Analysis of CD44v exon composition in normal myeloid and AML leukemic cells. RNA and cDNA were prepared as described in Materials and Methods. Using primers for HPRT, the amounts of cDNA were equilibrated to this internal standard. A CD44-specific PCR was performed and the PCR products were blotted and hybridized with³³P-labeled exon-specific probes indicated at each blot. Represented are the autoradiographs and the photos taken from the CD44 and HPRT-PCR reaction products as indicated. Negative controls (−) were performed by omitting the cDNA. (1) Normal myeloid cells: CD34⁺ cells, blot A, lanes 1, 2, 3, CD34⁻granulocytic precursors GP (blot A, lane 4), PMN (blot A, lane 5), and monocytes (blot A, lanes 6 and 7). RT-PCR has been performed on five distinct samples of PMN, monocytes, GP, and CD34⁺ cells. Similar results have been obtained (data not shown). (2) Leukemic cells from AML patients with the following FAB types: M1 (blot A, lanes 8 through 14), M2 (blot A, lanes 15 through 18), M3 (blot B, lanes 1 through 4), M4 (blot B, lanes 5 through 11) and M5 (blot B, lanes 12 through 16). The sample shown on blot B lane 17 is from a patient with acute lymphoid leukemia. (3) Control experiment: Lymphocytes (lane 1) or monocytes (lane 3) were isolated from a patient with a myeloblastic AML (M1) and mixed in a ratio 5:95, with HL60 cells that express variant exons only very weakly (CD44v^neg/low). The presence of 5% of lymphocytes from the AML patient did not result in the expression of any detectable 6v signal (lane 2), and only a faint expression of CD44-6v in the directly spliced version resulted from the presence of 5% of monocytes from the AML patient (lane 4). {/ANNT;4224n;;0n;0n}3