BCR and B-cell chronic lymphocytic leukemia: However, when we analyzed the proliferative effect of a combination of cytokines added after initial BCR stimulation (IgM ligation), we established that, even if BCR activation associated to [CD40L + IL-4] or [CD40L + IL-21] allowed a weak proliferation, the combination of anti-IgM with [CD40L + IL-4 + IL-21] induces a higher proliferation rate of CLL cells in soluble medium (Fig. 1A).