Pig-to-human kidney transplantation using brain-dead donors as recipients: One giant leap, or only one small step for transplantkind?

Pig kidney xenotransplantation is increasingly regarded as a realistic solution to the current shortage of human organ donors for patients with end-stage organ failure. Recently, the news of three pig-to-human transplantation cases has awakened public interest. Notably, the case by the Alabama team reported detailed and important findings for the xenotransplantation field. Using a genetically modified pig, two porcine kidneys were transplanted into a brain-dead recipient. They applied several approaches established in the preclinical NHP study, including gene-edited pig kidney graft and preoperative laboratory inspection such as crossmatching and infection screening. The pig-to-human kidney xenotransplantation had no unexpected events during surgery or evidence of hyperacute rejection. Unfortunately, the grafts did not work appropriately, and the study had to be terminated due to the decompensation of the recipient. While this study demonstrated the outstanding achievement in this research area, it also revealed remaining gaps to move xenotransplantation to the clinic. While brain-dead human recipients could reinforce the compatibility achievements of gene-edited pigs in NHP, their pro-inflammatory and pro-coagulant environment, in combination with short-duration of experiments will limit the assessment of kidney function, infection and rejection risk post-transplant, in particular antibody-mediated rejection. The use of successful immunosuppressive protocols of non-human primates xenotransplant experiments including anti-CD154 antibody will be critical to maximize the success in the first in-human trials.

Functional roles of graft-infiltrating lymphocytes during early-phase post-transplantation in mouse cardiac transplantation models.

Immunological behavior of graft-infiltrating lymphocytes (GILs) determines the graft fate (i.e., rejection or acceptance). Nevertheless, the functional alloreactivity and the phenotype of GILs at various times during the early post-transplantation phase have not been fully elucidated. We examined the immunological activities of early-phase GILs using a murine model of cardiac transplantation. GILs from 120-h allografts, but not 72-h allografts, showed robust activation and produced proinflammatory cytokines. In particular, a significant increase in CD69+ T-bet+ Nur77+ T cells was detected in 120-h allografts. Furthermore, isolated GILs were used to reconstitute BALB/c Rag2-/- γc-/- (BRG) mice. BRG mice reconstituted with 120-h GILs displayed donor-specific immune reactivity and rejected donor strain cardiac allografts; conversely, 72-h GILs exhibited weak anti-donor reactivity and did not reject allografts. These findings were confirmed by re-transplantation of cardiac allografts into BRG mice at 72-h post-transplantation. Re-transplanted allografts continued to function for >100 days, despite the presence of CD3+ GILs. In conclusion, the immunological behavior of GILs considerably differs over time during the early post-transplantation phase. A better understanding of the functional role of early-phase GILs may clarify the fate determination process in the graft-site microenvironment.

TCF1highPD-1+Ly108+CD8+ T Cells Are Associated with Graft Preservation in Sensitized Mice Treated with Non-Fc Receptor-Binding CD3 Antibodies.

The non-Fc-binding anti-CD3 Ab [anti-CD3F(ab')2] can induce graft acceptance depending on the therapeutic window in a rodent heart transplant model. The delayed protocol allows for early graft infiltration of lymphocytes, which may behave in an inhibitory manner. We investigated the most effective protocol for anti-CD3F(ab')2 in sensitized conditions to confirm the evidence for clinical application. C57BL/6 mice were sensitized with BALB/c tail skin grafts and transplanted with BALB/c heart grafts at 8-12 wk after sensitization. Fifty micrograms of anti-CD3F(ab')2 was administered daily for 5 consecutive days on days 1-5 (day 1 protocol) or days 3-7 (delayed protocol). In nonsensitized mice, the delayed protocol significantly prolonged graft survival after transplantation from BALB/c to naive B6 (median survival time [MST], >100 d). In contrast, the delayed protocol was unable to prevent graft rejection in sensitized mice (MST, 5 d). A significantly increased percentage of granzyme B+ CD8+ T cells was observed in the graft on day 3 posttransplantation in sensitized conditions. Further, the day 1 protocol significantly prolonged graft survival (MST, 18 d), even in sensitized conditions. Day 1 treatment significantly increased the percentage of Foxp3+CD25+CD4+ T cells and phenotypically changed CD8+ T cells in the graft (i.e., caused a significant increase in the proportion of Ly108+TCF1highPD-1+CD8+ T cells). In conclusion, different timings of delayed anti-CD3F(ab')2 treatment promoted allograft preservation in association with phenotypic changes in CD4+ and CD8+ T cells in the graft under sensitized conditions.

A humanized IL-2 mutein expands Tregs and prolongs transplant survival in preclinical models.

Long-term organ transplant survival remains suboptimal, and life-long immunosuppression predisposes transplant recipients to an increased risk of infection, malignancy, and kidney toxicity. Promoting the regulatory arm of the immune system by expanding Tregs may allow immunosuppression minimization and improve long-term graft outcomes. While low-dose IL-2 treatment can expand Tregs, it has a short half-life and off-target expansion of NK and effector T cells, limiting its clinical applicability. Here, we designed a humanized mutein IL-2 with high Treg selectivity and a prolonged half-life due to the fusion of an Fc domain, which we termed mIL-2. We showed selective and sustainable Treg expansion by mIL-2 in 2 murine models of skin transplantation. This expansion led to donor-specific tolerance through robust increases in polyclonal and antigen-specific Tregs, along with enhanced Treg-suppressive function. We also showed that Treg expansion by mIL-2 could overcome the failure of calcineurin inhibitors or costimulation blockade to prolong the survival of major-mismatched skin grafts. Validating its translational potential, mIL-2 induced a selective and sustainable in vivo Treg expansion in cynomolgus monkeys and showed selectivity for human Tregs in vitro and in a humanized mouse model. This work demonstrated that mIL-2 can enhance immune regulation and promote long-term allograft survival, potentially minimizing immunosuppression.

Long-term risk of a fatty liver in liver donors.

Aim: Approximately 30 years have passed since the first experience of living donor liver transplantation. The time to evaluate the long-term safety of living donors has been fulfilled. Meanwhile, nonalcoholic fatty liver disease is increasingly common and a critical problem. The aim of this study was to evaluate the safety of living donor, focusing on fatty liver postdonation hepatectomy. Methods: Living donors (n = 212, 1997-2019) were evaluated by computed tomography (CT) at >1-year postdonation. A liver to spleen (L/S) ratio of <1.1 was defined as fatty liver. Results: Among 212 living liver donors, 30 (14.2%) detected fatty liver at 5.3 ± 4.2 years postdonation. The cumulative incidence rates of fatty liver were 3.1%, 12.1%, 22.1%, and 27.7% at 2, 5, 10, and 15 years postdonation, respectively. Of 30 subjects who developed fatty liver, 18 (60%) displayed a severe steatosis (L/S ratio <0.9). Five (16.7%) had a prior history of excessive alcohol abuse. More than 30% developed metabolic syndrome including obesity, hyperlipidemia, and diabetes. Although six (20%) had a Fib-4 index of >1.3, which included a case with a Fib-4 index of >2.67, no significant increased Fib-4 index was observed in the subjects with fatty liver as compared to those without fatty liver (p = 0.66). The independent predictive risk factors for developing fatty liver were male sex, pediatric recipient, and higher body mass index (>25) at donation. Conclusion: Living donors with risk factors for developing fatty liver should be carefully followed-up for the prevention and management of metabolic syndrome.

Post-transplant donor-specific anti-HLA antibodies with a higher mean fluorescence intensity are associated with graft fibrosis in pediatric living donor liver transplantation.

The roles of post-transplant anti-HLA donor specific antibody (DSA) in pediatric liver transplantation (LT), including therapeutic strategies, remain controversial. This study aimed to identify the risks of post-transplant DSA for graft fibrosis progression in pediatric living donor LT (LDLT). We retrospectively evaluated 88 LDLT pediatric cases between December 1995 and November 2019. DSAs were assessed with single antigen bead test. Graft fibrosis was histopathologically scored with METAVIR and the centrilobular sinusoidal fibrosis system. Post-transplant DSAs were detected in 37 (52.9%) cases at 10.8 (1.3-26.9) years post-LDLT. The histopathological examination of 32 pediatric cases with post-transplant DSA revealed that 7 (21.9%) with a high DSA-MFI (≥9,378) showed graft fibrosis progression (≥F2). No graft fibrosis was observed in the subjects with a low DSA-MFI. The risk factors for developing graft fibrosis in pediatric cases with post-transplant DSA were an older graft age (>46.5 years old), lower platelet count (<10.7 × 104/ml) and higher Fib4 index (>0.7807, recipient age; >1.8952, donor age). Limited efficacy of additional immunosuppressants was observed in DSA positive pediatric cases. In conclusion, pediatric cases with a high DSA-MFI and risk factors should undergo a histological examination. The appropriate treatment for post-transplant DSA in pediatric LT needs to be determined.

Living Donor Liver Transplantation for Hepatic Venoocclusive Disease/Sinusoidal Obstruction Syndrome Originating from Hematopoietic Stem Cell Transplantation.

Background: Venoocclusive disease (VOD), also known as sinusoidal obstruction syndrome (SOS), is a life-threatening hematopoietic stem cell transplantation (HSCT) complication. Cases of mild and moderate VOD/SOS are self-limiting; however, the mortality for severe VOD/SOS has reached 80%. Recently, defibrotide became available and has been used for VOD/SOS; however, the outcome for patients with severe VOD/SOS is not satisfactory, and liver transplantation is attempted in these severe cases. Method: We describe a case of living donor liver transplantation (LDLT) for acute liver failure secondary to VOD/SOS that originates from HSCT. Result: Liver regeneration after LDLT was impaired, and several infections were developed before liver regeneration completion. Our patient suffered sepsis and finally died of multiorgan failure. Conclusion: Severe VOD/SOS originating from HSCT is associated with a very poor prognosis. The liver transplantation outcome for VOD/SOS has not been satisfied, but it may provide long-term survival if successful. We considered liver transplantation as a therapeutic option, especially in cases where sufficient graft volume is secured, considering impaired liver regeneration under bone marrow suppression after HSCT.

The impact of preformed donor-specific antibodies in living donor liver transplantation according to graft volume.

INTRODUCTION: The roles of preformed anti-HLA donor-specific antibodies (DSAs) in liver transplantation remain controversial. We evaluated the impact of preformed DSAs in living donor liver transplantation. METHODS: Adults who underwent living donor liver transplantation (n = 175) in our institute were included in this study. Lymphocyte cytotoxicity test (LCT), flow cytometric crossmatch (FCXM), and single-antigen bead assays were performed. RESULTS: Among adult living donor liver transplantation recipients, 27 (16.5%) and 14 (8.5%) had pretransplant FCXM-positive findings and LCT-positive findings, respectively. FCXM-positive patients displayed a significantly worse 5-year graft survival rate (77.3%; vs. DSA-negative, 91.6%). Six of 14 LCT-positive patients exhibited graft loss shortly after transplantation (5-year survival rate: 57.1%). All LCT-positive patients with graft loss underwent left lobe living donor liver transplantation. Significantly lower ratio of graft volume relative to standard liver volume (32.9 ± 5.7%) and smaller graft size (365.3 ± 57.9 g) were observed in patients with graft loss (p < .03, vs. surviving grafts). Significantly higher DSA-mean fluorescence intensity (MFI) values were present in patients with graft loss (p = .0012, vs. surviving grafts). CONCLUSIONS: Patients with preformed DSAs exhibited worse graft outcomes in living donor liver transplantation. Higher DSA-MFI values and smaller graft size were associated with worse outcomes in LCT-positive patients. High-risk patients with preformed DSAs should be considered for appropriate graft selection and application of a desensitization protocol.

Efficient multiple treatments including molecular targeting agents in a case of recurrent hepatocellular carcinoma, post-living donor liver transplantation.

Despite the promising efficacies of recently developed molecular targeting therapies for hepatocellular carcinoma, their role in liver transplantation is unknown. Here we report that multidisciplinary treatment, including novel molecular targeting therapy with lenvatinib, achieved long-term survival of a patient with post-liver transplantation recurrence of hepatocellular carcinoma. A 62 year-old man with hepatocellular carcinoma beyond the Milan criteria, arising from hepatitis B virus-associated cirrhotic liver, underwent living donor liver transplantation. However, alpha-fetoprotein level increased a month post-transplantation, and pleural dissemination and lung metastasis of hepatocellular carcinoma in the right lung were detected. The patient was initially treated with sorafenib and rapamycin, right pleurectomy and upper and middle lobectomies were attempted as the second treatment. However, remnant tumors started to grow. Subsequently, the newly molecular targeting agents; regorafenib and lenvatinib, approved for recurrent hepatocellular carcinoma in Japan, were administered. Lenvatinib efficiently reduced tumor volumes and the alpha-fetoprotein level, which contributed to maintaining better quality of life for 26 months as an outpatient. Unfortunately, sepsis caused by cholangitis and liver abscess required the discontinuation of lenvatinib, and the patient died 73 months after the recurrence of hepatocellular carcinoma. Multidisciplinary treatment including lenvatinib is potentially acceptable for recurrent hepatocellular carcinoma after liver transplantation.

The Efficacy of the Hepatocyte Spheroids for Hepatocyte Transplantation.

The safety and short-term efficacy of hepatocyte transplantation (HCTx) have been widely proven. However, issues such as reduced viability and/or function of hepatocytes, insufficient engraftment, and lack of a long-term effect have to be overcome for widespread application of HCTx. In this study, we evaluated hepatocyte spheroids (HSs), formed by self-aggregation of hepatocytes, as an alternative to hepatocytes in single-cell suspension. Hepatocytes were isolated from C57BL/6 J mice liver using a three-step collagenase perfusion technique and HSs were formed by the hanging drop method. After the spheroids formation, the HSs showed significantly higher mRNA expression of albumin, ornithine transcarbamylase, glucose-6-phosphate, alpha-1-antitrypsin, low density lipoprotein receptor, coagulation factors, and apolipoprotein E (ApoE) than 2 dimensional (2D)-cultured hepatocytes (p < 0.05). Albumin production by HSs was significantly higher than that by 2D-cultured hepatocytes (9.5 ± 2.5 vs 3.5 ± 1.8 µg/dL, p < 0.05). The HSs, but not single hepatocytes, maintained viability and albumin mRNA expression in suspension (92.0 ± 2.8% and 1.03 ± 0.09 at 6 h). HSs (3.6 × 106 cells) or isolated hepatocytes (fSH, 3.6 × 106 cells) were transplanted into the liver of ApoE knockout (KO-/-) mice via the portal vein. Following transplantation, serum ApoE concentration (ng/mL) of HS-transplanted mice (1w: 63.1 ± 56.7, 4w: 17.0 ± 10.9) was higher than that of fSH-transplanted mice (1 w: 33.4 ± 13.0, 4w: 13.7 ± 9.6). In both groups, the mRNA levels of pro-inflammatory cytokines (IL-6, IL-1ß, TNF-α, MCP-1, and MIP-1ß) were upregulated in the liver following transplantation; however, no significant differences were observed. Pathologically, transplanted HSs were observed as flat cell clusters in contact with the portal vein wall on day 7. Additionally, ApoE positive cells were observed in the liver parenchyma distant from the portal vein on day 28. Our results indicate that HS is a promising alternative to single hepatocytes and can be applied for HCTx.

Novel immunological approach to asses donor reactivity of transplant recipients using a humanized mouse model.

In organ transplantation, a reproducible and robust immune-monitoring assay has not been established to determine individually tailored immunosuppressants (IS). We applied humanized mice reconstituted with human (hu-) peripheral blood mononuclear cells (PBMCs) obtained from living donor liver transplant recipients to evaluate their immune status. Engraftment of 2.5 × 106 hu-PBMCs from healthy volunteers and recipients in the NSG mice was achieved successfully. The reconstituted lymphocytes consisted mainly of hu-CD3+ lymphocytes with predominant CD45RA-CD62Llo TEM and CCR6-CXCR3+CD4+ Th1 cells in hu-PBMC-NSG mice. Interestingly, T cell allo-reactivity of hu-PBMC-NSG mice was amplified significantly compared with that of freshly isolated PBMCs (p < 0.05). Furthermore, magnified hu-T cell responses to donor antigens (Ag) were observed in 2/10 immunosuppressed recipients with multiple acute rejection (AR) experiences, suggesting that the immunological assay in hu-PBMC-NSG mice revealed hidden risks of allograft rejection by IS. Furthermore, donor Ag-specific hyporesponsiveness was maintained in recipients who had been completely weaned off IS (n = 4), despite homeostatic proliferation of hu-T cells in the hu-PBMC-NSG mice. The immunological assay in humanized mice provides a new tool to assess recipient immunity in the absence of IS and explore the underlying mechanisms to maintaining operational tolerance.