The design, construction and function of a new chimeric anti-CD20 antibody

A novel murine IgM-type anti-human CD20 monoclonal antibody (mAb) 1–28 was prepared in our Lab, which can induce apoptosis and inhibit proliferation of Daudi and Raji cells. However, the efficacy of 1–28 mAb in human cancer therapy is likely to be limited by human anti-mouse antibody responses. A chimeric antibody, C1–28, containing 1–28 mAb variable region genes fused to human constant region genes (gamma 1, kappa) was constructed. However, C1–28 lost the antigen-binding activity. Here, using sequence similarity and known 3D structure of antibody variable regions as template, the spatial conformations of 1–28 variable regions (i.e. VH and VL) were analyzed with computer-guided homology modeling methods. According to the surface electrostatic distribution and interaction free energy analysis, the relationship between structure and stability of 1–28 variable regions was studied theoretically and a new chimeric anti-CD20 antibody scFv-Ig named 5S was designed. Expression level of 5S in the culture supernatant was determined to be around 50 μg/mL using sandwich ELISA method with chimeric antibody Rituxan as reference. 5S retained its murine counterpart's binding activity by fluorescence-activated cell-sorting analysis. Furthermore, it could kill CD20 positive Daudi and Raji cells by complement-dependent cytotoxicity. For binding affinity often decreased even lost when IgM antibody was constructed into chimeric IgG1 form, our success give a hint about how to construct a IgG1-type chimeric antibody from IgM-type murine antibody to preserve its binding activity.