Maximal Mylotarg binding to leukocyte subsets.

Maximal Mylotarg binding to different leukocyte subsets was analyzed prior to start of the first (hatched bars) and second (open bars) Mylotarg treatment cycle by incubating PB with an excess of Mylotarg in vitro, followed by detection with biotin-conjugated antihuman IgG4 and streptavidin-FITC. (A) Maximal Mylotarg binding to AML blast cells (cycle 1: n = 86; cycle 2: n = 35), monocytes (n = 33; n = 45), granulocytes (n = 55; n = 32), and lymphocytes (n = 61; n = 43). Patient numbers differ between leukocyte subsets and between cycle 1 and cycle 2 because not all patients received a second treatment cycle, in some patients the PB sample was not available or of too low quality, or too few events were available for a reliable analysis of all leukocyte subsets. (B) Maximal Mylotarg binding to AML blast cells from patients showing less than 5% blast cells in their PB just prior to the start of the second treatment cycle (blast cell reducers; n = 27) or 5% or more blasts in PB (blast cell nonreducers; n = 31 and n = 26 for cycle 1 and cycle 2, respectively). Maximal Mylotarg binding data for cycle 2 could not be obtained in the blast cell reducers, because the number of blast cells was too low to perform a reliable analysis. ND indicates no data. Data are expressed as mean ± SD. Significant differences (P < .05; indicated by the asterisks [unpairedt test]) were observed in maximal Mylotarg binding to blast cells between cycle 1 and cycle 2 and between cycle 1 data of the blast cell reducers and blast cell nonreducers.