Granulocyte-macrophage colony stimulating factor (GM-CSF) has been postulated to be a critical mediator in the initial tumor immune response and obvious antitumor immunomodulationg activity of autologous GM-CSF gene-transduced tumor vaccine therapy for various tumors including leukemia has been reported. Previously we demonstrated GM-CSF gene transduction into murine monocytic leukemia cell line of WEHI3B eliminated the tumorigenesity in vivo and the tumor regression started reproducibly around 10 days after tumor injection followed by disappearance within a week. We analyzed the gene expression of the transiently established tumor masses by the serial analysis of gene expression (SAGE) method to identify molecules associated with the antitumor effect. We identified that chemokine genes of TARC and RANTES were preferentially expressed in the GM-CSF-transduced tumors and the contribution of the two genes to the regression of GM-CSF-transduced tumors was suggested. To confirm the finding, we observed in vivo tumor formation of WEHI-3B cells transduced with a retroviral vector expressing murine GM-CSF, TARC, RANTES, GM-CSF+TARC or GM-CSF+RANTES, respectively. One million cells of each transduced cell group and non-transduced cell group were inoculated subcutaneously into syngeneic BALB/c mice. Then tumorigenecity and survival rate were observed. Both of the combination of GM-CSF with TARC or RANTES gene transduction profoundly inhibited tumor formation. In addition, the 2 groups demonstrated significantly longer survival than GM-CSF transduced group. To examine their therapeutic potency, 3×10^6 of irradiated WEHI3B cells retrovirally transduced with murine GM-CSF cDNA in combination with either recombinant TARC or RANTES were subcutaneously inoculated every 4 days for 4 times into syngeneic BALB/c mice preliminarily inoculated subcutaneously with 1×10^5 of wild type WEHI3B cells. Vaccinations were well tolerated without any major adverse events. The mice treated with the GM-CSF transduced cells with chemokines demonstrated significantly longer survival than the mice treated with GM-CSF transduced cells. Splenocytes harvested from mice treated with the former vaccines produced higher levels of IL-4, IL-6, IFN-γ, and TNF-α, suggesting a reinforcement of innate immunity as well as adaptive immunity. Immunohistochemical findings of the tumor section after vaccine treatment revealed more significant contribution of CD4+, CD8+ T cells to tumor repression in the combined vaccine groups than GM-CSF vaccine group. In coclusion, TARC and RANTES enhance immunological antitumor effect induced by GM-CSF in mouse WEHI3B tumor models and would be useful as the second generation GM-CSF immune gene therapy targeting leukemia.
Disclosure: No relevant conflicts of interest to declare.