Association of Flt3L with progenitor cell mass and Flt3 expression in AML cohort A. (A) Serum Flt3L measured by ELISA in healthy controls (range, 48.3-173.8 pg/mL; shaded region), individuals with heterozygous germline GATA2 mutation, acquired aplastic anemia (AA), MDS, APL (open symbols), and AML. Asterisks in the MDS cohort indicate patients with excess blasts. Where Flt3L was reported as undetectable, data were set to the limit of detection at 7 pg/mL. Numbers in each cohort are shown in parentheses. (B) Level of Flt3 (CD135) expression indicated by MFI (minus isotype control) in control CD34⁺ BM progenitors, APL blasts, and AML blasts. The numbers in each cohort are indicated in parentheses. Note MFI is a log scale. (C) Inverse relationship between CD135 expression and Flt3L in 14 AML and 4 APL patients in whom both measurements were performed.