Cytokine therapy with gene-transfected cells: Single injection of irradiated granulocyte-macrophage colony-stimulating factor-transduced cells accelerates hematopoietic recovery after cytotoxic chemotherapy in mice

Development of cell-based delivery systems that can release therapeutic levels of hematopoietic growth factors into the systemic circulation would facilitate treatment of patients requiring cytokine therapy. In this study, we have investigated the potential of granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting, irradiated syngeneic murine cells to accelerate hematopoietic recovery after cytotoxic chemotherapy. As a model, CMS-5 fibrosarcoma cells, were transduced with a retroviral vector containing the murine GM-CSF cDNA. Transduced cells secreted 38 ng GM-CSF/10⁶ cells in 24 hours. After irradiation, in vitro GM-CSF production initially increased up to fivefold and was measurable for about 2 weeks. One and 2 days after injection of irradiated, GM-CSF-secreting CMS-5 cells (N2/CMVGM-CSF/CMS5 # 6 cells) into mice, GM-CSF serum levels of 405 ± 58 pg/mL and 183 ± 36 pg/mL were measured, respectively. Serum levels were comparable with levels detected 3 hours after injection of 100 ng recombinant murine GM-CSF (rmGM-CSF) subcutaneously (90 pg/mL). Injection of N2/ CMVGM-CSF/CMS5 * 6 cells in cyclophosphamide-treated mice was as effective in accelerating neutrophil recovery as twice daily subcutaneous injections of rmGM-CSF. These data suggest that irradiated hematopoietic growth factor-secreting cells might offer an alternative to parenteral injections of recombinant cytokines in the treatment of neutropenic patients.