Blockade of costimulation through B7/CD28 inhibits experimental autoimmune uveoretinitis, but does not induce long-term tolerance

The current status of biological treatment for uveitis

INTRODUCTION

Noninfectious uveitis represents one of the leading causes of blindness in developed Countries, compromising patients' quality of life and social functioning. The main treatment goals are the control of ocular inflammation, to avert and treat sight-threatening complications, thus preserving and/or restoring visual function.

AREAS COVERED

This manuscript deals with systemic therapy with biologic drugs for noninfectious uveitis. An extensive literature search in the MEDLINE database (via PubMed) has been performed up to June 2020. The major classes of biologic molecules employed in ocular inflammatory diseases have been reviewed, focusing on TNF inhibitors, IL-1, IL-6, IL-17, IL-23 inhibitors, interferons, rituximab, and abatacept efficacy and safety. An overview of most recent developments in the field has been provided as well, with reference to the experience with JAK inhibitors and with biosimilar drugs.

EXPERT OPINION

The development of the concept of targeted therapy and the subsequent introduction of biologic molecules in clinical practice have revolutionized the prognosis of uveitis. The target of a rapid and sustained steroid-free remission of ocular inflammation should be pursued for all patients early in the disease course, in order to have a better chance to improve the final visual outcome.

Treating juvenile idiopathic arthritis (JIA)-related uveitis beyond TNF-α inhibition: a narrative review

Chronic anterior uveitis is the most frequent among extra-articular manifestations of juvenile idiopathic arthritis (JIA) and a relevant cause of ocular morbidity in children. Asymmetric arthritis, early onset disease, female sex, and anti-nuclear antibody (ANA) positivity are counted among risk factors for developing this complication. It usually has insidious onset and asymptomatic chronic-relapsing course, but the persistence of low-grade chronic inflammation can lead to irreversible structural ocular damage and to vision-threatening complications. For such reasons, achieving a complete absence of inflammation through early targeted and aggressive treatments is a primary therapeutic goal in these patients. This review is aimed at summarizing scientific evidence about biologic rescue therapy of JIA-related uveitis in patients who fail to achieve clinical remission, in spite of being treated with conventional disease-modifying anti-rheumatic drugs (cDMARDs) and at least one biologic tumor necrosis factor (TNF)-α inhibitor. Interleukin (IL)-6 inhibition appears a promising and safe option for refractory JIA-related uveitis. Abatacept and rituximab proved to be beneficial as well, but their efficacy together with some safety concerns needs to be more extensively evaluated.

Antagonist Anti-CD28 Therapeutics for the Treatment of Autoimmune Disorders

The effector functions of T lymphocytes are responsible for most autoimmune disorders and act by directly damaging tissues or by indirectly promoting inflammation and antibody responses. Co-stimulatory and co-inhibitory T cell receptor molecules are the primary pharmacological targets that enable interference with immune-mediated diseases. Among these, selective CD28 antagonists have drawn special interest, since they tip the co-stimulation/co-inhibition balance towards efficiently inhibiting effector T cells while promoting suppression by pre-existing regulatory T-cells. After having demonstrated outstanding therapeutic efficacy in multiple models of autoimmunity, inflammation and transplantation, and safety in phase-I studies in humans, selective CD28 antagonists are currently in early clinical development for the treatment of systemic lupus erythematous and rheumatoid arthritis. Here, we review the available proof of concept studies for CD28 antagonists in autoimmunity, with a special focus on the mechanisms of action.

Novel CD28 antagonist mPEG PV1-Fab' mitigates experimental autoimmune uveitis by suppressing CD4+ T lymphocyte activation and IFN-γ production

Autoimmune Uveitis is an important chronic inflammatory disease and a leading cause of impaired vision and blindness. This ocular autoimmune disorder is mainly mediated by T CD4⁺ lymphocytes poising a T_H1 phenotype. Costimulatory molecules are known to play an important role on T cell activation and therefore represent interesting therapeutical targets for autoimmune disorders. CD28 is the prototypical costimulatory molecule for T lymphocytes, and plays a crucial role in the initiation, and maintenance of immune responses. However, previous attempts to use this molecule in clinical practice achieved no success. Thus, we evaluated the efficacy of mPEG PV1-Fab’ (PV1), a novel selective CD28 antagonist monovalent Fab fragment in the treatment of Experimental Autoimmune Uveitis (EAU). Here, we showed that PV1 treatment decreases both average disease score and incidence of EAU. A decrease in the activation profile of both T CD4⁺ and T CD8⁺ eye-infiltrating lymphocytes was evidenced. In the periphery, T CD4⁺ cells from PV1-treated mice also showed a decrease in their activation status, with reduced expression of CD69, CD25, and PD-1 molecules. This suppression was not dependent on Treg cells, as both their frequency and absolute number were lower in PV1-treated mice. In addition, frequency of CD4⁺IFN-γ⁺ T cells was significantly lower in PV1-treated group, but not of IL-17-producing T cells. Moreover, after specific restimulation, PV1 blockade selectively blocked IFN-γ production by CD4⁺ lymphocytes Taken together, our data suggest that mPEG PV1-Fab’ acts mainly on IFN-γ-producing CD4⁺ T cells and emphasize that this specific CD28 blockade strategy is a potential specific and alternative tool for the treatment of autoimmune disorders in the eye.

Clinical efficacy of a new CD28-targeting antagonist of T cell co-stimulation in a non-human primate model of collagen-induced arthritis

T cells have a central pathogenic role in the aetiopathogenesis of rheumatoid arthritis (RA), and are therefore a favoured target of immunotherapy aiming at physical or functional elimination. Here we report an efficacy test of FR104, a new co-stimulation inhibitor directly targeting CD28 on T cells, in a translationally relevant model, the rhesus monkey model of collagen-induced arthritis (CIA). As a relevant comparator we used abatacept [cytotoxic T lymphocyte antigen immunoglobulin (CTLA Ig)], an antagonist of CTLA-4 binding to CD80/86 clinically approved for treatment of RA. Treatment with either compound was started at the day of CIA induction. Although FR104 previously demonstrated a higher control of T cell responses in vitro than abatacept, both compounds were equally potent in the suppression of CIA symptoms and biomarkers, such as the production of C-reactive protein (CRP) and interleukin (IL)-6 and anti-collagen type II (CII) serum antibody (IgM/IgG). However, in contrast to abatacept, FR104 showed effective suppression of CII-induced peripheral blood mononuclear cell (PBMC) proliferation. The current study demonstrates a strong potential of the new selective CD28 antagonist FR104 for treatment of RA.

The Future Is Now: Biologics for Non-Infectious Pediatric Anterior Uveitis

Anterior uveitis (AU), inflammation of the iris, choroid or ciliary body, can cause significant eye morbidity, including visual loss. In the pediatric age group, the most common underlying diagnosis for AU is juvenile idiopathic associated uveitis and idiopathic AU, which are the focus of this paper. AU is often resistant to medications such as topical corticosteroids and methotrexate. In the past 15 years, biologic agents (biologics) have transformed treatment. In this review, we discuss those in widespread use and those with more theoretical applications for anterior uveitis. Tumor necrosis factor alpha inhibitors (anti-TNFα) have been available the longest and are used widely to treat pediatric uveitis. The effects of anti-TNFα in children are described mostly in small retrospective case series. Together, the literature suggests that the majority of children treated with anti-TNFα achieve decreased uveitis activity and reduced corticosteroid burden. However, many will have disease flares even on treatment. Only a few small studies directly compare outcomes between alternate anti-TNFα (infliximab and adalimumab). The use of different uveitis grading systems, inclusion criteria, and outcome measures makes cross-study comparisons difficult. Whether the achievement and maintenance of inactive disease occurs more frequently with certain anti-TNFα remains controversial. Newer biologics that modulate the immune system differently (e.g., interfere with Th17 activation through IL-17a and IL-6 blockade, limit T lymphocyte costimulation, and deplete B lymphocytes), have shown promise for uveitis. Studies of these agents are small and include mostly adults. Additional biologics are also being explored to treat uveitis. With their advent, we are hopeful that outcomes will ultimately be improved for children with AU. With many biologics available, much work remains to identify the optimal inflammatory pathway to target in AU.

Abatacept in the Treatment of Severe, Longstanding, and Refractory Uveitis Associated with Juvenile Idiopathic Arthritis

Objective.

Abatacept (ABA), a selective T cell costimulation modulator that binds to CD80 and CD86 on antigen-presenting cells, was investigated for its antiinflammatory effect in treating severe chronic uveitis associated with juvenile idiopathic arthritis (JIA).

Methods.

Our retrospective study was conducted by members of the Multinational Interdisciplinary Working Group for Uveitis in Childhood (MIWGUC). Patients with JIA who are receiving ABA treatment for active uveitis were included. In all patients, uveitis had been refractory to previous topical and systemic corticosteroids, immunosuppressives, and at least 1 tumor necrosis factor–α inhibitor. A standardized protocol was used to document uveitis (MIWGUC) and arthritis. Baseline visit and visits at 3, 6, 9, and 12 months before and after ABA start were evaluated. Primary outcome measure was defined as achievement of uveitis inactivity; secondary outcome measures were tapering of corticosteroid and/or immunosuppressive treatment, and occurrence of complications.

Results.

In all, 21 patients (16 female) with active uveitis (n = 21) and arthritis (n = 18) were included (mean age 11.8 ± 3.6 yrs). In 7 of 18 patients with active arthritis at baseline, inactivity was achieved following ABA treatment. Uveitis inactivity was achieved in 11 patients, but recurred later in 8 of them, and remained active in another 10 cases. Systemic corticosteroids or immunosuppression were tapered in 3 patients, but uveitis recurred in all of them during further followup. Ocular complications secondary to uveitis were present in 17 patients at baseline, while 3 patients developed new ocular complications during followup.

Conclusion.

A sustained response to ABA was uncommon in patients with severe and refractory uveitis.

A comprehensive review and update on the biologic treatment of adult noninfectious uveitis: part II

INTRODUCTION

Treatment of adult, noninfectious uveitis remains a major challenge for ophthalmologists around the world, especially in regard to recalcitrant cases. It is reported to comprise approximately 10% of preventable blindness in the USA. The cause of uveitis can be idiopathic or associated with infectious and systemic disorders. The era of biologic medical therapies provides new options for patients with otherwise treatment-resistant inflammatory eye disease.

AREAS COVERED

This two-part review gives a comprehensive overview of the existing medical treatment options for patients with adult, noninfectious uveitis, as well as important advances for the treatment ocular inflammation. Part I covers classic immunomodulation and latest information on corticosteroid therapy. In part II, emerging therapies are discussed, including biologic response modifiers, experimental treatments and ongoing clinical studies for uveitis.

EXPERT OPINION

The hazard of chronic corticosteroid use in the treatment of adult, noninfectious uveitis is well documented. Corticosteroid-sparing therapies, which offer a very favorable risk-benefit profile when administered properly, should be substituted. Although nothing is currently approved for on-label use in this indication, many therapies, through either translation or novel basic science research, have the potential to fill the currently exposed gaps.

Immunotherapeutic strategies in autoimmune uveitis

Autoimmune uveitis is an organ-specific disorder characterized by irreversible lesions to the eye that predominantly affect people in their most productive years and is among the leading causes of visual deficit and blindness. Currently available therapies are effective in the treatment of a wide spectrum of uveitis, but are often associated with severe side effects. Here, we review ongoing research with promising immunomodulatory therapeutic strategies, describing their specific features, interactions and the responses triggered by the targeted immune molecules that aim to minimize clinical complications and the likelihood of disease relapse. We first review the main features of the disease, diagnostic tools, and traditional forms of therapy, as well as the animal models predominantly used to understand the pathogenesis and test the novel intervention approaches aiming to control the acute immune and inflammatory responses and to dampen chronic responses. Both exploratory research and clinical trials have targeted either the blockade of effector pathways or of their companion co-stimulatory molecules. Examples of targets are T cell receptors (CD3), their co-stimulatory receptors (CD28, CTLA-4) and corresponding ligands (B7-1 and B7-2, also known as CD80 and CD86), and cytokines like IL-2 and their receptors. Here, we summarize the available evidence on effectiveness of these treatments in human and experimental uveitis and highlight a novel CD28 antagonist monovalent Fab′ antibody, FR104, which has shown preclinical efficacy suppressing effector T cells while enhancing regulatory T cell function and immune tolerance in a humanized graft-versus-host disease (GVHD) mice model and is currently being tested in a mouse autoimmune uveitis model with encouraging results.

Targeting CD28, CTLA-4 and PD-L1 costimulation differentially controls immune synapses and function of human regulatory and conventional T-cells

CD28, CTLA-4 and PD-L1, the three identified ligands for CD80/86, are pivotal positive and negative costimulatory molecules that, among other functions, control T cell motility and formation of immune synapse between T cells and antigen-presenting cells (APCs). What remains incompletely understood is how CD28 leads to the activation of effector T cells (Teff) but inhibition of suppression by regulatory T cells (Tregs), while CTLA-4 and PD-L1 inhibit Teff function but are crucial for the suppressive function of Tregs. Using alloreactive human T cells and blocking antibodies, we show here by live cell dynamic microscopy that CD28, CTLA-4, and PD-L1 differentially control velocity, motility and immune synapse formation in activated Teff versus Tregs. Selectively antagonizing CD28 costimulation increased Treg dwell time with APCs and induced calcium mobilization which translated in increased Treg suppressive activity, in contrast with the dampening effect on Teff responses. The increase in Treg suppressive activity after CD28 blockade was also confirmed with polyclonal Tregs. Whereas CTLA-4 played a critical role in Teff by reversing TCR-induced STOP signals, it failed to affect motility in Tregs but was essential for formation of the Treg immune synapse. Furthermore, we identified a novel role for PD-L1-CD80 interactions in suppressing motility specifically in Tregs. Thus, our findings reveal that the three identified ligands of CD80/86, CD28, CTLA-4 and PD-L1, differentially control immune synapse formation and function of the human Teff and Treg cells analyzed here. Individually targeting CD28, CTLA-4 and PD-L1 might therefore represent a valuable therapeutic strategy to treat immune disorders where effector and regulatory T cell functions need to be differentially targeted.

Equivalent functions for B7.1 and B7.2 costimulation in mediating host resistance to Mycobacterium tuberculosis

B7.1 and B7.2 are homologous costimulatory molecules expressed predominantly on antigen-presenting cells (APC). Interaction of these B7 molecules with CD28 and CTLA-4 expressed on T cells is a critical step in T cell activation. Previously, we reported that Mycobacterium tuberculosis infection in the combined absence of B7.1 and B7.2 resulted in impaired host resistance to the pathogen. Despite their structural similarities, the individual contribution of B7.1 and B7.2 to the development of pathogenic T cells in autoimmune diseases and protective T cells in infectious diseases is markedly distinct. In the current study, we therefore examined whether B7.1 and B7.2 have discrete, equivalent, or overlapping functions in mediating host resistance to M. tuberculosis. We found that the individual absence of either B7.1 or B7.2 had no effect on the ability of the host to contain bacterial load in the lungs, recruit immune cells to the lung, generate a Th1 response, or induce a pulmonary granulomatous response. These results indicate that B7.1 and B7.2 molecules have equal ability to mediate host resistance to M. tuberculosis, underscoring the therapeutic utility of individual B7.1 and B7.2 antagonists in treating inflammatory disorders.

Antagonist properties of monoclonal antibodies targeting human CD28: role of valency and the heavy-chain constant domain

Antagonist antibodies targeting CD28 have been proposed as an alternative to the use of CD80/86 antagonists to modulate T cell responses in autoimmunity and transplantation. Advantages would be the blockade of CD28-mediated co-stimulatory signals without impeding the co-inhibitory signals dependent on CD80 interactions with CTLA-4 and PD-L1 that are important for the control of immune responses and for the function of regulatory T cells. Anti-CD28 antibodies are candidate antagonists only if they prevent access to the CD80/86 ligands without simultaneously stimulating CD28 itself, a process that is believed to depend on receptor multimerization. In this study, we evaluated the impact of different formats of a potentially antagonist anti-human CD28 antibody on T cell activation. In particular, we examined the role of valency and of the presence of an Fc domain, two components that might affect receptor multimerization either directly or in the presence of accessory cells expressing Fc receptors. Among monovalent (Fab', scFv), divalent (Fab'2), monovalent-Fc (Fv-Fc) and divalent-Fc (IgG) formats, only the monovalent formats showed consistent absence of induced CD28 multimerization and absence of associated activation of phosphoinositol-3-kinase, and clear antagonist properties in T cell stimulation assays. In contrast, divalent antibodies showed agonist properties that resulted in cell proliferation and cytokine release in an Fc-independent manner. Conjugation of monovalent antibodies with polyethylene glycol, α-1-antitrypsin or an Fc domain significantly extended their in vivo half-life without modifying their antagonist properties. In conclusion, these data indicate that monovalency is mandatory for maintaining the antagonistic activity of anti-CD28 monoclonal antibodies.

Clinical efficacy of abatacept in Japanese rheumatoid arthritis patients

OBJECTIVES

The purpose of this study was to examine the treatment retention and efficacy of abatacept, the first member of a new class of biologic agents, in Japanese rheumatoid arthritis (RA) patients during clinical practice.

METHODS

A retrospective multicenter study was conducted with patients who underwent abatacept therapy for 24 weeks (n = 143).

RESULTS

Patients at baseline had a mean age of 63.5 years, a mean disease duration of 11.3 years, and a mean disease activity score in 28 joints (DAS28) of 4.5. Overall retention of abatacept treatment was 83.2 % at 24 weeks, when 46.2 % of patients achieved DAS28-defined low disease activity (LDA; DAS28 <3.2) and 26.6 % achieved DAS28-defined remission (DAS28 <2.6). LDA was achieved in a significantly higher proportion of patients without prior biologics therapy compared to those with prior biologics (60.9 vs. 34.2 %, p = 0.001). There was no significant difference between patients with or without concomitant methotrexate (MTX) therapy (45.2 vs. 47.5 %).

CONCLUSIONS

Abatacept therapy appears to be highly effective and well tolerated during clinical treatment of RA. Abatacept was particularly effective in patients with no history of biologics use, and did not appear to be dependent on concomitant MTX therapy.

CD28-specific immunomodulating antibodies: what can be learned from experimental models?

Tolerance induction to alloantigens remains a major challenge in transplant immunology. Progress in the last decade of our understanding of T-cell activation has led to the development of new immunotherapeutic strategies to replace conventional immunosuppression which inhibits the immune system in a nonspecific way. In particular, positive and negative costimulatory molecules of the CD28 family have been consistently demonstrated to be critical for the development of productive immune responses as well as the establishment and maintenance of peripheral tolerance. However, recent discoveries of novel costimulatory interactions confer a novel dimension to the immunoregulatory interactions within the B7:CD28 family and compels a revised view within a "quintet" of costimulatory molecules: CD28/B7/CTLA-4/PD-L1/ICOSL. Complexity introduced in this more detailed costimulatory pathway has important implications in therapeutic interventions against human immunological diseases and, especially, highlight the fundamental differences in selectively targeting CD28 molecules instead of B7 counterparts. In this review, we discuss these differences and emphasize different CD28-specific immunomodulating strategies evaluated in experimental models of transplantation and autoimmune diseases.

Antigen-specific blocking of CD4-specific immunological synapse formation using BPI and current therapies for autoimmune diseases

In this review, we discuss T-cell activation, etiology, and the current therapies of autoimmune diseases (i.e., MS, T1D, and RA). T-cells are activated upon interaction with antigen-presenting cells (APC) followed by a "bull's eye"-like formation of the immunological synapse (IS) at the T-cell-APC interface. Although the various disease-modifying therapies developed so far have been shown to modulate the IS and thus help in the management of these diseases, they are also known to present some undesirable side effects. In this study, we describe a novel and selective way to suppress autoimmunity by using a bifunctional peptide inhibitor (BPI). BPI uses an intercellular adhesion molecule-1 (ICAM-1)-binding peptide to target antigenic peptides (e.g., proteolipid peptide, glutamic acid decarboxylase, and type II collagen) to the APC and therefore modulate the immune response. The central hypothesis is that BPI blocks the IS formation by simultaneously binding to major histocompatibility complex-II and ICAM-1 on the APC and selectively alters the activation of T cells from T(H)1 to T(reg) and/or T(H)2 phenotypes, leading to tolerance.

Model-based determination of abatacept exposure in support of the recommended dose for Japanese rheumatoid arthritis patients

The objective of this study was to provide support for a body weight-tiered dosing regimen by characterizing abatacept pharmacokinetics (PK) and the relationship between exposure and the ACR20 (American College of Rheumatology criteria for 20% improvement) response in Japanese patients with rheumatoid arthritis (RA). A population PK model was developed using NONMEM with 2,535 samples from 344 Japanese RA patients in two clinical trials. The exposure-response relationship was characterized using a Generalized Estimating Equation (GEE) logistic regression model, with time-varying actual trough concentrations and ACR20 responder rates over 6 months in a randomized, placebo-controlled phase 2 trial for stable methotrexate. Abatacept exposure was well characterized using a linear, two-compartment model, in which body weight and the empirically calculated glomerular filtration rate were significant covariates for clearance. The ACR20 response model was developed by examining the quasi-likelihood information criterion, and the cumulative logit in the final model was specified by the log-transformed trough concentration. The predicted ACR20 responder rate was consistent with the actual values in the clinical trial and this model revealed trough concentrations higher than the recommended body weight-tiered dose are unlikely to result in substantial increases in clinical efficacy. Considering that ACR20 is a longitudinal binary variable and the response to RA treatment is delayed, the GEE model was useful for predicting the probability of an ACR20 response. In conclusion, the same dosing regimen as non-Japanese patients is recommended because a body weight-tiered dosing regimen achieves similar exposures across the wide range of body weight.

Anti-CD3 antibody ameliorates experimental autoimmune uveitis by inducing both IL-10 and TGF-β dependent regulatory T cells

Chronic/recurrent autoimmune (idiopathic) uveitis is difficult to treat and they account for approximately 10% of legal blindness in the Western world. As it has been reported that anti-CD3 antibody can enhance T cell regulatory function, we investigated its effects in vivo on experimental autoimmune uveitis (EAU), a model for autoimmune uveitis in humans. B10RIII mice immunized with an uveitogenic peptide were treated with the F(ab')(2) fragment of anti-CD3 mAb either before or at clinical disease onset. Evaluation of EAU and cellular responses showed that disease was inhibited and the activation and expansion of pathogenic T cells selectively reduced, whereas functions of Treg in vivo were enhanced. Moreover, mice treated with anti-CD3 mAb were resistant to a second challenge with antigen and thus protected from recurrence of disease. Our results demonstrate that anti-CD3 mAb is a potent inhibitor of autoimmune uveitis.

Biological therapies of inflammatory bowel disease

Inflammatory bowel disease (IBD) is characterized by increasing morbidity and, if suboptimally treated, poor prognosis. Recent evidence strongly suggests that dysfunctional immune responses play an important role in the pathogenesis of IBD. Therefore, immunologically downregulating the overactivated innate and adaptive immune responses may be a better approach to treat IBD than currently used pharmaceutical therapies. In recent years, many new biological therapies have been developed. These therapies are shown to be effective for inducing remission, preventing complications, improving life quality of the patients, and reducing hospitalization and surgical rates. This article introduces and discusses these new biological agents that have been used effectively in clinic for IBD patients.

Protection from graft-versus-host disease with a novel B7 binding site–specific mouse anti–mouse CD28 monoclonal antibody

We studied the role of CD28 in T-cell biology and T cell–mediated pathology using a novel mouse anti–mouse CD28 antibody, E18, which recognizes an epitope close to the B7 binding site. In vitro, this antibody completely blocked binding of B7 molecules to CD28 expressed on mouse thymocytes but enhanced anti-CD3–induced proliferation of peripheral T cells. Injections of E18 monoclonal antibody into normal BALB/c mice in vivo, however, led to a reversible reduction in Treg cell frequencies among CD4+ cells, both in the thymus and in secondary lymphoid organs, suggesting that E18 acted as an inhibitor of CD28 signaling under these conditions. Antagonistic activity of E18 in vivo was further implied by suppressed responses of conventional CD4+ T cells to stimulation with the superantigen staphylococcal enterotoxin B and in a model of acute graft-versus-host disease. In contrast to healthy mice, intact monoclonal antibody E18, but not its nonstimulatory Fab fragment, increased the frequencies of Treg cells among CD4+ T cells in these pro-inflammatory settings allowing for efficacious protection from acute graft-versus-host disease. Thus, the agonistic signal generated by conventional, ie, nonsuperagonistic, anti-CD28 antibodies is important for their immunotherapeutic potential in vivo.

Anti-CD28 antibodies modify regulatory mechanisms and reinforce tolerance in CD40Ig-treated heart allograft recipients

Blockade of CD40-CD40 ligand (CD40L) costimulation has been shown to synergize with that of CTLA4/CD28-B7 to promote transplant tolerance. To date, however, CD28-B7 interactions have been prevented using B7-blocking reagents like CTLA4-Ig that inhibit CD28-B7 together with CTLA4-B7 interactions. In this study, we have tested anti-CD28 Abs to prevent selectively CD28-B7 interactions while preserving CTLA4-B7 in addition to CD40-CD40L blockade. In the LEW.1W to LEW.1A rat combination, interfering with CD40-CD40L interactions by CD40Ig administration through gene transfer resulted in indefinite heart allograft survival due to the appearance of clonotypic CD8+CD45RClow regulatory T cells that were capable of transferring the tolerant state to naive animals. However, cardiac transplants in these recipients systematically developed chronic rejection lesions. Whereas anti-CD28 Ab monotherapy only delayed acute rejection and failed to induce tolerance, coadministration of anti-CD28 Abs and CD40Ig resulted in the long-term acceptation of allografts without chronic rejection lesions in 60% of the recipients, reduced the level of intragraft mRNA transcripts for cytokines and immune factors, and fully abrogated alloantibody production. In addition, the nature of regulatory cells was modified: the CD8+CD45RClow clonotypic T cells described in the CD40Ig-treated animals could not be found in cotreated animals, and the other CD8+CD45RClow cells had no regulatory activity and a different cytokine expression profile. Instead, in cotreated recipients we found IDO-dependent non-T cells with regulatory activity in vitro. Thus, the addition of a short-term anti-CD28 treatment with CD40Ig resulted in decreased heart allograft chronic rejection lesions, complete inhibition of Ab production, and modified regulatory mechanisms.

Immunomodulatory properties of FK734, a humanized anti-CD28 monoclonal antibody with agonistic and antagonistic activities

BACKGROUND

We describe immunomodulatory effects of FK734, a humanized version of a mouse anti-human CD28 mAb (clone TN228), in vitro and in a chimeric human-mouse model of allograft rejection.

METHODS

Cytokine production and proliferation were assessed in a mixed lymphocyte reaction containing FK734, human T cells, and endothelial cells or monocytes. FK734 was also administered to SCID mice engrafted with human skin and adoptively transferred with human peripheral blood mononuclear cells allogeneic to the skin graft.

RESULTS

In vitro, FK734 enhanced secretion of interleukin-2 and interferon-gamma as well as proliferation of CD4+ and CD8+ T cells stimulated by allogeneic human leukocyte antigen (HLA)-DR+ human umbilical vein endothelial cells (which lack B7 molecules and FcgammaRs) or by blood monocytes (which express low levels of B7 molecules and FcgammaRs) compared with control mAb, but these effects were significantly smaller than those provided by mAb 28.2, a stimulatory mouse anti-human CD28 mAb, at comparable concentrations. However, FK734 generally inhibited cytokine secretion and T cell proliferation in cocultures with human umbilical vein endothelial cells transduced to express CD86. In vivo using SCID/beige mice bearing human skin with adoptively transferred peripheral blood mononuclear cells, administration of FK734 protected human endothelial cell-lined microvessels, significantly but incompletely reducing endothelial cell injury and T cell infiltration into the graft one or two weeks later.

CONCLUSIONS

FK734 is a partial agonist of CD28 signaling that can reduce human T cell alloresponses in the presence of strong costimulation by B7 molecules in vitro and can reduce T cell-mediated skin allograft rejection in vivo.

The role of the ICOS/B7RP-1 T cell costimulatory pathway in murine experimental autoimmune uveoretinitis

ICOS/B7RP-1 is a new member of the CD28/B7 family of costimulatory molecules and plays differential roles in autoimmune diseases. In this study, we examined the role of ICOS/B7RP-1 pathway in the pathogenesis of mouse experimental autoimmune uveoretinitis (EAU), an animal model of human autoimmune uveitis. ICOS expression was found on infiltrating CD4+ T cells in the region of the retina in EAU-induced mice. The anti-B7RP-1 monoclonal antibody (mAb)-treated or ICOS-deficient mice showed a substantial reduction of disease scores. Blockade of ICOS/B7RP-1 interaction during the effector phase ameliorated the disease, whereas its blockade during the induction phase exhibited no significant effect. Moreover, administration of anti-B7RP-1 mAb effectively ameliorated the disease induced by adoptive transfer of pathogenic T cells. The anti-B7RP-1 mAb treatment inhibited the expansion and/or effector function of pathogenic T cells, given that proliferative response and IFN-gamma production by lymph node cells were reduced upon restimulation with the antigen peptide in vitro. These results suggest that the ICOS/B7RP-1 interaction plays a critical role in the pathogenesis of uveitis. We also indicated that ICOS-mediated costimulation plays differential roles in EAU and experimental autoimmune encephalomyelitis, which is also a Th1 disease induced in the same manner as EAU.

Manipulation of Regulatory T‐Cell Number and Function with CD28‐Specific Monoclonal Antibodies

Suppressor or "regulatory" CD4 T cells play a key role in the control of autoimmunity and overshooting immune responses to foreign antigens, but can also obstruct effective anticancer therapies. The homeostasis and activation of these regulatory T cells (Treg cells) is tightly connected to that of effector CD4 T cells via the costimulatory receptor CD28 and the cytokine IL-2: Both subsets require costimulation to be activated by antigen, and Treg cells additionally depend on IL-2 produced by effector CD4 T cells in a costimulation-dependent fashion. Depending on the therapeutic aim, blockade, or stimulation of CD28 with monoclonal antibodies (mAb) can therefore profoundly affect the size and activity of the Treg compartment. In this chapter, experiments performed in rodents with distinct types of CD28-specific mAb, and the recent failure to translate CD28-driven Treg activation into humans, are discussed.

Prophylactic administration of abatacept prevents disease and bone destruction in a rat model of collagen-induced arthritis

Abatacept is the first in a new class of agents that selectively modulates T-cell activation by attenuating CD28-mediated co-stimulation. This study examined the effects of abatacept on disease development in a rat model of collagen-induced arthritis (CIA). The rats were treated with either abatacept (1mg/kg) or control IgG beginning at the time of induction of CIA. By day 16, significant paw swelling was observed in IgG-treated control animals that continued to increase, reaching a plateau on day 21. Prophylactic treatment with abatacept completely abrogated paw swelling throughout the study. Histopathology demonstrated a significant reduction in inflammation, cartilage destruction, bone resorption and pannus formation. Abatacept treatment resulted in 90% inhibition of circulating collagen-specific antibodies and decreased the serum expression of many cytokines and chemokines that were upregulated in diseased animals. Immunohistochemical analysis of the ankle joints demonstrated that interleukin-6 production was reduced in the tissues and the numbers of osteoclasts present in the joints were also decreased. Ankle microcomputer tomography (micro-CT) analyses dramatically demonstrated the protective effects of abatacept on bone destruction in these animals. Data presented here demonstrate that prophylactic administration of abatacept significantly inhibits the onset and progression of disease in a rat CIA model, with reductions in inflammation, inflammatory mediators, and bone and joint destruction.

Anti-CD28 antibody-induced kidney allograft tolerance related to tryptophan degradation and TCR class II B7 regulatory cells

B7/CTLA-4 interactions negatively regulate T-cell responses and are necessary for transplant tolerance induction. Tolerance induction may therefore be facilitated by selectively inhibiting the B7/CD28 pathway without blocking that of B7/CTLA-4. In this study, we selectively inhibited CD28/B7 interactions using a monoclonal antibody modulating CD28 in a rat model of acute kidney graft rejection. A short-term treatment abrogated both acute and chronic rejection. Tolerant recipients presented few alloantibodies against donor MHC class II molecules, whereas untreated rejecting controls developed anti-MHC class I and II alloantibodies. PBMC from tolerant animals were unable to proliferate against donor cells but could proliferate against third-party cells. The depletion of B7+, non-T cells fully restored this reactivity whereas purified T cells were fully reactive. Also, NK cells depletion restored PBMC reactivity in 60% of tolerant recipients. Conversely, NK cells from tolerant recipients dose-dependently inhibited alloreactivity. PBMC anti-donor reactivity could be partially restored in vitro by blocking indoleamine-2,3-dioxygenase (IDO) and iNOS. In vivo, pharmacologic inhibition of these enzymes led to the rejection of the otherwise tolerated transplants. This study demonstrates that an initial selective blockade of CD28 generates B7+ non-T regulatory cells and a kidney transplant tolerance sustained by the activity of IDO and iNOS.

Disruption of CD40/CD40-ligand interactions in a retinal autoimmunity model results in protection without tolerance

We examined the role of CD40/CD40L interactions on the development of experimental autoimmune uveoretinitis (EAU), a cell-mediated, Th1-driven autoimmune disease that serves as a model for autoimmune uveitis in humans. EAU-susceptible B10.RIII mice immunized with the retinal autoantigen interphotoreceptor retinoid binding protein in CFA and treated with anti-CD40L Ab (MR1) had reduced incidence and severity of disease. Real-time PCR analysis revealed that the innate and adaptive responses of protected mice were reduced, without an obvious shift toward a Th2 cytokine profile. In contrast to some other reports, no evidence was found for regulatory cells in adoptive transfer experiments. To determine whether CD40L blockade resulted in long-term tolerance, mice protected by treatment with MR1 Ab were rechallenged for uveitis after circulating MR1 Ab levels dropped below the detection limit of ELISA. MR1-treated mice developed severe EAU and strong cellular responses to interphotoreceptor retinoid binding protein, comparable to those of control mice. These responses were higher than in mice that had not received the primary immunization concurrently with anti-CD40L treatment. We conclude that 1) CD40/CD40L interaction is required for EAU and its disruption prevents disease development; 2) CD40L blockade inhibits the innate response to immunization and reduces priming, but does not result in immune deviation; and 3) protection is dependent on persistence of anti-CD40L Abs, and long-term tolerance is not induced. Furthermore, immunological memory develops under cover of CD40L blockade causing enhanced responses upon rechallenge. Taken together, our data suggest that ongoing CD40/CD40L blockade might be required to maintain a therapeutic effect against uveitis.

B7-1 and B7-2 selectively recruit CTLA-4 and CD28 to the immunological synapse

The reported affinity differences between CD28 and CTLA-4 binding to B7-1 and B7-2 may serve to selectively regulate CD28 and CTLA-4 function by differentially recruiting and/or stabilizing these molecules at the immunological synapse. Here we show that ligand binding is important for the accumulation of both CD28 and CTLA-4 at the synapse. While CD28 is recruited to the synapse in the absence of B7-1 and B7-2 binding, it is not effectively stabilized there, as its localization can be disrupted by CTLA-4. In the case of CTLA-4, ligand binding is critical for its concentration at the synapse. We also demonstrate that the affinity and avidity differences in ligand binding translate into selective recruitment of CD28 or CTLA-4 to the immunological synapse--B7-1 is the major ligand mediating CTLA-4 localization, while B7-2 is the main ligand for CD28 concentration at the synapse.

Regulation, counter-regulation, and immunotherapy of autoimmune responses to immunologically privileged retinal antigens

Our interests revolve around the study of biological mechanisms regulating self-tolerance to immunologically privileged retinal proteins that serve as targets in sight-threatening autoimmune uveitic disease. These studies are aimed at understanding how selftolerance to these antigens develops during ontogeny and is maintained during adulthood, the processes involved in its pathological breakdown, the regulatory mechanisms that bring about remission and recovery, and, finally, how we can utilize knowledge of these processes for therapeutic restoration of tolerance. To answer these questions, we use the experimental autoimmune uveitis (EAU) model in rats and mice. Because of the commonality of underlying immunological mechanisms, lessons and concepts learned in experimental ocular models are applicable to other disease entities, and, conversely, data gleaned from other autoimmune diseases are applicable to the study of uveitis.

Ocular transfer of retinal glial cells transduced ex vivo with adenovirus expressing viral IL-10 or CTLA4-Ig inhibits experimental autoimmune uveoretinitis

Gene transfer using immunomodulatory molecules is a promising tool for in vivo regulation of immune responses. Experimental autoimmune uveitis (EAU), which serves as a model for human ocular inflammation, is induced by systemic immunization with autoantigens, but its expression is restricted to the eye. Previously, we reported protection of rodents against EAU by intravenous or/and periocular injection of vIL-10-expressing adenovirus. Here, the expression of vIL-10 was targeted into the rat Lewis eye, by intravitreal injection of either the free virus or ex vivo transfected retinal Müller glial cells (RMG-vIL-10). As shown using GFP-expressing adenovirus, a longer expression of transgene was observed in the eye after transfer of transfected syngeneic RMG cells than was seen after injection of free virus. Intravitreal injection of RMG-vIL-10 led to significant decrease in ocular pathological manifestations, compared to control RMG cells. This was observed when cells were injected simultaneously with autoantigen, but also after a delayed administration of transfected cells. Finally, injection of RMG cells transfected with adenovirus expressing CTLA4 had a strongly protective effect. In conclusion, inhibition of antigen presentation at the site of expression of the autoimmune disorders represents an attractive alternative to treat ocular inflammation, and the transfer of ex vivo genetically modified cells provides a promising method to target the factor of interest into the eye.

Selective blockade of CD28 and not CTLA-4 with a single-chain Fv-alpha1-antitrypsin fusion antibody

B7-1 and B7-2 are costimulatory molecules expressed on antigen-presenting cells. The CD28/B7 costimulation pathway is critical for T-cell activation, proliferation, and Th polarization. Blocking both cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and CD28 interactions with a CTLA-4/Ig fusion protein inhibits various immune-mediated processes in vivo, such as allograft rejection and autoimmunity. However, selective blockade of CD28 may represent a better strategy for immunosuppression than B7 blockade, because CTLA-4/B7 interactions have been shown to participate in the extinction of the T-cell receptor-mediated activation signal and to be required for the induction of immunologic tolerance. In addition, selective CD28 inhibition specifically decreases the activation of alloreactive and autoreactive T cells, but not the activation of T cells stimulated by exogenous antigens presented in the context of self major histocompatibility complex (MHC) molecules. CD28 blockade cannot be obtained with anti-CD28 dimeric antibodies, which cluster their target and promote T-cell costimulation, whereas monovalent Fab fragments can block CD28 and reduce alloreactivity. In this study, we report the construction of a monovalent single-chain Fv antibody fragment from a high-affinity antihuman CD28 antibody (CD28.3) that blocked adhesion of T cells to cells expressing the CD28 receptor CD80. Genetic fusion with the long-lived serum protein alpha1-antitrypsin led to an extended half-life without altering its binding characteristics. The anti-CD28 fusion molecule showed biologic activity as an immuno-suppressant by inhibiting T-cell activation and proliferation in a mixed lymphocyte reaction.

Differential effect of CD28 versus B7 blockade on direct pathway of allorecognition and self-restricted responses

Immunosuppression with B7 antagonists might have 2 opposite effects: reducing T-cell costimulation through CD28 but also preventing CTLA-4 from transmitting its negative regulatory signal. We therefore hypothesized that a selective blockade of CD28 might be qualitatively different from blocking B7. It was previously reported that CD28 modulation prolongs allograft survival in the rat and reverses induction of experimental autoimmune encephalomyelitis in mice. However, whether CD28 or B7 blockade results in similar immunosuppression on alloimmune and self-restricted responses to soluble antigens has not yet been investigated. Here, we addressed this issue in vitro with antagonist anti-CD28 Fab fragments and in vivo using the modulating anti-rat JJ319 monoclonal antibody. As in the inhibition of B7 with CTLA4 immunoglobulin, anti-CD28 Fab fragments inhibited allogenic T-cell proliferation in mixed cultures. In vivo modulation of CD28 blocked the expansion of alloreactive T cells and promoted their apoptosis. In contrast, selective blockade of CD28 did not modify T-cell proliferative responses and antibody production to soluble antigens, whereas blocking B7 with CTLA4 immunoglobulin did. Our data show that blocking CD28, while leaving CTLA4-B7 interactions undisturbed, inhibits alloreactive CD4+ T-cell expansion but does not modify the response to nominal antigens presented in the context of a self-major histocompatibility complex. That B7 engagement is needed for self-restricted responses whereas engagement of CD28 is not essential adds to the suggestion that another unidentified ligand of B7 might deliver a costimulatory signal in the absence of CD28.

CD40/CD40L interaction is essential for the induction of EAE in the absence of CD28-mediated co-stimulation

CD28 provides a co-stimulatory signal critical for optimal T cell activation. We and others have shown that the B7/CD28 co-stimulatory pathway is a major regulatory pathway for the control of immune responses. Experimentally induced models of autoimmunity have been shown to be prevented or reduced in intensity in mice deficient for CD28. Here, we show that EAE and accompanying neuroantigen-specific immune responses are drastically reduced in the absence of CD28. However, we go on to show that EAE can be induced in CD28-deficient mice following two immunizations. After re-immunization, CD28-deficient mice develop severe EAE with myelin-specific responses equal to those of wildtype controls, and extensive demyelination in the spinal cord. Treatment of CD28-deficient mice with anti-CD40L at the time of immunization significantly reduced DTH responses and prevented the development of EAE following two immunizations, indicating a critical role for CD40/CD40L signaling in the absence of CD28. Taken together, our results indicate that CD28-mediated co-stimulation does not regulate immunological anergy. Instead, CD28 appears to adjust the threshold for activation and expansion of autoreactive cells.