CXCL12 and B-cell chronic lymphocytic leukemia: We also found that CXCR4 expression on the surface of CLL cells (based on standardized MFI index) positively correlates with their ability to secrete IL-10 in response to CXCL12 stimulation (Figure S5 in Supplementary Material), suggesting that CXCR4 expression could serve as a predictor of CXCL12-induced IL-10 response in CLL.