circMYBL2 knockdown impairs the tumorigenesis and infiltration of FLT3-ITD AML cells in vivo. (A) Wright-Giemsa staining of BM samples isolated from mice engrafted with human MOLM-13 cells cotransfected with sh-NC and sh-circMYBL2. hCD45⁺ cells in the mice are indicated by the black arrows. Original magnification ×400. (B) Representative images of lymph nodes from control and sh-circMYBL2-MOLM-13–treated mice. Reduced lymph node involvement in sh-circMYBL2-MOLM-13–treated mice compared with sh-NC-MOLM-13–treated control mice. (C) H&E staining showing infiltration of leukemic cells in the BM, spleen, and liver of mice engrafted with sh-circMYBL2 cells compared with that in control mice. hCD45⁺ cells in the tissues are indicated by the black arrows. (D) Flow cytometry showing substantially decreased levels of blasts in blood and BM samples from mice treated with circMYBL2-knockdown MOLM-13 cells relative to these levels in control mice. CD11b and CD14 marker expression was dramatically increased in sh-circMYBL2-MOLM-13–treated mice compared with that in sh-NC-MOLM-13–treated mice. (E-F) Scatter plots show the statistical values for panel D. (G) Kaplan-Meier survival curves for mice implanted with sh-NC or sh-circMYBL2 MOLM-13 cells (n = 5 mice per group). P values were calculated using a log-rank (Mantel-Cox) test. (H) Kaplan-Meier survival curves for mice implanted with sh-NC or sh-circMYBL2 MOLM-13-RQ cells (n = 6 mice per group). P values were calculated using a log-rank (Mantel-Cox) test. SSC, side scatter.