Increased Cytotoxicity Against B-Chronic Lymphocytic Leukemia by Cellular Manipulations: Potentials for Therapeutic Use

Abstract

B-cell chronic lymphocytic leukemia (CLL) is characterized by profound immune dysfunction and a marked resistance to apotosis. Understanding the cellular biology of immune effector cells from CLL patients as well as leukemic target cells is essential to developing immune mediated therapeutie strategies for CLL. In this study. an immortal CLL cell line called WSU-CLL has been used to study the characteristics of B-cell CLL as a tumor target for natural killer (NK), activated natural killer, and lymphokine activated killer (LAK) cells. The WSU-CLL cells were significantly less (p<0.001) susceptible to NK cell mediated cytotoxicity compared to K562. a standard tumor target cell line. In ivtro activation of effector cells with either short term, low dose IL-2 or long term, high dose IL-2 significantly increased the susceptibility of CLL cells for cell mediated killing. The addition of CDIa+/CD3-/CD4+/CD80+/CD83+ dendritic cells derived from human umbilical cord blood increased the cytotoxicity of LAK cells against WSU-CLL. There is an increased expression of Bcl-2 and decreased expression of Fas on WSU-CLL cells as determined by RT-PCR techniques indicating possible roles for these genes in exerting resistance to immune cell mediated lysis. When Bel-2 expression wils downregulated in WSU-CLL cells using gene specific antiscnse oligonucleotides, the susceptibility of WSU-CLL cells to the cytotoxicity of chemo-therapeutic agent Fludarabine was increased. Thus, our results suggest that in vitro activation with cytokines, addition of accessory cell populations such as dendritic cells and/or manipulation of key gene expression i.e. down regulation of Bcl-2 might be potential stratcgies to increase the antitumor cytotoxicity against CLL cells.