A NOVEL CELL GROWTH-PROMOTING FACTOR IDENTIFIED IN A B-CELL LEUKEMIA-CELL LINE, BALL-1

A novel leukemia cell gro-th-promoting activity has been identified in the culture supernatant from a human B cell leukemia cell line, BALL-1. The supernatant from unstimulated cultures or the BALL-1 cells significantly pro-ted the growth of 16 out of 24 leukemia/lymphoma cell lines of different lineages (T, B and non-lymphoid) in a minimal concentration of fetal bovine serum (FBS), and of 5 out of 12 cases of fresh leukemia cells in FBS-free medium. The growth-promoting activity in the BALL-1 supernatant has been further characterized using FPLC chromatography, molecular weight (MW) sieve filtration and dialysts. The MW of the factor was less than 10 kDa. The growth-promoting activity was heat and acid stable and resistant to trypsin treatment. The factor isolated from the BALL-1 supernatant was distinct from known polypeptide growth factors with MW below 10 kDa, such as epidermal growth factor, transforming growth factor alpha, insulin-like growth factor I (IGF-I), IGF-II and insulin, as determined by specific antibodies and by cell growth-promoting tests. The factor in the BALL-1 supernatant did not promote the proliferation of normal human fresh peripheral blood lymphocytes or mouse fibroblast cell line, BALB/c 3T3. In addition to the BALL-1 supernatant, a similar growth-promoting activity was found in the culture supernatants from 13 of 17 leukemia/lymphoma cell lines tested. The activity in these culture supernatants promoted the growth of leukemia/lymphoma cell lines in autocrine and/or paracrine fashions. These observations suggest that the low MW cell growth-promoting activity found in the BALL-1 culture supernatant is mediated by a novel factor which may well be responsible for the clonal expansion of particular leukemic clones.