16.SECTION FOR STUDIES ON HOST- IMMUNE RESPONSE
	�@The research in Section for Studies on Host- immune Response has focused on studies of gene therapy for cancer and the development of novel vectors. The Section has been collaborating with the Genetics Division and the Central RI Laboratory in the field of gene therapy research. Gene Therapy for Pancreatic Cancer Using Antisense K-ras RNA �@Previous reports from the Genetics Division showed that the transduction of antisense K- ras expression plasmid markedly inhibited the growth of pancreatic cancer cells. The strong expression of antisense K- ras RNA by adenovirus vector effectively induced cell death in the pancreatic cancer cell lines, AsPC- 1 and Panc- 1, in a dose- dependent manner, demonstrating that this strategy is not only cytostatic but also cytocidal. In addition, the growth suppression of normal cells (HUVEC)after antisense K- ras transduction was likely to be minimal. The combination transfer of the interferon- a gene with antisense K- ras clearly enhanced its cytotoxic activity, possibly by activation of 2',5'- oligoadenylate synthetase. To understand the role of K- ras mutation in pancreatic carcinogenesis, the downstream molecules activated by K- ras were investigated. Comparison of the mRNA profiles of AsPC- 1 and its antisense- K- ras transduced clones showed that the up- regulated genes were mitochondrial genes and the down- regulated genes included an oncogene, prostate tumor inducing- 1, and matrix metalloproteinase- 7, suggesting these genes are novel candidates for gene therapy of pancreatic cancer.(199) Polyethylenimine-based Gene Delivery into Peritoneal Dissemination �@More safe and efficient vectors are needed to develop a gene therapy for peritoneal dissemination. A linear form of polyethylenimine (PEI)showed higher gene transfer efficiency in comparison with various liposomes in several pancreatic cancer cell lines (AsPC- 1, MIAPaCa- 2, PSN- 1 and PGHAM- 1)in vitro. AsPC- 1 cells were inoculated into the peritoneal cavity of nude mice, and the luciferase expression plasmid was injected intraperitoneally as a DNA- PEI complex. A significantly high luciferase expession was observed only in intraperitoneally disseminated tumors, and a lower level of activity was found in some normal organs (stomach, spleen and skeletal muscle). Other major organs (brain, lung, heart, liver, kidney, and small intestine)did not show any luciferase activity, suggesting that this approach using the DNA- PEI complex is a simple and useful targeting method for peritoneal malignant dissemination. Development of Novel cDNA Selection Method Using Adenovirus Vector �@Adenovirus vectors have characterized by a broad host range with high infectivity;this range is also seen in nondividing cells. The section has tried to establish a novel cDNA selection method based on biological function using adenovirus vectors. In the first step, it was confirmed that a full- length recombinant adenovirus DNA could be constructed in vitro by the Cre/lox system.