Phenotypic and functional characteristics of in vivo-induced interleukin-12-activated killer cells

Presence of Cytotoxic B220+CD3+CD4−CD8− Cells Correlates with the Therapeutic Efficacy of Lymphoma Treatment with IL-2 and/or IL-12

Cancer treatment with IL-2 and IL-12 is thought to work via enhancement of proliferation and activity of T cells and NK cells. Incubation of cytotoxic T lymphocytes (CTLs) and NK cells with IL-2 and/or IL-12 results in propagation of a distinct cell type called lymphokine-activated killers (LAK) characterized by increased lytic activity against many tumor types. Here we address the question whether cytokine therapy may be efficient in treatment of a LAK-insensitive tumor and, if so, which cell type, other than classic LAK cells, is responsible for tumor cell killing. We used DBA/2 mice bearing metastasized SL2 lymphoma and treated them with locally applied IL-2 and /or IL-12 injections. We showed that IL-12 treatment is efficient, though there is a rather narrow range of effective doses because of toxicity. This toxicity may be alleviated by a single injection of IL-12 before treatment. Next, we showed that IL-12 synergistically enhances the efficacy of local IL-2 treatment. Moreover, our results indicate that the IL-2/IL-12-mediated therapeutic effect is greatest when it is given after establishment of an immune response to a tumor. Finally, we showed the existence of a unique population of lymphoid cells, namely B220+CD3+CD4-CD8-, at the site of tumor growth. These cells become highly cytotoxic to SL2 cells in mice treated with cytokines late (day 10-14) in the course of the immune response, but not in mice treated early (day 3-7), and cytotoxicity of this unique cell population correlates with the success of therapy.

Rejection of disseminated metastases of colon carcinoma by synergism of IL-12 gene therapy and 4-1BB costimulation

In an orthotopic model of metastatic colon carcinoma established in the liver of mice, we have previously shown that the natural killer (NK) cells were the major effectors after intratumoral delivery of a recombinant adenovirus expressing the murine IL-12 gene. However, tumor cure and long-term survival were achieved only in a minority of animals. In the present study, we generated an effective antitumoral CD8(+ ) T-cell response by the combination of IL-12 gene therapy and systemic delivery of an agonistic monoclonal antibody against 4-1BB, a costimulatory molecule expressed on activated T cells. In the IL-12 plus anti-4-1BB combination treatment, the effective dose of IL-12 could even be reduced even up to 18-fold and still achieved a better efficacy than the maximal dose of either treatment alone. We further demonstrate that the innate and the adaptive antitumoral immune responses were synergistic, as animals bearing hepatic as well as multiple pulmonary metastases were quantitatively cured of their diseases after IL-12 gene therapy + anti-4-1BB combination treatment. Both NK and CD8(+) T cells were necessary in maintaining the long-term antitumor immunity, as depletion of either cell type in the cured animals abolished their abilities to reject tumor cells implanted at distal sites. These results indicate that synergism between innate and adaptive immune responses may be effectively exploited to treat patients with metastatic diseases.

Anti-tumor immunity induced by interleukin-12 gene therapy in a metastatic model of breast cancer is mediated by natural killer cells

An intrahepatic tumor model for metastatic breast cancer was generated in syngeneic mice by direct inoculation of JC cells, a murine mammary adenocarcinoma cell line. Intratumoral administration of a recombinant adenoviral vector expressing the murine Interleukin-12 (ADV-mIL-12) resulted in significant reduction in the tumor volume compared to control vector. Tumor regression was also evident on histopathologic analysis of the liver, where inflammatory changes as opposed to nuclear atypia predominated after IL-12 vector treatment. There was a significant prolongation in the long term survival of IL-12 treated animals, with complete tumor rejection in 40% of the animals. In vivo depletion studies using specific monoclonal antibodies against the various lymphocyte subsets showed a significant reduction in long term survival after natural killer (NK) cell depletion. This suggests that the NK cell is a critical effector in the antitumor effect mediated by IL-12. These results strongly support the potential role of gene mediated cytokine therapy for the treatment of metastatic breast cancer.

Role of NK and T cells in IL-12-induced anti-tumor response against hepatic colon carcinoma

IL-12 is an immuno-regulatory cytokine that has been shown to generate a potent NK and Th1 response in a variety of laboratory models. However, the detailed immune development in the hepatic tumor model by IL-12-mediated gene therapy has not been clarified. In our previous study, intra-tumoral transfer of Adv.mIL-12 (5 x 10(8) pfu) to the MCA26 colon carcinoma liver tumor induced an effective anti-tumor response, extending the median survival time from 29 to over 54 days, while 25% of the animals became tumor-free after a single treatment. In this work, we show that NK cells are responsible for the early, and both NK and T cells for the long-term, Adv.mIL-12-induced immune response. Immunohistopathological analysis of the tumor and in vitro cytotoxicity study of the mononuclear cells of the liver show that NK cells are the first to infiltrate and mediate tumor cell killing, as early as 48 hr after Adv.mIL-12 treatment. In vivo and in vitro depletion of these cells completely abolishes this early anti-tumor response. This activity can be observed in both populations of conventional NK and NKT cells in vitro and in athymic nude mice in vivo. However, the early NK response alone is not sufficient. In vivo T-cell depletion in both the primary tumor treatment and the long-term survival rechallenge study reveals that T cells in addition to NK cells are required in the development of the long-term survival and immunity attributed to Adv.mIL-12 gene therapy in this orthotopic tumor model of colon carcinoma.