LEUKEMIC TRANSFORMATION OF PRIMARY MYELOFIBROSIS - IMMUNOPHENOTYPE, GENOTYPE AND GROWTH-CHARACTERISTICS OF BLAST CELLS

Blast cells from six patients with leukemic transformation of primary myelofibrosis (PMF) were studied by morphology, immunophenotype and ge notype as well as response to hematopoietic growth factors. The majori ty of the patients showed granulocytic or granulo-monocytic blasts, an d only one had T lymphoid-monocytic blasts. None of the patients showe d rearrangement of Ig or TCR genes, or the existence of the bcr-abl fu sed gene. A prominent growth response to GM-CSF and IL-3 was evident i n all of the patients examined in liquid as well as semisolid cultures . The response to G-CSF was observed in four of the six patients in su spension culture, and in two of three patients in the clonogenic assay . Stem cell factor (SCF) was a weak growth stimulant, however the comb ination of this factor with GM-CSF or IL-3 was synergistically stimula tory. These results suggest that leukemic transformation of PMF occurs mainly at the level of myeloid stem cell, and that GM-CSF, IL-3, G-CS F and SCF are major growth factors for the blast cells in these cases.