Pancreatic Islets Induce CD4+CD25−Foxp3+ T-Cell Regulated Tolerance to HY-Mismatched Skin Grafts

Donor-Specific Regulatory T Cell-Mediated Immune Tolerance in an Intrahepatic Murine Allogeneic Islet Transplantation Model with Short-Term Anti-CD154 mAb Single Treatment

Anti-CD154 blockade-based regimens remain unequaled in prolonging graft survival in various organ transplantation models. Several studies have focused on transplantation tolerance with the anti-CD154 blockade, but none of these studies has investigated the mechanisms associated with its use as the sole treatment in animal models, delaying our understanding of anti-CD154 blockade-mediated immune tolerance. The purpose of this study was to investigate the mechanism underlying the anti-CD154 monoclonal antibody (mAb) blockade in inducing immune tolerance using an intrahepatic murine allogeneic islet transplantation model. Allogeneic BALB/c AnHsd (BALB/c) islets were infused into the liver of diabetic C57BL/6 (B6) mice via the cecal vein. Anti-CD154 mAb (MR1) was administered on -1, 0, 1, 3, 5, and 7 d posttransplantation at 0.5 mg per mouse. We showed that short-term MR1 monotherapy could prolong the allogeneic islet grafts to more than 250 d in the murine intrahepatic islet transplantation model. The second islet grafts transplanted under the kidney capsule of the recipients were protected from rejection. We also found that rejection of same-donor skin grafts transplanted to the tolerant mice was modestly delayed. Using a DEREG mouse model, FoxP3+ regulatory T (Treg) cells were shown to play important roles in transplantation tolerance. In mixed lymphocyte reactions, Treg cells from the tolerant mice showed more potency in suppressing BALB/c splenocyte-stimulated Teff cell proliferation than those from naïve mice. In this study, we demonstrated for the first time that a short-term anti-CD154 mAb single treatment could induce FoxP3+ Treg cell-mediated immune tolerance in the intrahepatic murine allogeneic islet transplantation model.

A combination regimen of low-dose bortezomib and rapamycin prolonged the graft survival in a murine allogeneic islet transplantation model

As the first FDA-approved proteasome inhibitor drug, bortezomib has been used for the treatment of multiple myeloma and lymphoma. However, its effects alone or in combination with other immunosuppressants on allogeneic islet transplantation have not been reported so far. In this study, we showed that the short-term combination treatment of low-dose bortezomib and rapamycin significantly prolonged the survival of islet allografts. Short-term treatment of low-dose (0.05 mg/kg or 0.1 mg/kg) bortezomib reduced the MHC class II expression in dendritic cells (DCs) of alloantigen-sensitized mice, and prolonged the islet allograft survival for up to 50 days in diabetic mice. Notably, when bortezomib was combined with rapamycin, it induced islet-specific immunological tolerance which allowed the acceptance of a second graft without additional immunosuppression. This regimen dramatically reduced the alloantigen-specific IFN-γ-producing T cells in the spleen, and increased regulatory T cells both at the graft site and in the spleen. Therefore, we propose that short-term treatment of low-dose bortezomib and rapamycin could be a new tolerance-promoting immunosuppressive regimen for allogeneic islet transplantation.

Thioredoxin priming prolongs lung allograft survival by promoting immune tolerance

Tolerance to allograft antigen is the major challenge and final goal of transplant medicine. Our previous study demonstrated that thioredoxin-1 (Trx) priming of donor lung significantly protected allogeneic lung graft. To determine whether Trx priming of donor lung inhibits allograft rejection, extends allograft survival and induces immune tolerance, orthotopic left lung transplantation was performed from Lewis to Sprague-Dawley rats without immunosuppression. Donor lungs were primed with Trx at 4°C for 4 hr prior to transplantation. After up to 37 days post-transplantation, allograft lung morphology, recipient T cell and humoral alloantigen-specific immune responses were examined. We found that Trx-primed lungs exhibited much reduced acute rejection and associated lung injuries resulting in loss of graft functional area at 5-37 days post-transplant in contrast to the control groups. CD4⁺ T cells from the recipients with Trx-primed grafts responded to the stimulation of dendritic cells (DCs) of donor origin, in contrast to DCs from the third party, with significantly reduced proliferation. Consistent with above findings, we observed that CD4⁺Foxp3⁺ regulatory T cells in spleen cells from the recipients with Trx-primed grafts were significantly increased compared to controls, and CD4⁺ T cells from the recipients with Trx-primed grafts produced much higher levels of immunosuppressive cytokine, IL-10 when stimulated with allogeneic donor DCs. In addition, humoral immune tolerance was also induced as there was no significant increase levels of serum antibodies against donor antigens in Trx-lung recipients when re-challenged with allogeneic donor antigens. Our results demonstrate that one-time Trx-priming of donor lung grafts prior to transplantation significantly prolongs the survival of the grafts through inducing or promoting cellular and humoral alloantigen-specific immune tolerance, which might be associated with the induction of immunosuppressive regulatory T cells.

Deletion of naïve T cells recognizing the minor histocompatibility antigen HY with toxin-coupled peptide-MHC class I tetramers inhibits cognate CTL responses and alters immunodominance

Alloreactive T-cell responses directed against minor histocompatibility (H) antigens, which arise from diverse genetic disparities between donor and recipient outside the MHC, are an important cause of rejection of MHC-matched grafts. Because clinically significant responses appear to be directed at only a few antigens, the selective deletion of naïve T cells recognizing donor-specific, immunodominant minor H antigens in recipients before transplantation may be a useful tolerogenic strategy. We have previously demonstrated that peptide-MHC class I tetramers coupled to a toxin can efficiently eliminate specific TCR-transgenic T cells in vivo. Here, using the minor histocompatibility antigen HY as a model, we investigated whether toxic tetramers could inhibit the subsequent priming of the two H2-D(b)-restricted, immunodominant T-cell responses by deleting precursor CTL. Immunization of female mice with male bone marrow elicited robust CTL activity against the Uty and Smcy epitopes, with Uty constituting the major response. As hypothesized, toxic tetramer administration prior to immunization increased survival of cognate peptide-pulsed cells in an in vivo CTL assay, and reduced the frequency of corresponding T cells. However, tetramer-mediated decreases in either T-cell population magnified CTL responses against the non-targeted epitope, suggesting that D(b)-Uty(+) and D(b)-Smcy(+) T cells compete for a limited common resource during priming. Toxic tetramers conceivably could be used in combination to dissect manipulate CD8(+) T-cell immunodominance hierarchies, and to prevent the induction of donor-specific, minor H antigen CTL responses in allotransplantation.

Gene expression profiling of allogeneic islet grafts in an experimental mouse model before rejection or tolerance phenotypes arise

BACKGROUND

It has been reported that an HY antigen-mismatched islet transplantation can induce peripheral tolerance. However, the factors that initiate the peripheral tolerance are not clear. This study was designed to examine which genes were most important for the induction of peripheral tolerance.

METHODS

Islets from female Balb/c and male C57BL/6 mice were transplanted underneath the left perirenal capsule of female C57BL/6 recipient mice rendered diabetic by intraperitoneal injection of streptozotocin. Before rejection or tolerance phenotypes arose, we harvested islet grafts for cDNA microarray analysis.

RESULTS

Minor antigen-mismatched islets transplanted into recipient mice showed no rejection or tolerance phenotypes until 12 days posttransplantation. When we confirmed, decreased functional islet grafts and increased inflammatory cell infiltration. Gene expression profiles revealed differences in expression among groups. Major histocompatibility complex-mismatched islets induced upregulation of 209 genes and downregulation of 10 genes compared with the HY antigen-mismatched islet (2-fold; P < .05). Of these, 3 genes exhibited significant changes in expression levels in Balb/c donor islet grafts compared with C57BL/6 donor islet grafts: Gad1, Gdf10, and Scg2 (P < .01).

CONCLUSIONS

The present study suggested that 3 genes showed a significant relationship to protection against graft rejection. The identification of these genes may help to understand signaling pathways, involved in the communication between transplanted islet grafts and recipients in vivo.

Murine animal models for preclinical islet transplantation: No model fits all (research purposes)

Advances in islet transplantation research have led to remarkable improvements in the outcome in humans with type 1 diabetes. However, pitfalls, mainly linked both to early liver-specific inflammatory events and to pre-existing and transplant-induced auto- and allo-specific adaptive immune responses, still remain. In this scenario research into pancreatic islet transplantation, essential to investigate new strategies to overcome open issues, needs very well-designed preclinical studies to obtain consistent and reliable results and select only promising strategies that may be translated into the clinical practice. This review discusses the main shortcomings of the mouse models currently used in islet transplantation research, outlining the main factors and variables to take into account for the design of new preclinical studies. Since several parameters concerning both the graft (i.e., islets) and the recipient (i.e., diabetic mice) may influence transplant outcome, we recommend considering several critical points in designing future bench-to-bedside islet transplantation research.

An antibody to the sixth Ig-like domain of VCAM-1 inhibits leukocyte transendothelial migration without affecting adhesion

VCAM-1 plays a key role in leukocyte trafficking during inflammatory responses. However, molecular mechanisms underlying this function have not been clearly elucidated. In this study, using phage display technology, we developed a rabbit/human chimeric VCAM-1 Ab, termed VCAM-1 domain 6 (VCAM-1-D6), which specifically recognizes aa 511-599 within the sixth Ig-like domain. We report that the VCAM-1-D6 Ab blocked U937 cell transmigration across activated HUVECs but did not alter adhesion of U937 cells to the HUVECs. We also demonstrate that VCAM-1-D6 does not alter TNF-α-stimulated endothelial cell chemokine or cytokine production. Furthermore, through in vivo efficacy testing using a mouse islet allograft model, we demonstrate that VCAM-1-D6 significantly alleviates allograft rejection by blocking leukocyte infiltration to the grafted islets. Taken together, our results suggest that the VCAM-1-D6 Ab may block VCAM-1-mediated inflammation and could be a useful tool in treating inflammatory diseases.

Influence of Interferon-γ Deficiency in Immune Tolerance Induced by Male Islet Transplantation

Background

Traditionally, interferon-γ (IFN-γ) was regarded as a pro-inflammatory cytokine, however, recent reports suggested role of IFN-γ in immune tolerance. In our previous report, we could induce tolerance to male antigen (HY) just by male islet transplantation in wild type C57BL/6 mice without any immunological intervention. We tried to investigate the influence of IFN-γ deficiency on tolerance induction by male islet transplantation.

Methods

To examine the immunogenicity of male tissue in the absence of IFN-γ, we transplanted male IFN-γ knock-out (KO) skin to female IFN-γ KO mice. Next, we analyzed male IFN-γ KO islet to streptozotocin-induced diabetic female IFN-γ KO mice. And, we checked the functionality of grafted islet by graft removal and insulin staining.

Results

As our previous results in wild type C57BL/6 mice, female IFN-γ KO mice rejected male IFN-γ KO skin within 29 days, and did not reject male IFN-γ KO islet. The maintenance of normal blood glucose level was dependent on the presence of grafted male islet. And the male islet recipient did not reject 2nd challenge of male islet graft also.

Conclusion

Deficiency of IFN-γ does not have influence on the result of male skin graft and male islet transplantation. Conclusively, male islet transplantation induced T cell tolerance is not dependent on the presence of IFN-γ.

The role of co-inhibitory signals in spontaneous tolerance of weakly mismatched transplants

The immune system of female H-2(b) (C57BL/6) mice is a strong responder against the male minor-H antigen. However rejection or acceptance of such weakly mismatched grafts depends on the type of tissue transplanted. The mechanism responsible for such spontaneous graft acceptance, and its relationship to the natural mechanisms of tolerance of self antigens is unknown. Co-inhibitory molecules negatively regulate immune responses, and are important for self tolerance. We examined whether co-inhibitory molecules play a critical role in "spontaneous" allograft tolerance. Naïve or donor sensitized diabetic female C57BL/6 (B6) wild type (WT), PD-1(-/-), and BTLA(-/-) mice were transplanted with freshly isolated syngeneic male islet grafts. The role of co-inhibitors during priming of anti-donor responses and graft challenge was also assessed using monoclonal antibodies targeting co-inhibitory receptors. Among the co-inhibitor (CTLA-4, PD-1) specific antibodies tested, only anti-PD-1 showed some potential to prevent spontaneous acceptance of male islet grafts. All BTLA(-/-) and almost all PD-1(-/-) recipients maintained the ability to spontaneously accept male islet grafts. While spontaneous graft acceptance in naïve recipients was only weakly PD-1 dependent, tolerance induced by the accepted islets was found to be highly PD-1 dependent. Furthermore, spontaneous graft acceptance in pre-sensitized recipients showed an absolute requirement for recipient PD-1 but not BTLA. Thus, the PD-1 pathway, involved in self tolerance, plays a critical role in spontaneous tolerance induced by weakly mismatched grafts in naïve recipients and spontaneous graft acceptance in pre-sensitized recipients.

Placing regulatory T cells into global theories of immunity: an analysis of Cohn's challenge to integrity (Dembic)

In broadening the integrity model, Zlatko Dembic provided one of the few plausible explanations for the existence of regulatory T cells that has been postulated to date and at the same time highlighted deficiencies of the associative antigen recognition model. In defending the virtues of associative antigen recognition, Melvin Cohn has challenged the integrity model and the concept that regulatory T cells have a role in defining the specificity of immune responses. The critique of Cohn's analysis I present here suggests that a greater consideration of quantitative evolutionary constraints removes most of the challenges to integrity.