Rapid phenotyping of HPA-1a using either diabody-based hemagglutination or recombinant IgG1-based assays

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.

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.

A modified rapid monoclonal antibody-specific immobilization of platelet antigen assay for the detection of human platelet antigen (HPA) antibodies: a multicentre evaluation

BACKGROUND

The monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay is the cornerstone technique for the detection and identification of human platelet antigen (HPA) antibodies. However, the original technique described by Kiefel and colleagues requires approximately 8 h adding to diagnostic delay. Moreover, proficiency exercises indicate that there are substantial variations in the MAIPA protocol, and that these may account for interlaboratory differences in sensitivity and specificity.

STUDY DESIGN AND METHODS

A review of current MAIPA assay protocols from six laboratories together with performance in quality-assessment schemes identified several key variables potentially affecting the assay results. An optimized protocol was derived and assay time reduced to 5 h. The modified rapid MAIPA (MR-MAIPA) assay was evaluated using 61 samples with a range of HPA antibodies typically encountered in cases of fetomaternal alloimmune thrombocytopenia (n = 22), post-transfusion purpura (n = 8), platelet refractoriness (n = 7) and other platelet immune conditions (n = 24). The sensitivity of the assay was assessed using three international standards and the recombinant HPA-1a antibody CamTran007. The results obtained were compared with the original findings obtained with the local MAIPA assays. In addition, four different glycoprotein IIb/IIIa capture monoclonal antibodies were evaluated for their effect on assay sensitivity.

RESULTS

Complete concordance was found between the original MAIPA results and those obtained with the new assay when testing a selected panel of clinical samples. The modified assay had nanogram level sensitivity for the detection of HPA-1a antibodies and titration of HPA-1a and HPA-5b antibody sensitivity standards yielded end-points equal to or greater than the mean recorded in international workshops.

CONCLUSION

The MR-MAIPA assay offers improved turnaround for the detection of HPA antibodies without loss of sensitivity.

Molecular characterization of the variable domains of an ?IIb?3-specific immunoglobulin�M ? platelet cold agglutinin in a follicular lymphoma patient with treatment refractory autoimmune thrombocytopenia: idiotypic overlap between ?IIb?3 integrin antibodies

BACKGROUND

Cold hemagglutinins are generally immunoglobulin M (IgM) kappa antibodies reactive at temperatures below 37 degrees C and if of high titer may cause hemolysis. Platelet (PLT) cold agglutinins (CAs) are rare and poorly characterized. A detailed molecular characterization of the variable domains of a pathologic, PLT-reactive, CA is presented.

CASE REPORT

A 70-year-old woman was admitted with rectal bleeding accompanied by widespread petechiae, bruising, tongue and buccal mucosa bleeding, and epistaxes and proved refractory to HLA- and HPA-matched PLTs. Detailed investigation showed monoclonal heavy-chain gene rearrangement with an IgM paraprotein of 3.3 g per L and a trace of kappa Bence Jones protein in the urine, compatible with a diagnosis of secretory B-cell non-Hodgkin's lymphoma (B-NHL). PLT antibody (PAIg) investigations revealed a potent IgM kappa PLT CA. Sequencing of the rearranged variable domain genes of the malignant clone together with idiotype-specific antibodies obtained by DNA-based immunization of rabbits and matrix-assisted laser desorption/ionization-time-of-flight analysis of the PAIgM provided a irrefutable link between the thrombocytopenia, the IgM paraprotein, and the PAIgM against alphaIIbbeta3. The thrombocytopenia and bleeding were refractory to standard treatment and PLT transfusion, but treatment with rituximab resulted in a recovery of the PLT count and a complete remission of B-NHL.

CONCLUSION

The IgM kappa paraprotein derived from the malignant B-cell clone was a potent and clinically significant CA against alphaIIbbeta3. The testing for PLT CAs in patients with a paraprotein and refractory to matched PLTs may aid the selection of appropriate treatment.

Affinity maturation of Fab antibody fragments by fluorescent-activated cell sorting of yeast-displayed libraries

We report for the first time the affinity maturation of Fab antibody fragments using fluorescent-activated cell sorting (FACS) of yeast-displayed repertoires. A single yeast display vector which enables the inducible expression of an anchored heavy chain and a soluble light chain has been constructed. The assembly and functional display on the yeast cell surface of Fab antibodies specific for different protein targets has been demonstrated by flow cytometry and immunofluorescence microscopy. We have affinity matured a Fab antibody specific for the tetravalent antigen streptavidin using FACS of yeast-displayed repertoires diversified by error-prone polymerase chain reaction. A panel of variants with up to 10.7-fold improvement in affinity was obtained after selection. Two leading clones, R2H10 (3.2 nM) and R3B1 (5.5 nM), had mutations in light chain complementarity determining region 1 LC-CDR1 (H34R) and LC-CDR3 (Y96H or Y96F) and gave a 10.7-fold and 6.3-fold affinity improvement over the starting antibody, respectively. The ability to efficiently affinity mature Fab antibodies is an important component of the antibody development pipeline and we have shown that yeast display is an efficient method for this purpose.

Anti-HPA-1a-mediated platelet phagocytosis by monocytes in vitro and its inhibition by Fc gamma receptor (FcgammaR) reactive reagents

The study was undertaken to delineate mechanisms of platelet destruction by phagocytosis during fetal/neonatal alloimmune thrombocytopenia (FAIT/NAIT) because of maternal antibodies against human platelet antigen 1a (HPA-1a). By employing a platelet phagocytosis assay based on the ORPEGEN flow cytometric bacterial phagocytosis test, we measured monocyte ingestion of platelets mediated by anti-HPA-1a antibodies. Moreover, we tested, as potential therapeutic agents, FcgammaR reactive reagents, for their inhibition of this process. Four of six anti-HPA-1a sera tested mediated phagocytosis of HPA-1a-positive platelets in a concentration-dependent manner. Monocyte ingestion of platelets was almost completely inhibited by cytochalasin D. No anti-HPA-1a-mediated phagocytosis was observed with anti-HPA-1a-negative platelets. The humanised anti-FcgammaRI monoclonal antibody H22 at concentrations 1-100 microg/ml, completely inhibited anti-HPA-1a-mediated phagocytosis as did similar concentrations of ivIg. By contrast, a mouse monoclonal anti-FcgammaRII (IV.3, Fab) at 10 microg/ml caused little or no suppression of platelet phagocytosis mediated by two anti-HPA-1 sera. Furthermore, the addition of anti-FcgammaRII (10 microg/ml) to sub-optimal concentrations of H22 did not significantly increase the inhibitory effect of the latter compound. Monomeric IgG (0.1-10 microg/ml) failed to suppress anti-HPA-1 mediated platelet ingestion by the phagocytes, as did anti-FcgammaRIII. To our knowledge this is a rare example of an assay that measures platelet phagocytosis in vitro. The results suggest that FcgammaRI plays a major role in anti-HPA-1a-mediated platelet phagocytosis by monocytes while FcgammaRIIa, is of little or minor importance only. Moreover, the findings indicate the use of H22 as an alternative to interavenous Ig (ivIg) in the management of FAIT/NAIT.

Platelet alphaIIbbeta3 recombinant autoantibodies from the B-cell repertoire of a post-transfusion purpura patient

The biallelic human platelet alloantigen (HPA) 1 system encodes a leucine to proline substitution at position 33 in the beta3 integrin. Homozygous individuals can be immunized by the non-self allele-encoded protein following transfusion or during pregnancy. In post-transfusion purpura (PTP), a subsequent recall alloantibody response against the non-self form of beta3 is paralleled by the destruction of autologous platelets, leading to profound thrombocytopenia. Although serological evidence suggests platelet autoantibodies are responsible, such autoantibodies are poorly defined. We used variable gene phage display to isolate alphaIIbbeta3 autoantibodies formed in the acute phase of PTP and determined the epitopes recognized. An immunoglobulin G (IgG)-encoded variable heavy-chain domain (VH) gene repertoire containing 4.7 x 10(7) single-chain Fv fragments was cloned and three alphaIIbbeta3 antibodies were isolated (clones 2F2, E3 and B12). All three used different VH genes with a low level of somatic mutation for genes derived from gamma-encoding mRNA. Two (2F2 and E3) recognized an overlapping epitope and their binding was inhibited by sera from patients with PTP; all three recognized Ca2+-dependent compound epitopes on alphaIIbbeta3. Our results support the theory that a transient loss of tolerance for alphaIIbbeta3 with autoantibody formation occurs in PTP.

HPA-1a phenotype-genotype discrepancy reveals a naturally occurring Arg93Gln substitution in the platelet beta 3 integrin that disrupts the HPA-1a epitope

A single nucleotide polymorphism (SNP) at position 196 in the beta 3 integrin causes a Leu33Pro substitution in the mature protein. Alloimmunization against the beta 3Leu33 form (human platelet antigen [HPA]-1a, Pl(A1), Zw(a)) in patients who are beta 3Pro33 homozygous (HPA-1b1b, Pl(A2A2), Zw(bb)) causes neonatal alloimmune thrombocytopenia, posttransfusion purpura, or refractoriness to platelet transfusion. Studies with recombinant proteins have demonstrated that amino acids 1 to 66 and 288 to 490 of the beta 3 integrin contribute to HPA-1a epitope formation. In determining the HPA-1a status of more than 6000 donors, we identified a donor with an HPA-1a(weak) phenotype and an HPA-1a1b genotype. The platelets from this donor had normal levels of surface alpha IIb beta 3 but reacted only weakly with monoclonal and polyclonal anti-HPA-1a by whole blood enzyme-linked immunosorbent assay (ELISA), flow cytometry, and sandwich ELISA. We reasoned that an alteration in the primary nucleotide sequence of the beta 3Leu33 allele of this donor was disrupting the HPA-1a epitope. In agreement with this hypothesis, sequencing platelet RNA-derived alpha IIb and beta 3 cDNA identified a novel G/A SNP at position 376 of the beta 3 integrin that encodes for an Arg93Gln replacement in the beta 3Leu33 allele. Coexpression of the beta 3Leu33Gln93 encoding cDNA in Chinese hamster ovary cells with human alpha IIb cDNA showed that the surface-expressed alpha IIb beta 3 reacted normally with beta 3 integrin-specific monoclonal antibodies but only weakly with monoclonal anti-HPA-1a. Our results show that an Arg93Gln mutation in the beta 3Leu33 encoding allele disrupts the HPA-1a epitope, suggesting that Arg93 contributes to the formation of the HPA-1a B-cell epitope.

Recombinant monoclonal antibody technology

With the development of murine hybridoma technology over a quarter century ago, the ability to produce large quantities of well-characterized monoclonal antibody preparations revolutionized diagnostic and therapeutic medicine. For many applications in transfusion medicine, however, the production of serological reagents in mice has certain biological limitations relating to the difficulty in obtaining murine monoclonal antibodies specific for many human blood group antigens. Furthermore, for therapeutic purposes, the efficacy of murine-derived immunoglobulin preparations is limited by the induction of anti-mouse immune responses. Technical difficulties inherent in human hybridoma formation have led to novel molecular approaches that facilitate the isolation and production of human antibodies without the need for B-cell transformation, tissue culture, or even immunized individuals. These technologies, referred to as 'repertoire cloning' or 'Fab/phage display', involve the rapid cloning of immunoglobulin gene segments to create immune libraries from which antibodies with desired specificities can be selected. The use of such recombinant methods in transfusion medicine is anticipated to play an important role in the development and production of renewable supplies of low-cost reagents for diagnostic and therapeutic applications.

Expression of a bispecific dsFv-dsFv' antibody fragment in Escherichia coli

A bispecific disulfide-stabilized Fv antibody fragment (dsFv-dsFv') consisting of two different disulfide-stabilized Fv antibody fragments connected by flexible linker peptides was produced by secretion of three polypeptide chains into the periplasm of Escherichia coli. The dsFv-dsFv' molecules were enriched by immobilized metal affinity chromatography and further purified by anion-exchange chromatography. The recombinant antibody constructs retained the two parental antigen binding specificities and were able to cross-link the two different antigens. The described dsFv-dsFv' design might be of particular value for therapeutic in vivo applications since improved stability is expected to be combined with minimal immunogenicity.

Introduction to antibody engineering and phage display

The vertebrate immune system, capable of rapidly producing highly specific antibodies upon immunisation, has been used to produce murine monoclonal antibodies (mAbs) via immortalisation and isolation of antibody-secreting cells. These mAbs have had a profound impact in the fields of diagnostics and therapeutics. However, the therapeutic use of murine mAbs is complicated by their immunogenicity. To circumvent this immunogenicity, antibody engineering techniques which render murine mAbs more compatible with the human immune system have been devised. Over the last decade, the technique of antibody phage display, which facilitates the production of human mAbs, has been developed. This review serves as an introduction to antibody engineering, phage display and the development of antibody fragments into viable diagnostic and therapeutic reagents.

Functional human monoclonal antibodies of all isotypes constructed from phage display library-derived single-chain Fv antibody fragments

We have constructed a series of eukaryotic expression vectors that permit the rapid conversion of single chain (sc) Fv antibody fragments, derived from semi-synthetic phage display libraries, into intact fully human monoclonal antibodies (mAb) of each isotype. As a model, a scFv fragment specific for sheep red blood cells (SRBC) was isolated from a semi-synthetic phage antibody (Ab) display library, and used to produce human mAbs of IgM, IgG1-IgG4, IgA1, IgA2m(1) and IgE isotype in vitro in stably transfected cells. N-terminal protein sequence analysis of purified immunoglobulin heavy (H) and light (L) chains revealed precise proteolytic removal of the leader peptide. Biochemical analysis of purified recombinant human mAbs demonstrated that properly glycosylated molecules of the correct molecular size were produced. The IgG and IgA mAbs retained SRBC-binding activity, interacted with different Fc receptor-transfectants, and induced complement-mediated hemolysis and Ab-dependent phagocytosis of SRBC by neutrophils in a pattern consistent with the immunoglobulin (Ig) H chain isotype. We conclude that in vitro produced recombinant human mAbs constructed from phage display library-derived scFv fragments mirror their natural counterparts and may represent a source of mAbs for use in human therapy.