Long-term small bowel allograft function induced by short-term FK 506 application is associated with split tolerance

Update on Chronic Rejection After Intestinal Transplant: An Overview From Experimental Settings to Clinical Outcomes

Chronic rejection affects the long-term survival of solid-organ transplants, accounting for an incidence of between 5% and 10% after intestinal/multivisceral transplant. Because of unclear symptoms and signs and endoscopic findings, the diagnosis is often delayed. Presently, allograft removal represents the only available therapy due to the absence of effective pharmacologic approaches. Extensive research, through animal models, has been performed over the past 20 years to clarify the complex immune- and nonimmune-mediated mechanisms behind the development of chronic allograft enteropathy, with the aim of elucidating how to avert chronic rejection. The role of donor-specific antibodies and the way to challenge them in the clinic have gained acceptance among transplant centers as one of the main steps to prevent chronic rejection, although no common protocol exists that can be applied in a systematic fashion. The adjunct of a liver graft when retrans planting is needed in a sensitized recipient due to its protective effect against humoral immunity. Multicenter studies and clinical trials are required to better understand the pathogenesis of chronic rejection and to find the therapeutic answer to this clinical query.

Genetic Heterogeneity and Efficiency of Two Different Methods of Adenovirus-Mediated Gene Transfer in a Rat Liver Transplantation Model

PURPOSE

We used recombinant adenoviral vectors for gene therapy in liver transplantation, and investigated the efficacy of gene transfer and expression on the grafts and genetic heterogeneity, with two exogenous gene transfer methods in three different syngeneic rat strains.

METHODS

We transferred adenoviral vector encoding Escherichia coli beta-galactosidase via a donor tail vein 3 days before transplantation; via a recipient tail vein immediately after grafting; and ex vivo by perfusion and clamping during transplantation.

RESULTS

The high efficacy of beta-galactosidase gene transfer and expression was seen in both delivery systems, with 70% positivity for hepatocytes on day 3, which persisted for at least 3 weeks after transplantation. The efficacy of gene transfer and expression was similar in the three strains (DA, Lewis, and PVG).

CONCLUSIONS

These data suggest that adenovirus-mediated gene transfer delivers effective gene therapy by tail vein injection of a donor or a recipient, or by ex vivo graft perfusion in rat liver transplantation. It is not necessary to consider the differences in the strains. Furthermore, ex vivo graft perfusion is probably more suitable not only for rat liver transplantation but also possibly for future clinical application.

Short-term immunosuppression after rat parathyroid allotransplantation

The aim of this study was to evaluate whether short-term postoperative immunosuppression is able to sufficiently prolong graft survival after experimental allogeneic parathyroid transplantation. Heterotopic parathyroid transplantation was performed in 6 groups: 1) syngeneic control Lewis (LEW) to LEW; 2) allogeneic control Wistar-Furth (WF) to LEW; 3-5) WF to LEW plus short-term immunosuppression, postoperative days 1-13 (cyclosporine 5/10/20 mg/kg); and 6) WF to LEW plus 10 mg/kg CyA from preoperative day 7 to postoperative day 7. Graft function was examined up to 60 days; histological and immunohistological examination was performed on all grafts with impaired function. Graft function after syngeneic transplantation was indefinite, while recipients of allogeneic grafts turned hypocalcemic after 13 +/- 2 days. With immunosuppression, graft function was 21 +/- 2 days (groups 5 and 6) and 28 +/- 3 days (groups 3 and 4). Histologically, a cellular infiltrate responsible for graft destruction was found. The results show that indefinite parathyroid allograft survival cannot be achieved by short-term immunosuppression alone. Whether the combination of an additional graft pretreatment and immunosuppression has an impact on graft function will be further examined.

Short-course methotrexate and long-term acceptance of fully allogeneic rat cardiac grafts: a possible mechanism of tolerance

Although a short course of methotrexate (MTX) has a potential immunoregulatory effect on clinical allograft rejection, little data are available about the drug, and the mechanism of hyporeactivity after withdrawal is still unknown. In previous studies, we achieved permanent graft acceptance through administration of a short course of high-dose MTX during heterotopic ratheart transplantation (HHT) in a combination of DA (MHC haplotype; RT1(a)) to PVG/c (RT1(c)) rats. A 3-week course of MTX (0.25 mg/kg/day) was administered intraperitoneally to the PVG/c recipients of a DA heart graft, and 11 of 16 rats survived longer than 300 days after HHT. The splenic lymphocytes obtained from one recipient showed high reactivity against donor type splenic lymphocytes, but others did not. All serum samples from recipients showed immunosuppressive activity. The serum had anti-donor antibodies. These results showed that tolerance induced by short-course MTX was maintained by a serologic factor believed to be anti-idiotypic antibodies.

Orthotopic liver/small bowel transplantation in rats: a microsurgical model inducing tolerance

Liver cirrhosis in patients with short bowel syndrome is successfully treated in humans by simultaneous liver/small bowel transplantation. However, until now, a clinically relevant experimental rat model for this procedure has not existed. We therefore established a protocol that, for the first time in rats, allows the simultaneous transplantation of arterialized liver and small bowel into an orthotopic position. Short-term immunosuppression induced not only allograft acceptance but tolerance (as demonstrated by indicator heart/skin transplantation). The immunosuppressive dose required to achieve this result was dramatically less than that of protocols for successful small bowel transplantation alone. Immunohistochemistry detected a transient rejection crisis before tolerance. During this crisis, apoptotic recipient-type T lymphocytes, mainly CD8+ cells, accumulated in the liver but not in the small bowel allograft. The initiation of T-cell apoptosis is one possible explanation for the specific immunosuppressive effect of the liver allograft, which also supports the simultaneously transplanted small bowel allograft in our model.