Establishment and Characterization of Genetically Modified Cancer Cells for Experimental Cancer Therapy

Abstract

Purpose: To study whether a xenogeneic cell line engineered to express the herpes simplex virus thymidine kinase (HSVtk) and/or granulocyte-macrophage colony-stimulating factor (GM-CSF) can be used as cellular vaccine to repress tumor growth. Materials and Methods: The HSVtk gene, murine GM-CSF gene, or both were stably transfected into the human cervix cancer cell line HeLa, thus creating three different cell lines designated as H-tk, H-gm, and H-tk/gm. The tumor model we tested was the KBALB sarcoma cells in syngenic BALB/c mice. For in vivo studies, equal number of KBALB cells and H-tk, H-gm, or H-tk/gm cells were premixed and injected into the right flanks of mice. The tumor growth was monitored after ganciclovir (GCV) administration. Results: Two HSVtk-expressing clones (H-tk 2-3 and H-tk 12-2) were isolated. The established H-tk/gm or H-gm cell line was confirmed to express GM-CSF by supporting the growth of a GM-CSF-dependent cell line NSF6O. The right flank tumors in mice injected with premixed K-BALB and H-tk cells showed no definite growth retardation upon GCV administration. Further studies implied that the H-tk cells expressed HSVtk in the injection sites, but failed to confer bystander effect between homologous cells by in vitro studies. The right flanks of mice injected with premixed K-BALB and H-tk/gm or Hgm showed no detectable or much delayed tumor growth either with or without GCV administration; however, the left flank K-BALB tumor progressed with similar growth curve in each study group. Conclusion: Cur studies suggest that though HeLa cells can express HSVtk gene in vivo, they can not confer bystander killing effect to xenogeneic tumor (sarcoma) cells upon GCV administration. This might be because the HeLa cells are intrinsically resistant to metabolic cooperation with other cells. Local production of GM-CSF is able to suppress local tumor growth, but not potent enough to induce distant antitumor immunity. This inability might be related to insufficient duration or amount of GM-CSF action.