CD40 and B-cell chronic lymphocytic leukemia: Finally, B-cell chronic lymphocytic leukemia (B-CLL) is one of the most entirely studied forms of hematologic malignancies characterized by a progressive accumulation of monoclonal CD5+/CD19+, CD23+, CD21+, CD40+ B cells with prolonged cell survival and low proliferative index in the peripheral blood, bone marrow, and lymphoid organs (219).