EXPANSION OF BLOOD CD34- COMMITTED PRECURSOR EXPANSION DOES NOT AFFECT IMMATURE HEMATOPOIETIC PROGENITORS( CELLS )

The CD34 antigen is present at all differentiation stages of hematopoi etic cells, from immature progenitor cells to committed precursor cell s. In vivo, transplantation of CD34+ cells is sufficient to allow hema topoietic recovery after myeloablative chemotherapy, but a neutropenic period of 9-12 days still exists, even when hematopoietic growth fact ors are given posttransplantation. After ex vivo expansion cultures in the presence of cytokines, CD34+ cells can generate mature precursor cells in a stroma-free liquid culture system. This could lead to a sho rtening of the aplasia duration, but the persistence of primitive prog enitor cells in the expanded CD34+ compartment remains to be demonstra ted. In this study, CD34+ cells were isolated from eight peripheral bl ood (PB) and eight cord blood (CB) samples using either Isolex(TM) 50 (n = 6), Ceprate(TM) LC CD34 kit (n = 6), or Microcellector(TM) T-25 S tem Cell kit (n = 4). We have evaluated the functional potential of CD 34+ cells after 7 days of ex vivo expansion culture in the presence of 500 UI/ml of interleukin-l (IL-1), 10 ng/ml of IL-3, and 10 ng/ml of stem cell factor (SCF). The expansions of nucleated cells, granulocyte -macrophage colony-stimulating factor (GM-CSF)-responsive committed pr ecursors, IL-1 + IL-3 + SCF + erythropoietin (EPO)-responsive multilin eage progenitors, and 5-fluorouracil (5-FU)-resistant quiescent progen itor were 8-fold, 59-fold, 4.4-fold, and 2.2-fold, respectively. There was no significant difference in the amplification/expansion paramete rs between cultures initiated with CD34+ cells from PBSC or CB. Our da ta confirm that cytokine-mediated ex vivo expansion of blood CD34+ cel ls can produce large numbers of committed precursors and does not sign ificantly affect the compartment containing more immature progenitors. Cytokine-mediated expansion could be of great interest in autologous transplantation to decrease the duration of marrow aplasia.