To model the lymph node microenvironment of CLL, we used a well-established in vitro co-culture system utilizing NIH/3T3 mouse fibroblasts [26,31,32] were transfected with human CD40L to mimic interactions with activated T-cells that occur in the lymphoid tissues (Figure 4A). The gene discussed is CD40LG; the disease is B-cell chronic lymphocytic leukemia.