Design and testing of a humanized porcine donor for xenotransplantation.

Recent human decedent model studies1,2 and compassionate xenograft use3 have explored the promise of porcine organs for human transplantation. To proceed to human studies, a clinically ready porcine donor must be engineered and its xenograft successfully tested in nonhuman primates. Here we describe the design, creation and long-term life-supporting function of kidney grafts from a genetically engineered porcine donor transplanted into a cynomolgus monkey model. The porcine donor was engineered to carry 69 genomic edits, eliminating glycan antigens, overexpressing human transgenes and inactivating porcine endogenous retroviruses. In vitro functional analyses showed that the edited kidney endothelial cells modulated inflammation to an extent that was indistinguishable from that of human endothelial cells, suggesting that these edited cells acquired a high level of human immune compatibility. When transplanted into cynomolgus monkeys, the kidneys with three glycan antigen knockouts alone experienced poor graft survival, whereas those with glycan antigen knockouts and human transgene expression demonstrated significantly longer survival time, suggesting the benefit of human transgene expression in vivo. These results show that preclinical studies of renal xenotransplantation could be successfully conducted in nonhuman primates and bring us closer to clinical trials of genetically engineered porcine renal grafts.

Takotsubo cardiomyopathy following liver transplantation: A multicenter cohort study.

Takotsubo cardiomyopathy (TCM) is an acute, stress-mediated, reversible cardiomyopathy that occurs in the absence of hemodynamically significant coronary artery disease. We aimed to investigate the characteristics and outcomes of patients who developed TCM following liver transplantation (LT) in a multicenter study. Adult patients from 6 centers across the United States who developed TCM according to Mayo Clinic criteria following LT between 2008 and 2023 were included. Demographics, perioperative and long-term outcomes, and treatment modalities were assessed. Fifty-five patients were included. The center incidence of TCM ranged from 0.1% to 0.5%. The majority were female (54.5%) and Caucasian (87.2%), and the median age at transplant was 59 years. The primary etiologies for LT were alcohol-associated cirrhosis (49.1%) and metabolic dysfunction-associated steatotic liver disease cirrhosis (21.8%). The median time from LT to TCM diagnosis was 4 days. TCM was associated with a 60.9% reduction in left ventricular ejection fraction (LVEF) from a pretransplant median LVEF of 64.0%-25.0%. The most common treatment for TCM was diuretics (67.3%) and afterload reduction (54.5%), with only 27.3% of patients requiring vasopressor support. At a median follow-up of 31.5 months, 1-year and 3-year overall survivals (OSs) were 86.3% and 69.4%, respectively. A repeat echocardiogram performed at a median of 84 days demonstrated that 45/55 patients (81.8%) had recovered LVEF ≥50%. Patients with LVEF recovery to ≥50% had significantly improved OS compared to those without LVEF recovery >50% (106.4 vs. 12.2 mo, p = 0.001). TCM following LT is associated with a significant reduction in LVEF; however, the majority of patients recover LVEF to >50% with minimal perioperative mortality. Importantly, follow-up assessment of LVEF has significant implications as lack of recovery is associated with worse OS.

Detrimental impact of early biopsy-proven rejection in liver transplantation.

Existing literature offers conflicting conclusions about whether early acute cellular rejection influences long-term outcomes in liver transplantation. We retrospectively collected donor and recipient data on all adult, first-time liver transplants performed at a single center between 2008 and 2020. We divided this population into two cohorts based on the presence of early biopsy-proven acute cellular rejection (EBPR) within the first 90 days post-transplant and compared outcomes between the groups. There were 896 liver transplants that met inclusion criteria with 112 cases (12.5%) of EBPR. Recipients who developed EBPR had higher biochemical Model for End-Stage Liver Disease scores (28 vs. 24, p < .01), but other donor and recipient characteristics were similar. Recipients with EBPR had similar overall survival compared to patients without EBPR (p = .09) but had decreased graft survival (p < .05). EBPR was also associated with decreased time to first episode of late (> 90 days post-transplant) rejection (p < .0001) and increased vulnerability to bacterial and viral infection (p < .05). In subgroup analysis of recipients with autoimmune indications for liver transplantation, EBPR had a more pronounced association with patient death (hazard ratio [HR] 3.9, p < .05) and graft loss (HR 4.0, p < .01). EBPR after liver transplant is associated with inferior graft survival, increased susceptibility to late rejections, and increased vulnerability to infection.

Occult Hepatocellular Carcinoma Associated With Transjugular Intrahepatic Portosystemic Shunts in Liver Transplant Recipients.

Transplant eligibility for hepatocellular carcinoma (HCC) is determined by the imaging identification of tumor burden within the Milan criteria. Transjugular intrahepatic portosystemic shunt(s) (TIPS) reduce portal hypertension but may impact HCC visualization. It was hypothesized that the presence of pretransplant TIPS would correlate with occult HCC and reduced survival. A single-center, retrospective, case control study was performed among liver transplant recipients with HCC (2000-2017). The primary endpoint was occult disease on explant pathology. Backward stepwise logistic regression was performed. The secondary endpoints disease-free survival (DFS) and overall survival (OS) were evaluated with Kaplan-Meier curves and Cox regression analysis. Of 640 patients, 40 had TIPS and more frequently exhibited occult disease (80.0% versus 43.1%; P < 0.001; odds ratio [OR], 4.16; P < 0.001). Portal vein thrombosis (PVT) similarly correlated with occult disease (OR, 1.97; P = 0.02). Explant tumor burden was equivalent between TIPS subgroups; accordingly, TIPS status was not independently associated with reduced DFS or OS. However, exceeding the Milan criteria was associated with reduced DFS (hazard ratio, 3.21; P = 0.001), and TIPS status in patients with a single suspected lesion (n = 316) independently correlated with explant tumor burdens beyond these criteria (OR, 13.47; P = 0.001). TIPS on pretransplant imaging are associated with occult HCC on explant pathology. Comparable occult disease findings in patients with PVT suggest that the mechanism may involve altered hepatic perfusion, obscuring imaging diagnosis. TIPS are not independently associated with reduced DFS or OS but are associated with exceeding the Milan criteria for patients with a single suspected lesion. The presence of TIPS may necessitate a higher index of suspicion for occult HCC.

Defining postoperative transfusion thresholds in liver transplant recipients: A novel retrospective approach.

BACKGROUND: The optimal transfusion threshold for most patient populations has been defined as hematocrit (HCT) <21%. However, some specific patient populations are known to benefit from higher transfusion thresholds. To date, the optimal postoperative transfusion threshold for patients undergoing liver transplant has not been determined. To define the ideal transfusion threshold for liver transplant patients, we designed a retrospective study of 496 liver transplant recipients. METHODS: Using HCT prior to discharge as a surrogate marker for transfusion thresholds we grouped patients into three groups of transfusion thresholds (HCT <21%, <24%, and >30%). Transfusion rates (intra- and postoperative), graft and patient survival, and complications requiring readmission were compared between groups. RESULTS: Ninety-two percent of patients were transfused during their hospital stay. Graft survival, patient survival, and rates of readmission within 30 days of discharge were no different between the three discharge HCT groups. Patients discharged with HCT >30% were less likely to be readmitted with infectious complications; however, this group also had the lowest model of end-stage liver (MELD) score at time of transplantation and were less likely to have received a transfusion during their hospital stay. CONCLUSION: Transfusion thresholds of HCT <24%, and potentially as low as 21% are acceptable in postoperative liver transplant recipients. The conduct of a randomized clinical trial, as supported by these data, will be necessary to support the use of lower thresholds.

Incidence of Occult Intrahepatic Metastasis in Hepatocellular Carcinoma Treated With Transplantation Corresponds to Early Recurrence Rates After Partial Hepatectomy.

OBJECTIVE: This study aimed to compare the incidence of radiologically unrecognized (occult) hepatocellular carcinoma (HCC) lesions in explant hepatectomy specimens from orthotopic liver transplants (OLTs) performed for HCC with rates of HCC intrahepatic recurrence after resection. SUMMARY OF BACKGROUND DATA: Resection of HCC is associated with high rates of intrahepatic HCC recurrence. However, it is unclear whether these recurrences represent incomplete resection of unrecognized metastatic lesions from the primary tumor or subsequent de novo tumor formation due to inherent biological proclivity for HCC formation. METHODS: We collected patient, tumor, and pathology data on HCC patients treated surgically from 3696 OLTs in the Organ Procurement and Transplantation (OPTN) national database, 299 OLTs at a single transplant center, and 232 partial hepatectomies from a hepatobiliary cancer center. RESULTS: In the OPTN and high-volume transplant center cohorts, 37% and 42% of patients had occult HCC lesions on explant pathology, respectively. Among cancer center patients, the 2-year recurrence rate was 46%, and 74% of patients who recurred presented with liver only recurrence. CONCLUSION: Although the transplant and resection populations differ, occult multifocality is common in transplant explants and similar to the 46% early recurrence rate following partial hepatectomy. These data suggest that noncurative resection often results from occult intrahepatic multifocality present at the time of resection rather than a malignant predisposition of the remnant liver with de novo tumorigenesis.

Impact of prolonged dialysis prior to renal transplantation.

INTRODUCTION: The new kidney allocation system (KAS) prioritizes patients based on date of dialysis initiation or waitlisting, whichever is earlier. We hypothesized that this change would increase transplant rates for patients with prolonged pretransplant dialysis times (DT) and aimed to assess the impact of prolonged DT on post-transplant outcomes. METHODS: We used United Network for Organ Sharing registry data to assess outcomes for patients added to the renal transplant waitlist from January 1, 1998 to December 31, 2010 and patients transplanted from January 1, 1998 to December 3, 2012. RESULTS: Compared with patients transplanted pre-emptively, patients with <5 years, 5-9 years, and ≥10 years DT had progressively decreased graft and patient survival (P < .001). The rates of short-term complications including delayed graft function, graft loss within 30 days, and patient death within 30 days were significantly higher in cohorts with ≥10 years DT than in cohorts with less DT (P < .001). CONCLUSIONS: Patients with pretransplant DT of ≥10 years had worse outcomes than patients pre-emptively transplanted or transplanted with shorter DT. Durations of dialysis dependence beyond 10 years were associated with further deterioration in short-term but not long-term post-transplant outcomes.

Same policy, different impact: Center-level effects of share 35 liver allocation.

Early studies of national data suggest that the Share 35 allocation policy increased liver transplants without compromising posttransplant outcomes. Changes in center-specific volumes and practice patterns in response to the national policy change are not well characterized. Understanding center-level responses to Share 35 is crucial for optimizing the policy and constructing effective future policy revisions. Data from the United Network for Organ Sharing were analyzed to compare center-level volumes of allocation-Model for End-Stage Liver Disease (aMELD) ≥ 35 transplants before and after policy implementation. There was significant center-level variation in the number and proportion of aMELD ≥ 35 transplants performed from the pre- to post-Share 35 period; 8 centers accounted for 33.7% of the total national increase in aMELD ≥ 35 transplants performed in the 2.5-year post-Share 35 period, whereas 25 centers accounted for 65.0% of the national increase. This trend correlated with increased listing at these centers of patients with Model for End-Stage Liver Disease (MELD) ≥ 35 at the time of initial listing. These centers did not overrepresent the total national volume of liver transplants. Comparison of post-Share 35 aMELD to calculated time-of-transplant (TOT) laboratory MELD scores showed that only 69.6% of patients transplanted with aMELD ≥ 35 maintained a calculated laboratory MELD ≥ 35 at the TOT. In conclusion, Share 35 increased transplantation of aMELD ≥ 35 recipients on a national level, but the policy asymmetrically impacted practice patterns and volumes of a subset of centers. Longer-term data are necessary to assess outcomes at centers with markedly increased volumes of high-MELD transplants after Share 35. Liver Transplantation 23 741-750 2017 AASLD.

Differential Effects of HDAC6 Inhibition Versus Knockout During Hepatic Ischemia-Reperfusion Injury Highlight Importance of HDAC6 C-terminal Zinc-finger Ubiquitin-binding Domain.

BACKGROUND: Ischemia-reperfusion injury (IRI) causes significant morbidity in liver transplantation among other medical conditions. IRI following liver transplantation contributes to poor outcomes and early graft loss. Histone/protein deacetylases (HDACs) regulate diverse cellular processes, play a role in mediating tissue responses to IRI, and may represent a novel therapeutic target in preventing IRI in liver transplantation. METHODS: Using a previously described standardized model of murine liver warm IRI, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were assessed at 24 and 48 h after reperfusion to determine the effect of different HDAC inhibitors. RESULTS: Broad HDAC inhibition with trichostatin-A (TSA) was protective against hepatocellular damage ( P  < 0.01 for AST and P  < 0.05 for ALT). Although HDAC class I inhibition with MS-275 provided statistically insignificant benefit, tubastatin-A (TubA), an HDAC6 inhibitor with additional activity against HDAC10, provided significant protection against liver IRI ( P  < 0.01 for AST and P  < 0.001 for ALT). Surprisingly genetic deletion of HDAC6 or -10 did not replicate the protective effects of HDAC6 inhibition with TubA, whereas treatment with an HDAC6 BUZ-domain inhibitor, LakZnFD, eliminated the protective effect of TubA treatment in liver ischemia ( P  < 0.01 for AST and P  < 0.01 for ALT). CONCLUSIONS: Our findings suggest TubA, a class IIb HDAC inhibitor, can mitigate hepatic IRI in a manner distinct from previously described class I HDAC inhibition and requires the HDAC6 BUZ-domain activity. Our data corroborate previous findings that HDAC targets for therapeutic intervention of IRI may be tissue-specific, and identify HDAC6 inhibition as a possible target in the treatment of liver IRI.

Cardiac arrest associated with reperfusion of the liver during transplantation: incidence and proposal for a management algorithm.

Cardiac arrest associated with reperfusion of the liver allograft in a euvolemic patient is a rare but potentially devastating event. There are few case series describing experience with this complication and no published management protocols guiding treatment. This article is a retrospective case series of patients experiencing post-reperfusion intraoperative cardiac arrest between 1997 and 2011. Among 1581 liver transplants, 16 (1%) patients experienced post-reperfusion cardiac arrest. Among patients with intraoperative arrests, 14 (88%) patients required open cardiac massage. Seven (44%) were placed on cardiopulmonary bypass (CPB) when cardiac activity failed to adequately recover. Placement on CPB reversed cardiac pump failure and established a perfusing rhythm in six of seven (86%) recipients, leading to one of seven (14%) intraoperative mortality. Recovery of myocardial function was associated with low early survival with only 3/7 (43%) patients who underwent CPB surviving until discharge. Among all patients who survived the perioperative period, one-yr survival was 70% (N = 7), and five-yr survival was 50% (N = 5). Cardiac arrest during liver transplantation is associated with a poor prognosis during the perioperative period. In patients who do not recover cardiac activity after standard resuscitative measures, progression to physiologic support with systemic anticoagulation and CPB may allow correction of electrolyte derangements, maintenance of cerebral perfusion, and myocardial recovery.

Higher Fasting Pretransplant C-peptide Levels in Type 2 Diabetics Undergoing Simultaneous Pancreas-kidney Transplantation Are Associated With Posttransplant Pancreatic Graft Dysfunction.

BACKGROUND: Among selected patients with type 2 diabetes mellitus (T2DM), simultaneous pancreas and kidney (SPK) transplants can be an effective option. However, data are limited about outcomes in T2DM SPK recipients based on the pretransplant C-peptide levels. METHODS: In this study, we reviewed all T2DM SPK recipients and categorized them based on the pretransplant fasting C-peptide levels into 3 groups: low (≤2 ng/mL), medium (>2-8 ng/mL), and high (>8 ng/mL). Several measures of graft failures (GFs), graft dysfunction, and composite outcomes were of interest. RESULTS: There were a total of 76 SPK recipients (low, n = 14; medium, n = 47; high, n = 15). At the last follow-up, the low group did not reach any outcome; in contrast, 11 (23%) in the medium group and 5 (33%) in the high group reached the uncensored composite outcome; 6 (13%) in the medium group and 2 (13%) in the high group had GF; and 8 (17%) in the medium group and 4 (26.7%) in the high group reached the death-censored composite outcomes. In a fully adjusted model, each pretransplant C-peptide unit was not associated with an increased risk of the composite outcome, GF, or death-censored composite outcomes. However, in multivariate analysis with limited adjustment, pretransplant C-peptide was associated with the composite outcome (hazard ratio: 1.18, 95% confidence interval, 1.01-1.38; P = 0.03) and death-censored composite outcome (hazard ratio: 1.20; 95% confidence interval, 1.01-1.42; P = 0.03). CONCLUSIONS: Although limited by the small sample size, we found excellent outcomes among T2DM SPK recipients overall. However, higher levels of pretransplant C-peptide may be associated with inferior posttransplant outcomes that include graft dysfunction.

Liver Transplantation for Refractory Congenital Cytomegaloviral Hepatitis.

Congenital cytomegalovirus (cCMV) is the most common congenital infection. Here, we report on a case of severe, refractory cCMV hepatitis resulting in end-stage liver disease. A male infant born at 37 weeks gestational age presented with petechiae, splenomegaly, and jaundice associated with a direct hyperbilirubinemia, elevated transaminases, and thrombocytopenia. Urine screen was positive for CMV, and he was treated with valganciclovir. He progressed to decompensated cirrhosis with ascites, hypoglycemia, and coagulopathy and was listed for liver transplant at 4 months of age. At 5 months of age, he developed massive hematemesis with hemorrhagic shock and underwent emergent portocaval shunt followed by living donor liver transplant with a left lateral segment graft. Postoperatively, he received CMV immune globulin and intravenous ganciclovir and cleared his viremia by 2 months post-transplant. This case illustrates the diagnostic and management challenges of severe cCMV hepatitis and reports a successful liver transplantation despite active CMV viremia.

A Randomized Controlled Trial of Envarsus Versus Immediate Release Tacrolimus in Kidney Transplant Recipients With Delayed Graft Function.

BACKGROUND: The incidence of delayed graft function (DGF) among kidney transplant recipients (KTRs) in the United States continues to increase. The effect of immediate-release tacrolimus (tacrolimus) compared with extended-release tacrolimus (Envarsus) among recipients with DGF is unknown. METHODS: This was a single-center open-label randomized control trial among KTRs with DGF (ClinicalTrials. gov, NCT03864926). KTRs were randomized either to continue on tacrolimus or switch to Envarsus at a 1:1 ratio. Duration of DGF (study period), number of dialysis treatments, and need for adjustment of calcineurin inhibitor (CNI) doses during the study period were outcomes of interest. RESULTS: A total of 100 KTRs were enrolled, 50 in the Envarsus arm and 50 in the tacrolimus arm; of those, 49 in the Envarsus arm and 48 in the tacrolimus arm were included for analysis. There were no differences in the baseline characteristics, all P > .5, except donors in the Envarsus arm had higher body mass index (mean body mass index 32.9 ± 11.3 vs 29.4 ± 7.6 kg/m2 [P = .007]) compared with the tacrolimus arm. The median duration of DGF (5 days vs 4 days, P = .71) and the number of dialysis treatments (2 vs 2, P = .83) were similar between the groups. However, the median number of CNI dose adjustments during the study period in the Envarsus group was significantly lower (3 vs 4, P = .002). CONCLUSIONS: Envarsus patients had less fluctuation in the CNI level, requiring fewer CNI dose adjustments. However, there were no differences in the DGF recovery duration or number of dialysis treatments.

Hyperbaric oxygen therapy in necrotizing soft tissue infections.

BACKGROUND: Surgical debridement and antibiotics are the mainstays of therapy for patients with necrotizing soft tissue infections (NSTIs), but hyperbaric oxygen therapy (HBO) is often used as an adjunctive measure. Despite this, the efficacy of HBO remains unclear. We hypothesized that HBO would have no effect on mortality or amputation rates. METHODS: We performed a retrospective analysis of our institutional experience from 2005 to 2009. Inclusion criteria were age > 18 y and discharge diagnosis of NSTI. We abstracted baseline demographics, physiology, laboratory values, and operative course from the medical record. The primary endpoint was in-hospital mortality; the secondary endpoint was extremity amputation rate. We compared baseline variables using Mann-Whitney, chi-square, and Fisher's exact test, as appropriate. Significance was set at P < 0.05. RESULTS: We identified 80 cases over the study period. The cohort was 54% male (n = 43) and 53% white (n = 43), and had a mean age of 55 ± 16 y. There were no significant differences in demographics, physiology, or comorbidities between groups. In-hospital mortality was not different between groups (16% in the HBO group versus 19% in the non-HBO group; P = 0.77). In patients with extremity NSTI, the amputation rate did not differ significantly between patients who did not receive HBO and those who did (17% versus 25%; P = 0.46). CONCLUSIONS: Hyperbaric oxygen therapy does not appear to decrease in-hospital mortality or amputation rate after in patients with NSTI. There may be a role for HBO in treatment of NSTI; nevertheless, consideration of HBO should never delay operative therapy. Further evidence of efficacy is necessary before HBO can be considered the standard of care in NSTI.

Beyond Ice and the Cooler: Machine Perfusion Strategies in Liver Transplantation.

Machine perfusion (MP) has emerged as a promising preservation technique to reduce the risks associated with transplant of high risk (steatotic, elderly, and donation after circulatory death) hepatic allografts. Multiple strategies for MP are under investigation. MP facilitates assessment of organ viability and enables liver-directed therapy before transplant. Clinical trials suggest MP may improve the use of hepatic allografts, mitigate ischemia-reperfusion injury, and reduce the incidences of early allograft dysfunction, biliary complications, and ischemic cholangiopathy. As MP sees more widespread use outside of trial settings, more investigation will be needed to establish optimal application of this technology.

Not as Rare as Initially Described: Transplant Ureter Incarceration Within Inguinal Hernia. Two Cases, Literature Review, and Management Algorithm.

BACKGROUND: Obstructive uropathy after kidney transplant can present as acute kidney injury, urosepsis, and more rarely kidney allograft failure. We present a recent series of 2 cases and a literature review of 1 late etiology of ureteric obstruction: incarceration of the transplant ureter within an inguinal hernia. METHODS: We reviewed 2 cases of patients with ureteric incarceration in an inguinal hernia after kidney transplant and conducted a contemporary structured literature review. Relevant patient factors, management decisions, operative approaches, and clinical outcomes were abstracted and summarized. RESULTS: Two cases of ureteric involvement in an inguinal hernia from 2 institutions as well as a literature review of 14 case reports are provided. The clinical features most commonly associated with this condition were male sex, obesity, and decade or more delay between kidney transplantation and presentation. Preoperative management with nephrostomy tube with or without antegrade ureteric stent was most frequently employed. Ultimately, most patients underwent surgical hernia repair, which occasionally required additional surgery for distal ureteric resection or re-anastomosis. CONCLUSIONS: Incarceration of a transplant allograft ureter in inguinal hernia is likely not as rare as initially described, although a true incidence rate has not been established. This surgically correctible condition most frequently presents as a late complication after kidney transplantation. We present a management algorithm that can be used for the workup and treatment of patients with history of kidney transplant who present with ureteric obstruction owing to incarceration within an inguinal hernia.

HDAC2 targeting stabilizes the CoREST complex in renal tubular cells and protects against renal ischemia/reperfusion injury.

Histone/protein deacetylases (HDAC) 1 and 2 are typically viewed as structurally and functionally similar enzymes present within various co-regulatory complexes. We tested differential effects of these isoforms in renal ischemia reperfusion injury (IRI) using inducible knockout mice and found no significant change in ischemic tolerance with HDAC1 deletion, but mitigation of ischemic injury with HDAC2 deletion. Restriction of HDAC2 deletion to the kidney via transplantation or PAX8-controlled proximal renal tubule-specific Cre resulted in renal IRI protection. Pharmacologic inhibition of HDAC2 increased histone acetylation in the kidney but did not extend renal protection. Protein analysis demonstrated increased HDAC1-associated CoREST protein in HDAC2-/- versus WT cells, suggesting that in the absence of HDAC2, increased CoREST complex occupancy of HDAC1 can stabilize this complex. In vivo administration of a CoREST inhibitor exacerbated renal injury in WT mice and eliminated the benefit of HDAC2 deletion. Gene expression analysis of endothelin showed decreased endothelin levels in HDAC2 deletion. These data demonstrate that contrasting effects of HDAC1 and 2 on CoREST complex stability within renal tubules can affect outcomes of renal IRI and implicate endothelin as a potential downstream mediator.

Improved renal ischemia tolerance in females influences kidney transplantation outcomes.

Experimentally, females show an improved ability to recover from ischemia-reperfusion injury (IRI) compared with males; however, this sex-dependent response is less established in humans. Here, we developed a series of murine renal ischemia and transplant models to investigate sex-specific effects on recovery after IRI. We found that IRI tolerance is profoundly increased in female mice compared with that observed in male mice and discovered an intermediate phenotype after neutering of either sex. Transplantation of adult kidneys from either sex into a recipient of the opposite sex followed by ischemia at a remote time resulted in ischemia recovery that reflected the sex of the recipient, not the donor, revealing that the host sex determines recovery. Likewise, renal IRI was exacerbated in female estrogen receptor α-KO mice, while female mice receiving supplemental estrogen before ischemia were protected. We examined data from the United Network for Organ Sharing (UNOS) to determine whether there is an association between sex and delayed graft function (DGF) in patients who received deceased donor renal transplants. A multivariable logistic regression analysis determined that there was a greater association with DGF in male recipients than in female recipients. Together, our results demonstrate that sex affects renal IRI tolerance in mice and humans and indicate that estrogen administration has potential as a therapeutic intervention to clinically improve ischemia tolerance.