Genetically engineered pigs and target-specific immunomodulation provide significant graft survival and hope for clinical cardiac xenotransplantation

ObjectivesCardiac transplantation and available mechanical alternatives are the only possible solutions for end-stage cardiac disease. Unfortunately, because of the limited supply of human organs, xenotransplantation may be the ideal method to overcome this shortage. We have recently seen significant prolongation of heterotopic cardiac xenograft survival from 3 to 12 months and beyond.MethodsHearts from genetically engineered piglets that were alpha 1-3 galactosidase transferase knockout and expressed the human complement regulatory gene, CD46 (groups A-C), and the human thrombomodulin gene (group D) were heterotropically transplanted in baboons treated with antithymocyte globulin, cobra venom factor, anti-CD20 antibody, and costimulation blockade (anti-CD154 antibody [clone 5C8]) in group A, anti-CD40 antibody (clone 3A8; 20 mg/kg) in group B, clone 2C10R4 (25 mg/kg) in group C, or clone 2C10R4 (50 mg/kg) in group D, along with conventional nonspecific immunosuppressive agents.ResultsGroup A grafts (n = 8) survived for an average of 70 days, with the longest survival of 236 days. Some animals in this group (n = 3) developed microvascular thrombosis due to platelet activation and consumption, which resulted in spontaneous hemorrhage. The median survival time was 21 days in group B (n = 3), 80 days in group C (n = 6), and more than 200 days in group D (n = 5). Three grafts in group D are still contracting well, with the longest ongoing graft survival surpassing the 1-year mark.ConclusionsGenetically engineered pig hearts (GTKOhTg.hCD46.hTBM) with modified targeted immunosuppression (anti-CD40 monoclonal antibody) achieved long-term cardiac xenograft survival. This potentially paves the way for clinical xenotransplantation if similar survival can be reproduced in an orthotopic transplantation model

Surface modification of pig endothelial cells with a branched heparin conjugate improves their compatibility with human blood

Corline Heparin Conjugate (CHC), a compound of multiple unfractionated heparin chains, coats cells with a glycocalyx-like layer and may inhibit (xeno) transplant-associated activation of the plasma cascade systems. Here, we investigated the use of CHC to protect WT and genetically modified (GTKO. hCD46. hTBM) pig aortic endothelial cells (PAEC) in two pig-to-human in vitro xenotransplantation settings. Model 1: incubation of untreated or hTNFa-treated PAEC with 10% human plasma induced complement C3b/c and C5b-9 deposition, cellular activation and coagulation activation in WT and GTKO. hCD46. hTBM PAEC. Coating of untreated or hTNFa-treated PAEC with CHC (100 mu g/ml) protected against human plasma-induced endothelial activation and damage. Model 2: PAEC were grown on microcarrier beads, coated with CHC, and incubated with non-anticoagulated whole human blood. Genetically modified PAEC significantly prolonged clotting time of human blood (115.0 +/- 16.1 min, p < 0.001) compared to WT PAEC (34.0 +/- 8.2 min). Surface CHC significantly improved the human blood compatibility of PAEC, as shown by increased clotting time (WT: 84.3 +/- 11.3 min, p < 0.001;GTKO. hCD46. hTBM: 146.2 +/- 20.4 min, p < 0.05) and reduced platelet adhesion, complement activation, coagulation activation and inhibition of fibrinolysis. The combination of CHC coating and genetic modification provided the greatest compatibility with human blood, suggesting that pre-transplant perfusion of genetically modified porcine organs with CHC may benefit post-transplant xenograft function

Chimeric 2C10R4 anti-CD40 antibody therapy is critical for long-term survival of GTKO.hCD46.hTBM pig-to-primate cardiac xenograft

Preventing xenograft rejection is one of the greatest challenges of transplantation medicine. Here, we describe a reproducible, long-term survival of cardiac xenografts from alpha 1-3 galactosyltransferase gene knockout pigs, which express human complement regulatory protein CD46 and human thrombomodulin (GTKO.hCD46.hTBM), that were transplanted into baboons. Our immunomodulatory drug regimen includes induction with anti-thymocyte globulin and alpha CD20 antibody, followed by maintenance with mycophenolate mofetil and an intensively dosed alpha CD40 (2C10R4) antibody. Median (298 days) and longest (945 days) graft survival in five consecutive recipients using this regimen is significantly prolonged over our recently established survival benchmarks (180 and 500 days, respectively). Remarkably, the reduction of aCD40 antibody dose on day 100 or after 1 year resulted in recrudescence of anti-pig antibody and graft failure. In conclusion, genetic modifications (GTKO.hCD46.hTBM) combined with the treatment regimen tested here consistently prevent humoral rejection and systemic coagulation pathway dysregulation, sustaining long-term cardiac xenograft survival beyond 900 days

Incidence and cytotoxicity of antibodies in cynomolgus monkeys directed to nonGal antigens, and their relevance for experimental models

The recent availability of pigs homozygous for alpha1,3-galactosyltransferase gene-knockout (GT-KO) has enabled the study of incidence and cytotoxicity of antibodies of cynomolgus monkeys directed to antigens other than Galalpha1,3Gal (Gal), termed nonGal antigens. To this aim, sera from 21 cynomolgus monkeys were tested by flow cytometry for binding of IgM and IgG to peripheral blood mononuclear cells (PBMC) from wild-type (WT) and GT-KO pigs. The sera were also tested for complement-dependent cytotoxicity to WT and GT-KO PBMC. Anti-WT IgM and IgG were found in 100% and 95%, respectively, and anti-GT-KO IgM and IgG in 76% and 66%, respectively, in the sera of the monkeys tested (P &lt; 0.01). Whereas 100% of sera were cytotoxic to WT PBMC, only 76% were cytotoxic to GT-KO PBMC, and the level of cytotoxicity was significantly less (P &lt; 0.01). Although the incidence and cytotoxicity of antibodies in monkey sera to GT-KO pig PBMC are significantly less than to WT PBMC, approximately three-quarters of the monkeys tested had cytotoxic antibodies to GT-KO PBMC. This incidence of cytotoxicity is significantly higher than that found in baboons and humans, suggesting the baboon may be an easier and possibly more suitable model to study antibody-mediated rejection of transplanted GT-KO pig organs and cells.</p

Inhibition of DNA methyltransferase 1 expression in bovine fibroblast cells used for nuclear transfer

The aberrant expression of DNA methyltransferase 1 (DNMT1) in cloned embryos has been implicated as a possible factor in the improper donor genome reprogramming during nuclear transfer. DNMT1 is responsible for maintaining DNA methylation and the subsequent differentiation status of somatic cells. The presence of DNMT1 transcript in the donor cell may contribute to perpetuation of the highly methylated status of the somatic nuclei in cloned embryos. The objective of the present study was to determine the methylation pattern of cloned embryos reconstructed with cells treated with DNMT1-specific small interfering RNA (siRNA). Bovine fibroblasts were transfected with a DNMT1-specific siRNA under optimised conditions. The expression patterns of DNMT1 were characterised by Q-PCR using the CT method. The level of DNMT1 was successfully decreased in bovine fibroblast cells using a DNMT1-specific siRNA. Additionally, reduction in the expression of DNMT1 mRNA and DNMT1 protein led to a moderate hypomethylation pattern in the siRNA-treated cells. The use of siRNA-treated cells as donor nuclei during nuclear transplantation induced a reduction in methylation levels compared with controls but did not reduce methylation levels to that of IVF embryos. Further studies are required to determine if this level of reduced methylation is sufficient to improve subsequent development. © 2009 CSIRO

Initial In Vitro Investigation of the Human Immune Response to Corneal Cells from Genetically Engineered Pigs

PURPOSE. To compare the in vitro human humoral and cellular immune responses to wild-type (WT) pig corneal endothelial cells (pCECs) with those to pig aortic endothelial cells (pAECs). These responses were further compared with CECs from genetically engineered pigs (␣1,3-galactosyltransferase gene-knockout [GTKO] pigs and pigs expressing a human complement-regulatory protein [CD46]) and human donors. METHODS. The expression of Gal␣1,3Gal (Gal), swine leukocyte antigen (SLA) class I and class II on pCECs and pAECs, with or without activation by porcine IFN-␥, was tested by flow cytometry. Pooled human serum was used to measure IgM/IgG binding to and complement-dependent cytotoxicity (CDC) to cells from WT, GTKO, and GTKO/CD46 pigs. The human CD4 ϩ T-cell response to cells from WT, GTKO, GTKO/CD46 pigs and human was tested by mixed lymphocyte reaction (MLR). RESULTS. There was a lower level of expression of the Gal antigen and of SLA class I and II on the WT pCECs than on the WT pAECs, resulting in less antibody binding and reduced human CD4 ϩ T-cell proliferation. However, lysis of the WT pCECs was equivalent to that of the pAECs, suggesting more susceptibility to injury. There were significantly weaker humoral and cellular responses to the pCECs from GTKO/CD46 pigs compared with the WT pCECs, although the cellular response to the GTKO/CD46 pCECs was greater than to the human CECs. CONCLUSIONS. These data provide the first report of in vitro investigations of CECs from genetically engineered pigs and suggest that pig corneas may provide an acceptable alternative to human corneas for clinical transplantation. (Invest Ophthalmol Vis Sci. 2011;52:5278 -5286

Chimeric 2C10R4 anti-CD40 antibody therapy is critical for long-term survival of GTKO.hCD46.hTBM pig-to-primate cardiac xenograft

Preventing xenograft rejection is one of the greatest challenges of transplantation medicine. Here, we describe a reproducible, long-term survival of cardiac xenografts from alpha 1-3 galactosyltransferase gene knockout pigs, which express human complement regulatory protein CD46 and human thrombomodulin (GTKO.hCD46.hTBM), that were transplanted into baboons. Our immunomodulatory drug regimen includes induction with anti-thymocyte globulin and alpha CD20 antibody, followed by maintenance with mycophenolate mofetil and an intensively dosed alpha CD40 (2C10R4) antibody. Median (298 days) and longest (945 days) graft survival in five consecutive recipients using this regimen is significantly prolonged over our recently established survival benchmarks (180 and 500 days, respectively). Remarkably, the reduction of aCD40 antibody dose on day 100 or after 1 year resulted in recrudescence of anti-pig antibody and graft failure. In conclusion, genetic modifications (GTKO.hCD46.hTBM) combined with the treatment regimen tested here consistently prevent humoral rejection and systemic coagulation pathway dysregulation, sustaining long-term cardiac xenograft survival beyond 900 days

Multiple genetically modified GTKO/hCD46/HLA-E/hβ2−mg porcine hearts are protected from complement activation and natural killer cell infiltration during ex vivo perfusion with human blood

Background In pig‐to‐human xenotransplantation, early cellular rejection reactions are mediated by natural killer cells (NK cells). Human NK cells are inhibited by HLA‐E via CD94/NKG2A receptors. To protect porcine grafts against human NK cell responses, transgenic GTKO pigs expressing hCD46 and HLA‐E have been generated. The aim of this study was to test the effect of this genetic modification on xenogeneic, and in particular human NK cell response, using an ex vivo perfusion model of pig hearts with human blood. Methods Cardiopleged and explanted genetically modified (gm) pig hearts (GTKO/hCD46/HLA‐E/hβ2‐microglobulin) and wild‐type (wt) controls (n = 6 each) were reperfused and tested in an 8 hours ex vivo perfusion system using freshly drawn human blood. Cardiac function was evaluated during a 165‐minute period in working heart mode. Myocardial damage, antibody deposition, complement activation, and coagulation parameters were evaluated histologically at the end of perfusion. The number of NK cells in the perfusate was determined by flow cytometry at baseline and at 8 hours; tissue infiltration by NK cells was quantified by immunofluorescence microscopy using NKp46 staining of frozen sections. Results Deposition of IgG (1.2 ± 1 × 107 vs 8.8 ± 2.9 × 106; P .01) was lower in gm than wt hearts. NK cell percentages of leukocytes in the perfusate decreased from 0.94 ± 0.77% to 0.21 ± 0.25% (P = .04) during xenoperfusion of wt hearts. In contrast, the ratio of NK cells did not decrease significantly in the gm hearts. In this group, NK cell myocardial infiltration after 480 minutes of perfusion was lower than in wt organs (2.5 ± 3.7 × 104/mm3 vs 1.3 ± 1.4 × 105/mm3; P = .0001). The function of gm hearts was better preserved compared to wt organs, as demonstrated by higher cardiac index during the first 2 hours of ex vivo perfusion. Conclusion GTKO, hCD46, and HLA‐E expression in porcine hearts reduced complement deposition, complement dependent injury, and myocardial NK cell infiltration during perfusion with human blood. This tested combination of genetic modifications may minimize damage from acute human‐anti‐pig rejection reactions and improve myocardial function after xenotransplantation