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Backgruound: Islet transplantation holds promise for treating selected type 1 diabetes mellitus patients, yet the scarcity of human donor organs impedes widespread adoption. Porcine islets, deemed a viable alternative, recently demonstrated successful longterm survival without zoonotic risks in a clinically relevant pig-to-non-human primate islet transplantation model. This success prompted the development of a clinical trial protocol for porcine islet xenotransplantation in humans., Methods: A single-center, open-label clinical trial initiated by the sponsor will assess the safety and efficacy of porcine islet transplantation for diabetes patients at Gachon Hospital. The protocol received approval from the Gachon Hospital Institutional Review Board (IRB) and the Korean Ministry of Food and Drug Safety (MFDS) under the Investigational New Drug (IND) process. Two diabetic patients, experiencing inadequate glycemic control despite intensive insulin treatment and frequent hypoglycemic unawareness, will be enrolled. Participants and their family members will engage in deliberation before xenotransplantation during the screening period. Each patient will receive islets isolated from designated pathogen-free pigs. Immunosuppressants and systemic infection prophylaxis will follow the program schedule. The primary endpoint is to confirm the safety of porcine islets in patients, and the secondary endpoint is to assess whether porcine islets can reduce insulin dose and the frequency of hypoglycemic unawareness., Conclusion: A clinical trial protocol adhering to global consensus guidelines for porcine islet xenotransplantation is presented, facilitating streamlined implementation of comparable human trials worldwide.

Xenotransplantation offers the potential to meet the critical need for heart and lung transplantation presently constrained by the current human donor organ supply. Much was learned over the past decades regarding gene editing to prevent the immune activation and inflammation that cause early organ injury, and strategies for maintenance of immunosuppression to promote longer-term xenograft survival. However, many scientific questions remain regarding further requirements for genetic modification of donor organs, appropriate contexts for xenotransplantation research (including nonhuman primates, recently deceased humans, and living human recipients), and risk of xenozoonotic disease transmission. Related ethical questions include the appropriate selection of clinical trial participants, challenges with obtaining informed consent, animal rights and welfare considerations, and cost. Research involving recently deceased humans has also emerged as a potentially novel way to understand how xeno-organs will impact the human body. Clinical xenotransplantation and research involving decedents also raise ethical questions and will require consensus regarding regulatory oversight and protocol review. These considerations and the related opportunities for xenotransplantation research were discussed in a workshop sponsored by the National Heart, Lung, and Blood Institute, and are summarized in this meeting report., Competing Interests: Declaration of competing interest The authors of this manuscript have conflicts of interest to disclose as described by the American Journal of Transplantation. Kiran K. Khush: recipient of NHLBI research grant on donor heart evaluation for transplantation (R01HL125303). Brendan Parent: recipient of Applebaum Foundation grant to study ethics of xenotransplantation. Karen J. Maschke and Michael Gusmano: recipients of NCATS research grant on ethical translation of xenotransplantation clinical trials (1R01TR003844-0). The views expressed in this manuscript are those of the authors and do not necessarily represent the views of the National Heart, Lung, and Blood Institute; the National Institutes of Health; or the U.S. Department of Health and Human Services., (Copyright © 2024 American Society of Transplantation & American Society of Transplant Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: The xenotransplant clinical trial with human subjects seems to be technically feasible, however, it needs the strict regulatory framework from the domestic as well as the international level to make sure the safety of the human subject and the general public., Methods: The authors reviewed and introduced the current regulations regarding the xenotransplant clinical trial in Korea focusing on the recently stipulated act (Advanced Regenerative Medicine and Biopharmacology Act, ARMBA) and the role of the related government agencies and health institutions., Results and Conclusion: Korea is ready to conduct the xenotransplant clinical trial with human subjects in the current regulatory framework satisfying the requirements of the international guidance. The responsible governmental agencies would collaborate in control the xenotransplant clinical trial under the ARMBA and other related acts and guidance., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Xenogeneic islet transplantation using porcine pancreata has been a promising option for substituting human islet transplantation. Moreover, recent advances in pre-clinical results have put islet xenotransplantation closer to the possibility of clinical application. While preparing for the era of clinical xenotransplantation, developing non-invasive immune monitoring method which could predict the graft fate could benefit the patient. However, there are few reports showing predictive immune parameters associated with the fate of the graft in islet xenotransplantation., Methods: The absolute number and ratio of T-cell subsets have been measured via flow cytometry from the peripheral blood of 16 rhesus monkeys before and after porcine islet xenotransplantation. The correlation between the graft survival and the absolute number or ratio of T cells was retrospectively analyzed., Results: The ratio of CD4 + versus CD8 + T cells was significantly reduced due to CD8 + effector memory cells' increase. Correlation analyses revealed that CD4 + /CD8 + , CD4 + /CD8 + naïve, CD4 + naïve/CD8 + naïve, and CD4 + central memory/CD8 + naïve cell ratios negatively correlated with the duration of graft survival. Conversely, further analyses discovered strong, positive correlation of CD4 + /CD8 + cell ratios within the early graft-rejected monkeys (≤60 days)., Conclusions: This retrospective study demonstrated that CD4 + /CD8 + ratios correlated with graft survival, especially in recipients which rejected the graft in early post-transplantation periods. CD4 + /CD8 + ratios could be used as a surrogate marker to predict the graft fate in pig-to-NHP islet xenotransplantation., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Anti-CD154 monoclonal antibody (mAb) treatment has been known to have potential to induce immune tolerance in organ transplantation. Several studies have suggested the involvement of CD4 + regulatory T cells (T reg s) in xeno-immune tolerance. However, the characteristics of T reg s and the mechanisms of their regulatory functions in islet xenotransplantation have not been clearly defined., Method: Adult porcine islet cells were isolated and purified, and were transplanted under the kidney capsule of diabetic C57BL/6J mice with the administration of 0.5 mg/mouse of anti-CD154 mAb on 0, 1, 3, 5, and 7 days post-transplantation (DPT). The graft survival was monitored by blood glucose level. The islet graft and recipients' cells were analyzed by immunohistochemistry (IHC), flow cytometry, enzyme-linked immunosorbent spot (ELISPOT) assay, and mixed-lymphocyte reaction., Results: Short-term anti-CD154 mAb monotherapy enabled the porcine islet graft to survive indefinitely in diabetic mice (n = 18). Immunohistochemical staining showed significantly higher ratio of CD4 + Foxp3 + T reg s in the peri-graft site, but not in the spleen and kidney-draining lymph node of the recipient mice. Depletion of T reg s evoked graft rejection, and adoptive transfer of T reg s from anti-CD154 mAb-treated recipients provided protection to the graft from rejection. These T reg s showed more potent suppressive capacity than those from the untreated control and were found to be porcine antigen-specific., Conclusions: In this study, we showed that anti-CD154 mAb monotherapy resulted in indefinite porcine islet graft survival in mice. The porcine-specific CD4 + Foxp3 + T reg s in the peri-graft site played the critical role in the protection of islet graft from rejection, which suggests a prospective immunosuppressive strategy for islet xenotransplantation., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Pig-to-nonhuman primate (NHP) islet transplantation has been widely conducted as a preclinical xenotransplantation model prior to human clinical trial. Portal vein thrombosis is one of the complications associated with islet infusion through the portal vein into the liver. Here, we briefly report severe case of ascites formation accompanied by portal vein thrombi after pig-to-NHP islet xenotransplantation in a rhesus monkey. Meticulous prophylactic treatment such as continuous heparin infusion should be implemented to prevent portal vein thrombi in pig-to-NHP islet transplantation models., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: The development of a precise and easy-to-use tool for monitoring islet graft function is important in clarifying the causes of graft loss, identifying appropriate therapy, and ensuring graft survival in the nonhuman primate (NHP) model of porcine islet transplantation (PITx). Glycated albumin (GA) is an indicator of intermediate-term changes in blood glucose control and is useful in clinical diabetes management. The validity of GA for monitoring graft function in NHP recipients of PITx was evaluated using a retrospective analysis of cohort samples., Methods: Data from a total of 23 PITxs performed in 20 recipients (3 were retransplanted) were included in this study. Islet clusters purified from adult wild-type pigs were transplanted via the intraportal route into streptozotocin-induced diabetic rhesus monkeys with immune suppression. Blood samples were obtained once per week from the recipients until they lost insulin-independence. Blood samples were also obtained from 69 non-diabetic monkeys that served as a control group. The levels of GA and albumin in stored plasma aliquots were measured using each enzymatic method, and the GA result was expressed as the percentage of GA level to the total albumin level., Results: The median level of GA in the recipients on the day of PITx (median 18.6%, 95% confidence interval [CI] 16.7%-20.4%) was significantly higher than that of healthy controls (median 9.14%, 95% CI 9.0%-9.3%, P < .0001). However, the level decreased after PITx and remained low or increased depending on the extent of residual graft function. The GA level at a nadir (median 11.6%, 95% CI 10.8%-13.0%) and the time to reach a nadir (median 43 days, 95% CI 21.7-69.3 days) both correlated with the duration of insulin-independence (rho [ρ] = -.605, P = .0028 and ρ = .662, P = .0008, respectively). The GA level strongly correlated with K G , the glucose disappearance rate during intravenous glucose tolerance testing (ρ = -.76, P < .0001). At post-transplant week (PTW) 3 and at PTW 4, the GA levels in recipients with long-term insulin-independence (>90 days) were significantly lower than those with short-term insulin-independence, which revealed the excellent performance for the prediction of long-term insulin-independence that is comparable to that of porcine C-peptide (historic data)., Conclusions: As a surrogate indicator for graft function, serial measurement of GA may provide Supporting Information to that obtained from conventional monitoring techniques of graft function for assessing porcine islet grafts in NHP models., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Islet transplantation is an effective therapy for selected patients with type 1 diabetes with labile glycemic control and hypoglycemic unawareness, but donor organs are limited. Islet xenotransplantation using porcine islets will potentially solve this problem. Although successful proof of concept studies using clinically inapplicable anti-CD154 monoclonal antibody (mAb) in pig-to-non-human primate (NHP) islet xenotransplantation has been demonstrated by several groups worldwide, potentially clinically applicable anti-CD40 (2C10R4) mAb-based studies have not been reported., Methods: Nine streptozotocin (STZ)-induced diabetic rhesus monkeys were transplanted with adult porcine islets isolated from designated pathogen-free (DPF) miniature pigs. They were treated with anti-CD40 mAb-based immunosuppressive regimen and were divided into 3 groups: anti-CD40 only group (n = 2), belatacept group (anti-CD40 mAb+belatacept, n = 2), and tacrolimus group (anti-CD40 mAb+tacrolimus, n = 5). All monkeys received anti-thymocyte globulin (ATG), cobra venom factor (CVF), adalimumab, and sirolimus. Blood glucose levels (BGL) and serum porcine C-peptide concentrations were measured. Humoral and cellular immune responses were assessed by ELISA and ELISPOT, respectively. Liver biopsy and subsequent immunohistochemistry were conducted., Results: All animals restored normoglycemia immediately after porcine islet transplantation and finished the follow-up without any severe adverse effects except for one animal (R092). Most animals maintained their body weight. Median survival, as defined by a serum porcine C-peptide concentration of >0.15 ng/mL, was 31, 27, and 60 days for anti-CD40 only, belatacept, and tacrolimus groups, respectively. Anti-αGal IgG levels in serum and the number of interferon-γ secreting T cells in peripheral blood mononuclear cells did not increase in most animals., Conclusion: These results showed that anti-CD40 mAb combined with tacrolimus was effective in prolonging porcine islet graft survival, but anti-CD40 mAb was not as effective as anti-CD154 mAb in terms of preventing early islet loss., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Pig islet xenotransplantation is a promising alternative to allogeneic transplantation. However, the wide immunologic barrier between pigs and primates limits the long-term survival of the graft. MD-3, a novel monoclonal antibody (mAb) that recognizes a particular epitope of human ICAM-1, can render T cells tolerant to a xenograft by arresting dendritic cell maturation. We report the long-term survival of adult wild-type pig islets and successful retransplantation in nonhuman primates using a protocol comprising induction with MD-3 mAb and maintenance with anti-CD154 mAb and sirolimus., Methods: Eleven rhesus monkeys were assigned to three groups. Group 1 (n = 4) involved treatment with MD-3 induction, short-term (<4 months) administration of anti-CD154 mAb, and maintenance therapy with sirolimus. Group 2 (n = 4) involved treatment with MD-3 induction and long-term maintenance therapy with anti-CD154 mAb and sirolimus. Group 3 (n = 3) involved only maintenance therapy with anti-CD154 mAb and sirolimus. Diabetes was induced in monkeys by streptozotocin, and pig islets (61 000-112 000 IEQ/kg for each transplant; up to 280 000 IEQ/kg per recipient) were infused through the portal vein. The in vivo functional potency of the isolated islets was tested by minimal model transplant in streptozotocin-induced diabetic NOD/SCID mice, and the mean AUC of blood glucose level divided by the number of follow-up days was calculated., Results: The islet grafts survived more than 6 months (between 225 and 727 days) in nine of 12 transplants of MD-3-treated groups 1 and 2, whereas in the absence of MD-3 mAb, survival was <40 days. In three transplants of the MD-3-treated Group 2, functional graft survival was only for 104, 125, and 154 days. In these cases, a retrospective analysis suggested that the relatively short survival duration was associated with the relatively high AUC value in the NOD/SCID bioassay. Notably, when retransplantation was performed in Group 3, blood glucose control was extended up to 956 days, which was supported by MD-3 mAb-based suppression of adaptive immunity. No replication of cytomegalovirus genes was observed., Conclusions: Long-term survival of pig islet xenografts and successful retransplantation were achieved with MD-3 mAb-based immunosuppression regimen in this pig-to-monkey transplantation model. It should be emphasized that these encouraging results were achieved following the transplantation of islets from pigs that had not been genetically modified. Considering that it is possible to further substantially reduce the destruction of grafted islet using genetically modified pig islet, the islet requirement could be reduced and much longer graft survival can be achieved., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Corneal xenotransplantation is an effective solution for the shortage of human donor corneas, and the porcine cornea may be a suitable candidate for the donor cornea because of its optical similarity with humans. However, it is necessary to administer additional immunosuppressants to overcome antigenic differences. We aimed to investigate the feasibility of porcine corneas with anti-CD40 antibody-mediated costimulation blockade in a clinically applicable pig-to-non-human primate corneal xenotransplantation model., Methods: Five Chinese rhesus macaques underwent deep-lamellar corneal transplantation using clinically acceptable sized (7.5 mm diameter) porcine corneal grafts. The anti-CD40 antibody was intravenously administered on a programmed schedule. Graft survival, central corneal thickness, and intraocular pressure were evaluated. Changes in effector and memory T and B cell subsets and anti-αGal and donor-specific antibodies were investigated in the blood, and the changes in complement levels in the aqueous humor and blood were evaluated. Memory cell profiles in the anti-CD40 antibody-treated group were compared with those from the anti-CD154 antibody-treated group or rejected controls presented in our previous report. The changes in anti-αGal, non-αGal, and donor-specific antibodies after 6 months were compared with baseline values., Results: Anti-CD40 antibody-mediated costimulation blockade resulted in the successful survival of xenocorneal grafts (>389, >382, >236, >201, and >61 days), with 80% reaching 6 months of survival. Injection of anti-CD40 antibody considerably reduced the infiltration of inflammatory cells into the grafts and significantly blocked the complement response in the aqueous humor (P=.0159, Mann-Whitney U test). Systemic expansion of central or effector memory T cells was abrogated in the anti-CD40 antibody-treated primates compared with those in the rejected controls (P<.05, Mann-Whitney U test) or those in the anti-CD154 antibody-treated primates (P>.05, Mann-Whitney U test). The levels of anti-αGal, non-αGal, and donor-specific antibodies at 6 months were not significantly increased compared with baseline levels (P>.05, Wilcoxon signed rank test)., Conclusions: An anti-CD40 antibody-mediated blockade appears to be effective immunosuppressive approach for porcine corneal deep-lamellar xenotransplantation in primates., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Several immunosuppression (IS) regimens achieve long-term graft survival in non-human primates (NHPs) after porcine islet transplantation (PITx), but their success rates vary. To understand the mechanism of graft loss, we investigated the relationships between graft survival and humoral or inflammatory responses for maintenance IS in NHPs after PITx., Methods: Islets purified from adult wild-type pigs were intraportally transplanted into streptozotocin-induced diabetic rhesus monkeys. Three monkeys received an IS regimen without anti-CD154 monoclonal antibody (mAb, transplant [Tpl]-control) and 11 received IS with anti-CD154 mAb (Tpl-aCD154). Blood samples were obtained weekly from the recipients until graft function ceased and weekly from three healthy monkeys (non-Tpl-control) for 6 months. Levels of D-dimer, C-reactive protein (CRP), and anti-Galα1,3Gal (Gal) IgG, IgG1, IgG2, and IgM were measured. Liver biopsy sections were immunostained for fibrin, insulin, and human CD31., Results: Tpl-control monkeys had higher time-weighted average levels (levels twavrg ) of Δanti-Gal IgG (Δ, difference from level at day 0) and D-dimer than Tpl-aCD154 or non-Tpl-control. The levels twavrg of Δanti-Gal IgG, IgG1, IgG2, and IgM did not differ between Tpl-aCD154 and non-Tpl-control. The levels twavrg of D-dimer and Δanti-Gal IgG2 negatively correlated with graft survival. Liver biopsy sections revealed many spots of fibrin deposition inside islet grafts that were well vascularized by human CD31-positive cells. Level of D-dimer positively correlated with Δanti-Gal IgG1 in Tpl-control and with Δanti-Gal IgG2 in Tpl-aCD154., Conclusions: Intravascular coagulation, in association with immune responses against xenografts, may partly contribute to loss of islet grafts in NHPs after PITx., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Islet microencapsulation is an attractive strategy for the minimization or avoidance of life-long immunosuppression after transplantation. However, the clinical implementation of this technique is currently limited by incomplete biocompatibility. Thus, the aim of the present study was to demonstrate the improved biocompatibility of rapamycin-containing polyethylene glycol (Rapa-PEG)-coating on alginate microcapsules containing xenogeneic islets. The Rapa-PEG-coating on the alginate layer was observed using scanning electron microscopy (SEM) and the molecular cut-off weight of the microcapsules was approximately 70 kDa. The viabilities of the alginate-encapsulated and Rapa-PEG-coated alginate-encapsulated islets were lower than the viability of the naked islets just after encapsulation, but these the differences diminished over time in culture dishes. Rapa-PEG-coating on the alginate capsules effectively decreased the proliferation of macrophage cells compared to the non-coating and alginate coating of xenogeneic pancreas tissues. Glucose-stimulated insulin secretion did not significantly differ among the groups prior to transplantation. The random blood glucose levels of diabetic mice significantly improved following the transplantation of alginate-encapsulated and Rapa-PEG-coated alginate-encapsulated islets, but there were no significant differences between these two groups. However, there was a significant decrease in the number of microcapsules with fibrotic cell infiltration in the Rapa-PEG-coated alginate microcapsule group compared to the alginate microcapsule group. In conclusion, Rapa-PEG-coating might be an effective technique with which to improve the biocompatibility of microcapsules containing xenogeneic islets. Copyright © 2015 John Wiley & Sons, Ltd., (Copyright © 2015 John Wiley & Sons, Ltd.)

Background: Islet allotransplantation is a promising way to treat some type 1 diabetic (T1D) patients with frequent hypoglycemic unawareness, and islet xenotransplantation is emerging to overcome the problem of donor organ shortage. Our recent study showing reproducible long-term survival of porcine islets in non-human primates (NHPs) allows us to examine whether autologous regulatory T-cell (Treg) infusion at peri-transplantation period would induce transplantation tolerance in xenotransplantation setting., Methods: Two diabetic rhesus monkeys were transplanted with porcine islets from wild-type adult Seoul National University (SNU) miniature pigs with immunosuppression by anti-thymoglobulin (ATG), cobra venom factor, anti-CD154 monoclonal antibody (mAb), and sirolimus. CD4(+) CD25(high) CD127(low) autologous regulatory T cells from the recipients were isolated, ex vivo expanded, and infused at the peri-transplantation period. Blood glucose and porcine C-peptide from the recipients were measured up to 1000 days. Maintenance immunosuppressants including a CD40-CD154 blockade were deliberately discontinued to confirm whether transplantation tolerance was induced by adoptively transferred Tregs., Results: After pig islet transplantation via portal vein, blood glucose levels of diabetic recipients became normalized and maintained over 6 months while in immunosuppressive maintenance with a CD40-CD154 blockade and sirolimus. However, the engrafted pig islets in the long-term period were fully rejected by activated immune cells, particularly T cells, when immunosuppressants were stopped, showing a failure of transplantation tolerance induction by autologous Tregs., Conclusions: Taken together, autologous Tregs infused at the peri-transplantation period failed to induce transplantation tolerance in pig-to-NHP islet xenotransplantation setting., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Recent progress in xenotransplantation of porcine islets to non-human primates (NHPs) gives hope for human clinical trials in the near future. Thus, implementation of an appropriate monitoring method to detect the development of detrimental porcine antigen-specific cellular immune responses is necessary. The enzyme-linked immunospot (ELISpot) assay has been widely used to monitor antigen-specific alloreactive T-cell responses in humans; however, the utility of porcine islet-specific ELISpot assay has not yet been thoroughly evaluated for pig-to-NHPs intraportal islet xenotransplantation., Methods: The optimal ELISpot assay conditions, including the number of responder and stimulator cells and the provision of costimulation, were determined. Then, ELISpot assays were conducted on serial stocks of peripheral blood mononuclear cell (PBMC) samples previously isolated from NHP recipients transplanted with porcine islets. Either splenocytes from donor pigs or pancreatic islets from third-party pigs were used for antigen stimulation. At the same time, the ratio of CD4(+) /CD8(+) T cells and the percentage of CD4(+) FoxP3(+) T cells in the peripheral blood were evaluated. Finally, liver biopsy samples were evaluated to assess the immunopathology of the grafts., Results: The optimal conditions for the ELISpot assay were defined as 2.5 × 10(5) responder cells incubated with 5.0 × 10(5) stimulator cells in 96-well, flat-bottom plates without further costimulation. Using donor splenocytes as stimulators, a serial interferon-gamma (IFN-γ) ELISpot assay with PBMCs from the monkeys with prolonged porcine islet grafts (>180 days) demonstrated that the number of donor antigen-specific IFN-γ-producing cells significantly increased upon overt graft rejection. However, use of third-party porcine islets as stimulators did not reflect graft rejection, suggesting that the use of donor-specific PBMCs, and not tissue (porcine islet)-specific cells, as stimulators could better serve the purpose of this assay in adult porcine islet transplantation. IFN-γ spot number was neither influenced by the peripheral blood CD4(+) /CD8(+) T-cell ratio nor the percentage of CD4(+) FoxP3(+) T cells. Finally, in cases of overt graft rejection, the number of IFN-γ spots and the graft-infiltrating T cells in biopsied liver samples increased simultaneously., Conclusion: Use of PBMCs in a porcine antigen-specific IFN-γ ELISpot assay is a reliable method for monitoring T-cell-mediated rejection in pig-to-NHP islet xenotransplantation., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Islet xenotransplantation represents an attractive solution to overcome the shortage of human islets for use in type 1 diabetes. The wide-scale application of clinical islet xenotransplantation, however, requires that such a procedure takes place in a specifically and tightly regulated environment. With a view to promoting the safe application of clinical islet xenotransplantation, a few years ago the International Xenotransplantation Association (IXA) published a Consensus Statement that outlined the key ethical and regulatory requirements to be satisfied before the initiation of xenotransplantation studies in diabetic patients. This earlier IXA Statement also documented a disparate regulatory landscape among different geographical areas. This situation clearly fell short of the 2004 World Health Assembly Resolution WHA57.18 that urged Member States "to cooperate in the formulation of recommendations and guidelines to harmonize global practices" to ensure the highest ethical and regulatory standards on a global scale. In this new IXA report, IXA members who are active in xenotransplantation research in their respective geographic areas herewith briefly describe changes in the regulatory frameworks that have taken place in the intervening period in the various geographic areas or countries. The key reassuring take-home message of the present report is that many countries have embraced the encouragement of the WHO to harmonize the procedures in a more global scale. Indeed, important regulatory changes have taken place or are in progress in several geographic areas that include Europe, Korea, Japan, and China. Such significant regulatory changes encompass the most diverse facets of the clinical application of xenotransplantation and comprise ethical aspects, source animals and product specifications, study supervision, sample archiving, patient follow-up and even insurance coverage in some legislations. All these measures are expected to provide a better care and protection of recipients of xenotransplants but also a higher safety profile to xenotransplantation procedures with an ultimate net gain in terms of international public health., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

In 2009, the International Xenotransplantation Association (IXA) published a consensus document that provided guidelines and "recommendations" (not regulations) for those contemplating clinical trials of porcine islet transplantation. These guidelines included the IXA's opinion on what constituted "rigorous pre-clinical studies using the most relevant animal models" and were based on "non-human primate testing." We now report our discussion following a careful review of the 2009 guidelines as they relate to pre-clinical testing. In summary, we do not believe there is a need to greatly modify the conclusions and recommendations of the original consensus document. Pre-clinical studies should be sufficiently rigorous to provide optimism that a clinical trial is likely to be safe and has a realistic chance of success, but need not be so demanding that success might only be achieved by very prolonged experimentation, as this would not be in the interests of patients whose quality of life might benefit immensely from a successful islet xenotransplant. We believe these guidelines will be of benefit to both investigators planning a clinical trial and to institutions and regulatory authorities considering a proposal for a clinical trial. In addition, we suggest consideration should be given to establishing an IXA Clinical Trial Advisory Committee that would be available to advise (but not regulate) researchers considering initiating a clinical trial of xenotransplantation., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

To develop an international consensus regarding the appropriate conditions for undertaking clinical trials in xenocorneal transplantation, here we review specific ethical, logistical, scientific, and regulatory issues regarding xenocorneal transplantation, and propose guidelines for conduct of clinical xenocorneal transplantation trials. These proposed guidelines are modeled on the published consensus statement of the International Xenotransplantation Association regarding recommended guidelines for conduct of clinical islet xenotransplantation. It is expected that this initial consensus statement will be revised over time in response to scientific advances in the field, and changes in the regulatory framework based on accumulating clinical experience., (© 2014 John Wiley & Sons A/S Published by John Wiley & Sons Ltd.)

Background: Among the bone graft sources used currently, the availability of autografts is limited and allografts are expensive. Therefore, xenobone grafts have drawn attention as a new source of bone grafts, although immunologic rejection issues are unresolved. This study used a GalT knockout mouse model to investigate the effects of reducing the alpha-gal epitope using alpha-galactosidase on the union of porcine xenobone grafts., Methods: Sixty-eight alpha-gal knockout C57/BL6 mice and eight wild-type mice were used. The mice were divided into five groups: In group 1 (26 alpha-gal knockout mice), an alpha-galactosidase-treated porcine xenograft was transplanted into the mouse femur to reduce antigenicity, and intramedullary fixation was performed. In group 2 (26 alpha-gal knockout mice), a non-treated porcine xenobone graft was performed. In group 3 (eight alpha-gal knockout C57/BL6 mice), syngenic bone grafts were performed. In group 4 (eight wild-type C57/BL6 mice), syngenic bone grafts were performed. In group 5 (eight C57/BL6 alpha-gal knockout mice), a bone defect model was obtained by maintaining the gap of the osteotomy site. Groups 3, 4, and 5 were used for positive and negative control groups. Qualitative immunohistochemical analysis of the porcine bone was performed to detect the presence of the alpha-gal epitope in groups 1 and 2. The concentration of the anti-alpha-gal antibody was evaluated using a quantitative enzyme-linked immunosorbent assay (ELISA) at the time of sacrifice (3, 4, and 5 weeks after the operation). Histologic and radiologic results (Goldberg method) for the bone union were compared., Results: The qualitative immunohistochemical analysis showed that the alpha-gal epitope was reduced when xenobone grafts were treated with alpha-galactosidase. Compared with group 2, group 1 showed a low anti-alpha-gal antibody concentration in the ELISA results. In group 2, the anti-alpha-gal antibody concentration increased with time. Group 1 showed significantly better histologic union than group 2, but the amount of radiologic union was similar in the two groups., Conclusions: Alpha-galactosidase treatment of a porcine xenobone graft can reduce the alpha-gal epitope. This reduction in the antigen could significantly reduce the humoral immune response to the alpha-gal antigen in C57/BL6 alpha-gal knockout mice, leading to significant improvements in histologic union. This study provides a relevant GalT knockout mouse model for detecting the effects of alpha-gal epitope reduction by alpha-galactosidase on the union of porcine xenobone grafts., (© 2014 John Wiley & Sons A/S.)

The purpose of this study is to investigate cross-reactivity between hypertonic saline-treated decellularized porcine corneal lamellae for corneal xenobridging and subsequent corneal allotransplants. Five Chinese rhesus macaques, which had undergone anterior partial thickness corneal transplantation using hypertonic saline-treated decellularized porcine corneal lamellae in preceding experiments, were used as recipients for subsequent full-thickness corneal allografts. To determine whether sensitization of recipients to xenoantigens leads to cross-reactivity against alloantigens, we compared; (i) allogeneic one-way mixed lymphocyte reaction (MLR) of peripheral blood mononuclear cells (PBMCs) from xeno-sensitized recipients with that of PBMCs from naïve rhesus macaques, and (ii) amounts of IgG antibodies that bound to the PBMCs of a rhesus panel (five monkeys) before and after xeno-sensitization. Graft survival and immunologic profiles including memory T-cell subsets and donor rhesus-specific antibodies were also evaluated. No hyperacute or acute rejection was observed within a month of subsequent allotransplantation in any recipient. Alloreactivity by MLR was not different between xeno-sensitized rhesus recipients and naïve rhesus monkeys. Panel-reactive IgG antibodies were unchanged after xeno-sensitization, and no change in donor rhesus-specific antibodies was observed in any recipient. No significant changes in memory T-cell subsets were observed during the early post-operative period in any recipient. Decellularized porcine corneal lamellae may not increase cross-reactivity to alloantigens, and thus, porcine corneal lamellae may be used as a bridge to subsequent corneal allografting.

Pancreatic islet transplantation is a promising treatment option for Type 1 diabetes, but organ supply shortage limits its wide adoption. Pig islets are the most promising alternative source and many important measures such as donor animal selection, pig islet production release criteria, preclinical data and zoonosis surveillance prior to human clinical trials have been put forward as a consensus through the efforts of the International Xenotransplantation Association. To bring pig islet transplantation to clinical reality, the development of clinically applicable immunosuppression regimens and methods to minimize immunosuppression to reduce side effects should be established. This review encompasses immune rejection mechanisms in islet xenotransplantation, immunosuppression regimens that have enabled long-term graft survival in pig-to-nonhuman primate experiments and strategies for minimizing immunosuppression in islet xenotransplantation. By thoroughly examining the drugs that are currently available and in development and their individual targets within the immune response, the best strategy for enabling clinical trials of pig islets for Type 1 diabetes will be proposed.

Background: To establish the consensus about the conditions for undertaking clinical trials in xenocorneal transplantation in Korea, specific issues regarding the xenocorneal transplantation on ethical and regulatory aspects are addressed, and the guidelines to conduct clinical trial of the xenocorneal transplantation are proposed., Method and Results: Chapter 1 reviews the key ethical requirements and progress of a Korean regulatory framework for clinical trials of xenocorneal transplantation. Chapters 2-7 provide recommendations on source pigs, quality control of porcine corneal procurement, preclinical efficacy required to justify a clinical trial, strategies to prevent transmission of porcine endogenous retrovirus (PERV), patient selection for clinical trials, and informed consent in xenocorneal transplantation using either cellularized or decellularized porcine graft, which are essentially based on the International Xenotransplantation Association (IXA) islet xenotransplantation consensus statement. The consensus statement of the inclusion criteria for the patients' selection has been made by the executive board members in Korean External Eye Disease Society., Conclusions: This consensus statement will be a good initiative for Korean Food and Drug Administration to discuss final regulatory guidelines in conducting clinical trials of xenocorneal transplantation in Korea and for International Xenotransplantation Association to develop International Consensus Standards of Xenocorneal Transplantation., (© 2013 John Wiley & Sons A/S.)

Maximum engraftment of transplanted islets is essential for the clinical application of a subcutaneous site. Significant barriers to the current approaches are associated with their low effectiveness, complexity and unproven biosafety. Here, we evaluated and optimized a fibrin-islet composite for effective glycemic control in a subcutaneous site whose environment is highly hypoxic due to low vascularization potential. In the setting of xenogeneic porcine islet transplantation into the subcutaneous space of a diabetic mouse, the in vivo islet functions were greatly affected by the concentrations of fibrinogen and thrombin. The optimized hydrogel-type fibrin remarkably reduced the marginal islet mass to approximately one tenth that of islets without fibrin. This marginal islet mass was comparable to that in the setting of the subcapsular space of the kidney, which is a highly vascularized organ. Highly vascularized structures were generated inside and on the outer surface of the grafts. A hydrogel-type fibrin-islet composite established early diabetic control within an average of 3.4days after the transplantation. In the mechanistic studies, fibrin promoted local angiogenesis, enhanced islet viability and prevented fragmentation of islets into single cells. In conclusion, in situ application of hydrogel-type fibrin-islet composite may be a promising modality in the clinical success of subcutaneous islet transplantation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Background: Intravascular thrombosis and systemic coagulation abnormalities are major hurdles to successful xenotransplantation and are signs of acute humoral rejection. Increased expression of tissue factor (TF) is associated with the development of microvascular thrombosis in xenografts. To develop an effective strategy to prevent accelerated coagulation in xenografts, we investigated the mechanism by which porcine endothelial cells (PECs) become procoagulant after contact with human blood., Methods: The changes in TF mRNA levels and activity in PECs after incubation with 20% human serum or human bioactive molecules, including C5a, tumor necrosis factor-α (TNFα) and interleukin (IL)-1α, were evaluated using real-time PCR and the factor Xa chromogenic assay, respectively. The procoagulant changes in PECs by these agonists were evaluated by measuring the coagulation time of human citrated plasma suspended with PECs pretreated with each agonist. TF expression and coagulation times were also assessed in PECs transfected with short interfering RNA (siRNA) designed to knock down porcine TF. We also examined the production of proinflammatory cytokines in human whole-blood or plasma after contact with PECs, which were screened using the cytometric bead array system. TNFα levels were measured using ELISA in whole-blood after contact with PECs, with or without the addition of xenoreactive antibodies or C1 esterase inhibitor., Results: Porcine TF mRNA and activity in PECs were up-regulated in response to human TNFα and IL-1α but were not affected by C5a or 20% human serum. Up-regulation of TF expression by human TNFα or IL-1α shortened PEC-induced coagulation time, while siRNA-mediated knockdown of TF expression prolonged coagulation time. The incubation of PECs with human whole-blood led to a significant increase in human TNFα levels in the blood, which was promoted by the addition of xenoreactive antibodies and prevented by C1 esterase inhibitor., Conclusions: Human TNFα level increases in human blood after contact with PECs, which is attributed to xenoreactive antibody binding and subsequent complement activation. Human TNFα induces procoagulant changes in PECs with increased TF expression. This study suggests that human TNFα may be one of the mediators linking complement activation with procoagulant changes in the xenoendothelium., (© 2012 John Wiley & Sons A/S.)

Background: It has been reported that hyperacute rejection (HAR) does not occur after pig-to-nonhuman corneal xenotransplantation. However, considering that immune privilege is already disrupted in most human corneal recipients, and the expression of αGal can be gradually reduced after pig-to-rat corneal transplantation, the long-term survival of corneal grafts from wild-type pigs cannot be guaranteed. Accordingly, we aimed to investigate the effect of αGal on the change in anti-Gal antibodies, using sensitized α1,3-galactosyltransferase gene-knockout (GTKO) mice recipients., Methods: C57BL/6 (B6) and GTKO mice were divided into 5 groups and underwent orthotopically full thickness cormeal transplantation as follows (n=4 for each group): (1) group 1: B6 to B6; (2) group 2: fresh porcine posterior corneal lamella to B6; (3) fresh porcine posterior corneal lamella to GTKO; (4) group 4: decellularized porcine posterior corneal lamella to GTKO, and (5) group 5: B6 to GTKO. Before transplantation, all GTKO recipients were sensitized using intraperitoneal injections of rabbit blood cells. Median survival times (MST) for the corneal grafts of the different groups were compared and plasma concentrations of IgG/IgM anti-Gal antibodies were evaluated at 1 week, 2 weeks and 3 weeks post-transplantation., Results: There were no differences in MSTs between groups. Although there was no HAR of fresh porcine posterior corneal grafts even in sensitized GTKO recipients, αGal expression was induced in the transplanted fresh porcine corneal grafts and plasma concentration of IgG anti-Gal antibody was gradually increased in fresh porcine cornea-grafted GTKO recipients. On the contrary, αGal expression did not increase in the grafts and plasma concentration of anti-Gal antibodies did not change after transplantation using decellularized porcine corneas., Conclusions: Our findings suggest that αGal may affect the long-term survival of porcine corneal xenografts via antibody-mediated rejection, although αGal does not have an effect on acute rejection and decellularized porcine corneas may enable the long-term survival of porcine corneal xenografts., (© 2011 John Wiley & Sons A/S.)

Purpose of Review: Donor shortage in corneal transplantation is a significant problem in Asian countries and is an emerging issue worldwide. This review will discuss current knowledge of the pathogenesis of the rejection mechanism, recent advances in xenocorneal transplantation, and feasibility of porcine xenocorneal graft., Recent Findings: α-Gal epitopes which are expressed on the porcine cornea, however less than in other vascularized organs. A small animal model provided evidence of complement-mediated or antibody-mediated rejection in porcine xenocorneal transplantation. Recent progress in genetic engineering of the pig or biomedical engineering for removal of the α-Gal epitope appears to have resulted in reduction of antibody-mediated rejection. Porcine corneal xenograft is not rejected hyperacutely in all animal models. T cells predominantly mediate xenocorneal rejection through various animal models. Survival of lamellar fresh porcine grafts is longer than that of full-thickness fresh porcine grafts. Decellularized porcine grafts also demonstrate significantly longer survival than fresh grafts do., Summary: Recent studies have documented the potential of the porcine corneal graft as a substitute for use in human allograft and have highlighted the mechanisms of rejection of xenocorneal transplantation. Antibody-mediated or complement-mediated xenogeneic rejection should be further explored in a large animal model.

Background: We have demonstrated earlier that porcine corneal xenografts underwent an acute cell-mediated rejection in mice despite the absence of T cells. In the present study, we investigated the effect of complement depletion by cobra venom factor (CVF) on the corneal xenograft rejection in a pig-to-mouse model., Methods: Porcine corneas were orthotopically transplanted into C57BL/6 (B6) and severe combined immunodeficiency (SCID) mice. For complement depletion, 25 microg of CVF (1 g/kg bodyweight) was injected intraperitoneally on the day before and 1, 3, 5, and 7 days after transplantation. Graft survival was clinically assessed by slit lamp biomicroscopy and the median survival time (MST) was calculated. The grafts were histologically evaluated serially after transplantation using antibodies against CD4, CD8, NK1.1, and F4/80., Results: The CVF treatment significantly prolonged the porcine corneal xenograft survival in both B6 (MST 9.4 vs. 15.5 days; P = 0.0011) and SCID mice (MST 16.4 vs. 20.5 days; P = 0.0474). Histologically, whereas macrophages and CD4(+) T cells were progressively infiltrated into porcine corneal grafts in CVF-untreated B6 mice, the infiltration by both cells was markedly delayed and decreased in the xenografts in CVF-treated B6 mice. Likewise, macrophage infiltration, which was prominent in rejected porcine xenografts in SCID mice, was also reduced in CVF-treated SCID mice., Conclusions: Our results suggest that complement depletion by CVF delayed, although did not prevent, an acute cell-mediated rejection in a pig-to-mouse corneal xenotransplantation.

Prediction of islet yield and posttransplant outcome is essential for clinical porcine islet xenotransplantation. Although several histomorphometric parameters of biopsied porcine pancreases are predictive of islet yield, their role in the prediction of in vivo islet potency is unknown. We investigated which histomorphometrical parameter best predicts islet yield and function, and determined whether it enhanced the predictive value of in vitro islet function tests for the prediction of posttransplant outcome. We analyzed the histomorphometry of pancreases from which 60 adult pig islet isolations were obtained. Islet function was assessed using the beta-cell viability index based on flow cytometry analysis, oxygen consumption rate, ADP/ATP ratio, and/or concurrent transplantation into NOD/SCID mice. Receiver operating characteristic (ROC) analysis revealed that only islet equivalent (IEQ)/cm(2) and the number of islets >200 microm in diameter significantly predicted an islet yield of >2000 IEQ/g (p < 0.001 for both) and in vivo islet potency (p = 0.024 and p = 0.019, respectively). Although not predictive of islet yield, a high proportion of large islets (>100 microm in diameter) best predicted diabetes reversal (p = 0.001). Multiple regression analysis revealed that the beta-cell viability index (p = 0.003) and the proportion of islets >100 microm in diameter (p = 0.048) independently predicted mean posttransplant blood glucose level (BGL). When BGL was estimated using both these parameters [area under the ROC curve (AUC), 0.868; 95% confidence interval (CI), 0.730-1.006], it predicted posttransplant outcome more accurately than the beta-cell viability index alone (AUC, 0.742; 95% CI, 0.544-0.939). In conclusion, we identified the best histomorphometric predictors of islet yield and posttransplant outcome. This further enhanced the predictive value of the flow cytometry analysis. These parameters should be useful for predicting islet yield and in vivo potency before clinical adult porcine islet xenotransplantation.

Background: To investigate the role of T cells and natural killer (NK) cells in mediating corneal xenograft rejection in a pig-to-mouse model., Methods: Pig corneas were orthotopically transplanted into BALB/c, C57BL/6, nude, severe combined immunodeficiency (SCID), and NOD/SCID/gammac(null) (NOG) mice. Graft survival was clinically assessed by slit-lamp biomicroscopy and median survival times (MST) were calculated. The rejected grafts were histologically evaluated using antibodies against CD4, CD8, NK1.1, and F4/80., Results: The pig corneal xenografts were acutely rejected by BALB/c and C57BL/6 mice (MST 9.0 days), while nude, SCID and NOG mice rejected pig corneas in a more delayed fashion (MST 16.0, 16.4, and 16.9 days, respectively). The majority of infiltrating cells found in rejected grafts in C57BL/6 mice were macrophages and CD4(+) T cells, while CD8(+) T cells and NK cells were rarely found. The grafts in nude mice had markedly decreased inflammatory infiltration with small numbers of macrophages and CD4(+) T cells. Infiltration was even more modest in grafts in SCID and NOG mice., Conclusions: T cells play an important role in acute rejection of pig corneal xenografts in mice, although acute rejection is not solely the result of T-cell-mediated immunity. NK cells are less likely to be involved in the rejection process.

To evaluate the differences in graft survival and histopathological characteristics between full-thickness and lamellar orthotopic corneal xenotransplantation in a pig-to-rabbit model, we orthotopically transplanted a full-thickness or the anterior half of a pig's cornea onto the OD of 16 rabbits. As a result, the median survival were 16.83 and 29.07 days for the full-thickness and lamellar xenografts, respectively (P = 0.0005). Histologically, the full-thickness corneal xenografts had massive infiltration by eosinophils, whereas the lamellar xenografts showed predominantly mononuclear infiltrates (P < 0.05). Given these preliminary findings, lamellar corneal xenografts in rabbits survived longer than the full-thickness xenografts and each type of graft demonstrated different rejection mechanisms.

Instant blood-mediated inflammatory reaction (IBMIR) causes rapid islet loss in portal vein islet transplantation. Endothelial cells are known to protect against complement-mediated lysis and activation of coagulation. We tested composite pig islet-human endothelial cell grafts as a strategy to overcome IBMIR. Porcine islets were cocultured with human endothelial cells in specially modified culture medium composed of M199 and M200 for 1-9 days. A positive control group, negative control group, and the endothelial cell-coated group were examined with an in vitro tubing loop assay using human blood. The endothelial cell-coated group was subdivided and analyzed by degree of surface coverage by endothelial cells (< or = 50% vs. > 50%) or coculture time (< 5 days vs. > or = 5 days). Platelet consumption and complement and coagulation activation were assessed by platelet count, C3a, and thrombin-antithrombin complex (TAT), respectively. After 60-min incubation in human blood, the endothelial cell-coated group showed platelet consumption inhibition and low C3a and TAT assay results compared to uncoated controls. When the endothelial cell-coated group was subdivided by degree of surface coverage, the < or = 50% coated group showed less platelet consumption and less activation of complement and coagulation compared with the positive control (uncoated) group. On analysis by coculture time, only the subgroup cocultured for < 5 days showed the same protective effect. Human endothelial cell-coated pig islets, especially the partially coated and short-term cocultured pig islet-human endothelial cell composites, reduced all components of IBMIR. If the optimal endothelial cell-islet coculture method could be identified, human endothelial cell coating of pig islets would offer new strategies to improve xenogenic islet transplantation outcomes.

Background: The dynamic pattern of the cellular infiltration and mRNA expression of chemokines in rat-to-mouse skin xenografts were examined to gain an understanding of the possible role of chemokines in the stronger cellular immune responses to xenografts compared with the allo-response., Methods: The mean survival time of the xenografts was approximately 2 days less than that of allografts (10.7 +/- 0.9 days vs. 8.9 +/- 0.7 days, P < 0.05). In comparison with the allografts, the xenografts were characterized by a very early infiltration of monocytes/macrophages (day 3) and a larger number of CD4+ and CD8+ cells, as well as neutrophil infiltration in the early phase (day 5), and larger number of CD8+ and CD11b+ cells, as well as macrophage infiltration, in the later phase (day 7). Xenografts showed stronger interferon (IFN)-inducible 10-kDa protein (IP-10) and monokine induced by IFN (MIG) mRNA expression levels, which appeared earlier than in the allografts. In the later phase, strong expression of regulated on activation, normal T cell expressed and secreted was observed. Cytokine mRNA expression in the xenografts could be summarized by higher expression of IFN-gamma, interleukin (IL)1beta, IL6, and transforming growth factor -beta1 mRNA than in the allografts. These results suggest that the early increased CXC-chemokine expression, such as IP-10 and MIG, which has been known to be mainly produced by macrophages, may play a critical role in the stronger cellular xenograft rejection compared with allograft rejection. Therefore, MIG antiserum or CXCR3 antiserum was administered to the rat skin-engrafted mice every other day until rejection., Results: Compared with the control normal rabbit serum-treated mice, either the MIG antiserum- or CXCR3 antiserum-treated mice showed a delayed rejection of approximately 2 days (8.3 +/- 0.5 days vs. 10.6 +/- 0.5 days or 10.8 +/- 1.9 days, respectively, P < 0.05)., Conclusion: Overall, these results suggest that the more aggressive rejection of xenografts compared with allografts is due to the earlier expression of CXC-chemokines, IP-10 and MIG, and subsequent adjuvant effects of proinflammatory cytokines.