INTERFERON-ALPHA-MEDIATED PREVENTION OF IN-VITRO APOPTOSIS OF CHRONICLYMPHOCYTIC-LEUKEMIA B-CELLS - ROLE OF BCL-2 AND C-MYC

Chronic B lymphocytic leukemia cells (B-CLL), characterized by the acc umulation in vivo of long-life span B cells, exhibit spontaneous progr ammed cell death or apoptosis when cultured in vitro. We show that int erferon-alpha (IFN-alpha), although able to decrease in vivo the numbe r of leukemic cells, protects chronic B lymphocytic leukemia cells fro m in vitro programmed cell death or apoptosis. This inhibition of spon taneous in vitro apoptosis of leukemic B cells was observed after 24-4 8 hr of culture with 100-1000 U of either Interferon-alpha 2a or 2b. T he protective activity was observed in the majority of the patients te sted (6 out of 8) independent of the amount of apoptosis observed. Fur thermore, in contrast to IL-4, IFN-alpha did not up-regulate the expre ssion of Bcl-2. This suggests that B-CLL cells can be prevented from u ndergoing apoptosis in vitro by at least two different mechanisms: one , triggered for instance by IL-4, is associated with Bcl-2 production and the second triggered by Interferon-alpha-2 independent. To elucida te the pathways mobilized by Interferon-alpha we also studied the regu lation of c-myc expression in our experimental system. We found that ( i) induction of in vitro B-CLL apoptosis was not associated with up-re gulation of c-myc, (ii) c-myc expression as assessed by mRNA and prote in determinations was increased after in vitro or in vivo Interferon-a lpha ation. Additional experiments using c-myc specific oligonucleotid es demonstrated that when Interferon-alpha-mediated c-myc expression w as decreased by 60%, the in vitro protective effect of Interferon-cy w as not modified. Thus our data show that in contrast to the situation in. vivo, Interferon-alpha prevents spontaneous in vitro B-CLL cells a poptosis through a Bcl-2-independent pathway which is probably not rel ated to c-myc up-regulation. (C) 1991 Academic Press, Inc.