Bcl-2/Bax ratios in chronic lymphocytic leukaemia and their correlation with in vitro apoptosis and clinical resistance

The bcl-2 gene is overexpressed in the absence of gene rearrangements in most cases of B-cell chronic lymphocytic leukaemia (B-CLL) and the proto-oncogene product Bcl-2 has been shown to be a regulator of apoptosis. The activity of this protein is opposed by Bax, a homologous protein that accelerates the rate of cell death. B-lymphocyte Bcl-2 and Bax protein levels were found to be significantly altered in B-CLL and increased Bcl-2/Bax ratios were observed in both the treated and untreated patients compared with those of normal controls. These alterations were particularly pronounced in those treated patients found to be clinically unresponsive to chemotherapy. In order to determine whether Bcl-2/Bax ratios affected cell survival via an anti-apoptotic mechanism, cell death was induced in B-CLL cells in vitro using chlorambucil, and apoptosis was monitored by Annexin V and propidium iodide staining. Confirmation that the labelled cells were apoptotic was achieved by morphological assessment of cytospin preparations of cell-sorted populations. Drug-induced apoptosis in B-CLL cells was inversely related to Bcl-2/Bax ratios.