Effects of recombinant human GM-CSF on proliferation of clonogenic cells in acute myeloblastic leukemia

Abstract Proliferation of acute myeloblastic leukemia (AML) cells in vitro is limited in most cases to a small subset of blasts that have several properties of stem cells. These leukemic colony-forming cells (AML-CFU) generally require addition of exogenous growth factors for proliferation in agar or methylcellulose. These factors can be supplied by media conditioned by phytohemagglutinin-stimulated normal leukocytes or by CSF-secreting tumor cell lines. However, the exact factor or factors required for stimulation of AML-CFU growth have not been defined. We compared the AML-CFU stimulatory activity of a human recombinant GM-CSF with that of GCT-CM, Mo-CM, and the PHA-leukocyte feeder system in 15 cases of AML. In each of the 12 cases that required exogenous growth factors for maximum AML-CFU growth, recombinant GM-CSF could replace either GM-CSF or Mo-CM, and could partially replace the PHA-leukocyte feeder system. These results indicate that this GM-CSF is a growth promoter of AML-CFU in these culture systems.</jats:p

Effects of recombinant human GM-CSF on proliferation of clonogenic cells in acute myeloblastic leukemia

Proliferation of acute myeloblastic leukemia (AML) cells in vitro is limited in most cases to a small subset of blasts that have several properties of stem cells. These leukemic colony-forming cells (AML-CFU) generally require addition of exogenous growth factors for proliferation in agar or methylcellulose. These factors can be supplied by media conditioned by phytohemagglutinin-stimulated normal leukocytes or by CSF-secreting tumor cell lines. However, the exact factor or factors required for stimulation of AML-CFU growth have not been defined. We compared the AML-CFU stimulatory activity of a human recombinant GM-CSF with that of GCT-CM, Mo-CM, and the PHA-leukocyte feeder system in 15 cases of AML. In each of the 12 cases that required exogenous growth factors for maximum AML-CFU growth, recombinant GM-CSF could replace either GM-CSF or Mo-CM, and could partially replace the PHA-leukocyte feeder system. These results indicate that this GM-CSF is a growth promoter of AML-CFU in these culture systems.</jats:p

Differential expression of HLA-DR antigens in subsets of human CFU-GM

Expression of HLA-DR surface antigens by granulocyte/monocyte colony- forming cells (CFU-GM) may be important in the regulation of proliferation of these cells. Using immunological techniques to enrich for progenitor cells, we investigated the expression of HLA-DR in subsets of CFU-GM. “Early” (day 14) CFU-GM express higher levels of HLA- DR than do “late” (day 7) CFU-GM. Among late CFU-GM, cells destined to form monocyte (alpha-naphthyl acetate esterase-positive) colonies express higher levels of HLA-DR than do CFU-GM destined to form granulocyte (chloroacetate esterase-positive) colonies. Because high- level expression of DR antigen was a marker for monocyte differentiation, we examined several lymphokines for their effects on both DR expression and in vitro commitment to monocyte differentiation by myeloid precursor cells. DR antigen density could be increased by more than twofold over 48 hours upon exposure to gamma-interferon (gamma-IFN), whereas colony-stimulating factors had no effect. This was associated with a dose-dependent inhibition of total CFU-GM number, and a relative, but not absolute, increase in the ratio of monocyte colonies to granulocyte colonies. Similarly, in day 7 suspension cultures of purified myeloid precursor cells, gamma-IFN inhibited cell proliferation and increased the ratio of monocytes to granulocytes. Thus, despite the induction of high levels of HLA-DR antigen on precursor cells (a marker of monocyte commitment), the dominant in vitro effect of gamma-IFN was inhibition of granulocyte differentiation.</jats:p

Differential expression of HLA-DR antigens in subsets of human CFU-GM

Abstract Expression of HLA-DR surface antigens by granulocyte/monocyte colony- forming cells (CFU-GM) may be important in the regulation of proliferation of these cells. Using immunological techniques to enrich for progenitor cells, we investigated the expression of HLA-DR in subsets of CFU-GM. “Early” (day 14) CFU-GM express higher levels of HLA- DR than do “late” (day 7) CFU-GM. Among late CFU-GM, cells destined to form monocyte (alpha-naphthyl acetate esterase-positive) colonies express higher levels of HLA-DR than do CFU-GM destined to form granulocyte (chloroacetate esterase-positive) colonies. Because high- level expression of DR antigen was a marker for monocyte differentiation, we examined several lymphokines for their effects on both DR expression and in vitro commitment to monocyte differentiation by myeloid precursor cells. DR antigen density could be increased by more than twofold over 48 hours upon exposure to gamma-interferon (gamma-IFN), whereas colony-stimulating factors had no effect. This was associated with a dose-dependent inhibition of total CFU-GM number, and a relative, but not absolute, increase in the ratio of monocyte colonies to granulocyte colonies. Similarly, in day 7 suspension cultures of purified myeloid precursor cells, gamma-IFN inhibited cell proliferation and increased the ratio of monocytes to granulocytes. Thus, despite the induction of high levels of HLA-DR antigen on precursor cells (a marker of monocyte commitment), the dominant in vitro effect of gamma-IFN was inhibition of granulocyte differentiation.</jats:p