PD-L1 blockade overrides Salmonella typhimurium-mediated diabetes prevention in NOD mice: no role for Tregs.

Increasingly, evidence suggests that there is a strong environmental component to the development of the autoimmune disease type 1 diabetes. Our previous data showed that NOD mice are protected from developing diabetes after infection with Salmonella typhimurium and there is some evidence that changes within the DC compartment play a crucial role in this protective effect. This paper further characterises this Salmonella-modulated protective phenotype. We find that, contrary to other infection-mediated models of type 1 diabetes protection, there was no expansion of Foxp3(+) Tregs. Furthermore, transcriptome analysis of DCs identified a distinct Salmonella-induced signature in which the inhibitory receptor PD-L1 was up-regulated. This was confirmed by flow cytometry. In vivo blockade of the PD1/PD-L1 interaction was found to ablate the protective function of Salmonella infection. These data provide evidence for a novel regulatory DC phenotype proficient at controlling autoreactive T cells for an extended duration in the NOD mouse model of diabetes.

Epigenetic changes at Il12rb2 and Tbx21 in relation to plasticity behavior of Th17 cells.

Plasticity within Th cell populations may play a role in enabling site-specific immune responses to infections while limiting tissue destruction. Epigenetic processes are fundamental to such plasticity; however, to date, most investigations have focused on in vitro-generated T cells. In this study, we have examined the molecular mechanisms underpinning murine Th17 plasticity in vivo by assessing H3K4 and H3K27 trimethylation marks at Tbx21, Rorc, Il17a, Ifng, and Il12rb2 loci in purified ex vivo-isolated and in vitro-generated Th17 cells. Although both populations had largely comparable epigenetic signatures, including bivalent marks at Tbx21, freshly isolated ex vivo Th17 cells displayed restricted expression from Il12rb2 due to the presence of repressive chromatin modifications. This receptor, however, could be upregulated on isolated ex vivo Th17 cells after in vitro activation or by in vivo immunization and was augmented by the presence of IFN-γ. Such activated cells could then be deviated toward a Th1-like profile. We show that IL-12 stimulation removes H3K27 trimethylation modifications at Tbx21/T-bet leading to enhanced T-bet expression with in vitro Th17 cells. Our study reveals important potential phenotypic differences between ex vivo- and in vitro-generated Th17 cells and provides mechanistic insight into Th17 cell plasticity.

Roles for TGF-beta and programmed cell death 1 ligand 1 in regulatory T cell expansion and diabetes suppression by zymosan in nonobese diabetic mice.

Zymosan is a complex fungal component shown to be capable of both promoting and suppressing the development of autoimmune disorders in mice. In this study, we show that a single injection of zymosan just prior to diabetes onset can significantly delay the progression of disease in NOD mice. Zymosan treatment of NOD mice induced the production of biologically active TGF-beta from cells infiltrating the pancreas and was associated with expansion of programmed cell death 1 ligand 1(+)TGF-beta(+) macrophages and Foxp3(+) regulatory T cells in vivo. Neutralization of either TGF-beta or programmed cell death 1 ligand 1 abrogated the protective effects of zymosan. Zymosan acted through TLR2 as well as ERK and p38 MAPK to induce macrophage secretion of TGF-beta and promotion of Foxp3(+) regulatory T cells in vitro and in vivo.

Type 1 diabetes development requires both CD4+ and CD8+ T cells and can be reversed by non-depleting antibodies targeting both T cell populations.

Type 1 diabetes development in NOD mice appears to require both CD4(+) and CD8(+) T cells. However, there are some situations where it has been suggested that either CD4(+) or CD8(+) T cells are able to mediate diabetes in the absence of the other population. In the case of transgenic mice, this may reflect the numbers of antigen-specific T cells able to access the pancreas and recruit other cell types such as macrophages leading to a release of high concentrations of damaging cytokines. Previous studies examining the requirement for CD8(+) T cells have used antibodies specific for CD8alpha. It is known that CD8alpha is expressed not only on alphabeta T cells, but also on other cell types, including a DC population that may be critical for presenting islet antigen in the pancreatic draining lymph nodes. Therefore, we have re-examined the need for both CD4(+) and CD8(+) T cell populations in diabetes development in NOD mice using an antibody to CD8beta. Our studies indicate that by using highly purified populations of T cells and antibodies specific for CD8(+) T cells, there is indeed a need for both cell types. In accordance with some other reports, we found that CD4(+) T cells appeared to be able to access the pancreas more readily than CD8(+) T cells. Despite the ability of CD4(+) T cells to recruit CD11b class II positive cells, diabetes did not develop in the absence of CD8(+) T cells. These studies support the observation that CD8(+) T cells may be final effector cells. As both T cell populations are clearly implicated in diabetes development, we have used a combination of non-depleting antibodies to target both CD4-positive and CD8-positive cells and found that this antibody combination was able to reverse diabetes onset in NOD mice as effectively as anti-CD3 antibodies.

Validated germline-competent embryonic stem cell lines from nonobese diabetic mice.

Nonobese diabetic (NOD) mice provide an excellent model of type 1 diabetes. The genetic contribution to this disease is complex, with more than 20 loci implicated in diabetes onset. One of the challenges for researchers using the NOD mouse model (and, indeed, other models of spontaneous autoimmune disease) has been the high density of sequence variation within candidate chromosomal segments. Furthermore, the scope for analyzing many putative disease loci via gene targeting has been hampered by the lack of NOD embryonic stem (ES) cells. We describe here the derivation of NOD ES cell lines capable of generating chimeric mice after stable genetic modification. These NOD ES cell lines also show efficient germline transmission, with offspring developing diabetes. The availability of these cells will not only enable the dissection of closely linked loci and the role they have in the onset of type 1 diabetes but also facilitate the generation of new transgenics.

Highly purified Th17 cells from BDC2.5NOD mice convert into Th1-like cells in NOD/SCID recipient mice.

Th17 cells are involved in the pathogenesis of many autoimmune diseases, but it is not clear whether they play a pathogenic role in type 1 diabetes. Here we investigated whether mouse Th17 cells with specificity for an islet antigen can induce diabetes upon transfer into NOD/SCID recipient mice. Induction of diabetes in NOD/SCID mice via adoptive transfer of Th1 cells from BDC2.5 transgenic mice was prevented by treatment of the recipient mice with a neutralizing IFN-γ-specific antibody. This result suggested a major role of Th1 cells in the induction of disease in this model of type 1 diabetes. Nevertheless, transfer of highly purified Th17 cells from BDC2.5 transgenic mice caused diabetes in NOD/SCID recipients with similar rates of onset as in transfer of Th1 cells. However, treatment with neutralizing IL-17-specific antibodies did not prevent disease. Instead, the transferred Th17 cells, completely devoid of IFN-γ at the time of transfer, rapidly converted to secrete IFN-γ in the NOD/SCID recipients. Purified Th17 cells also upregulated Tbet and secreted IFN-γ upon exposure to IL-12 in vitro and in vivo in NOD/SCID recipients. These results indicate substantial plasticity of Th17 commitment toward a Th1-like profile.

Both central and peripheral tolerance mechanisms play roles in diabetes prevention in NOD-E transgenic mice.

The non-obese diabetic (NOD) mouse spontaneously develops diabetes and is a widely used model of Type 1 Diabetes in humans. The major histocompatibility complex class II plays an important role in governing disease susceptibility in NOD mice. NOD mice express a rare I-A allele, I-A(g7), and do not express I-E molecules. Interestingly, transgenic NOD mice which express I-E (NOD-E) fail to develop diabetes although, the protective mechanism(s) are incompletely understood. Initially, we explored whether diabetes prevention was due to deletion of autoreactive T cells. Through adoptive transfer with depletion of CD25+ T cells, we demonstrated that autoreactive T cells were present in the periphery of NOD-E mice. Although, BDC2.5NOD T cells proliferated less in the pancreatic lymph nodes of NOD-E mice, we found that they transferred disease with a similar kinetic in NOD.scid and NOD-E.scid recipients suggesting that there was little difference in peripheral antigen presentation in NOD-E mice. We also found that there were no proportional or functional differences between NOD and NOD-E T regs. Our studies indicate that autoreactive T cells are present within the periphery of NOD-E mice but that these cells are present in low numbers suggesting that peripheral tolerogenic mechanisms are able to prevent them from inducing diabetes.

An early age-related increase in the frequency of CD4+ Foxp3+ cells in BDC2.5NOD mice.

The role of regulatory T cells (Treg) in maintaining tolerance to self has been intensively scrutinized, particularly since the discovery of Foxp3 as a Treg-specific transcription factor. The BDC2.5NOD transgenic mouse is an excellent model of immunoregulation because it has a very low incidence of diabetes despite a highly autoreactive T-cell repertoire. It has previously been shown that reactivity against islets decreases with age in BDC2.5NOD mice. Here we show that there is a markedly higher frequency of Foxp3(+) Treg in the CD4(+) subset of 16-20-week-old mice compared with 4- or 8-week-old mice. This phenomenon can be observed in the spleen, thymus, pancreatic draining lymph nodes and the pancreas itself. We show that this early age-related increase in the frequency of Foxp3(+) cells does not occur in wild-type NOD, BALB/c or C57BL/6 mice. Further, we show that, in contrast to some reports on Treg in wild-type NOD mice, the suppressive function of BDC2.5NOD Treg from 16- to 20-week-old mice is intact and comparable to that from 4- to 8-week-old mice both in vitro and in vivo. Our data offer insights into the long-term protection of BDC2.5NOD mice from diabetes and an explanation for the age-related decrease in anti-islet responses seen in BDC2.5NOD mice.

Diabetes in non-obese diabetic mice is not associated with quantitative changes in CD4+ CD25+ Foxp3+ regulatory T cells.

The role of regulatory T cells (Tregs) in maintaining self tolerance has been intensively researched and there is a growing consensus that a decline in Treg function is an important step towards the development of autoimmune diseases, including diabetes. Although we show here that CD25+ cells delay diabetes onset in non-obese diabetic (NOD) mice, we found, in contrast to previous reports, neither an age-related decline nor a decline following onset of diabetes in the frequency of CD4+ CD25+ Foxp3+ regulatory T cells. Furthermore, we demonstrate that CD4+ CD25+ cells from both the spleen and pancreatic draining lymph nodes of diabetic and non-diabetic NOD mice are able to suppress the proliferation of CD4+ CD25- cells to a similar extent in vitro. We also found that pretreatment of NOD mice with anti-CD25 antibody allowed T cells with a known reactivity to islet antigen to proliferate more in the pancreatic draining lymph nodes of NOD mice, regardless of age. In addition, we demonstrated that onset of diabetes in NOD.scid mice is faster when recipients are co-administered splenocytes from diabetic NOD donors and anti-CD25. Finally, we found that although diabetic CD4+ CD25+ T cells are not as suppressive in cotransfers with effectors into NOD.scid recipients, this may not indicate a decline in Treg function in diabetic mice because over 10% of CD4+ CD25+ T cells are non-Foxp3 and the phenotype of the CD25- contaminating population significantly differs in non-diabetic and diabetic mice. This work questions whether onset of diabetes in NOD mice is associated with a decline in Treg function.

Patients with chronic pancreatitis have islet progenitor cells in their ducts, but reversal of overt diabetes in NOD mice by anti-CD3 shows no evidence for islet regeneration.

Monoclonal antibodies to T-cell coreceptors have been shown to tolerise autoreactive T-cells and prevent or even reverse autoimmune pathology. In type 1 diabetes, there is a loss of insulin-secreting beta-cells, and a cure for type 1 diabetes would require not only tolerance induction but also recovery of the functional beta-cell mass. Although we have previously shown that diabetic mice have increased numbers of ductal progenitors in the pancreas, there is no evidence of any increase of insulin-secreting cells in the ducts. In contrast, in the adult human pancreas of patients with chronic pancreatitis, we can demonstrate, in the ducts, increased numbers of insulin-containing cells, as well as cells containing other endocrine and exocrine markers. There are also significantly increased numbers of cells expressing the homeodomain protein, pancreatic duodenal homeobox-1. Anti-CD3 has been shown to reverse overt diabetes in NOD mice; thus, we have used this model to ask whether monoclonal antibody-mediated inhibition of ongoing beta-cell destruction enables islet regeneration to occur. We find no evidence that such monoclonal antibody therapy results in either regeneration of insulin-secreting beta-cells or of increased proliferation of islet beta-cells.

Loss of invariant chain protects nonobese diabetic mice against type 1 diabetes.

The invariant (Ii) chain acts as an essential chaperone to promote MHC class II surface expression, Ag presentation, and selection of CD4(+) T cells. We have examined its role in the development of type 1 diabetes in NOD mice and show that Ii chain-deficient NOD mice fail to develop type 1 diabetes. Surprisingly, Ii chain functional loss fails to disrupt in vitro presentation of islet Ags, in the context of NOD I-A(g7) molecules. Moreover, pathogenic effector cells could be shown to be present in Ii chain-deficient NOD mice because they were able to transfer diabetes to NOD.scid recipients. The ability of these cells to transfer diabetes was markedly enhanced by depletion of CD25 cells coupled with in vivo anti-CD25 treatment of recipient mice. The numbers of CD4(+)CD25(+)Foxp3(+) T cells in thymus and periphery of Ii chain-deficient NOD mice were similar to those found in normal NOD mice, in contrast to conventional CD4(+) T cells whose numbers were reduced. This suggests that regulatory T cells are unaffected in their selection and survival by the absence of Ii chain and that an alteration in the balance of effector to regulatory T cells contributes to diabetes prevention.

MAdCAM-1 is needed for diabetes development mediated by the T cell clone, BDC-2.5.

The NOD-derived islet-reactive CD4(+) T cell clone, BDC-2.5, is able to transfer diabetes to neonatal non-obese diabetic (NOD) mice but is unable to transfer disease to either adult NOD or NOD scid recipients. Transfer of diabetes to adult recipients by BDC-2.5 is only accomplished by cotransfer of CD8(+) T cells from a diabetic donor. To understand why this CD4(+) T cell clone is able to mediate diabetes in neonatal but not the adult recipients we examined the ability of the clone to traffic in the different recipients. Our studies showed that MAdCAM-1 has a very different expression pattern in the neonatal and adult pancreas. Blockade of this addressin prevents the clone from transferring diabetes to neonatal mice, suggesting that the differential pancreatic expression of MAdCAM-1 in neonatal and adult pancreas provides an explanation of the differences in diabetes development.

Nondepleting anti-CD4 and soluble interleukin-1 receptor prevent autoimmune destruction of syngeneic islet grafts in diabetic NOD mice.

BACKGROUND: Successful islet transplantation in type 1 diabetes requires tolerance induction of both allo- and autoreactive T-cell responses. Monoclonal antibodies targeting the CD4 coreceptor on T-helper cells have been shown to be effective in this regard. In type 1 diabetes, there is some evidence to suggest that cytokines such as interleukin (IL)-1 may be involved in beta-cell destruction. The high glucose levels associated with type 1 diabetes are also known to be toxic to beta cells. METHOD: The tempo of T-cell and macrophage infiltration into syngeneic islets transplanted into diabetic nonobese diabetic (NOD) mice was examined by immunohistochemistry. We investigated the ability of a nondepleting anti-CD4 monoclonal antibody (YTS177) to induce tolerance to syngeneic islet grafts in female spontaneous diabetic NOD mice and in an adoptive transfer model of diabetes in NOD mice. The spontaneous model was used to test the effect on graft function of perioperative insulin therapy in mice treated with YTS177. The ability of soluble interleukin (sIL)-1 receptor (R) type II (sIL-1RII) to inhibit IL-1 effects in syngeneic islet transplants was also assessed. RESULTS: Cellular infiltration of CD3 cells and macrophages into the islet graft coincided with loss of graft function in untreated mice. Self-tolerance to beta cells was restored with YTS177, allowing long-term graft survival in a proportion of animals. The use of perioperative insulin therapy increased the number of successful grafts in spontaneously diabetic NOD mice treated with YTS177. The combination of YTS177 with sIL-1RII significantly improved the rates of graft survival compared with graft survival in YTS177-treated spontaneously diabetic NOD mice. CONCLUSIONS: Nondepleting anti-CD4 antibodies restore self tolerance to syngeneic islet transplants in diabetic NOD mice. Insulin therapy improves graft survival in mice treated with YTS177. Preventing the action of IL-1 greatly improves graft survival induced with YTS177.