Long-term tolerance to factor VIII is achieved by administration of interleukin-2/interleukin-2 monoclonal antibody complexes and low dosages of factor VIII

Induction of long-term tolerance to a specific antigen using anti-CD3 lipid nanoparticles following gene therapy

Development of factor VIII (FVIII) inhibitors is a serious complication in the treatment of hemophilia A (HemA) patients. In clinical trials, anti-CD3 antibody therapy effectively modulates the immune response of allograft rejection or autoimmune diseases without eliciting major adverse effects. In this study, we delivered mRNA-encapsulated lipid nanoparticles (LNPs) encoding therapeutic anti-CD3 antibody (αCD3 LNPs) to overcome the anti-FVIII immune responses in HemA mice. It was found that αCD3 LNPs encoding the single-chain antibodies (Fc-scFv) can efficiently deplete CD3+ and CD4+ effector T cells, whereas αCD3 LNPs encoding double-chain antibodies cannot. Concomitantly, mice treated with αCD3 (Fc-scFv) LNPs showed an increase in the CD4+CD25+Foxp3+ regulatory T cell percentages, which modulated the anti-FVIII immune responses. All T cells returned to normal levels within 2 months. HemA mice treated with αCD3 LNPs prior to hydrodynamic injection of liver-specific FVIII plasmids achieved persistent FVIII gene expression without formation of FVIII inhibitors. Furthermore, transgene expression was increased and persistent following secondary plasmid challenge, indicating induction of long-term tolerance to FVIII. Moreover, the treated mice maintained their immune competence against other antigens. In conclusion, our study established a potential new strategy to induce long-term antigen-specific tolerance using an αCD3 LNP formulation.

A review of the rationale for gene therapy for hemophilia A with inhibitors: one-shot tolerance and treatment?

The therapeutic landscape for people living with hemophilia A (PwHA) has changed dramatically in recent years, but many clinical challenges remain, including the development of inhibitory antibodies directed against factor VIII (FVIII) that occur in approximately 30% of people with severe hemophilia A. Emicizumab, an FVIII mimetic bispecific monoclonal antibody, provides safe and effective bleeding prophylaxis for many PwHA, but clinicians still explore therapeutic strategies that result in immunologic tolerance to FVIII to enable effective treatment with FVIII for problematic bleeding events. This immune tolerance induction (ITI) to FVIII is typically accomplished through repeated long-term exposure to FVIII using a variety of protocols. Meanwhile, gene therapy has recently emerged as a novel ITI option that provides an intrinsic, consistent source of FVIII. As gene therapy and other therapies now expand therapeutic options for PwHA, we review the persistent unmet medical needs with respect to FVIII inhibitors and effective ITI in PwHA, the immunology of FVIII tolerization, the latest research on tolerization strategies, and the role of liver-directed gene therapy to mediate FVIII ITI.

Association between interleukin-2 (rs2069762) gene polymorphism and FVIII inhibitor development in Indonesian patients with severe hemophilia A

BACKGROUND Factor VIII (FVIII) inhibitors in hemophilia A (HA) patients render FVIII replacement therapy ineffective. Although its development cause is unclear, it has been classified into therapeutic and genetic-related etiologies. Single nucleotide polymorphisms (SNPs) in several cytokine genes, including interleukin (IL)-2, could increase the risk of FVIII inhibitor development. This study aimed to evaluate the association between IL-2 (rs2069762) gene SNP and FVIII inhibitor development in Indonesian patients with severe HA. METHODS The IL-2 (rs2069762) gene SNP was examined in 119 HA patients. The presence of FVIII inhibitors was quantified using an enzyme-linked immunosorbent assay, with a titer of <0.28 ng/ml considered negative. Patients were divided into two groups: 59 with FVIII inhibitors (positive group) and 60 without inhibitors (negative group). The genotype of the subjects was determined using peripheral blood mononuclear cells and tetra-primer amplification refractory mutation system-polymerase chain reaction. RESULTS There was no association between IL-2 (rs2069762) gene polymorphism and FVIII inhibitor development on genotypes (p = 0.138) and allele frequencies (p = 0.780). CONCLUSIONS IL-2 (rs2069762) gene polymorphism is not a risk factor in the development of FVIII inhibitors in Indonesian patients with severe HA. Thus, further polymorphism studies in other cytokine genes are required to gain a comprehensive understanding of the FVIII inhibitor development.

Immune complications and their management in inherited and acquired bleeding disorders

Disorders of coagulation, resulting in serious risks for bleeding, may be caused by autoantibody formation or by mutations in genes encoding coagulation factors. In the latter case, antidrug antibodies (ADAs) may form against the clotting factor protein drugs used in replacement therapy, as is well documented in the treatment of the X-linked disease hemophilia. Such neutralizing antibodies against factors VIII or IX substantially complicate treatment. Autoantibody formation against factor VIII leads to acquired hemophilia. Although rare, antibody formation may occur in the treatment of other clotting factor deficiencies (eg, against von Willebrand factor [VWF]). The main strategies that have emerged to address these immune responses include (1) clinical immune tolerance induction (ITI) protocols; (2) immune suppression therapies (ISTs); and (3) the development of drugs that can improve hemostasis while bypassing the antibodies against coagulation factors altogether (some of these nonfactor therapies/NFTs are antibody-based, but they are distinct from traditional immunotherapy as they do not target the immune system). Choice of immune or alternative therapy and criteria for selection of a specific regimen for inherited and autoimmune bleeding disorders are explained. ITI serves as an important proof of principle that antigen-specific immune tolerance can be achieved in humans through repeated antigen administration, even in the absence of immune suppression. Finally, novel immunotherapy approaches that are still in the preclinical phase, such as cellular (for instance, regulatory T cell [Treg]) immunotherapies, gene therapy, and oral antigen administration, are discussed.

In Vivo Expansion of Antigen-Specific Regulatory T Cells through Staggered Fc.IL-2 Mutein Dosing and Antigen-Specific Immunotherapy

In mice, Ag administration in the absence of adjuvant typically elicits tolerogenic immune responses through the deletion or inactivation of conventional CD4 T cells and the formation or expansion of regulatory CD4 T cells (Treg). Although these "Ag-specific immunotherapy" (ASI) approaches are currently under clinical development to treat autoinflammatory conditions, efficacy and safety may be variable and unpredictable because of the diverse activation states of immune cells in subjects with autoimmune and allergic diseases. To reliably induce Ag-specific tolerance in patients, novel methods to control T cell responses during ASI are needed, and strategies that permanently increase Treg frequencies among Ag-specific CD4 T cells may provide long-lasting immunosuppression between treatments. In this study, we present an approach to durably increase the frequency of Ag-specific Treg in mice by administering ASI when Treg numbers are transiently increased with individual doses of a half-life-extended Treg-selective IL-2 mutein. Repeated weekly cycles of IL-2 mutein doses (day 0) followed by ASI (day 3) resulted in a 3- to 5-fold enrichment in Treg among Ag-responsive CD4 T cells. Expanded Ag-specific Treg persisted for more than 3 wk following treatment cessation, as well as through an inflammatory T cell response to an Ag-expressing virus. Combining Treg enrichment with ASI has the potential to durably treat autoimmune disease or allergy by increasing the Treg/conventional CD4 T cell ratio among autoantigen- or allergen-specific T cells.

CD4+ T cells engineered with FVIII-CAR and murine Foxp3 suppress anti-factor VIII immune responses in hemophilia a mice

Although protein replacement therapy provides effective treatment for hemophilia A patients, about a third of severe patients develop neutralizing inhibitor antibodies to factor VIII. Adoptive transfer of regulatory T cells (Tregs) has shown promise in treating unwanted immune responses. In previous studies, transferred polyclonal Tregs ameliorated the anti-factor VIII immune responses in hemophilia A mice. In addition, factor VIII-primed Tregs demonstrated increased suppressive function. However, antigen-specific Tregs are a small fraction of the total lymphocyte population. To generate large numbers of factor VIII-specific Tregs, the more abundant murine primary CD4⁺ T cells were lentivirally transduced ex vivo to express Foxp3 and a chimeric antigen receptor specific to factor VIII (F8CAR). Transduced cells significantly inhibited the proliferation of factor VIII-specific effector T cells in suppression assays. To monitor the suppressive function of the transduced chimeric antigen receptor expressing T cells in vivo, engineered CD4⁺CD25⁺Foxp3⁺F8CAR-Tregs were sorted and adoptively transferred into hemophilia A mice that are treated with hydrodynamically injected factor VIII plasmid. Mice receiving engineered F8CAR-Tregs showed maintenance of factor VIII clotting activity and did not develop anti-factor VIII inhibitors, while control CD4⁺T cell or PBS recipient mice developed inhibitors and had a sharp decrease in factor VIII activity. These results show that CD4⁺ cells lentivirally transduced to express Foxp3 and F8CAR can promote factor VIII tolerance in a murine model. With further development and testing, this approach could potentially be applied to human hemophilia patients.

Regulatory T cell therapy: Current and future design perspectives

Regulatory T cells (Tregs) maintain immune equilibrium by suppressing immune responses through various multistep contact dependent and independent mechanisms. Cellular therapy using polyclonal Tregs in transplantation and autoimmune diseases has shown promise in preclinical models and clinical trials. Although novel approaches have been developed to improve specificity and efficacy of antigen specific Treg based therapies, widespread application is currently restricted. To date, design-based approaches to improve the potency and persistence of engineered chimeric antigen receptor (CAR) Tregs are limited. Here, we describe currently available Treg based therapies, their advantages and limitations for implementation in clinical studies. We also examine various strategies for improving CAR T cell design that can potentially be applied to CAR Tregs, such as identifying co-stimulatory signalling domains that enhance suppressive ability, determining optimal scFv affinity/avidity, and co-expression of accessory molecules. Finally, we discuss the importance of tailoring CAR Treg design to suit the individual disease.

A Treg-Selective IL-2 Mutein Prevents the Formation of Factor VIII Inhibitors in Hemophilia Mice Treated With Factor VIII Gene Therapy

Hemophilia A is a genetic disorder that results in the deficiency of functional factor VIII protein, which plays a key role in blood coagulation. Currently, the majority of hemophilia A patients are treated with repeated infusions of factor VIII protein. Approximately 30% of severe hemophilia A patients develop neutralizing antibodies to factor VIII (known as factor VIII inhibitors) due to treatment, rendering factor VIII protein infusions ineffective. Previously, mice receiving murine IL-2 complexed with α-murine IL-2 mAbs (JES6-1A12) showed a lack of factor VIII inhibitor formation after factor VIII treatment, which was associated with the proliferation and the activation of factor VIII-specific regulatory T cells (Tregs). In this paper, we evaluated if an Fc-fused mutated protein analog of mouse IL-2, named Fc.Mut24, engineered to selectively promote the expansion of Tregs in vivo can modulate factor VIII-specific immune responses. The mice received one intraperitoneal injection of Fc.Mut24. When the regulatory T cell population reached its highest frequency and peak activation, the mice received a hydrodynamic injection of factor VIII plasmid (day 4) followed by a second Fc.Mut24 dose (day 7). Peripheral blood was collected weekly. Flow cytometry was used to characterize the peripheral blood cell populations, while ELISA and Bethesda assays were used to assess the inhibitor concentrations and the functional titers in plasma. The activated partial thromboplastin time assay was used to assess the functional activities of factor VIII in blood. The mice receiving Fc.Mut24 showed a dramatic and transient increase in the population of activated Tregs after Fc.Mut24 injection. Factor VIII gene therapy via hydrodynamic injection resulted in high anti-factor VIII inhibitor concentrations in control PBS-injected mice, whereas the mice treated with Fc.Mut24 produced no inhibitors. Most significantly, there were no inhibitors generated after a second hydrodynamic injection of factor VIII plasmid administered at 19 weeks after the first injection in Fc.Mut24-treated mice. The mice receiving Fc.Mut24 maintained high levels of factor VIII activity throughout the experiment, while the control mice had the factor VIII activity dropped to undetectable levels a few weeks after the first factor VIII plasmid injection. Our data show that human therapies analogous to Fc.Mut24 could potentially provide a method to prevent inhibitor formation and induce long-term immune tolerance to factor VIII in hemophilia patients.

Treatment of Hemophilia A Using Factor VIII Messenger RNA Lipid Nanoparticles

Hemophilia A (HemA) patients are currently treated with costly and inconvenient replacement therapy of short-lived factor VIII (FVIII) protein. Development of lipid nanoparticle (LNP)-encapsulated mRNA encoding FVIII can change this paradigm. LNP technology constitutes a biocompatible and scalable system to efficiently package and deliver mRNA to the target site. Mice intravenously infused with the luciferase mRNA LNPs showed luminescence signals predominantly in the liver 4 h after injection. Repeated injections of LNPs did not induce elevation of liver transaminases. We next injected LNPs carrying mRNAs encoding different variants of human FVIII (F8 LNPs) into HemA mice. A single injection of B domain-deleted F8 LNPs using different dosing regimens achieved a wide range of therapeutic activities rapidly, which can be beneficial for various usages in hemophilia treatment. The expression slowly declined yet remained above therapeutic levels up to 5–7 days post-injection. Furthermore, routine repeated injections of F8 LNPs in immunodeficient mice produced consistent expression of FVIII over time. In conclusion, F8 LNP treatment produced rapid and prolonged duration of FVIII expression that could be applied to prophylactic treatment and potentially various other treatment options. Our study showed potential for a safe and effective platform of new mRNA therapies for HemA.

Combined anti-CD20 and mTOR inhibition with factor VIII for immune tolerance induction in hemophilia A patients with refractory inhibitors

BACKGROUND

Hemophilia A (HA) inhibitor patients that fail traditional immune tolerance induction (ITI) have increased morbidity and mortality. Preclinical studies support factor VIII (FVIII) tolerance induction with a combined approach of anti-CD20 mediated transient B cell depletion and rapamycin mediated regulatory T cell (Treg) induction.

METHODS

Two refractory HA inhibitor patients were treated with rituximab, rapamycin, and FVIII ITI. Their clinical course, anti-FVIII immunoglobulins, cytokines, and select lymphocytes were followed.

RESULTS

One patient achieved complete and the other partial FVIII tolerance; both had marked annualized bleeding rate improvement. FVIII-specific immunoglobulins, but not total Treg counts, correlated with tolerance induction. IL-6 and IL-21 correlation with complete tolerance induction may support that down-regulation of T effectors and IgG4 production, respectively, contribute to the pathogenesis of tolerance induction.

CONCLUSIONS

This regimen may be considered to induce FVIII tolerance in HA patients with refractory inhibitors. Further characterization of the FVIII-specific immune response is necessary to clarify the mechanism of immune tolerance.

Escape or Fight: Inhibitors in Hemophilia A

Replacement therapy with coagulation factor VIII (FVIII) represents the current clinical treatment for patients affected by hemophilia A (HA). This treatment while effective is, however, hampered by the formation of antibodies which inhibit the activity of infused FVIII in up to 30% of treated patients. Immune tolerance induction (ITI) protocols, which envisage frequent infusions of high doses of FVIII to confront this side effect, dramatically increase the already high costs associated to a patient's therapy and are not always effective in all treated patients. Therefore, there are clear unmet needs that must be addressed in order to improve the outcome of these treatments for HA patients. Taking advantage of preclinical mouse models of hemophilia, several strategies have been proposed in recent years to prevent inhibitor formation and eradicate the pre-existing immunity to FVIII inhibitor positive patients. Herein, we will review some of the most promising strategies developed to avoid and eradicate inhibitors, including the use of immunomodulatory drugs or molecules, oral or transplacental delivery as well as cell and gene therapy approaches. The goal is to improve and potentiate the current ITI protocols and eventually make them obsolete.

Antigen-specific in vitro expansion of factor VIII-specific regulatory T cells induces tolerance in hemophilia A mice

BACKGROUND

Following protein replacement therapy, one-third of severe hemophilia A patients develop antibodies to factor VIII (FVIII), which also hinders the efficacy of gene therapy. Regulatory T cells (Tregs) have a naturally suppressive function that potentially reduces the immune response to FVIII therapy. Furthermore, antigen-specific Tregs are functionally much more potent than polyclonal cells. Adoptive transfer of antigen-specific Tregs can effectively suppress anti-FVIII antibody responses.

OBJECTIVE

Develop a clinically feasible protocol to enrich and expand Tregs specific to FVIII for suppressing anti-FVIII immune responses.

METHODS

Regulatory T cells are isolated from FVIII-sensitized mice, sorted on CD25high markers, and expanded specifically with FVIII, antigen-presenting cells, and interleukin 2 (IL 2). Subsequently, Tregs are further cultured with anti-CD3/anti-CD28 beads, anti-Crry antibodies, and IL 2 to achieve 10-fold to 20-fold expansion. Expanded Tregs are characterized and tested for their suppressive activity in vitro and in vivo.

RESULTS

In vitro FVIII-specific suppressive assays indicate that FVIII specifically expanded Tregs are more suppressive than non-specifically expanded and naive Tregs. Adoptive transfer of expanded Tregs into HemA mice showed that FVIII-specifically expanded Tregs are significantly more potent in suppressing anti-FVIII immune responses in FVIII plasmid-treated HemA mice. Moreover, the FVIII-specific immune tolerance is maintained after a secondary challenge with FVIII plasmid.

CONCLUSIONS

Our results demonstrate that the FVIII-specific sensitization and expansion protocol yields more potent Tregs to suppress anti-FVIII antibody responses and induce long-term tolerance to FVIII, increasing the potential for adoptive Treg cell therapy to modulate anti-FVIII immune responses.

New technologies in gene therapy for inducing immune tolerance in hemophilia A

INTRODUCTION

Conventional hemophilia treatment is based on repeated infusion of the missing clotting factor. This therapy is lifelong, expensive and can result in the formation of neutralizing antibodies, thus causing failure of the treatment and requiring higher doses of the replacement drug. Areas covered: Gene and cell therapies offer the advantage of providing a definitive and long-lasting correction of the mutated gene, promoting its physiological expression and preventing neutralizing antibody development. This review focuses on the most recent approaches that have been shown to prevent and even eradicate immune response toward the replaced factor. Expert commentary: Despite the encouraging data demonstrated by ongoing clinical trials and pre-clinical studies, more extensive investigations are necessary to establish the long-term safety and efficacy of gene therapy treatments in maintaining immune tolerance.

Targeting Antigen-Specific B Cells Using Antigen-Expressing Transduced Regulatory T Cells

Controlling immune responses in autoimmunity and to biotherapeutics is an unmet need. In hemophilia, for example, up to one third of patients receiving therapeutic factor VIII (FVIII) infusions develop neutralizing Abs termed "inhibitors." To address this problem in a mouse model of hemophilia A, we used an Ag-specific regulatory T cell (Treg) approach in which we created a novel B cell-targeting chimeric receptor composed of an FVIII Ag domain linked with the CD28-CD3ζ transmembrane and signaling domains. We termed these "BAR" for B cell-targeting Ab receptors. CD4⁺CD25^hiCD127^low human Tregs were retrovirally transduced to express a BAR containing the immunodominant FVIII C2 or A2 domains (C2- and A2-BAR). Such BAR-Tregs specifically suppressed the recall Ab response of spleen cultures from FVIII-immunized mice in vitro and completely prevented anti-FVIII Ab development in response to FVIII immunization. Mechanistic studies with purified B cells and T cells from tolerized or control recipients demonstrated that the FVIII-specific B cells were directly suppressed or anergized, whereas the T cell response remained intact. Taken together, we report in this study a successful proof-of-principle strategy using Ag-expressing Tregs to directly target specific B cells, an approach which could be adapted to address other adverse immune responses as well.

Dexamethasone promotes durable factor VIII-specific tolerance in hemophilia A mice via thymic mechanisms

The development of inhibitory antibodies to factor VIII is the most serious complication of replacement therapy in hemophilia A. Activation of the innate immune system during exposure to this protein contributes to inhibitor development. However, avoidance of factor VIII exposure during innate immune system activation by external stimuli (e.g., vaccines) has not been consistently shown to prevent inhibitors. We hypothesized that dexamethasone, a drug with potent anti-inflammatory effects, could prevent inhibitors by promoting immunologic tolerance to factor VIII in hemophilia A mice. Transient dexamethasone treatment during ainitial factor VIII exposure reduced the incidence of anti-factor VIII immunoglobulin G in both a conventional hemophilia A mouse model (E16KO, 77% vs. 100%, P=0.048) and a hemophilia A mouse model with a humanized major histocompatibility complex type II transgene (E17KO/hMHC, 6% vs. 33%, P=0.0048). More importantly, among E17KO/hMHC mice that did not develop anti-factor VIII immunoglobulin G after initial exposure, dexamethasone-treated mice were less likely to develop a response after re-exposure six (7% vs. 52%, P=0.005) and 16 weeks later (7% vs. 50%, P=0.097). Similar results were obtained even when factor VIII re-exposure occurred in the context of lipopolysaccharide (30% vs. 100%, P=0.069). The ability of these mice to develop immunoglobulin G to human von Willebrand factor, a structurally unrelated antigen, remained unaffected by treatment. Transient dexamethasone administration therefore promotes antigen-specific immunologic tolerance to factor VIII. This effect is associated with an increase in the percentage of thymic regulatory T cells (12.06% vs. 4.73%, P<0.001) and changes in the thymic messenger ribonucleic acid transcription profile.

Innovative Approaches for Immune Tolerance to Factor VIII in the Treatment of Hemophilia A

Hemophilia A (coagulation factor VIII deficiency) is a debilitating genetic disorder that is primarily treated with intravenous replacement therapy. Despite a variety of factor VIII protein formulations available, the risk of developing anti-dug antibodies (“inhibitors”) remains. Overall, 20–30% of patients with severe disease develop inhibitors. Current clinical immune tolerance induction protocols to eliminate inhibitors are not effective in all patients, and there are no prophylactic protocols to prevent the immune response. New experimental therapies, such as gene and cell therapies, show promising results in pre-clinical studies in animal models of hemophilia. Examples include hepatic gene transfer with viral vectors, genetically engineered regulatory T cells (Treg), in vivo Treg induction using immune modulatory drugs, and maternal antigen transfer. Furthermore, an oral tolerance protocol is being developed based on transgenic lettuce plants, which suppressed inhibitor formation in hemophilic mice and dogs. Hopefully, some of these innovative approaches will reduce the risk of and/or more effectively eliminate inhibitor formation in future treatment of hemophilia A.

Large scale studies assessing anti-factor VIII antibody development in previously untreated haemophilia A: what has been learned, what to believe and how to learn more

Minimizing the risk of inhibitor development by acting on modifiable risk factors remains a sensible goal for treatment optimization in haemophilia A. By critically appraising published studies assessing inhibitor development, this review addresses the role of studies in previously untreated patients (PUPs) for establishing the immunogenicity of new concentrates, suggest novel research design to be adopted in future studies and discuss clinical practice implications of the reported differential immunogenicity of Kogenate Bayer and Advate factor VIII concentrates. Three considerations are relevant here: (i) all of the existing concentrates, when tested following the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee recommendation, were shown to be safe; as a consequence, (ii) when considering using any newly introduced product, one should be aware that it could, in future, turn out to be as immunogenic as Kogenate Bayer, and (iii) at the population level, it might be wiser not to use Kogenate Bayer in PUPs, if the choice is against Advate. When presenting the risk of developing inhibitors to the individual patient (or their family), the message remains that the risk can be as high as 40%, without any efficient instrument to predict individual inhibitor risk. Patients should be invited to enrol into a randomized registry trial, including random assignment to trials with new investigational products.

In vivo induction of regulatory T cells for immune tolerance in hemophilia

Current therapy for the X-linked coagulation disorder hemophilia is based on intravenous infusion of the specifically deficient coagulation factor. However, 20-30% of hemophilia A patients (factor VIII, FVIII, deficiency) generate inhibitory antibodies against FVIII. While formation of inhibitors directed against factor IX, FIX, resulting from hemophilia B treatment is comparatively rare, a serious complication that is often associated with additional immunotoxicities, e.g. anaphylaxis, occurs. Current immune tolerance protocols to eradiate inhibitors are lengthy, expensive, not effective in all patients, and there are no prophylactic tolerance regimens to prevent inhibitor formation. The outcomes of recent experiments in animal models of hemophilia demonstrate that regulatory CD4(+) T cells (Treg) are of paramount importance in controlling B cell responses to FVIII and FIX. This article reviews several novel strategies designed to in vivo induce coagulation factor-specific Treg cells and discusses the subsets of Treg that may promote immune tolerance in hemophilia. Among others, drug- and gene transfer-based protocols, lymphocyte transplant, and oral tolerance are reviewed.

Strategies to target long-lived plasma cells for treating hemophilia A inhibitors

Long-lived plasma cells (LLPCs) can persistently produce anti-factor VIII (FVIII) antibodies which disrupt therapeutic effect of FVIII in hemophilia A patients with inhibitors. The migration of plasma cells to BM where they become LLPCs is largely controlled by an interaction between the chemokine ligand CXCL12 and its receptor CXCR4. AMD3100 combined with G-CSF inhibit their interactions, thus facilitating the mobilization of CD34(+) cells and blocking the homing of LLPCs. These reagents were combined with anti-CD20 to reduce B-cells and the specific IL-2/IL-2mAb (JES6-1) complexes to induce Treg expansion for targeting anti-FVIII immune responses. Groups of mice primed with FVIII plasmid and protein respectively were treated with the combined regimen for six weeks, and a significant reduction of anti-FVIII inhibitor titers was observed, associated with the dramatic decrease of circulating and bone marrow CXCR4(+) plasma cells. The combination regimens are highly promising in modulating pre-existing anti-FVIII antibodies in FVIII primed subjects.

Plant-based oral tolerance to hemophilia therapy employs a complex immune regulatory response including LAP+CD4+ T cells

Coagulation factor replacement therapy for the X-linked bleeding disorder hemophilia is severely complicated by antibody ("inhibitor") formation. We previously found that oral delivery to hemophilic mice of cholera toxin B subunit-coagulation factor fusion proteins expressed in chloroplasts of transgenic plants suppressed inhibitor formation directed against factors VIII and IX and anaphylaxis against factor IX (FIX). This observation and the relatively high concentration of antigen in the chloroplasts prompted us to evaluate the underlying tolerance mechanisms. The combination of oral delivery of bioencapsulated FIX and intravenous replacement therapy induced a complex, interleukin-10 (IL-10)-dependent, antigen-specific systemic immune suppression of pathogenic antibody formation (immunoglobulin [Ig] 1/inhibitors, IgE) in hemophilia B mice. Tolerance induction was also successful in preimmune mice but required prolonged oral delivery once replacement therapy was resumed. Orally delivered antigen, initially targeted to epithelial cells, was taken up by dendritic cells throughout the small intestine and additionally by F4/80(+) cells in the duodenum. Consistent with the immunomodulatory responses, frequencies of tolerogenic CD103(+) and plasmacytoid dendritic cells were increased. Ultimately, latency-associated peptide expressing CD4(+) regulatory T cells (CD4(+)CD25(-)LAP(+) cells with upregulated IL-10 and transforming growth factor-β (TGF-β) expression) as well as conventional CD4(+)CD25(+) regulatory T cells systemically suppressed anti-FIX responses.