Improvement of a dendritic cell-based therapeutic cancer vaccine with components of Toxoplasma gondii

Abstract

The use of dendritic cells (DCs) as a cellular adjuvant is a promising approach to the immunotherapy of cancer. It has previously been demonstrated that DCs pulsed ex vivo with Toxoplasma gondii antigens trigger a systemic Th1-biased specific immune response and induce protective and specific antitoxoplasma immunity. In the present study, we demonstrate that tumor antigen-pulsed DCs matured in the presence of Toxoplasma gondii components induce a potent antitumor response in a mouse model of fibrosarcoma. Bone-marrow derived DCs (BMDCs) were cultured in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4. After 5 days, tumor lysates with or without the T. gondii lysate were added to the culture for another 2 days. The cytokine production in the BMDC culture and the coculture supernatants of DCs and splenic cells was evaluated. For immunization, 7 days after tumor challenge, different groups of BALB/c mice received different kinds of DCs subcutaneously around the tumor site. Tumor growth was monitored, and 2 weeks after DC immunotherapy, the cytotoxic activity and the infiltration of CD8(+) T cells were monitored in different groups. According to the findings, immunotherapy with T. gondii-matured DCs led to a significant increase in the activity of cytotoxic T cells and decreased the rate of growth of the tumor in immunized animals. Immature DCs did not cause any change in cytotoxic activity or the tumor growth rate compared to that in the healthy controls. The current study suggests that a specific antitumor immune response can be induced by DCs matured with T. gondii components and provide the basis for the use of T. gondii in DC-targeted clinical therapies.

FIG. 1.

Phenotypic changes of BMDCs in response to LPS and T. gondii lysate (T.L). Day 5 immature and day 7 mature BMDCs were analyzed by flow cytometry for the expression of DC maturation markers. The data are presented as the percentages of positive cells for each marker and are representative of those from three separate experiments.

FIG. 2.

Production of IL-12 by IM-DCs and after maturation with T. gondii lysate (T.L) and LPS. The cytokines in the supernatants of IM-DCs, T. gondii lysate-DCs, and LPS-DCs were quantified by an IL-12 (p70)-specific ELISA.

FIG. 3.

Proliferative response and cytokine production of T cells elicited by BMDCs. T cells were stimulated with autologous IM-DCs and DCs matured in the presence of T. gondii lysate (T.L) and LPS. After stimulation, T-cell proliferation (a) and the production of IFN-γ (b) and IL-10 (c) were evaluated. T-cell proliferation was measured by the BrdU-based ELISA method, and the cytokine concentrations were determined by specific ELISAs. The results are the means of three independent experiments.

FIG. 4.

CTL responses in mice treated with DCs. Specific cytotoxicity against WEHI 164 cells as the target cells (a) and nonspecific cytotoxicity against an unrelated tumor cell line (CT26 cells) (b) were evaluated in the different groups. The mice treated with T. gondii lysate-DCs (T.L-DC) and LPS-DCs showed the highest specific CTL response when the response was compared to the responses of the other groups. In contrast, there were no significant differences in the nonspecific CTL responses between selected groups.

FIG. 5.

Protective effect of T. gondii lysate-DC (T.L-DC) and LPS-DC in a subcutaneous challenged WEHI 164 tumor model. Mean tumor growth rate per 48 h (a) and the percentage of animals that survived (b) are shown for each group. Each group consisted of five mice.

FIG. 6.

Percentage of CD8⁺ cells in tumor tissue in different groups treated with various types of DCs.