BCR-ABL1-positive microvesicles transform normal hematopoietic transplants through genomic instability: implications for donor cell leukemia.

Malignant transformation of normal hematopoietic transplants induced by residual leukemia cells is considered as a pivotal mechanism of donor cell leukemia (DCL). The effects of leukemia cell-derived microvesicles (MVs) in this transformation were examined. We found that MVs derived from K562 leukemia cells contained the breakpoint cluster region-Abelson leukemia gene human homolog 1 (BCR-ABL1) mRNA. Following incubation with BCR-ABL1-positive MVs, mononuclear cells derived from normal transplants exhibited a leukemia-like malignant phenotype both in vitro and in vivo. Horizontal transfer of BCR-ABL1 mRNA from MVs into the recipient cells was critical to the transformation. Relative genomic instability was observed and considered the main mechanism in the recipient cells. MVs contributed to genomic instability by two distinct pathways: via consequent overexpression of activation-induced cytidine deaminase and reactive oxygen species, which mediated DNA breakage and recombination; and via upregulation of methyltransferases and global DNA hypermethylation. We demonstrated that BCR-ABL1-positive MVs could initiate malignant transformation of normal hematopoietic transplants through genomic instability, which might serve as a convenient and operable model for investigating leukemogenesis, especially for DCL. Furthermore, MVs themselves could act as an early warning indicator and a novel tool to detect and prevent the occurrence of DCL.