Effects of interferon and retinoic acid on the growth and differentiation of clonogenic leukemic cells from acute myelogenous leukemia patients treated with recombinant leukocyte-alpha A interferon.

Studies with human myeloid leukemia cell lines indicate that combined interferon (INF) and retinoic acid (RA) have greater effects in inhibiting cell growth and in inducing terminal differentiation than either agent alone. Consequently, we studied the effects of these agents, singly and in combination, on fresh leukemic blast cells obtained from 13 acute myelogenous leukemia (AML) patients, most of whom were subsequently treated with recombinant leukocyte-alpha A interferon (rINF-alpha A). The in-vitro response to rINF-alpha A and RA was assessed in an established myeloid leukemic blast cell clonogenic assay containing conditioned medium from phytohemagglutinin-stimulated lymphocytes. Strong inhibition of colony cell growth (greater than or equal to 50%) was observed in 4/10 cases treated with rINF-alpha A alone, but only at high concentration (greater than or equal to 2500 U/ml) and in 4/10 cases treated with RA alone (5 X 10(-8) M or 5 X 10(-7) M). Combined rINF-alpha A and RA augmented the inhibition of primary or secondary colony cell growth in 5/8 evaluable cases. Stimulation of leukemic cell differentiation was observed in 1/8 cases by rINF-alpha A alone and in 4/7 cases by RA alone. Combined rINF-alpha A and RA enhanced cell differentiation in 4/7 cases. In addition, increased inhibition of clonal cell growth and/or differentiation by RA alone was observed in 2/5 cases following in-vivo rINF-alpha A treatment. These results suggest that treatment with combined rINF-alpha A and RA may be rewarding in some cases of AML.