Objective: To evaluate the use of herpes simplex viral (HSV) amplicon vectors for production of tumor vaccines and to determine if such vaccines expressing combinations of immunostimulatory agents may be effective in the treatment of experimental liver cancer.
Methods: A hepatic metastatic tumor model using CT-26 colorectal cancer in syngeneic Balb/C mice was utilized. Tumor vaccines were produced by brief (20 minutes) exposure of irradiated tumor cells to herpes amplicon vectors carrying the transgene for RANTES, B7.1, or GM-CSF. The antitumor efficacy of vaccination using tumor cells secreting GM-CSF (single agent) or a combination of RANTES/B7.1/GM-CSF (multiagent) was tested. The effect of 60% hepatectomy or T-cell depletion was also tested in this model.
Results: In vitro assays confirmed high-level cytokine or costimulatory molecule production by cells transduced with amplicons. Antitumor efficacy was observed with single-agent or multiagent treatment. Without hepatectomy, immunization with single-agent or multiagent vaccine therapy appears equivalent. When administered in the setting of hepatectomy, multiagent regimens produced a higher cure rate than single-agent therapy (50% vs. 12.5%, =.03). Animals treated with GM-CSF alone had an average nodule count of 40 +/- 19 ( <.006 vs. Hep control 232 +/- 30), while animals treated with multiagent therapy had an average nodule count of 11 +/- 7 ( <.0004 vs. control). CD4 and CD8 lymphocyte blockade abrogated observed efficacy, confirming a lymphocyte-mediated response.
Conclusions: Tumor vaccines produced using HSV amplicon-mediated gene transfer may be useful in the treatment of liver malignancies. In the setting of hepatectomy, multiagent vaccine therapy offers an advantage over single-agent therapy. These data encourage consideration of such HSV-based neoadjuvant immunotherapy for treatment of liver malignancies.