CD40 glycoforms and TNF-receptors 1 and 2 in the formation of CD40 receptor(s) in autoimmunity

Canine diabetes mellitus demonstrates multiple markers of chronic inflammation including Th40 cell increases and elevated systemic-immune inflammation index, consistent with autoimmune dysregulation

Introduction

Canine diabetes mellitus (CDM) is a relatively common endocrine disease in dogs. Many CDM clinical features resemble human type 1 diabetes mellitus (T1DM), but lack of autoimmune biomarkers makes calling the disease autoimmune controversial. Autoimmune biomarkers linking CDM and T1DM would create an alternative model for drug development impacting both human and canine disease.

Methods

We examined peripheral blood of diagnosed CDM dog patients comparing it to healthy control (HC) dogs. Dogs were recruited to a study at the Colorado State University Veterinary Teaching Hospital and blood samples collected for blood chemistry panels, complete blood counts (CBC), and immunologic analysis. Markers of disease progression such as glycated albumin (fructosamine, the canine equivalent of human HbA1c) and c-peptide were addressed.

Results

Significant differences in adaptive immune lymphocytes, innate immune macrophages/monocytes and neutrophils and differences in platelets were detected between CDM and HC based on CBC. Significant differences in serum glucose, cholesterol and the liver function enzyme alkaline phosphatase were also detected. A systemic immune inflammation index (SII) and chronic inflammation index (CII) as measures of dynamic changes in adaptive and innate cells between inflammatory and non-inflammatory conditions were created with highly significant differences between CDM and HC. Th40 cells (CD4+CD40+ T cells) that are demonstrably pathogenic in mouse T1DM and able to differentiate diabetic from non-diabetic subjects in human T1DM were significantly expanded in peripheral blood mononuclear cells.

Conclusions

Based on each clinical finding, CDM can be categorized as an autoimmune condition. The association of significantly elevated Th40 cells in CDM when compared to HC or to osteoarthritis, a chronic but non-autoimmune disease, suggests peripheral blood Th40 cell numbers as a biomarker that reflects CDM chronic inflammation. The differences in SII and CII further underscore those findings.

Modulating CD40 and integrin signaling in the proinflammatory nexus using a 15-amino-acid peptide, KGYY15

CD40 signaling has long been a target in autoimmunity. Attempts to block signaling between CD40 and CD154 during clinical trials using monoclonal antibodies suffered severe adverse events. Previously, we developed a peptide, KGYY15, that targets CD40 and, in preclinical trials, prevents type 1 diabetes in >90% of cases and reverses new-onset hyperglycemia in 56% of cases. It did so by establishing normal effector T-cell levels rather than ablating the cells and causing immunosuppression. However, the relationship between KGYY15 and other elements of the complex signaling network of CD40 is not clear. Studying interactions between proteins from autoimmune and nonautoimmune mice, we demonstrate interactions between CD40 and integrin CD11a/CD18, which complicates the understanding of the inflammatory nexus and how to prevent autoinflammation. In addition to interacting with CD40, KGYY15 interacts with the integrins CD11a/CD18 and CD11b/CD18. We argue that modulation of CD40-CD154 signaling may be more advantageous than complete inhibition because it may preserve normal immunity to pathogens.

Ocrevus reduces TH40 cells, a biomarker of systemic inflammation, in relapsing multiple sclerosis (RMS) and in progressive multiple sclerosis (PMS)

Treating MS has been difficult. One successful drug is Ocrelizumab (anti-CD20), used for the chronic relapsing MS (RMS) and the progressive MS (PMS) forms. TH40 cells are pathogenic effector T cells that increase in percentage and numbers during chronic inflammation. Here we show that in the earliest MS course, clinically isolated syndrome (CIS), TH40 cells expand in number. In PMS TH40 cell numbers remain expanded demonstrating sustained chronic inflammation. In RMS TH40 cells were found in CSF and express CD20. Ocrelizumab reduced TH40 cells to healthy control levels in patients. During treatment inflammatory cytokine producing TH40 cells were decreased.

A CD40 targeting peptide prevents severe symptoms in experimental autoimmune encephalomyelitis

CD40/CD154-interaction is critical in the development of Experimental Autoimmune Encephalomyelitis (EAE; mouse model of Multiple Sclerosis). Culprit CD4⁺CD40⁺ T cells drive a more severe form of EAE than conventional CD4 T cells. Blocking CD40/CD154-interaction with CD154-antibody prevents or ameliorates disease but had thrombotic complications in clinical trials. We targeted CD40 using a CD154-sequence based peptide. Peptides in human therapeutics demonstrate good safety. A small peptide, KGYY₆, ameliorates EAE when given as pretreatment or at first symptoms. KGYY₆ binds Th40 and memory T cells, affecting expression of CD69 and IL-10 in the CD4 T cell compartment, ultimately hampering disease development.

Biomarker discovery in pre-Type 1 Diabetes; Th40 cells as a predictive risk factor

CONTEXT

The incidence of Type 1 Diabetes (T1D) is increasing worldwide. The quest to understand T1D etiology as well as how to predict diabetes is ongoing and, in many ways, those goals intertwine. While genetic components associate with T1D, not all T1D individuals have those components and not all subjects with those components develop disease.

OBJECTIVE

More robust methods for prediction of T1D are needed. Can high CD4+CD40+ T cell (Th40) levels be used as a biomarker in addition to other markers?

METHODS

Th40 levels were assessed along with other parameters in blood collected from prediabetic TrialNet subjects.

RESULTS

Pre-diabetic subjects, stratified according to their Th40 cell levels, demonstrate patterns that parallel those seen between control and T1D subjects. Cytokine patterns are significantly different between Th40-high and -low subjects and a CD4/CD8 double-positive population is more represented in Th40-high groups. Subjects experiencing impaired glucose tolerance present a significantly higher Th40 level than control subjects do. HLA DR4/DR4 and DQ8/DQ8, HLAs associated with T1D, are more likely found among Th40-high subjects. Interestingly, HLA DR4/DR4 subjects were significantly older compared with all other subjects, suggesting that this haplotype together with a high Th40 level may represent someone who will onset after age 30, which is reported for 42% of T1D cases.

CONCLUSION

Considering the differences found in relation to prediabetic Th40 cell level, it may be possible to devise methods that more accurately predicts who will proceed toward diabetes and, possibly, at what stage of prediabetes a subject is.

A Drosophila Tumor Suppressor Gene Prevents Tonic TNF Signaling through Receptor N-Glycosylation

Drosophila tumor suppressor genes have revealed molecular pathways that control tissue growth, but mechanisms that regulate mitogenic signaling are far from understood. Here we report that the Drosophila TSG tumorous imaginal discs (tid), whose phenotypes were previously attributed to mutations in a DnaJ-like chaperone, are in fact driven by the loss of the N-linked glycosylation pathway component ALG3. tid/alg3 imaginal discs display tissue growth and architecture defects that share characteristics of both neoplastic and hyperplastic mutants. Tumorous growth is driven by inhibited Hippo signaling, induced by excess Jun N-terminal kinase (JNK) activity. We show that ectopic JNK activation is caused by aberrant glycosylation of a single protein, the fly tumor necrosis factor (TNF) receptor homolog, which results in increased binding to the continually circulating TNF. Our results suggest that N-linked glycosylation sets the threshold of TNF receptor signaling by modifying ligand-receptor interactions and that cells may alter this modification to respond appropriately to physiological cues.

CD40-mediated signalling influences trafficking, T-cell receptor expression, and T-cell pathogenesis, in the NOD model of type 1 diabetes

CD40 plays a critical role in the pathogenesis of type 1 diabetes (T1D). The mechanism of action, however, is undetermined, probably because CD40 expression has been grossly underestimated. CD40 is expressed on numerous cell types that now include T cells and pancreatic β cells. CD40⁺ CD4⁺ cells [T helper type 40 (TH40)] prove highly pathogenic in NOD mice and in translational human T1D studies. We generated BDC2.5.CD40^-/- and re-derived NOD.CD154^-/- mice to better understand the CD40 mechanism of action. Fully functional CD40 expression is required not only for T1D development but also for insulitis. In NOD mice, TH40 cell expansion in pancreatic lymph nodes occurs before insulitis and demonstrates an activated phenotype compared with conventional CD4⁺ cells, apparently regardless of antigen specificity. TH40 T-cell receptor (TCR) usage demonstrates increases in several Vα and Vβ species, particularly Vα3.2⁺ that arise early and are sustained throughout disease development. TH40 cells isolated from diabetic pancreas demonstrate a relatively broad TCR repertoire rather than restricted clonal expansions. The expansion of the Vα/Vβ species associated with diabetes depends upon CD40 signalling; NOD.CD154^-/- mice do not expand the same TCR species. Finally, CD40-mediated signals significantly increase pro-inflammatory Th1- and Th17-associated cytokines whereas CD28 co-stimulus alternatively promotes regulatory cytokines.

Th40 cells (CD4+CD40+ Tcells) drive a more severe form of Experimental Autoimmune Encephalomyelitis than conventional CD4 T cells

CD40-CD154 interaction is critically involved in autoimmune diseases, and CD4 T cells play a dominant role in the Experimental Autoimmune Encephalomyelitis (EAE) model of Multiple Sclerosis (MS). CD4 T cells expressing CD40 (Th40) are pathogenic in type I diabetes but have not been evaluated in EAE. We demonstrate here that Th40 cells drive a rapid, more severe EAE disease course than conventional CD4 T cells. Adoptively transferred Th40 cells are present in lesions in the CNS and are associated with wide spread demyelination. Primary Th40 cells from EAE-induced donors adoptively transfer EAE without further in-vitro expansion and without requiring the administration of the EAE induction regimen to the recipient animals. This has not been accomplished with primary, non-TCR-transgenic donor cells previously. If co-injection of Th40 donor cells with Freund's adjuvant (CFA) in the recipient animals is done, the disease course is more severe. The CFA component of the EAE induction regimen causes generalized inflammation, promoting expansion of Th40 cells and infiltration of the CNS, while MOG-antigen shapes the antigen-specific TCR repertoire. Those events are both necessary to precipitate disease. In MS, viral infections or trauma may induce generalized inflammation in susceptible individuals with subsequent disease onset. It will be important to further understand the events leading up to disease onset and to elucidate the contributions of the Th40 T cell subset. Also, evaluating Th40 levels as predictors of disease onset would be highly useful because if either the generalized inflammation event or the TCR-honing can be interrupted, disease onset may be prevented.

Overlooked Mechanisms in Type 1 Diabetes Etiology: How Unique Costimulatory Molecules Contribute to Diabetogenesis

Type 1 Diabetes (T1D) develops when immune cells invade the pancreatic islets resulting in loss of insulin production in beta cells. T cells have been proven to be central players in that process. What is surprising, however, is that classic mechanisms of tolerance cannot explain diabetogenesis; alternate mechanisms must now be considered. T cell receptor (TCR) revision is the process whereby T cells in the periphery alter TCR expression, outside the safety-net of thymic selection pressures. This process results in an expanded T cell repertoire, capable of responding to a universe of pathogens, but limitations are that increased risk for autoimmune disease development occurs. Classic T cell costimulators including the CD28 family have long been thought to be the major drivers for full T cell activation. In actuality, CD28 and its family member counterparts, ICOS and CTLA-4, all drive regulatory responses. Inflammation is driven by CD40, not CD28. CD40 as a costimulus has been largely overlooked. When naïve T cells interact with antigen presenting cell CD154, the major ligand for CD40, is induced. This creates a milieu for T cell (CD40)-T cell (CD154) interaction, leading to inflammation. Finally, defined pathogenic effector cells including TH40 (CD4⁺CD40⁺) cells can express FOXP3 but are not Tregs. The cells loose FOXP3 to become pathogenic effector cells. Each of these mechanisms creates novel options to better understand diabetogenesis and create new therapeutic targets for T1D.

Of the multiple mechanisms leading to type 1 diabetes, T cell receptor revision may play a prominent role (is type 1 diabetes more than a single disease?)

A single determinant factor for autoimmunity does not exist; disease development probably involves contributions from genetics, the environment and immune dysfunction. Type 1 diabetes is no exception. Genomewide-associated studies (GWAS) analysis in T1D has proved disappointing in revealing contributors to disease prediction; the only reliable marker has been human leucocyte antigen (HLA). Specific HLAs include DR3/DR4/DQ2/DQ8, for example. Because HLA molecules present antigen to T cells, it is reasonable that certain HLA molecules have a higher affinity to present self-antigen. Recent studies have shown that additional polymorphisms in HLA that are restricted to autoimmune conditions are further contributory. A caveat is that not all individuals with the appropriate 'pro-autoimmune' HLA develop an autoimmune disease. Another crucial component is autoaggressive T cells. Finding a biomarker to discriminate autoaggressive T cells has been elusive. However, a subset of CD4 helper cells that express the CD40 receptor have been described as becoming pathogenic. An interesting function of CD40 on T cells is to induce the recombination-activating gene (RAG)1/RAG2 T cell receptor recombination machinery. This observation is contrary to immunology paradigms that changes in TCR molecules cannot take place outside the thymic microenvironment. Alteration in TCR, called TCR revision, not only occurs, but may help to account for the development of autoaggressive T cells. Another interesting facet is that type 1 diabetes (T1D) may be more than a single disease; that is, multiple cellular components contribute uniquely, but result ultimately in the same clinical outcome, T1D. This review considers the process of T cell maturation and how that could favor auto-aggressive T cell development in T1D. The potential contribution of TCR revision to autoimmunity is also considered.

A CD40-targeted peptide controls and reverses type 1 diabetes in NOD mice

AIMS/HYPOTHESIS

The CD40-CD154 interaction directs autoimmune inflammation. Therefore, a long-standing goal in the treatment of autoimmune disease has been to control the formation of that interaction and thereby prevent destructive inflammation. Antibodies blocking CD154 are successful in mouse models of autoimmune disease but, while promising when used in humans, unfortunate thrombotic events have occurred, forcing the termination of those studies.

METHODS

To address the clinical problem of thrombotic events caused by anti-CD154 antibody treatment, we created a series of small peptides based on the CD154 domain that interacts with CD40 and tested the ability of these peptides to target CD40 and prevent type 1 diabetes in NOD mice.

RESULTS

We identified a lead candidate, the 15-mer KGYY15 peptide, which specifically targets CD40-positive cells in a size- and sequence-dependent manner. It is highly efficient in preventing hyperglycaemia in NOD mice that spontaneously develop type 1 diabetes. Importantly, KGYY15 can also reverse new-onset hyperglycaemia. KGYY15 is well tolerated and functions to control the cytokine profile of culprit Th40 effector T cells. The KGYY15 peptide is 87% homologous to the human sequence, suggesting that it is an important candidate for translational studies.

CONCLUSIONS/INTERPRETATION

Peptide KGYY15 constitutes a viable therapeutic option to antibody therapy in targeting the CD40-CD154 interaction in type 1 diabetes. Given the involvement of CD40 in autoimmunity in general, it will also be important to evaluate KGYY15 in the treatment of other autoimmune diseases. This alternative therapeutic approach opens new avenues of exploration in targeting receptor-ligand interactions.

Pro-inflammatory T-lymphocytes rapidly infiltrate into the brain and contribute to neuronal injury following cardiac arrest and cardiopulmonary resuscitation

Although inflammatory mechanisms have been linked to neuronal injury following global cerebral ischemia, the presence of infiltrating peripheral immune cells remains understudied. We performed flow cytometry of single cell suspensions obtained from the brains of mice at varying time points after global cerebral ischemia induced by cardiac arrest and cardiopulmonary resuscitation (CA/CPR) to characterize the influx of lymphocytes into the injured brain. We observed that CA/CPR caused a large influx of lymphocytes within 3h of resuscitation that was maintained for the 3day duration of our experiments. Using cell staining flow cytometry we observed that the large majority of infiltrating lymphocytes were CD4(+) T cells. Intracellular stains revealed a large proportion of pro-inflammatory T cells expressing either TNFα or INFγ. Importantly, the lack of functional T cells in TCRα knockout mice reduced neuronal injury following CA/CPR, implicating pro-inflammatory T cells in the progression of ischemic neuronal injury. Finally, we made the remarkable observation that the novel CD4(+)CD40(+) (Th40) population of pro-inflammatory T cells that are strongly associated with autoimmunity are present in large numbers in the injured brain. These data indicate that studies investigating the neuro-immune response after global cerebral ischemia should consider the role of infiltrating T cells in orchestrating the acute and sustained immune response.

Defining a new biomarker for the autoimmune component of Multiple Sclerosis: Th40 cells

Multiple Sclerosis (MS) is a chronic inflammatory, neurodegenerative disease. Diagnosis is very difficult requiring defined symptoms and multiple CNS imaging. A complicating issue is that almost all symptoms are not disease specific for MS. Autoimmunity is evident, yet the only immune-related diagnostic tool is cerebral-spinal fluid examination for oligoclonal bands. This study addresses the impact of Th40 cells, a pathogenic effector subset of helper T cells, in MS. MS patients including relapsing/remitting MS, secondary progressive MS and primary progressive MS were examined for Th40 cell levels in peripheral blood and, similar to our findings in autoimmune type 1 diabetes, the levels were significantly (p<0.0001) elevated compared to controls including healthy non-autoimmune subjects and another non-autoimmune chronic disease. Classically identified Tregs were at levels equivalent to non-autoimmune controls but the Th40/Treg ratio still predicted autoimmunity. The cohort displayed a wide range of HLA haplotypes including the GWAS identified predictive HLA-DRB1*1501 (DR2). However half the subjects did not carry DR2 and regardless of HLA haplotype, Th40 cells were expanded during disease. In RRMS Th40 cells demonstrated a limited TCR clonality. Mechanistically, Th40 cells demonstrated a wide array of response to CNS associated self-antigens that was dependent upon HLA haplotype. Th40 cells were predominantly memory phenotype producing IL-17 and IFNγ with a significant portion producing both inflammatory cytokines simultaneously suggesting an intermediary between Th1 and Th17 phenotypes.

CD40 interacts directly with RAG1 and RAG2 in autoaggressive T cells and Fas prevents CD40-induced RAG expression

CD4(+) T cells expressing CD40 (Th40 cells) constitute a pathogenic T-cell subset that is necessary and sufficient to transfer autoimmune disease. We have previously demonstrated that CD40 signals peripheral Th40 cells to induce RAG1 and RAG2 expression, proteins necessary for the expression of T-cell receptor (TCR), leading to TCR revision. The dependency of TCR expression in the thymus on RAG proteins has long been known. However, despite numerous publications, there is controversy as to whether TCR expression can be altered in the periphery, post-thymic selective pressures. Therefore, a better understanding of TCR expression in primary peripheral cells is needed. We now show that the CD40 protein itself interacts with RAG1 and RAG2 as well as with Ku70 and translocates to the nucleus in Th40 cells. This indicates that the CD40 molecule is closely involved in the mechanism of TCR expression in the periphery. In addition, Fas signals act as a silencing mechanism for CD40-induced RAGs and prevent CD40 translocation to the nucleus. It will be important to further understand the involvement of CD40 in peripheral TCR expression and how TCR revision impacts auto-antigen recognition in order to effectively target and tolerize autoaggressive T cells in autoimmune disease.

An alternative role for Foxp3 as an effector T cell regulator controlled through CD40

The BDC2.5 T cell clone is highly diabetogenic, but the transgenic mouse generated from that clone is surprisingly slow in diabetes development. Although defining pathogenic effector T cells in autoimmunity has been inconsistent, CD4(+) cells expressing the CD40 receptor (Th40 cells) are highly diabetogenic in NOD mice, and NOD.BDC2.5.TCR.Tg mice possess large numbers of these cells. Given the importance of CD40 for pathogenic T cell development, BDC2.5.CD40(-/-) mice were created. Regulatory T cells, CD4(+)CD25(hi)Foxp3(+), develop normally, but pathogenic effector cells are severely reduced in number. Th40 cells from diabetic BDC2.5 mice rapidly induce diabetes in NOD.scid recipients, but Th40 cells from prediabetic mice transfer diabetes very slowly. Demonstrating an important paradigm shift, effector Th40 cells from prediabetic mice are Foxp3(+). As mice age, moving to type 1 diabetes development, Th40 cells lose Foxp3. When Th40 cells that are Foxp3(+) are transferred to NOD.scid recipients, disease is delayed. Th40 cells that are Foxp3(-) rapidly transfer disease. Th40 cells from BDC2.5.CD40(-/-) mice do not transfer disease nor do they lose Foxp3 expression. Mechanistically, Foxp3(+) cells produce IL-17 but do not produce IFN-γ, whereas Foxp3(-) Th40 cells produce IFN-γ and IL-2. This poses a new consideration for the function of Foxp3, as directly impacting effector T cell function.

Galectin-9 controls CD40 signaling through a Tim-3 independent mechanism and redirects the cytokine profile of pathogenic T cells in autoimmunity

While it has long been understood that CD40 plays a critical role in the etiology of autoimmunity, glycobiology is emerging as an important contributor. CD40 signaling is also gaining further interest in transplantation and cancer therapies. Work on CD40 signaling has focused on signaling outcomes and blocking of its ligand, CD154, while little is known about the actual receptor itself and its control. We demonstrated that CD40 is in fact several receptors occurring as constellations of differentially glycosylated forms of the protein that can sometimes form hybrid receptors with other proteins. An enticing area of autoimmunity is differential glycosylation of immune molecules leading to altered signaling. Galectins interact with carbohydrates on proteins to effect such signaling alterations. Studying autoimmune prone NOD and non-autoimmune BALB/c mice, here we reveal that in-vivo CD40 signals alter the glycosylation status of non-autoimmune derived CD4 T cells to resemble that of autoimmune derived CD4 T cells. Galectin-9 interacts with CD40 and, at higher concentrations, prevents CD40 induced proliferative responses of CD4^loCD40⁺ effector T cells and induces cell death through a Tim-3 independent mechanism. Interestingly, galectin-9, at lower concentrations, alters the surface expression of CD3, CD4, and TCR, regulating access to those molecules and thereby redirects the inflammatory cytokine phenotype and CD3 induced proliferation of autoimmune CD4^loCD40⁺ T cells. Understanding the dynamics of the CD40 receptor(s) and the impact of glycosylation status in immunity will gain insight into how to maintain useful CD40 signals while shutting down detrimental ones.

CD40 engagement of CD4+ CD40+ T cells in a neo-self antigen disease model ablates CTLA-4 expression and indirectly impacts tolerance

Biomarkers defining pathogenic effector T (Teff) cells slowly have been forthcoming and towards this we identified CD4(+) T cells that express CD40 (CD4(+) CD40(+) ) as pathogenic in the NOD type 1 diabetes (T1D) model. CD4(+) CD40(+) T cells rapidly and efficiently transfer T1D to NOD.scid recipients. To study the origin of CD4(+) CD40(+) T cells and disease pathogenesis, we employed a dual transgenic model expressing OVA(323-339) peptide as a neo-self antigen on islet β cells and medullary thymic epithelial cells (mTECs) and a transgenic TCR recognizing the OVA(323-339) peptide. CD4(+) CD40(+) T cells and Treg cells each recognizing the cognate neo-antigen, rather than being deleted through central tolerance, drastically expanded in the thymus. In pancreatic lymph nodes of DO11.RIPmOVA mice, CD4(+) CD40(+) T cells and Treg cells are expanded in number compared with DO11 mice and importantly, Treg cells remain functional throughout the disease process. When exposed to neo-self antigen, CD4(+) CD40(+) T cells do not express the auto-regulatory CTLA-4 molecule while naïve CD4(+) CD40(+) T cells do. DO11.RIPmOVA mice develop autoimmune-type diabetes. CD40 engagement has been shown to prevent CTLA-4 expression and injecting anti-CD40 in DO11.RIPmOVA mice significantly exacerbates disease. These data suggest a unique means by which CD4(+) CD40(+) T cells thwart tolerance.