EFFECTS OF RECOMBINANT HUMAN STEM CELL FACTOR ON HEMATOPOIESIS

本项目的目标是研究重组人干细胞因子(RhSCF)在体内和体外对造血的生物学效应。重组人干细胞因子是人c-kit分子的配体，是一种具有酪氨酸激酶活性的细胞表面受体。在体外，SCF本身对人和狒狒骨髓造血集落形成细胞(CFCs)的增殖几乎没有刺激作用，但与其他造血生长因子(包括IL-3、G-CSF、GM-CSF和EPO)联合使用时确实具有刺激作用。在体内，SCF刺激剂量依赖的白细胞增多，增加血液中的中性粒细胞、单核细胞、嗜酸性粒细胞、嗜碱性粒细胞以及T和B淋巴细胞。SCF还能刺激网织红细胞增多，增加红细胞数量和红细胞压积。在骨髓中，SCF刺激细胞密度和形态上不成熟的红系和粒细胞呈剂量依赖性增加。重要的是，SCF增加了骨髓和血液中造血祖细胞的数量。在每天服用200克/公斤干细胞的动物中，血液中的祖细胞数量从10倍增加到1000倍，血液中CD34+细胞的数量也随之增加。我们还表明，在受到致命性照射的狒狒中，能够拯救和重建淋巴造血的可移植细胞在血液中通过高剂量的SCF治疗而增加。SCF与G-CSF在体内也有协同作用。每天25g/kg的SCF，与单独使用G-CSF相比，单独使用G-CSF不会刺激白细胞增加或外周血祖细胞增加，从而增加循环中WBC的增加速度和达到的最大WBC。最重要的是，与单独使用G-CSF相比，这种剂量的SCF与G-CSF联合使用可显著增强祖细胞和骨髓再生细胞的循环。移植了在刺激过程中收集的血细胞的动物比移植仅用G-CSF刺激过程中收集的细胞的动物更快地植入了SCF+G-CSF。研究正在进行中，以确定干细胞因子与其他生长因子相结合，是否可以在体外扩大骨髓和血液中的祖细胞数量，以及这些扩大的细胞是否可以移植到受到致命辐射的狒狒体内。

The goal of this project is to study the in vivo and in vitro biological effects on hematopoiesis of recombinant human stem cell factor (rhSCF), a ligand for the human c-kit molecule, a cell surface receptor with tyrosine kinase activity. In vitro, SCF by itself stimulates little proliferation of human and baboon marrow hematopoietic colony-forming cells (CFC), but does have stimulating effects when combined with other hematopoietic growth factors, including IL-3, G-CSF, GM-CSF, and Epo. In vivo, SCF stimulates a dose-dependent leukocytosis, with increases in neutrophils, monocytes, eosinophils, basophils, and T and B lymphocytes in the blood. SCF also stimulates a reticulocytosis and increases in the numbers of red blood cells and in hematocrit. In marrow, SCF stimulates a dose-dependent increase in cellularity and morphologically immature erythroid and granulocytic cells. Importantly, SCF increases the number of hematopoietic colony-forming progenitor cells in marrow and blood. The number of progenitor cells in blood increases from 10-fold to >1000-fold in animals given SCF at a dose of 200 g/Kg/day, with an associated increase in numbers of CD34+ cells in blood. We have also shown that transplantable cells capable of rescuing and reconstituting lymphohematopoiesis in lethally irradiated baboons are increased in the blood by treatment with high doses of SCF. SCF also has in vivo synergy with G-CSF. SCF at 25 g/kg/day, which alone does not stimulate a leukocytosis or an increase in peripheral blood progenitors, when administered with G-CSF increases the rate at which circulating WBC increase as well as the maximum WBC achieved, compared with G-CSF alone. Most importantly, this dose of SCF when combined with G-CSF dramatically enhances the circulation of progenitor cells as well as marrow repopulating cells compared with G-CSF alone. Animals transplanted with blood cells collected during stimulation with the combination of SCF plus G-CSF engraft much more rapidly than do animals transplanted with cells collected during stimulation with G-CSF alone. Studies are in progress to determine if SCF, in combination with other growth factors, can be used to expand the number of progenitors from marrow and blood in vitro and if these expanded cells can engraft lethally irradiated baboons.