Until recently, liver transplantation in patients with hepatitis B was associated with a high rate of graft loss and poor survival because of viral recurrence. 1-3 Favorable outcome following liver transplantation for hepatitis B virus (HBV)-related liver disease was made possible with long-term, high-dose, passive immunoprophylaxis using hepatitis B immune globulin (HBIG). 4,5 Hepatitis B still recurs, however, despite HBIG. Recurrence may be caused by saturation of the antibody binding capacity of HBIG by a high viral load, or by mutations in the hepatitis B surface antigen (HBsAg) molecule that render HBIG ineffective. 6,7 Overall recurrence rates with HBIG monotherapy vary from approximately 15% to 50%. 4,5,[8][9][10][11] Using a different dosing schedule, in early experience from our own institution HBV recurrence on HBIG was 44%. 12 The wide disparity in the data reflects differing patient populations, e.g., patients who are HBV-DNA-positive at the time of transplantation have higher rates of recurrence. Moreover, the different dosing regimens of HBIG are also likely to influence recurrence rates. 5,11,13 An alternative approach to preventing HBV recurrence became possible using the purine nucleoside analog reversetranscriptase inhibitor, lamivudine. Demonstration of its efficacy, in the nontransplantation setting, in suppressing HBV-DNA synthesis 14,15 led to studies using lamivudine following liver transplantation as prophylaxis against hepatitis B recurrence, 16,17 or as treatment of de novo or recurrent hepatitis B. 17,18 Although a DNA virus, HBV replicates via an RNA intermediate. As is seen in human immunodeficiency virus, 19 lamivudine escape mutations in the tyrosine, methionine, aspartate, aspartate (YMDD) locus of the HBV-DNA polymerase are increasingly being reported. [20][21][22][23] While prophylactic failures of HBIG have been treated successfully with lamivudine, there are no reports documenting successful treatment of patients with lamivudine-resistant HBV.Mechanistic evidence suggests that HBIG and lamivudine would be synergistic. By inhibiting viral replication with lamivudine, it would be less likely that the viral binding capacity of HBIG would be overwhelmed; furthermore, there would be little pressure to select for HBIG-resistant mutations in the HBsAg molecule. By providing humoral immunity, HBIG may limit viral spread, confining the virus to extraheAbbreviations: HBV, hepatitis B virus; HBIG, hepatitis B immune globulin; HBsAg, hepatitis B surface antigen; anti-HBs, antibodies against hepatitis B surface antigen; PCR, polymerase chain reaction; HCC, hepatocellular carcinoma; HBeAg, hepatitis B envelope antigen.From

The normal development of T cells in the thymus requires both positive and negative selection. During positive selection, thymocytes mature only if their T-cell receptors react with some specificity to host major histocompatibility complex (MHC) and host peptides. During negative selection, thymocytes die if their T-cell receptors react with too high an affinity to the presenting cell, self MHC, and peptides to which they are exposed. These two processes are important for the development of the T-cell repertoire and the acquisition of self-tolerance, but their precise location and temporal relationship are not known. We have used the keratin 14 (K14) promoter to re-express a class II MHC antigen (I-Ab) in class II-negative mice. The transgenic I-A molecule is expressed only on thymic cortical epithelium; thymic medullary epithelium and bone-marrow-derived cells are I-A negative. CD4+ cells are positively selected in K14 mice, but clonal deletion does not ocur in K14 mice or in relB-negative mice, which lack a thymic medulla. The K14 CD4 cells are autoreactive, as they proliferate extensively to and specifically lyse I-Ab-positive target cells. These autoreactive cells make up 5% of the peripheral CD4 T cells, providing and estimate of the minimal frequency of positively selected cells that must subsequently undergo negative selection for self-tolerance to be preserved. Thus positive and negative selection occur in anatomically distinct sites.

Liver transplantation provides excellent patient and graft survival rates for patients affected with PSC independent of pretransplant biliary tract surgery. Incidental cholangiocarcinoma does not affect patient survival significantly. However, known CCA or common duct frozen section biopsy specimen or both showing CCA are associated with poor recipient survival, and OLT should be proscribed in these cases. Recurrent PSC occurs in approximately 9% of cases but does not affect patient survival. Post-transplant colectomy does not affect patient survival adversely.

ObjectiveThe authors determined the long-term outcome of patients undergoing hepatic retransplantation at their institution. Donor, operative, and recipient factors impacting on outcome as well as parameters of patient resource utilization were examined. Summary Background DataHepatic retransplantation provides the only available option for liver transplant recipients in whom an existing graft has failed. However, such patients are known to exhibit patient and graft survival after retransplantation that is inferior to that expected using the same organs in narive recipients. The critical shortage of donor organs and resultant prolonged patient waiting periods before transplantation prompted the authors to evaluate the results of a liberal policy of retransplantation and to examine the factors contributing to the inferior outcome observed in retransplanted patients. MethodsA total of 2053 liver transplants were performed at the UCLA Medical Center during a 13-year period from February 1, 1984, to October 1, 1996. A total of 356 retransplants were performed in 299 patients (retransplant rate = 17%). Multivariate regression analysis was performed to identify variables associated with survival. Additionally, a case-control comparison was performed between the last 150 retransplanted patients and 150 primarily transplanted patients who were matched for age and United Network of Organ Sharing (UNOS) status. Differences between these groups in donor, operative, and recipient variables were studied for their correlation with patient survival. Days of hospital and intensive care unit stay, and hospital charges incurred during the transplant admissions were compared for retransplanted patients and control patients.

In vitro studies have revealed several pathways by which T cells can respond to alloantigens, including CD4+ direct responses to allogeneic class 11 antigens, CD8+ direct responses to allogeneic class I antigens, and CD4+ "indirect" responses to peptides of alloantigens presented in association with responder class 11 molecules. In vivo studies of skin graft rejection, however, have so far provided dear evidence for the contribution of only the two direct pathways and not for indirect recognition. We have used major histocompatibility complex class 11-deficient mice as donors to test the role of indirect recognition in rejection of skin grafts. Class 11-deficient skin was always rejected without delay by normal recipients. Removal of recipient CD8+ cells (to leave the animals dependent on CD4+ function) or depletion of recipient CD4+ cells revealed that CD4+ cells were usually involved and sometimes absolutely required in this rapid rejection. Since the donor grafts lacked class II antigens, the CD4+ cells must have recognized donor antigens presented in association with recipient class 11 molecules. These results therefore indicate that indirect recognition can initiate rapid skin graft rejection.Theories to explain the special importance of major histocompatibility complex (MHC) antigens in graft rejection and the extraordinary strength of the immune response to these antigens are all based on the capacity of T cells to recognize allogeneic MHC antigens directly without the usual requirement that their peptides be processed and presented by recipient antigen presenting cells (APCs) (1-3). As a result, studies of the mechanisms of graft rejection have been dominated by concern with the direct pathways of alloreactivity. A few investigators, however, have considered the possibility that graft rejection might also occur through more classical immunologic mechanisms in which peptides of donor antigens are presented in association with recipient MHC molecules. La Rosa and Talmage (4) described this possibility as "indirect" recognition, but the actual role of this pathway in graft rejection has been difficult to determine.Recently, "knockout" mice lacking MHC class II antigens have been produced by the technique of targeted gene disruption by homologous recombination in embryonic stem cells (5, 6). Since these mice lack the MHC class II antigens responsible for stimulating CD4+ T cells, grafts from these mice can be used to examine rejection in the absence of direct stimulation of these helper T cells. The experiments described in this report suggest that in the absence of donor class II antigens, indirect recognition remains an effective pathway of alloreactivity leading to rapid graft rejection. MATERIALS AND METHODSClass II-Deficient Mice. The development and initial characterization of the class II-deficient mice used in these experiments have been described (5). Briefly, the Apb gene was disrupted in the D3 embryonic stem cell line of 129/Sv origin by the technique of homologous recombination. Cloned e...