Use of the continuous glucose monitoring system in Goettingen Minipigs, with a special focus on the evaluation of insulin-dependent diabetes

OBJECTIVES

Adult pig islet isolation has greatly improved in the past few years. Islet grafts may now be tested in large animals. Continuous Glucose Monitoring System (CGMS) was applied to diabetic Goettingen Minipigs (GMP) to improve the management of hyperglycemia and hypoglycemia and their welfare before transplantation.

METHODS

GMP (25-35 kg) received a minipig diet once daily. Diabetes was induced by streptozotocin (STZ; 150 mg/kg intravenous [IV]; n = 5) or by surgical pancreatectomy (PGMP; n = 3). Interstitial glucose concentration (IGC) was monitored continuously with an implanted sensor; CGMS was calibrated using conventional blood glucose tests 3-4 times per day; CGMS data were fed into the monitor memory and analyzed using CGMS software.

RESULTS

Glucose sensors were handled accurately. Diabetes occurred 2-3 days after STZ or immediately after pancreatectomy with basal C-peptide secretion of <0.4 ng/mL (measured using intravenous glucose tolerance test) and prompt loss of body weight. Insulin substitution was necessary to keep the GMP in good condition for up to 5-6 months, with stable body weight and normal behavior. Some GMP became hypoglycemic, which was only documented by CGMS, but not by conventional glucose assays. Tight glucose control and substitution of exocrine enzymes (Creon 25,000 E/d) reduced morbidity of the PGMP, which was then comparable with that of STZ-GMP.

CONCLUSIONS

The CGMS, developed for humans, is equally suitable for the 2 GMP diabetes models. Close-meshed glucose monitoring and insulin treatment improved the general condition of the diabetic GMP, ie, the islet graft recipients, and will thus greatly add to posttransplantation success.

Gewinnung mesenchymaler Progenitorzellen aus der humanen Nabelschnur

BACKGROUND

Mesenchymal progenitor cells (MPCs or mesenchymal stem cells, MSC) have the capability for differentiation into various lineages of mesenchymal tissue. MPCs are widely distributed in a variety of tissues in the adult human body and also present in the fetal environment. However, MPCs are a rare population in these tissues. In this study we evaluated the possibility that MPCs or cells with MPC-like potency are present in the umbilical cord (UC).

METHODS

Term UCs were collected and stored in sterile saline solution. The UCs (10 cm) were cut into 1 cm length, the vessels were striped manually and the tissue immersed in an enzyme cocktail for 3 h at 37 degrees C. The isolated umbilical cord mesenchymal progenitor cells (UCMPCs) were pelleted by low speed centrifugation, suspended and cultured.

RESULTS

(1) Umbilical cord mesenchymal progenitor cells (UMPCs) could be isolated in sufficient quantities and (2) could be cultured easily. (3) These cells demonstrated a fibroblast-like phenotype. (4) They could be expanded in culture and induced to form several different types of cells. (5) In immunochemistry these cells express mesenchymal markers (CD 13, CD 105) but not haematopoetic lineage markers (CD 14 and CD 34).

CONCLUSION

Our observation suggested that MPCs are present in human umbilical cord. Instead, it should be considered a valuable resource for the isolation of potent cells for cell-based therapies, especially in general and pediatric surgery.

MHC Class II–Mediated Antigen Presentation by Alloreactive Rat CD4+ T Cells Does Not Induce Regulatory Properties

Activated CD4+ T cells have the capacity to express major histocompatibility complex (MHC) class II molecules and to present processed antigens to T cells. Because the role of MHC class II positive T cells in allograft rejection is unknown, the purpose of this study was to investigate their function as antigen-presenting cells (APCs) in the allogeneic immune response. For this, alloreactive CD4+ T cells were induced in Lewis rats by immunization with the allogeneic peptide P1. The P1-specific T cells are involved in the rejection of allografts from Wistar Furth rats. With monoclonal antibodies specific for the alphabeta T-cell receptor (clone R73) and MHC class II molecules (clone Ox6), the presence of antigen-specific T cells, with and without expression of MHC class II molecules, was demonstrated. Concerning their ability to bind these antibodies they were characterized as R73(pos), Ox6(pos) and R73(pos), Ox6(neg), respectively. The R73(pos), Ox6(pos) T cells loaded with P1 were indeed very effective in restimulating R73(pos), Ox6(neg) T cells but not vice versa. Further on, R73(pos), Ox6(pos) T cells, but not R73(pos), Ox6(neg) T cells, were able to activate naïve allogeneic T cells demonstrating their capacity to express co-stimulatory molecules. In addition, specific mRNA for CD86, MHC class II, and CIITA, the master regulator of MHC class II expression, were detectable in the R73(pos), Ox6(pos) T cells only. In conclusion, the R73(pos), Ox6(pos) T cells act as professional APCs with the possible biological capability of amplifying the local immune response to the allograft.

Immunogenicity of parathyroid allografts in the rat: immunosuppressive dosages effective in passenger leukocyte-rich small bowel transplants are not effective in parathyroid gland transplants with few passenger leukocytes

BACKGROUND AND AIMS

The passenger leukocytes harboured within an allograft induce a massive allo-immune response that leads to allograft rejection if not countered by immunosuppression. We compared the response to short-term immunosuppression of parathyroid gland transplants possessing few passenger leukocytes with that of passenger leukocyte-rich small bowel transplants.

METHODS

Heterotopic parathyroid and orthotopic small bowel transplantation was performed in a Wistar Furth-to-Lewis rat strain combination. Immunosuppression with cyclosporine A (CsA) was administered in different dosages for 14 days. Dysfunctional allografts were examined immunohistologically.

RESULTS

CsA more effectively suppressed the immune response provoked by immunogenic small bowel grafts than that induced by less-immunogenic parathyroid grafts. Immunosuppression with 20 mg/kg per day induced long-term survival in the small bowel (165+/-21 days) but not in the parathyroid (28+/-3 days). All rejected grafts featured massive cellular infiltration by activated T cells as a sign of immune rejection.

CONCLUSION

Immunosuppressive dosages effective in passenger leukocyte-rich small bowel transplants were not as effective in parathyroid gland transplants harbouring few passenger leukocytes. In spite of the paucity of passenger leukocytes in parathyroid grafts it is more difficult to control by immunosuppression the immune response to them than that to the passenger leukocyte-rich small bowel.

Highly efficient isolation of porcine islets of Langerhans for xenotransplantation: numbers, purity, yield and in vitro function

Xenogeneic transplantation of porcine islets of Langerhans is regarded as a potential future treatment for diabetes mellitus. Despite considerable biotechnological progress, however, it is still very difficult and often unreliable to isolate sufficient numbers of highly purified, intact islets from the porcine pancreas with good in vitro function.

OBJECTIVE

Of this study was to describe an efficient and reliable method to isolate sufficient numbers of highly purified islets of Langerhans with good in vitro function from adult as well as from young hybrid pigs.

METHODS

Islets were isolated from the pancreas of young (4-6 months) hybrid pigs and old (2-3 years) retired breeders using Liberase PI and digestion-filtration. Average islet size was detected by dithizone staining of tissue sections prior to isolation; only organs with an average islet size > or = 200 microns were used. Density gradient purification with OptiPrep was performed in a COBE 2991 cell processor. Viability was investigated using fluorescence staining. Perifusion studies were carried out to asses in vitro function of isolated islets.

RESULTS

Islets were successfully isolated from young hybrid pigs (3,671 +/- 598 IEQ/g) and old retired breeders (5,182 +/- 545 IEQ/g). After purification islet purity was 92% for retired breeders and 87% for young hybrid pigs. Yield after purification was still not satisfactory: 64% for retired breeders (3,209 +/- 444 IEQ/g) and 44% for young hybrid pigs (1,669 +/- 386 IEQ/g). Viability of isolated islets was 80-95%. Perifusion studies of porcine islets showed sufficient insulin release upon glucose challenge; however, the level of insulin release depended on the density of islets within the perifusion chamber. Low temperature culture (24 degrees C) prior to perifusion studies had no detrimental effect on insulin release. Long-term culture over 11 days was followed by a dramatic loss of islet function.

CONCLUSIONS

If xenograft rejection can be overcome and the risk of xenosis can be minimised, sufficient numbers of purified porcine islets with good in vitro function can be isolated to serve as a potential source for islet transplantation in diabetic patients.

Influence of donor MHC class I antigen expression on graft survival after rat parathyroid allotransplantation

BACKGROUND AND AIMS

We investigated the influence of donor MHC antigen expression on graft survival after parathyroid transplantation in three different strain combinations.

METHODS

MHC class I and II expression on parathyroid tissue of Lewis (LEW), Dark Agouti (DA), and Wistar-Furth (WF) rats was first analysed semiquantitatively by immunohistochemistry. Additionally, five groups were transplanted: (1) LEW to LEW, (2) DA to DA, (3) LEW to DA, (4) WF to LEW, and (5) DA to LEW.

METHODS

MHC class I expression was strong in DA, moderate in WF, and weak in LEW rats; MHC class II expression was negative in all three strains. In the interstitium of all investigated tissue specimens, the proportion of MHC class II-expressing cells was low.

RESULTS

After syngeneic transplantation, graft survival could be documented over the whole observation period. A mean graft survival of 20 (+/-2) days was observed following transplantation from LEW to DA, grafts in the group WF to LEW were rejected after 13 (+/-1) days, and graft function lasted 8 (+/-2) days in the group DA to LEW. The number of intragraft leukocytes expressing MHC class II molecules was equal in all groups, whereas increased levels of MHC class I on rat parathyroid tissue before transplantation resulted in a more rapid rejection.

CONCLUSION

These results demonstrate that immunogenicity of rat parathyroid tissue seems to be determined by the amount of MHC class I expressed on donor parenchymal cells.

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.

Rat parathyroid allotransplantation: Influence of MHC antigen expression on graft survival

MHC antigen expression in parathyroid tissue and its influence on graft survival after allogeneic transplantation were investigated using a heterotopic rat transplantation model. MHC class I and II expression in parathyroid tissue of Lewis (LEW), Dark Agouti (DA), and Wistar-Furth (WF) rats was analysed semi-quantitatively by using immunohistochemistry. MHC class I expression was strong in DA, moderate in WF, and weak in LEW rats parenchyma, whereas MHC class II expression was negative. In the interstitium of all investigated tissue specimens, the proportion of MHC class II-expressing cells was low. Additionally, four groups were transplanted: 1) LEW to LEW, 2) DA to DA, 3) LEW to DA, and 4) WF to LEW. After syngeneic transplantation, graft survival could be documented over the whole observation period. A median graft survival of 20 (+/-2) days was observed after transplantation from LEW to DA, whereas grafts in the group WF to LEW were rejected after 13 (+/-1) days. The number of intra-graft leucocytes expressing MHC class II molecules was the same in all groups, whereas increased levels of MHC class I in parathyroid tissue before transplantation resulted in a more rapid rejection. These results indicate that immunogenicity of rat parathyroid tissue might be determined by the amount of MHC class I expressed in donor parenchymal cells. Further experiments are necessary to validate this observation.

Persistence of stable intragraft cell chimerism in rat liver allografts after drug-induced tolerance

BACKGROUND

Drug-induced tolerance of rat liver allografts is well documented. We analyzed cellular events during immunosuppressive therapy on day (d) 10 and in the late phase (d 100) after transplantation to assess for characteristics in the intrahepatic leukocyte (IHL) population in the phase of tolerance.

METHODS

Lewis rats served as recipients of Dark Agouti rat livers. Temporary immunosuppression with either cyclosporine (CsA) monotherapy (3 mg/kg/d) or triple therapy that consisted of a subtherapeutic CsA dosage (0.25 mg/kg/d) and monoclonal antibodies directed against the interleukin-2 receptor (IL-2R, CD25) and the intercellular adhesion molecule-1 (ICAM-1, CD54) was administered from postoperative d 0 to d 13. Cell migration and cell activation within liver grafts was assessed by standard histology and flow cytometry. IHL apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL).

RESULTS

Both CsA monotherapy and triple therapy prolonged liver allograft survival to more than 100 d and led to the induction of donor-specific tolerance. Untreated recipients rejected their allografts within 14 d. In both groups, donor-specific IHLs initially dropped to 18% to 25% on d 10, but they rebounded to as much as 40% on d 100 as a common characteristic of both groups. Within this population, donor-specific T cells were dominant. In both groups, increased numbers of activated (IL-2R+) CD8+ T lymphocytes were present on d 100. No accumulation of apoptotic IHL was observed on d 100. Their proportion was unchanged in the triple therapy group and slightly decreased in the CsA group compared to the syngeneic controls.

CONCLUSIONS

The present study reveals that tolerant liver allografts are repopulated by donor-specific T lymphocytes. This phenomenon is independent of the type of applied immunosuppression. The persistence of activated CD8+ T cells in the phase of proven donor-specific tolerance on d 100 indicates that liver tolerance is associated with the state of a permanent intragraft immune activation. It seems that the coexistence of donor cells with infiltrating recipient cells within liver grafts, termed intrahepatic cell chimerism, is characteristic for tolerated liver allografts.

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

Functional long-term allograft survival after experimental small bowel transplantation (SBT) is limited by chronic rejection. Initial application of high-dose FK 506 has been shown to induce stable long-term graft function. In order to examine whether this long-term function is associated with donor-specific tolerance, we analyzed the functional status of recipient T cells in vivo and in vitro. One-step orthotopic SBT was performed in the allogeneic Brown Norway (BN)-to-Lewis rat strain combination. FK 506 was given daily at a dose of 2 mg/kg from days 0-5 in the rejection model and from days 0-9 in the long-term functional model. Mean survival time in the rejection model was 98 +/- 2.8 days. Histological examination of these small bowel allografts disclosed signs of chronic rejection. In contrast, all animals of the long-term functional model survived long term (> 250 days) without clinical signs of chronic rejection. The latter model, furthermore, produced evidence of donor-specific tolerance. Whereas heterotopic Dark Agouti (DA) hearts were rejected regularly within 7 days, BN hearts survived indefinitely (> 70 days). In vitro, mixed leukocyte reactivity of CD4+ T cells was similarly strong against donor (BN) antigens as against third-party (DA) antigens. The split tolerance revealed by our in vivo and in vitro results enabled acceptance of both the small bowel allograft without signs of chronic rejection and of donor-specific heart allografts.

"Tolerogenic effect" of the liver for a small bowel allograft

A newly developed liver/small bowel transplantation model (LSBTx) was used to investigate the tolerogenic effect of a liver allograft toward a simultaneously transplanted small bowel. Small bowel transplantation (SBTx) under high-dose immunosuppression was compared to LSBTx with a lower FK506 dosage. Syngeneic Lewis [(LEW) to LEW] and two fully allogeneic rat strain combinations (Brown Norway-to-LEW and Dark Agouti-to-LEW) were used. Clinical course and histological findings after SBTx demonstrated a chronic rejection of the small bowel allograft within 100 days. However, after LSBTx long-term acceptance (> 150 days) was achieved after a transient rejection crisis, although initial immunosuppression was significantly lower. Furthermore, indicator heart transplantations demonstrated the induction of donor-specific tolerance in both allogeneic strain combinations. In contrast to other LSBTx rat models, these results reflect observations after human LSBTx, in which the rate of acute and chronic rejection is also significantly lower than after human SBTx.

Analysis of cellular events in hepatic allografts: donor progenitors induce intragraft chimerism

Long-term graft acceptance and tolerance induction after allogeneic rat liver transplantation are well described. However, the underlying mechanisms remain unclear. In this study we investigated the cellular events within the liver graft during initial immunosuppression and long-term acceptance. Orthotopic liver transplantation was performed in the Dark Agouti (DA)-to-Lewis (LEW) and LEW-to-DA rat strain combination. In order to achieve long-term acceptance, LEW recipients of DA livers were treated with two different short-term therapies. Non-parenchymal cells (NPC) were isolated from liver allografts on days + 10 and + 100 after transplantation and donor-specific leukocytes were immunophenotyped by flow cytometry. Both the monotherapy and triple therapy prolonged graft survival (> 100 days). Liver allografts from LEW donors into DA recipients were spontaneously accepted across a complete MHC mismatch without immunosuppression. Liver allograft rejection was induced by infiltrating alloreactive immunocompetent cells. But the intensities of cell infiltration in the early and late phases after transplantation did not correlate with eventual outcome. Donor-specific NPC decreased to 18-25% on day + 10 in both therapeutic groups, but had rebounded to up to 40% by day + 100. Recurrence of donor-specific cells was caused almost exclusively by rising T cell counts. The persistence of dendritic cells in the late phase after transplantation could be clearly demonstrated. Repopulation by donor-specific T lymphocytes was observed in long-term accepted liver grafts. This recurrence may be based on the differentiation of liver-derived progenitor cells. The persistent coexistence of donor and recipient cells within the liver allograft (intrahepatic chimerism) appears to be characteristic and may be important for long-term acceptance.

Different kinetics of donor cell populations after isolated liver and combined liver/small bowel transplantation

Spontaneous tolerance induction after liver transplantation also supports additional transplants, e.g. a small bowel graft, from the same donor (tolerogenic effect). Chimerism serves as a possible explanation of this phenomenon. Isolated liver (LTx) and combined liver/small bowel transplantation (LSBTx) are compared. LSBTx and LTx were performed in the BN --> LEW rat strain combination without immunosuppression. Parenchymal damage during rejection was monitored by sequential standard histology. Donor/recipient populations were identified and further differentiated for immunohistochemical single and double staining. A small number of donor specific leukocytes can be detected on all days in host organs (microchimerism). A significantly larger donor leukocyte population survives long-term in the sinusoids of liver (graft chimerism). Sinusoidal donor leukocytes survive rejection and recover in number after tolerance induction. Rejection of liver allografts and infiltration by host leukocytes are more pronounced after LSBTx than after LTx. Accordingly, during rejection a steeper decline of sinusoidal donor leukocytes is observed after LSBTx and recovery after tolerance induction is not as marked. Microchimerism apparently plays no significant role in either transplantation model. The number of sinusoidal donor leukocytes, however, mirrors closely host immune responses.

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.