Pancreas-graft immunogenicity and pretreatment with anti-class II monoclonal antibodies

Ex vivo perfusion of canine pancreaticoduodenal allografts using class-II-specific monoclonal antibody delays the onset of acute rejection

In the following study, we investigated whether ex vivo perfusion of canine pancreaticoduodenal allografts prior to transplantation using a class-II-specific monoclonal antibody (MoAb) OKIa1) could prevent acute rejection. Untreated grafts were rejected within 6 days after transplantation, and all of these recipients suffered severe hyperglycemia. In contrast, in recipients who received grafts which underwent ex vivo class-II-specific MoAb perfusion treatment, the mean urinary amylase levels were sustained significantly higher (11,733 +/- 4493 vs. 3274 +/- 2108 U/L on day 7, P < 0.005), and mean fasting blood glucose (FBG) levels remained within the normal range (13.4 +/- 5.8 vs. 23.4 +/- 3.9 mM on day 7, P < 0.0005). Low doses of cyclosporin A (CsA) were necessary in order to maintain lower FBG levels. Histopathology analysis on day 7 after transplantation showed that endotheliitis and necrosis were much less prominent in the MoAb-treated grafts. In the light of our results, we conclude that ex vivo perfusion of canine pancreaticoduodenal allografts using a class-II-specific MoAb is effective in delaying the onset of acute rejection, and low doses of CsA could extend this effect.

Immunological characteristics of pancreas transplantation: review and our experimental experience

Pancreas and islet transplantation is the only treatment that can cure type 1 diabetes mellitus (DM). With the recent advances of operative procedure and immunosuppression, pancreas graft survivals have become better than before, but some problems still remain. It is extremely difficult to establish tolerance and to reverse rejection once it has been initiated because the pancreas graft itself has a strong immunogenicity. It is also known that pancreatic graft failure is sometimes due to autoimmune recurrence. In the clinical situation, however, these immunologic events actually coexist within the pancreatic graft. Thus, it is rather difficult to analyze each of them independently, but possible to delineate each of these immunologic mechanisms with using animal models of type 1 DM such as BB (BioBreeding) rats or NOD (nonobese diabetic) mice. In the current study, we reviewed the immunological characteristics in pancreas transplantation (PTx) based on our experimental experiences together with that of others and investigated the possibility of tolerance induction in PTx.

Pretreatment of kidney allografts with monoclonal antibodies to CD45: results of a multicentre study. CD45 Study Group

The perfusion of human renal allografts with CD45-specific monoclonal antibodies (mAbs) may reduce their immunogenicity and the incidence of rejection. We performed a safety study in 40 patients receiving their first cadaveric renal transplant. Two milligrams each of the rat CD45 specific mAbs YTH 24.5 and YTH 54.12 were perfused into the grafts prior to transplantation. The patients were followed for 3 months. No patient died, and four grafts were lost, three to vascular causes not considered to be related to antibody perfusion and one to severe rejection. Two patients developed an anti-rat antibody response. Immunohistological double-labelling performed on cortical biopsies taken post-perfusion and prior to wound closure showed that at least 60% of the CD45+ cells were coated by perfused anti-CD45 ('antibody uptake'). Among the patients studied for uptake and episodes of rejection, the incidence of rejection was 75% in 12 patients whose antibody uptake was < 95% compared with 22% in 18 patients with antibody uptake > or = 95% (P = 0.01). We conclude that this treatment was free of adverse effects and that there is a correlation between the uptake of antibody by passenger leucocytes and reduction in acute rejection episodes.

Co-culture of pancreatic islets and allogeneic lymphocytes: alterations of responder and stimulator cells

Mixed lymphocyte cultures have been used, e.g., in clinical transplantation, for donor-recipient selections. In experimental research, the mixed lymphocyte culture is valuable in studying several aspects of lymphocyte activation by allogeneic major histocompatibility complex (MHC) antigens and, therefore, in proving new strategies of interrupting lymphocyte activation and proliferation. However, this in vitro model is donor-specific but not antigen-specific. Therefore, we used islets of Langerhans, the donor tissue for grafting diabetic recipients, to stimulate allogeneic mononuclear cells prepared from spleens of healthy LEW.1A, LEW.1W, or WF rats and from diabetes-prone normoglycemic BB/OK rats. The considerable advantage of the mixed lymphocyte islet culture is not only the antigen specificity but also the possibility to separate lymphocytes from islets after the co-culture. In addition to lymphocyte activation, we investigated cytokine secretion and changes of antigen expression on the stimulatory islet cells. After allogeneic co-culture, lymphocyte activation was found by an increased release of the cytokines interferon-gamma, interleukin 2, and macrophage inflammatory protein 2, as well as by an enhanced expression of the interleukin 2 receptor on CD4+ T and CD8+ T cells. We also demonstrated changes in antigen expression on the surface of stimulatory islet cells after co-culture with allogeneic lymphocytes. These changes comprised not only the enhancement of MHC class I and intercellular adhesion molecule 1 but also the induction of MHC class II antigens on pancreatic beta cells. Activation of responding lymphocytes, cytokine secretion, and changes in islet cell antigen expression were time dependent. We did not find major differences in the effects induced by allogeneic lymphocytes obtained from the different donor rat strains. In a syngeneic control mixed lymphocyte islet culture, lymphocytes were not activated and no induction of MHC class II antigens on beta cells was observed. However, up-regulation of intercellular adhesion molecule 1 was found. The enhancement and induction of MHC antigens and an adhesion molecule improve the binding of effector and target cells supporting our hypothesis that the change of antigen expression on target cells induced by allogeneic lymphocytes might contribute to their destruction. Since lymphocytes obtained from healthy or diabetes-prone rats induce very similar effects, we conclude that the results described are of general importance.

Pretreatment of renal transplants with anti-CD45 antibodies: optimization of perfusion technique

Pig kidneys were perfused ex vivo with a monoclonal anti-pig CD45 antibody to determine optimum conditions for human kidney anti-CD45 perfusion, as such pretreatment may prolong renal allograft survival. Efficacy of perfused antibody uptake was assessed by immunohistochemical double-labelling of multiple renal biopsies. Antibody uptake by CD45+ cells was rapid, and maximal within one hour of perfusion. An antibody concentration of 40 micrograms/ml more effectively saturated available CD45 binding sites than lower concentrations. Whilst cortical perfusion was homogeneous (median uptake > 99%, minimum 90.0%) after 25, 50 or 100 ml perfusion with 40 micrograms/ml monoclonal antibody (mAb), the medulla was less evenly perfused with 25 ml (median uptake 82.6%) than with 50 or 100 ml (median uptake 98.5% and 98.7%, respectively). Prolongation of renal cold ischaemia of up to 46 hours prior to mAb perfusion did not adversely affect antibody binding. Clamping of the renal vein during and after mAb perfusion was associated with better cortical and medullary mAb uptake than if the vein was left unclamped. These data show that the vast majority of the kidney's CD45+ antigen-presenting cells can be bound by anti-CD45 mAb perfused ex vivo, if an adequate volume and concentration of mAb perfusate is employed and the renal vein is clamped during and after the process.

Natural regulatory mechanisms of insulin degradation by insulin degrading enzyme

Insulin-degrading enzyme (IDE) accounts for most of the insulin degrading activity in extracts of several tissues and plays an important role in the intracellular degradation of insulin. Using newly developed sandwich radioimmunoassay for rat IDE, this enzyme was detectable in all tissues we examined and liver had the highest level of IDE. The ratio of insulin degrading activity to IDE concentration was roughly the same in liver, brain and muscle, however, twice as high in kidney as compared with other tissues. On the contrary, its degrading activity in these tissue extracts, including kidney, was completely lost after immunoprecipitation of IDE. These results suggest that IDE degrades insulin in the initial step of cleavage and that there are some mechanisms to regulate insulin degrading activity by IDE in the tissues.