CLL cells co-cultured on the growth-arrested CD40L-expressing fibroblasts showed a rapid increase in activation of RelB and p52 which occurred within 4 h, peaked at 24 h (Figure 5A, left panel), and persisted throughout the 7 day co-culture period (Figure 5A, right panel). This evidence concerns the gene CD40LG and B-cell chronic lymphocytic leukemia.