Donor-derived alloantigen-presenting cells persist in the liver allograft during tolerance induction

The predictive value of chimerism was evaluated in three different transplantation models in the rat without immunosuppression: small bowel- (SBTx), liver- (LTx), and liver/small bowel transplantation (LSBTx) were performed in the Brown Norway (BN)-to-Lewis-(LEW) strain combination. Immunohistochemistry and flow cytometry were used to identify donor cells in the recipient's spleen. Their number did not change significantly during transient rejection or tolerance after LTx and LSBTx. However, the amount of donor-derived nonparenchymal cells within the liver allograft including antigen-presenting cells (APCs), such as dendritic and Kupffer cells, clearly mirrored the recipient's immune status: as expected, their number decreased during rejection, but recovered considerably during and after tolerance induction. We conclude that donor cells in the periphery of the recipient correlate with the presence of the allograft, but do not seem to influence graft acceptance actively. However, the kinetics of the detected donor APC population in the liver suggests their important role in modifying the recipient's immune response towards tolerance.

Donor-derived alloantigen-presenting cells persist in the liver allograft during tolerance induction

The predictive value of chimerism was evaluated in three different transplantation models in the rat without immunosuppression: small bowel- (SBTx), liver- (LTx), and liver/small bowel transplantation (LSBTx) were performed in the Brown Norway (BN)-to-Lewis-(LEW) strain combination. Immunohistochemistry and flow cytometry were used to identify donor cells in the recipient's spleen. Their number did not change significantly during transient rejection or tolerance after LTx and LSBTx. However, the amount of donor-derived nonparenchymal cells within the liver allograft including antigen-presenting cells (APCs), such as dendritic and Kupffer cells, clearly mirrored the recipient's immune status: as expected, their number decreased during rejection, but recovered considerably during and after tolerance induction. We conclude that donor cells in the periphery of the recipient correlate with the presence of the allograft, but do not seem to influence graft acceptance actively. However, the kinetics of the detected donor APC population in the liver suggests their important role in modifying the recipient's immune response towards tolerance.

Tolerance of rat liver allografts induced by short-term selective immunosuppression combining monoclonal antibodies directed against CD25 and CD54 with subtherapeutic cyclosporine

BACKGROUND

Our purpose was to develop and evaluate protocols for selective immunosuppression after liver transplantation using the monoclonal antibodies (mAbs) NDS-61, directed against the interleukin-2 receptor (CD25), and 1A29, directed against the intercellular adhesion molecule-1 (CD54), in combination with subtherapeutic cyclosporine (CsA).

METHODS

Orthotopic rat liver transplantation (ORLT) was performed in a DA-to-LEW strain combination. Immunosuppression was administered from day 0 to +13. Functional parameters such as survival time, body weight, and serum bilirubin levels were measured and the liver grafts were evaluated histologically.

RESULTS

A stepwise tapering of CsA from 3 to 0.25 mg/kg/day reduced the long-term survival rate. All animals died at a CsA dosage of 0.25 mg/kg/day, which was therefore defined as subtherapeutic. Monotherapy with the anti-CD25 mAb was performed at dosages of 600 and 1800 microg/kg/day. The lower mAb dosage resulted in a long-term survival rate of 12% and was defined as subtherapeutic. The combination therapy of CsA (0.25 mg/kg/day) and anti-CD25 mAb (600 microg/kg/day) produced a synergistic effect and led to a long-term survival rate of 84%. This survival rate was significantly higher than those after either CsA (P<0.005) or anti-CD25 mAb (P<0.001) monotherapy. Both dosages (10 and 30 microg/kg/day) of anti-CD54 mAb monotherapy as well as anti-CD54 mAb combined with a subtherapeutic dosage of CsA were ineffective in preventing acute allograft rejection. The addition of anti-CD54 mAb (30 microg/kg/day) to combined CsA plus anti-CD25 mAb therapy (triple therapy), however, increased the long-term survival rate to 100%. In the triple therapy group there was no rejection process in the liver allografts at any time, and donor-specific tolerance could be shown by donor-specific and third-party heterotopic heart transplantation.

CONCLUSIONS

The synergistic action of subtherapeutic CsA plus anti-CD25 mAb NDS-60 could be demonstrated, whereas anti-CD54 mAb only had a positive effect in a triple therapy group. Triple therapy prevented both acute and chronic rejection and induced donor-specific tolerance.

Non-invasive evaluation of the location, the functional integrity and the oxygen supply of implants: 19F nuclear magnetic resonance imaging of perfluorocarbon-loaded Ba2+-alginate beads

19F nuclear magnetic resonance imaging (MRI) can be used as a non-invasive tool to simultaneously determine the location, the integrity and the oxygen supply of Ba2+-alginate implants. This requires that the beads (implants) are pre-loaded with the perfluorocarbon compound F-44E. Implantation of solid 19F-labelled beads into the peritoneum, below the kidney capsule or into the muscle of Wistar WU rats demonstrated that these beads could be detected by 19F-MRI for up to 18 months after implantation. This indicated that F-44E is not considerably released from the beads during implantation. The signal to noise ratio of liquid-core beads was higher by a factor of 4 than the signal to noise ratio of solid beads, but liquid-core beads were more fragile and also too large for implantation under the kidney capsule and into the intramuscular tissue. Quantitative 2-dimensional 19F-T1 maps (resolution 0.5 x 0.5 mm) could be deduced from 19F-MRI measurements. These T1-maps correlated to the local pO2-values. The partial oxygen pressure estimated in F-44E-loaded Ba2+-alginate beads showed that the oxygen supply inside the beads was very poor when they were implanted below the kidney capsule or into the peritoneal cavity. These low pO2-values obtained for the renal subcapsular site and the peritoneum may explain the failure of previous immunoisolated islet transplantation studies using these locations.

[Transplantation of porcine Langerhans islets for therapy of type I diabetes. The way to clinical application]

Transplantation of isolated pancreatic islets provides an interesting alternative to the present cure for diabetes: insulin injections and pumps. These are characterized by an insufficient glucose haemostasis and in the long run can induce kidney failure, blindness, heart failure, and amputations. Up to now more than 293 allogeneic islet transplantations have been performed in diabetics with chronical kidney failure. Despite some success, no real breakthrough has been yet achieved, though great efforts are being made to improve the various methodological steps on the way to clinical transplantation. The use of animal (xenogeneic) organs could be a solution to overcome the shortage of allogeneic donors. The current experimental and clinical research focuses on the use of pigs as organ donors, which have a number of advantages over the immunologically more compatible primates. This article reports on success and open questions concerning the efforts to isolate porcine islets for future clinical transplantation: the search for a suitable pig breed, the various isolation steps, purification and in vitro culture, transplantation models using-small and large animals, first clinical trials, and immunological reactions against the xenogeneic tissue. In addition, strategies to circumvent tissue rejection and future perspectives are discussed.

Videomicroscopic imaging of graft mucosa for monitoring immunosuppressive therapy after small intestinal transplantation in rats

BACKGROUND

Early diagnosis of rejection and effective immunosuppressive treatment are essential after small intestinal transplantation. To date little is known about microscopic alterations of the intestinal mucosa of the graft during rejection. We attempted to determine whether videomicroscopic imaging of the graft mucosa is a suitable method for monitoring immunosuppressive therapy.

METHODS

Real-time videomicroscopic imaging of an ileostoma was performed daily after allogeneic heterotopic small bowel transplantation in the rat (BN to LEW) with and without FK506 immunosuppression. Subsequently, the videomicroscopic findings were compared with the histologically determined grade of rejection.

RESULTS

A semiquantitative staging system was established for the intravital mucosal changes during graft rejection. The earliest changes related to rejection appeared on POD 6 in the untreated allogeneic group. The mucosa developed patchy paleness and the mucosal architecture was interrupted in places. The crypts were slightly widened and their color turned dark red (stage I). These alterations spread progressively over the mucosa on POD 7 (stage II). On POD 9 the mucosa appeared pale, the villi were shortened, and the crypts appeared wide and rounded (stage III). In the animals treated with FK506 similar changes were observed, but with a delayed onset. When FK506 was administered as antirejection therapy at the onset of rejection, a temporary improvement of mucosal alterations was observed (stage II --> stage I). The video-microscopic stages correlated with the histological grade of rejection.

CONCLUSIONS

The introduction of videomicroscopy has made computer-based high resolution imaging of mucosal microarchitecture possible. With videomi-croscopy beginning rejection can be detected, although it can still be reversed with antirejection therapy. This is a new noninvasive technique that might be of high clinical relevance.

Expression pattern of extracellular matrix proteins in the pancreas of various domestic pig breeds, the Goettingen Minipig and the Wild Boar

In spite of progress in biotechnology, isolation of porcine pancreatic islets remains a difficult task with unpredictable results. One reason could be the lack of knowledge as to the expression of extracellular matrix proteins in porcine exocrine and endocrine tissues, particularly in "islet capsules". Such proteins are subject to digestion by proteases, yet they might have a protective function for the fragile islets.

OBJECTIVE

Of our study was a detailed histological analysis of the extracellular matrix proteins in various pig breeds. A broad panel of commercial, human-specific antibodies were used, since antibodies against porcine tissue were not available.

METHODS

Frozen pancreatic tissue section of 7 domestic pig breeds, the Goettingen Minipig and the Wild Boar were stained with antibodies against collagen types I, II, III, IV, V, VI, VII, IX, laminin, fibronectin, vitronectin and elastin. Binding of antibodies was detected by immunoperoxidase and evaluated microscopically. Human and rat tissue was treated in the same way.

RESULTS

(1) With the exception of anti-collagen type II, type VII and vitronectin, all antibodies revealed distinct binding patterns in the pancreas of the different pig breeds. However these antibodies bound on human cartilage and skin. (2) Collagen types I, III, IV, laminin and fibronectin are expressed on porcine pancreatic "islet capsules". (3) Expression levels of these proteins on "islet capsules" vary in the different pig breeds. However, no significant differences could be found in the expression pattern of collagen types I, III, IV, laminin and fibronectin, comparing domestic, experimental and wild type pigs. (4) Older individuals (Goettingen Minipig) appear to express higher levels of proteins on "islet capsules" than younger ones.

CONCLUSIONS

Antibodies with specificity for human extracellular matrix proteins can be used successfully in the porcine pancreas. Thus, analysis of the structure and composition of porcine pancreatic tissue can be performed even without pig-specific antibodies. Particularly, the effects of various proteases and collagenases on the pancreatic tissue can now be monitored by immunohistochemical analysis allowing a rational design of protease mixtures for the isolation of pancreatic islets.

Apoptosis of T lymphocytes in liver and/or small bowel allografts during tolerance induction

BACKGROUND

Apoptosis of parenchymal cells has been described during allograft rejection. Immunologically privileged tissue in the mouse has been found to prevent rejection by initiating apoptosis of infiltrating lymphocytes. The aim of this study was to investigate whether apoptosis may play a role in T-cell regulation during rejection and subsequent tolerance induction after liver transplantation (LTx) and combined liver/small bowel transplantation (LSBTx).

METHODS

LTx and LSBTx (Brown Norway-->Lewis) were performed without immunosuppression. Cell migration, activation, and apoptosis were investigated by means of sequential histology, immunohistochemistry, and the terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling assay. Donor (Brown Norway) and third-party (Dark Agouti) cardiac allografts were transplanted into LSBTx recipients to determine specific tolerance.

RESULTS

Transient acute cellular rejection occurred after LTx and LSBTx and was followed by specific tolerance. The kinetics of apoptosis were similar in liver allografts after LTx and LSBTx, but differed from the processes in small bowel allografts after LSBTx. Apoptosis of parenchymal cells in the grafted livers correlated directly with interleukin-2 receptor expression of the infiltrating T cells. During the late phase of rejection, a peak of apoptosis in the lymphocyte infiltrate was demonstrated, characterized as predominantly apoptotic CD8+ T lymphocytes.

CONCLUSIONS

These results demonstrate that specific tolerance is achieved in both LTx and LSBTx after a transient rejection crisis. Apoptosis is involved in graft rejection and tolerance induction. Activation of T lymphocytes correlates with parenchymal cell apoptosis in the allograft. T-cell inactivation seems to result in apoptosis of cytotoxic T cells and tolerance, which appears to be unique to the liver allograft.

[Cellular immune reactivity in xenogenic "human-anti-pig" transplant combination]

The worldwide lack of human organ donors puts the pig as potential xenogeneic donor species into the prime of interest. Aim of the present in vitro study is the analysis of T-cell activation in the clinically attractive combination "pig-to-human". Peripheral human blood leukocytes (hPBL) and peripheral porcine blood leukocytes (pPBL) were co-cultured for 4-8 days in the xenogeneic mixed lymphocyte reaction (xMLR) and cell proliferation was measured by 3H-thymidine uptake. Both cell populations were separated into T-cells and antigen presenting cells (APC) to analyze direct and indirect antigen recognition. The results show that (a) activation of human T-cells occurs, (b) the strength of activation depends e.g. on the human responder ("high" and "low" responders), (c) the strength of activation is independent of the responder's HLA-DR status, and (d) direct T-cell activation dominates over indirect activation. Thus, T-cell activation is another immunological barrier that has to be overcome before xenotransplantation can be clinically approached.