To in vitro reproduce the microenvironment that CLL cells find in the proliferative centers in vivo, we co-cultured primary CLL cells with the BMSC cell line UE6E7T-2, soluble CD40L and CpG ODN which induce proliferation and chemoresistance in primary CLL cells as we have recently shown [15]. Here, CD40LG is linked to B-cell chronic lymphocytic leukemia.