Interestingly, IL21’s negative effect on CLL viability is less pronounced in combination with CD40L + IL4 (median viability 32% in the HS5-IL21 co-culture vs. 48% in HS5-CD40L-IL4-IL21 co-culture, P = 0.002; Fig. 1F), allowing us to use these three factors together. Here, IL21 is linked to B-cell chronic lymphocytic leukemia.