Disruption of Type‐I IFN Pathway Ameliorates Preservation Damage in Mouse Orthotopic Liver Transplantation via HO‐1 Dependent Mechanism

Ischemia/reperfusion injury (IRI) remains unresolved problem in clinical organ transplantation. We analyzed the role of Type‐I interferon (IFN) pathway in a clinically relevant murine model of extended hepatic cold preservation followed by orthotopic liver transplantation (OLT). Livers from Type‐I IFN receptor (IFNAR) knockout (KO) or wild‐type (WT) mice (C57/BL6) were harvested, preserved at 4°C in UW solution for 20 h and transplanted to groups of syngeneic IFNAR KO or WT recipients. Liver graft but not recipient IFNAR deficiency was required to consistently ameliorate IRI in OLTs. Indeed, disruption of Type‐I IFN signaling decreased serum alanine aminotransferase (sALT) levels (p < 0.001), diminished Suzuki's score of histological OLT damage (p < 0.01) and improved 14‐day survival (from 42%[5/12] in WT to 92%[11/12] in IFNAR KO; p < 0.05). Unlike in WT group, IFNAR deficiency attenuated OLT expression of TNF‐α, IL‐1β, IL‐6, MCP‐1, CXCL‐10, ICAM‐1; diminished infiltration by macrophages/PMNs; and enhanced expression of antioxidant HO‐1/Nrf2. The frequency of TUNEL+ apoptotic cells and caspase‐3 activity/expression selectively decreased in IFNAR KO group. Small interfering (si)RNA‐directed targeting of HO‐1 restored cardinal features of liver IRI in otherwise resistant IFNAR‐deficient OLTs. Thus, intact Type‐I IFN signaling is required for hepatic IRI, whereas HO‐1 is needed for cytoprotection against innate immunity‐dominated organ preservation damage in IFNAR‐deficient liver transplants.     

Heme oxygenase‐1 regulates sirtuin‐1–autophagy pathway in liver transplantation: From mouse to human

Liver ischemia–reperfusion injury (IRI) represents a major risk factor of early graft dysfunction and a key obstacle to expanding the donor pool in orthotopic liver transplantation (OLT). Although graft autophagy is essential for resistance against hepatic IRI, its significance in clinical OLT remains unknown. Despite recent data identifying heme oxygenase‐1 (HO‐1) as a putative autophagy inducer, its role in OLT and interactions with sirtuin‐1 (SIRT1), a key autophagy regulator, have not been studied. We aimed to examine HO‐1–mediated autophagy induction in human OLT and in a murine OLT model with extended (20 hours) cold storage, as well as to analyze the requirement for SIRT1 in autophagy regulation by HO‐1. Fifty‐one hepatic biopsy specimens from OLT patients were collected under an institutional review board protocol 2 hours after portal reperfusion, followed by Western blot analyses. High HO‐1 levels correlated with well‐preserved hepatocellular function and enhanced SIRT1/LC3B expression. In mice, HO‐1 overexpression by genetically modified HO‐1 macrophage therapy was accompanied by decreased OLT damage and increased SIRT1/LC3B expression, whereas adjunctive inhibition of SIRT1 signaling diminished HO‐1–mediated hepatoprotection and autophagy induction. Our translational study confirms the clinical relevance of HO‐1 cytoprotection and identifies SIRT1‐mediated autophagy pathway as a new essential regulator of HO‐1 function in IR‐stressed OLT.     

Serelaxin induces Notch1 signaling and alleviates hepatocellular damage in orthotopic liver transplantation

Liver ischemia‐reperfusion injury (IRI) represents a risk factor for early graft dysfunction and an obstacle to expanding donor pool in orthotopic liver transplantation (OLT). We have reported on the crucial role of macrophage Notch1 signaling in mouse warm hepatic IRI model. However, its clinical relevance or therapeutic potential remain unknown. Here, we used Serelaxin (SER), to verify Notch1 induction and putative hepatoprotective function in ischemia‐reperfusion–stressed OLT. C57BL/6 mouse livers subjected to extended (18‐hour) cold storage were transplanted to syngeneic recipients. SER treatment at reperfusion ameliorated IRI, improved post‐OLT survival, decreased neutrophil/macrophage infiltration, and suppressed proinflammatory cytokine programs, while simultaneously increasing Notch intracellular domain (NICD) and hairy and enhancer of split 1 (Hes1) target genes. In bone marrow–derived macrophage cultures, SER suppressed proinflammatory while enhancing antiinflammatory gene expression concomitantly with increased NICD and Hes1. Hepatic biopsies from 21 adult primary liver transplant patients (2 hours postreperfusion) were divided into low‐NICD (n = 11) and high‐NICD (n = 10) expression groups (western blots). Consistent with our murine findings, human livers characterized by high NICD were relatively IRI resistant, as shown by serum alanine aminotransferase (ALT) levels at day 1 post‐OLT. Our study documents the efficacy of SER–Notch1 signaling in mouse OLT and highlights the protective function of Notch1 in liver transplant patients.     

Posttransplant muscle mass measured by urinary creatinine excretion rate predicts long‐term outcomes after liver transplantation

Long‐term survival in orthotopic liver transplant (OLT) recipients remains impaired because of many contributing factors, including a low pretransplant muscle mass (or sarcopenia). However, influence of posttransplant muscle mass on survival is currently unknown. We hypothesized that posttransplant urinary creatinine excretion rate (CER), an established noninvasive marker of total body muscle mass, is associated with long‐term survival after OLT. In a single‐center cohort study of 382 adult OLT recipients, mean ± standard deviation CER at 1 year posttransplantation was 13.3 ± 3.7 mmol/24 h in men and 9.4 ± 2.6 mmol/24 h in women. During median follow‐up for 9.8 y (interquartile range 6.4‐15.0 y), 104 (27.2%) OLT recipients died and 44 (11.5%) developed graft failure. In Cox regression analyses, as continuous variable, low CER was associated with increased risk for mortality (HR = 0.43, 95% CI: 0.26‐0.71, P = .001) and graft failure (HR = 0.42, 95% CI: 0.20‐0.90, P = .03), independent of age, sex, and body surface area. Similarly, OLT recipients in the lowest tertile had an increased risk for mortality (HR = 2.69; 95% CI: 1.47‐4.91, P = .001) and graft failure (HR = 2.77, 95% CI: 1.04‐7.39, P = .04), compared to OLT recipients in the highest tertile. We conclude that 1 year posttransplant low total body muscle mass is associated with long‐term risk of mortality and graft failure in OLT recipients.     

Negative CD4 + TIM‐3 Signaling Confers Resistance Against Cold Preservation Damage in Mouse Liver Transplantation

Ischemia‐reperfusion injury (IRI), an innate immunity‐driven local inflammation, remains the major problem in clinical organ transplantation. T cell immunoglobulin and mucin domain (TIM‐3)–Galectin‐9 (Gal‐9) signaling regulates CD4+ Th1 immune responses. Here, we explored TIM‐3–Gal‐9 function in a clinically relevant murine model of hepatic cold storage and orthotopic liver transplantation (OLT). C57BL/6 livers, preserved for 20 h at 4°C in UW solution, were transplanted to syngeneic mouse recipients. Up‐regulation of TIM‐3 on OLT‐infiltrating activated CD4+ T cells was observed in the early IRI phase (1 h). By 6 h of reperfusion, OLTs in recipients treated with a blocking anti‐TIM‐3 Ab were characterized by: (1) enhanced hepatocellular damage (sALT levels, liver Suzuki's histological score); (2) polarized cell infiltrate towards Th1/Th17‐type phenotype; (3) depressed T cell exhaustion markers (PD‐1, LAG3); and (4) elevated neutrophil and macrophage infiltration/activation. In parallel studies, adoptive transfer of CD4+ T cells from naïve WT, but not from TIM‐3 Tg donors, readily recreated OLT damage in otherwise IR‐resistant RAG^?/? test recipients. Furthermore, pre‐treatment of mice with rGal‐9 promoted hepatoprotection against preservation‐association liver damage, accompanied by enhanced TIM‐3 expression in OLTs. Thus, CD4+ T cell‐dependent “negative” TIM‐3 costimulation is essential for hepatic homeostasis and resistance against IR stress in OLTs.

     

Population level outcomes and cost‐effectiveness of hepatitis C treatment pre‐ vs postkidney transplantation

Direct‐acting antivirals approved for use in patients with end‐stage renal disease (ESRD) now exist. HCV‐positive (HCV+) ESRD patients have the opportunity to decrease the waiting times for transplantation by accepting HCV‐infected kidneys. The optimal timing for HCV treatment (pre‐ vs posttransplant) among kidney transplant candidates is unknown. Monte Carlo microsimulation of 100 000 candidates was used to examine the cost‐effectiveness of HCV treatment pretransplant vs posttransplant by liver fibrosis stage and waiting time over a lifetime time horizon using 2 regimens approved for ESRD patients. Treatment pretransplant yielded higher quality‐adjusted life years (QALYs) compared with posttransplant treatment in all subgroups except those with Meta‐analysis of Histological Data in Viral Hepatitis stage F0 (pretransplant: 5.7 QALYs vs posttransplant: 5.8 QALYs). However, treatment posttransplant was cost‐saving due to decreased dialysis duration with the use of HCV‐infected kidneys (pretransplant: $735 700 vs posttransplant: $682 400). Using a willingness‐to‐pay threshold of $100 000, treatment pretransplant was not cost‐effective except for those with Meta‐analysis of Histological Data in Viral Hepatitis stage F3 whose fibrosis progression was halted. If HCV+ candidates had access to HCV‐infected donors and were transplanted ≥9 months sooner than HCV‐negative candidates, treatment pretransplant was no longer cost‐effective (incremental cost‐effectiveness ratio [ICER]: $107 100). In conclusion, optimal timing of treatment depends on fibrosis stage and access to HCV+ kidneys but generally favors posttransplant HCV eradication.     

Comparison of de novo IgM and IgG anti‐HLA DSAs between belatacept‐ and calcineurin‐treated patients: An analysis of the BENEFIT and BENEFIT‐EXT trial cohorts

Preventing conversion of donor‐specific anti‐HLA antibodies (DSAs) from an IgM‐to‐IgG could a way to prevent chronic rejection. We evaluated whether belatacept‐treated patients (belatacept less‐intensive [LI] or more‐intensive [MI] regimens) have a lower rate of conversion than do cyclosporine A (CsA)–treated patients. We included 330 HLA‐mismatched patients from 2 phase 3 trials with either (a) complete donor/recipient HLA‐A, ‐B, ‐DR, and ‐DQ loci typing or (b) incomplete HLA typing with IgG DSAs detected pretransplant or posttransplant. IgM and IgG DSAs were tested with single antigen beads at 0, 6, 12, 24, and 36 months posttransplant. The overall (preexisting or de novo) rates of IgM‐ and IgG‐positive DSAs were 29% and 34%, respectively. The pretransplant IgM and IgG DSA‐positive frequencies were similar between treatment groups. The IgG‐positive dnDSA rate was significantly higher in the CsA‐treated group (34%) compared with the belatacept‐LI (8%) and belatacept‐MI (11%) (P < .001) groups. In IgM‐positive dnDSA patients, the IgG‐positive dnDSA rate of conversion was 2.8 times higher in the CsA group than in the combined belatacept groups (P = .006). However, the observed association between belatacept treatment and more limited conversion of IgM‐to‐IgG dnDSAs was based on a limited number of patients and requires further validation.     

Development and outcomes of de novo donor‐specific antibodies in low,moderate, and high immunological risk kidney transplant recipients

De novo donor‐specific antibodies (dnDSA) play an important role in antibody‐mediated rejection (ABMR) and graft failure, yet their development in kidney transplant recipients (KTx) of higher immunological risk has not been characterized. We prospectively determined the incidence of dnDSA at 3 and 12 months posttransplant and assessed their associations with outcomes in recipients stratified by low, moderate, and high immunological risk. Adult KTx were screened for DSA pretransplant, months 3 and 12 posttransplant, and when clinically indicated. Outcomes included incidence of dnDSA, death‐censored graft survival (DCGS), and ABMR. Of 371 recipients, 154 (42%) were transplanted across a pretransplant DSA that became undetectable by 12 months posttransplant in 78% of cases. dnDSA were detected in 16% (95% confidence interval [CI]: 12‐20%) by 3 months and 23% (95% CI: 18‐29%) by 12 months posttransplant. Incidence at 12 months was higher in the moderate (30%) and high‐risk groups (29%) compared to the low‐risk group (16%). dnDSA were associated with an increased risk of ABMR (hazard ratio [HR] 2.2; 95% CI: 1.1‐4.4; P = .04) but were not an independent risk factor for DCGS. In conclusion, dnDSA were more frequent in transplant recipients of higher immune risk and associated with an increased risk of ABMR.     

Opposite acute potassium and sodium shifts during transplantation of hypothermic machine perfused donor livers

Liver transplantation is frequently associated with hyperkalemia, especially after graft reperfusion. Dual hypothermic oxygenated machine perfusion (DHOPE) reduces ischemia/reperfusion injury and improves graft function, compared to conventional static cold storage (SCS). We examined the effect of DHOPE on ex situ and in vivo shifts of potassium and sodium. Potassium and sodium shifts were derived from balance measurements in a preclinical study of livers that underwent DHOPE (n = 6) or SCS alone (n = 9), followed by ex situ normothermic reperfusion. Similar measurements were performed in a clinical study of DHOPE‐preserved livers (n = 10) and control livers that were transplanted after SCS only (n = 9). During DHOPE, preclinical and clinical livers released a mean of 17 ± 2 and 34 ± 6 mmol potassium and took up 25 ± 9 and 24 ± 14 mmol sodium, respectively. After subsequent normothermic reperfusion, DHOPE‐preserved livers took up a mean of 19 ± 3 mmol potassium, while controls released 8 ± 5 mmol potassium. During liver transplantation, blood potassium levels decreased upon reperfusion of DHOPE‐preserved livers while levels increased after reperfusion of SCS‐preserved liver, delta potassium levels were ‐0.77 ± 0.20 vs. +0.64 ± 0.37 mmol/L, respectively (P = .002). While hyperkalemia is generally anticipated during transplantation of SCS‐preserved livers, reperfusion of hypothermic machine perfused livers can lead to decreased blood potassium or even hypokalemia in the recipient.     

Necrostatin‐1 inhibits Hmgb1‐IL‐23/IL‐17 pathway and attenuates cardiac ischemia reperfusion injury

Ischemia reperfusion (IR) injury is a major issue in cardiac transplantation and inflammatory processes play a major role in myocardial IR injury. Necrostatin‐1 (Nec‐1) is a small molecule capable of inhibiting RIP1 kinase activity and attenuates inflammation‐mediated tissue injury. In our study, hearts of C57Bl/6 mice were flushed and stored in cold Bretschneider solution for 8 h and then transplanted into syngeneic recipients. We found that Nec‐1 decreased cardiomyocyte necrosis and recruitment of neutrophils and macrophages. Troponin T (TnT) production on 24 h after myocardial IR injury was reduced by Nec‐1 administration. Cardiac output at 60 mmHg of afterload pressure was significantly increased in hearts with Nec‐1 administration and the cardiac allograft survival in Nec‐1‐treated animals was significantly prolonged (MST = 90 days in IR + Nec‐1 group, P < 0.05 as compared with IR group, MST = 83.5 days). Nec‐1 treatment attenuated ROS generation and increased expression of NOS2 and COX‐2. The expression of Hmgb1, IL‐23, and IL‐17A were also decreased with Nec‐1 administration. Furthermore, the decreased TnT expression induced by Nec‐1 was abrogated with exogenous Hmgb1 administration. In conclusion, Nec‐1 played a protective role in cardiomyocyte IR injury, and this was associated with inhibited Hmgb1‐IL‐23/IL‐17 pathway.     

Specificity,strength, and evolution of pretransplant donor‐specific HLA antibodies determine outcome after kidney transplantation

In this cohort study (N = 924), we investigated the evolution and clinical significance of pretransplant donor‐specific HLA antibodies (preDSA), detected in the single‐antigen beads assay but complement‐dependent cytotoxicity crossmatch‐negative. Donor specificity of the preDSA (N = 107) was determined by high‐resolution genotyping of donor‐recipient pairs. We found that in 52% of the patients with preDSA, preDSA spontaneously resolved within the first 3 months posttransplant. PreDSA that persisted posttransplant had higher pretransplant median fluorescence intensity values and more specificity against DQ. Patients with both resolved and persistent DSA had a high incidence of histological picture of antibody‐mediated rejection (ABMR_h; 54% and 59% respectively). Patients with preDSA that persisted posttransplant had worse 10‐year graft survival compared to resolved DSA and preDSA‐negative patients. Compared to cases without preDSA, Cox modeling revealed an increased risk of graft failure only in the patients with persistent DSA, in the presence (hazard ratio [HR] = 8.3) but also in the absence (HR = 4.3) of ABMR_h. In contrast, no increased risk of graft failure was seen in patients with resolved DSA. We conclude that persistence of preDSA posttransplant has a negative impact on graft survival, beyond ABMR_h. Even in the absence of antibody‐targeting therapy, low median fluorescence intensity DSA and non‐DQ preDSA often disappear early posttransplantation and are not deleterious for graft outcome.     

Liver transplantation for critically ill cirrhotic patients: Stratifying utility based on pretransplant factors

The aim of this study was to produce a prognostic model to help predict posttransplant survival in patients transplanted with grade‐3 acute‐on‐chronic liver failure (ACLF‐3). Patients with ACLF‐3 who underwent liver transplantation (LT) between 2007 and 2017 in 5 transplant centers were included (n = 152). Predictors of 1‐year mortality were retrospectively screened and tested on a single center training cohort and subsequently tested on an independent multicenter cohort composed of the 4 other centers. Four independent pretransplant risk factors were associated with 1‐year mortality after transplantation in the training cohort: age ≥53 years (P = .044), pre‐LT arterial lactate level ≥4 mml/L (P = .013), mechanical ventilation with PaO₂/FiO₂ ≤ 200 mm Hg (P = .026), and pre‐LT leukocyte count ≤10 G/L (P = .004). A simplified version of the model was derived by assigning 1 point to each risk factor: the transplantation for Aclf‐3 model (TAM) score. A cut‐off at 2 points distinguished a high‐risk group (score >2) from a low‐risk group (score ≤2) with 1‐year survival of 8.3% vs 83.9% respectively (P < .001). This model was subsequently validated in the independent multicenter cohort. The TAM score can help stratify posttransplant survival and identify an optimal transplantation window for patients with ACLF‐3.     

Thrombomodulin Attenuates Inflammatory Damage Due to Liver Ischemia and Reperfusion Injury in Mice in Toll‐Like Receptor 4–Dependent Manner

Liver ischemia reperfusion injury (IRI) is an important problem in liver transplantation. Thrombomodulin (TM), an effective drug for disseminated intravascular coagulation, is also known to exhibit an anti‐inflammatory effect through binding to the high‐mobility group box 1 protein (HMGB‐1) known as a proinflammatory mediator. We examined the effect of recombinant human TM (rTM) on a partial warm hepatic IRI model in wild‐type (WT) and toll‐like receptor 4 (TLR‐4) KO mice focusing on the HMGB‐1/TLR‐4 axis. As in vitro experiments, peritoneal macrophages were stimulated with recombinant HMGB‐1 protein. The rTM showed a protective effect on liver IRI. The rTM diminished the downstream signals of TLR‐4 and also HMGB‐1 expression in liver cells, as well as release of HMGB‐1 from the liver. Interestingly, neither rTM treatment in vivo nor HMGB‐1 treatment in vitro showed any effect on TLR‐4 KO mice. Parallel in vitro studies have confirmed that rTM interfered with the interaction between HMGB‐1 and TLR‐4. Furthermore, the recombinant N‐terminal lectin‐like domain 1 (D1) subunit of TM (rTMD1) also ameliorated liver IRI to the same extent as whole rTM. Not only rTM but also rTMD1 might be a novel and useful medicine for liver transplantation. This is the first report clarifying that rTM ameliorates inflammation such as IRI in a TLR‐4 pathway–dependent manner.     

Early emergence of anti‐HCV antibody implicates donor origin in recipients of an HCV‐infected organ

Hepatitis C virus (HCV) seroconversion among HCV‐uninfected transplant recipients from HCV‐infected (NAT+/Antibody+) or HCV‐exposed (NAT?/Antibody+) donors has been reported. However, the origin of anti‐HCV antibody and the implications of seroconversion remain unknown. We longitudinally tested plasma from HCV‐uninfected kidney (n = 31) or heart transplant recipients (n = 9) of an HCV NAT+ organ for anti‐HCV antibody (both IgG and IgM isotypes). Almost half of all participants had detectable anti‐HCV antibody at any point during follow‐up. The majority of antibody‐positive individuals became positive within 1‐3 days of transplantation, and 6 recipients had detectable antibody on the first day posttransplant. Notably, all anti‐HCV antibody was IgG, even in samples collected posttransplant day 1. Late seroconversion was uncommon (≈20%‐25% of antibody+ recipients). Early antibody persisted over 30 days in kidney recipients, whereas early antibody dropped below detection in 50% of heart recipients within 2 weeks after transplant. Anti‐HCV antibody is common in HCV‐uninfected recipients of an HCV NAT+ organ. The IgG isotype of this antibody and the kinetics of its appearance and durability suggest that anti‐HCV antibody is donor derived and is likely produced by a cellular source. Our data suggest that transfer of donor humoral immunity to a recipient may be much more common than previously appreciated.     

VEGF mitigates histone‐induced pyroptosis in the remote liver injury associated with renal allograft ischemia–reperfusion injury in rats

Clinical evidence has indicated a possible link between renal injury and remote liver injury. We investigated whether extracellular histone mediates remote hepatic damage after renal graft ischemia–reperfusion injury, while vascular endothelial growth factor (VEGF) is protective against remote hepatic injury. In vitro, hepatocyte HepG2 cultures were treated with histone. In vivo, the Brown‐Norway renal graft was stored in 4°C preservation solution for 24 hours and then transplanted into a Lewis rat recipient; blood samples and livers from recipients were harvested 24 hours after surgery. Prolonged cold ischemia in renal grafts enhanced liver injury 24 hours after engraftment. Caspase‐1, ASC, NLRP3, and AIM2 expressions in hepatocyte, CD68⁺‐infiltrating macrophages, tissue, and serum interleukin‐1β and ‐18 were greatly elevated, indicating that pyroptosis occurred in the liver and resulted in acute liver functional impairment. Blocking the caspase‐1 pathway decreased the number of necrotic hepatocytes. VEGF treatment suppressed the hepatocyte pyroptosis and liver function was partially restored. Our data suggested that renal allograft ischemia–reperfusion injury is likely associated with acute liver damage due to hepatocyte pyroptosis induced by histone and such injury may be protected by VEGF administration. VEGF, therefore, may serve as a new strategy against other remote organ injuries related to renal transplantation.     

Optimal timing of hepatitis C treatment among HIV/HCV coinfected ESRD patients: Pre‐ vs posttransplant

Patients with end‐stage renal disease (ESRD) who are coinfected with hepatitis C virus (HCV) and human immunodeficiency virus (HIV) have access to effective treatment options for HCV infection. However, they also have access to HCV‐infected kidneys, which historically afford shorter times to transplantation. Given the high waitlist mortality and rapid progression of liver fibrosis among coinfected kidney‐only transplant candidates, identification of the optimal treatment strategy is paramount. Two strategies, treatment pre‐ and posttransplant, were compared using Monte Carlo microsimulation of 1 000 000 candidates. The microsimulation was stratified by liver fibrosis stage at waitlist addition and wait‐time over a lifetime time horizon. Treatment posttransplant was consistently cost‐saving as compared to treatment pretransplant due to the high cost of dialysis. Among patients with low fibrosis disease (F0‐F1), treatment posttransplant also yielded higher life months (LM) and quality‐adjusted life months (QALM), except among F1 candidates with wait times ≥ 18 months. For candidates with advanced liver disease (F2‐F4), treatment pretransplant afforded more LM and QALM unless wait time was <18 months. Moreover, treatment pretransplant was cost‐effective for F2 candidates with wait times >71 months and F3 candidates with wait times >18 months. Thus, optimal timing of HCV treatment differs based on liver disease severity and wait time, favoring pretransplant treatment when cirrhosis development prior to transplant seems likely.     

Geographic disparities in liver supply/demand ratio within fixed‐distance and fixed‐population circles

Recent OPTN proposals to address geographic disparity in liver allocation have involved circular boundaries: the policy selected 12/17 allocated to 150‐mile circles in addition to DSAs/regions, and the policy selected 12/18 allocated to 150‐mile circles eliminating DSA/region boundaries. However, methods to reduce geographic disparity remain controversial, within the OPTN and the transplant community. To inform ongoing discussions, we studied center‐level supply/demand ratios using SRTR data (07/2013‐06/2017) for 27 334 transplanted deceased donor livers and 44 652 incident waitlist candidates. Supply was the number of donors from an allocation unit (DSA or circle), allocated proportionally (by waitlist size) to the centers drawing on these donors. We measured geographic disparity as variance in log‐transformed supply/demand ratio, comparing allocation based on DSAs, fixed‐distance circles (150‐ or 400‐mile radius), and fixed‐population (12‐ or 50‐million) circles. The recently proposed 150‐mile radius circles (variance = 0.11, P = .9) or 12‐million‐population circles (variance = 0.08, P = .1) did not reduce the geographic disparity compared to DSA‐based allocation (variance = 0.11). However, geographic disparity decreased substantially to 0.02 in both larger fixed‐distance (400‐mile, P < .001) and larger fixed‐population (50‐million, P < .001) circles (P = .9 comparing fixed distance and fixed population). For allocation circles to reduce geographic disparities, they must be larger than a 150‐mile radius; additionally, fixed‐population circles are not superior to fixed‐distance circles.     

Optimization of heart allocation: The transplant risk score

The new French heart allocation system is designed to minimize waitlist mortality and extend the donor pool without a detrimental effect on posttransplant survival. This study was designed to construct a 1‐year posttransplant graft‐loss risk score incorporating recipient and donor characteristics. The study included all adult first single‐organ recipients transplanted between 2010 and 2014 (N = 1776). This population was randomly divided in a 2:1 ratio into derivation and validation cohorts. The association of variables with 1‐year graft loss was determined with a mixed Cox model with center as random effect. The predictors were used to generate a transplant‐risk score (TRS). Donor‐recipient matching was assessed using 2 separate recipient‐ and donor‐risk scores. Factors associated with 1‐year graft loss were recipient age >50 years, valvular cardiomyopathy and congenital heart disease, previous cardiac surgery, diabetes, mechanical ventilation, glomerular filtration rate and bilirubin, donor age >55 years, and donor sex: female. The C‐index of the final model was 0.70. Correlation between observed and predicted graft loss rate was excellent for the overall cohort (r = 0.90). Hearts from high‐risk donors transplanted to low‐risk recipients had similar survival as those from low‐risk donors. The TRS provides an accurate prediction of 1‐year graft‐loss risk and allows optimal donor‐recipient matching.