CLONING AND EXPRESSION OF THE CDNA-ENCODING RAT GRANULOCYTE-COLONY-STIMULATING FACTOR

Granulocyte colony-stimulating factor (G-CSF) acts on precursor hemato poietic cells to control the production and maintenance of neutrophils . Recombinant G-CSF (re-G-CSF)is used clinically to treat patients wit h neutropenia and has greatly reduced the infection risk associated wi th bone marrow transplantation. Cyclic hematopoiesis, a stem cell defe ct characterized by severe recurrent neutropenia, occurs in man and gr ey collie dogs, and can be treated by administration of re-G-CSF. Avai lability of the rat G-CSF cDNA would benefit the use of rats as models of gene therapy for the treatment of cyclic hematopoiesis. In prelimi nary rat experiments, retroviral-mediated expression of canine G-CSF c aused neutralizing antibody formation which precluded longterm increas es in neutrophil counts. To overcome this problem we cloned the rat G- CSF cDNA from RNA isolated from skin fibroblasts. The rat G-CSF sequen ce shared a high degree of identity in both the coding and non-coding regions with both the murine G-CSF (85%) and human G-CSF (74%). The si gnal peptides of murine and human G-CSF both contained 30 amino acids (aa), whereas the deduced signal sequence for rat G-CSF possessed 21 a a. A retrovirus encoding the rat G-CSF cDNA synthesized bioactive G-CS F from transduced vascular smooth muscle cells.