educated mesenchymal stem cells (MSCs) promote therapy resistance via crosstalk with tumor-initiating cells (TICs), a resistant tumor cell subset that initiates tumorigenesis and metastasis. In response to gemcitabine chemotherapy, MSCs colonized pancreatic adenocarcinomas in large numbers and resided in close proximity to TICs. Furthermore, gemcitabine-educated MSCs promoted the enrichment of TICs in vitro and enhance tumor growth in vivo. These effects were dependent on the secretion of CXCL10 by gemcitabine-educated MSCs and subsequent activation of the CXCL10-CXCR3 axis in TICs. In an orthotopic pancreatic tumor model, targeting TICs using nano-vesicles (called nano-ghosts) derived from MSC membranes and loaded with a CXCR3 antagonist enhanced therapy outcome and delayed tumor re-growth when administered in combination with gemcitabine. Overall, our results establish a mechanism through which MSCs promote chemoresistance, and propose a novel drug delivery system to target TICs and overcome this resistance.