Immunization with a tissue vaccine enhances the effect of irradiation on prostate tumors

Recent studies on immunotherapy as a means to treat prostate cancer presents an interesting opportunity for combination therapy with radiation. This work was undertaken to determine if immunization with a prostate cancer tissue vaccine could enhance the effect of radiation treatment. Groups of Lobund-Wistar (LW) rats were subcutaneously administered PAIII prostate cancer cells (Day 0). Tumor-bearing rats were then either left untreated, vaccinated on Days 11 and 14 with a vaccine composed of glutaraldehyde-fixed harvested tumor tissue (GFT), irradiated with 15 Gy on Days 21 and 23 (Irr), or vaccinated with the GFT vaccine on Days 11 and 14 and irradiated on Days 21 and 23 (GFT/ Irr). The tumors were measured on Day 11 and at the time of euthanasia (Day 30) and tumor volume was calculated. On Day 30, the tumors were harvested, weighed and fixed for histopathological evaluation. The mean tumor weight was significantly less (p≤0.05) in the Irr rats (7.21 g) compared to the untreated (13.04 g) and GFT-treated (10.64 g) rats. In contrast, the mean tumor weight of the GFT/Irr rats (3.37 g) was significantly less than the untreated and the GFT-treated tumors (p≤0.001), as well as the Irr tumors (p≤0.01). The GFT/Irr rats were the only group in which the tumor volume decreased during the study (14% decrease) compared to the untreated (147% increase), the GFT-treated (115% increase), and the Irr (12% increase) rats. Immunization with a tissue vaccine prior to radiation treatment enhances the therapeutic effect of radiation.