BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Although actinomycin D, by itself had no effect, it blocked the development of CML caused by K562 EVs (Figures 2A, 2B and 2C-a), i.e., the hyperplastic bone marrow and neutrophilia in the K562 EVs-treated mice were no longer observed (Figures 3A and 3B), indicating that there was de novo transcription of BCR/ABL mRNA, as well as protein synthesis in vivo.