IL21 and B-cell chronic lymphocytic leukemia: This revealed a significant CLL cell proliferation of 7% cells (on day 7) in HS5-CD40L-IL4 co-cultures (P = 0.019), and 44% in HS5-CD40L-IL4-IL21 co-cultures (P < 0.001; Figure 1Di, Supplementary Fig. 1C).