IL21 and B-cell chronic lymphocytic leukemia: Numerous cytokines, including IL-2, IL-4, IL-6, IL-10, IL-12, IL-15, IL-21, BAFF and APRIL individually or in some cases in combination, have been implicated in the regulation of B-CLL cell apoptosis in vitro[8], [9], [19], [20], [21], [22], [24], [25], [27].