Combining radiation therapy with interleukin-3 gene immunotherapy.

The goal of this study was to explore immunological strategies to increase local and systemic tumor control in patients receiving radiation therapy. In previous studies, interleukin-3 (IL-3) gene expression within murine tumors was shown to increase their response to irradiation through immune mechanisms. In this study, the efficacy of systemically administered IL-3 gene-transduced irradiated tumor cell vaccines was tested for their ability to augment radiation responses against established immunogenic (FSAR) and nonimmunogenic (FSAN) tumors. Vaccines of irradiated FSAR/FSAN or FSAN-JmIL-3/FSAR-JmIL-3 cells were given intraperitoneally just before and after local irradiation of parental tumors with diameters of 8 mm, as well as in two booster doses. The IL-3 gene-transduced tumor cell vaccines were more effective than the parental vaccines at delaying tumor growth after irradiation, although no complete cures resulted. Responses were largely specific to the tumor type, indicating that tumor-specific immunity was enhanced by IL-3 vaccine administration. When the experiment was repeated in the C3H/HeJ mice, which are deficient in tumor necrosis factor-alpha production, the vaccines were still effective, but less so than in C3H/HeN mice. Systemic IL-3 vaccine treatment increased intratumoral levels of intercellular adhesion molecule-1, Mac-1, EB22/5.3, tumor necrosis factor-alpha, and IL-1 mRNA in irradiated tumors, indicating that cellular infiltration was part of the response. The study demonstrates that local radiation therapy can enhance the efficacy of genetically altered vaccine-based immunotherapy for cancer by decreasing tumor burden. At the same time, tumor cell vaccines may improve the cure rate of local radiation therapy by eliminating residual cancer cells. Although less effective than intratumoral gene expression, administration of IL-3 gene-transduced tumor cell vaccines is clinically a more feasible strategy that may be useful in situations in which the tumor load is small.