Several human leukocyte subsets including natural killer (NK) cells, cytotoxic T lymphocytes (CTL), and polymorphonuclear neutrophils (PMN) participate in cellular immune responses directed against vascularized pig-to-human xenografts. As these leukocytes express the death receptor Fas either constitutively (PMN) or upon activation (NK, CTL), we explored in vitro whether the transgenic expression of membrane-bound human Fas ligand (mFasL) on porcine fetal fibroblasts is a valuable strategy to protect porcine xenografts. cDNA of mFasL carrying the deletion at the cleavage site with metalloproteinase and lacking the death domain in its cytoplasmic tail was subcloned into pCAGGS expression vector driven by the chicken β-actin promoter containing blastidin- resistance cassette. The mFasL expression vector was transfected into mini-pig fetal fibroblasts by lipofection method. Blastidin-resistant cells were screened by PCR and FISH. The expression of mFasL was confirmed by Western blot and FACS with the mouse anti-human FasL antibody. Interaction of two transgenic clonal cell lines with human leukocytes was analyzed using functional assay for cytotoxicity. mFasL expressed on porcine fetal fibroblasts protected porcine fetal fibroblasts against killing mediated by human NK cells. The rate of NK cell mediated cytotoxicity was significantly reduced in transgenic clonal cells (54±10.80%) compared to normal minipig fetal fibroblasts. This result indicated that grafts of transgenic pigs expressing mFasL could control the cellular immune response to xenografts, and create a window of opportunity to facilitate xenograft survival.

• Da-Young Park(MGEN, Inc.)
• Ki-Myung Choi(MGEN, Inc.)
• Young-Chul Park(MGEN, Inc.)
• Yun-Jin Yun(MGEN, Inc.)
• Jae-Goo Seol(MGEN, Inc.)