Ethical and legislative advances in xenotransplantation for clinical translation: focusing on cardiac, kidney and islet cell xenotransplantation

In this state-of-the-art review we detail the journey of xenotransplantation from its infancy, detailing one of the first published cases and the subsequent journey the field took in its inception and development. With a focus on the science, technological advances, precautions required along with the potential limitations in application, the ethics, guidance's, and legislative advances that are required to reach the safe and efficacious clinical application of xenotransplantation. Along with a view over the past several decades with the overall significant advancements in pre-clinical study outcomes particularly in islet, kidney, and heart xenotransplantation, to ultimately reach the pinnacle of successful clinical heart and kidney xenotransplants. It outlines the importance for the appropriate guidance's required to have been developed by experts, scientists, clinicians, and other players who helped develop the field over the past decades. It also touches upon patient advocacy along with perspectives and expectations of patients, along with public opinion and media influence on the understanding and perception of xenotransplantation. It discusses the legislative environment in different jurisdictions which are reviewed in line with current clinical practices. All of which are ultimately based upon the guidance's developed from a strong long-term collaboration between the International Xenotransplantation Association, the World Health Organisation and The Transplantation Society; each having constantly undertaken consultation and outreach to help develop best practice for clinical xenotransplantation application. These clearly helped forge the legislative frameworks required along with harmonization and standardization of regulations which are detailed here. Also, in relation to the significant advances in the context of initial xeno-kidney trials and the even greater potential for clinical xeno-islet trials to commence we discuss the significant advantages of xenotransplantation and the ultimate benefit to our patients.

Is Salvage of a Kidney Graft Possible as a Result of Hyperacute Rejection Immediately After Kidney Transplantation?

Hyperacute rejection is a rare complication of renal transplantation. It is mainly caused by preformed human leukocyte antigen antibodies and can lead to the loss of the transplanted kidney. Renal transplantation is a highly beneficial treatment for people with end-stage renal disease, greatly improving their quality of life. However, antibody-mediated rejection is a significant challenge for the long-term survival of transplanted kidneys. An 18-year-old male with nephrotic syndrome, who underwent bilateral renal nephrectomy due to severe proteinuria, received a living donor kidney. Pretransplant panel reactive antibodies were low. Cytotoxic T- and B-cell and non-HLA cross-match was negative. The graft became cyanotic and mottled within half an hour of transplantation. Allograft was quickly extracted, and a biopsy showed hyperacute rejection. The patient was treated with plasmapheresis, intravenous immunoglobulin, and eculizumab. The graft was successfully re-implanted after 18 hours. Further treatment included additional sessions of plasmapheresis, intravenous immunoglobulin, eculizumab, T-cell-depleting agent, and immunosuppressive therapy. Serum creatinine became stable, and renal biopsy after one month demonstrated intact parenchyma with no inflammation or fibrosis. This case highlights the critical importance of promptly removing the transplanted kidney and using aggressive immunotherapy to save renal allografts in cases of hyperacute rejection.

Ethics and Theoretical Issues in Kidney Xenotransplantation

Xenotransplantation has seen recent global interest peak as a result of several clinical xenotransplants being performed in decedents and a live cardiac recipient. However, underpinning these latest transplants have been decades of invested scientific research programs that have been developing the ideal donor source animals to avoid the overwhelming hyperacute xenograft rejection seen using nongenetically modified animal organs, tissues, and cells. However, this also needs to be undertaken along with the development of safe and efficacious xenotransplantation technologies, immunosuppression, monitoring, disease screening, patient selection, societal education, and acceptance. Paralleling the advent of such extraordinary transplants have been several decades of establishment of world xenotransplantation authorities such as the International Xenotransplantation Association, and the development of guidance documents and regulations for the assessment of these cutting-edge technologies. Similar to all new technologies there remain outdated concerns and fears of the theoretical potential for transmission of xenozoonosis, ethical concerns, and outdated or appropriately educated societal concerns and religious views of the benefits or risks and issues for xenotransplantation use of organs, tissues, or cells from animals to human beings. Here, we discuss the development of xenotransplantation and the intricate balance in managing the various challenges with which we are faced: in the absolute benefits of xenotransplantation and the dichotomy in balancing the pros and cons of xenotransplantation with social, religious, ethical, scientific, and medical opinions. Ultimately, the benefits are to those patients suffering from the many and various diseases that drive the need for xenotransplantation. The hope is that it will be implemented as soon as possible to help the many millions of patients who can truly benefit.

Liver and Hepatocyte Transplantation: What Can Pigs Contribute?

About one-fifth of the population suffers from liver diseases in China, meaning that liver disorders are prominent causative factors relating to the Chinese mortality rate. For patients with end-stage liver diseases such as hepatocellular carcinoma or acute liver diseases with life-threatening liver dysfunction, allogeneic liver transplantation is the only life-saving treatment. Hepatocyte transplantation is a promising alternative for patients with acute liver failure or those considered high risk for major surgery, particularly for the bridge-to-transplant period. However, the lack of donors has become a serious global problem. The clinical application of porcine xenogeneic livers and hepatocytes remains a potential solution to alleviate the donor shortage. Pig grafts of xenotransplantation play roles in providing liver support in recipients, together with the occurrence of rejection, thrombocytopenia, and blood coagulation dysfunction. In this review, we present an overview of the development, potential therapeutic impact, and remaining barriers in the clinical application of pig liver and hepatocyte xenotransplantation to humans and non-human primates. Donor pigs with optimized genetic modification combinations and highly effective immunosuppressive regimens should be further explored to improve the outcomes of xenogeneic liver and hepatocyte transplantation.

Establishment of a Hyperacute Rejection Model of ABO-Incompatible Renal Transplantation in Nonhuman Primates

The establishment of a hyperacute rejection (HAR) model of ABO-incompatible kidney transplantation (ABOi-KTx) in nonhuman primates is of great significance for the study of the relevant clinical pathophysiological processes and related interventions in ABOi-KTx. In this study, blood group B cynomolgus monkeys were presensitized with synthetic blood group A-antigen conjugated to keyhole limpet hemocyanin (A-KLH) to boost circulating anti-A antibody levels. The serum anti-A antibody levels were measured by flow cytometry using type A human reagent red blood cells (RBCs) or monkey primary renal tubular epithelial cells (RTECs) as target cells. ABOi-KTx was performed in type B monkeys using type A monkeys as donors. After 14 days of A-KLH sensitization, 12 of 16 (75%) type B monkeys had significantly elevated anti-A antibody levels. We found that in order to avoid irregular results in the detection of blood group antibodies by flow cytometry, it was more effective to use RTECs rather than RBCs as target cells. In the absence of presensitization, ABOi-KTx in three monkeys with relatively high levels of natural anti-A antibodies did not produce HAR. However, when four Type B monkeys with significantly increased anti-A antibodies after presensitization were randomly selected as recipients for ABOi-KTx, the allografts in all four monkeys developed HAR with typical pathologic characteristics. Thus, we have successfully established a monkey model of HAR in ABOi-KTx via blood group antigen presensitization, which will be helpful for the further study of rejection, accommodation, and clinical intervention in ABOi-KTx.

Successful kidney transplantation across a positive complement-dependent cytotoxicity crossmatch by using C1q assay-directed, bortezomib-assisted desensitization: A case report

RATIONALE

Human leukocyte antigen (HLA) is the major immunologic barrier in kidney transplantation (KT). Various desensitization protocols to overcome the HLA barrier have increased the opportunity for transplantation in sensitized patients. In addition, technological advances in solid-phase assays have permitted more comprehensive assessment of donor-specific antibodies. Although various desensitization therapies and immunologic techniques have been developed, the final transplantation decision is still based on the classic complement-dependent cytotoxicity (CDC) crossmatch (XM) technique. Some patients who fail to achieve negative XM have lost their transplant opportunities, even after receiving sufficient desensitization therapies.

PATIENT CONCERNS

A 57-year-old male with end-stage renal disease secondary to chronic glomerulonephritis was scheduled to have a second transplant from his son, but CDC XM was positive.

DIAGNOSES

Initial CDC XM (Initial T-AHG 1:32) and flow-cytometry XM were positive. Anti-HLA-B59 donor specific antibody was detected by Luminex single antigen assay.

INTERVENTIONS

Herein, we report a successful case of KT across a positive CDC XM (T-AHG 1:8 at the time of transplantation) by using C1q assay-directed, bortezomib-assisted desensitization. After confirming a negative conversion in the C1q donor-specific antibody, we decided to perform KT accepting a positive AHG-CDC XM of 1:8 at the time of transplantation.

OUTCOMES

The posttransplant course was uneventful and a protocol biopsy at 3 months showed no evidence of rejection. The patient had excellent graft function at 12 months posttransplant.

LESSONS

The results of XM test and solid-phase assay should be interpreted in the context of the individual patient.

Effect of miR-146a and miR-155 on cardiac xenotransplantation

The aim of the present study was to investigate the expression levels of miR-146a and miR-155 in a cardiac xenograft model treated with the immunosuppressant FK506, and to construct lentiviral vectors to further study the roles of miR-146a and miR-155 in cardiac xenotransplantation. Expression levels of miR-146a and miR-155 were examined by quantitative polymerase chain reaction analysis and protein expression of RelA, which is a member of the nuclear factor-κB family, was examined by western blot analysis. Pre-miR-146a and pre-miR-155 fragments were designed and synthesized according to MiRBase and were cloned into the plasmid pCDH1-MCS1-EF1-copGFP. Recombinant plasmids were identified by enzyme digestion and sequencing. Survival time of cardiac grafts in the FK506 treatment group was significantly increased in comparison with the control group (P<0.05). In addition, the histopathological grading results were significantly decreased in the treatment group (P<0.05). A significant decrease in RelA protein expression levels was observed in the treatment group (P<0.05), along with a significant increase in miR-146a expression levels (P<0.05) and a significant decrease in miR-155 expression levels (P<0.05). Digestion and sequencing findings demonstrated that the insertion of miRNA into the plasmid pCDH1-MCS1-EF1-copGFP conformed with the pre-miRNAs, and the lentiviral vectors were concentrated to a titer of 5×10⁷ IFU/ml. These findings demonstrated that FK506 is able to inhibit the rejection effect in a mouse-to-rat cardiac xenotransplantation model. FK506 treatment altered the expression levels of miR-146a and miR-155, indicating that they may have an important role in regulating the immune response to the rejection effect. miR-146a and miR-155 lentiviral vectors were successfully constructed for further experiments both in vitro and in vivo.

Eculizumab reverses the potentially fatal effects of kidney graft reperfusion injury

Half an hour after reperfusion, the kidney, transplanted to the infant from an adult brain dead standard criteria donor, became flabby and acquired blue color. Hyperacute rejection was suspected as a consequence of false negative cross match, and eculizumab was administered with the purpose to treat antibody-mediated injury, with fast and clear effect. The patient's blood was tested for donor-specific antibodies on the next day, and results were negative. We attribute graft damage to reperfusion injury and explain eculizumab's effectiveness to its ability to prevent progression of reperfusion injury.

Sustained function of genetically modified porcine lungs in an ex vivo model of pulmonary xenotransplantation

BACKGROUND

Xenotransplantation could provide a solution to the donor shortage that is currently the major barrier to solid-organ transplantation. The ability to breed pigs with multiple genetic modifications provides a unique opportunity to explore the immunologic challenges of pulmonary xenotransplantation.

METHODS

Explanted lungs from wild-type and 3 groups of genetically modified pigs were studied: (i) α1,3-galactosyltransferase gene knockout (GTKO); (ii) GTKO pigs expressing the human complementary regulatory proteins CD55 and CD59 (GTKO/CD55-59); and (iii) GTKO pigs expressing both CD55-59 and CD39 (GTKO/CD55-59/CD39). The physiologic, immunologic and histologic properties of porcine lungs were evaluated on an ex vivo rig after perfusion with human blood.

RESULTS

Lungs from genetically modified pigs demonstrated stable pulmonary vascular resistance and better oxygenation of the perfusate, and survived longer than wild-type lungs. Physiologic function was inversely correlated with the degree of platelet sequestration into the xenograft. Despite superior physiologic profiles, lungs from genetically modified pigs still showed evidence of intravascular thrombosis and coagulopathy after perfusion with human blood.

CONCLUSIONS

The ability to breed pigs with multiple genetic modifications, and to evaluate lung physiology and histology in real-time on an ex vivo rig, represent significant advances toward better understanding the challenges inherent to pulmonary xenotransplantation.

The kinetics of donor HLA class I-specific antibody absorption following a combined split liver and kidney transplant

Hyperacute rejection of a transplanted liver is rare even when the recipient has circulating donor-specific alloantibodies (DSA). There is also evidence that a transplanted liver may provide immunological protection for other organs transplanted from the same donor. We monitored the kinetics of circulating DSA in a highly sensitized recipient of a combined split liver and kidney transplant and demonstrated a reduction in antibody titres immediately after liver perfusion. The absorption of DSA was not compromised by the smaller liver mass transplanted. DSA titres remained low at 3 months post-transplant, and the recipient did not experience antibody-mediated rejection.

High molecular weight blood group A trisaccharide-polyacrylamide glycoconjugates as synthetic blood group A antigens for anti-A antibody removal devices

Specific immunoadsorption of blood group antibodies by synthetic antigens immobilized on support matrices in the peri-transplantation period provides a promising solution to hyperacute rejection risk following ABO-incompatible transplantation. In this study, we investigated binding interactions between anti-A antibodies and synthetic blood group A trisaccharide conjugated with polyacrylamide of different molecular weights (30 and 1000 kDa). The glycopolymers were equipped with biotin tags and deposited on streptavidin-coated sensor chips. The affinity and kinetics of anti-A antibodies binding to glycoconjugates were studied using surface plasmon resonance (SPR). The high molecular weight conjugate (Atri-PAA(1000)-biotin) enhanced antibody binding capacity by two to three fold compared with the low molecular weight conjugate (Atri-PAA(30)-biotin), whereas varying the carbohydrate content in Atri-PAA(1000)-biotin (20 mol % or 50 mol %) did not affect antibody binding capacity of the glycoconjugate. The obtained results suggest that immunoadsorption devices, especially hollow fiber-based antibody filters which are limited in available surface area for antigen immobilization, may greatly benefit from the new synthetic high molecular weight polyacrylamide glycoconjugates.

Complement insufficiency limits efficacy in a xenograft model of hyperacute rejection for cancer therapy

Hyperacute rejection (HAR) is a rapid immunological response to an organ xenotransplant caused by recognition of endothelial galactose(alpha1,3)galactose (alphaGal) epitopes and complement-mediated cell lysis by host anti-alphaGal antibody ('natural antibody'). The alphaGal epitope is synthesised by a galactosyl transferase ((alpha1,3)GT) which humans lack. Because human cells transduced with (alpha1,3)GT are sensitised to natural antibody/complement-mediated lysis in human serum, delivery of (alpha1,3)GT to tumour vasculature in patients is a potential therapeutic strategy, by mimicking the pathophysiology of organ rejection. We therefore sought to develop an animal model of HAR for cancer therapy. Nude/(alpha1,3)GT knock-out mice allowed the growth of human tumour xenografts and the use of ecotropic retrovirus producer cells to generate expression of alphaGal on tumour vasculature. Lysis of alphaGal-positive murine endothelial cells with rabbit complement in conjunction with murine anti-alphaGal antibody in vitro was used to define the conditions necessary for HAR. However, tumour growth retardation and destruction of alphaGal-positive tumour endothelium were minimal after their administration, despite sera retaining post hoc cytolytic activity with fresh complement. The major limitation of this experimental system, of relevance to other therapeutic approaches, results from the use of a xenograft, in which additional xenoreactivities lead to complement insufficiency. Development of a tractable preclinical model in which to evaluate HAR for cancer therapy requires a syngeneic experimental system.

Efficient production by sperm-mediated gene transfer of human decay accelerating factor (hDAF) transgenic pigs for xenotransplantation

A large number of hDAF transgenic pigs to be used for xenotransplantation research were generated by using sperm-mediated gene transfer (SMGT). The efficiency of transgenesis obtained with SMGT was much greater than with any other method. In the experiments reported, up to 80% of pigs had the transgene integrated into the genome. Most of the pigs carrying the hDAF gene transcribed it in a stable manner (64%). The great majority of pigs that transcribed the gene expressed the protein (83%). The hDAF gene was transmitted to progeny. Expression was stable and found in caveolae as it is in human cells. The expressed gene was functional based on in vitro experiments performed on peripheral blood mononuclear cells. These results show that our SMGT approach to transgenesis provides an efficient procedure for studies involving large animal models.

Evidence for hyperacute rejection of human liver grafts: The case of the canary kidneys

Sequential liver and kidney transplantation from the same donor was performed in 2 patients. The kidney in Patient 1, which was transplanted after the liver, was hyperacutely rejected and removed 6 hours later. The first liver as well as another liver transplanted 3 days later developed widespread hemorrhagic necrosis. Although the cytotoxic crossmatch of preoperative recipient serum with both donors was negative, patchy widespread IgM and C(1q) deposits were found in all 3 organs. In Patient 2, who had a strongly positive cytotoxic crossmatch with his donor, the liver suffered a massive but reversible injury, while the kidney never functioned. Both patients developed a coagulopathy a few minutes after liver revascularization. The kidneys in these cases had served like the canaries which miners once used to detect a hostile environment and their presence made more understandable how an indolent version of hyperacute rejection of the liver can take place.