IL21 and B-cell chronic lymphocytic leukemia: In this regard, it has been suggested that the crosstalk between B- and T-lymphocytes via the CD40-CD40L and the cytokines/chemokines released by both the tumor and T-cell compartments (e.g., CCL3, CCL4, CCL22, and IFN-γ, IL4, IL21, sCD40L, respectively) might activate signaling pathways that promote the proliferation and survival of CLL cells [12,16,42,49,50].