Figure 3. MPN myeloid cells stimulate MSCs to overproduce OBCs.

(A) Schematic of the in vitro co-culture/imaging approach. MSCs or OBCs isolated from β-actin-gfp mice were cultured with Ctrl or BA BM cells and imaged for the number of GFP⁺ cells per colony using an IN Cell Analyzer 2000. Representative images are of wells containing MSC- and OBC-derived GFP⁺ colonies after 10 days culture with Ctrl and BA BM cells. Scale bar, 1 mm. (B) Average numbers of GFP⁺ cells obtained per MSC or OBC colony after 10 days culture ± Ctrl or BA BM cells (n ≥ 3 per group, with at least 11 individual colonies scored per condition; nd: not determined). (C) Frequencies of EdU⁺ cells in re-sorted MSC-derived GFP⁺ cells cultured with Ctrl or BA BM cells for 7 days and pulsed with 10 μM EdU for 3 hours (n = 7–8 per group). (D) Frequencies of hematopoietic cells stained with the indicated markers in unfractionated and myeloid-enriched (my) Ctrl and BA BMs, and average numbers of GFP⁺ cells obtained per MSC colony after 10 days culture with Ctrl or BA myBM cells (n ≥ 3 per group, with at least 65 individual colonies scored per condition). (E) Schematic of the in vivo MPN regression experiment. Primary diseased BA and age-matched Ctrl mice were re-exposed for 2 or 4 months (m) to doxycline (+dox) to block BCR/ABL expression (n = 3–6 mice per group). (F) Percentage of Gr-1⁺/Mac-1⁺ myeloid cells in the BM of re-exposed mice and Masson’s trichrome staining of sternums from the indicated mice. Scale bar, 100 μm.

Data are means ± SD; *p ≤ 0.05, ***p ≤ 0.001. See also Figure S3.