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The article discusses the historic progress in xenotransplantation, specifically the successful transplantation of genetically-edited pig kidneys into living recipients. The transplantation of genetically-edited porcine hearts and kidneys into gravely ill patients has been performed at the University of Maryland and Massachusetts General Hospital, respectively. These transplants are considered major milestones in advancing clinical xenotransplantation and are based on decades of preclinical research. Other centers, such as NYU Langone Medical Center, have also made advancements in xenotransplantation, including the dual transplant of a device and thymo-kidney in a living recipient. These efforts aim to provide more readily available organs to patients and depend on the collaboration of large multispecialty teams and industrial partners. The article acknowledges the courage and support of the recipients and their families in advancing the field of xenotransplantation. [Extracted from the article]

We report orthotopic (life‐supporting) survival of genetically engineered porcine cardiac xenografts (with six gene modifications) for almost 9 months in baboon recipients. This work builds on our previously reported heterotopic cardiac xenograft (three gene modifications) survival up to 945 days with an anti‐CD40 monoclonal antibody‐based immunosuppression. In this current study, life‐supporting xenografts containing multiple human complement regulatory, thromboregulatory, and anti‐inflammatory proteins, in addition to growth hormone receptor knockout (KO) and carbohydrate antigen KOs, were transplanted in the baboons. Selective "multi‐gene" xenografts demonstrate survival greater than 8 months without the requirement of adjunctive medications and without evidence of abnormal xenograft thickness or rejection. These data demonstrate that selective "multi‐gene" modifications improve cardiac xenograft survival significantly and may be foundational for paving the way to bridge transplantation in humans. [ABSTRACT FROM AUTHOR]

Background: Xenotransplantation has made tremendous progress over the last decade. Methods: We discuss kidney and heart xenotransplantation, which are nearing initial clinical trials. Results: Life sustaining genetically modified kidney xenografts can now last for approximately 500 days and orthotopic heart xenografts for 200 days in non‐human primates. Anti‐swine specific antibody screening, preemptive desensitization protocols, complement inhibition and targeted immunosuppression are currently being adapted to xenotransplantation with the hope to achieve better control of antibody‐mediated rejection (AMR) and improve xenograft longevity. These newest advances could probably facilitate future clinical trials, a significant step for the medical community, given that dialysis remains difficult for many patients and can have prohibitive costs. Performing a successful pig‐to‐human clinical kidney xenograft, that could last for more than a year after transplant, seems feasible but it still has significant potential hurdles to overcome. The risk/benefit balance is progressively reaching an acceptable equilibrium for future human recipients, e.g. those with a life expectancy inferior to two years. The ultimate question at this stage would be to determine if a "proof of concept" in humans is desirable, or whether further experimental/pre‐clinical advances are still needed to demonstrate longer xenograft survival in non‐human primates. Conclusion: In this review, we discuss the most recent advances in kidney and heart xenotransplantation, with a focus on the prevention and treatment of AMR and on the recipient's selection, two aspects that will likely be the major points of discussion in the first pig organ xenotransplantation clinical trials. [ABSTRACT FROM AUTHOR]

Partial heart transplantation is a new type of transplant that delivers growing heart valve replacements for babies. Partial heart transplantation differs from orthotopic heart transplantation because only the part of the heart containing the heart valve is transplanted. It also differs from homograft valve replacement because viability of the graft is preserved by tissue matching, minimizing donor ischemia times, and recipient immunosuppression. This preserves partial heart transplant viability and allows the grafts to fulfill biological functions such as growth and self‐repair. These advantages over conventional heart valve prostheses are balanced by similar disadvantages as other organ transplants, most importantly limitations in donor graft availability. Prodigious progress in xenotransplantation promises to solve this problem by providing an unlimited source of donor grafts. In order to study partial heart xenotransplantation, a suitable large animal model is important. Here we describe our research protocol for partial heart xenotransplantation in nonhuman primates. [ABSTRACT FROM AUTHOR]

We have been testing genetically engineered (GE) pig hearts and optimizing immunosuppression (IS) in non‐human primates (NHPs) since 2005. We demonstrate how we translated this preclinical investigation into a US Food and Drug Administration (FDA)‐approved clinical cardiac xenotransplantation. First, genetically engineered (GE) pig hearts were transplanted into the abdomen of NHP along with IS, which included anti‐CD20 and anti‐CD40‐based co‐stimulation blockade antibodies. We reported 945 days of survival of three gene GE pig hearts in NHPs. Building on this proof‐of‐concept, we tested 3–10 gene‐modified GE pig hearts (in order to improve the immunocompatibility of the xenograft further) in a life‐supporting orthotopic model, but had limited success due to perioperative cardiac xenograft dysfunction (PCXD). With novel non‐ischemic continuous perfusion preservation (NICP), using the XVIVO Heart solution (XHS), life‐supporting survival was extended to 9 months. We approached the FDA under an application for "Expanded Access" (EA), to transplant a GE pig heart in a patient with end‐stage non‐ischemic cardiomyopathy. He was without other therapeutic options and dependent on VA‐ECMO. A team of FDA reviewers reviewed our preclinical research experience and data and allowed us to proceed. This clinical cardiac xenotransplantation was performed, and the patient survived for 60 days, demonstrating the translational preclinical investigation of cardiac xenotransplantation from bench to bedside. The ultimate etiology of graft failure is currently a topic of investigation and lessons learned will progress the field forward. [ABSTRACT FROM AUTHOR]

Post‐transplantation cardiac xenograft growth in an orthotopic pig to baboon model is a life‐limiting phenomenon that is poorly understood. Possible causes of growth include both intrinsic and extrinsic etiologies. Extrinsic causes are thought to be attributed to maladaptive hypertrophy as a result of increased mean arterial pressure experienced by the cardiac xenograft after transplantation. Intrinsic causes are thought to be a result of discordant growth between pig xenografts and recipients. This results in intrinsic xenograft growth that parallels the donor and continues in a recipient in which growth is relatively minimal, controlled in part by the growth hormone receptor, IGF‐1 axis. Recently, Zaman, et al. published a study titled, "Selective loss of resident macrophage‐derived insulin‐like growth factor‐1 abolishes adaptive cardiac growth to stress," in Immunity, Volume 54; Issue 9, pp. 2057–2071. They demonstrated that insulin growth factor‐secreting resident macrophages that sense hypertensive stress are a mechanistic link to hypertension and maladaptive hypertrophy in the setting of hypertension. While notable in its own right, we comment on how this work may shed light on a new underlying mechanism for the use of growth hormone receptor knockout (GHRKO) pig donors and its role in addressing post‐transplantation xenograft growth. We hypothesize that GHRKO pig donors contain syngeneic resident cardiac macrophages that abrogate IGF‐1 mediated maladaptive hypertrophy from hypertension. Futures studies in post‐transplantation cardiac xenotransplantation growth should examine this mechanism as a potential contributor. [ABSTRACT FROM AUTHOR]

Abstract: The field of cardiac xenotransplantation has entered an exciting era due to recent advances in the field. Although several hurdles remain, the use of rapidly evolving transgenic technology has the potential to address current allogeneic donor pool constraints and mechanical circulatory system device limitations. The success of xenotransplantation will undoubtedly be dependent on specific patient selection criteria. Defining these particular indications for xenotransplantation is important as we approach the possibility of clinical applications. [ABSTRACT FROM AUTHOR]

Abstract: Background: CD4+CD25HiFoxP3+ T (Treg) cells are a small subset of CD4+ T cells that have been shown to exhibit immunoregulatory function. Although the absolute number of Treg cells in peripheral blood lymphocytes (PBL) is very small, they play an important role in suppressing immune reactivity. Several studies have demonstrated that the number of Treg cells, rather than their intrinsic suppressive capacity, may contribute to determining the long‐term fate of transplanted grafts. In this study, we analyzed Treg cells in PBL of long‐term baboon recipients who have received genetically modified cardiac xenografts from pig donors. Methods: Heterotopic cardiac xenotransplantation was performed on baboons using hearts obtained from GTKO.hCD46 (n = 8) and GTKO.hCD46.TBM (n = 5) genetically modified pigs. Modified immunosuppression regimen included antithymocyte globulin (ATG), anti‐CD20, mycophenolate mofetil (MMF), cobra venom factor (CVF), and costimulation blockade (anti‐CD154/anti‐CD40 monoclonal antibody). FACS analysis was performed on PBLs labeled with anti‐human CD4, CD25, and FoxP3 monoclonal antibodies (mAb) to analyze the percentage of Treg cells in six baboons that survived longer than 2 months (range: 42‐945 days) after receiving a pig cardiac xenograft. Results: Total WBC count was low due to immunosuppression in baboons who received cardiac xenograft from GTKO.hCD46 and GTKO.hCD46.hTBM donor pigs. However, absolute numbers of CD4+CD25HiFoxP3 Treg cells in PBLs of long‐term xenograft cardiac xenograft surviving baboon recipients were found to be increased (15.13 ± 1.50 vs 7.38 ± 2.92; P < .018) as compared to naïve or pre‐transplant baboons. Xenograft rejection in these animals was correlated with decreased numbers of regulatory T cells. Conclusion: Our results suggest that regulatory T (Treg) cells may contribute to preventing or delaying xenograft rejection by controlling the activation and expansion of donor‐reactive T cells, thereby masking the antidonor immune response, leading to long‐term survival of cardiac xenografts. [ABSTRACT FROM AUTHOR]

Background Innovations in transgenic technology have facilitated improved xenograft survival. Additional gene expression appears to be necessary to overcome the remaining immune and biologic incompatibilities. We report for the first time the novel use of six-gene modifications within a pig-to-baboon cardiac xenotransplantation model. Methods Baboons (8-15 kg) underwent heterotopic cardiac transplantation using xenografts obtained from genetically engineered pigs. Along with previously described modifications ( GTKO, hCD46), additional expression of human transgenes for thromboregulation (endothelial protein C receptor, tissue factor pathway inhibitor, thrombomodulin), complement inhibition (decay accelerating factor), and cellular immune suppression ( hCD39, hCD47) was used. Immunosuppression consisted of targeted T-cell and B-cell depletion and conventional anti-rejection agents. Results Heterotopic cardiac transplantations were performed without complication. Flow cytometry and immunohistochemistry on donor biopsies confirmed transgenic phenotype. In contrast to the prior three-gene generation, significant coagulopathy or consumptive thrombocytopenia has not been observed in the six-gene cohort. As a result, these recipients have experienced decreased bleeding-related complications. Pro-inflammatory responses also appear to be mitigated based on cytokine analysis. Baboons survived the critical 30-day post-operative period when mortality has historically been highest, with no evidence of graft rejection. Conclusions The inclusion of additional human genes in genetically engineered pigs appears to confer superior xenograft outcomes. Introduction of these genes has not been associated with adverse outcomes. This multifactorial approach to genetic engineering furthers the prospect of long-term cardiac xenograft survival and subsequent clinical application. [ABSTRACT FROM AUTHOR]

Information about several papers discussed at the Joint U.S. Food and Drug Administration (FDA)-International Xenotransplantation Association (IXA) Symposium held in Baltimore, Maryland on September 20, 2017 is presented. Topics include scientific advances in xenotransplantation, infection and risk-benefit of xenotransplantation, and regulatory considerations of xenotransplantation products. The symposium featured several speakers including David Cooper, Jay Fishman, and Judith Arcidiacono.

We describe the incidence of early graft failure ( EGF, defined as loss of function from any cause within 3 days after transplant) in a large cohort of Gal TKO pig organs transplanted into baboons in three centers, and the effect of additional expression of a human complement pathway-regulatory protein, CD46 or CD55 (Gal TKO. hCPRP). Baboon recipients of life-supporting Gal TKO kidney (n = 7) or heterotopic heart (n = 14) grafts received either no immunosuppression (n = 4), or one of several partial or full immunosuppressive regimens (n = 17). Fourteen additional baboons received a Gal TKO. hCPRP kidney (n = 5) or heart (n = 9) and similar treatment regimens. Immunologic, pathologic, and coagulation parameters were measured at frequent intervals. EGF of Gal TKO organs occurred in 9/21 baboons (43%). hCPRP expression reduced the Gal TKO EGF incidence to 7% (1/14; P < 0.01 vs. Gal TKO alone). At 30 mins, complement deposits were more intense in organs in which EGF developed (P < 0.005). The intensity of peri-transplant platelet activation (as β-thromboglobulin release) correlated with EGF, as did the cumulative coagulation score (P < 0.01). We conclude that (i) the transgenic expression of a hCPRP on the vascular endothelium of a Gal TKO pig reduces the incidence of EGF and reduces complement deposition, (ii) complement deposition and platelet activation correlate with early Gal TKO organ failure, and (iii) the expression of a hCPRP reduces EGF but does not prevent systemic coagulation activation. Additional strategies will be required to control coagulation activation. [ABSTRACT FROM AUTHOR]

The article discusses the third World Health Organization (WHO) Global conference on regulatory requirements for Xenotransplantation clinical trials that was held in Changsha, China on 12–14 December, 2018. It mentions recent advances in the development of technologies for solid organ xenotransplantation; and also mentions Dr. Megan Sykes reviewed the current technologies and studies in the development of tolerance and use of regulatory T cells.

A combination of genetic manipulations of donor organs and target‐specific immunosuppression is instrumental in achieving long‐term cardiac xenograft survival. Recently, results from our preclinical pig‐to‐baboon heterotopic cardiac xenotransplantation model suggest that a three‐pronged approach is successful in extending xenograft survival: (a) α‐1,3‐galactosyl transferase (Gal) gene knockout in donor pigs (GTKO) to prevent Gal‐specific antibody‐mediated rejection; (b) transgenic expression of human complement regulatory proteins (hCRP; hCD46) and human thromboregulatory protein thrombomodulin (hTBM) to avoid complement activation and coagulation dysregulation; and (c) effective induction and maintenance of immunomodulation, particularly through co‐stimulation blockade of CD40‐CD40L pathways with anti‐CD40 (2C10R4) monoclonal antibody (mAb). Using this combination of manipulations, we reported significant improvement in cardiac xenograft survival. In this study, we are reporting the survival of cardiac xenotransplantation recipients (n = 3) receiving xenografts from pigs without the expression of hTBM (GTKO.CD46). We observed that all grafts underwent rejection at an early time point (median 70 days) despite utilization of our previously reported successful immunosuppression regimen and effective control of non‐Gal antibody response. These results support our hypothesis that transgenic expression of human thrombomodulin in donor pigs confers an independent protective effect for xenograft survival in the setting of a co‐stimulation blockade‐based immunomodulatory regimen. [ABSTRACT FROM AUTHOR]