The long-term survival of baboon-to-monkey kidney and liver xenografts

Current Status of Genetically Engineered Pig to Monkey Kidney Xenotransplantation in Korea

BACKGROUND

In South Korea, pig-to-nonhuman primate trials of solid organs have only been performed recently, and the results are not sufficiently satisfactory to initiate clinical trials. Since November 2011, we have performed 30 kidney pig-to-nonhuman primate xenotransplantations at Konkuk University Hospital.

METHODS

Donor αGal-knockout-based transgenic pigs were obtained from 3 institutes. The knock-in genes were CD39, CD46, CD55, CD73, and thrombomodulin, and 2-4 transgenic modifications with GTKO were done. The recipient animal was the cynomolgus monkey. We used the immunosuppressants anti-CD154, rituximab, anti-thymocyte globulin, tacrolimus, mycophenolate mofetil, and steroids.

RESULTS

The mean survival duration of the recipients was 39 days. Except for a few cases for which survival durations were <2 days because of technical failure, 24 grafts survived for >7 days, with an average survival duration of 50 days. Long-term survival was observed 115 days after the removal of the contralateral kidney, which is currently the longest-recorded graft survival in Korea. We confirmed functioning grafts for the surviving transplanted kidneys after the second-look operation, and no signs of hyperacute rejection were observed.

CONCLUSIONS

Although our survival results are relatively poor, they are the best-recorded results in South Korea, and the ongoing results are improving. With the support of government funds and the volunteering activities of clinical experts, we aim to further improve our experiments and contribute to the commencement of clinical trials of kidney xenotransplantation in Korea.

Current status of xenotransplantation research and the strategies for preventing xenograft rejection

Transplantation is often the last resort for end-stage organ failures, e.g., kidney, liver, heart, lung, and pancreas. The shortage of donor organs is the main limiting factor for successful transplantation in humans. Except living donations, other alternatives are needed, e.g., xenotransplantation of pig organs. However, immune rejection remains the major challenge to overcome in xenotransplantation. There are three different xenogeneic types of rejections, based on the responses and mechanisms involved. It includes hyperacute rejection (HAR), delayed xenograft rejection (DXR) and chronic rejection. DXR, sometimes involves acute humoral xenograft rejection (AHR) and cellular xenograft rejection (CXR), which cannot be strictly distinguished from each other in pathological process. In this review, we comprehensively discussed the mechanism of these immunological rejections and summarized the strategies for preventing them, such as generation of gene knock out donors by different genome editing tools and the use of immunosuppressive regimens. We also addressed organ-specific barriers and challenges needed to pave the way for clinical xenotransplantation. Taken together, this information will benefit the current immunological research in the field of xenotransplantation.

Posttransplant Lymphoproliferative Disorders in Neuronal Xenotransplanted Macaques

Posttransplant lymphoproliferative disorders (PTLDs) are a heterogeneous group of lymphoid proliferations that occur in the setting of depressed T-cell function due to immunosuppressive therapy used following solid organ transplantation, hematopoietic stem cell transplantation, and also xenotransplantation. In the present study, 28 immunosuppressed parkinsonian Macaca fascicularis were intracerebrally injected with wild-type or CTLA4-Ig transgenic porcine xenografts to identify a suitable strategy to enable long-term cell survival, maturation, and differentiation. Nine of 28 (32%) immunosuppressed primates developed masses compatible with PTLD, located mainly in the gastrointestinal tract and/or nasal cavity. The masses were classified as monomorphic PTLD according to the World Health Organization classification. Immunohistochemistry and polymerase chain reaction (PCR) analyses revealed that the PTLDs were associated with macaca lymphocryptovirus as confirmed by double-labeling immunohistochemistry for CD20 and Epstein-Barr nuclear antigen 2 (EBNA-2), where the viral protein was located within the CD20+ neoplastic B cells. In sera from 3 distinct phases of the experimental life of the primates, testing by quantitative PCR revealed a progression of the viral load that paralleled the PTLD progression and no evidence of zoonotic transmission of porcine lymphotropic herpesvirus through xenoneuronal grafts. These data suggest that monitoring the variation of macaca lymphocryptovirus DNA in primates could be used as a possible early diagnostic tool for PTLD progression, allowing preemptive treatment such as immunosuppression therapy reduction.

Causes of intra-abdominal hemorrhage in rhesus monkeys after liver transplantation

AIM: To analyze the causes of abdominal hemorrhage in rhesus monkeys after liver transplantation.

METHODS: Healthy male rhesus monkeys weighing 7.2-11.5 kg were used as recipients, while healthy females or males weighing 5.3-8.1 kg were use as donors. Donor operation was performed quickly by making a big crucial incision in the abdomen. The improved dual-cuff of the portal vein and inferior vena cava was completed except for keeping biliary support tube within the donor liver. Classical orthotopic liver transplantation was performed in recipients.

RESULTS: Classical orthotopic liver transplantation was successful in all 25 rhesus monkeys. Eleven rhesus monkeys suffered from abdominal hemorrhage in the early postoperative stage, and 5 of them died. The distribution of abdominal hemorrhage site was as follows: anastomotic hemorrhage of the inferior vena cava in 5 cases, anastomotic hemorrhage of the portal vein in 5 cases, anastomotic hemorrhage of the superior vena cava in 4 cases, anastomotic hemorrhage of the liver bed in 4 cases, hemorrhage from mechanical injury in 3 cases, subcapsular hemorrhage of the liver in 3 cases, and hemorrhage of the right suprarenal vein and lumbar vein in 2 cases.

CONCLUSION: The most common cause of abdominal hemorrhage in rhesus monkeys after classical orthotopic liver transplantation is anastomotic hemorrhage of the inferior vena cava and portal vein.

Pig liver xenotransplantation as a bridge to allotransplantation: which patients might benefit?

Acute liver failure is a potentially devastating clinical syndrome that, without liver transplantation (Tx), is associated with high mortality. Rapid deterioration in clinical status and a shortage of deceased human organs prohibits liver Tx in many patients. Bridging to liver Tx has been attempted by various approaches, for example, bioartificial liver support, extracorporeal pig liver perfusion, and hepatocyte Tx, but none of these approaches has convincingly improved patient survival. The orthotopic Tx of a genetically engineered pig liver could theoretically provide successful bridging. Immediate availability, perfect metabolic condition, adequate size-match and hepatocyte mass, and freedom from potentially pathogenic microorganisms could be assured. The advantages and disadvantages of bridging by pig liver Tx compared with other approaches are discussed. The selection of patients for an initial clinical trial of pig liver Tx would be similar to that of various prior trials in patients experiencing rapid and severe deterioration in liver function. The ability to give truly informed consent for a pig bridging procedure at the time of listing for liver Tx renders the patient with acute-on-chronic liver failure or primary allograft failure is a preferable candidate for this procedure than a patient who is admitted urgently with acute (fulminant) liver failure in whom consent may not be possible. Although several barriers to successful pig organ xenoTx remain, for example, coagulation dysfunction between pig and primate, if these can be resolved by further genetic engineering of the organ-source pigs, a pig liver may prove life saving to patients dying rapidly of liver failure.

Liver xenografts for the treatment of acute liver failure: clinical and experimental experience and remaining immunologic barriers

A critical element restricting the application of liver transplantation is the shortage of human deceased donor organs. Xenotransplantation using pig organs might be a solution to this shortage. Although the problems that still require resolution include the immunologic barrier, the potential risk of transferring infectious agents with the transplanted organ, and uncertainty about whether the transplanted organ will function satisfactorily in the human environment, recent progress in the genetic manipulation of pigs has led to the prospect that clinical xenografting, at least as a bridge to allotransplantation, may be possible in the foreseeable future. Experience with clinical auxiliary and orthotopic liver xenotransplantation and experimental liver xenotransplantation in nonhuman primate and other large animal models is reviewed, and the remaining immunologic problems are discussed. Evidence suggests that, in patients with hepatic failure, the pig liver may be less susceptible to antibody-mediated injury than other pig organs, such as the heart or kidney. Pig Kupffer cells and other macrophages will recognize and phagocytose primate red blood cells, but this problem should be overcome by pretransplant depletion of macrophages from the organ-source pig. From the evidence currently available, it does not seem unduly optimistic to anticipate that a liver from an alpha1,3-galactosyltransferase gene-knockout pig would survive at least long enough to function as a successful bridge to allotransplantation.

Gal knockout and beyond

Recently, Galalpha1-3Galbeta1-4GlcNAc (Gal) knockout (k/o) pigs have been developed using genetic cloning technologies. This remarkable achievement has generated great enthusiasm in xenotransplantation studies. This review summarizes the current status of nonhuman primate experiments using Gal k/o pig organs. Briefly, when Gal k/o pig organs are transplanted into primates, hyperacute rejection does not occur. Although graft survival has been prolonged up to a few months in some cases, the overall results were not better than those using Gal-positive pig organs with human complement regulatory protein transgenes. Gal k/o pig kidneys rapidly developed rejection which was associated with increased anti-non-Gal antibodies. Although the precise mechanisms of Gal k/o pig organ rejection are not clear, it could result from incomplete deletion of Gal, up-regulation of new antigen (non-Gal antigen) and/or production of non-Gal antibodies. Future work in xenotransplantation should place emphasis on further modification of donors, such as combining human complement regulatory genes with Gal k/o, deleting non-Gal antigens and adding protective/surviving genes or a gene that inhibits coagulation. Induction of donor-specific T- and B-cell tolerance and promotion of accommodation are also warranted.