Synergistic anti-tumor effect of combination radio- and immunotherapy by electro-gene therapy plus intra-tumor injection of dendritic cells.

Interleukin-2 (IL-2) and granulocyte-macrophage colony stimulating factor (GM-CSF) facilitate the maturation and functioning of injected DC. We developed a method of in situ electroporation using IL-2 and GM-CSF genes (EGT/cytokines), followed by intra-tumoral (i.t.) immature DC to determine the immune response at the tumor site using prostate-specific antigen-transfected CT26 cells. Three cycles of EGT/cytokines and i.t. DC inhibited tumor growth most effectively, but not superior to EGT/cytokines alone. However, the role of i.t. DC became significant when radiation was given after immunotherapy, which may have clinical implications on achieving better local control and prevention of systemic relapse.