Eliminating major xenoantigens in pig cells has drastically reduced human antibody-mediated hyperacute xenograft rejection (HXR). Despite these advancements, acute xenograft rejection (AXR) remains one of the major obstacles to clinical xenotransplantation, mediated by innate immune cells, including macrophages, neutrophils, and natural killer (NK) cells. NK cells play an ‘effector’ role by releasing cytotoxicity granules against xenogeneic cells and an ‘affecter’ role on other immune cells through cytokine secretion. We highlight the key receptor-ligand interactions that determine the NK cell response to target cells, focusing on the regulation of NK cell activating receptor (NKG2D, DNAM1) and inhibitory receptor (KIR2DL1-4, NKG2A, and LIR-1) signaling pathways. Inhibition of NK cell activity may protect xenografts from cytotoxicity. Recent successful approaches to reducing NK cell-mediated HXR and AXR are reviewed, including genetic modifications of porcine xenografts aimed at improving pig-to-human compatibility. Future directions to promote xenograft acceptance are discussed, including NK cell tolerance in pregnancy and NK cell evasion in viral infection.

We consider the motion of a rigid body in a viscoplastic material. This material is modeled by the 3D Bingham equations, and the Newton laws govern the displacement of the rigid body. Our main result is the existence of a weak solution for the corresponding system. The weak formulation is an inequality (due to the plasticity of the fluid), and it involves a free boundary (due to the motion of the rigid body). We approximate it by regularizing the convex terms in the Bingham fluid and by using a penalty method to take into account the presence of the rigid body.

Background:   Pig-to-human xenotransplantation (XTx) is a promising solution to the organ shortage. Genetically engineered pigs lacking major xenoantigens have reduced hyperacute rejection and prolonged xenograft survival. Despite these advancements, acute xenograft rejection (AXR) remains a major barrier to clinical XTx. AXR is mediated by multiple immune cells, of which natural killer (NK) cells play a crucial role. Previous studies have shown that human HLA-E suppresses NK cell activation through the inhibitory receptor NKG2A. We seek to improve pig-to-human compatibility by expressing HLA-E in a genetically modified pig endothelial cell (pEC) line. This cell line 5GKO/ HLA-G+ has mutations in five genes encoding for xenoantigens and expresses HLA-G, an inhibitory ligand of the NK cell receptor KIR2DL4. In this study, the 5GKO/HLA-G+/HLA-E+ pEC line was established to examine whether co-expression of inhibitory ligands promotes NK cell tolerance.      Methods:   The HLA-Eα/pCDNA3.1 plasmid containing the HLA-E α-chain (HLA-Eα) cDNA driven by a CMV promoter was linearized and introduced into 106 cells of the 5GKO/HLA-G+ pEC line by electroporation. After 48 hours, HLA-E expression was analyzed by flow cytometry. HLA-E+ pECs were isolated by flow cytometry sort and co-cultured with human peripheral blood mononuclear cells (PBMCs) stimulated by IL-2. NK cell degranulation was compared between the 5GKO/HLA-G+ and 5GKO/HLA-G+/HLA-E+ pEC lines by measuring CD107a expression in the CD3- CD56+ cell population.          Results:   HLA-E molecules were successfully expressed on the pECs surface, indicating the HLA-E a chain can pair with the existing b2-microglobulin (B2M). The transfection efficiency was 38.2%. Three weeks later, the 5GKO/HLA-G+/HLA-E+ pEC was successfully established, confirming via flow cytometric analysis. The analysis of NK cell degranulation (CD107a) is underway.     Conclusion:   We established a 5GKO/HLA-G+/HLA-E+ pEC line, which is a valuable tool to study human-to-pig xenoreactive immune response in vitro, with the goal of improving pig-to-human xenograft immunotolerance.