Background: Clinical xenotransplantation is not possible because humans possess antibodies that recognize antigens on the surface of pig cells. and N-glycolylneuraminic acid (Neu5Gc) are two known xenoantigens. Methods: We report the homozygous disruption of the a1, 3-galactosyltransferase (GGTA1) and the cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAH) genes in liver-derived female pig cells using zinc-finger nucleases (ZFNs). Somatic cell nuclear transfer (SCNT) was used to produce healthy cloned piglets from the genetically modified liver cells. Antibody-binding and antibody-mediated complement-dependent cytotoxicity assays were used to examine the immunoreactivity of pig cells deficient in Neu5Gc and Gal. Results: This approach enabled rapid production of a pig strain deficient in multiple genes without extensive breeding protocols. Immune recognition studies showed that pigs lacking both CMAH and GGTA1 gene activities reduce the humoral barrier to xenotransplantation, further than pigs lacking only GGTA1. Conclusions: This technology will accelerate the development of pigs for xenotransplantation research.
Many waitlisted patients have minimal xenoreactive antibody binding to the triple KO pig, but some HLA antibodies in sensitized patients cross-react with class I SLA. SLA class I is a target for genome editing in xenotransplantation.
Reducing xenoantigens in donor pigs and chemical immunosuppression can be used to achieve prolonged renal xenograft survival in a preclinical model, suggesting that if a negative cross-match can be obtained for humans then prolonged survival could be achieved.
Pigs are emerging as important large animal models for biomedical research, and may represent a source of organs for xenotransplantation. The MHC is pivotal to the function of the immune system in health and disease, and is particularly important in infection and transplant rejection. Pigs deficient in class I MHC could serve as important reagents to study viral immunity, allograft and xenograft rejection. We report the creation and characterization of class I MHC knockout pigs using the Cas9 nuclease and gRNAs. Pig fetal fibroblasts were genetically engineered using Cas9 and gRNAs, and class I MHC negative cells were then used as nuclear donors for somatic cell nuclear transfer. We produced 3 piglets devoid of all cell surface class I proteins. Though these animals have reduced levels of CD4−CD8+ T cells in peripheral blood, the pigs appear healthy and are developing normally. These pigs are a promising reagent for immunological research.
Our observation of pig LSEC phagocytosis of human platelets describes a novel mechanism of large-particle uptake in the liver. The creation of a model system to study xenotransplantation-induced thrombocytopenia makes possible the investigation into mechanisms that mediate platelet loss.
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