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Background: Multiple listing (ML) at >1 transplant center is one mechanism to combat the geographic disparities in liver transplantation (LT) rates. The objective of our study was to determine the impact of multiple listing on LT rates., Methods: We examined the United Network of Organ Sharing database from 2002 to 2016 after excluding those listed for multiple organs, hepatocellular carcinoma, or living donor LT. The waitlist mortality and LT rates for the ML groups and the single listed (SL) group were compared after stratifying patients by the Model for End-Stage Liver Disease (MELD) with a cutoff at 15 (<15 and ≥15)., Results: Of the 83 935 listed during the study period, 80 351 were listed in a single center (SL group), and 3584 were listed in >1 center (ML group). Of the ML groups, 2028 (2.4%) were listed at multiple donor service areas but within the same region (ML-SR) and 1556 (1.9%) listed in different regions (ML-DR). The median MELD at LT was 20, 21, and 24 for ML-DR, ML-SR, and SL groups, respectively (P = 0.001). Although the probability of receiving LT was significantly higher for the ML groups relative to the SL group for both MELD groups (<15 and ≥15), the impact was the highest for ML-DR group. At MELD score <15, the probability of LT was 72% for ML-DR, 38% for ML-SR, and 32% for SL groups. At MELD score ≥15, the probability of LT was 79% for ML-DR, 67% for ML-SR, and 61% for SL groups., Conclusions: Multiple listing appeared to considerably improve a patient's chance of receiving LT and survival with the highest benefit for those with low MELD scores (<15) listed at multiple regions.

Background: Inbred miniature swine provide a large animal model in which the effects of selective major histocompatibility complex (MHC) matching can be reproducibly studied. We have previously demonstrated that although a 12-day course of cyclosporine uniformly induces tolerance to class I-mismatched renal allografts, it does not induce tolerance across full MHC barriers. In this study, we assessed whether and at what dose tacrolimus might permit allografts to induce tolerance across different MHC barriers., Methods: Recipients of MHC disparate renal allografts were treated with a 12-day course of tacrolimus by continuous intravenous infusion. Groups were divided as follows: (1) class I-mismatched kidneys with 0.3 mg/kg/day tacrolimus (n=3); (2) fully MHC-mismatched kidneys with 0.3 mg/kg/day tacrolimus (n=2); and (3) fully MHC-mismatched kidneys with 0.12-0.16 mg/kg/day tacrolimus (n=4)., Results: In groups 1 and 2, recipients with tacrolimus levels of 45-80 ng/ml accepted renal allografts long-term with stable renal function. Donor-specific hyporesponsiveness was demonstrated by cell-mediated lymphocytotoxicity and mixed lymphocyte response, and subsequent donor-matched grafts were also accepted, without further immunosuppression (n=4), confirming systemic tolerance. In group 3, recipients that achieved tacrolimus levels of 35 ng/ml (n=2) accepted their grafts without chronic changes, whereas recipients with levels of 20-26 ng/ml (n=2) developed chronic allograft glomerulopathy, suggesting 35 ng/ml as the threshold blood level for tolerance induction. In vitro assays demonstrated that peripheral blood lymphocytes from tolerant animals produced inhibitory cytokines, suggesting the involvement of regulatory mechanisms., Conclusions: To our knowledge, this study represents the first demonstration of the induction of transplant tolerance across a two-haplotype full MHC barrier with a short course of immunosuppression in a large animal model. These studies may also have clinical applicability, because the time course required to induce tolerance was sufficiently short that the high drug levels required might be expected to be tolerated clinically with only transient toxicity.

Background: Xenogeneic donor-specific tolerance can be induced by transplanting fetal pig thymus and liver tissue (FP THY/LIV) to thymectomized (ATX), T/NK cell-depleted mice. By using neonatal pig tissue, we hoped to overcome two obstacles that arise with the use of fetal pig tissue: (1) the inability to keep fetal pigs alive after harvesting their thymic tissue, resulting in unavailability of their skin or other organs for grafting; and (2) the limited fetal thymic tissue yield, making application to large animals and humans more difficult., Methods: Neonatal pig thymus tissue (NP THY) was grafted into ATX, T/NK cell-depleted, 3Gy whole body-irradiated, originally immunocompetent B6 mice to evaluate the ability of NP THY to reconstitute mouse CD4+ T cells and to induce xenogeneic tolerance to donor pig skin grafts., Results: Repopulation of mouse CD4+ T cells in the peripheral tissues was observed in T/NK cell-depleted, ATX B6 mice that received NP THY with or without neonatal pig spleen (NP SPL), but not in those receiving NP SPL alone, indicating that pig thymus grafting was necessary and sufficient for mouse T cell recovery. Seven of nine NP THY/SPL-grafted ATX mice and two of six NP THY-grafted ATX mice that reconstituted >5% CD4+ cells in PBL accepted donor pig skin long-term without lymphocyte infiltration, whereas they rejected allogeneic BALB/c skin and third party pig skin grafts as rapidly as euthymic mice., Conclusions: NP THY can support the development of mouse CD4+ T cells that are functional and specifically tolerant to donor pig antigens in ATX, T/NK cell-depleted, 3 Gy whole body-irradiated, originally immunocompetent B6 mice. Additional grafting of NP SPL with NP THY improves the efficiency of tolerance induction in this model.

Background: Previous studies in our laboratory have demonstrated the importance of the thymus for rapid and stable tolerance induction in an allotransplant model. The focus of the present study was to explore the feasibility of autologous thymic transplantation to produce a new transplantable organ (thymokidney) and to examine the function of subsequent vascularized thymokidney transplants in T cell development., Materials and Methods: Eight juvenile swine received autologous thymic grafts under the renal capsule. Thymic tissue was obtained through a partial (n=6) or complete (n=2) thymectomy, and growth of the autologous thymic graft was compared between partially and completely thymectomized animals. Two of the partially thymectomized animals received irradiated (1000 cGy) as well as non-irradiated autologous thymic grafts. Graft survival, growth and evidence of thymocyte development was determined by (a) macroscopic examination of the implanted tissue, (b) histological examination, and (c) flow cytometry. Naive CD4 SP T cells were identified by CD45RA-expression., Results: Growth of transplanted thymic tissue was demonstrated in all thymic graft recipients. No difference was seen between partially and completely thymectomized animals. By POD 60, the thymic grafts exhibited normal macroscopic and microscopic structure, and normal thymocyte composition. Irradiated thymic tissue displayed a similar pattern of development, but growth was markedly delayed. To evaluate thymic function of the graft, a composite thymokidney was transplanted into a recipient which had previously been thymectomized, had few circulating CD4-single positive cells and had lost MLR reactivity. The number of CD4+/CD45RA+ cells in this animal increased steadily from POD 30 to POD 150, indicating that the thymus of the composite thymokidney allograft was functional; in addition, MLR assays demonstrated that the recipient recovered immunocompetence., Conclusions: The establishment of a thymokidney by thymic autografting to the renal subcapsular space results in normal thymic growth and function, and may provide a valuable tool for studying the role of the thymus in tolerance induction. As far as we are aware, we provide the first evidence of functional vascularized thymic graft reconstituting T cells and leading to a return of a immunocompetence in a large animal model.

Xenotransplantation between phylogenetically distant species is prevented by hyperacute rejection (HAR), a process that is thought to be initiated by the binding of naturally occurring xenoreactive antibodies (NAb) to the endothelium of the xenograft (Xg) with subsequent activation of the classical pathway of C. The relative role of direct alternative pathway C activation in HAR is controversial. To evaluate the role of NAb in HAR of discordant rodent Xg, LEW rats were treated from the day of birth with i.p. injections of rabbit anti-rat IgM antiserum (RARM), or with mAb specific for rat kappa-light chain (OX12) or rat class II MHC (14-4-4S, Y-3P, or 10-2.16), in an effort to deplete B cells and NAb. These rats then underwent xenotransplantation with discordant guinea pig hearts. RARM was effective in depleting rats (n = 5) of B cells, serum IgM, and rat NAb directed against guinea pig cells, but guinea pig cardiac Xg survival was not prolonged compared with PBS-treated controls (n = 5), possibly due to the rabbit NAb specific for guinea pig cardiac tissue that were passively transferred in the RARM preparation. Of the anti-B cell mAb used to avoid this passive transfer of NAb, mAb 14-4-4S was highly effective (n = 9) in depleting the peripheral blood and spleen of B cells and the serum of IgM and NAb. Guinea pig cardiac Xg survival, however, was again not prolonged (n = 5), and rejected Xg from the B cell- and NAb-depleted recipients demonstrated rat C3 deposition in the absence of rat IgM and IgG. This study demonstrates that while neonatal anti-B cell antibody treatment can effectively deplete B cells and NAb in the rat, such treatment does not significantly prolong cardiac Xg survival in this well-established guinea pig to rat xenotransplantation model. These findings suggest that in addition to NAb depletion, inhibition of alternative C pathway activation and other humoral mechanisms may be necessary to prevent HAR and allow successful xenotransplantation.

A microcytotoxicity assay was used to search for cell-mediated cytotoxicity, serum-blocking factors, and antibody-dependent cell-mediated cytotoxicity (ADCC) against fibroblasts of donor origin in 19 human renal allograft recipients. Peripheral mononuclear cells (PMC) were frequently cytotoxic when they were obtained within 6 days prior to rejection, following sustained rejections, and within 1 month after removal of rejected grafts, but the toxicity was usually nonspecific. Recipient PMC were noncytotoxic when they were obtained within 6 days after the onset of an acute reversed rejection and during quiescent intervals when there was no evidence of rejection within 6 days before or after the assay. These data suggest that, regardless of its lack of specificity, there is some relationship between cytotoxicity of recipient PMC and allograft rejection. In none of 69 post-transplant serum samples was ADCC against donor target cells detected with the microcytotoxicity assay.

Spontaneous blastogenesis of peripheral blood mononuclear cells in recipients of renal allografts was studied by incorporation of 3H-thymidine. Three different levels of reactivity were observed that correlated with the patient's clinical course. Low levels of blast activity (i.e., median 680 dpm/million cells with 95% confidence interval (CI) of 480 to 880 dpm) were observed in pretransplant patients. A moderate elevation (median 3,00 dpm with CI of 2,300 to 5,300 dpm) was noted post-transplantation during quiescent intervals and following the onset of acute reversed rejection. Marked elevations, i.e., values greater than 10,000 dpm frequently were observed within 6 days prior to rejections (median 21,000 with CI of 7,400 to 34,000 dpm) and during sustained rejections (median 14,000 with CI of 8,800 to 19,600 dpm).