HOXB6 overexpression expands myeloid precursors and impairs B lymphopoiesis. (A) Representative FACS plots from bone marrow suspensions of primary transplant chimeras killed 1 to 2 months after transplantation. For all plots, EGFP expression (a marker for transduced cells) is represented on the x-axis, and the y-axis represents staining with Mac-1, B220, or no antibody (also see Figure S1). (B) HOXB6 and HOXB6WG transplant chimeras have an increase in frequency of myeloid cells (Mac-1⁺) in the bone marrow. n = 5 for MIG and HOXB6, 3 for HOXB6WG, and 2 for HOXB6NA. *P less than .05 versus MIG. (C) The increase in myeloid progenitors was due to a predominance of myeloid forms among HOXB6- and HOXB6WG-transduced cells. Additionally, HOXB6-transduced marrow had a decrease in B220⁺ cells, whereas a similar trend existed for HOXB6WG. *P < .05 versus MIG. Results from panels B and C represent mean percentages ± SD. (D) HOXB6 and HOXB6WG overexpression produced an approximately 5-fold increase in CFC production. Results shown are mean CFC production per 10 000 cells plated ± SEM. n = 4 mice for MIG and 3 for HOXB6, HOXB6WG, and HOXB6NA. The increase in CFC was due almost entirely to expansion of CFU-GMs. *P = .03 versus MIG. (E) HOXB6 and HOXB6WG marrow had significantly increased CFU-Bs when compared with MIG controls. Results represent mean percentages ± SD. n as for panel D. †P = .001 and .01, respectively, for HOXB6 and HOXB6WG versus MIG. (F) Bone marrow from HOXB6 and HOXB6WG chimeras had an increase in spleen colony-forming cells (SCFCs) as measured by the CFU-S₁₂ assay. Results represent mean SCFCs per 1 × 10⁴ cells injected ± SEM for 3 (MIG and HOXB6WG) or 2 (HOXB6 and HOXB6NA) individual experiments. n = 20, 12, 19, and 10 recipients for MIG, HOXB6, HOXB6WG, and HOXB6NA, respectively. ‡P less than .005 versus MIG.