Justification of specific genetic modifications in pigs for clinical organ xenotransplantation

Xenotransplantation research has made considerable progress in recent years, largely through the increasing availability of pigs with multiple genetic modifications. We suggest that a pig with nine genetic modifications (ie, currently available) will provide organs (initially kidneys and hearts) that would function for a clinically valuable period of time, for example, >12 months, after transplantation into patients with end‐stage organ failure. The national regulatory authorities, however, will likely require evidence, based on in vitro and/or in vivo experimental data, to justify the inclusion of each individual genetic modification in the pig. We provide data both from our own experience and that of others on the advantages of pigs in which (a) all three known carbohydrate xenoantigens have been deleted (triple‐knockout pigs), (b) two human complement‐regulatory proteins (CD46, CD55) and two human coagulation‐regulatory proteins (thrombomodulin, endothelial cell protein C receptor) are expressed, (c) the anti‐apoptotic and “anti‐inflammatory” molecule, human hemeoxygenase‐1 is expressed, and (d) human CD47 is expressed to suppress elements of the macrophage and T‐cell responses. Although many alternative genetic modifications could be made to an organ‐source pig, we suggest that the genetic manipulations we identify above will all contribute to the success of the initial clinical pig kidney or heart transplants, and that the beneficial contribution of each individual manipulation is supported by considerable experimental evidence.     

Costimulation blockade in pig artery patch xenotransplantation - a simple model to monitor the adaptive immune response in nonhuman primates

Ezzelarab MB, Ekser B, Echeverri G, Hara H, Ezzelarab C, Long C, Bajona P, Garcia B, Murase N, Ayares D, Cooper DKC. Costimulation blockade in pig artery patch xenotransplantation – a simple model to monitor the adaptive immune response in nonhuman primates. Xenotransplantation 2012; 19: 221–232. © 2012 John Wiley & Sons A/S. Abstract: Background: CD154 blockade‐based immunosuppression successfully prevents both humoral and cellular adaptive immune responses in baboons receiving α1,3‐galactosyltransferase gene‐knockout (GTKO) pig organs. Using a GTKO pig artery transplantation model in baboons, we evaluated the efficacy of CD28/B7 costimulatory pathway blockade in comparison with CD154 blockade. Methods: Baboons received artery patch grafts from GTKO pigs, with no (Group1), anti‐CD154mAb‐based (Group2), or CTLA4‐Ig‐based (Group3) immunosuppressive therapy. Anti‐pig IgM and IgG antibody and cellular responses were monitored. Xenografts were immunohistologically evaluated for antibody and complement deposition, and cellular infiltration. Results: Group1 baboons developed increased IgM and IgG antibody and cellular responses against GTKO antigens. In Group2, anti‐CD154mAb alone prevented the development of both IgM and IgG antibody and cellular responses,but not cellular infiltration of the graft. In the single baboon that received anti‐thymocyte globulin (ATG) + mycophenolate mofetil (MMF) + anti‐CD154mAb, cellular infiltration of the graft was not seen. In Group3, CTLA4‐Ig with ATG + MMF inhibited the cellular proliferative response to pig antigens but did not prevent the IgG response or cellular infiltration. Conclusions: (i) Artery patch transplantation is a simple model to monitor the adaptive immune response to xenografts; (ii) anti‐CD154mAb prevents sensitization but not cellular infiltration (but, without anticoagulation, may result in early thrombosis of a pig xenograft); (iii) although in only one baboon, the addition of ATG and MMF prevents cellular infiltration and (iv) replacement of anti‐CD154mAb by CTLA4‐Ig (at the doses used), even in combination with ATG and MMF, prevents the cellular proliferative response to GTKO pig antigens but is insufficient to prevent the development of anti‐pig antibodies.     

Progressive improvement in short‐, medium‐ and long‐term graft survival in kidney transplantation patients in Ireland – a retrospective study

It is often quoted that while short‐term graft survival in kidney transplantation has improved in recent years, it has not translated into a commensurate improvement in long‐term graft survival. We considered whether this was true of the entire experience of the national kidney transplant program in Ireland. A retrospective analysis of the National Kidney Transplant Service (NKTS) database was undertaken to investigate patient and graft survival for all adult first deceased donor kidney transplant recipients in Ireland, 1971–2015. Three thousand two hundred and sixty recipients were included in this study. Kaplan–Meier methods were used to estimate survival at each time period post transplant for the various eras of transplantation. Uncensored graft survival has improved over the course of the program in Ireland at various time points despite risk factors for graft failure progressively increasing over successive eras. For example the graft survival at 15 years post transplant has increased from 10% in 1971–1975 to 45% by 1996–2000. Ireland has experienced a progressive improvement in long‐term graft survival following kidney transplantation. Whether these trends are attributable to biological or nonbiological factors is unclear but likely involves a combination of both.     

Failure to remove de novo donor‐specific HLA antibodies is influenced by antibody properties and identifies kidney recipients with late antibody‐mediated rejection destined to graft loss – a retrospective study

Current research is focusing on identifying bioclinical parameters for risk stratification of renal allograft loss, largely due to antibody‐mediated rejection (AMR). We retrospectively investigated graft outcome predictors in 24 unsensitized pediatric kidney recipients developing HLA de novo donor‐specific antibodies (dnDSAs), and treated for late AMR with plasmapheresis + low‐dose IVIG + Rituximab or high‐dose IVIG + Rituximab. Renal function and DSA properties were assessed before and longitudinally post treatment. The estimated GFR (eGFR) decline after treatment was dependent on a negative % eGFR variation in the year preceding treatment (P = 0.021) but not on eGFR at treatment (P = 0.74). At a median follow‐up of 36 months from AMR diagnosis, 10 patients lost their graft. Altered eGFR (P < 0.001) and presence of C3d‐binding DSAs (P = 0.005) at treatment, and failure to remove DSAs (P = 0.01) were negatively associated with graft survival in the univariable analysis. Given the relevance of DSA removal for therapeutic success, we analyzed antibody properties dictating resistance to anti‐humoral treatment. In the multivariable analysis, C3d‐binding ability (P < 0.05), but not C1q‐binding, and high mean fluorescence intensity (P < 0.05) were independent factors characterizing DSAs scarcely susceptible to removal. The poor prognosis of late AMR is related to deterioration of graft function prior to treatment and failure to remove C3d binding and/or high‐MFI DSAs.     

Higher calcineurin inhibitor levels predict better kidney graft survival in patients with de novo donor‐specific anti‐HLA antibodies: a cohort study

The development of de novo anti‐HLA donor‐specific antibodies (dnDSA) is associated with poorer outcomes in kidney transplant recipients. Despite this, antibody screening post‐transplant is not widespread, largely because the optimal management of patients with dnDSA remains undetermined. We hypothesized that in this population, calcineurin inhibitor blood levels would be an independent predictor of graft loss. We analyzed a cohort of unsensitized patients for whom anti‐HLA antibody screening was performed prospectively post‐transplant. During the screening period between January 2005 and April 2016, 42 patients developed dnDSA. There was no difference in the clinical characteristics or the histological scores of patients biopsied for clinical indication versus those biopsied solely due to detection of dnDSA. Cox modeling revealed a strong relationship between mean tacrolimus levels following dnDSA detection and graft loss, with a hazard ratio of 0.49 (95% CI, 0.33–0.75), which persisted following adjustment for established independent predictors (HR, 0.52, 95% CI, 0.30–0.89). Kaplan–Meier analysis by tertiles of tacrolimus levels and receiver operating curve analysis concurred to show that a threshold of 5.3 ng/ml could be predictive of graft loss. These data suggest that anti‐HLA antibody monitoring post‐transplant could guide maintenance immunosuppression and improve graft outcomes.     

Perioperative administration of high‐dose recombinant human erythropoietin for delayed graft function prevention in kidney transplantation: a meta‐analysis

Delayed graft function (DGF) due to ischemia–reperfusion injury is a major early complication of kidney transplantation (KT). Recombinant human erythropoietin (rHuEPO) has been shown to exert nephroprotective action in animal models. We conducted a meta‐analysis to explore the impact of rHuEPO on DGF in KT. Eligible studies comparing perioperative high‐dose rHuEPO with placebo or no therapy for prevention of DGF were identified through MEDLINE, CENTRAL, and Transplant Library. Their design and data were assessed by two independent reviewers. Among 737 examined studies, four randomized controlled trials, involving 356 recipients of kidney allografts from deceased donors, fulfilled inclusion criteria. Statistical heterogeneity across studies was not significant (P = 0.98, I² = 0%). In a random effects model, no significant difference was found in the occurrence of DGF (odds ratio: 0,74, 95% CI: 0.47–1.18, P = 0.21). At 4 weeks after KT, the rHuEPO group exhibited higher systolic blood pressure (mean difference: 6.47 mmHg, 95% CI: 1.25–11.68, P = 0.02). Perioperative, high‐dose rHuEPO administration does not prevent DGF in deceased donor KT. Furthermore, it is associated with higher systolic blood pressure leading to safety concerns. Nonerythropoietic rHuEPO derivatives, designed for nephroprotective action without increasing cardiovascular risk, might prove an alternative but still are at early stages of development.     

Four‐year allograft survival in a highly sensitized combined liver–kidney transplant patient despite unsuccessful anti‐HLA antibody reduction with rituximab,splenectomy, and bortezomib

Although donor‐specific lymphocytotoxic antibodies are regarded as a contraindication for kidney transplantation (KTx), the data available for liver or combined liver or kidney transplantation (cLKTx) are scarce. Here, we report a case of a highly sensitized young man receiving his sixth liver and second kidney graft. Multiple anti‐HLA antibodies were present at the time of transplantation. As a result of suspected antibody‐mediated graft damage, the patient was treated with rituximab, plasmapheresis, intravenous immunoglobulins, splenectomy, and bortezomib to decrease the antibody production. So far, patient and allograft survival has reached 4 years despite failure to achieve a permanent reduction of anti‐HLA antibodies, and particularly nondonor directed antibodies.     

First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes—Chapter 4: pre‐clinical efficacy and complication data required to justify a clinical trial

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.     

Outcomes and risk stratification for late antibody‐mediated rejection in recipients of ABO‐incompatible kidney transplants: a retrospective study

The required intensity of monitoring for antibody‐mediated rejection (AMR) after of ABO‐incompatible (ABOi) kidney transplantation is not clearly formulized. We retrospectively evaluated a single‐center cohort of 115 ABO‐incompatible (ABOi) kidney transplant recipients, of which 32% were also HLA incompatible (ABOi/HLAi) with their donors. We used an adjusted negative binomial model to evaluate risk factors for late AMR. Using this model, we risk‐stratified patients into high‐ and low‐risk groups for the development of late AMR; 26% of patients had at least one AMR episode; 49% of AMR episodes occurred within 30‐days after transplant and were considered early AMR. Patients with an early AMR episode had a 5.5‐fold greater incidence of developing late AMR [IRR = 5.5, (95% CI: 1.5–19.3), P = 0.01]. ABOi/HLAi recipients trended toward increased late AMR risk [IRR = 1.9, (95% CI: 0.5–6.6), P = 0.3]. High‐risk recipients (those with an early AMR or those who were ABOi/HLAi) had a sixfold increased incidence of late AMR [IRR = 6.3, (95% CI: 1.6–24.6), P = 0.008] versus low‐risk recipients. The overall incidence of late AMR was 20.8% vs. 1.5% in low‐risk recipients. Changes in anti‐A/B titer did not correlate with late AMR (IRR = 0.9 per log titer increase, P = 0.7). This risk‐stratification scheme uses information available within 30 days of ABOi transplantation to determine risk for late AMR and can help direct longitudinal follow‐up for individual patients.     

Impact of anti‐HCV direct antiviral agents on graft function and immunosuppressive drug levels in kidney transplant recipients: a call to attention in the mid‐term follow‐up in a single‐center cohort study

The medium‐term impact on graft function and immunosuppressive drug pharmacokinetics of direct antiviral agents (DAA s) among hepatitis C virus (HCV )‐infected kidney transplant (KT ) recipients remain unclear. We compared pre‐ and post‐treatment 12‐month trajectories of estimated glomerular filtration rate (ΔeGFR ) and 24‐h proteinuria (Δ24‐h proteinuria) in 49 recipients treated with DAA s (mostly sofosbuvir plus ledipasvir). Among evaluable patients, 66.7% and 100.0% had undetectable viral load by week 4 and end of therapy (EoT). The sustained virologic response rate at 12 weeks was 95.8%. Overall, 80.6% of patients receiving tacrolimus required dose escalation while on DAA ‐based therapy (median increase of 66.7%) to maintain target levels. Tacrolimus levels resulted to be higher at 12 months compared to EoT (7.8 ± 2.1 vs. 6.7 ± 2.0 ng/ml ; P ‐value = 0.002). No changes in graft function during the course of therapy were observed. However, eGFR significantly decreased (P ‐value <0.001) throughout the first 12 months after EoT. Median ΔeGFR and Δ24‐h over pre‐ and post‐treatment periods were 3.9% and ?6.1% (P ‐value = 0.002) and ?5.3% and 26.2% (P ‐value = 0.057). Caution should be exercised when adjusting immunosuppression in HCV ‐infected KT recipients upon initiation of DAA s, followed by mid‐term monitoring of immunosuppressive drug levels and graft function.     

Effect of mammalian target of rapamycin inhibitors on cytomegalovirus infection in kidney transplant recipients receiving polyclonal antilymphocyte globulins: a propensity score‐matching analysis

Mammalian target of rapamycin inhibitors (mTORi) prevents cytomegalovirus (CMV) infection in kidney transplant (KT) patients. From May 2010 to December 2013, all KT recipients were retrospectively analysed. Maintenance immunosuppression regimen was divided into mTORi or calcineurin inhibitors (CNI)‐based regimen. Since June 2011, CMV‐seropositive recipients (R+) treated with high‐intensity immunosuppression and mTORi did not receive anti‐CMV prophylaxis. We analysed 350 consecutive patients, of which 95 (27%) received mTORi and 255 (73%) CNI‐based immunosuppression. A Cox‐regression multivariate analysis showed that the use of mTORi‐based immunosuppression during all follow‐up reduced the risk of CMV infection (HR 0.36, 95% CI 0.15–0.89, P = 0.028) and confirmed in a propensity score‐matched cohort (HR 0.4, 95% CI 0.1–0.9, P = 0.047). Early discontinuation of mTORi increased the risk of CMV infection (HR 3.2; 95% CI 1.7–6.0) in univariate analysis. The incidence of CMV infection was not higher among CMV R+ patients on mTORi and requiring high‐intensity immunosuppression when CMV prophylaxis was not given. The use of mTORi protected for CMV infection in KT patients, allowing to avoid antiviral prophylaxis for R+ patients receiving high‐intensity immunosuppression. The increased risk of CMV infection after early discontinuation of mTORi warrants further research.     

Absolute quantification of donor‐derived cell‐free DNA as a marker of rejection and graft injury in kidney transplantation: Results from a prospective observational study

Donor‐derived cell‐free DNA (dd‐cfDNA) is a noninvasive biomarker for comprehensive monitoring of allograft injury and rejection in kidney transplantation (KTx). dd‐cfDNA quantification of copies/mL plasma (dd‐cfDNA[cp/mL]) was compared to dd‐cfDNA fraction (dd‐cfDNA[%]) at prespecified visits in 189 patients over 1 year post KTx. In patients (N = 15, n = 22 samples) with biopsy‐proven rejection (BPR), median dd‐cfDNA(cp/mL) was 3.3‐fold and median dd‐cfDNA(%) 2.0‐fold higher (82 cp/mL; 0.57%, respectively) than medians in Stable Phase patients (N = 83, n = 408) without rejection (25 cp/mL; 0.29%). Results for acute tubular necrosis (ATN) were not significantly different from those with biopsy‐proven rejection (BPR). dd‐cfDNA identified unnecessary biopsies triggered by a rise in plasma creatinine. Receiver operating characteristic (ROC) analysis showed superior performance (P = .02) of measuring dd‐cfDNA(cp/mL) (AUC = 0.83) compared to dd‐cfDNA(%) (area under the curve [AUC] = 0.73). Diagnostic odds ratios were 7.31 for dd‐cfDNA(cp/mL), and 6.02 for dd‐cfDNA(%) at thresholds of 52 cp/mL and 0.43%, respectively. Plasma creatinine showed a low correlation (r = 0.37) with dd‐cfDNA(cp/mL). In a patient subset (N = 24) there was a significantly higher rate of patients with elevated dd‐cfDNA(cp/mL) with lower tacrolimus levels (<8 μg/L) compared to the group with higher tacrolimus concentrations (P = .0036) suggesting that dd‐cfDNA may detect inadequate immunosuppression resulting in subclinical graft damage. Absolute dd‐cfDNA(cp/mL) allowed for better discrimination than dd‐cfDNA(%) of KTx patients with BPR and is useful to avoid unnecessary biopsies.     

‘Suspended in a paradox’—patient attitudes to wait‐listing for kidney transplantation: systematic review and thematic synthesis of qualitative studies

Patients on waiting lists for kidney transplantation have higher mortality rates and have specific anxieties about their eligibility, process, and outcomes of wait‐listing. We aimed to describe patient experiences and attitudes to wait‐listing for kidney transplantation. Electronic databases were searched to September 2014. Thematic synthesis was used to analyze the findings. From 22 studies (n = 795 patients), we identified six themes: accepting the only option (chance to regain normality, avoiding guilt, impulsive decision‐making); maintaining hope (determined optimism, appreciating a fortuitous gift, enduring for optimal outcomes, trust in clinical judgment); burden of testing (strenuous commitment, losing the battle, medical mistrust); permeating vulnerability (eligibility enigma, being threatened, angst of timing uncertainty, desperate urgency, living in limbo, spiraling doubt and disappointment, residual ambivalence); deprived of opportunity (unfairly dismissed, unexpected disqualification, self‐resignation and acceptance, jealousy, suspicious of inequity); and moral guilt (awaiting someone's death, questioning deservingness). The waiting list offered hope of restored normality. However, the demands of workup, uncertainty about eligibility, and waiting times that exceeded expectations impelled patients to disillusionment, despair, and suspicion of inequity. Managing patient expectations and ensuring transparency of wait‐listing and allocation decisions may allay patient disappointment and skepticism, to improve patient satisfaction and treatment outcomes.