Study on the tumorgenesis and therapeutic approaches in a murine model of leukemia

• Main Authors: Bor-Yu Tsai, 蔡博宇
• Other Authors: Bor-Luen Chiang
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/47567573838047093230

博士 === 國立臺灣大學 === 免疫學研究所 === 96 === Leukemia is a cancer of white blood cells that are disseminated by blood circulation. Because their features differ from solid tumors, leukemia cells metastasize to other tissues and organs more easily through the blood or lymphatic systems. RL ♂1 cell, which expressed CD4, CD25, IL-10, TGF-b and also expressed Foxp3, is a regulatory T cell (Treg)-like leukemia cell line. In this study, we established a murine model of leukemia with RL ♂1 to study the pathogenic mechanism of leukemia and intend to look for applicable approaches for cancer therapy. In the part I of the studies, we tried to improve conventional dendritic cells (DCs) based immunotherapy by administering engineered DCs that transduced with adenoviral vector expressing IL-12 (AdIL-12) pulsed with tumor cell lysate (TCL). Tumor mice treated with engineered DCs had a longer survival rate of 75% at day forty significantly improved the survival rate, 33% and 50%, of tumor mice treated with DCs pulsed with TCL alone or transduced with AdIL-12 respectively. In addition, IL-12 transduced and TCL pulsed DCs treated mice had higher CTL response compared to that of control group. Depletion of CD8+ T cells with specific antibodies abrogated the protective effects in tumor mice with DCs treatment. The results suggested that IL-12 gene modified DCs pulsed with TCL can stimulate immune response against tumor better than conventional DCs based tumor immunotherapy in animal model of leukemia. However, many studies have shown that DC-based tumor vaccines in animal tumor models can inhibit tumor growth and induce autoantibodies transiently. In this study, anti-ds DNA monoclonal antibodies recognized RL ♂1 cells but not normal cells by FACs analysis. The autoantibodies were demonstrated to lyse tumor cells via complement-mediated reaction in vitro and also exhibit the antitumor effects when the antibody was injected into tumor implanted mice. The data suggested that autoantibodies exert anti-tumor activity in vivo. In the future, it would be important to clarify the surface molecule of tumor recognized by autoantibody induced by DCs. The second part of the thesis discussed the mechanism of leukemia development in vivo and tried to explore adequate solution for cancer therapy. The data suggested that RL ♂1 cells lost Foxp3 expression and the ability of tumor growth simultaneously when subcutaneously transplanted into mice after in vitro culture for several generations. Interestingly, the phenomenon could be rescued or reversed after in vivo passage in the peritoneal cavity of mice. In addition, we transfer Foxp3 siRNA into tumor cells using lentiviral transduction system to inhibit Foxp3 expression. With infection of Lenti-Foxp3-siRNA in RL ♂ 1 cells, Foxp3 gene expression was abrogated and decreased the suppressive function to CD4+CD25- effector cells stimulated with ConA. Furthermore, lentiviral-mediated Foxp3 RNAi transduced into RL ♂ 1 cell or intratumoral injection of Lenti-Foxp3 siRNA showed suppressive effects of tumor growth and prolonged the survial time of tumor-transplanted mice. These results suggested that inhibition of Foxp3 gene expression by shRNAs effectively decreased tumor growth of regulatory T cell-like leukemia. In the study, engineered DCs activate specific immune response and produce autoantibodies inhibit tumor growth. In addition, Lenti-Foxp3-siRNA abrogates the chance of tumor to escape from immunosurveillance system. The studies in the thesis might provide a novel strategy for future clinical immunotherapy of leukemia