Robert A. Bosselman

Identification, purification, and biological characterization of hematopoietic stem cell factor from buffalo rat liver-conditioned medium

We have identified a novel growth factor, stem cell factor (SCF), for primitive hematopoietic progenitors based on its activity on bone marrow cells derived from mice treated with 5-fluorouracil. The protein was isolated from the medium conditioned by Buffalo rat liver cells. It is heavily glycosylated, with both N-linked and O-linked carbohydrate. Amino acid sequence following removal of N-terminal pyroglutamate is presented. The protein has potent synergistic activities in semisolid bone marrow cultures in conjunction with colony-stimulating factors. It is also a growth factor for mast cells. In two companion papers, we present the sequences of partial SCF cDNAs, identify SCF as a c-kit ligand, and map the SCF gene to the Sl locus of the mouse.

Stem cell factor

Stem cell factor (SCF) is the ligand for the tyrosine kinase receptor okit, which is expressed on both primitive and mature hematopoietic progenitor cells. In vitro, SCF synergizes with other growth factors, such as granulocyte colony‐stimulating factor (G–CSF), granulocyte macrophage–colony‐stimulating factor, and interleukin‐3 to stimulate the proliferation and differentiation of cells of the lymphoid, myeloid, erythroid, and megakaryocytic lineages. In vivo, SCF also synergizes with other growth factors and has been shown to enhance the mobilization of peripheral blood progenitor cells in combination with G–CSF. In phase I/II clinical studies administration of the combination of SCF and G‐CSF resulted in a two‐ to threefold increase in cells that express the CD34 antigen compared with G–CSF alone. Other potential clinical uses include ex vivo expansion protocols and in vitro culture for gene therapy. J. Leukoc. Biol. 58: 14–22; 1995.

Generation of competent virus in the REV helper cell line C3

We have studied the generation of replication-competent virus in cultures of the helper cell line C3, which harbors a packaging-defective provirus derived from reticuloendotheliosis virus. We transfected the C3 line with a defective provirus encoding the chicken growth hormone gene and carrying the HSV-1 tk gene. The appearance of competent virus was assayed by infection of Spafas C/E CEF, monitoring reverse transcriptase activity, and rescue of the TKTU assayed on BRLtk- cells. Our results indicate that cultures of C3 producing TKTU can release viruses which have variable growth characteristics and which can remain latent in culture for extended periods of time.