These cells were prepared as described in Materials and Methods. The RT-PCR were performed as described ³² and scored semi-quantitatively on a scale of − to ++++: −, negative; +/−, faint, not clearly above background; +, weakly positive; ++, moderately positive; +++ and ++++, strongly positive. Total CD44 and CD44v-containing isoforms were immunostained using specific MoAbs as described. Cells of interest were analyzed by flow cytometry using both specific electronic gating (PMN, monocytes, HPC, leukemic cells), and double-staining with an MoAb directed to a lineage-specific antigen (CD34 for CD34⁺ cells, CD14 for monocytic cells, CD15 for granulocytic cells). Immunostainings of total CD44 and of the CD44v-containing isoforms were also scored semi-quantitatively on a scale of − to ++: −, negative (<5% of positive cells); +, positive (5% to 20% of positive cells); ++, strongly positive (>20% of positive cells).

Abbreviations: AML, leukemic cells from AML patients; ND, not done.