Systemic Hematological Effects of Granulocyte Colony-Stimulating Factor Produced by Irradiated Gene-Transfected Fibroblasts

Abstract

Although long-term expression of therapeutic molecules is necessary for the treatment of permanent deficiencies, short-term expression of therapeutic molecules inducing local or systemic effects is preferable in clinical situations where temporary substitution is the goal. One such clinical setting is the administration of hematopoietic growth factors in cancer chemotherapy-induced myelosuppression. Several plasmid vectors containing the human granulocyte colony-stimulating factor (G-CSF) gene under transcriptional control of different regulatory elements were constructed. In vitro production of G-CSF by nonvirally transfected murine fibroblast clones initially increased after lethal irradiation and was detectable for at least 12 days. We also demonstrate that a single injection of irradiated G-CSF-secreting fibroblasts leads to accelerated hematopoietic recovery and mobilization of committed peripheral blood progenitor cells equivalent to that achieved by twice daily s.c. administration of high doses of recombinant human G-CSF. Using dicistronic vectors, high levels of G-CSF secretion were also obtained in human fibroblasts.

Overview summary

This paper describes the feasibility of using irradiated nonvirally transfected fibroblast clones for the systemic delivery of biologically active gene products. Mouse fibroblasts were genetically modified to express human G-CSF and irradiated to inhibit cellular proliferation. These cells continued to secrete biologically active cytokine into culture media for at least 12 days in vitro. In vivo, serum levels correlated with in vitro expression and were detectable up to at least 6 days. Increased numbers of circulating committed progenitor cells, accelerated recovery of peripheral blood leukocyte counts, as well as marked rebound leukocytosis after a single s.c. injection of irradiated G-CSF gene-transfected fibroblasts in chemotherapy-treated mice, demonstrated the efficient distribution of the recombinant gene product from the dermal localization. Our results highlight the potential of using irradiated genetically modified fibroblasts for the systemic delivery of therapeutic molecules in appropriate therapeutic situations where transient substitution is necessary, such as supportive treatment of chemotherapy-induced neutropenia.