Hidetaka Hara

Liver NK cells expressing TRAIL are toxic against self hepatocytes in mice.

Although it is known that activation of natural killer (NK) cells causes liver injury, the mechanisms underlying NK cell‐induced killing of self‐hepatocytes are not clear. We demonstrated that liver NK cells have cytotoxicity against normal syngeneic hepatocytes in mice. Polyinosinic‐polycytidylic acid (poly I:C) treatment enhanced hepatocyte toxicity of liver NK cells but not that of spleen NK cells. Unlike NK cells in other tissues, approximately 30%–40% of liver NK cells constitutively express tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL). An in vitro NK cell cytotoxic assay revealed that hepatocyte toxicity of liver NK cells from both naïve and poly I:C‐treated mice was inhibited partially by an anti‐TRAIL monoclonal antibody (mAb) alone and completely by the combination with anti‐Fas ligand (FasL) mAb and a perforin inhibitor, concanamycin A, indicating contribution of TRAIL to NK cell‐mediated hepatocyte toxicity. The majority of TRAIL+ NK cells lacked expression of Ly‐49 inhibitory receptors recognizing self‐major histocompatibility complex class I, indicating a propensity to targeting self‐hepatocytes. Poly I:C treatment significantly upregulated the expression of Ly‐49 receptors on TRAIL− NK cells. This might be a compensatory mechanism to protect self‐class I‐expressing cells from activated NK cell‐mediated killing. However, such compensatory alteration was not seen at all in the TRAIL+ NK cell fraction. Thus, liver TRAIL+ NK cells have less capacity for self‐recognition, and this might be involved in NK cell‐dependent self‐hepatocyte toxicity. In conclusion, our findings are consistent with a model in which TRAIL‐expressing NK cells play a critical role in self‐hepatocyte killing through poor recognition of MHC. (HEPATOLOGY 2004;39:1321–1331.)

Liver Sinusoidal Endothelial Cells Tolerize T Cells across MHC Barriers in Mice

Although livers transplanted across MHC barriers in mice are normally accepted without recipient immune suppression, the underlying mechanisms remain to be clarified. To identify the cell type that contributes to induction of such a tolerance state, we established a mixed hepatic constituent cell-lymphocyte reaction (MHLR) assay. Irradiated C57BL/6 (B6) or BALB/c mouse hepatic constituent cells (HCs) and CFSE-labeled B6 splenocytes were cocultured. In allogeneic MHLR, whole HCs did not promote T cell proliferation. When liver sinusoidal endothelial cells (LSECs) were depleted from HC stimulators, allogeneic MHLR resulted in marked proliferation of reactive CD4+ and CD8+ T cells. To test the tolerizing capacity of the LSECs toward alloreactive T cells, B6 splenocytes that had transmigrated through monolayers of B6, BALB/c, or SJL/j LSECs were restimulated with irradiated BALB/c splenocytes. Nonresponsiveness of T cells that had transmigrated through allogeneic BALB/c LSECs and marked proliferation of T cells transmigrated through syngeneic B6 or third-party SJL/j LSECs were observed after the restimulation. Transmigration across the Fas ligand-deficient BALB/c LSECs failed to render CD4+ T cells tolerant. Thus, we demonstrate that Fas ligand expressed on naive LSECs can impart tolerogenic potential upon alloantigen recognition via the direct pathway. This presents a novel relevant mechanism of liver allograft tolerance. In conclusion, LSECs are capable of regulating a polyclonal population of T cells with direct allospecificity, and the Fas/Fas ligand pathway is involved in such LSEC-mediated T cell regulation.

Antibody‐ and complement‐independent phagocytotic and cytolytic activities of human macrophages toward porcine cells

Abstract:u2002 Background:u2002 It has been speculated that host macrophages contribute to rapid clearance of transplanted xenogeneic cells. To address such a possibility, phagocytotic and cytolytic activities of human macrophages toward xenogeneic porcine cells were evaluated in vitro in the absence of antibodies and complement factors.

Hepatic Function After Genetically Engineered Pig Liver Transplantation in Baboons

Background. If “bridging” to allo-transplantation (Tx) is to be achieved by a pig liver xenograft, adequate hepatic function needs to be assured. Methods. We have studied hepatic function in baboons after Tx of livers from &agr;1,3-galactosyltransferase gene-knockout (GTKO, n=1) or GTKO pigs transgenic for CD46 (GTKO/CD46, n=5). Monitoring was by liver function tests and coagulation parameters. Pig-specific proteins in the baboon serum/plasma were identified by Western blot. In four baboons, coagulation factors were measured. The results were compared with values from healthy humans, baboons, and pigs. Results. Recipient baboons died or were euthanized after 4 to 7 days after internal bleeding associated with profound thrombocytopenia. However, parameters of liver function, including coagulation, remained in the near-normal range, except for some cholestasis. Western blot demonstrated that pig proteins (albumin, fibrinogen, haptoglobin, and plasminogen) were produced by the liver from day 1. Production of several pig coagulation factors was confirmed. Conclusions. After the Tx of genetically engineered pig livers into baboons (1) many parameters of hepatic function, including coagulation, were normal or near normal; (2) there was evidence for production of pig proteins, including coagulation factors; and (3) these appeared to function adequately in baboons although interspecies compatibility of such proteins remains to be confirmed.

Liver Sinusoidal Endothelial Cells That Endocytose Allogeneic Cells Suppress T Cells with Indirect Allospecificity

A portal venous injection of allogeneic donor cells is known to prolong the survival of subsequently transplanted allografts. In this study, we investigated the role of liver sinusoidal endothelial cells (LSECs) in immunosuppressive effects induced by a portal injection of allogeneic cells on T cells with indirect allospecificity. To eliminate the direct CD4+ T cell response, C57BL/6 (B6) MHC class II-deficient C2tatm1Ccum (C2D) mice were used as donors. After portal injection of irradiated B6 C2D splenocytes into BALB/c mice, the host LSECs that endocytosed the irradiated allogeneic splenocytes showed enhanced expression of MHC class II molecules, CD80, and Fas ligand (FasL). Due to transmigration across the LSECs from BALB/c mice treated with a portal injection of B6 C2D splenocytes, the naive BALB/c CD4+ T cells lost their responsiveness to stimulus of BALB/c splenic APCs that endocytose donor-type B6 C2D alloantigens, while maintaining a normal response to stimulus of BALB/c splenic APCs that endocytose third-party C3H alloantigens. Similar results were not observed for naive BALB/c CD4+ T cells that transmigrated across the LSECs from BALB/c FasL-deficient mice treated with a portal injection of B6 C2D splenocytes. Adaptive transfer of BALB/c LSECs that had endocytosed B6 C2D splenocytes into BALB/c mice via the portal vein prolonged the survival of subsequently transplanted B6 C2D hearts; however, a similar effect was not observed for BALB/c FasL-deficient LSECs. These findings indicate that LSECs that had endocytosed allogeneic splenocytes have immunosuppressive effects on T cells with indirect allospecificity, at least partially via the Fas/FasL pathway.

New concepts of immune modulation in xenotransplantation.

Abstract The shortage of human organs for transplantation has focused research on the possibility of transplanting pig organs into humans. Many factors contribute to the failure of a pig organ graft in a primate. A rapid innate immune response (natural anti-pig antibody, complement activation, and an innate cellular response; e.g., neutrophils, monocytes, macrophages, and natural killer cells) is followed by an adaptive immune response, although T-cell infiltration of the graft has rarely been reported. Other factors (e.g., coagulation dysregulation and inflammation) appear to play a significantly greater role than in allotransplantation. The immune responses to a pig xenograft cannot therefore be controlled simply by suppression of T-cell activity. Before xenotransplantation can be introduced successfully into the clinic, the problems of the innate, coagulopathic, and inflammatory responses will have to be overcome, most likely by the transplantation of organs from genetically engineered pigs. Many of the genetic manipulations aimed at protecting against these responses also reduce the adaptive response. The T-cell and elicited antibody responses can be prevented by the biological and/or pharmacologic agents currently available, in particular, by costimulation blockade-based regimens. The exogenous immunosuppressive regimen may be significantly reduced by the presence of a graft from a pig transgenic for a mutant (human) class II transactivator gene, resulting in down-regulation of swine leukocyte antigen class II expression, or from a pig with “local” vascular endothelial cell expression of an immunosuppressive gene (e.g., CTLA4-Ig). The immunomodulatory efficacy of regulatory T cells or mesenchymal stromal cells has been demonstrated in vitro but not yet in vivo.

The potential of genetically-engineered pigs in providing an alternative source of organs and cells for transplantation.

There is a critical shortage of organs, cells, and corneas from deceased human donors worldwide. There are also shortages of human blood for transfusion. A potential solution to all of these problems is the transplantation of organs, cells, and corneas from a readily available animal species, such as the pig, and the transfusion of red blood cells from pigs into humans. However, to achieve these ends, major immunologic and other barriers have to be overcome. Considerable progress has been made in this respect by the genetic modification of pigs to protect their tissues from the primate immune response and to correct several molecular incompatibilities that exist between pig and primate. These have included knockout of genes responsible for the expression of major antigenic targets for primate natural anti-pig antibodies, insertion of human complement- and coagulation-regulatory transgenes, and knockdown of swine leukocyte antigens that stimulate the primates adaptive immune response. As a result of these manipulations, the administration of novel immunosuppressive agents, and other innovations, pig hearts have now functioned in baboons for 6-8 months, pig islets have maintained normoglycemia in diabetic monkeys for > 1 year, and pig corneas have maintained transparency for several months. Clinical trials of pig islet transplantation are already in progress. Future developments will involve further genetic manipulations of the organ-source pig, with most of the genes that are likely to be beneficial already identified.

NOD/SCID mice engrafted with human peripheral blood lymphocytes can be a model for investigating B cells responding to blood group A carbohydrate determinant

Human antibodies (Abs) against blood group A or B carbohydrate determinant are a major barrier to ABO-incompatible organ transplantation; however, the phenotype and other properties of B cell types responding to A or B carbohydrate epitopes have not been defined. Studies here, which use fluorescein-labeled synthetic A determinant (GalNAcalpha1-3Fucalpha1-2Gal), demonstrate that B cells bearing surface IgM (sIgM) receptors recognizing blood group A carbohydrate determinant are found exclusively in a small B cell subpopulation, i.e. sIgM+ CD11b+ CD5+ B1 cells, in blood group O human peripheral blood mononuclear cells (PBMC). In order to test anti-A Abs producing capacity of the human PBMC, nonobese diabetic (NOD)/severe combined immune-deficient (SCID) mice that have been treated with rabbit anti-asialo GM1 serum to deplete natural killer cells and with 3 Gy of whole body irradiation were engrafted with blood group O or A human PBMC, followed by sensitization of human blood group A red blood cells. Anti-A-specific human Abs were detected in the sera of the mice that received blood group O human PBMC, whereas they were not detected in the sera of the mice that received blood group A human PBMC, indicating profound tolerance of auto-reactive B cells. The human PBMC-NOD/SCID chimera developed by injection of blood group O human PBMC might be a useful in vivo model to test effects of immunosuppressants or other approaches on human B cells that respond to blood group A antigens.

Atorvastatin down-regulates the primate cellular response to porcine aortic endothelial cells in vitro.

Using mixed lymphocyte reaction (MLR), the effect of atorvastatin on proliferation of human and baboon peripheral blood mononuclear cells (PBMCs) and human CD4+ T cells in response to wild-type (WT) and &agr;-1,3-galactosyltransferase gene-knockout (GTKO) porcine aortic endothelial cells (pAECs) was investigated. swine leukocyte antigen class-II (SLA II) expression on pAEC before and after porcine interferon gamma (pIFN-&ggr;) stimulation, and the effect of atorvastatin on this expression was assessed. Added to the MLR, atorvastatin reduced (i) the human PBMC response to unstimulated (P<0.05) and (ii) the human and baboon PBMC responses to stimulated (P<0.05) WT and GTKO pAEC. Atorvastatin treatment of human PBMC before MLR reduced their response to stimulated WT (P<0.05) and GTKO (P<0.05) pAEC. Stimulation of pAEC with pIFN-&ggr; increased SLA II expression 20- to 60-fold, which was down-regulated by atorvastatin. Atorvastatin treatment of stimulated pAEC before MLR reduced proliferation of human PBMC (P<0.05) and CD4+ T cells (P<0.05). Atorvastatin down-regulates the primate cellular xenoresponse, possibly through its antiproliferative effect on PBMCs and the reduction of SLA II on pAECs.

Genetically engineered pig red blood cells for clinical transfusion: initial in vitro studies.

BACKGROUND: Pigs are a potential source of red blood cells (RBCs) and could resolve the shortage of human blood for transfusion. This study investigated in vitro the compatibility of genetically engineered pig RBCs (pRBCs) with the human innate immune response.