Faculty Bibliography

BACKGROUND:Porcine genome editing has revolutionized xenotransplantation, recently enabling the first pig-to-human heart xenotransplants. However, the xeno-immune response in heart xenografts remains largely unexplored. This study aimed to precisely characterize the xeno-immune response and injury in two heart xenografts, transplanted from 10-gene-edited pigs into brain-dead human recipients. METHODS:We analyzed xenograft biopsies at 66-hour post-reperfusion using a multimodal phenotyping approach combining: morphological evaluation, immunophenotyping, ultrastructural assessment, automated quantification of multiplex immunofluorescence staining and gene expression profiling. Xenografts before implantation and wild-type pig hearts with and without ischemia reperfusion injury and brain death were used as controls. RESULTS:Both xenografts showed evidence of endothelial activation and mild microvascular inflammation without capillary C4d deposition. Immune infiltrates were mainly composed of CD15+ and CD68+ innate immune cells. Ultrastructural assessment showed endothelial swelling with occasional intravascular leucocytes. Deep-learning based automated multiplex immunofluorescence analysis confirmed that microvascular inflammation was primarily associated with CD15+ and CD68+ innate immune cells. Both xenografts showed increased expression of genes and pathways associated with monocyte/macrophage activation, neutrophil activation, interferon-gamma response, natural killer cell burden, endothelial activation, apoptosis and injury repair. This phenotype was absent in all control pig hearts, independently from ischemia reperfusion injury and brain death. CONCLUSIONS:Multimodal phenotyping of pig-to-human heart xenografts revealed early signs of xeno-immune response, characterized by mild innate microvascular inflammation, endothelial activation, and molecular signature characteristic of antibody-mediated rejection. Developing such precision diagnostic system could improve graft monitoring in future clinical settings.

The increasing demand for donor hearts presents both a critical challenge and a significant opportunity for innovation in cardiac transplantation. Advancements in immunosuppressive regimens and genetic engineering have reignited recent interest in xenotransplantation. Notably, 2 human patients have received genetically modified pig hearts under expanded-access authorization. They survived for 40 and 60 days, with xenograft failure preceding death in both cases. Concurrently, decedent studies have focused on monitoring the short-term physiological function of genetically modified cardiac xenografts in legally brain-dead recipients, representing a novel experimental paradigm for preclinical testing to help bridge the gap between nonhuman primate studies and clinical trials. These contemporary achievements build on a large body of exploratory efforts in cardiac xenotransplantation in nonhuman primates. Despite significant progress in overcoming hyperacute rejection, adaptive cellular and humoral immunological barriers remain. This review aims to critically evaluate the current advancements in xenotransplantation, to explore ongoing challenges, and to discuss the future potential of this innovative approach in addressing the growing demand for donor organs in cardiac transplantation.

BACKGROUND:As donation after circulatory determination of death (DCD) heart transplantation (HT) becomes more widely adopted, there is a need to establish the most clinically effective method of organ procurement. OBJECTIVE:This international, multicenter study compares outcomes of DCD-HT across Europe and the United States (US) between recipients whose donor hearts were retrieved using thoraco-abdominal normothermic regional perfusion (taNRP) to those whose hearts were recovered using direct procurement and perfusion (DPP). METHODS:This was a retrospective observational study across 20 heart transplant centers in Belgium, Spain, the United Kingdom (UK) and the US. This study included all patients undergoing DCD-HT at participating centers, from the start of each center's DCD program through 01/01/2023. DCD-HT with recovery using either taNRP or DPP were compared to one-another. Post-transplant outcomes included (i)survival at 1-year, (ii)incidence of severe primary graft dysfunction (PGD), (iii)episodes of treated, biopsy-proven acute-cellular rejection (ACR) in the first year following transplantation. RESULTS:504 DCD-HT took place in the study period. Survival at one year was similar for taNRP and DPP recipients (91% vs 88%, p=0.1). taNRP recipients had a lower rate of severe PGD (7.6% vs 19.2%, p<0.001) and fewer episodes of biopsy-proven, ACR requiring treatment in the first-year post-transplantation (13% vs 25%,p<0.001). CONCLUSION/CONCLUSIONS:In an international study of DCD-HT, recipients of hearts retrieved by taNRP technique had lower rates of severe PGD and fewer episodes of biopsy-proven ACR in the first year when compared with those retrieved utilizing DPP. These results should be further investigated with randomized control trials.

CLINICAL CONDITION/UNASSIGNED:The authors present the case of a young man who presented with cardiogenic shock requiring venoarterial extracorporeal membrane oxygenation and microaxial flow pump complicated by acute spinal cord infarction (SCI) leading to bilateral lower extremity paraplegia. KEY QUESTIONS/UNASSIGNED:The key questions included the following: 1) What is the incidence and pathophysiology for SCI with mechanical circulatory support (MCS)?; 2) Which configurations of MCS carry a greater risk of SCI? How do we approach MCS escalation, recognizing that with each device we carry additive risk of complications?; 3) What data guide anticoagulation strategies for MCS?; and 4) What strategies can we implement to support patients who have suffered SCI from MCS? OUTCOME/RESULTS:Our patient was transitioned to a right ventricular assist device with Impella 5.5 as a bridge to therapy, and underwent cardiac transplantation 4 weeks after presentation with ongoing inpatient rehabilitation. TAKE-HOME MESSAGES/CONCLUSIONS:Contemporary MCS carries a small but significant risk of SCI which is often irreversible. More data are required to guide anticoagulation strategies for MCS and mitigate risk.

BACKGROUND/UNASSIGNED:Donation after circulatory death (DCD) with cardiopulmonary bypass for thoracoabdominal normothermic regional perfusion (TA-NRP) has led to increased use of donor hearts. Rejection rates and long-term survival outcomes are not known. METHODS/UNASSIGNED:A single-center retrospective cohort review of patients who underwent DCD heart transplantation from January 2020 to December 2023 was performed. Donor and recipient characteristics, operative characteristics, and posttransplantation outcomes were analyzed. Subgroup analysis comparing co-localized vs distant donors and recipients was performed. The primary end point was 1-year survival. Secondary end points included incidences of primary graft dysfunction (PGD), cardiac allograft vasculopathy (CAV), rejection rate, and overall mortality. Our TA-NRP protocol has remained the same, consisting of sternotomy, ligation of aortic arch vessels, establishment of cardiopulmonary bypass, reintubation, resuscitation of the heart, and cold static storage during transport. RESULTS/UNASSIGNED:< .005) ischemia times, without any other differences. CONCLUSIONS/UNASSIGNED:Outcomes after DCD heart transplantation using TA-NRP remain encouraging with acceptable rates of rejection, PGD, CAV, and survival at 1 year.

OBJECTIVE/UNASSIGNED:Anticoagulation monitoring in patients supported on extracorporeal membrane oxygenation is challenging given the risks of both bleeding and thrombotic complications. Based on our early clinical experience, we revised our heparin protocol by reducing our target anti-factor Xa assay from 0.3 to 0.7 U/mL to 0.15 to 0.5 U/mL, while instituting a partial thromboplastin time cutoff of 70 seconds. We evaluated the impact of this change on bleeding/thrombotic complications. METHODS/UNASSIGNED:A single-center retrospective study of adult patients on extracorporeal membrane oxygenation support was conducted from January 2015 to August 2022. Patients were stratified into groups based on protocol revision: Pre-Revision (2015-2018) or Post-Revision (2019-2022). Our primary end point was the incidence of bleeding/thrombotic complications. Time in therapeutic range was calculated to determine protocol adherence. Poisson regression was performed to correlate time in therapeutic range with the likelihood of complication. RESULTS/UNASSIGNED:008). CONCLUSIONS/UNASSIGNED:A modified heparin monitoring protocol defined by a lower therapeutic anti-factor Xa assay target and a set partial thromboplastin time cutoff correlated with decreases in bleeding/thrombotic complications in patients on extracorporeal membrane oxygenation.

IMPORTANCE/UNASSIGNED:The advanced ambulatory heart failure (HF) population comprises patients who have progressed beyond the pillars of recommended stage C HF therapies but can still find meaningful life-years ahead. Although these patients are commonly encountered in practice, national databases selectively capture the small groups accepted for heart transplant listing or left ventricular assist devices. The epidemiology, trajectories, and therapies for other ambulatory patients with advanced HF are poorly understood. OBSERVATIONS/UNASSIGNED:In December 2022, the National Heart, Lung and Blood Institute convened a team of experts to identify knowledge gaps and research priorities for the ambulatory population with limiting daily symptoms and transition toward refractory end-stage D HF, designated as stage C2D. This article summarizes the findings from that 3-day workshop. Workshop participants surveyed the initial challenges and knowledge gaps for (1) recognition of ambulatory C2D HF, (2) estimation of the magnitude of the affected population and identifiable subpopulations, and (3) physiologic phenotypes, such as low cardiac output, right HF, cardiorenal syndromes, congestive hepatopathy and frailty, which offer distinct targets for existing and emerging therapies. Social drivers of HF and patient preferences for quality/length of survival were highlighted as essential modifiers for personalization of therapies. CONCLUSIONS AND RELEVANCE/UNASSIGNED:Ten key points summarized workshop findings, with target cohorts for study proposed as a crucial next step. This workshop summary is intended as a call for action to address knowledge gaps and develop new strategies to improve outcomes in the large ambulatory population with C2D HF.

BACKGROUND:In the 2018 Organ Procurement and Transplantation Network donor heart allocation system, patients listed for re-transplantation due to cardiac allograft vasculopathy (CAV) are assigned to Status 4 unless hemodynamic criteria are met. We aim to examine waitlist outcomes of CAV patients among adult heart transplant candidates. METHODS:We examined waitlist mortality stratified by CAV and waitlist status among adult heart transplant candidates using Scientific Registry of Transplant Recipients data from 10/1/2018-11/1/2023. We analyzed waitlist mortality using Kaplan-Meier curves and doubly-robust Cox regressions adjusted for age, gender, sex, race, and dialysis. We compared CAV to non-CAV patients by initial waitlist status, first status of interest, and time-dependent status. RESULTS:Of 21,586 listed patients, 368 were listed for CAV. CAV patients were most often listed at Status 4 with lower proportions at Status 3/2/1 compared with non-CAV patients. Status 4 and Status 3 CAV candidates demonstrated higher than expected waitlist mortality compared to non-CAV counterparts (Status 4: HR 0.51, 95% CI 0.31-0.84; p < 0.01; Status 3: HR 0.61, 95% CI 0.23-1.64; p = 0.33) with similar mortality to non-CAV patients in Status 3 and 2, respectively (Status 4: HR 0.80, 95% CI 0.48-1.35; p = 0.4; Status 3: HR 1.07, 95% CI 0.40-2.86; p = 0.89). When stratifying by status tier, CAV waitlist patients ever listed at Status 4 and 3 had a higher probability of death compared to their non-CAV counterparts (Status 4: HR 1.99, 95% CI 1.20-3.31, p < 0.01; Status 3: HR 3.06, 95% CI 1.06-8.87, p = 0.04). CONCLUSIONS:After 2018, CAV patients had a higher risk of waitlist mortality at Status 4 and 3 compared to non-CAV patients. These results suggest that CAV patients are underprioritized in the current allocation system.