Effects of IgG and its F(ab')2 fragments of some patients with idiopathic thrombocytopenic purpura on platelet aggregation

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Development and implementation of a novel immune thrombocytopenia bleeding score for dogs

Background

A method of quantifying clinical bleeding in dogs with immune thrombocytopenia (ITP) is needed because ITP patients have variable bleeding tendencies that inconsistently correlate with platelet count. A scoring system will facilitate patient comparisons and allow stratification based on bleeding severity in clinical trials.

Hypothesis/Objectives

To develop and evaluate a bleeding assessment tool for dogs, and a training course for improving its consistent implementation.

Animals

Client‐owned dogs (n = 61) with platelet counts <50,000/μL; 34 classified as primary ITP, 17 as secondary ITP, and 10 as non‐ITP.

Methods

A novel bleeding assessment tool, DOGiBAT, comprising bleeding grades from 0 (none) to 2 (severe) at 9 anatomic sites, was developed. Clinicians and technicians completed a training course and quiz before scoring thrombocytopenic patients. The training course was assessed by randomizing student volunteers to take the quiz with or without prior training. A logistic regression model assessed the association between training and quiz performance. The correlation of DOGiBAT score with platelet count and outcome measures was assessed in the thrombocytopenic dogs.

Results

Clinicians and technicians consistently applied the DOGiBAT, correctly scoring all quiz cases. The odds of trained students answering correctly were higher than those of untrained students (P < .0001). In clinical cases, DOGiBAT score and platelet count were inversely correlated (r_s = −0.527, P < .0001), and DOGiBAT directly correlated with transfusion requirements (r_s = 0.512, P < .0001) and hospitalization duration (r_s = 0.35, P = .006).

Conclusions and Clinical Importance

The DOGiBAT and assessment quiz are simple tools to standardize evaluation of bleeding severity. With further validation, the DOGiBAT may provide a clinically relevant metric to characterize ITP severity and monitor response in treatment trials.

Antibody Engineering for Pursuing a Healthier Future

Since the development of antibody-production techniques, a number of immunoglobulins have been developed on a large scale using conventional methods. Hybridoma technology opened a new horizon in the production of antibodies against target antigens of infectious pathogens, malignant diseases including autoimmune disorders, and numerous potent toxins. However, these clinical humanized or chimeric murine antibodies have several limitations and complexities. Therefore, to overcome these difficulties, recent advances in genetic engineering techniques and phage display technique have allowed the production of highly specific recombinant antibodies. These engineered antibodies have been constructed in the hunt for novel therapeutic drugs equipped with enhanced immunoprotective abilities, such as engaging immune effector functions, effective development of fusion proteins, efficient tumor and tissue penetration, and high-affinity antibodies directed against conserved targets. Advanced antibody engineering techniques have extensive applications in the fields of immunology, biotechnology, diagnostics, and therapeutic medicines. However, there is limited knowledge regarding dynamic antibody development approaches. Therefore, this review extends beyond our understanding of conventional polyclonal and monoclonal antibodies. Furthermore, recent advances in antibody engineering techniques together with antibody fragments, display technologies, immunomodulation, and broad applications of antibodies are discussed to enhance innovative antibody production in pursuit of a healthier future for humans.

Study of a humanized inhibitory anti-platelet glycoprotein VI phage antibody from a phage antibody library

Objective The aims of the study were to study the effect of anti-platelet glycoprotein (GP) VI auto-antibodies on platelet aggregation and use phage surface display technology to produce anti-platelet GPVI phage antibody fragment, which may be developed to inhibit platelet aggregation in the treatment of cardiovascular disease. Methods Plasma samples from patients with immune thrombocytopenia (ITP) were screened by monoclonal antibody immobilization of the platelet antigen assay and the platelet aggregation test for anti-platelet GPVI auto-antibody with an inhibitory effect. The humanized anti-platelet GPVI phage antibody was produced by phage surface display technology. The function of the phage antibody fragment against platelet aggregation was examined by the platelet aggregation test. Results Of 726 ITP patients, 2 (0.27%) patients' plasma significantly inhibited platelet aggregation induced by collagen-1. After five rounds of selection, enrichment, and purification, a soluble phage antibody fragment was produced, which can inhibit platelet aggregation induced by collagen-1. The results demonstrate that only a few of the screened anti-platelet GPVI auto-antibodies showed an inhibitory effect on platelet aggregation. Discussion A completely humanized anti-GPVI soluble phage antibody can be produced by phage surface display technology. The antibody was able to specifically block collagen-induced platelet aggregation without influencing the aggregation responses to other agonists. Conclusions Results of the present study suggest that very few anti-platelet GPVI auto-antibodies inhibit the aggregation function of platelet. The humanized anti-platelet GPVI produced by phage surface display technology is promising to be used to inhibit platelet aggregation in the treatment of cardiovascular disease.

Phage display--a powerful technique for immunotherapy: 1. Introduction and potential of therapeutic applications

One of the most effective molecular diversity techniques is phage display. This technology is based on a direct linkage between phage phenotype and its encapsulated genotype, which leads to presentation of molecule libraries on the phage surface. Phage display is utilized in studying protein-ligand interactions, receptor binding sites and in improving or modifying the affinity of proteins for their binding partners. Generating monoclonal antibodies and improving their affinity, cloning antibodies from unstable hybridoma cells and identifying epitopes, mimotopes and functional or accessible sites from antigens are also important advantages of this technology. Techniques originating from phage display have been applied to transfusion medicine, neurological disorders, mapping vascular addresses and tissue homing of peptides. Phages have been applicable to immunization therapies, which may lead to development of new tools used for treating autoimmune and cancer diseases. This review describes the phage display technology and presents the recent advancements in therapeutic applications of phage display.

Antiaggregatory and proangiogenic effects of a novel recombinant human dual specificity anti-integrin antibody

BACKGROUND

beta(3)-Integrins are involved in platelet aggregation via alpha(IIb)beta(3) [glycoprotein (GP)IIb-GPIIIa], and in angiogenesis via endothelial alpha(V)beta(3). Cross-reactive ligands with antiaggregatory and proangiogenic effects, both desirable in peripheral vasculopathies, have not yet been described.

OBJECTIVES

In vitro and in vivo characterization of antiaggregatory and proangiogenic effects of two recombinant human Fab fragments, with emphasis on beta(3)-integrins.

METHODS

Recombinant Fab fragments were obtained by phage display technology. Specificity, affinity and IC(50) were determined by immunodot assays, enzyme-linked immunosorbent assay (ELISA), and Scatchard plot analysis, and by means of human umbilical vein endothelial cells (HUVECs). Functional analyses included ELISA for interaction with fibrinogen binding to GPIIb-GPIIIa, flow cytometry for measurement of activation parameters and competitive inhibition experiments, human platelet aggregometry, and proliferation, tube formation and the chorioallantoic membrane (CAM) assay for measurement of angiogenic effects.

RESULTS

We observed specific and high-affinity binding to an intact GPIIb-GPIIIa receptor complex of two human Fab autoantibody fragments, with no platelet activation. Dose-dependent fibrinogen binding to GPIIb-GPIIIa and platelet aggregation were completely inhibited. One Fab fragment was competitively inhibited by abciximab and its murine analog monoclonal antibody (mAb) 7E3, whereas the other Fab fragment bound to cultured HUVECs, suggesting cross-reactivity with alpha(V)beta(3), and also demonstrated proangiogenic effects in tube formation and CAM assays.

CONCLUSIONS

These Fab fragments are the first entirely human anti-GPIIb-GPIIIa Fab fragments with full antiaggregatory properties; furthermore, they do not activate platelets. The unique dual-specificity anti-beta(3)-integrin Fab fragment may represent a new tool for the study and management of peripheral arterial vasculopathies.

Platelet function to estimate the bleeding risk in autoimmune thrombocytopenia

BACKGROUND

Knowledge of platelet function may assist in patient care in chronic autoimmune thrombocytopenia (cAITP).

MATERIALS AND METHODS

We evaluated the association of platelet function with haemorrhage in 41 patients, median age 41 years (range 14-82 years, 24 females) with chronic autoimmune thrombocytopenia (cAITP). Samples were investigated for platelet P-selectin, and adhesion and aggregate formation under high shear conditions. Data were compared to those from 28 healthy controls (median age 39 years, range 23-70 years, 17 females) and correlated with a bleeding score of 0 (no bleeding) to 3 (overt mucosal bleedings).

RESULTS

P-selectin levels were higher in patients than in controls (P < 0.0004). Compared to controls, the patients' samples responded to high shear with decreased adhesion to the polystyrene surface (P < 0.0001), but formed aggregates of normal size. P-selectin expression was neither correlated with platelet counts, nor platelet adhesion, nor the bleeding score. Only the size of formed aggregates correlated with P-selectin (P = 0.01). Platelet counts (odds ratio 0.5, 95% confidence interval 0.22-0.88; P = 0.04) and adhesion (odds ratio 0.45, 95% confidence interval 0.17-0.87; P = 0.04) were independently inversely correlated with bleeding symptoms.

CONCLUSION

Platelet adhesion correlates with bleeding symptoms, while the size of aggregates that are formed under high shear correlates with in vivo platelet activation. The determination of these parameters may assist in estimating an individual bleeding risk and thus a decision for treatment.

Agonist-inducible platelet activation in chronic idiopathic autoimmune thrombocytopenia

OBJECTIVE

There are only few studies on agonist-inducible platelet activation in chronic idiopathic autoimmune thrombocytopenia (cAITP).

MATERIALS AND METHODS

We compared agonist (TRAP-6, ADP, Arachidonic acid, Epinephrine, and Ristocetin) -inducible P-selectin expression and PAC-1 binding in 40 patients with cAITP (f/m ratio 23/17) with those in 20 healthy controls. Results were correlated with platelet counts, detectable platelet antibodies, and reticulated platelets.

RESULTS

The in vivo activation of platelets determined the in vitro inducible response to agonists. The stronger the in vivo activation the less the number of platelets responding to agonists, as illustrated by the inverse correlation of P-selectin expression ex vivo and the relative increase after the exogenous addition of agonists. The agonist-inducible platelet activation was not associated with the presence of detectable platelet antibodies to GPIb/IX or GPIIb/IIIa. Agonist-inducible platelet activation was also not correlated with counts of reticulated platelets.

CONCLUSION

Agonist-inducible activation of platelets in cAITP is affected mainly by their in vivo activation.