Granulocyte Colony-Stimulating Factor Expression from Transduced Vascular Smooth Muscle Cells Provides Sustained Neutrophil Increases in Rats

Abstract

Granulocyte colony-stimulating factor (G-CSF) regulates granulocyte precursor cell proliferation, neutrophil survival, and activation. Cyclic hematopoiesis, a disease that occurs both in humans and grey collie dogs is characterized by cyclical variations in blood neutrophils. Although the underlying molecular defect is not known, long-term daily administration of recombinant G-CSF eliminates the severe recurrent neutropenia, indicating that expression of G-CSF by gene therapy would be beneficial. As a prelude to preclinical studies in affected collie dogs, we monitored hematopoiesis in rats receiving vascular smooth muscle cells transduced to express G-CSF. Cells transduced with LrGSN, a retrovirus expressing rat G-CSF, were implanted in the carotid artery and control animals received cells transduced with LASN, a retrovirus expressing human adenosine deaminase (ADA). Test animals showed significant increases in neutrophil counts for at least 7 weeks, with mean values of 3,670 ± 740 cells/μl in comparison to 1,870 ± 460 cells/μl in controls (p < 0.001). Thus, in rats G-CSF gene transfer targeted at vascular smooth muscle cells initiated sustained production of 1,800 neutrophils/μl, a cell number that would provide clinical benefit to patients. Lymphocytes, red cells and platelets were not different between control and test animals (p > 0.05). These studies indicate that retrovirally transduced vascular smooth muscle cells can provide sustained clinically useful levels of neutrophils in vivo.

Overview summary

Cyclic hematopoiesis is a disease that occurs both in humans and grey collie dogs and is characterized by cyclical variations in blood neutrophils. Although the underlying molecular defect is unknown, long-term daily administration of recombinant granulocyte colony-stimulating factor (G-CSF) eliminates the severe recurrent neutropenia, indicating that expression of G-CSF by gene therapy would be beneficial. In a preclinical rat model, we monitored neutrophil production in rats receiving vascular smooth muscle cells transduced to express G-CSF. Cells transduced with LrGSN, a retrovirus expressing rat G-CSF, were implanted in the carotid artery and control animals received cells transduced with LASN, a retrovirus encoding human adenosine deaminase. Test animals showed a doubling of neutrophil counts for at least 7 weeks, with mean values of 3,670 ± 740 cells/μl in comparison to 1,870 ± 460 cells/μl in controls (p < 0.001). This suggests that G-CSF gene transfer targeted at vascular smooth muscle cells mediated production of 1,800 cells/μl, a neutrophil count that would provide clinical benefit to patients. These studies show that retrovirally transduced vascular smooth muscle cells can provide sustained clinically relevant levels of neutrophils in vivo.