Joshua D. Mezrich

An Interaction between Kynurenine and the Aryl Hydrocarbon Receptor Can Generate Regulatory T Cells

The aryl hydrocarbon receptor (AHR) has been known to cause immunosuppression after binding dioxin. It has recently been discovered that the receptor may be central to T cell differentiation into FoxP3+ regulatory T cells (Tregs) versus Th17 cells. In this paper, we demonstrate that kynurenine, the first breakdown product in the IDO-dependent tryptophan degradation pathway, activates the AHR. We furthermore show that this activation leads to AHR-dependent Treg generation. We additionally investigate the dependence of TGF-β on the AHR for optimal Treg generation, which may be secondary to the upregulation of this receptor that is seen in T cells postexposure to TGF-β. These results shed light on the relationship of IDO to the generation of Tregs, in addition to highlighting the central importance of the AHR in T cell differentiation. All tissues and cells were derived from mice.

The aryl hydrocarbon receptor: a perspective on potential roles in the immune system

The aryl hydrocarbon receptor (AHR) is a protein best known for its role in mediating toxicity. Over 30 years of research has uncovered additional roles for the AHR in xenobiotic metabolism and normal vascular development. Activation of the AHR has long been known to cause immunotoxicity, including thymic involution. Recent data suggesting a role for the AHR in regulatory T‐cell (Treg) and T‐helper 17 (Th17) cell development have only added to the excitement about this biology. In this review, we will attempt to illustrate what is currently known about AHR biology in the hope that data from fields as diverse as evolutionary biology and pharmacology will help elucidate the mechanism by which AHR modifies immune responses. We also will discuss the complexities of AHR pharmacology and genetics that may influence future studies of AHR in the immune system.

Efficacy of neoadjuvant chemoradiation, followed by liver transplantation, for perihilar cholangiocarcinoma at 12 US centers.

BACKGROUND & AIMS Excellent single-center outcomes of neoadjuvant chemoradiation and liver transplantation for unresectable perihilar cholangiocarcinoma caused the United Network of Organ Sharing to offer a standardized model of end-stage liver disease (MELD) exception for this disease. We analyzed data from multiple centers to determine the effectiveness of this treatment and the appropriateness of the MELD exception. METHODS We collected and analyzed data from 12 large-volume transplant centers in the United States. These centers met the inclusion criteria of treating 3 or more patients with perihilar cholangiocarcinoma using neoadjuvant therapy, followed by liver transplantation, from 1993 to 2010 (n = 287 total patients). Center-specific protocols and medical charts were reviewed on-site. RESULTS The patients completed external radiation (99%), brachytherapy (75%), radiosensitizing therapy (98%), and/or maintenance chemotherapy (65%). Seventy-one patients dropped out before liver transplantation (rate, 11.5% in 3 months). Intent-to-treat survival rates were 68% and 53%, 2 and 5 years after therapy, respectively; post-transplant, recurrence-free survival rates were 78% and 65%, respectively. Patients outside the United Network of Organ Sharing criteria (those with tumor mass >3 cm, transperitoneal tumor biopsy, or metastatic disease) or with a prior malignancy had significantly shorter survival times (P < .001). There were no differences in outcomes among patients based on differences in surgical staging or brachytherapy. Although most patients came from 1 center (n = 193), the other 11 centers had similar survival times after therapy. CONCLUSIONS Patients with perihilar cholangiocarcinoma who were treated with neoadjuvant therapy followed up by liver transplantation at 12 US centers had a 65% rate of recurrence-free survival after 5 years, showing this therapy to be highly effective. An 11.5% drop-out rate after 3.5 months of therapy indicates the appropriateness of the MELD exception. Rigorous selection is important for the continued success of this treatment.

The Significance of Donor-Specific HLA Antibodies in Rejection and Ductopenia Development in ABO Compatible Liver Transplantation

The role of humoral alloreactivity in ABO‐compatible liver transplantation remains unclear. To understand the significance of donor‐specific HLA alloantibodies (DSA) in liver rejection, we applied the currently used strategy for detection of antibody‐mediated rejection of other solid allografts. For this purpose we reviewed the data on 43 recipients of ABO identical/compatible donor livers who had indication liver biopsy stained for complement element C4d and contemporaneous circulating DSA determination. Seventeen (40%) patients had significant circulating DSA in association with diffuse portal C4d deposition (DSA+/diffuse C4d+). These DSA+/diffuse C4d+ subjects had higher frequency of acute cellular rejection (ACR) 15/17 versus 13/26 (88% vs. 50%), p = 0.02, and steroid resistant rejection 7/17 versus 5/26 (41% vs. 19%), p = 0.03. Based on detection of the combination DSA+/diffuse C4d+, 53.6% of cases of ACR had evidence of concurrent humoral alloreactivity. Six of the 10 patients with ductopenic rejection had circulating DSA and diffuse portal C4d, three of whom (2 early and 1 late posttransplantation) developed unrelenting cholestasis, necessitating specific antibody‐depleting therapy to salvage the allografts. Thus, in ABO‐compatible liver transplantation humoral alloreactivity mediated by antibodies against donor HLA molecules appears to be frequently intertwined with cellular mechanisms of rejection, and to play a role in ductopenia development.

Donation after cardiac death: A 29-year experience

OBJECTIVE To report the long-term outcomes of 1218 organs transplanted from donation after cardiac death (DCD) donors from January 1980 through December 2008. METHODS One-thousand two-hundred-eighteen organs were transplanted into 1137 recipients from 577 DCD donors. This includes 1038 kidneys (RTX), 87 livers (LTX), 72 pancreas (PTX), and 21 DCD lungs. The outcomes were compared with 3470 RTX, 1157 LTX, 903 PTX, and 409 lung transplants from donors after brain death (DBD). RESULTS Both patient and graft survival is comparable between DBD and DCD transplant recipients for kidney, pancreas, and lung after 1, 3, and 10 years. Our findings reveal a significant difference for patient and graft survival of DCD livers at each of these time points. In contrast to the overall kidney transplant experience, the most recent 16-year period (n = 396 DCD and 1,937 DBD) revealed no difference in patient and graft survival, rejection rates, or surgical complications but delayed graft function was higher (44.7% vs 22.0%; P < .001). In DCD LTX, biliary complications (51% vs 33.4%; P < .01) and retransplantation for ischemic cholangiopathy (13.9% vs 0.2%; P < .01) were increased. PTX recipients had no difference in surgical complications, rejection, and hemoglobin A1c levels. Surgical complications were equivalent between DCD and DBD lung recipients. CONCLUSION This series represents the largest single center experience with more than 1000 DCD transplants and given the critical demand for organs, demonstrates successful kidney, pancreas, liver, and lung allografts from DCD donors.

Histocompatible miniature swine: an inbred large-animal model1

Three herds of miniature swine, each homozygous for a different set of alleles at the major histocompatibility complex (MHC), and five intra-MHC recombinant strains, have been reported by the authors’ laboratory. One herd (SLAdd) was selected for further inbreeding to achieve a histocompatible line. It has undergone seven additional generations of sequential brother-sister or father-daughter matings (termed G7). To determine the level of histocompatibility of these animals, the authors performed skin and heart transplantation without immunosuppression. In contrast to MHC-matched, minor antigen-mismatched animals that rejected skin in 11 days (median survival time [MST], n=6) and hearts in 35 days (MST, n=4), G7 animals accepted skin for greater than 340 days (>340, >448, and >677 days) and hearts for greater than 265 days (>265 and >269 days). Nevertheless, rejection of second grafts could be induced by sensitization, indicating that weak minor antigens remain, requiring further inbreeding to achieve full histocompatibility. We conclude that G7 animals are sufficiently inbred to accept first set skin and heart grafts indefinitely.

Exposure to Atmospheric Particulate Matter Enhances Th17 Polarization through the Aryl Hydrocarbon Receptor

Lung diseases, including asthma, COPD, and other autoimmune lung pathologies are aggravated by exposure to particulate matter (PM) found in air pollution. IL-17 has been shown to exacerbate airway disease in animal models. As PM is known to contain aryl hydrocarbon receptor (AHR) ligands and the AHR has recently been shown to play a role in differentiation of Th17 T cells, the aim of this study was to determine whether exposure to PM could impact Th17 polarization in an AHR-dependent manner. This study used both cell culture techniques and in vivo exposure in mice to examine the response of T cells to PM. Initially experiments were conducted with urban dust particles from a standard reference material, and ultimately repeated with freshly collected samples of diesel exhaust and cigarette smoke. The readout for the assays was increased T cell differentiation as indicated by increased generation of IL-17A in culture, and increased populations of IL-17 producing cells by intracellular flow cytometry. The data illustrate that Th17 polarization was significantly enhanced by addition of urban dust in a dose dependent fashion in cultures of wild-type but not AHR-/- mice. The data further suggest that polycyclic aromatic hydrocarbons played a primary role in this enhancement. There was both an increase of Th17 cell differentiation, and also an increase in the amount of IL-17 secreted by the cells. In summary, this paper identifies a novel mechanism whereby PM can directly act on the AHR in T cells, leading to enhanced Th17 differentiation. Further understanding of the molecular mechanisms responsible for pathologic Th17 differentiation and autoimmunity seen after exposure to pollution will allow direct targeting of proteins involved in AHR activation and function for treatment of PM exposures.

COMPLICATIONS ASSOCIATED WITH LIVER TRANSPLANTATION IN THE OBESE RECIPIENT

The prevalence of the metabolic syndrome with attendant morbid obesity continues to increase nationwide. A concomitant increase in non‐alcoholic steatohepatitis (NASH) and associated end‐stage liver disease requiring transplantation is expected to parallel this trend. Between January 1, 1997 and December 31, 2008, our center performed 813 solitary adult deceased‐donor liver transplants. Patients were divided into groups based on the World Health Organization International Classification of obesity. Patients within each obesity class were compared to normal weight recipients. Preoperative demographics among all groups were similar. NASH was more common in higher BMI groups. Operative time, blood product usage, ICU length of stay, infectious complications, and biliary complications requiring intervention were all higher in obese recipients. Deep venous thrombosis occurred more commonly in patients with Class III obesity. Patients with Class II obesity had lower patient (HR 1.82, CI 1.09–3.01, p = 0.02) and allograft survival (HR 1.62, CI 1.02–2.65, p = 0.04). Obesity class did not reach statistical significance on multivariate analysis. Despite increased technical operative challenges and medical complexities associated with increasing recipient BMI, morbid obesity in and of itself should not be an absolute contraindication to liver transplantation as these patients have reasonable long‐term outcomes.

The Aryl Hydrocarbon Receptor Meets Immunology: Friend or Foe? A Little of Both

The aryl hydrocarbon receptor (AHR) has long been studied by toxicologists as a ligand-activated transcription factor that is activated by dioxin and other environmental pollutants such as polycyclic aromatic hydrocarbons (PAHs). The hallmark of AHR activation is the upregulation of the cytochrome P450 enzymes that metabolize many of these toxic compounds. However, recent findings demonstrate that both exogenous and endogenous AHR ligands can alter innate and adaptive immune responses including effects on T-cell differentiation. Kynurenine, a tryptophan breakdown product, is one such endogenous ligand of the AHR. Expression of indoleamine 2,3-dioxygenase by dendritic cells causes accumulation of kynurenine and results in subsequent tolerogenic effects including increased regulatory T-cell activity. At the same time, PAHs found in pollution enhance Th17 differentiation in the lungs of exposed mice via the AHR. In this perspective, we will discuss the importance of the AHR in the immune system and the role this might play in normal physiology and response to disease.

Antithymocyte Globulin is Associated with a Lower Incidence of De Novo Donor-Specific Antibodies in Moderately Sensitized Renal Transplant Recipients

Background Recent evidence suggests that de novo donor-specific antibodies (dnDSA) are associated with antibody-mediated rejection (ABMR) and graft failure after kidney transplantation. The effects of induction immunosuppression on dnDSA are unknown. Methods The study population comprised 114 consecutive moderately sensitized (positive DSA and negative flow crossmatch) recipients who received deceased donor renal transplants between December 2009 and November 2011. Patients were divided into two groups based on induction immunosuppression: antithymocyte globulin (ATG) (n=85) or basiliximab (n=29) and were followed up for 36 months. Results Patients in the ATG group received a mean dose of 4.98 mg/kg±7.9 mg/kg, had a significantly higher PRA, and received more plasmapheresis and IVIG at the time of transplant. The incidence of dnDSA (P=0.02, HR=0.33, 95% CI 0.09–1.24) and ABMR (P=0.001, HR=0.9, 95% CI 0.04–0.87) was significantly lower in the ATG group. In multivariate regression analyses, ATG induction was the single most important variable associated with both ABMR and dnDSA. Conclusions In moderately sensitized deceased donor renal transplant recipients, induction with ATG is associated with a reduction in the occurrence of dnDSA and ABMR when compared with basiliximab.