The human leukocyte antigen G1 (HLA-G1), a non-classical class I major histocompatibility complex (MHC-I) protein, is a potent immunomodulatory molecule at the maternal/fetal interface and other environments to regulate the cellular immune response. We created GGTA1-/HLAG1+ pigs to explore their use as organ and cell donors that may extend xenograft survival and function in both preclinical nonhuman primate (NHP) models and future clinical trials. In the present study, HLA-G1 was expressed from the porcine ROSA26 locus by homology directed repair (HDR) mediated knock-in (KI) with simultaneous deletion of α-1-3-galactotransferase gene (GGTA1; GTKO) using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas9) gene-editing system. GTKO/HLAG1+ pigs showing immune inhibitory functions were generated through somatic cell nuclear transfer (SCNT). The presence of HLA-G1 at the ROSA26 locus and the deletion of GGTA1 were confirmed by next generation sequencing (NGS) and Sanger’s sequencing. Fibroblasts from piglets, biopsies from transplantable organs, and islets were positive for HLA-G1 expression by confocal microscopy, flow cytometry, or q-PCR. The expression of cell surface HLA-G1 molecule associated with endogenous β2-microglobulin (β2m) was confirmed by staining genetically engineered cells with fluorescently labeled recombinant ILT2 protein. Fibroblasts obtained from GTKO/HLAG1+ pigs were shown to modulate the immune response by lowering IFN-γ production by T cells and proliferation of CD4+ and CD8+ T cells, B cells and natural killer (NK) cells, as well as by augmenting phosphorylation of Src homology region 2 domain-containing phosphatase-2 (SHP-2), which plays a central role in immune suppression. Islets isolated from GTKO/HLA-G1+ genetically engineered pigs and transplanted into streptozotocin-diabetic nude mice restored normoglycemia, suggesting that the expression of HLA-G1 did not interfere with their ability to reverse diabetes. The findings presented here suggest that the HLA-G1+ transgene can be stably expressed from the ROSA26 locus of non-fetal maternal tissue at the cell surface. By providing an immunomodulatory signal, expression of HLA-G1+ may extend survival of porcine pancreatic islet and organ xenografts.
Introduction Macrophages contribute to xenograft rejection by direct cytotoxicity and by amplifying T cell–mediated immune responses. It has been shown that transgenic expression of hCD47 protects porcine cells from human macrophages by restoring the CD47‐SIRPα self‐recognition signal. It has also been reported that the long 3′ untranslated region (3′UTR) of the hCD47 gene, which is missing from constructs previously used to make hCD47 transgenic pigs, is critical for efficient cell surface expression in human cells. The aim of this study was to investigate the impact of a modified form of the 3′UTR on the expression, localization, and function of hCD47 in transfected porcine cells. Methods hCD47 constructs with and without the modified 3′UTR were knocked into the GGTA1 locus in porcine fetal fibroblasts using CRISPR. Flow cytometry of the transfected cells was used to analyze hCD47 localization. Endoplasmic reticulum (ER), mitochondrial, and oxidative stress were examined by gene expression analysis and confocal microscopy. Phagocytosis of transfected cells by human macrophages was measured by flow cytometry, and stimulation of human/non‐human (NHP) primate lymphocytes by the cells was examined using a PBMCs proliferation assay. Results Cells transfected with the construct lacking the 3′UTR (hCD47(3′UTR−)) exhibited predominantly intracellular expression of hCD47, and showed evidence of ER stress, dysregulated mitochondrial biogenesis, oxidative stress, and autophagy. Inclusion of the 3′UTR (hCD47(3′UTR+)) decreased intracellular expression of hCD47 by 36% and increased cell surface expression by 53%. This was associated with a significant reduction in cellular stress markers and a higher level of protection from phagocytosis by human macrophages. Furthermore, hCD47(3′UTR+) porcine cells stimulated significantly less proliferation of human/NHP T cells than hCD47(3′UTR−) cells. Conclusion Our results suggest the potential benefits of using hCD47 constructs containing the 3′UTR to generate genetically engineered hCD47‐expressing donor pigs.
Background Genetically engineered porcine donors are a potential solution for the shortage of human organs for transplantation. Incompatibilities between humans and porcine donors are largely due to carbohydrate xenoantigens on the surface of porcine cells, provoking an immune response which leads to xenograft rejection. Materials and Methods Multiplex genetic knockout of GGTA1, β4GalNT2, and CMAH is predicted to increase the rate of xenograft survival, as described previously for GGTA1. In this study, the clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeats–associated protein 9 system was used to target genes relevant to xenotransplantation, and a method for highly efficient editing of multiple genes in primary porcine fibroblasts was described. Results Editing efficiencies greater than 85% were achieved for knockout of GGTA1, β4GalNT2, and CMAH. Conclusion The high-efficiency protocol presented here reduces scale and cost while accelerating the production of genetically engineered primary porcine fibroblast cells for in vitro studies and the production of animal models.
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