[Show abstract][Hide abstract] ABSTRACT: Current flu vaccines provide only limited coverage against seasonal strains of influenza viruses. The identification of V(H)1-69 antibodies that broadly neutralize almost all influenza A group 1 viruses constituted a breakthrough in the influenza field. Here, we report the isolation and characterization of a human monoclonal antibody CR8020 with broad neutralizing activity against most group 2 viruses, including H3N2 and H7N7, which cause severe human infection. The crystal structure of Fab CR8020 with the 1968 pandemic H3 hemagglutinin (HA) reveals a highly conserved epitope in the HA stalk distinct from the epitope recognized by the V(H)1-69 group 1 antibodies. Thus, a cocktail of two antibodies may be sufficient to neutralize most influenza A subtypes and, hence, enable development of a universal flu vaccine and broad-spectrum antibody therapies.
[Show abstract][Hide abstract] ABSTRACT: To study the contribution of antibody light (L) chains to the diversity and binding properties of immune repertoires, a phage display repertoire was constructed from a single human antibody L chain and a large collection of antibody heavy (H) chains harvested from the blood of two human donors immunized with tetanus toxoid (TT) vaccine. After selection for binding to TT, 129 unique antibodies representing 53 variable immunoglobulin H chain (V(H)) gene rearrangements were isolated. This panel of anti-TT antibodies restricted to a single variable immunoglobulin L chain (V(L)) could be organized into 17 groups binding non-competing epitopes on the TT molecule. Comparison of the V(H) regions in this V(L)-restricted panel with a previously published repertoire of anti-TT V(H) regions with cognate V(H)-V(L) pairing showed a very similar distribution of V(H), D(H) and J(H) gene segment utilization and length of the complementarity-determining region 3 of the H chain. Surface plasmon resonance analysis of the single-V(L) anti-TT repertoire unveiled a range of affinities, with a median monovalent affinity of 2 nM. When the single-V(L) anti-TT V(H) repertoire was combined with a collection of naïve V(L) regions and again selected for binding to TT, many of the V(H) genes were recovered in combination with a diversity of V(L) regions. The affinities of a panel of antibodies consisting of a single promiscuous anti-TT V(H) combined with 15 diverse V(L) chains were determined and found to be identical to each other and to the original isolate restricted to a single-V(L) chain. Based on previous estimates of the clonal size of the human anti-TT repertoire, we conclude that up to 25% of human anti-TT-encoding V(H) regions from an immunized repertoire have promiscuous features. These V(H) regions readily combine with a single antibody L chain to result in a large panel of anti-TT antibodies that conserve the expected epitope diversity, V(H) region diversity and affinity of a natural repertoire.
[Show abstract][Hide abstract] ABSTRACT: The hemagglutinin (HA) glycoprotein is the principal target of protective humoral immune responses to influenza virus infections but such antibody responses only provide efficient protection against a narrow spectrum of HA antigenic variants within a given virus subtype. Avian influenza viruses such as H5N1 are currently panzootic and pose a pandemic threat. These viruses are antigenically diverse and protective strategies need to cross protect against diverse viral clades. Furthermore, there are 16 different HA subtypes and no certainty the next pandemic will be caused by an H5 subtype, thus it is important to develop prophylactic and therapeutic interventions that provide heterosubtypic protection.
Here we describe a panel of 13 monoclonal antibodies (mAbs) recovered from combinatorial display libraries that were constructed from human IgM(+) memory B cells of recent (seasonal) influenza vaccinees. The mAbs have broad heterosubtypic neutralizing activity against antigenically diverse H1, H2, H5, H6, H8 and H9 influenza subtypes. Restriction to variable heavy chain gene IGHV1-69 in the high affinity mAb panel was associated with binding to a conserved hydrophobic pocket in the stem domain of HA. The most potent antibody (CR6261) was protective in mice when given before and after lethal H5N1 or H1N1 challenge.
The human monoclonal CR6261 described in this study could be developed for use as a broad spectrum agent for prophylaxis or treatment of human or avian influenza infections without prior strain characterization. Moreover, the CR6261 epitope could be applied in targeted vaccine strategies or in the design of novel antivirals. Finally our approach of screening the IgM(+) memory repertoire could be applied to identify conserved and functionally relevant targets on other rapidly evolving pathogens.
PLoS ONE 02/2008; 3(12):e3942. DOI:10.1371/journal.pone.0003942 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Experimental animal data show that protection against severe acute respiratory syndrome coronavirus (SARS-CoV) infection with human monoclonal antibodies (mAbs) is feasible. For an effective immune prophylaxis in humans, broad coverage of different strains of SARS-CoV and control of potential neutralization escape variants will be required. Combinations of virus-neutralizing, noncompeting mAbs may have these properties.
Human mAb CR3014 has been shown to completely prevent lung pathology and abolish pharyngeal shedding of SARS-CoV in infected ferrets. We generated in vitro SARS-CoV variants escaping neutralization by CR3014, which all had a single P462L mutation in the glycoprotein spike (S) of the escape virus. In vitro experiments confirmed that binding of CR3014 to a recombinant S fragment (amino acid residues 318-510) harboring this mutation was abolished. We therefore screened an antibody-phage library derived from blood of a convalescent SARS patient for antibodies complementary to CR3014. A novel mAb, CR3022, was identified that neutralized CR3014 escape viruses, did not compete with CR3014 for binding to recombinant S1 fragments, and bound to S1 fragments derived from the civet cat SARS-CoV-like strain SZ3. No escape variants could be generated with CR3022. The mixture of both mAbs showed neutralization of SARS-CoV in a synergistic fashion by recognizing different epitopes on the receptor-binding domain. Dose reduction indices of 4.5 and 20.5 were observed for CR3014 and CR3022, respectively, at 100% neutralization. Because enhancement of SARS-CoV infection by subneutralizing antibody concentrations is of concern, we show here that anti-SARS-CoV antibodies do not convert the abortive infection of primary human macrophages by SARS-CoV into a productive one.
The combination of two noncompeting human mAbs CR3014 and CR3022 potentially controls immune escape and extends the breadth of protection. At the same time, synergy between CR3014 and CR3022 may allow for a lower total antibody dose to be administered for passive immune prophylaxis of SARS-CoV infection.
PLoS Medicine 08/2006; 3(7):e237. DOI:10.1371/journal.pmed.0030237 · 14.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Application of antibody phage display to the identification of cell surface antigens with restricted expression patterns is often complicated by the inability to demonstrate specific binding to a certain cell type. The specificity of an antibody can only be properly assessed when the antibody is of sufficient high affinity to detect low-density antigens on cell surfaces. Therefore, a robust and simple assay for the prediction of relative antibody affinities was developed and compared to data obtained using surface plasmon resonance (SPR) technology. A panel of eight anti-CD46 antibody fragments with different affinities was selected from phage display libraries and reformatted into complete human IgG1 molecules. SPR was used to determine K(D) values for these antibodies. The association and dissociation of the antibodies for binding to CD46 expressed on cell surfaces were analysed using FACS-based assays. We show that ranking of the antibodies based on FACS data correlates well with ranking based on K(D) values as measured by SPR and can therefore be used to discriminate between high- and low-affinity antibodies. Finally, we show that a low-affinity antibody may only detect high expression levels of a surface marker while failing to detect lower expression levels of this molecule, which may lead to a false interpretation of antibody specificity.
[Show abstract][Hide abstract] ABSTRACT: Human monoclonal antibodies (MAbs) were selected from semisynthetic antibody phage display libraries by using whole irradiated severe acute respiratory syndrome (SARS) coronavirus (CoV) virions as target. We identified eight human MAbs binding to virus and infected cells, six of which could be mapped to two SARS-CoV structural proteins: the nucleocapsid (N) and spike (S) proteins. Two MAbs reacted with N protein. One of the N protein MAbs recognized a linear epitope conserved between all published human and animal SARS-CoV isolates, and the other bound to a nonlinear N epitope. These two N MAbs did not compete for binding to SARS-CoV. Four MAbs reacted with the S glycoprotein, and three of these MAbs neutralized SARS-CoV in vitro. All three neutralizing anti-S MAbs bound a recombinant S1 fragment comprising residues 318 to 510, a region previously identified as the SARS-CoV S receptor binding domain; the nonneutralizing MAb did not. Two strongly neutralizing anti-S1 MAbs blocked the binding of a recombinant S fragment (residues 1 to 565) to SARS-CoV-susceptible Vero cells completely, whereas a poorly neutralizing S1 MAb blocked binding only partially. The MAb ability to block S1-receptor binding and the level of neutralization of the two strongly neutralizing S1 MAbs correlated with the binding affinity to the S1 domain. Finally, epitope mapping, using recombinant S fragments (residues 318 to 510) containing naturally occurring mutations, revealed the importance of residue N479 for the binding of the most potent neutralizing MAb, CR3014. The complete set of SARS-CoV MAbs described here may be useful for diagnosis, chemoprophylaxis, and therapy of SARS-CoV infection and disease.
Journal of Virology 03/2005; 79(3):1635-44. DOI:10.1128/JVI.79.3.1635-1644.2005 · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tumour-associated cell surface markers are potential targets for antibody-based therapies. We have obtained a panel of myeloid cell binding single chain variable fragments (scFv) by applying phage display selection on myeloid cell lines followed by a selection round on freshly isolated acute myeloid leukaemia (AML) blasts using flow cytometry. To identify the target antigens, the scFv were recloned and expressed in an IgG(1) format and tested for their ability to immunoprecipitate cell surface proteins. The IgGs that reacted with distinct cell membrane extractable proteins were used in large-scale affinity purification of the target antigen followed by mass-spectrometry-based identification. Well-characterised cell surface antigens, such as leukocyte antigen-related receptor protein tyrosine phosphatase (LAR PTP) and activated leukocyte adhesion molecule (ALCAM) in addition to several unknown proteins, like ATAD3A, were identified. These experiments demonstrate that phage antibody selection in combination with affinity chromatography and mass spectrometry can be exploited successfully to identify novel antibody target molecules on malignant cells.
European Journal of Cancer 02/2005; 41(1):178-87. DOI:10.1016/j.ejca.2004.10.008 · 4.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Phage display is a widely used technology for the isolation of peptides and proteins with specific binding properties from large libraries of these molecules. A drawback of the common phagemid/helper phage systems is the high infective background of phages that do not display the protein of interest, but are propagated due to non-specific binding to selection targets. This and the enhanced growth rates of bacteria harboring aberrant phagemids not expressing recombinant proteins leads to a serious decrease in selection efficiency. Here we describe a VCSM13-derived helper phage that circumvents this problem, because it lacks the genetic information for the infectivity domains of phage coat protein pIII. Rescue of a library with this novel CT helper phage yields phages that are only infectious when they contain a phagemid-encoded pIII-fusion protein, since phages without a displayed protein carry truncated pIII only and are lost upon re-infection. Importantly, the CT helper phage can be produced in quantities similar to the VCSM13 helper phage. The superiority of CT over VCSM13 during selection was demonstrated by a higher percentage of positive clones isolated from an antibody library after two selection rounds on a complex cellular target. We conclude that the CT helper phage considerably improves the efficiency of selections using phagemid-based protein libraries.
Nucleic Acids Research 07/2003; 31(11):e59. · 9.11 Impact Factor