David J. Hawksworth

Generation and Characterization of Chimeric Antibodies against NS3, NS4, NS5, and Core Antigens of Hepatitis C Virus

ABSTRACT Mouse-human chimeric antibodies (cAbs) against hepatitis C virus (HCV) core, NS3 (nonstructural), NS4, and NS5 antigens were developed as quality control (QC) reagents to replace the use of human sera/plasma for Abbott HCV immunoassays. The cAb retains the mouse monoclonal antibody (MAb) specificity and affinity but still reacts in the existing HCV assay format, which measures human anti-HCV immunoglobulin. Mouse heavy-chain (VH) and light-chain (VL) variable regions of anti-HCV core, NS3, NS4, and NS5 antigens were PCR amplified from hybridoma lines and then cloned with human IgG1 heavy-chain (CH) and light-chain (CL) constant regions, respectively. A single mammalian expression plasmid containing both heavy-chain and light-chain immunoglobulin genes was constructed and transfected into dihydrofolate reductase (DHFR)-deficient Chinese hamster ovary (CHO) cells. The transfected CHO cells were selected using hypoxanthine- and thymidine-free medium and screened by an enzyme immunoassay (EIA). The clone secreting the highest level of antibody was isolated from the CHO transfectants and further subcloned. Each cAb-expressing CHO cell line was weaned into serum-free medium, and the cAb was purified by protein A affinity chromatography. The levels of cAb production for the various CHO cell lines varied from 10 to 20 mg/liter. Purified anti-HCV cAbs were tested with Abbott HCV immunoassays and showed reactivity. Moreover, yeast surface display combined with alanine-scanning mutagenesis was used to map the epitope at the individual amino acid level. Our results suggest that these HCV cAbs are ideal controls, calibrators, and/or QC reagents for HCV assay standardization.

Monoclonal antibodies to an HIV-1 group O envelope recombinant.

Monoclonal antibodies were developed to a recombinant HIV-I group O envelope protein derived from the isolate HAM112. These monoclonal antibodies were characterized for reactivity to a series of overlapping synthetic peptides (29-30 mers) covering gp120 C-terminal and gp41 ectodomain regions of the HIV-1 group O envelope protein. Most of these monoclonal antibodies reacted with peptides spanning sequences analogous to HIV-1 group M epitopes identified from studies in mice and humans. However, several of the antibodies that were nonreactive to individual peptides did react to a mixture of longer peptides from the N-terminal and C-terminal helical regions of the gp41 ectodomain. The monoclonal antibodies described in this study are valuable tools for characterization of antigenic differences between HIV-1 group O and group M viruses.

Generation of Human Neutrophil Gelatinase-Associated Lipocalin Monoclonal Antibodies for Use in ARCHITECT® Assay

Development of a robust immunoassay requires the selection of monoclonal antibodies with desired properties. These properties generally include kinetics parameters such as on-rate and off-rate (i.e., binding affinity), and, often times, the ability to form a sandwich with the analyte of interest. We sought to obtain antibodies suitable for development of an immunoassay capable of detecting human neutrophil gelatinase-associated lipocalin (NGAL), a glycosylated lipocalin of 25 kDa expressed in kidney tubules in response to injury that has been shown to be a urinary biomarker capable of diagnosing acute kidney injury. We immunized CAF1/J and RBF/DnJ mouse strains with recombinant NGAL, and a robust immune response, as measured by serum antibody titer, was observed among all CAF1/J mice. Antibodies secreted from mouse B cell-myeloma hybridomas were screened by enzyme immunoassay (EIA) and by surface plasmon resonance using a method we termed hybrid supernatant kinetic screening. Approximately 300 hybrid clones were evaluated by this technique to identify antibodies with the kinetic binding parameters meeting criteria required for further assay development (i.e., rapid association and slow dissociation). This data, along with epitope grouping, cell growth, cell viability, and antibody secretion, were used to identify antibodies for testing in the ARCHITECT assay.