Faculty Bibliography

INTRODUCTION/BACKGROUND:Predicting graft failure risk in pediatric liver transplantation (LT) recipients could identify areas for improving management. Persistent cognitive, motor, academic, and functional deficits are common in recipients and their impact on graft survival following LT helps inform risk prediction. METHODS:Using SRTR data 2008-2023, we evaluated the cognitive, motor, academic, and functional deficits of LT recipients at time of transplant to 14 years post-LT. We compared all cause graft failure (ACGF) among patients with versus without pre-LT and 1-year post-LT deficits using Cox regression, adjusting for recipient characteristics. We calculated an individual risk score for ACGF. RESULTS:In 8062 pediatric LT recipients median age 3 (IQR: 1, 10), 28.0%, 29.5%, 35.0%, and 79.8% of recipients had pre-LT deficits in cognition, motor, academic activity, and functional status respectively. This decreased to 23.0%, 18.1%, 14.2%, and 38.7% 1-year post-LT. Increased hazard of ACGF was noted in recipients with pre-LT decreased functional status (aHR = 1.13 (per 10% decrease), 95% CI: 1.10-1.15, p < 0.001), definite motor delay (aHR = 1.60, 95% CI: 1.21-2.10, p < 0.001), and inability to participate in academics (aHR = 1.49, 95% CI: 1.08-1.89, p = 0.01), but not delays in cognition (aHR = 0.91, 95% CI: 0.69-1.21, p = 0.19). Our risk score predicting ACGF demonstrated improved predictive performance compared to clinical parameters alone (C-statistic = 0.70 (0.67, 0.72) vs. 0.66 (0.64, 0.69), p < 0.001). CONCLUSIONS:Pediatric LT recipients with pre- or post-LT motor, academic, and functional deficits are at higher risk for ACGF. Care should be taken to assess deficits to identify patients who may benefit from functional intervention to potentially reduce ACGF risk.

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.

The large deficit in donated organs required to provide transplantation to patients with end-stage organ disease is a global health crisis, exacerbated by regional differences in clinical practice and available resources. This deficit highlights the need for better tools to determine organ suitability for transplantation and to enhance the recovery of potential donor organs which are currently not transplanted due to concerns about organ quality. Novel organ assessment approaches, including epidemiological predictive models, advanced functional biometrics, and refined histological analysis, show potential to better identify donated organs suitable for transplantation. In addition, novel machine perfusion platforms have shown remarkable capacities to preserve and potentially modify injured organs, and a series of xenotransplantation experiments suggest a viable pathway to create a new organ supply. Collectively, these technologies will gradually alleviate the organ shortage and expand access to life-saving transplants.

The gastrointestinal tract is continuously exposed to foreign antigens in food and commensal microbes with potential to induce adaptive immune responses. Peripherally induced T regulatory (pTreg) cells are essential for mitigating inflammatory responses to these agents^1-4. While RORγt⁺ antigen-presenting cells (RORγt-APCs) were shown to program gut microbiota-specific pTreg^5-7, their definition remains incomplete, and the APC responsible for food tolerance has remained elusive. Here, we identify an APC subset required for differentiation of both food- and microbiota-specific pTreg cells and for establishment of oral tolerance. Development and function of these APCs require expression of the transcription factors Prdm16 and RORγt, as well as a unique Rorc(t) cis-regulatory element. Gene expression, chromatin accessibility, and surface marker analysis establish the pTreg-inducing APCs as myeloid in origin, distinct from ILC3, and sharing epigenetic profiles with classical dendritic cells (cDC), and designate them Prdm16⁺ RORγt⁺ tolerizing DC (tolDC). Upon genetic perturbation of tolDC, we observe a substantial increase in food antigen-specific T helper 2 (Th2) cells in lieu of pTreg, leading to compromised tolerance in mouse models of asthma and food allergy. Single-cell analyses of freshly resected mesenteric lymph nodes from a human organ donor, as well as multiple specimens of human intestine and tonsil, reveal candidate tolDC with co-expression of PRDM16 and RORC and an extensive transcriptome shared with mice, highlighting an evolutionarily conserved role across species. Our findings suggest that a better understanding of how tolDC develop and how they regulate T cell responses to food and microbial antigens could offer new insights into developing therapeutic strategies for autoimmune and allergic diseases as well as organ transplant tolerance.

OBJECTIVES/OBJECTIVE:To systematically review the safety and efficacy of nonbiological (NBAL) or biological artificial liver support systems (BAL) and whole-organ extracorporeal liver perfusion (W-ECLP) systems, in adults with acute liver failure (ALF) and acute-on-chronic liver failure (ACLF). DATA SOURCES/METHODS:Eligible NBAL/BAL studies from PubMed/Embase searches were randomized controlled trials (RCTs) in adult patients with ALF/ACLF, greater than or equal to ten patients per group, reporting outcomes related to survival, adverse events, transplantation rate, and hepatic encephalopathy, and published in English from January 2000 to July 2023. Separately, we searched for studies evaluating W-ECLP in adult patients with ALF or ACLF published between January1990 and July 2023. STUDY SELECTION AND DATA EXTRACTION/METHODS:Two researchers independently screened citations for eligibility and, of eligible studies, retrieved data related to study characteristics, patients and interventions, outcomes definition, and intervention effects. The Cochrane Risk of Bias 2 tool and Joanna Briggs Institute checklists were used to assess individual study risk of bias. Meta-analysis of mortality at 28-30 days post-support system initiation and frequency of at least one serious adverse event (SAE) generated pooled risk ratios (RRs), based on random (mortality) or fixed (SAE) effects models. DATA SYNTHESIS/RESULTS:Of 17 trials evaluating NBAL/BAL systems, 11 reported 28-30 days mortality and five reported frequency of at least one SAE. Overall, NBAL/BAL was not statistically associated with mortality at 28-30 days (RR, 0.85; 95% CI, 0.67-1.07; p = 0.169) or frequency of at least one SAE (RR, 1.15; 95% CI, 0.99-1.33; p = 0.059), compared with standard medical treatment. Subgroup results on ALF patients suggest possible benefit for mortality (RR, 0.67; 95% CI, 0.44-1.03; p = 0.069). From six reports of W-ECLP (12 patients), more than half (58%) of severe patients were bridged to transplantation and survived without transmission of porcine retroviruses. CONCLUSIONS:Despite no significant pooled effects of NBAL/BAL devices, the available evidence calls for further research and development of extracorporeal liver support systems, with larger RCTs and optimization of patient selection, perfusion durability, and treatment protocols.

BACKGROUND:Xenotransplantation of genetically engineered porcine organs has the potential to address the challenge of organ donor shortage. Two cases of porcine-to-human kidney xenotransplantation were performed, yet the physiological effects on the xenografts and the recipients' immune responses remain largely uncharacterized. METHODS:We performed single-cell RNA sequencing (scRNA-seq) and longitudinal RNA-seq analyses of the porcine kidneys to dissect xenotransplantation-associated cellular dynamics and xenograft-recipient interactions. We additionally performed longitudinal scRNA-seq of the peripheral blood mononuclear cells (PBMCs) to detect recipient immune responses across time. FINDINGS/RESULTS:Although no hyperacute rejection signals were detected, scRNA-seq analyses of the xenografts found evidence of endothelial cell and immune response activation, indicating early signs of antibody-mediated rejection. Tracing the cells' species origin, we found human immune cell infiltration in both xenografts. Human transcripts in the longitudinal bulk RNA-seq revealed that human immune cell infiltration and the activation of interferon-gamma-induced chemokine expression occurred by 12 and 48 h post-xenotransplantation, respectively. Concordantly, longitudinal scRNA-seq of PBMCs also revealed two phases of the recipients' immune responses at 12 and 48-53 h. Lastly, we observed global expression signatures of xenotransplantation-associated kidney tissue damage in the xenografts. Surprisingly, we detected a rapid increase of proliferative cells in both xenografts, indicating the activation of the porcine tissue repair program. CONCLUSIONS:Longitudinal and single-cell transcriptomic analyses of porcine kidneys and the recipient's PBMCs revealed time-resolved cellular dynamics of xenograft-recipient interactions during xenotransplantation. These cues can be leveraged for designing gene edits and immunosuppression regimens to optimize xenotransplantation outcomes. FUNDING/BACKGROUND:This work was supported by NIH RM1HG009491 and DP5OD033430.

With the increasing incidence of hepatocellular carcinoma (HCC) in both the United States and globally, the role of liver transplantation in management continues to be an area of active conversation as it is often considered the gold standard in the treatment of HCC. The use of living donor liver transplantation (LDLT) and the indications in the setting of malignancy, both generally and in HCC specifically, are frequently debated. In terms of both overall survival and recurrence-free survival, LDLT is at least equivalent to DDLT, especially when performed for disease within Milan criteria. Emerging and compelling evidence suggests that LDLT is superior to DDLT in treating HCC as there is a significant decrease in waitlist mortality. As the oncologic indications for liver transplantation continue to expand and the gap between organ demand and organ availability continues to worsen, high volumes centers should consider using LDLT to shrink the ever-expanding waitlist.

BACKGROUND AIMS/UNASSIGNED:In liver transplantation, cold preservation induces ischemia, resulting in significant reperfusion injury. Hypothermic Oxygenated Machine Perfusion (HMP-O2) has shown benefit compared to static cold storage (SCS) by limiting ischemia-reperfusion injury. This study reports outcomes using a novel portable HMP-O2 device in the first US randomized control trial. APPROACH RESULTS/UNASSIGNED:The PILOT™ trial (NCT03484455) was a multicenter, randomized, open-label, non-inferiority trial, with participants randomized to HMP-O2 or SCS. HMP-O2 livers were preserved using the Lifeport® Liver Transporter and Vasosol® perfusion solution. Primary outcome was early allograft dysfunction (EAD). Non-inferiority margin was 7.5%. From 4/3/19-7/12/22, 179 patients were randomized to HMP-O2 (n=90) or SCS (n=89). Per protocol cohort included 63 HMP-O2 and 73 SCS. EAD occurred in 11.1% HMP-O2 (N=7) and 16.4% SCS (N=12). The risk difference between HMP-O2 and SCS was -5.33% (one-sided 95% upper confidence limit of 5.81%), establishing noninferiority. Risk of graft failure as predicted by L-GrAFT7 was lower with HMP-O2 (median [IQR] 3.4% [2.4-6.5] vs. 4.5% [2.9-9.4], p=0.024). Primary nonfunction occurred in 2.2%, all SCS (n=3, p=0.10). Biliary strictures occurred in 16.4% SCS (n=12) and 6.3% (n=4) HMP-O2 (p=0.18). Non-anastomotic biliary strictures occurred only in SCS (n=4). CONCLUSIONS:HMP-O2 demonstrates safety and noninferior efficacy for liver graft preservation in comparison to SCS. EAD by L-GrAFT7 was lower in HMP-O2, suggesting improved early clinical function. Recipients of HMP-O2 livers also demonstrated a lower incidence PNF and biliary strictures, although this difference did not reach significance.