Until now, problems related to shortage of organ for transplantation have been continuing. Pigs are the most suitable animal for xenotransplantation. Although primates are most similar to humans, they are not suitable because they have low productivity. Pigs are more productive than primates, and their organ size and physiological characteristics are similar to humans, with the exception of primates. In this study, we breeding the transgenic minipigs using natural mating to produce transgenic pigs. And, transgenic pigs has transmission rate that follow mendel’s rule. There are 20% hDAF gene, 20% US11 gene and 50% both hDAF and US11 gene in transgenic offsprings. Furthermore, transgenic pigs followed normal litter size, and piglets also has normal sex ratio. To suppress the immune function, experiments were performed using porcine ear fibroblast that transfected with hDAF and US11gene. In Cytotoxicity experiment against human complement, hDAF gene and double transgenic cell with both hDAF and US11 gene showed effect to reduce cytotoxicity rate in all of human complement condition. US11 gene and double transgenic cell were significantly reduce the cytotoxicity ratio in human NK cell. Besides, hDAF gene transgenic cell also reduce immune response in 10:1 concentration of human NK cell. In conclusion, natural mating was efficient method for breeding transgenic pigs. And, hDAF and US11 genes has effect for reduce cytotoxicity against human NK cell and human complement conditions.

Xenotransplantation is proposed as a solution to the problem of organ shortage. However, transplantation of xenogeneic organs induces an antigen-antibody reaction in α-1,3-gal structure that are not present in humans and primates, and thus complement is also activated and organs die within minutes or hours. In this study, we used FasL gene, which is involved in the immune response of NK cell, and US11, which suppresses MHC Class I cell membrane surface expression, to inhibit cell mediated rejection in the interspecific immunity rejection, and also hDAF(CD55) was introduced to confirm the response to C3 complement. These genes were tranfeced into Korean native pig fetal fibroblasts using pCAGGS vector. And cytotoxicity of NK cell and human complement was confirmed in each cell line. The US11 inhibited the cytotoxicity of NK cell and, in addition, the simultaneous expression of US11 and Fas ligand showed excellent suppress to T-lymphocyte cytotoxicity, hDAF showed weak resistance to cytotoxicity of natural killer cell but not in CD8+ CTLs. Cytotoxicity study with human complement showed that hDAF was effective for reducing complement reaction. In this studies have demonstrated that each gene is effective in reducing immune rejection.

Pigs may be considered as a suitable organ source for its characteristics in xenotransplantation if significant immunological barriers can be overcome. However, xenograft could be rejected by T cells, especially CD8+ cytotoxic T lymphocytes (CTL)-mediated response, because these elements show great cytotoxicity against xenograft by recognizing Swine Leukocyte Antigen (SLA)-I. Human cytomegalovirus (HCMV) encodes unique short (US) 11 gene, which interferes with cellular immune responses by inducing rapid degradation of newly synthesized heavy chains (HC) of MHC class I from endoplasmic reticulum (ER) to the cytosol. In this study we established two US11 clonal cell lines by transfection into minipig fetal fibroblasts and confirmed the integration of US11 gene by PCR and FISH. The reduction of Swine Leukocyte Antigen (SLA)-I which was expressed on the cell surface by US11 was also detected by flow cytometry assay. The level (14.6 % to 21.2%) of SLA-I expression in US11 clonal cell lines was decreased relative to the control. The reconstructed embryos were produced with these clonal cells and transferred to nine surrogate gilts. Ultrasound examination of recipient surrogates on days 35 after embryo transfer confirmed established pregnancies in two recipients. One recipient delivered one piglet with normal birth weight. PCR analysis revealed that transgene vector was integrated in the offspring genome. Transgene-expression analysis and CTL assay are currently underway. The present results show that transgenic pig was produced with US11 cDNA for controlling cell-mediated rejection. This result indicated that grafts of transgenic pigs expressing human cytomegalovirus protein US11 could control the cellular immune response to xenografts, and create a window of opportunity to facilitate xenograft survival. This research was supported by the BioGreen 21 Program (#20110301-061-541- 001-05-00), Rural Development Administration, Republic of Korea.