De novo identification of cell-type specific antibody-antigen pairs by phage display subtraction

Obligate Multivalent Recognition of Cell Surface Tomoregulin following Selection from a Multivalent Phage Antibody Library

A therapeutic antibody candidate (AT-19) isolated using multivalent phage display binds native tomoregulin (TR) as a mul-timer not as a monomer. This report raises the importance of screening and selecting phage antibodies on native antigen and reemphasizes the possibility that potentially valuable antibodies are discarded when a monomeric phage display system is used for screening. A detailed live cell panning selection and screening method to isolate multivalently active antibodies is described. AT-19 is a fully human antibody recognizing the cell surface protein TR, a proposed prostate cancer target for therapeutic antibody internalization. AT-19 was isolated from a multivalent single-chain variable fragment (scFv) antibody library rescued with hyperphage. The required multivalency for isolation of AT-19 is supported by fluorescence activated cell sorting data demonstrating binding of the multivalent AT-19 phage particles at high phage concentrations and failure of monovalent particles to bind. Pure monomeric scFv AT-19 does not bind native receptor on cells, whereas dimeric scFv or immunoglobulin G binds with nanomolar affinity. The isolation of AT-19 antibody with obligate bivalent binding activity to native TR is attributed to the use of a multivalent display of scFv on phage and the method for selecting and screening by alternate use of 2 recombinant cell lines.

Synthetic antibodies: concepts, potential and practical considerations

The last 100 years of enquiry into the fundamental basis of humoral immunity has resulted in the identification of antibodies as key molecular sentinels responsible for the in vivo surveillance, neutralization and clearance of foreign substances. Intense efforts aimed at understanding and exploiting their exquisite molecular specificity have positioned antibodies as a cornerstone supporting basic research, diagnostics and therapeutic applications [1]. More recently, efforts have aimed to circumvent the limitations of developing antibodies in animals by developing wholly in vitro techniques for designing antibodies of tailored specificity. This has been realized with the advent of synthetic antibody libraries that possess diversity outside the scope of natural immune repertoires and are thus capable of yielding specificities not otherwise attainable. This review examines the convergence of technologies that have contributed to the development of combinatorial phage-displayed antibody libraries. It further explores the practical concepts that underlie phage display, antibody diversity and the methods used in the generation of and selection from phage-displayed synthetic antibody libraries, highlighting specific applications in which design approaches gave rise to specificities that could not easily be obtained with libraries based upon natural immune repertories.

Kinetin-induced differentiation of normal human keratinocytes undergoing aging in vitro

Kinetin (N(6)-furfuryladenine) is a cytokinin growth factor having several anti-aging effects reported for human cells and fruit flies. We have observed that short-term culturing of human keratinocytes in the presence of 40 to 200 microM kinetin results in a significant inhibition of cell growth. Studies were undertaken to analyze the process of differentiation as a reason for growth inhibition. Keratinocytes at different passage levels were treated with fetal calf serum (FCS) and calcium as differentiation-inducing positive controls, with different concentrations of kinetin, and with a combination of kinetin and calcium. The induction and progression of differentiation was monitored by morphological observations and by using several differentiation markers, including keratins (K10 and K14), involucrin, epidermal transglutaminase, and some new keratinocyte-specific antibodies isolated by the phage display method. In young keratinocytes, two days of calcium treatment reduced the K14 level by 78%, and increased the levels of K10 and involucrin by 40% and 29%, respectively. In comparison, 40 microM kinetin had no effect on the K14 level, but increased the K10 level by 28% and that of involucrin by four-fold. The combination of calcium and 40 microM kinetin led to a decrease by 23% in the K14 level, to an increase in the level of K10 by 55%, and to a two-fold rise in the involucrin level. These results suggest that the rate, extent, and quality of differentiation depend on the inducing agent, and that kinetin may be useful in promoting the differentiation of human keratinocytes, especially in the presence of calcium.

A Novel Subtractive Antibody Phage Display Method to Discover Disease Markers

Today's research demands fast identification of potential diagnostic and therapeutic targets. We describe a novel phage display strategy to identify disease-related proteins that are specifically expressed in a certain (diseased) tissue or cells. Phages displaying antibody fragments are selected on complex protein mixtures in a two-step manner combining subtractive selection in solution with further enrichment of specific phages on two-dimensional Western blots. Targets recognized by the resulting recombinant antibodies are immunoaffinity-purified and identified by mass spectrometry. We used antibody fragment libraries from autoimmune patients to discover apoptosis-specific and disease-related targets. One of the three identified targets is the U1-70K protein, a marker for systemic lupus erythematosus overlap disease. Interestingly the epitope on U1-70K recognized by the selected recombinant antibody was shown to be apoptosis-dependent, and such epitopes are believed to be involved in breaking tolerance to self-antigens. The other two proteins were identified as polypyrimidine tract-binding protein-associated splicing factor (PSF)/nuclear RNA- and DNA-binding protein of 54 kDa (p54nrb) and heterogeneous ribonucleoprotein C.

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.

Isolation of monoclonal antibodies recognizing rare and dominant epitopes in plant vascular cell walls by phage display subtraction

A combination of phage display antibody technology and a subtraction method provides a powerful tool for the isolation of novel biomarkers. However, the dilemma that high stringency screening often reduces the diversity in the subtracted phage antibody repertoires and that it is difficult to isolate phage antibody against rare epitopes remain. Therefore, we carefully monitored the occupancy of differentiation-specific clones in a phage antibody library through an enrichment process, and succeeded in isolating monoclonal antibodies against rare and dominant epitopes in plant vascular cell walls. We also report that clones with stop and frameshift mutations significantly survived the enrichment process, owing to noncanonical translation mechanisms.