Identification of phage antibodies toward the Werner protein by selection on Western blots

Epsilon haemoglobin specific antibodies with applications in noninvasive prenatal diagnosis

Invasive procedures for prenatal diagnosis are associated with increased risk of abortion; thus, development of noninvasive procedures would be beneficial. Based on the observation that embryonic nucleated red blood cell (NRBC) crosses the placenta and enters the circulation of pregnant women, the ability to identify such cell would allow development of such procedures. Identification of NRBCs in blood samples would be possible provided that specific antibodies are available. Here we have isolated recombinant antibodies using phage display. From the panel of antibody fragments specifically recognising epsilon-Hb, one was chosen for further characterization, DAb1. DAb1 binds to epsilon-Hb both in Western blots and immunocytochemistry. Several epsilon-Hb positive cells were detected in a blood sample taken as postchorionic villus sampling (CVS). To evaluate the sensitivity of the method, K562 cells (which express epsilon-Hb) were spiked in a blood sample followed by staining in solution and FACS analysis.

Multivalent scFv Display of Phagemid Repertoires for the Selection of Carbohydrate-specific Antibodies and its Application to the Thomsen–Friedenreich Antigen

The Thomsen-Friedenreich disaccharide (TF) is a promising target antigen for tumor immunotherapy, since it is almost exclusively expressed in carcinoma tissues. The TF-specific antibodies generated so far are IgMs of mouse origin with limited therapeutic potential. Phage-displayed scFv repertoires are an established source for recombinant antibodies; however, we were unable to identify scFvs binding to TF when applying libraries in the standard monovalent display format of phagemid systems. Here, we report on the successful selection of TF-specific antibody fragments using a multivalent scFv phagemid library format based on shortened linkers (one amino acid residue). The libraries were constructed from mice immunized with asialoglycophorin and selected using TF displayed on two different carrier molecules in combination with the proteolytically cleavable helper phage KM13. All isolated clones encoded the same framework genes and the same complementarity-determining regions. After affinity maturation only scFv with the founder sequence were selected from secondary repertoires. This indicates a very narrow sequence window for TF-specific antibodies. Investigating other linker-length formats revealed a clear inverse correlation between linker length and binding activity both as soluble proteins and displayed on phages. The highest affinity was obtained with the tetrameric format. The selected scFv was specific for TF on various carrier molecules and tumor cells and performed well in ELISA and immunohistochemistry. We postulate that scFv phagemid library formats with short linkers (i.e. multimeric scFvs) may, in general, be advantageous in selections for the generation of scFvs against carbohydrate epitopes or other epitopes associated with low intrinsic affinity per binding site), and expect that they will be superior in applications for diagnosis or therapy.

Identification of keratinocyte-specific markers using phage display and mass spectrometry

Specific molecular markers for various normal and pathogenic cell states and cell types provide knowledge of basic biological systems and have a direct application in targeted therapy. We describe a proteomic method based on the combination of new and improved phage display antibody technologies and mass spectrometry that allows identification of cell type-specific protein markers. The most important features of the method are (i) reduction of experimental noise originating from background binding of phage particles and (ii) isolation of affinity binders after a single round of selection, which assures a high diversity of binders. The method demonstrates, for the first time, the ability to detect, identify, and analyze both secreted and membrane-associated extracellular proteins as well as a variety of different cellular structures including proteins and carbohydrates. The optimized phage display method was applied to analysis of human skin keratinocytes resulting in the isolation of a panel of antibodies. Fourteen of these antibodies were further characterized, half of which predominantly recognized keratinocytes in a screen of a range of different cell types. Three cognate keratinocyte antigens were subsequently identified by mass spectrometry as laminin-5, plectin, and fibronectin. The combination of phage display technology with mass spectrometry methods for protein identification is a general and promising approach for proteomic analysis of cell surface complexity.

Selection of large diversities of antiidiotypic antibody fragments by phage display

Antiidiotypic antibodies (Ab2) are needed as tools for a better understanding of molecular mimicry and the immunological network, and for many potential applications in the biomedical and pharmaceutical field. Antiidiotypic antibodies mimicking carbohydrate or conformational epitopes (Ab2beta) are of considerable interest as surrogate immunogens for cancer vaccination. However, it has so far been difficult and tedious to produce Ab2s to a given antigen. Here we describe a fast and reliable technique for generating large diversities of antiidiotypic single chain antibody fragments from non-immunized phagemid libraries using phage display. Key elements are a specific elution with the original antigen followed by trypsin treatment of the eluted phages in combination with the protease sensitive helperphage KM13. This novel method was compared with various conventional selection and elution methods, including, specific elution with or without trypsin treatment, elution with glycine at pH 2.2 with or without trypsin treatment, and elution by trypsin treatment only. The results clearly show that specific elution in combination with trypsin treatment of the eluted phages is by far superior to the other conventional methods, enabling for the first time the generation of a large variety of Ab2s after only two to three rounds of selection, thereby maintaining maximum diversity. We obtained 28 to 88 antiidiotypes out of 96 tested clones after two to three rounds of selection with a diversity of 55-90 %. This was achieved for two carbohydrate (di-, and tetrasaccharides) and one conformational protein epitope using two large naïve libraries and their corresponding monoclonal Ab1. The antiidiotypic nature of the selected scFv-phages was verified by ELISA and immunocytochemistry inhibition experiments.

High-throughput antibody isolation

To define the proteome of an organism, there is a need for robust and reproducible methods for the quantitative detection of all the polypeptides in a cell. High-density arrays of receptors specific for each of the polypeptides in a complex sample hold great promise for the analysis of complex protein mixtures. Because of their high affinity, specificity and their ability to bind to virtually any protein, antibodies appear particularly promising as the receptor element in protein-detection arrays. For proteomic-scale analyses, the ability to isolate and produce antibodies en masse to large numbers of target molecules is critical. A variety of systems for the high-throughput isolation of antibodies from combinatorial libraries are being developed and are outlined in this review. However, there are several other important considerations to be borne in mind before such systems can realistically be applied on a large scale.