T cell response to FVIII.

Several lines of evidence indicate that the immune response to Factor VIII (FVIII) in patients with hemophilia A is T cell-dependent. This review highlights the link between the epitope specificity of FVIII-specific T cells and their potential roles in different categories of patients. FVIII-specific T cells able to recognize wild-type (i.e. therapeutic) FVIII but not the mutated self FVIII of hemophilia patients have been identified in patients with mild/moderate hemophilia carrying some point mutations. Such T cells likely contribute to the higher frequency of neutralizing anti-FVIII antibodies (inhibitors) development in these patients. In contrast, as yet no T cells have been identified that can differentiate between FVIII molecules with non-hemophilia-causing single amino acid variants encoded by non-synonymous single-nucleotide polymorphisms in the F8 gene. Other mechanisms are therefore still to be identified that will explain the clinically noted differences in the incidence of inhibitor development between patients of different races who are known to have differences at these sites. Beside information about the mechanism of inhibitor development, the analysis of FVIII-specific T cells has provided tools to develop novel diagnostic and therapeutic approaches, such as the generation of FVIII-specific regulatory T cells that may be useful in preventing or suppressing the immune response to FVIII.

Placental growth factor contributes to bronchial neutrophilic inflammation and edema in allergic asthma.

Placental growth factor (PlGF) and its receptor vascular endothelial growth factor receptor 1 (VEGFR1) play an important role in pathological conditions related to angiogenesis, vascular leakage, and inflammation. This study investigated their contributions to inflammation and the formation of edema in allergic asthma. The expression of PlGF and VEGFR1 was measured in induced sputum of patients with asthma (n = 11) and healthy subjects (n = 11), and in bronchial biopsies of house dust mite (HDM)-allergic patients stimulated with HDM allergens. The effects of the endonasal administration of human PlGF-2 and PlGF deficiency on inflammation and edema were evaluated in a murine model of allergic asthma. The migration of human neutrophils in response to hPlGF-2 was tested in vitro. The expression of PlGF and VEGFR1 was significantly higher in the sputum of patients with asthma, and in Der p 1-induced PlGF in biopsies from HDM-allergic patients. PlGF was increased in the bronchi of ovalbumin (OVA)-challenged mice compared with control mice (65 ± 17 pg/mg versus 18 ± 1 pg/mg, respectively; P < 0.01), and VEGFR1 was expressed in bronchial epithelium, endothelium (control mice), and inflammatory cells (OVA-challenged mice). The endonasal instillation of hPlGF-2 in wild-type, OVA-challenged mice led to an increase in bronchial neutrophils, lung tissue wet/dry ratio, and IL-17. PlGF-deficient mice showed lower numbers of BAL-infiltrating neutrophils, a reduced lung wet/dry ratio, and lower production of IL-17, macrophage inflammatory protein-2, and granulocyte chemotactic protein-2/LPS-induced chemokine compared with wild-type, OVA-challenged mice. hPlGF-2 induced the migration of human neutrophils in vitro in a VEGFR1-dependent way. PlGF and its receptor VEGFR1 are up-regulated in allergic asthma and play a proinflammatory role by inducing tissue edema, and increasing tissue neutrophilia and the production of IL-17.

Antielastin B-cell and T-cell immunity in patients with chronic obstructive pulmonary disease.

RATIONALE: Antielastin autoimmunity has been hypothesised to drive disease progression in chronic obstructive pulmonary disease (COPD). The proposed mechanism is currently disputed by conflicting data. The authors aimed to explore antibody responses against elastin in a large and extensively characterised COPD population and to assess elastin-specific peripheral T-cell reactivity in a representative subgroup. METHODS: Antielastin antibodies were analysed with indirect ELISA on the plasma of 320 patients with COPD (Global Initiative for Chronic Obstructive Lung Disease 1-4) and 143 smoking controls. In a second group of 40 patients with COPD and smoking controls, T-cell responses against extracellular matrix (elastin, collagen I and collagen V) were determined with enzyme-linked immunosorbent spot (EliSpot) (interferon γ (IFNγ) and interleukin-2) on peripheral blood mononuclear cells and compared with the responses of 11 never-smoking controls. RESULTS: Antielastin antibody titres were not elevated in patients with COPD compared with smoking controls and even decreased significantly with increasing severity of COPD (p<0.001). Lower antielastin antibody titres were also found in a subgroup of patients with CT-proven emphysema. Elastin-specific INFγ-mediated T helper 1 responses could not be revealed in smoking subjects with and without COPD. Collagen I-mediated T-cell responses were also absent, which contrasted with a significant increased anticollagen V response in the smoking controls and patients with COPD compared with the never smokers (p=0.008). Collagen V-mediated T-cell responses could not discriminate between patients with COPD and smoking controls. CONCLUSION: A systemic immune response against elastin could not be identified in patients with COPD. By contrast, collagen V-mediated autoimmunity was increased in the subgroup of smokers and may potentially contribute to the pathogenesis of COPD.

Activation of human endothelial cells from specific vascular beds induces the release of a FVIII storage pool.

Although the liver is known to be the main site of factor VIII (FVIII) production, other organs are probably also important for the regulation of FVIII secretion. However, the study of the regulation of extrahepatic FVIII production has been hampered by the lack of definitive identification of human tissues able to secrete FVIII. Recent studies have shown that lung endothelial cells can synthesize FVIII. We therefore studied the production of FVIII by endothelial cells purified from other vascular beds. Because physiologic stress results in a rapid elevation of FVIII, we also investigated whether endothelial cells can store FVIII and secrete it after treatment with agonists. Microvascular endothelial cells from lung, heart, intestine, and skin as well as endothelial cells from pulmonary artery constitutively secreted FVIII and released it after treatment with phorbol-myristate acetate and epinephrine. By contrast, endothelial cells from the aorta, umbilical artery and umbilical vein did not constitutively secrete FVIII or release it after treatment with agonists, probably because of a lack of FVIII synthesis. Extrahepatic endothelial cells from certain vascular beds therefore appear to be an important FVIII production and storage site with the potential to regulate FVIII secretion in chronic and acute conditions.

Establishing an allergic eczema model employing recombinant house dust mite allergens Der p 1 and Der p 2 in BALB/c mice.

The major house dust mite allergens Der p 1 and Der p 2 are prevalent inducers of eczema. Der p 1 is a cysteine protease disrupting epithelial barriers, whereas Der p 2 functionally mimics the LPS-binding compound MD-2 within the TLR4 complex. In this work, we tested the percutaneous sensitizing capacity of recombinant (r) Der p 1 and Der p 2 in BALB/c mice. Mice were sensitized by percutaneous application of low (10 µg/application) and high dose (100 µg) rDer p 1 or rDer p 2, or with rDer p 1 followed by rDer p 2. Allergen-specific and total IgE antibodies were determined by ELISA. Eczema of BALB/c was classified by the itching score and corresponded to erosions. Infiltrating immune cells were identified by haematoxylin/eosin and Giemsa staining for eosinophils or mast cells, CD3 staining for T lymphocytes. Percutaneous treatments with rDer p 1, but not rDer p 2-induced specific IgG1. However, cotreatment with rDer p 1 led to increase in anti-Der p 2 IgG titres. Both allergens elicited skin erosions because of scratching, thickening of the epidermis, and eosinophil and T-cell infiltration. Our data indicate that recombinant mite allergens in the absence of adjuvant are sufficient for inducing eczema in BALB/c mice. As the enzymatic activity of an allergen might be an important cofactor for specific sensitization via the skin, Der p 1 may act as adjuvant for other allergens too. The presented mouse model is suitable for investigating the mechanisms of allergic eczema.

Models for assessing immunogenicity and efficacy of new therapeutics for the treatment of haemophilia.

Inhibitor development remains a challenge to appropriate haemophilia treatment. This challenge is being addressed, in part, by an expanding knowledge of the mechanisms that drive inhibitor development including how elements of the innate immune response play a role in inhibitor development. There are promising therapies that may suppress an active immune response. Models to assess the immune responses are becoming ever more sophisticated. Newer models can be used at the preclinical level to evaluate the role of MHC-class II presentation of antigens in both in vitro cell culture studies and in vivo in transgenic mice that express either the protein to be studied or that express human MHC-class II proteins. Parallel to work designed to reduce or reverse inhibitors is development of improved therapies including bypassing agents to treat patients with inhibitors. With these new treatment modalities comes the problem of assessing efficacy at the preclinical level. Models to evaluate bleeding are being developed that may give a more subtle assessment of bypassing agents. These models represent in part an attempt to incorporate the role of ongoing bleeding into the evaluation. Overall, these newer models have great potential in preclinical studies to evaluate the risk of inhibitor development of new therapeutics and to assess the functionality of these new therapeutics.

Retroviral vectors induce epigenetic chromatin modifications and IL-10 production in transduced B cells via activation of toll-like receptor 2.

The immune response toward viral vectors used for gene therapy and genetic vaccination appears to be critically important in determining the therapeutic outcome. However, the mechanisms that control the immune response following gene transfer are poorly understood. Unexpectedly, we found that integrating retroviral vector particles induce stable interleukin-10 (IL-10) production in murine (BALB/c H-2(d)) transduced B cells. This requires a novel mechanism whereby the interaction of retroviral vector particle with its cognate cellular receptor activates intracellular signaling pathways resulting in stable epigenetic modifications. Murine B cells exposed to retroviral vector particles triggered the colocalization of the retroviral cellular receptor [mouse cationic amino acid transporter 1 (mCAT1)] and Toll-like receptor 2 (TLR2) into lipid microrafts, which in turn activated TLR2 signaling pathways. TLR2 activation induced STAT3 phosphorylation and increased phosphorylated histone 3 (H3) at the STAT3-binding site of the IL-10 promoter. In addition, TLR2 activation during transduction activates nuclear factor of κ light polypeptide gene enhancer in B-cells inhibitor, α (NFKBIA), thereby preventing the translocation of the nuclear factor-κB (NF-κB) complex to the nucleus and the transcription of proinflammatory cytokines. These findings open new perspectives for controlling immune responses following gene therapy and genetic vaccination.

In vivo induction of type 1-like regulatory T cells using genetically modified B cells confers long-term IL-10-dependent antigen-specific unresponsiveness.

Regulatory T cells (Tregs) hold much promise for the therapy of allergy and autoimmunity, but their use is hampered by lack of Ag specificity (natural Tregs) and difficulty to expand in vitro or in vivo (adaptive Tregs). We designed a method for in vivo induction of Ag-specific Tregs, in BALB/c H-2d, that share characteristics with type 1 Tregs (Tr1). A retroviral vector was constructed encoding a major T cell epitope of a common allergen, Der p 2, fused to an endosomal targeting sequence (gp75) for efficient MHC class II presentation. B cells transduced with such construct were adoptively transferred to BALB/c mice before or after peptide immunization. Long-lasting Ag-specific immune tolerance was achieved in both cases. Genetically modified B cells constitutively expressed the transgene for at least 3 mo. B cells from IL-10(-/-) mice were unable to induce tolerance. Upon transfer, B cells induced Foxp3(-)CD4(+) T cells showing phenotypic and functional characteristics comparable to Tr1-cells, including production of IL-10 but not of TGF-beta, and high expression of CTLA-4. Adoptive transfer of such T cells conferred unresponsiveness to allergen immunization and prevented the development of Der p 2-induced asthma. Functional Tr1-like cells can therefore be induced in vivo using retrovirally transduced B cells.

Mimotopes identify conformational B-cell epitopes on the two major house dust mite allergens Der p 1 and Der p 2.

House dust mite allergy occurs in 10-20% of the population. Improvement of the present immunotherapy requires detailed knowledge about the structure of the allergens. Mimotopes selected from phage peptide libraries imitate the conformational epitopes of a natural allergen. The aim of our study was to generate epitope mimics for the two major allergens of house dust mite. When the monoclonal anti-Der p 1 and anti-Der p 2 antibodies were used for biopannings, mimotopes were selected which bound also specific IgE from human allergic patients' sera. The conformational matching of these mimotopes on the 3D structure of the natural allergens determined discontinuous epitopes in both cases, representing conformational B-cell epitopes relevant for binding of human IgE. Therefore, these mimotopes are potential candidates for the directed induction of blocking antibodies and epitope-specific immunotherapy of mite allergy.

Factor VIII bypasses CD91/LRP for endocytosis by dendritic cells leading to T-cell activation.

BACKGROUND: The development of factor VIII (FVIII) inhibitors remains the major hurdle in the clinical management of patients with hemophilia A. FVIII uptake by professional antigen-presenting cells (APC) is the first step involved in initiation of immune responses to FVIII. Studies on FVIII catabolism have highlighted the role played by CD91/LRP as a potential target for increasing FVIII half-life in patients and prolonging treatment efficiency. We investigated the involvement of CD91 in FVIII endocytosis by human dendritic cells (DC), a model of professional APC. DESIGN AND METHODS: Immature DC were generated from circulating monocytes from healthy donors. Surface expression of CD91 was assessed by flow cytometry. Uptake of fluorescein isothiocyanate-conjugated ligands by immature DC was studied in the presence of various blocking agents. RESULTS: CD91 was expressed on approximately 20% of DC and mediated the internalization of its model ligand, alpha2-macroglobulin. DC internalized FVIII and activated a human FVIII-specific T-cell clone in a dose-dependent manner. FVIII uptake by DC and subsequent T-cell activation were not inhibited by receptor-associated protein. CONCLUSIONS: Our results indicate that CD91 and other members of the LDL receptor family are not strongly implicated in FVIII internalization by monocyte-derived DC, and suggest the involvement of alternative divalent ion-dependent endocytic receptors.

Corrigendum: Thioreductase-Containing Epitopes Inhibit the Development of Type 1 Diabetes in the NOD Mouse Model.

[This corrects the article DOI: 10.3389/fimmu.2016.00067.].

The prevalence of proteolytic antibodies against factor VIII in hemophilia A.

BACKGROUND: Factor VIII inhibitors are IgG alloantibodies that arise during replacement therapy in 25 to 50 percent of patients with severe hemophilia A. The hydrolysis of factor VIII by anti--factor VIII antibodies has been proposed as a mechanism of inactivation of factor VIII. METHODS: We purified IgG from patients with severe hemophilia A. The proteolytic activity of the antibodies was assessed by incubating the IgG with biotinylated human factor VIII and analyzing patterns of factor VIII cleavage by sodium dodecyl sulfate--polyacrylamide-gel electrophoresis and immunoblotting. The controls were normal human IgG and IgG purified from plasma of patients with hemophilia who did not have inhibitory antibodies. RESULTS: Significant proteolytic activity was detected in IgG from 13 of 24 inhibitor-positive patients. No hydrolytic activity was detected in control antibodies of IgG from patients without inhibitors. The rate of hydrolysis of factor VIII by purified IgG correlated positively with the factor VIII--neutralizing activity of IgG in plasma (r2=0.67, P=0.029). Principal-component analysis of migration profiles of digestion fragments demonstrated the heterogeneity of the catalytic potential of factor VIII inhibitors among patients. CONCLUSIONS: Proteolysis is a mechanism by which IgG antibodies against factor VIII can inactivate factor VIII.

Thioreductase-Containing Epitopes Inhibit the Development of Type 1 Diabetes in the NOD Mouse Model.

Autoreactive CD4(+) T cells recognizing islet-derived antigens play a primary role in type 1 diabetes. Specific suppression of such cells therefore represents a strategic target for the cure of the disease. We have developed a methodology by which CD4(+) T cells acquire apoptosis-inducing properties on antigen-presenting cells after cognate recognition of natural sequence epitopes. We describe here that inclusion of a thiol-disulfide oxidoreductase (thioreductase) motif within the flanking residues of a single MHC class II-restricted GAD65 epitope induces GAD65-specific cytolytic CD4(+) T cells (cCD4(+) T). The latter, obtained either in vitro or by active immunization, acquire an effector memory phenotype and lyse APCs by a Fas-FasL interaction. Furthermore, cCD4(+) T cells eliminate by apoptosis activated bystander CD4(+) T cells recognizing alternative epitopes processed by the same APC. Active immunization with a GAD65 class II-restricted thioreductase-containing T cell epitope protects mice from diabetes and abrogates insulitis. Passive transfer of in vitro-elicited cCD4(+) T cells establishes that such cells are efficient in suppressing autoimmunity. These findings provide strong evidence for a new vaccination strategy to prevent type 1 diabetes.

Suppression of Immune Response to Adenovirus Serotype 5 Vector by Immunization with Peptides Containing an MHC Class II Epitope and a Thio-Oxidoreductase Motif.

The main obstacle to viral vector-mediated gene therapy remains the elicitation of an immune response to the vector, resulting in clearance of transgene and resistance to further transgenesis. Specific antibody production contributes to such immune responses. A single class II-restricted epitope of adenovirus serotype 5 (Ad5) vector hexon-6 capsid protein containing a thiol-oxidoreductase motif was used in an attempt to prevent specific antibody production in response to Ad5 vectors. We demonstrate here that such immunization carried out before intravenous administration of Ad5 vectors prevents antibody production to the ensemble of Ad5 vector proteins in both BALB/c and C57BL/6 mice. The antibody response to Ad5 is dependent on innate immune activation, seemingly involving natural killer T (NKT) cells. We observed that immunization with a class II-restricted Ad5 peptide prevents such NKT cell activation. Increased transgenesis and prolonged transgene expression result from such immunization, providing a simple protocol for improving gene therapy.

MHC Class II-Restricted Epitopes Containing an Oxidoreductase Activity Prompt CD4(+) T Cells with Apoptosis-Inducing Properties.

Abrogating an unwanted immune response toward a specific antigen without compromising the entire immune system is a hoped-for goal in immunotherapy. Instead of manipulating dendritic cells and suppressive regulatory T cells, depleting effector T cells or blocking their co-stimulatory pathways, we describe a method to specifically inhibit the presentation of an antigen eliciting an unwanted immune reaction. Inclusion of an oxidoreductase motif within the flanking residues of MHC class II epitopes polarizes CD4(+) T cells to cytolytic cells capable of inducing apoptosis in antigen presenting cells (APCs) displaying cognate peptides through MHC class II molecules. This novel function results from an increased synapse formation between both cells. Moreover, these cells eliminate by apoptosis bystander CD4(+) T cells activated at the surface of the APC. We hypothesize that they would thereby block the recruitment of cells of alternative specificity for the same autoantigen or cells specific for another antigen associated with the pathology, providing a system by which response against multiple antigens linked with the same disease can be suppressed. These findings open the way toward a novel form of antigen-specific immunosuppression.

Efficiency of onco-retroviral and lentiviral gene transfer into primary mouse and human B-lymphocytes is pseudotype dependent.

B lymphocytes are attractive targets for gene therapy of genetic diseases associated with B-cell dysfunction and for immunotherapy. Transduction of B lymphocytes was evaluated using green fluorescent protein (GFP)-encoding onco-retroviral and HIV-derived lentiviral vectors which were pseudotyped with ecotropic, amphotropic or vesicular stomatitis virus (VSV-G) envelopes. Transduction of mouse B lymphocytes activated with lipopolysaccharides (LPS) or by cross-linking CD40 in conjunction with interleukin-4 (IL-4) was significantly more efficient (p < 0.003) with ecotropic (11%) than with VSV-G pseudotyped onco-retroviral vectors (1%). Using high-titer cell-free ecotropic viral supernatant or by coculture with ecotropic onco-retroviral vector-producing cells, transduction efficiency increased significantly (p < 0.001) to approximately 50%, whereas transduction efficiency by coculture with VSV-G pseudotyped vector-producing cells remained low (< 2%). Similarly, transduction of mouse B lymphocytes was significantly more efficient (twofold, p < 0.01) with the ecotropic (7%) than with the VSV-G pseudotyped lentiviral vectors although gene transfer efficiency remained low because of dose-limiting toxicity of the concentrated vector preparations on the LPS-activated murine B cells. Consistent with murine B-cell transduction, human B cells activated with CD40L and IL-4 were also found to be relatively refractory to VSV-G pseudotyped onco-retroviral vectors (< 1%). However, higher transduction efficiencies could be achieved in activated primary human B lymphocytes using VSV-G pseudotyped lentiviral vectors instead (5%-6%). Contrary to the significant increase in mouse B-cell transduction efficiency with ecotropic vectors, the use of amphotropic onco-retroviral or lentiviral vectors did not increase transduction efficiency in primary human B cells. The present study shows that the transduction efficiency of onco-retroviral and lentiviral vectors in human and mouse B lymphocytes is pseudotype-dependent and challenges the widely held assumption that VSV-G pseudotyping facilitates gene transfer into all cell types.

Von Willebrand factor modulates factor VIII immunogenicity: comparative study of different factor VIII concentrates in a haemophilia A mouse model.

The development of an immune response towards factor VIII (FVIII) remains the major complication of haemophilia A replacement therapy. Product-related risk factors have recently been identified on the basis of epidemiological studies, but the mechanism is not understood. To this end, various commercially available FVIII concentrates were administered by the IV route to FVIII-knockout mice and the resulting immune response was characterised. Significantly higher inhibitor titres (Bethesda assay) were observed for one recombinant FVIII and one plasma-derived FVIII product depleted in von Willebrand factor (VWF). Inhibitor titres were reduced upon pre-incubation of FVIII with purified VWF. Epitope specificity of anti-FVIII IgG was characterised using FVIII-fragments produced in E. coli. Concentrates with no or reduced VWF-level elicited antibodies recognising predominantly the acidic a1 and a3 regions. Addition of VWF prior to injection also modified the epitope specificity. FVIII concentrates, therefore, show qualitative and quantitative variations in immunogenicity, which are at least partly modulated by VWF.

Anti-heavy-chain monoclonal antibodies directed to the acidic regions of the factor VIII molecule inhibit the binding of factor VIII to phospholipids and von Willebrand factor.

Recent studies have shown that inhibitors develop against acidic regions of the FVIII molecule, which contain important functional sites. However, their mechanisms of inhibition are not well understood. In this study, two anti-human FVIII mouse monoclonal antibodies (MAbs), directed towards the exposed acidic regions of the FVIII molecule, were developed, characterised and their mechanisms of inhibition investigated. The two MAbs, F7B4 and F26F6, had inhibitory titres of 32 and 944 BU/mg respectively, had high affinities for the FVIII molecule (K(D) approximately nM range) and recognised sequences V(357)-F(360) on the acidic a1 region and E(724)-L(731) on the acidic a2 region of the FVIII heavy-chain (HC), respectively. F7B4 inhibited the rate of FXa generation by activated FVIII, whilst both antibodies inhibited FVIII activation by thrombin and blocked thrombin cleavage of FVIII. Furthermore, F7B4 and F26F6 inhibited FVIII binding to (a) phospholipids (IC(50): 77 nM and 40 nM respectively), and (b) VWF (IC(50): 93 nM and 267 nM respectively), despite both having HC specificity. Experiments with F(ab')(2) fragments confirmed the above findings. Taken together these data represent novel findings in that anti-acidic HC antibodies can inhibit FVIII function by a variety of mechanisms, in particular by interfering with the binding of FVIII to phospholipids & VWF.

Epitope specificity of anti-FVIII antibodies during immune tolerance therapy with factor VIII preparation containing von Willebrand factor.

The study aimed at characterizing the putative changes in the epitope specificity of anti-FVIII antibodies during a successful immune tolerance treatment of the haemophilia A patient with the factor VIII (FVIII) preparation containing the von Willebrand factor (VWF). At the beginning of treatment, anti-FVIII inhibitory antibodies recognizing predominantly the light chain of FVIII were prevalent and persisted throughout the treatment. More detailed characterization of the FVIII antibody epitope specificity by using GST-fusion proteins corresponding to different FVIII domains revealed the prevalence of C1-domain-specific antibodies, while a remarkably lower amount of antibodies were targeted at the C2 and the a3 domains of the FVIII light chain and towards the A2 and the A1 domain of the FVIII heavy chain. The epitope specificity of antibodies remained rather unchanged throughout treatment except the elevated level of C2-domain-specific FVIII antibodies after a temporary interruption of treatment. The patient's antibodies were unable to interfere with the FVIII binding to VWF or to phospholipids, but inhibited FXa generation and the binding of FX to FVIII on the phospholipid monolayer. Thus, a unique pattern of the epitope specificity of FVIII antibodies and the mechanism to inhibit FVIII:C activity by FVIII-light-chain-specific antibodies were characterized.