Modulation of NF-kappa B activity and apoptosis in chronic lymphocytic leukemia B cells

Chronic lymphocytic leukemia (CLL) is an indolent malignancy of CD5+ B lymp hocytes, CLL cells express CD40, a key regulator of B cell proliferation, d ifferentiation, and survival. In nonmalignant B cells, CD40 ligation result s in nuclear translocation and activation of NF-kappa B proteins. Based on observations that in some CLL cases, the tumor cells express both CD40 and its ligand, CD154 (CD40 Ligand), we proposed a model for CLL pathogenesis d ue to CD40 ligation within the tumor. To evaluate this issue, we used fresh ly isolated CLL B cells to examine constitutive and inducible NF-kappa B ac tivity by electrophoretic mobility shift assay. We consistently observed hi gh levels of nuclear NF-kappa B-binding activity in unstimulated CLL B cell s relative to that detected in nonmalignant human B cells, In each case exa mined, CD40 ligation further augmented NF-kappa B activity and prolonged CL L cell survival in vitro. The principle NF-kappa B proteins in stimulated C LL cells appear to be quite similar to those in nonmalignant human B cells and include p50, p65, and c-Rel, In a CD154-positive case, blocking CD154 e ngagement by mAb to CD154 resulted in inhibition of NF-kappa B activity in the CLL cells. The addition of anti-CD154 mAb resulted in accelerated CLL c ell death to a similar degree as was observed in cells exposed to dexametha sone. These data indicate that CD40 engagement has a profound influence on NF-kappa B activity and survival in CLL B cells, and are consistent with a role for CD154-expressing T and B cells in CLL pathogenesis. The data suppo rt the development of novel therapies based on blocking the CD154-CD40 inte raction in CLL.