Inhibition of antigen-induced mediator release from IgE-sensitized cells by a monoclonal anti-Fc epsilon RI alpha-chain receptor antibody: implications for the involvement of the membrane-proximal alpha-chain region in Fc epsilon RI-mediated cell activation

Controlled antibody/(bio-) conjugation of inorganic nanoparticles for targeted delivery

Arguably targeting is one of the biggest problems for controlled drug delivery. In the case that drugs can be directed with high efficiency to the target tissue, side effects of medication are drastically reduced. Colloidal inorganic nanoparticles (NPs) have been proposed and described in the last 10years as new platforms for in vivo delivery. However, though NPs can introduce plentiful functional properties (such as controlled destruction of tissue by local heating or local generation of free radicals), targeting remains an issue of intense research efforts. While passive targeting of NPs has been reported (the so-called enhanced permeation and retention, EPR effect), still improved active targeting would be highly desirable. One classical approach for active targeting is mediated by molecular recognition via capture molecules, i.e. antibodies (Abs) specific for the target. In order to apply this strategy for NPs, they need to be conjugated with Abs against specific biomarkers. Though many approaches have been reported in this direction, the controlled bioconjugation of NPs is still a challenge. In this article the strategies of controlled bioconjugation of NPs will be reviewed giving particular emphasis to the following questions: 1) how can the number of capture molecules per NP be precisely adjusted, and 2) how can the Abs be attached to NP surfaces in an oriented way. Solution of both questions is a cornerstone in controlled targeting of the inorganic NPs bioconjugates.

DARPins as bispecific receptor antagonists analyzed for immunoglobulin E receptor blockage

The concept of multispecific antibodies is of high therapeutic interest but has failed to produce pharmaceutical products due to the poor biophysical properties of such molecules. Here, we propose an alternative and simple way to generate bispecific binding molecules using designed ankyrin repeat proteins (DARPins). For this purpose, monovalent DARPins with different epitope specificities were selected against the alpha chain of the high-affinity receptor for human immunoglobulin E (IgE) (FcepsilonRIalpha). Two of the isolated binders interfering with IgE binding to the receptor were joined to each other or to themselves via a flexible protein linker. The resulting bivalent and bispecific DARPins were tested for their ability to prevent allergen-induced cell degranulation using rat basophilic leukemia cells stably transfected with human FcepsilonRIalpha. The bispecific DARPin construct was the most potent one, efficiently blocking the IgE-FcepsilonRI interaction and preventing the release of proinflammatory mediators. Noteworthy, the multivalent and multispecific DARPin construct did not show any alteration of the beneficial biophysical properties of the monovalent parental DARPins. Hence, bispecific DARPins may be used to generate receptor antagonists simultaneously targeting different epitopes on the same molecule. Moreover, they easily overcome the limiting immunoglobulin binding paradigm (one binding molecule=one epitope) and thereby represent an alternative to monoclonal antibodies in cases where the immunoglobulin scaffold is unsuitable.

Protection of IgE-mediated allergic sensitization by active immunization with IgE loops constrained in GFP protein scaffold

Green fluorescent protein (GFP) exhibits a rigid central beta-barrel, formed by eleven beta-strands with floppy loops spanning between the stands. Herein, we evaluate whether the rigid beta-barrel may serve as a scaffold that can constrain the loops of a foreign protein, and thus its antigenicity. The spanning loops, site 6 of GFP, were engineered with RE cloning sites for inserting oligonucleotides corresponding to FcepsilonRI-binding sequence of human IgE. In a high-throughput format, shortened oligonucleotides encoding eight amino acid residues of the receptor-binding regions were inserted into site 6 of GFP by PCR, followed by enabling sequences for in vitro transcription and translation at the 5' end. Antigenized C2-3 linker (C2-3L) was shown by immuno-blots with polyclonal anti-IgE under native gel electrophoresis and transfer. Recombinant antigenized GFP was expressed and purified to homogeneity by metal affinity column, followed by Sephacryl S-200 high resolution gel filtration. Hyperimmune sera from mice immunized with C2-3L antigenized GFP contain anti-IgE reactive with JW8 murine/human chimeric IgE. Further, elevated serum anti-C2-3L and affinity pure antibodies effectively inhibits binding of JW8 IgE to recombinant FcepsilonRIalpha, and desensitizes JW8 to rat RBL-2H3 transfected with human FcepsilonRIalpha. This observation raised the possibility that active IgE vaccine may be employed in raising active protective anti-IgE in allergic patients as an alternative to passive immunization with MAb-E25 anti-IgE. Taken together, GFP appears suitable protein scaffold for spanning/constraining the C2-3L of human IgE as active vaccine; and this technique may be generally employed for eliciting antibodies to specific B-cell epitopes of other proteins.

Inhibition of human cord blood-derived mast cell responses by anti-Fc epsilon RI mAb 15/1 versus anti-IgE Omalizumab

Aggregation of the alpha-chain of the high affinity IgE receptor (Fc epsilon RI alpha) on mast cells or basophils after cross-linking of receptor-bound IgE by its antigen or an anti-IgE antibody results in cell activation and release of inflammatory mediators. Omalizumab (Xolair), Novartis Pharmaceuticals; Genentech Inc.) is a recombinant humanized anti-IgE mAb developed for the treatment of severe allergic asthma. It complexes with free serum IgE, which prevents its binding to Fc epsilon RI and thereby interrupts the allergic cascade. Administration of an inhibitory anti-Fc epsilon RI alpha mAb may represent an alternative strategy to neutralize IgE-mediated receptor activation. In the present report, for the first time, we have performed direct side of side comparison between the inhibitory anti-Fc epsilon RI alpha mAb designated 15/1 and Omalizumab for their effects on human cord blood-derived mast cells. We provide the first evidence that both 15/1 mAb and Omalizumab efficiently inhibit Fc epsilon RI-mediated human mast cell responses in vitro (degranulation, activation, release of IL-8 and IL-13, phosphorylation of Akt) and that mAb 15/1 is a non-anaphylactogenic antibody, which compared to Omalizumab, displays markedly higher inhibitory potency in the presence of high IgE levels.

Different stabilities of the structurally related receptors for IgE and IgG on the cell surface are determined by length of the stalk region in their alpha-chains

A variant of the high affinity IgE receptor FcepsilonRI, which is composed of alpha- and gamma-chains without the beta-chain, is expressed on human APC, such as dendritic cells, and has been suggested to facilitate Ag uptake through IgE and hence to facilitate Ag presentation to T cells. The level of FcepsilonRI on these cells is correlated with the serum IgE concentration, suggesting IgE mediates the up-regulation of the alphagamma2-type FcepsilonRI. The IgE-mediated FcepsilonRI up-regulation on mast cells and basophils has been shown to enhance the ability of these cells to release chemical mediators and cytokines that are responsible for allergic inflammatory reactions. Here, to elucidate the mechanism controlling FcepsilonRI expression, we compared two structurally related Ig receptors, human FcepsilonRI and FcgammaRIIIA, which carry different alpha-chains but the same gamma-chains. The half-life of FcepsilonRI on the cell surface was short unless it bound IgE, whereas FcgammaRIIIA was stably expressed without IgG binding. Shuffling of the non Ig-binding portions of the FcepsilonRIalpha and FcgammaRIIIAalpha chains revealed that the stalk region was critical in determining the difference in their stability and ligand-induced up-regulation. Unexpectedly, analyses with added or deleted amino acids in the stalk region strongly suggested that the length rather than the amino acid sequence of the stalk region was of major importance in determining the different stabilities of FcepsilonRI and FcgammaRIIIA on the cell surface. This finding provides new insights into the mechanism regulating surface FcepsilonRI expression.

A high-affinity natural autoantibody from human cord blood defines a physiologically relevant epitope on the FcepsilonRIalpha

Natural Abs represent the indigenous immune repertoire and are thus present at birth and persist throughout life. Previously, human autoantibodies to the alpha domain of the high-affinity IgE receptor (FcepsilonRIalpha) have been isolated from Ab libraries derived from normal donors and patients with chronic urticaria. To investigate whether these anti-FcepsilonRIalpha Abs are present in the germline repertoire, we constructed a phage Fab display library from human cord blood, which represents the naive immune repertoire before exposure to exogenous Ags. All isolated clones specific to the FcepsilonRIalpha had the same sequence. This single IgM Ab, named CBMalpha8, was strictly in germline configuration and had high affinity and functional in vitro anaphylactogenic activity. Inhibition experiments indicated an overlapping epitope on the FcepsilonRIalpha recognized by both CBMalpha8 and the previously isolated anti-FcepsilonRIalpha Abs from autoimmune and healthy donors. This common epitope on FcepsilonRIalpha coincides with the binding site for IgE. Affinity measurements demonstrated the presence of Abs showing CBMalpha8-like specificity, but with a significantly lower affinity in i.v. Ig, a therapeutic multidonor IgG preparation. We propose a hypothesis of escape mutants, whereby the resulting lower affinity IgG anti-FcepsilonRIalpha Abs are rendered less likely to compete with IgE for binding to FcepsilonRIalpha.

A Highly Conserved Interspecies V H in the Human Genome

Idiotype conservation between human and mouse antibodies has been observed in association with various infectious and autoimmune diseases. We have isolated a human anti-idiotypic antibody to a mouse monoclonal anti-IgE antibody (BSW17) suggesting a conserved interspecies idiotype associated with an anti-IgE response. To find the homologue of BSW17 in the human genome we applied the guided selection strategy. Combining V(H) of BSW17 with a human V(L) repertoire resulted in three light chains. The three V(L) chains were then combined with a human V(H) repertoire resulting in three clones specific for human IgE. Surprisingly, one clone, Hu41, had the same epitope specificity and functional in vitro activity as BSW17 and V(H) complementarity-determining regions identical with that of BSW17. Real-time PCR analysis confirmed the presence of the Hu41 V(H) sequence in the human genome. These data document the first example of the isolation of a human antibody where high sequence similarity to the original murine V(H) sequence is associated with common antigen and epitope specificity.

Comparative effects of human Ig alpha and Ig beta in inducing autoreactive antibodies against B cells in mice

Human and mouse Ig alpha molecules share only 58% amino acid sequence identity in their extracellular regions. However, mice immunized with a recombinant Fc fusion protein containing the extracellular portion of human Ig alpha produced significant amounts of IgG capable of binding to Ig alpha on mouse B cells. The induced auto/cross-reactive Abs could down-regulate B cell levels and the consequent humoral immune responses against an irrelevant Ag in treated mice. Analogous immunization with an Fc fusion protein containing the extracellular portion of human Ig beta gave a much weaker response to mouse Ig beta, although human and mouse Ig beta, like their Ig alpha counterparts, share 56% sequence identity in their extracellular regions. Protein sequence analyses indicated that a potential immunogenic segment, located at the C-terminal loop of the extracellular domain, has an amino acid sequence that is identical between human and mouse Ig alpha. A mAb A01, which could bind to both human and mouse Ig alpha, was found to be specific to a peptide encompassing this immunogenic segment. These findings suggest that specific auto/cross-reactivity against self Ig alpha can be induced by a molecular mimicry presented by a foreign Ig alpha.

Survey of the year 2001 commercial optical biosensor literature

We have assembled references of 700 articles published in 2001 that describe work performed using commercially available optical biosensors. To illustrate the technology's diversity, the citation list is divided into reviews, methods and specific applications, as well as instrument type. We noted marked improvements in the utilization of biosensors and the presentation of kinetic data over previous years. These advances reflect a maturing of the technology, which has become a standard method for characterizing biomolecular interactions.