Flow cytometric immunophenotyping of FLT3W51/PML-RARα leukemias demonstrates that they are composed of immature myeloid cells.
(A) FSC/SSC, ungated. (B) CD45/SSC, gate = R1. (C) GFP, gate = R1 and R2. Remaining panels: gate = R1 and R2 and R3. Results of a representative leukemia (no. 747) are shown. (D) Dotted line in the Ly-6G (Gr-1) histogram represents an isotype control antibody. Numbers in parentheses at the top right of the histograms indicate the range of percent expression of the given marker compared with control antibody for the leukemias analyzed. (E) Of particular note, though leukemia number 747 expressed CD11b (Mac-1) moderately strongly, other leukemias analyzed showed weak and variable expression. (I) F4/80 also had heterogenous expression; 2 leukemias (nos. 1128 and 1087) had moderately strong expression, and expression in the remaining was very low. Mean ± standard deviation for the markers was as follows: (D) Ly-6G (Gr-1), 80.7 ± 13.2 (% of GFP-positive cells); (E) CD11b (Mac-1), 56.8 ± 32.2; (F) CD117 (c-kit), 69.7 ± 14.2; (G) CD31, 54.2 ± 18.3; (H) CD61, 94.1 ± 5.2; (I) Ly-71 (F4/80), 19.4 ± 33.8; (J) CD86, 6.6 ± 6.0; (K) Ly-76 (Ter119) < 0.5; (L) CD3 < 0.5; (M) CD19, 0.7 ± 1.4. Because CD117 (c-kit) and Ly-6G (Gr-1) were each expressed on more than 50% of GFP-positive cells in 5 leukemias, it is clear that these markers are coexpressed by leukemic immature forms/blasts. This coexpression is depicted in the final panel (N) showing coexpression of CD117 and Ly-6G on leukemia number 1128.
