PREVALENCE AND GROWTH-CHARACTERISTICS OF MALIGNANT STEM-CELLS IN B-LINEAGE ACUTE LYMPHOBLASTIC-LEUKEMIA

We used a stroma-supported culture method to study the prevalence and growth characteristics of malignant stem cells in acute lymphoblastic leukemia (ALL). In 51 of 108 B-lineage ALL samples, bone marrow-derive d stroma oat only inhibited apoptosis of ALL cells but also supported their proliferation in serum-free medium. When single leukemic cells w ere placed in the stroma-coated wells of microtiter plates, the percen tage of wells with leukemic cell growth after 2 to 5 months of culture ranged from 6% to 20% (median, 15%; 5 experiments). The immunophenoty pes and genetic features of cells recovered from these cultures were i dentical to those noted before culture. All cells maintained their str oma dependency and self-renewal capacity. Leukemic clones derived from single cells contained approximately 10(3) to 10(6) cells after 1 mon th of culture; other clones became detectable only after prolonged cul ture. Cell growth in stroma-coated wells correlated with the number of initially seeded cells (1 or 10: r = .87). However, the observed perc entages of positive wells seeded with 10 cells always exceeded values predicted from results with single-cell-initiated cultures (P < .003 b y paired t-test), suggesting stimulation of leukemic cell growth by pa racrine factors. In conclusion, the proportion of ALL cells with clono genic potential may be considerably higher than previously thought. (C ) 1997 by The American Society of Hematology.