276 PRODUCTION OF TRANSGENIC MINI-PIG CELL LINES EXPRESSING HUMAN CYTOMEGALOVIRUS US2.

Xenotransplantation has the potential to resolve the chronic shortage of donor organs if immunological barriers can be overcome. In particular, the initial type of rejection following xenotransplantation is acute cellular rejection by host CD8+ cytotoxic T lymphocyte (CTL) cells that react to the donor class I major histocompatibility complex (MHC). The human cytomegalovirus (HCMV) glycoprotein US2 specifically targets class I MHC heavy chains for dislocation from the endoplasmic reticulum (ER) membrane to the cytosol, where they are degraded by the proteasome. In this study, the recombinant expression vector pCX-US2 was stably transfected into mini-pig fetal fibroblasts by lipofection. The integration of US2 into the host genome was confirmed by PCR and Southern blot assay. The reduction of swine leukocyte antigen class I (SLA-I, MHC protein class I) by US2 was detected by flow cytometry analysis (FACS). FACS analysis of US2 clonal cell lines demonstrated substantial reductions in SLA surface expression. The decrease in the level of class I MHC expression for US2 clonal cell lines ranged from 22 to 34% relative to the non-transfected control. US2 clonal cell lines were also tested to determine if the resulting reduction in cell surface SLA would reduce in vitro cytotoxicity by CTL. The US2 clonal cell line demonstrated 5- to 6-fold reduction of specific lysis by primed CD8+ CTL. In conclusion, US2 can directly protect pig clonal cell lines from human CTL cells. These results indicate that the expression of US2 in pig cells may provide a new approach toward overcoming CTL-mediated immunity to xenotransplantation.This work was supported by the National Livestock Research Institute (6132-211-303-1). [ABSTRACT FROM AUTHOR]