Identification of Cross-Reactive and Restricted Epitopes Localized on Human Chorionic Gonadotropin Beta-Subunit by Monoclonal Antibodies

Hersintuzumab: A novel humanized anti-HER2 monoclonal antibody induces potent tumor growth inhibition

Humanized monoclonal antibodies (mAbs) against HER2 including trastuzumab and pertuzumab are widely used to treat HER2 overexpressing metastatic breast cancers. These two mAbs recognize distinct epitopes on HER2 and their combination induces a more potent blockade of HER2 signaling than trastuzumab alone. Recently, we have reported characterization of a new chimeric mAb (c-1T0) which binds to an epitope different from that recognized by trastuzumab and significantly inhibits proliferation of HER2 overexpressing tumor cells. Here, we describe humanization of this mAb by grafting all six complementarity determining regions (CDRs) onto human variable germline genes. Humanized VH and VL sequences were synthesized and ligated to human γ1 and κ constant region genes using splice overlap extension (SOE) PCR. Subsequently, the humanized antibody designated hersintuzumab was expressed and characterized by ELISA, Western blot and flow cytometry. The purified humanized mAb binds to recombinant HER2 and HER2-overexpressing tumor cells with an affinity comparable with the chimeric and parental mouse mAbs. It recognizes an epitope distinct from those recognized by trastuzumab and pertuzumab. Binding of hersintuzumab to HER2 overexpressing tumor cells induces G1 cell cycle arrest, inhibition of ERK and AKT signaling pathways and growth inhibition. Moreover, hersintuzumab could induce antibody-dependent cell cytotoxicity (ADCC) on BT-474 cells. This new humanized mAb is a potentially valuable tool for single or combination breast cancer therapy.

Construction and characterization of a new chimeric antibody against HER2

Aim: Immunotherapy with anti-HER2 antibodies has shown promising results in patients with HER2-positive breast cancer. We have recently reported characterization of a mouse monoclonal antibody (mAb) against HER2, which binds to an epitope different from that recognized by trastuzumab and specifically inhibits proliferation of tumor cells overexpressing HER2. In the present study we report chimerization of this antibody. Materials & methods: The immunoglobulin variable region heavy and light chain genes of 1T0 hybridoma cells were amplified and ligated to human γ-1 and κ constant region genes using splice overlap extension PCR. The chimeric antibody was subsequently expressed and characterized by ELISA, western blot and flow cytometry. Results: The purified chimeric antibody specifically binds to recombinant HER2 and HER2-overexpressing tumor cells and inhibits proliferation of these cells. The binding affinity of the chimeric mAb was comparable with the parental mouse mAb. Conclusion: This chimeric anti-HER2 mAb is a potentially valuable tool for targeted immunotherapy.

Epitope mapping of recombinant hepatitis B surface antigen by murine monoclonal antibodies

Hepatitis B surface antigen (HBsAg) induces a potent protective antibody response in immunized healthy individuals. The antibody response in humans is largely directed to a restricted conformational immunodominant region of HBsAg, identified as "a" determinant. Our aim was generation and characterization of murine monoclonal antibodies (MAbs) against recombinant HBsAg and their use for epitope mapping of the antigen. Hybridoma cells were established from Balb/c mice immunized with recombinant HBsAg of the "adw" subtype and cloned by limiting dilution. Specificity of MAbs was studied by indirect ELISA and immunoblotting. Topology of the epitopes was analyzed by competitive and inhibition ELISA. Eight hybridoma clones producing MAbs specific for the immunogen were established. Five of the MAbs recognized overlapping conformational epitopes, whereas the remaining three MAbs were found to identify linear epitopes. Cross-inhibition studies suggest recognition of mutually exclusive epitopes by these MAbs. Our data suggest that, similar to the human system, the mouse antibody response is largely directed to restricted conformational overlapping epitopes of HBsAg.