Targeting CD22 reprograms B-cells and reverses autoimmune diabetes

Efforts to prevent and halt autoimmune beta cell destruction

Despite improvements in understanding of the natural history of type 1 diabetes (T1D), an intervention capable of consistently and safely preventing or reversing the disease has not been developed. The inability to cure this disorder is largely because of the complex pathophysiology of T1D, continued struggles to identify its precise etiologic triggers, and voids in understanding of the immunologic mechanisms that specifically target pancreatic beta cells. Rapidly improving technologies for managing T1D require critical discussions about equipoise, especially when considering interventions deemed high risk in terms of their safety. This article reviews the conceptual basis for prevention versus intervention trials in settings of T1D, past experiences of clinical trials studying these purposes, and controversial issues regarding disease interdiction, and seeks to provide a roadmap for future efforts to cure this disorder.

B1 cells promote pancreas infiltration by autoreactive T cells

The entry of autoreactive T cells into the pancreas is a critical checkpoint in the development of autoimmune diabetes. In this study, we identify a role for B1 cells in this process using the DO11 x RIP-mOVA mouse model. In transgenic mice with islet-specific T cells, but no B cells, T cells are primed in the pancreatic lymph node but fail to enter the pancreas. Reconstitution of the B1 cell population by adoptive transfer permits extensive T cell pancreas infiltration. Reconstituted B1 cells traffic to the pancreas and modify expression of adhesion molecules on pancreatic vasculature, notably VCAM-1. Despite substantial pancreas infiltration, islet destruction is minimal unless regulatory T cells are depleted. These data identify a role for B1 cells in permitting circulating islet-specific T cells to access their Ag-bearing tissue and emphasize the existence of multiple checkpoints to regulate autoimmune disease.

Therapeutic targeting of Syk in autoimmune diabetes

In APCs, the protein tyrosine kinase Syk is required for signaling of several immunoreceptors, including the BCR and FcR. We show that conditional ablation of the syk gene in dendritic cells (DCs) abrogates FcgammaR-mediated cross priming of diabetogenic T cells in RIP-mOVA mice, a situation phenocopied in wild-type RIP-mOVA mice treated with the selective Syk inhibitor R788. In addition to blocking FcgammaR-mediated events, R788 also blocked BCR-mediated Ag presentation, thus broadly interrupting the humoral contributions to T cell-driven autoimmunity. Indeed, oral administration of R788 significantly delayed spontaneous diabetes onset in NOD mice and successfully delayed progression of early-established diabetes even when treatment was initiated after the development of glucose intolerance. At the DC level, R788 treatment was associated with reduced insulin-specific CD8 priming and decreased DC numbers. At the B cell level, R788 reduced total B cell numbers and total Ig concentrations. Interestingly, R788 increased the number of IL-10-producing B cells, thus inducing a tolerogenic B cell population with immunomodulatory activity. Taken together, we show by genetic and pharmacologic approaches that Syk in APCs is an attractive target in T cell-mediated autoimmune diseases such as type 1 diabetes.

Emerging roles for B lymphocytes in Type 1 diabetes

Self-reactive B lymphocytes play two main pathological roles in autoimmune diseases: as secretors of autoantibodies and as specialized antigen-presenting cells that present self-components to autoreactive T lymphocytes. In recognition of these roles, recent clinical trials have utilized B-lymphocyte-depleting monoclonal antibodies to treat various autoimmune diseases, with encouraging results in those where humoral autoimmunity is clearly important. Surprisingly, recent results in animal models suggest that B-lymphocyte depletion may also be effective in the treatment of T-lymphocyte-mediated autoimmune diseases, such as Type 1 diabetes (T1D). This article reviews the experimental evidence that has uncovered pathogenic as well as regulatory roles for B lymphocytes in the prodrome of T1D and how this information is being used to develop novel therapeutic strategies to treat the disease.

Alpha4beta7 integrin/MAdCAM-1 adhesion pathway is crucial for B cell migration into pancreatic lymph nodes in nonobese diabetic mice

Although B cells are crucial antigen-presenting cells in the initiation of T cell autoimmunity to islet beta cell autoantigens in type 1 diabetes (T1D), adhesion molecules that control migration of B cells into pancreatic lymph nodes (PanLN) in the nonobese diabetic (NOD) mouse model of human T1D have not been defined. In this study, we found that B cells from PanLN of 3-4-week-old female NOD mice expressed high levels of alpha(4) integrin and LFA-1 and intermediate levels of beta(7) integrin; half of B cells were L-selectin(high). In short-term in vivo lymphocyte migration assays, B cells migrated from the bloodstream into PanLN more efficiently than into peripheral LNs. Moreover, antibodies to mucosal addressin cell adhesion molecule 1 (MAdCAM-1) and alpha(4)beta(7) integrin inhibited >90% of B cell migration into PanLN. In contrast, antibodies to peripheral node addressin, L-selectin or LFA-1 partially inhibited B cell migration into PanLN. Furthermore, one intraperitoneal injection of anti-MAdCAM-1 antibody into 3-week-old NOD mice significantly inhibited entry of B cells into PanLN for at least 2 weeks. Taken together, these results indicate that the alpha(4)beta(7) integrin/MAdCAM-1 adhesion pathway plays a predominant role in migration of B cells into PanLN in NOD mice. Thus, specific blockage of alpha(4)beta(7) integrin/MAdCAM-1 adhesion pathway-mediated B cell migration may be a potential treatment for T1D.

Effector and regulatory B cells: modulators of CD4+ T cell immunity

B cells are essential for humoral immunity, but the role that they have in regulating CD4(+) T cell responses remains controversial. However, new data showing that the transient depletion of B cells potently influences the induction, maintenance and reactivation of CD4(+) T cells, with the recent identification of antibody-independent functions of B cells, have reinvigorated interest in the many roles of B cells in both infectious and autoimmune diseases. In this Review, we discuss recent data showing how effector and regulatory B cells modulate CD4(+) T cell responses to pathogens and autoantigens.

Reduced diabetes in btk-deficient nonobese diabetic mice and restoration of diabetes with provision of an anti-insulin IgH chain transgene

Type 1 diabetes results from T cell-mediated destruction of insulin-producing beta cells. Although elimination of B lymphocytes has proven successful at preventing disease, modulation of B cell function as a means to prevent type 1 diabetes has not been investigated. The development, fate, and function of B lymphocytes depend upon BCR signaling, which is mediated in part by Bruton's tyrosine kinase (BTK). When introduced into NOD mice, btk deficiency only modestly reduces B cell numbers, but dramatically protects against diabetes. In NOD, btk deficiency mirrors changes in B cell subsets seen in other strains, but also improves B cell-related tolerance, as indicated by failure to generate insulin autoantibodies. Introduction of an anti-insulin BCR H chain transgene restores diabetes in btk-deficient NOD mice, indicating that btk-deficient B cells are functionally capable of promoting autoimmune diabetes if they have a critical autoimmune specificity. This suggests that the disease-protective effect of btk deficiency may reflect a lack of autoreactive specificities in the B cell repertoire. Thus, signaling via BTK can be modulated to improve B cell tolerance, and prevent T cell-mediated autoimmune diabetes.

Translational Mini-Review Series on B Cell-Directed Therapies: B cell-directed therapy for autoimmune diseases

B cells play an important role in the pathogenesis of both systemic and organ-specific autoimmune diseases. Autoreactive B cells not only produce autoantibodies, but are also specialized to present specific autoantigens efficiently to T cells. Furthermore, these B cells can secrete proinflammatory cytokines and can amplify the vicious cycle of self-destruction. Thus, B cell-directed therapies are potentially an important approach for treating autoimmune diseases. On the other hand, like T cells, there are subsets of B cells that produce anti-inflammatory cytokines and are immunosuppressive. These regulatory B cell subsets can protect against and ameliorate autoimmune diseases. Thus targeting B cells therapeutically will require this balance to be considered. Here we summarize the roles of pathogenic and regulatory B cells and current applications of B cell-directed therapy in autoimmune diseases. Considerations for future development of B cell-directed therapy for autoimmune diseases have also been discussed.

Potent small molecule mouse CD22-inhibitors: exploring the interaction of the residue at C-2 of sialic acid scaffold

Our previous study revealed that compound 1 (9-(4'-hydroxy-4-biphenyl)acetamido-9-deoxy-Neu5Gcalpha2-6GalOMP) has the most promising affinity for mCD22. Replacing the subterminal galactose residue of 1 with benzyl or biphenylmethyl as aglycone led to 38- and 20-fold higher potency, respectively. This discovery represents a new direction in inhibitor design suitable for pharmaceutical development.

Change you can B(cell)eive in: recent progress confirms a critical role for B cells in type 1 diabetes

PURPOSE OF REVIEW

Here we review extant recent findings regarding the multiple roles of B cells in type 1 diabetes (T1D) and discuss how autoreactive B cells may become activated by a breach in B cell tolerance, and thereby initiate disease. Finally, we discuss the use of B cell-targeted therapies for treatment of autoimmunity.

RECENT FINDINGS

Anti-CD20-specific depletion of B cells prevents and reverses diabetes in human CD20/non-obese diabetic (NOD) mice. Correspondingly, in nontransgenic NOD mice, B cells are effectively depleted with high dose antimouse CD20 mAbs of varying isotypes, and this also prevents diabetes in more than 60% of the mice when administered early, and significantly delays disease in 15-week-old animals. A separate study revealed that targeting B cells with anti-CD22/cal monoclonal antibody therapy delays diabetes onset in prediabetic NOD mice and restores normoglycemia in new-onset hyperglycemic NOD mice. In humans, a clinical trial of rituximab in new onset type 1 diabetics has yielded promising preliminary findings.

SUMMARY

B cells are major players in T1D in humans, and clearly essential for disease development in the NOD mouse model of T1D. In this review, we discuss the silencing of autoreactive B cells and how failure of this process may contribute to autoimmunity. Further, we describe the most recent advances in studies of therapeutic effects of B cell depletion in T1D, and provide recent data indicating the diverse functions by which B cells may mediate disease.

CD4(+)CD25(+) T-cells control autoimmunity in the absence of B-cells

OBJECTIVE

Tumor necrosis factor ligand family members B-cell-activating factor (BAFF) and a proliferation-inducing ligand (APRIL) can exert powerful effects on B-cell activation and development, type 1 T-helper cell (Th1) immune responses, and autoimmunity. We examined the effect of blocking BAFF and APRIL on the development of autoimmune diabetes.

RESEARCH DESIGN AND METHODS

Female NOD mice were administered B-cell maturation antigen (BCMA)-Fc from 9 to 15 weeks of age. Diabetes incidence, islet pathology, and T- and B-cell populations were examined.

RESULTS

BCMA-Fc treatment reduced the severity of insulitis and prevented diabetes development in NOD mice. BCMA-Fc-treated mice showed reduced follicular, marginal-zone, and T2MZ B-cells. B-cell reduction was accompanied by decreased frequencies of pathogenic CD4(+)CD40(+) T-cells and reduced Th1 cytokines IL-7, IL-15, and IL-17. Thus, T-cell activation was blunted with reduced B-cells. However, BCMA-Fc-treated mice still harbored detectable diabetogenic T-cells, suggesting that regulatory mechanisms contributed to diabetes prevention. Indeed, BCMA-Fc-treated mice accumulated increased CD4(+)CD25(+) regulatory T-cells (Tregs) with age. CD4(+)CD25(+) cells were essential for maintaining euglycemia because their depletion abrogated BCMA-Fc-mediated protection. BCMA-Fc did not directly affect Treg homeostasis given that CD4(+)CD25(+)Foxp3(+) T-cells did not express TACI or BR3 receptors and that CD4(+)CD25(+)Foxp3(+) T-cell frequencies were equivalent in wild-type, BAFF(-/-), TACI(-/-), BCMA(-/-), and BR3(-/-) mice. Rather, B-cell depletion resulted in CD4(+)CD25(+) T-cell-mediated protection from diabetes because anti-CD25 monoclonal antibody treatment precipitated diabetes in both diabetes-resistant NOD.microMT(-/-) and BCMA-Fc-treated mice.

CONCLUSIONS

BAFF/APRIL blockade prevents diabetes. BCMA-Fc reduces B-cells, subsequently blunting autoimmune activity and allowing endogenous regulatory mechanisms to preserve a prehyperglycemic state.

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.

B cell-targeted therapies in autoimmunity: rationale and progress

B cells are recognized as main actors in the autoimmune process. Autoreactive B cells can arise in the bone marrow or in the periphery and, if not properly inhibited or eliminated, can lead to autoimmune diseases through several mechanisms: autoantibody production and immune complex formation, cytokine and chemokine synthesis, antigen presentation, T cell activation, and ectopic lymphogenesis. The availability of agents capable of depleting B cells (that is, anti-CD20 and anti-CD22 monoclonal antibodies) or targeting B cell survival factors (atacicept and belimumab) opens new perspectives in the treatment of diseases such as systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes, and multiple sclerosis.