Faculty Bibliography

This review focuses on our recent studies involving nonmyeloablative bone marrow transplantation as an approach to inducing organ allograft tolerance across MHC barriers in nonhuman primates and in patients. The clinical studies are focused on mechanisms of tolerance involved in a protocol carried out at Massachusetts General Hospital in HLA-mismatched haploidentical combinations for the induction of renal allograft tolerance. These studies, in which chimerism was only transient and GVHD did not occur, suggest an early role for donor-specific regulatory T cells in tolerance induction, followed by partial and gradual deletion of donor-reactive T cells. We utilized high-throughput sequencing methodologies in a novel way to identify and track large numbers of alloreactive T cell receptors (TCRs). This method has been shown to identify biologically significant alloreactive TCRs in transplant patients and pointed to clonal deletion as a major mechanism of long-term tolerance in these patients. More recently, we adapted this sequencing method to optimally identify the donor-specific regulatory T cell (Treg) repertoire. Interrogation of the early posttransplant repertoire demonstrated expansion of donor-specific Tregs in association with tolerance. Our studies suggest a role for the kidney graft in tolerance by these mechanisms in patients who had only transient chimerism. Nonhuman primate studies indicate that other organs, including the heart, the lungs and the liver, are less readily tolerated following a period of transient mixed chimerism. Our efforts to extend the reach of mixed chimerism for tolerance induction beyond the kidney are therefore focused on the addition of recipient Tregs to the protocol. This approach has the potential to enhance chimerism while further reducing the risk of GVHD.

The human liver is an organ with a diverse array of immunologic functions. Its unique anatomic position that leads to it receiving all the mesenteric venous blood, combined with its unique micro anatomy, allows it to serve as a sentinel for the body's immune system. Hepatocytes, biliary epithelial cells, Kupffer cells, stellate cells, and liver sinusoidal endothelial cells express key molecules that recruit and activate innate and adaptive immunity. Additionally, a diverse array of lymphoid and myeloid immune cells resides within and traffics to the liver in specific circumstances. Derangement of these trafficking mechanisms underlies the pathophysiology of autoimmune liver diseases, nonalcoholic steatohepatitis, and liver transplantation. Here, we review these pathways and interactions along with potential targets that have been identified to be exploited for therapeutic purposes.

OBJECTIVE:There are multiple approaches to manage the clinical complications of portal hypertension (PHTN) to treat/prevent spontaneous hemorrhage by mitigating thrombocytopenia. No single approach is ideal for all patients given the heterogeneity of this population. Our goal was to determine whether partial splenic embolization (PSE) was safe and effective in the pediatric population. METHODS:This is a retrospective review of our single-center experience for all patients ages 0 to 21 who underwent PSE between January 2010 and August 2017. The embolized splenic volume targeted was 60% to 70%. RESULTS:Twenty-six patients underwent PSE due to thrombocytopenia and/or recurrent variceal bleeding. Patients ranged in age from 18 months to 20 years (mean 13.1 years). The median platelet count before PSE was 53.0 (×10/L). The platelet count improved after PSE with values >100,000 in 21 patients (80.8%). Children with prior esophageal varices showed improvement after PSE with only 9 (34.6%) requiring further endoscopic therapy. After PSE, patients developed transient abdominal pain, distention, fever, and perisplenic fluid collections. Serious complications such as splenic abscess, splenic rupture, bleeding, pancreatic infarction, opportunistic infection, or death were not observed. One patient experienced thrombotic complications after PSE and was later diagnosed with myelodysplastic syndrome. CONCLUSIONS:PSE is a safe and effective alternative in the management of pediatric PHTN in select populations. PSE may be a favorable alternative to splenectomy and portal systemic shunting because it preserves functional spleen mass and avoids postprocedure accelerated liver disease or encephalopathy.

Human intestinal transplantation often results in long-term mixed chimerism of donor and recipient blood in transplant patients. We followed the phenotypes of chimeric peripheral blood cells in 21 patients receiving intestinal allografts over 5 years. Donor lymphocyte phenotypes suggested a contribution of hematopoietic stem and progenitor cells (HSPCs) from the graft. Surprisingly, we detected donor-derived HSPCs in intestinal mucosa, Peyer's patches, mesenteric lymph nodes, and liver. Human gut HSPCs are phenotypically similar to bone marrow HSPCs and have multilineage differentiation potential in vitro and in vivo. Analysis of circulating post-transplant donor T cells suggests that they undergo selection in recipient lymphoid organs to acquire immune tolerance. Our longitudinal study of human HSPCs carried in intestinal allografts demonstrates their turnover kinetics and gradual replacement of donor-derived HSPCs from a circulating pool. Thus, we have demonstrated the existence of functioning HSPCs in human intestines with implications for promoting tolerance in transplant recipients.

PURPOSE OF REVIEW:The aim of this study was to review the recent progress in xenotransplantation achieved through genetic engineering and discuss the potential of tolerance induction to overcome remaining barriers to extended xenograft survival. RECENT FINDINGS:The success of life-saving allotransplantation has created a demand for organ transplantation that cannot be met by the supply of human organs. Xenotransplantation is one possible solution that would allow for a nearly unlimited supply of organs. Recent genetic engineering of swine has decreased the reactivity of preformed antibodies to some, but not all, potential human recipients. Experiments using genetically modified swine organs have now resulted in survival of life-supporting kidneys for over a year. However, the grafts show evidence of antibody-mediated rejection on histology, suggesting additional measures will be required for further extension of graft survival. Tolerance induction through mixed chimerism or thymic transplantation across xenogeneic barriers would be well suited for patients with a positive crossmatch to genetically modified swine or relatively negative crossmatches to genetically modified swine, respectively. SUMMARY:This review highlights the current understanding of the immunologic processes in xenotransplantation and describes the development and application of strategies designed to overcome them from the genetic modification of the source animal to the induction of tolerance to xenografts.

OBJECTIVE:In order to minimize the impact of donation, fully laparoscopic donor hepatectomy (LDH) is being investigated at a few centers throughout the world. We report here our experience with 51 living donor pure laparoscopic hepatectomies. BACKGROUND:Adoption of minimal access techniques to living donor liver transplantation (LDLT) has been slowed by concerns about donor safety and the quality of the grafts. METHODS:Of 344 donor hepatectomies (DHs) for living donor liver transplantation (LDLT) since 1998, 51 pure LDH have been performed since 2009. We report here our experience with 51 living donor pure laparoscopic hepatectomy (LH), based on prospectively collected data. There were 31 left lateral sectionectomy and 20 full lobectomies LH. We matched full lobe LH to open DH prior to introduction of LH. RESULTS:LH increased from 21% of all DH in first 5 years of performing LH to 45% of DH in the most recent 3 years. Laparoscopic donors were more likely female, had lower body mass index, smaller total livers, and smaller allografts but longer operating room times. In the total LD experience, total 5 donors were converted to open surgery (10%), 2 donors required transfusion (4%), and there was 2 donor bile leaks (4%). Recipient patient and graft 1-year survival was 98% and 94%. CONCLUSIONS:Our experience indicates that LDH for LDLT can be safely used with appropriate attention to learning curve and progression from left lateral sectionectomy to right hepatectomy.

The goal of the study is to characterize the relationship between portal vein thrombosis (PVT) and hepatic atrophy in patients without cirrhosis and the effect of various types of surgical shunts on liver regeneration and splenomegaly. Patients without cirrhosis with PVT suffer from presinusoidal portal hypertension, and often hepatic atrophy is a topic that has received little attention. We hypothesized that patients with PVT have decreased liver volumes, and shunts that preserve intrahepatic portal flow enhance liver regeneration. Sixty-four adult and pediatric patients with PVT who underwent surgical shunt placement between 1998 and 2011 were included in a retrospective study. Baseline liver volumes from adult patients were compared with standard liver volume (SLV) as well as a group of healthy controls undergoing evaluation for liver donation. Clinical assessment, liver function tests, and liver and spleen volumes from cross-sectional imaging were compared before and after surgery. A total of 40 patients received portal flow-preserving shunts (32 mesoportal and 8 selective splenorenal), whereas 24 received portal flow-diverting shunts (16 nonselective splenorenal and 8 mesocaval). Baseline adult liver volumes were 26% smaller than SLV (1248 versus 1624 cm³ ; P = 0.02) and 20% smaller than the control volumes (1248 versus 1552 cm³ ; P = 0.02). Baseline adult spleen volumes were larger compared with controls (1258 versus 229 cm³ ; P < 0.001). Preserving shunts were associated with significant increase in liver volumes (886 versus 1131 cm³ ; P = 0.01), whereas diverting shunts were not. Diverting shunts significantly improved splenomegaly. In conclusion, we have demonstrated that patients without cirrhosis with PVT have significant liver atrophy and splenomegaly. Significant liver regeneration was achieved after portal flow-preserving shunts. Liver Transplantation 24 881-887 2018 AASLD.

BACKGROUND:Despite high survival in pediatric living donor liver transplantation (LDLT), only 10% of liver transplants in children in the United States are from living donors, reflecting reluctance to embrace this approach. In addition to optimal timing and graft quality, LDLT may offer immunologic benefit because most donors are haploidentical parents. We sought to quantify the benefit of LDLT compared to deceased donor liver transplantation (DDLT) using granular clinical and immunologic outcomes over the long term. METHODS:A retrospective cohort of children (age <18 years) surviving 1 year or longer posttransplant was evaluated to determine the impact of donor type on graft survival and immunologic outcomes. RESULTS:Two hundred forty-one children (177 DDLT and 64 LDLT) were assessed. In multivariable analysis, LDLT was associated with a lower rate of acute cellular rejection (hazard ratio [HR], 0.53; 95% confidence interval [CI], 0.29-0.98; P = 0.04), a lower rate of chronic rejection (HR, 0.12; 95% CI, 0.03-0.56; P = 0.007), better graft survival on monotherapy immunosuppression at 3 years posttransplant (87.7% vs 46.7%; odds ratio, 7.41; 95% CI, 2.80-19.66; P < 0.001), and a lower rate of graft loss (HR, 0.29; 95% CI, 0.10-0.88; P = 0.03). Graft type was not an independent predictor of posttransplant mortality (LDLT HR, 0.57; 95% CI, 0.16-2.01; P = 0.38). Maternal graft LDLT was associated with a lower rate of acute cellular rejection (HR, 0.13; 95% CI, 0.03-0.64; P = 0.01) and posttransplant lymphoproliferative disorder (HR, 0.04; 95% CI, 0.004-0.44; P = 0.008) compared with paternal grafts. CONCLUSIONS:This study demonstrates the potential benefit of LDLT, particularly with maternal grafts, for pediatric liver transplant recipients on multiple clinical parameters over long-term follow-up.