Objective: To study the biological characters of tumor cell vaccines modified by interleukin 12 (IL-12) and co-stimulatory molecule B(7 - 1) and their combination therapeutic effect on rat ovarian cancer animal model.
Methods: Retroviral vector pLmB(7 - 1)SN, which expressed murine B(7 - 1) was constructed. An epithelial ovarian cancer cell line NuTu-19 was infected with pLmIL-12SN and/or pLmB(7 - 1)SN by lipofectin-mediated gene transfer system. Cell lines that could highly express either or both of these cytokines were named NuTu-19/IL-12, NuTu-19/B(7 - 1) or NuTu-19/IL-12-B(7 - 1), according to the results of enzyme-linked immunosorbent assay (ELISA) and flow cytometry (FCM). NuTu-19/Neo, the cell line that was transfected by vector pLXSN was used as a control. Various types of cytokine-modified tumor cells were injected subcutaneously into syngeneic rats Fischer 344 and their tumorigenecities were recorded. After being immunized twice by various types of mitomycin C treated gene modified tumor cells, the survival time of the intraperitoneal disseminating ovarian cancer animal model was observed, and the anti-tumor mechanisms of different gene modified tumor cell lines were discussed.
Results: The reconstruction of pLmB(7 - 1)SN was successful. Stable IL-12 and B(7 - 1) expression in cell lines NuTu-19/B(7 - 1), NuTu-19/IL-12 and NuTu-19/IL-12-B(7 - 1) were confirmed by ELISA and FCM. Tumorigenecities of various gene modified tumor cells decreased in syngeneic rats. The splenic lymphocytes proliferation indices (PI) in B(7 - 1) group (NuTu-19/B(7 - 1) immunized group) and IL-12 group (NuTu-19/IL-12 immunized group) were 2.4 and 4.6 (the letter P < 0.05 compared with that in control group), while PI in B(7 - 1) and IL-12 combination group (NuTu-19/IL-12-B(7 - 1) immunized group) increase to 10.2, being of significantly difference compared with those in control or B(7 - 1) or IL - 12 group (P < 0.01). More significant cytotoxic effects of cytotoxic lymphocytes (CTLs) on syngeneic tumor cells could be observed in B(7 - 1) group (15.0%) or IL-12 group (31.5%) (P < 0.05 or P < 0.01, compared with 2.6% in control group), while coexpression of IL-12 and B(7 - 1) was of great importance in enhancing CTL activity (52.4%), compared with that in control or B(7 - 1) or IL-12 group (P < 0.05, respectively). The life spans of ovarian cancer-bearing rats immunized by IL-12 (59.8 d) or B(7 - 1) (56.2 d) tumor cell vaccines were a little longer than that in control group (53.4 d), but no significant differences existed (P > 0.05), whereas in the animal models who had received IL-12 and B(7 - 1) co-immunization, prolonged survival time was showed which had statistical significance compared with that in control group (66.0 d, P < 0.05).
Conclusion: B(7 - 1) and IL-12 modified tumor cell vaccines can induce anti-tumor immunity through stimulating lymphocytes proliferation and inducing recognition and cytotoxic effects of CTLs on tumor cells. An obvious synergistic effect exists when the two cytokines are combined. Combined immunogenic therapy with IL-12 and B(7 - 1) should prove to be a promising therapeutic strategy in ovarian cancer.