Cell-surface antigen expression in early and term gestation fetal hematopoietic progenitor cells.

The objective of this study was to compare the expression of primitive cell-surface antigens on CD34+ cells from early in gestation to those from term gestations. Fetal blood samples were obtained from 10 early gestation (21.0+/-0.8 [SE] weeks) and 12 term gestation (39.3+/-0.4 weeks) fetuses. The mononuclear cell population was separated by red cell lysis. Two-color flow cytometry was used to assess cell surface antigen coexpression of CD34 with CD33, CD38, and HLA-DR as well as staining by a cocktail of monoclonal antibodies for lineage-associated (Lin) antigens (CD2, CD10, CD11b, CD19, CD20, CD33, CD36, 7B9, and Glycophorin-A). The frequency of CD34+ cells (5.5+/-0.9 versus 1.5+/-0.2, p < 0.001) was significantly higher in the early gestational age group. Within the CD34+ population, the frequency of CD34+/CD38- cells (81.8+/-9.9 versus 51.3+/-7.7, p = 0.02) and CD34+/DR- cells (15.3+/-7.4 versus 8.2+/-2.7, p = 0.05) was also higher in the early gestational age group. In contrast, CD34+/CD33- (51.8+/-10.1 versus 83.0+/-6.1, p = 0.02) and CD34+/Lin- cells (15.9+/-7.0 versus 51.8 +/-6.9, p < 0.01) were higher in the term gestation group. The high percentage of CD34+, CD34+/CD38-, and CD34+/DR- cells supports our hypothesis that early gestational age fetal blood has a higher frequency of primitive hematopoietic progenitor/stem cells than does umbilical cord blood at term. This suggests that hematopoietic progenitor/stem cells in early fetal blood may be a desirable target for in utero gene therapy. However, further studies to characterize the functional properties of CD34+ cell subsets at different stages of fetal development will be necessary to determine the appropriateness of targeting fetal hematopoietic cells for in utero gene therapy. The higher frequency of CD34+/CD33- and CD34+/Lin- cells from term gestational age fetuses was unexpected, and the significance of this finding is unclear at this time.

In vivo synergy between recombinant human stem cell factor and recombinant human granulocyte colony-stimulating factor in baboons enhanced circulation of progenitor cells.

Recombinant human stem cell factor (rhSCF) and recombinant human granulocyte colony-stimulating factor (rhG-CSF) are synergistic in vitro in stimulating the proliferation of hematopoietic progenitor cells and their precursors. We examined the in vivo synergy of rhSCF with rhG-CSF for stimulating hematopoiesis in vivo in baboons. Administration of low-dose (LD) rhSCF (25 micrograms/kg) alone did not stimulate changes in circulating WBCs. In comparison, administration of LD rhSCF in combination with rhG-CSF at 10 micrograms/kg or 100 micrograms/kg stimulated increases in circulating WBCs of multiple types up to twofold higher than was stimulated by administration of the same dose of rhG-CSF alone. When the dose of rhG-CSF is increased to 250 micrograms/kg, the administration of LD rhSCF does not further increase the circulating WBC counts. Administration of LD rhSCF in combination with rhG-CSF also stimulated increased circulation of hematopoietic progenitors. LD rhSCF alone stimulated less of an increase in circulating progenitors, per milliliter of blood, than did administration of rhG-CSF alone at 100 micrograms/kg. Baboons administered LD rhSCF together with rhG-CSF at 10, 100, or 250 micrograms/kg had 3.5- to 16-fold higher numbers per milliliter of blood of progenitors cells of multiple types, including colony-forming units granulocyte/macrophage (CFU-GM), burst-forming unit-erythroid (BFU-E), and colony-forming and burst-forming units-megakaryocyte (CFU-MK and BFU-MK) compared with animals given the same dose of rhG-CSF without rhSCF, regardless of the rhG-CSF dose. The increased circulation of progenitor cells stimulated by the combination of rhSCF plus rhG-CSF was not necessarily directly related to the increase in WBCs, as this effect on peripheral blood progenitors was observed even at an rhG-CSF dose of 250 micrograms/kg, where coadministration of LD rhSCF did not further increase WBC counts. Administration of very-low-dose rhSCF (2.5 micrograms/kg) with rhG-CSF, 10 micrograms/kg, did not stimulate increases in circulating WBCs, but did increase the number of megakaryocyte progenitor cells in blood compared with rhG-CSF alone. LD rhSCF administered alone for 7 days before rhG-CSF did not result in increased levels of circulating WBCs or progenitors compared with rhG-CSF alone. Thus, the synergistic effects of rhSCF with rhG-CSF were both dose- and time-dependent. The doses of rhSCF used in these studies have been tolerated in vivo in humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell surface expression of c-kit receptors by childhood acute myeloid leukemia blasts is not of prognostic value: a report from the Childrens Cancer Group.

The prognostic significance of c-kit receptor expression on leukemic blast cells was determined in 122 children with acute myeloid leukemia (AML) entered onto Childrens Cancer Group protocol 213. Clinical and laboratory characteristics as well as outcome were analyzed according to the percentage of blast cells expressing c-kit receptors and the relative number of c-kit receptors per cell as determined by indirect immunofluorescence. c-kit receptor expression was strongly associated with the expression of the CD34 antigen. However, contrary to findings in adult patients with AML, c-kit receptor expression by childhood AML blast cells was not predictive of a poor response to therapy.