Cancer immunotherapy is widely used to treat various cancers to augment the weakened host immune response against tumors. Dendritic cells (DCs) are specialized antigen-presenting cells that play dual roles in inducing innate and adaptive immunity. Toxoplasma gondii is a protozoan parasite that exhibits anti-tumor activity against certain types of cancers. However, little is known about the anti-tumor effects of T. gondii or tumor/parasite antigen-pulsed DCs (DC vaccines, DCV) in breast cancer. In this study, C57BL/6 mice were administered E0771 mouse breast cancer cells (Cancer-injected) subcutaneously, T. gondii Me49 cysts orally (TG-injected), or DCs pulsed with breast cancer cell lysate antigen and T. gondii lysate antigens (DCV-injected) intraperitoneally. Tumor size and immunological characteristics were subsequently evaluated. We also evaluated matrix metalloproteinase (MMP)-2 and MMP-9 levels in E0771 mouse breast cancer cells co-cultured with T. gondii or DCs by RT-PCR. The tumor volumes of mice injected with breast cancer cells and antigen-pulsed DCs (Cancer/DCV-injected mice) were similar to those of Cancer-injected mice
however, they were significantly reduced in T. gondii-infected tumor-bearing (TG/Cancer-injected) mice. Moreover, tumor volumes were significantly reduced by adding antigen-pulsed DCs (TG/Cancer/DCV-injected mice) compared to TG/Cancer-injected mice. The levels of IFN-γ, serum IgG2a levels, and CD8+ T cell populations were significantly higher in DCV- and TG-injected mice than in control mice, while no significant differences between Cancer- and Cancer/DCV-injected mice were observed. The levels of IFN-γ, the IgG2a levels, and the percentage of CD8+ T cells were significantly increased in TG/Cancer- and TG/Cancer/DCV-injected mice than in Cancer-injected mice. IFN-γ levels and serum IgG2a levels were further increased in TG/Cancer/DCV-injected mice than in TG/Cancer-injected mice. The MMP-2 and MMP-9 mRNA expressions were significantly decreased in mouse breast cancer cells co-cultured with live T. gondii, T. gondii lysate antigen, or antigen-pulsed DCs (DCV) but not in inactivated DCs. These results indicate that T. gondii induces anti-tumor effects in breast cancer-bearing mice through the induction of strong Th1 immune responses, but not in antigen-pulsed DCs alone. The addition of antigen-pulsed DCs further augments the anti-tumor effects of T. gondii.