Interferon-alpha up-regulates bcl-2 expression and protects B-CLL cells from apoptosis in vitro and in vivo

The bcl-2 oncoprotein, which is involved in the t(14,18) translocation, protects cells against apoptosis. We examined the effects of interferon-alpha (IFN-α) on bcl-2 protein expression and apoptosis in B-chronic lymphocytic leukaemia (B-CLL) cells. None of 12 patients with B-CLL examined expressed the t(14,18) translocation; however, all these, and seven other patients, expressed significant levels of bcl-2 protein. In vitro, IFN-α (500 U/ml over 18 h) increased bcl-2 expression on CLL cells (to 200 ± 23% of control MCF, as determined by indirect immunofluorescence and flow cytometry, n = 10, P < 0.001). All of eight patients who received IFN-α (3 mega units subcutaneously three times a week) demonstrated an increase in bcl-2 expression on circulating malignant cells. CLL cells undergo apoptotic cell death when cultured in vitro (35.6 ± 10.3% DNA fragmentation after 18 h, n = 10). In the presence of IFN-α, however, DNA fragmentation was reduced to 6.6 ± 5.8% (n = 10, P < 0.001). IFN-α also protected CLL cells against apoptosis induced by hydrocortisone and gamma irradiation (reducing DNA fragmentation from 63.9 ± 12.6% to 10.8 ± 4.5% and from 80 ± 2.9% to 5.4 ± 1.6%, respectively, P < 0.001 for both). The protective effect of IFN-α was dose dependent, and maintained for up to 24 h. Our data demonstrate that bcl-2 expression and apoptosis of CLL cells can be influenced by cytokines. In addition, it seems unlikely that the observed clinical responses to IFN-α in patients with CLL are due to a direct effect on the malignant cells.