Restoration of immune abnormalities in diabetic BB rats after pancreas transplantation. I. Macrochimerism of donor-graft-derived RT6+ T cells responsible for restoration of immune responsiveness and suppression of autoimmune reaction

Pancreas transplantation using type I and type II spontaneously diabetic rats--our experimental experience

Pancreas transplantation (PTx) is the only therapy that can cure type 1 diabetes mellitus. With the recent advance of surgical procedures and immunosuppression, the outcome of PTx has become better than it used to be before, but some problems still remain. It is rather difficult to induce tolerance and to reverse rejection once it occurred because pancreas graft itself has a strong immunogenicity. Another important issue is regarding the recurrence of autoimmune disease in the pancreatic graft, therefore, some animal models are necessary to delineate and regulate those immune responses specific for PTx. Recently, PTx is also clinically applicable for type 2 diabetic patients with end-stage renal disease. It has been shown that insulin resistance was improved by PTx in type 2 diabetic recipients. In the current study, we have introduced some useful type 1 and type 2 diabetic models mainly based on our experimental experiences.

The potent role of graft-derived NKR-P1+TCRalphabeta+ T (NKT) cells in the spontaneous acceptance of rat liver allografts

BACKGROUND

The mechanism involved in the spontaneous acceptance of liver allografts in some rat strain combinations remains unclear. Immunoregulatory NKR-P1TCRalphabetaT (NKT) cells primarily produce IL-4 and IFN-gamma, and enhance the polarization of immune responses to Th2 and Th1, respectively. The aim of this study was to clarify the role of graft-derived NKT cells in inducing the spontaneous acceptance of rat orthotopic liver transplantation (OLTx)

METHODS

The experimental groups were divided as follows: Group 1, BN to LEW "low responder (acceptor)" combination; Group 2, DA to LEW "high responder (rejector)" combination; naïve BN (Group 3) or LEW recipients (Group 4) with liver allografts from irradiated BN donors. The recipients had liver allografts from irradiated donors reconstituted from the following cell populations 24 hr before harvesting, spleen cells (SPCs, Group 5), IgSPCs (Group 6), IgNKR-P1SPCs (Group 7), and IgTCRabSPCs (Group 8)

RESULTS

In Group 1, the percent of graft-derived NKT cells harvested on day 7 posttransplant were significantly higher than in Group 2. In the case of BN liver allografts that had been irradiated and reconstituted with cell populations including NKT cells (Groups 5 and 6), the mean graft survival (MST) was extended to 39.2+/-5.7 and 38.8+/-8.0 days, respectively. In contrast, when NKT cells were excluded (Groups 7 and 8), the grafts were acutely rejected within MST of 17.8+/-4.0 and 18.8+/-7.7 days, respectively. The concentrations of IL-10 and TGF-beta, but not IL-4 in IgGICs culture supernatants were predominant in the acceptor, whereas those with IFN-gamma predominated in the rejector.

CONCLUSIONS

Graft-derived NKT cells might be responsible for spontaneous acceptance in the rat OLTx.

Development of Donor-Specific Immunoregulatory T-Cells After Local CTLA4Ig Gene Transfer to Pancreatic Allograft

BACKGROUND

CTLA4Ig gene transfer directly to graft tissue might have the potential to avoid the need for systemic immunosuppression. In our previous studies of bio-breeding (BB) rats, local adenovirus-mediated CTLA4Ig gene transfer protected the pancreas from autoimmune and alloimmune responses. This study investigated the potency of local CD28/B7 costimulatory blockade for induction of donor-specific tolerance and further examined the existing mechanisms.

METHODS

Brown Norway (BN; RT1)-pancreaticoduodenal grafts transfected with Ad.CTLA4Ig via intraarterial ex vivo perfusion were transplanted into streptozotocin-induced diabetic Lewis (LEW; RT1) rats.

RESULTS

Ad.CTLA4Ig transduced grafts combined with a short course of FK506 resulted in indefinitely prolonged survival (>156 days vs. 19.5 days with FK506 alone). CTLA4Ig was predominantly expressed in grafts on day 4. The expression was gradually diminished and was only slightly detectable at day >100. The proliferative responses against BN antigen were remarkably enhanced among recipients with rejected grafts, but the T-cells from tolerant recipients (>100 days) showed poor cytotoxic responses. On adoptive transfer assay, the splenic T-cells of tolerant recipients were able to suppress the rejection of BN, but not third-party Wistar Furth (WF; RT1) hearts in irradiated (480 cGy) LEW recipients. The percentage of CD4CD25 splenic T-cells was significantly increased in tolerant recipients (13.53 +/- 4.06% vs. 6.06 +/- 0.56% in naive rats).

CONCLUSION

CTLA4Ig gene transfer to the pancreaticoduodenal allograft combined with a short course of FK506 induces donor-specific tolerance. The mechanism of maintaining tolerance could be explained by development of splenic T suppressor cells.

Stage-dependent effect of pancreatic transplantation on diabetic ocular complications in the Spontaneously Diabetic Torii rat

BACKGROUND

In terms of the temporal relationship between pancreas transplantation (PTx) and reversal of diabetic ocular complications, it has been difficult but important to determine a "point of no return." Thus, it is of great clinical interest to evaluate the efficacy of PTx on diabetic ocular complications.

METHODS

A spontaneous type 2 diabetic model of Spontaneously Diabetic Torii (SDT; RT1) rats was used in the present study, and syngeneic PTx was performed.

RESULTS

In the control SDT rats that received no treatment, hyperglycemia (>250 mg/dL) was developed from 25.2+/-3.9 weeks of age. Lens opacity was observed in all rats at 15 weeks after the onset of diabetes. Fluorescein angiography and immunohistochemistry detected the nonperfusion area and neovascularization in the retina at 5 weeks of diabetes. Daily insulin treatment could not prevent or reverse the ocular changes in our experiment. Fluorescein filling defect of the retinal vessels was observed at 10 weeks of diabetes. However, in the PTx rats, normoglycemia was achieved at all experimental time points. Diabetic cataract and retinopathy could have been prevented and improved if PTx had been performed at 5 weeks, but not at 10 weeks after the onset of diabetes. With PTx treatment, an inhibition of angiogenesis in the retina at 5 weeks after the onset of diabetes was demonstrated by immunohistochemistry.

CONCLUSIONS

Our results indicate that the potential use of the SDT rat for diabetes study and the positive effect of PTx performed before the "point of no return" could prevent and cure diabetic ocular complications.

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.

HMG-CoA reductase inhibitor cerivastatin prolonged rat cardiac allograft survival by blocking intercellular signals

BACKGROUND

The development of atherosclerotic cardiovascular complications caused by hyperlipidemia is a common and serious problem for long-term survivors of organ transplantation. However, adhesion molecules such as intercellular adhesion molecule (ICAM)-1 and lymphocyte function-associated antigen (LFA)-1 are involved in allograft rejection, possibly by providing costimulatory signals. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor cerivastatin has been shown to suppress ICAM-1 expression in acute inflammatory responses.

METHODS

In this study, we evaluated the immunosuppressive effects of cerivastatin in rat cardiac allografts. The hearts of Fischer rats were transplanted heterotopically into Lewis rats. Cerivastatin (2 mg/kg) was administrated intraperitoneally to recipients for 7 consecutive days from the day before transplantation.

RESULTS

Graft survival in the cerivastatin-treated group (n = 8) was significantly longer than in controls (n = 10) (24.6 +/- 2.2 days vs 10.2 +/- 1.3 days, p < 0.05). Mixed lymphocyte reaction (MLR) showed that on Day 8 after grafting, the proliferative response of alloreactive T cells against F344 alloantigen in cerivastatin-treated rats was significantly more suppressed than in Lewis rats. The Interleukin-2 concentration of supernatant in MLR cultures in the cerivastatin-treated group was lower than in the control group. Immunohistochemical analysis showed that the percentage of CD4-positive cells to infiltrating mononuclear cells was less prominent in the cerivastatin-treated group (9.8% +/- 2.2%) than in the control group (20.9% +/- 3.2%).

CONCLUSIONS

The HMG-CoA reductase inhibitor cerivastatin effectively suppressed acute graft rejection, possibly by blocking intercellular signals via ICAM/LFA-1, and cerivastatin may be a candidate for treating patients with hyperlipidemia who undergo organ transplantation.

Significant role of intragraft lymphoid tissues in preventing insulin-dependent diabetes mellitus recurrence in whole pancreaticoduodenal transplantation

Graft recurrence of insulin-dependent diabetes mellitus (IDDM) was examined. Islet transplantation or pancreas-alone transplantation excluding the duodenum and peripancreatic lymph nodes was compared with whole pancreaticoduodenal transplantation. A Wistar Furth (WF; RT1(u), RT6.2) to major histocompatibility complex (MHC)-compatible diabetes-prone (DP; RT1(u), RT6.1 gene carrier)-biobreeding (BB) rat transplantation model was used. Only DP recipients that had been transplanted with whole pancreaticoduodenal grafts were free from IDDM recurrence (>60 days postgrafting) when treated with anti-intercellular adhesion moluecule-1 (ICAM)-1/leukocyte function-associated antigen-1 (LFA-1) monoclonal antibodies (mAbs). In the spleen cells of the DP rats that had accepted pancreatic grafts (60 days postgrafting), flow cytometric analysis showed that NKR-P1(+)TCRalphabeta(+) (NKT) cells had proliferated markedly, with the proportion of 12.8 +/- 1.7% in the total splenic T cells, most of which (86.2%) were derived from the donor (RT6.2(+)). By enzyme-linked immunonosorbent assay (ELISA), serum interferon gamma (IFN-gamma) was not detected (<13 pg/ml) in all rats. However, interleukin-4 (IL-4) was detected as 158.8 +/- 28.0 pg/ml in the nonrecurrent DP recipients. These data suggested that to prevent IDDM recurrence in the pancreatic graft, the lymphocytes in the pancreaticoduodenal grafts are necessary. Also, the donor-derived NKT cells might have some immunoregulatory functions with a Th2 deviation.

Donor-specific tolerance by perioperative intrathymic injection of bone marrow cells in the rat cardiac allograft model: use of FK506 can shorten the necessary duration of pretransplant intrathymic conditioning

BACKGROUND

Many strategies of tolerance induction by intrathymic (IT) injection of donor alloantigens have been reported to date; however, the timing of IT injection is usually 1-3 weeks before transplantation.

METHODS

To apply IT injection to cadaveric organ transplantation, 1 x 10(8) fully allogeneic bone marrow cells (BMC) of Buffalo (BUF; RT1b) rats were intrathymically injected into Wistar Furth (WF; RT1u) rats at the time of BUF cardiac allografting with short-course therapy of antilymphocyte serum (ALS) and FK506 in our experimental model.

RESULTS

Allogeneic IT injection of BUF BMC with ALS and FK506 indefinitely prolonged graft survival (mean survival time > 210 days) in all WF rats. On day 130 after grafting, tolerant WF rats accepted donor BUF skin grafts (> 120 days) but not third-party Lewis skin grafts. In control groups, syngeneic IT injection of WF BMC or intravenous injection of donor BUF BMC in combination with ALS/FK506 therapy failed to induce tolerance. In vivo testing was performed during induction (1 month) or during maintenance (6 months of tolerance. In the mixed lymphocyte reaction (MLR), spleen T cells of tolerant rats at 1 month after grafting displayed hyporesponsiveness after stimulation with donor cells. The addition of interleukin (IL)-2 to MLR culture did not restore T-cell responsiveness. Tolerant rats had a significantly decreased frequency of T cytotoxic cell precursors (fTcp) of 1:4,926, and frequency of IL-2-producing T helper cell precursors (fThp) of 1:23,925, compared with naive rats (1: 2,158 and 1:4,266, respectively). By 6 months after grafting, however, the anti-donor MLR proliferative responses of tolerant rats had been restored to the levels of naive splenic T cells. These tolerant rats displayed restoration of the (fTcp) of 1:2,842 and of the (fThp) of 1:5,630, which were comparable frequencies of naive rats. Suppressor T cells did not contribute in this model. In cardiac grafts of tolerant rats induced by IT injection, expression of both Th1 (interferon-gamma and IL-2) and Th2 (IL-4 and IL-10) cytokines was detected in the early phase; thereafter, expression was completely inhibited, except for interferon-gamma in the chronic phase.

CONCLUSIONS

Perfect donor-specific tolerance was obtained by IT injection of donor BMC at the time of transplantation, while alloimmune responses were maintained at levels similar to those of naive rats.