Flt3 Ligand Enhances the Yield of Primitive Cells After Ex Vivo Cultivation of CD34 CD38 Cells and CD34 CD38 CD33 HLA-DR Cells

Flt3 ligand (FL) has been proposed as a possible modulator hanced or depleted the number of precommitted cells in expansion culture, CD34 CD38 and HLA-DR fractions of early hematopoietic cell growth. The purpose of this study was to analyze the impact of FL on ex vivo expansion of were incubated in liquid culture and analyzed by flow cytometry. Inclusion of FL enhanced the absolute number of primihematopoietic cells obtained from adult donors. We sought to precisely identify hematopoietic populations responsive tive CD34 CD33 cells and CD34 HLA-DR cells after 5 to 12 days of cultivation. To confirm immunophenotypic to FL and to quantitate the ability of FL to enhance the survival and/or proliferation of early hematopoietic precursors data, the effect of FL on long-term culture-initiating cells (LTCIC) was determined. After 2 weeks of incubation of in a stroma-free culture system. Towards that end, four CD34 subsets were isolated and their response to FL was CD34 CD38 or HLA-DR cultures, LTCIC recoveries were significantly higher with FL in 5 of 6 trials (PÚ .05). For HLAcharacterized. In methylcellulose, FL significantly increased colony formation by CD34 CD38 cells but not CD34 DR cells, LTCIC recoveries averaged 214% Ô 87% of input with FL and 24% Ô 16% without FL. In contrast, HLA-DR CD38 cells. In suspension culture, the enhancement of cell expansion by FL was 10 times greater with the CD34 LTCIC could not be maintained in stroma-free culture. We conclude that less than 10% of CD34 cells respond vigorCD38 fraction than the CD34 CD38 fraction. FL stimulated the generation of colony-forming unit–granulocyteously to FL and that those cells are contained within the HLA-DR fraction. FL stimulates the expansion of total cells, macrophage (CFU-GM) from the CD34CD38 fraction by 14.5Ô 5.6-fold. To determine if CD34 CD38 cells reCD34 cells, and CFU-GM and enhances the pool of early CD34 CD33 cells, CD34 HLA-DR cells, and LTCIC. sponded uniformly to FL, the population was subdivided into a CD34 CD38 CD33 HLA-DR (HLA-DR) fraction and a These data indicate that it is possible to expand hematopoietic progenitors from adult donors without losing precursors CD34 CD38 CD33 HLA-DR (HLA-DR) fraction. FL was far more effective at stimulating cell and progenitor from the precommitted cell pool. q 1997 by The American Society of Hematology. growth from the HLA-DR fraction. To determine if FL en-