Shirine Dada

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.

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.

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.

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.