Development of Human Granulocyte-Macrophage Colony-Stimulating Factor-Transfected Tumor Cell Vaccines for the Treatment of Spontaneous Canine Cancer

Cytokine gene-engineered tumor vaccines are currently an area of intense investigation in both basic research and clinical medicine. Our efforts to utilize tumor vaccines in an immunotherapeutic manner involve canines with spontaneous tumors. We hypothesized that canine tumor cells, transfected with human granulocyte-macrophage colony-stimulating factor (hGM-CSF) cDNA in a plasmid vector, would prove nontoxic following intradermal administration, generate biologically relevant levels of protein, effect local histological changes at the sites of vaccination, and create a systemic antitumor response. Sixteen tumor-bearing dogs were admitted to a study of ex vivo gene therapy. Tumor tissue was surgically removed, enzymatically and mechanically dissociated, irradiated, transfected, and intradermally injected back into the patients. The dogs were vaccinated with primary autologous tumor cells transfected with hGM-CSF or a reporter control gene. hGM-CSF protein was detected (0.07 to 14.15 ng/vaccination site) at 24 hr postinjection and dramatic histological changes were observed, characterized by neutrophil and macrophage infiltration at the sites of injection of hGM-CSF-transfected tumor cells. This was in stark contrast to the lesser neutrophilic and eosinophilic infiltrates found at control vaccination sites. Objective evidence of an antitumor response was observed in three animals. These data, in a large animal translational model of spontaneous tumors, demonstrate in vivo biological activity of hGM-CSF-transfected autologous tumor cell vaccines.

Overview summary

Immunotherapy of cancer utilizing cytokine gene-engineered tumor cells has demonstrated exciting results in numerous preclinical studies in murine models. Dogs provide a valid translational model for clinical experimentation of novel human cancer therapeutics owing to their large size, biological similarity, similar environmental influences, relative outbreeding, and rates of development of spontaneous tumors. We utilized particle-mediated gene transfer of hGM-CSF in a plasmid vector into surgically excised, autologous, primary canine tumor cells, irradiated, and injected intradermally in the form of a vaccine back into the patient. Biopsy samples obtained from the sites of injection demonstrated biologically active hGM-CSF protein as determined by ELISA. Histopathologic review showed significant differences between the sites of injection of either hGM-CSF-transfected, irradiated tumor cells or control-transfected, irradiated tumor cells. Tumor vaccines were well tolerated by all animals entered into this phase I clinical trial. Antitumor responses were observed in 3 of 16 animals (19%).