Use of stroma-supported cultures of leukemic cells to assess antileukemic drugs. I. Cytotoxicity of interferon alpha in acute lymphoblastic leukemia.

Leukemic cells from most cases of acute lymphoblastic leukemia (ALL) rapidly die by apoptosis in vitro, unless they are cultured onto bone marrow-derived stromal layers. We have recently established a stroma-supported tissue culture technique that allows long-term culture of leukemic lymphoblasts. In this study, we used this technique to examine interferon alpha (IFN alpha) cytotoxicity to ALL blasts. In 16 ALL cases tested (14 B-lineage ALL, 2 T-ALL), the number of cells recovered after 7 days of culture on stromal feeder layers was 60-178% (median, 108%) of those originally seeded. The percentage of lymphoblasts killed by 2000 U/ml IFN alpha 2b after 7 days of culture, ranged from < 1% to 91% (median, 56%). Cytotoxicity was (i) dose-dependent, (ii) eliminated by a neutralizing antibody to IFN alpha, and (iii) accompanied by tyrosine phosphorylation of a 135 kDa protein, which was detectable after 5 minutes of treatment. Numbers of residual normal lymphoid cells in the cultures remained low and conditioned medium prepared from IFN alpha-stimulated T, NK, and stromal cells was not cytotoxic to ALL blast cells. In contrast to results in freshly isolated ALL cells, six ALL cell lines tested were completely resistant to IFN alpha cytotoxicity. We conclude that IFN alpha is directly cytotoxic in most ALL cases but that the intensity of its effects varies widely among cases. The method used in this study may be applied to evaluate leukemic blast cell sensitivity to compounds with potential antileukemic activity, and to select patients to be entered in to clinical trials.