B7h (ICOS-L) maintains tolerance at the fetomaternal interface.

In a successful pregnancy, the semiallogeneic fetus is not rejected by the maternal immune system, which implies tolerance mechanisms protecting fetal tissues from maternal immune attack. Here we report that the ICOS-B7h costimulatory pathway plays a critical role in maintaining the equilibrium at the fetomaternal interface. Blockade of this pathway increased fetal resorption and decreased fetal survival in an allogeneic pregnancy model (CBA female × B6 male). Locally in the placenta, levels of regulatory markers such as IDO and TGF-ß1 were reduced after anti-B7h monoclonal antibody treatment, whereas levels of effector cytokines (eg, IFN-γ) were significantly increased. In secondary lymphoid organs, enhanced IFN-γ and granzyme B production (predominantly by CD8(+) T cells) was observed in the anti-B7h-treated group. The deleterious effect of B7h blockade in pregnancy was maintained only in CD4 knockout mice, not in CD8 knockout mice, which suggests a role for CD8(+) T cells in immune regulation by the ICOS-B7h pathway. In accord, regulatory CD8(+) T cells (in particular, CD8(+)CD103(+) cells) were significantly decreased after anti-B7h monoclonal antibody treatment, and adoptive transfer of this subset abrogated the deleterious effect of B7h blockade in fetomaternal tolerance. Taken together, these data support the hypothesis that B7h blockade abrogates tolerance at the fetomaternal interface by enhancing CD8(+) effector response and reducing local immunomodulation mediated by CD8(+) regulatory T cells.

Anti-CD3 mAb treatment cures PDL1-/-.NOD mice of diabetes but precipitates fatal myocarditis.

Anti-CD3 mAb is an effective therapy that can reverse diabetes in NOD mice and has therapeutic potential in patients with type 1 diabetes (T1D). We administered anti-CD3 to PDL1-/-.NOD mice in order to determine whether this treatment would reverse the development of diabetes in these mice. Mice injected with anti-CD3 mAb neonatally were protected from T1D. However, all of these anti-CD3 mAb treated PDL1-/-.NOD mice developed a wasting disease between 12 and 20 weeks of age with sudden deterioration and weight loss, leading to death within 3-5 days of development of illness. Histology revealed severe inflammation in the heart and skeletal muscles. These results suggest that deficiency of PDL1 in NOD background has the potential to lead to immune-mediated tissue damage in organs other than the pancreas, but this cannot be appreciated in PDL1-/-.NOD mice as the mice develop T1D at an early age and die from diabetes prior to manifesting other autoimmune diseases.

Immunomodulatory function of bone marrow-derived mesenchymal stem cells in experimental autoimmune type 1 diabetes.

Human clinical trials in type 1 diabetes (T1D) patients using mesenchymal stem cells (MSC) are presently underway without prior validation in a mouse model for the disease. In response to this void, we characterized bone marrow-derived murine MSC for their ability to modulate immune responses in the context of T1D, as represented in NOD mice. In comparison to NOD mice, BALB/c-MSC mice were found to express higher levels of the negative costimulatory molecule PD-L1 and to promote a shift toward Th2-like responses in treated NOD mice. In addition, transfer of MSC from resistant strains (i.e., nonobese resistant mice or BALB/c), but not from NOD mice, delayed the onset of diabetes when administered to prediabetic NOD mice. The number of BALB/c-MSC trafficking to the pancreatic lymph nodes of NOD mice was higher than in NOD mice provided autologous NOD-MSC. Administration of BALB/c-MSC temporarily resulted in reversal of hyperglycemia in 90% of NOD mice (p = 0.002). Transfer of autologous NOD-MSC imparted no such therapeutic benefit. We also noted soft tissue and visceral tumors in NOD-MSC-treated mice, which were uniquely observed in this setting (i.e., no tumors were present with BALB/c- or nonobese resistant mice-MSC transfer). The importance of this observation remains to be explored in humans, as inbred mice such as NOD may be more susceptible to tumor formation. These data provide important preclinical data supporting the basis for further development of allogeneic MSC-based therapies for T1D and, potentially, for other autoimmune disorders.

Critical role of donor tissue expression of programmed death ligand-1 in regulating cardiac allograft rejection and vasculopathy.

BACKGROUND: Allograft vasculopathy is a major limiting factor in the long-term success of cardiac transplantation. T cells play a critical role in initiation of cardiac allograft rejection and allograft vasculopathy. The negative T-cell costimulatory pathway PD-1:PDL1/PDL2 (programmed death-1:programmed death ligand-1/2) plays an important role in regulating alloimmune responses. We investigated the role of recipient versus donor PD-1 ligands in the pathogenesis of allograft rejection with emphasis on the role of tissue expression in regulating this alloimmune response in vivo. METHODS AND RESULTS: We used established major histocompatibility complex class II- and class I-mismatched models of vascularized cardiac allograft rejection, blocking anti-PDL1 and anti-PDL2 antibodies, and PDL1- and PDL2-deficient mice (as donors or recipients) to study the role of the PD-1:PDL1/PDL2 pathway in chronic rejection. We also used PDL1-deficient and wild-type mice and bone marrow transplantation to generate chimeric animals that express PDL1 exclusively on either hematopoietic or parenchymal cells. PDL1 but not PDL2 blockade significantly accelerated cardiac allograft rejection in the bm12-into-B6 and B6-into-bm12 models. Although wild-type cardiac allografts survived long term, PDL1-/- donor hearts transplanted into wild-type bm12 mice exhibited accelerated rejection and vasculopathy associated with enhanced recipient T-cell alloreactivity. Interestingly, PDL1-/- recipients did not exhibit an accelerated tempo of cardiac allograft rejection. Using chimeric animals as donors, we show that PDL1 expression on cardiac tissue alone significantly prolonged graft survival compared with full PDL1-/- donor grafts in transplanted wild-type recipients. CONCLUSIONS: This is the first report to demonstrate that expression of the negative costimulatory molecule PDL1 on donor cardiac tissue regulates recipient alloimmune responses, allograft rejection, and vasculopathy.

mTORC2 regulates PGE2-mediated endothelial cell survival and migration.

Prostaglandin E(2) (PGE(2)) promotes angiogenesis by in part inducing endothelial cell survival and migration. The present study examined the role of mTOR and its two complexes, mTORC1 and mTORC2, in PGE(2)-mediated endothelial cell responses. We used small interfering RNA (siRNA) to raptor or rictor to block mTORC1 or mTORC2, respectively. We observed that down-regulation of mTORC2 but not mTORC1 reduced baseline and PGE(2)-induced endothelial cell survival and migration. At the molecular level, we found that knockdown of mTORC2 inhibited PGE(2)-mediated Rac and Akt activation two important signaling intermediaries in endothelial cell migration and survival, respectively. In addition, inhibition of mTORC2 by prolonged exposure of endothelial cells to rapamycin also prevented PGE(2)-mediated endothelial cell survival and migration confirming the results obtained with the siRNA approach. Taken together these results show that mTORC2 but not mTORC1 is an important signaling intermediary in PGE(2)-mediated endothelial cell responses.

Programmed cell death in the lithium pilocarpine model: evidence for NMDA receptor and ceramide-mediated mechanisms.

Ceramide is known to induce programmed cell death (PCD) in neural and non-neural tissues and to increase after kainic acid (KA) status epilepticus (SE). Ceramide increases have been shown to depend on NMDA receptor activation in the KA model, but these changes have not been studied in the lithium pilocarpine (LiPC) model. Thus, the purpose of this study was to determine if hippocampal ceramide levels increase after LiPC induced SE and if NMDA receptor blockade prevents PCD and any such ceramide increases. We found that LiPC induced SE resulted in ceramide increases and DNA fragmentation in the hippocampus of adult, P21, and P7 rats. The administration of MK-801, the NMDA receptor antagonist, in adults, 15min prior to pilocarpine, prevented ceramide increases, and DNA fragmentation.

Role of ICOS pathway in autoimmune and alloimmune responses in NOD mice.

Islet allografts are subject to alloimmune and autoimmune destruction when transplanted into autoimmune prone animals or humans. The ICOS-B7h pathway plays a role in alloimmune responses, but its function in autoimmunity against islet cells is controversial. We investigated the role of ICOS signaling in autoimmune and alloimmune responses in NOD mice. ICOS blockade prevents development of spontaneous disease in pre-diabetic NOD mice. Furthermore, while ICOS blockade prolongs graft survival in a fully mismatched non-autoimmune islet allograft model in C57BL/6 recipients, it has no beneficial effect in reversing diabetes in models of islet transplantation in NOD mice involving autoimmunity alone or both allo- and autoimmunity. Interestingly, ICOS blockade is effective in prolonging heart allograft (not subject to tissue-specific autoimmunity) survival in NOD mice. We conclude that in islet transplantation and autoimmune diabetes, ICOS blockade can be effective in inhibiting alloimmunity and preventing autoimmunity but is ineffective in inhibiting recurrence of autoimmunity.

Targeting CD22 reprograms B-cells and reverses autoimmune diabetes.

OBJECTIVES: To investigate a B-cell-depleting strategy to reverse diabetes in naïve NOD mice. RESEARCH DESIGN AND METHODS: We targeted the CD22 receptor on B-cells of naïve NOD mice to deplete and reprogram B-cells to effectively reverse autoimmune diabetes. RESULTS: Anti-CD22/cal monoclonal antibody (mAb) therapy resulted in early and prolonged B-cell depletion and delayed disease in pre-diabetic mice. Importantly, when new-onset hyperglycemic mice were treated with the anti-CD22/cal mAb, 100% of B-cell-depleted mice became normoglycemic by 2 days, and 70% of them maintained a state of long-term normoglycemia. Early therapy after onset of hyperglycemia and complete B-cell depletion are essential for optimal efficacy. Treated mice showed an increase in percentage of regulatory T-cells in islets and pancreatic lymph nodes and a diminished immune response to islet peptides in vitro. Transcriptome analysis of reemerging B-cells showed significant changes of a set of proinflammatory genes. Functionally, reemerging B-cells failed to present autoantigen and prevented diabetes when cotransferred with autoreactive CD4(+) T-cells into NOD.SCID hosts. CONCLUSIONS: Targeting CD22 depletes and reprograms B-cells and reverses autoimmune diabetes, thereby providing a blueprint for development of novel therapies to cure autoimmune diabetes.

A link between PDL1 and T regulatory cells in fetomaternal tolerance.

Acceptance of the fetus expressing allogeneic paternal Ags by the mother is a physiologic model of transplantation tolerance. Various mechanisms contribute to fetal evasion from immune attack by maternal leukocytes. We have recently demonstrated that the inhibitory costimulatory molecule PDL1 plays a critical role in fetomaternal tolerance in that PDL1 blockade or deficiency resulted in decreased allogeneic fetal survival rates. CD4(+)CD25(+) T regulatory cells (Tregs) have also been demonstrated to play an important role in fetomaternal tolerance. Since PDL1 is expressed on Tregs, we explored the interactions between PDL1 and Tregs in vivo in a mouse model of fetomaternal tolerance. Depletion of CD25(+) T cells abrogated the effect of anti-PDL1 Ab indicating that the effect of PDL1 is possibly mediated by CD25(+) Tregs. Adoptive transfer of Tregs from wild-type but not PDL1-deficient mice into PDL1-deficient recipients significantly improved fetal survival. The frequency, phenotype and placental trafficking of Tregs from PDL1-deficient mice were similar to those of wild-type controls, but were defective in inhibiting alloreactive Th1 cells in vitro. This is the first report providing evidence for a link between PDL1 and T regulatory cells in mediating fetomaternal tolerance.

Mechanisms of PDL1-mediated regulation of autoimmune diabetes.

The PD-1-PDL1 pathway plays a critical role in regulating autoimmune diabetes as blockade or deficiency of PD-1 or PDL1 results in accelerated disease in NOD mice. We explored the cellular mechanisms involved in the regulation of these autoimmune responses by investigations involving various gene-deficient mice on the NOD background. Administration of blocking anti-PDL1 antibody to CD4+ T cell-deficient, CD8+ T cell-deficient and B cell-deficient mice demonstrated that PDL1-mediated regulation of autoreactive CD4+ and CD8+ T cells is critical for diabetes development. This concept was confirmed by adoptive transfer studies utilizing lymphocytes from BDC2.5 and 4.1 (CD4+) TCR transgenic mice and 8.3 (CD8+) TCR transgenic mice; efforts showing increased proliferation of both CD4+ and CD8+ T cells following PDL1 blockade in vivo. Furthermore, we observed that anti-PDL1-mediated acceleration is dependent upon events occurring in the pancreatic lymph nodes during early disease stages, but becomes independent of the pancreatic lymph nodes during later disease stages. These data provide strong evidence that PDL1 regulates autoimmune diabetes by limiting the expansion of CD4+ and CD8+ autoreactive T cells, and define the timing and locale of PDL1-mediated regulation of type 1 diabetes.