Evolving Antibody Therapies for the Treatment of Type 1 Diabetes.

Type 1 diabetes (T1D) is widely considered to be a T cell driven autoimmune disease resulting in reduced insulin production due to dysfunction/destruction of pancreatic ß cells. Currently, there continues to be a need for immunotherapies that selectively reestablish persistent ß cell-specific self-tolerance for the prevention and remission of T1D in the clinic. The utilization of monoclonal antibodies (mAb) is one strategy to target specific immune cell populations inducing autoimmune-driven pathology. Several mAb have proven to be clinically safe and exhibit varying degrees of efficacy in modulating autoimmunity, including T1D. Traditionally, mAb therapies have been used to deplete a targeted cell population regardless of antigenic specificity. However, this treatment strategy can prove detrimental resulting in the loss of acquired protective immunity. Nondepleting mAb have also been applied to modulate the function of immune effector cells. Recent studies have begun to define novel mechanisms associated with mAb-based immunotherapy that alter the function of targeted effector cell pools. These results suggest short course mAb therapies may have persistent effects for regaining and maintaining self-tolerance. Furthermore, the flexibility to manipulate mAb properties permits the development of novel strategies to target multiple antigens and/or deliver therapeutic drugs by a single mAb molecule. Here, we discuss current and potential future therapeutic mAb treatment strategies for T1D, and T cell-mediated autoimmunity.

The Role of T Cell Receptor Signaling in the Development of Type 1 Diabetes.

T cell receptor (TCR) signaling influences multiple aspects of CD4+ and CD8+ T cell immunobiology including thymic development, peripheral homeostasis, effector subset differentiation/function, and memory formation. Additional T cell signaling cues triggered by co-stimulatory molecules and cytokines also affect TCR signaling duration, as well as accessory pathways that further shape a T cell response. Type 1 diabetes (T1D) is a T cell-driven autoimmune disease targeting the insulin producing ß cells in the pancreas. Evidence indicates that dysregulated TCR signaling events in T1D impact the efficacy of central and peripheral tolerance-inducing mechanisms. In this review, we will discuss how the strength and nature of TCR signaling events influence the development of self-reactive T cells and drive the progression of T1D through effects on T cell gene expression, lineage commitment, and maintenance of pathogenic anti-self T cell effector function.

Lack of acute xenogeneic graft- versus-host disease, but retention of T-cell function following engraftment of human peripheral blood mononuclear cells in NSG mice deficient in MHC class I and II expression.

Immunodeficient mice engrafted with human peripheral blood mononuclear cells (PBMCs) support preclinical studies of human pathogens, allograft rejection, and human T-cell function. However, a major limitation of PBMC engraftment is development of acute xenogeneic graft- versus-host disease (GVHD) due to human T-cell recognition of murine major histocompatibility complex (MHC). To address this, we created 2 NOD- scid IL-2 receptor subunit γ ( IL2rg) null (NSG) strains that lack murine MHC class I and II [NSG-ß-2-microglobulin ( B2M) null ( IA IE)null and NSG -( Kb Db) null ( IAnull)]. We observed rapid human IgG clearance in NSG- B2Mnull ( IA IE) null mice whereas clearance in NSG -( Kb Db) null ( IAnull) mice and NSG mice was comparable. Injection of human PBMCs into both strains enabled long-term engraftment of human CD4+ and CD8+ T cells without acute GVHD. Engrafted human T-cell function was documented by rejection of human islet allografts. Administration of human IL-2 to NSG -( Kb Db) null ( IAnull) mice via adeno-associated virus vector increased human CD45+ cell engraftment, including an increase in human regulatory T cells. However, high IL-2 levels also induced the development of GVHD. These data document that NSG mice deficient in murine MHC support studies of human immunity in the absence of acute GVHD and enable evaluation of human antibody therapeutics targeting human T cells.-Brehm, M. A., Kenney, L. L., Wiles, M. V., Low, B. E., Tisch, R. M., Burzenski, L., Mueller, C., Greiner, D. L., Shultz, L. D. Lack of acute xenogeneic graft- versus-host disease, but retention of T-cell function following engraftment of human peripheral blood mononuclear cells in NSG mice deficient in MHC class I and II expression.

Therapies to Suppress ß Cell Autoimmunity in Type 1 Diabetes.

Type 1 diabetes (T1D) is an autoimmune disease that is generally considered to be T cell-driven. Accordingly, most strategies of immunotherapy for T1D prevention and treatment in the clinic have targeted the T cell compartment. To date, however, immunotherapy has had only limited clinical success. Although certain immunotherapies have promoted a protective effect, efficacy is often short-term and acquired immunity may be impacted. This has led to the consideration of combining different approaches with the goal of achieving a synergistic therapeutic response. In this review, we will discuss the status of various T1D therapeutic strategies tested in the clinic, as well as possible combinatorial approaches to restore ß cell tolerance.

Prevention of Type 1 Diabetes with Acetalated Dextran Microparticles Containing Rapamycin and Pancreatic Peptide P31.

Type 1 diabetes (T1D) is a common autoimmune disease with no cure. T1D subjects are dependent on daily exogenous insulin administration, due to the loss of functional insulin-producing ß cells. Needed are immunotherapies that prevent and/or treat T1D. One approach of immunotherapy is to administer an autoantigen to selectively tolerize diabetogenic effector T cells without global immunosuppression. To date, however, strategies of antigen-specific immunotherapy are largely ineffective in the clinic. Using an antigen-specific approach, a biodegradable polymeric delivery vehicle, acetalated dextran microparticles (Ace-DEX MPs), is applied and T1D development is prevented through coadministration of the immunosuppressant rapamycin and the diabetogenic peptide P31 (Rapa/P31/MPs), via alterations of both innate and adaptive immunity. Ex vivo, adoptively transferred CD4+ T cells exhibit reduced proliferation and an increased ratio of FoxP3+ to IFNγ+ T cells. In vitro analysis indicates dendritic cells exhibit a less mature phenotype following coculture with Rapa/P31/MPs, which results in reduced CD4+ T cell proliferation and proinflammatory cytokine production (IFNγ and IL-2), but promotes PD-1 expression. Together these results demonstrate Ace-DEX MP-based antigen-specific therapy effectively tolerizes diabetogenic CD4+ T cells to prevent T1D, thereby demonstrating one of the first successful attempts of T1D prevention using a single-formulation particulate delivery platform.

Gene Therapy with an Adeno-Associated Viral Vector Expressing Human Interleukin-2 Alters Immune System Homeostasis in Humanized Mice.

Recombinant adeno-associated viruses (rAAVs) serve as vectors for in vivo gene delivery in both mice and humans, and have broad applicability for the treatment of genetic diseases. Clinical trials with AAV vectors have demonstrated promise and safety in several human diseases. However, the in vivo validation of novel AAV constructs expressing products that act specifically on human cells and tissues is limited by a paucity of effective translatable models. Humanized mice that are engrafted with human cells, tissues, and immune systems offer strong potential to test the biological effectiveness of AAV vectors on human cells and tissues. Using the BLT (bone marrow, liver, thymus) humanized NOD-scid Il2rgnull (NSG) mouse model, which enables efficient development of HLA-restricted effector and regulatory T cells (Tregs), we have evaluated the delivery and function of human interleukin (IL)-2 by an AAV vector. Humanized mice treated with an AAV vector expressing human IL-2 showed a significant and sustained increase in the number of functional human FOXP3+CD4+ Tregs. The expression of human IL-2 did not significantly change the levels or activation status of conventional T-cell subsets. Numbers of activated human natural killer cells were also increased significantly in humanized mice treated with the IL-2 vector. These data recapitulate observations in clinical trials of IL-2 therapy and collectively show that humanized mouse models offer a translational platform for testing the efficacy of AAV vectors targeting human immune cells.

Type 1 Diabetes: A Chronic Anti-Self-Inflammatory Response.

Inflammation is typically induced in response to a microbial infection. The release of proinflammatory cytokines enhances the stimulatory capacity of antigen-presenting cells, as well as recruits adaptive and innate immune effectors to the site of infection. Once the microbe is cleared, inflammation is resolved by various mechanisms to avoid unnecessary tissue damage. Autoimmunity arises when aberrant immune responses target self-tissues causing inflammation. In type 1 diabetes (T1D), T cells attack the insulin producing ß cells in the pancreatic islets. Genetic and environmental factors increase T1D risk by in part altering central and peripheral tolerance inducing events. This results in the development and expansion of ß cell-specific effector T cells (Teff) which mediate islet inflammation. Unlike protective immunity where inflammation is terminated, autoimmunity is sustained by chronic inflammation. In this review, we will highlight the key events which initiate and sustain T cell-driven pancreatic islet inflammation in nonobese diabetic mice and in human T1D. Specifically, we will discuss: (i) dysregulation of thymic selection events, (ii) the role of intrinsic and extrinsic factors that enhance the expansion and pathogenicity of Teff, (iii) defects which impair homeostasis and suppressor activity of FoxP3-expressing regulatory T cells, and (iv) properties of ß cells which contribute to islet inflammation.

Manipulating T cell-mediated pathology: targets and functions of monoclonal antibody immunotherapy.

Monoclonal antibody (mAb) technology has revolutionized treatment options for T cell mediated diseases. However, a safe, clinically available anti-T cell antibody (ab) remains elusive. Experience with anti-T cell agents and their propensity for causing immune-mediated toxicities have hampered the development of anti-T cell mAb's. Furthermore, misunderstanding regarding mechanism(s) of action of particular antibodies can influence development and clinical prescription habits. For example, the anti-CD3 Ab OKT3 is consistently described as a depleting Ab even though original studies showed the mechanism to be non-lytic. Future anti-T cell mAbs are likely to be non-depletional and focused on the expansion of regulatory T cells. This review discusses how the properties of Abs can be exploited for manipulating pathological T cell responses in the clinic.

Cumulative autoimmunity: T cell clones recognizing several self-epitopes exhibit enhanced pathogenicity.

T cell receptor (TCR) recognition is intrinsically polyspecific. In the field of autoimmunity, recognition of both self- and microbial peptides by a single TCR has led to the concept of molecular mimicry. However, findings made by our group and others clearly demonstrate that a given TCR can also recognize multiple distinct self-peptides. Based on experimental data we argue that recognition of several self-peptides increases the pathogenicity of an autoreactive T cell; a property we refer to as "cumulative autoimmunity." The mechanisms of such increased pathogenicity, and the implications of cumulative autoimmunity regarding the pathophysiology of T cell-mediated autoimmune diseases will be discussed.

Toxin-coupled MHC class I tetramers can specifically ablate autoreactive CD8+ T cells and delay diabetes in nonobese diabetic mice.

There is compelling evidence that self-reactive CD8(+) T cells are a major factor in development and progression of type 1 diabetes in animals and humans. Hence, great effort has been expended to define the specificity of autoimmune CD8(+) T cells and to alter their responses. Much work has focused on tolerization of T cells using proteins or peptides. A weakness in this approach is that residual autoreactive T cells may be activated and exacerbate disease. In this report, we use a novel approach, toxin-coupled MHC class I tetramers. Used for some time to identify Ag-specific cells, in this study, we use that same property to delete the Ag-specific cells. We show that saporin-coupled tetramers can delete islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-reactive T cells in vitro and in vivo. Sequence analysis of TCRbeta-chains of IGRP(+) cells reveals the repertoire complexity in the islets is markedly decreased as NOD mice age and significantly altered in toxic tetramer-treated NOD mice. Further tetramer(+) T cells in the islets are almost completely deleted, and, surprisingly, loss of tetramer(+) T cells in the islets is long lasting. Finally, we show deletion at 8 wk of age of IGRP(+) CD8(+) T cells, but not dystophia myotonica kinase- or insulin B-reactive cells, significantly delays diabetes in NOD mice.

ANCA patients have T cells responsive to complementary PR-3 antigen.

Some patients with proteinase 3 specific anti-neutrophil cytoplasmic autoantibodies (PR3-ANCA) also have antibodies that react to complementary-PR3 (cPR3), a protein encoded by the antisense RNA of the PR3 gene. To study whether patients with anti-cPR3 antibodies have cPR3-responsive memory T cells we selected conditions that allowed cultivation of memory cells but not naïve cells. About half of the patients were found to have CD4+TH1 memory cells responsive to the cPR3(138-169)-peptide; while only a third of the patients had HI-PR3 protein responsive T cells. A significant number of T cells from patients responded to cPR3(138-169) peptide and to HI-PR3 protein by proliferation and/or secretion of IFN-gamma, compared to healthy controls while there was no response to scrambled peptide. Cells responsive to cPR3(138-169)-peptide were not detected in MPO-ANCA patients suggesting that this response is specific. The HLADRB1(*) 15 allele was significantly overrepresented in our patient group and is predicted to bind cPR3(138-169) peptide with high affinity. Regression analysis showed a significant likelihood that anti-cPR3 antibodies and cPR3-specific T cells coexist in individuals, consistent with an immunological history of encounter with a PR3-complementary protein. We suggest that the presence of cells reacting to potential complementary protein pairs might provide an alternative mechanism for auto-immune diseases.

B lymphocyte depletion by CD20 monoclonal antibody prevents diabetes in nonobese diabetic mice despite isotype-specific differences in Fc gamma R effector functions.

NOD mice deficient for B lymphocytes from birth fail to develop autoimmune or type 1 diabetes. To assess whether B cell depletion influences type 1 diabetes in mice with an intact immune system, NOD female mice representing early and late preclinical stages of disease were treated with mouse anti-mouse CD20 mAbs. Short-term CD20 mAb treatment in 5-wk-old NOD female mice reduced B cell numbers by approximately 95%, decreased subsequent insulitis, and prevented diabetes in >60% of littermates. In addition, CD20 mAb treatment of 15-wk-old NOD female mice significantly delayed, but did not prevent, diabetes onset. Protection from diabetes did not result from altered T cell numbers or subset distributions, or regulatory/suppressor T cell generation. Rather, impaired CD4+ and CD8+ T cell activation in the lymph nodes of B cell-depleted NOD mice may delay diabetes onset. B cell depletion was achieved despite reduced sensitivity of NOD mice to CD20 mAbs compared with C57BL/6 mice. Decreased B cell depletion resulted from deficient FcgammaRI binding of IgG2a/c CD20 mAbs and 60% reduced spleen monocyte numbers, which in combination reduced Ab-dependent cellular cytotoxicity. With high-dose CD20 mAb treatment (250 microg) in NOD mice, FcgammaRIII and FcgammaRIV compensated for inadequate FcgammaRI function and mediated B cell depletion. Thereby, NOD mice provide a model for human FcgammaR polymorphisms that reduce therapeutic mAb efficacy in vivo. Moreover, this study defines a new, clinically relevant approach whereby B cell depletion early in the course of disease development may prevent diabetes or delay progression of disease.

On the pathogenicity of autoantigen-specific T-cell receptors.

OBJECTIVE: Type 1 diabetes is mediated by T-cell entry into pancreatic islets and destruction of insulin-producing beta-cells. The relative contribution of T-cells specific for different autoantigens is largely unknown because relatively few have been assessed in vivo. RESEARCH DESIGN AND METHODS: We generated mice possessing a monoclonal population of T-cells expressing 1 of 17 T-cell receptors (TCR) specific for either known autoantigens (GAD65, insulinoma-associated protein 2 (IA2), IA2beta/phogrin, and insulin), unknown islet antigens, or control antigens on a NOD.scid background using retroviral-mediated stem cell gene transfer and 2A-linked multicistronic retroviral vectors (referred to herein as retrogenic [Rg] mice). The TCR Rg approach provides a mechanism by which T-cells with broad phenotypic differences can be directly compared. RESULTS: Neither GAD- nor IA2-specific TCRs mediated T-cell islet infiltration or diabetes even though T-cells developed in these Rg mice and responded to their cognate epitope. IA2beta/phogrin and insulin-specific Rg T-cells produced variable levels of insulitis, with one TCR producing delayed diabetes. Three TCRs specific for unknown islet antigens produced a hierarchy of insulitogenic and diabetogenic potential (BDC-2.5 > NY4.1 > BDC-6.9), while a fourth (BDC-10.1) mediated dramatically accelerated disease, with all mice diabetic by day 33, well before full T-cell reconstitution (days 42-56). Remarkably, as few as 1,000 BDC-10.1 Rg T-cells caused rapid diabetes following adoptive transfer into NOD.scid mice. CONCLUSIONS; Our data show that relatively few autoantigen-specific TCRs can mediate islet infiltration and beta-cell destruction on their own and that autoreactivity does not necessarily imply pathogenicity.

Therapeutic B cell depletion impairs adaptive and autoreactive CD4+ T cell activation in mice.

CD20 antibody depletion of B lymphocytes effectively ameliorates multiple T cell-mediated autoimmune diseases through mechanisms that remain unclear. To address this, a mouse CD20 antibody that depletes >95% of mature B cells in mice with otherwise intact immune systems was used to assess the role of B cells in CD4(+) and CD8(+) T cell activation and expansion in vivo. B cell depletion had no direct effect on T cell subsets or the activation status of CD4(+) and CD8(+) T cells in naive mice. However, B cell depletion impaired CD4(+) T cell activation and clonal expansion in response to protein antigens and pathogen challenge, whereas CD8(+) T cell activation was not affected. In vivo dendritic cell ablation, along with CD20 immunotherapy, revealed that optimal antigen-specific CD4(+) T cell priming required both B cells and dendritic cells. Most importantly, B cell depletion inhibited antigen-specific CD4(+) T cell expansion in both collagen-induced arthritis and autoimmune diabetes mouse models. These results provide direct evidence that B cells contribute to T cell activation and expansion in vivo and offer insights into the mechanism of action for B cell depletion therapy in the treatment of autoimmunity.

Alphaviral vector-transduced dendritic cells are successful therapeutic vaccines against neu-overexpressing tumors in wild-type mice.

While dendritic cell (DC) vaccines can protect hosts from tumor challenge, their ability to effectively inhibit the growth of established tumors remains indeterminate. Previously, we have shown that human DCs transduced with Venezuelan equine encephalitis virus replicon particles (VRPs) were potent stimulators of antigen-specific T cells in vitro. Therefore, we investigated the ability of VRP-transduced DCs (VRP-DCs) to induce therapeutic immunity in vivo against tumors overexpressing the neu oncoprotein. Transduction of murine DCs with VRPs resulted in high-level transgene expression, DC maturation and secretion of proinflammatory cytokines. Vaccination with VRP-DCs expressing a truncated neu oncoprotein induced robust neu-specific CD8(+) T cell and anti-neu IgG responses. Furthermore, a single vaccination with VRP-DCs induced the regression of large established tumors in wild-type mice. Interestingly, depletion of CD4(+), but not CD8(+), T cells completely abrogated inhibition of tumor growth following vaccination. Taken together, our results demonstrate that VRP-DC vaccines induce potent immunity against established tumors, and emphasize the importance of the generation of both CD4(+) T cell and B cell responses for efficient tumor inhibition. These findings provide the rationale for future evaluation of VRP-DC vaccines in the clinical setting.

Apoptotic cells induce Mer tyrosine kinase-dependent blockade of NF-kappaB activation in dendritic cells.

Dendritic cells (DCs) play a key role in immune homeostasis and maintenance of self-tolerance. Tolerogenic DCs can be established by an encounter with apoptotic cells (ACs) and subsequent inhibition of maturation and effector functions. The receptor(s) and signaling pathway(s) involved in AC-induced inhibition of DCs have yet to be defined. We demonstrate that pretreatment with apoptotic but not necrotic cells inhibits activation of IkappaB kinase (IKK) and downstream NF-kappaB. Notably, receptor tyrosine kinase Mer (MerTK) binding of ACs is required for mediating this effect. Monocyte-derived DCs lacking MerTK expression (MerTKKD) or treated with blocking MerTK-specific antibodies (Abs) are resistant to AC-induced inhibition and continue to activate NF-kappaB and secrete proinflammatory cytokines. Blocking MerTK activation of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway prevents AC-induced inhibition. These results demonstrate an essential role for MerTK-mediated regulation of the PI3K/AKT and NF-kappaB pathways in AC-induced inhibition of monocyte-derived DCs.

EBV latent membrane protein 2A induces autoreactive B cell activation and TLR hypersensitivity.

EBV is associated with systemic lupus erythematosus (SLE), but how it might contribute to the etiology is not clear. Since EBV-encoded latent membrane protein 2A (LMP2A) interferes with normal B cell differentiation and function, we sought to determine its effect on B cell tolerance. Mice transgenic for both LMP2A and the Ig transgene 2-12H specific for the ribonucleoprotein Smith (Sm), a target of the immune system in SLE, develop a spontaneous anti-Sm response. LMP2A allows anti-Sm B cells to overcome the regulatory checkpoint at the early preplasma cell stage by a self-Ag-dependent mechanism. LMP2A induces a heightened sensitivity to TLR ligand stimulation, resulting in increased proliferation or Ab-secreting cell differentiation or both. Thus, we propose a model whereby LMP2A induces hypersensitivity to TLR stimulation, leading to activation of anti-Sm B cells through the BCR/TLR pathway. These data further implicate TLRs in the etiology of SLE and suggest a mechanistic link between EBV infection and SLE.

Critical roles of tumor necrosis factor-related apoptosis-inducing ligand in type 1 diabetes.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis of tumor cells but not most normal cells. Its roles in normal nontransformed tissues are not clear. To explore the potential roles of TRAIL in type 1 diabetes, we examined the consequences of TRAIL blockade or TRAIL deficiency in two animal models of autoimmune diabetes. In the first model, NOD mice received an injection of a soluble TRAIL receptor to block TRAIL function. This significantly accelerated the diabetes and increased the degree of autoimmune inflammation in both pancreatic islets and salivary glands. The GAD65-specific immune responses were also significantly enhanced in animals that received the soluble TRAIL receptor. In the second model, we treated normal and TRAIL-deficient C57BL/6 mice with multiple low-dose streptozotocin to induce diabetes. We found that both the incidence and the degree of islet inflammation were significantly enhanced in TRAIL-deficient animals. On the basis of these observations, we conclude that TRAIL deficiency accelerates autoimmune diabetes and enhances autoimmune responses.

The preferential ability of B lymphocytes to act as diabetogenic APC in NOD mice depends on expression of self-antigen-specific immunoglobulin receptors.

B lymphocytes partially contribute to autoimmune type 1 diabetes (T1D) as a subset of APC with a preferential ability to trigger pathogenic CD4 T cells. We hypothesized that this resulted from the unique ability of B lymphocytes to take up pancreatic beta cell proteins through Ig mediated capture. T1D was significantly delayed, but not prevented, in a NOD stock in which the B lymphocyte Ig repertoire was strongly restricted because of the allelic exclusion induced by transgenic Ig molecules specific for the disease irrelevant hen egg lysozyme (HEL) protein (NOD.IgHEL mice). However, introducing the Ig(mu)null mutation to eliminate the small residual numbers of non-transgenic B lymphocytes in the NOD.IgHEL stock strongly suppressed T1D to the same low levels that characterize B lymphocyte deficient NOD.Ig(mu)null mice. In contrast to standard NOD mice, both the NOD.IgHEL.Ig(mu)null and NOD.Ig(mu)null stocks were unable to generate T cell responses against the candidate diabetes autoantigen, glutamic acid decarboxylase. These results indicate that Ig-mediated capture of beta cell autoantigens accounts for why B lymphocytes have a greater capacity than other APC subtypes to trigger diabetogenic T cells. Hence, defects in B lymphocyte, as well as T lymphocyte, tolerance induction mechanisms may contribute to T1D in NOD mice.