Cell culture systems: The A20 cell line is grown and maintained in FBS supplemented RPMI culture medium. Normal primary cultures are maintained with selective media. On the other hand, the survival of human CLL cells in culture is dependent on several unique microenvironmental factors, including antigen stimulation of the B-cell BCR, T cell help through the CD40-CD40L interaction, stimulation from the bone marrow stromal cell-derived CXCL12 chemokine and stimulation of Toll-Like Receptor 9. These conditions will be mimicked in vitro (26) by addition to the culture medium of anti-IgM (to crosslink the BCRs), co-culture with fibroblasts expressing CD40L, addition of recombinant CXCL12 and CpG dinucleotides respectively. These conditions will be used to test the specificity and efficacy of human PDCs against cryopreserved samples of patient CLL cells and normal human lymphocytes (controls).