Thus, our demonstration that CXCL12–CXCR4 interaction induces phosphorylation of S727-STAT3, leading to IL-10 secretion by B-CLL cells and then to IL-10-induced Y705-STAT3-phosphorylation in T cells, resulting in their suppression, represents a novel route to immunosuppression associated with CLL. Here, IL10 is linked to B-cell chronic lymphocytic leukemia.