Figure 8. CXCL4 and CXCL7 promote resistance to DAC in CD34⁺ and primary CMML specimens.

(A) Colony formation was inhibited by DAC but restored with the combination of CXCL4 and CXCL7. CD34⁺ cells were treated with 1 dose of CXCL4, CXCL7, or both (50 ng/ml each) or with vehicle (PBS containing 0.1% BSA) and daily 10-nM doses of DAC for 3 days. After 3 days of in vitro treatment with DAC, cells were plated in methylcellulose and incubated for 12 to 15 days before colonies were counted. Data represent the mean ± SD. Treatment with 10 nM DAC significantly decreased colony formation but failed to do so in the presence of CXCL7 and CXCL4 together. Shown in the 3 panels are the results of 3 independent experiments. Error bars represent the SD. (B) CXCL4 and CXCL7 abrogated the effect of DAC on the viability of primary CMML MNCs. CMML MNCs were treated in vitro for 72 hours with 10 nM DAC alone or in the presence of 50 ng/ml CXCL4, CXCL7, or both. Data represent the mean ± SD. Treatment with DAC alone significantly reduced the viability of these cells, but this effect was lost when CXCL4 or CXCL7 was added to the culture. All data represent independent experiments performed in 3 different CMML patients. Error bars represent the SD. *P < 0.05 and **P < 0.01 by unpaired 2-tailed Student’s t test.