BCR-ABL1-positive microvesicles malignantly transform human bone marrow mesenchymal stem cells in vitro

The intercellular communication between leukemia cells and bone marrow mesenchymal stem cells (BM-MSCs) plays more important role in chronic myeloid leukemia (CML) than we previously understood. Recently, we found that microvesicles released from human leukemia cell line K562 (K562-MVs) containing BCR-ABL1 mRNA malignantly transformed normal hematopoietic transplants. Here, we investigated whether K562-MVs contribute to the transformation of human bone marrow mesenchymal stem cells (BM-MSCs). We showed that K562-MVs could be integrated into co-cultured normal BM-MSCs and dose-dependently enhanced the proliferation of BM-MSCs. Meanwhile, K562-MVs (400 ng/mL) significantly increased the expression of BCR-ABL1 in these BM-MSCs, accompanied by the enhanced secretion of TGF-beta 1. These BM-MSCs in turn could trigger the TGF-beta 1-dependent proliferation of K562 cells. Moreover, we confirmed the presence of BCR-ABL1 in circulating MVs from 11 CML patients. Compared to the normal BM-MSCs, the BM-MSCs from CML patients more effectively increased the BCR-ABL1 expression and TGF-beta 1 secretion in K562 cells as well as the proliferation of K562 cells. Our findings enrich the mechanisms involved in the interaction between leukemia cells and BM-MSCs and provide novel ways to monitor minimal residual disease and worthwhile approaches to treat CML.