Increased cytotoxicity against B-chronic lymphocytic leukemia by cellular manipulations: Potentials for therapeutic use

B-cell chronic lymphocytic leukemia (CLL) is characterized by profound immu ne dysfunction and a marked resistance to apoptosis. Understanding the cell ular biology of immune effector cells from CLL patients as well as leukemic target cells is essential to developing immune mediated therapeutic strate gies for CLL. In this study, an immortal CLL cell line called WSU-CLL has b een used to study the characteristics of B-cell CLL as a tumor target for n atural killer (NK), activated natural killer, and lymphokine activated kill er (LAK) cells. The WSU-CLL cells were significantly less (p<0.001) suscept ible to NK cell mediated cytotoxicity compared to K562, a standard tumor ta rget cell line. In vitro activation of effector cells with either short ter m, low dose IL-2 or long term, high dose IL-2 significantly increased the s usceptibility of CLL cells for cell mediated killing. The addition of CD 1a +/CD3-/CD4+/CD80+/CD83+ dendritic cells derived from human umbilical cord b lood increased the cytotoxicity of LAK cells against WSU-CLL. There is an i ncreased expression of Bcl-2 and decreased expression of Fas on WSU-CLL cel ls as determined by RT-PCR techniques indicating possible roles for these g enes in exerting resistance to immune cell mediated lysis. When Bcl-2 expre ssion was downregulated in WSU-CLL cells using gene specific antisense olig onucleotides, the susceptibility of WSU-CLL cells to the cytotoxicity of ch emotherapeutic agent Fludarabine was increased. Thus, our results suggest t hat in vitro activation with cytokines, addition of accessory cell populati ons such as dendritic cells and/or manipulation of key gene expression i.e. down regulation of Bcl-2 might be potential strategies to increase the ant itumor cytotoxicity against CLL cells.