A novel antibody fragment targeting HAb18G/CD147 with cytotoxicity and decreased immunogenicity

[(131)I]Metuximab injection (Licartin) was an efficient therapeutic anti-hepatocellular carcinoma (HCC) radioimmunological agent generated by labeling (131)I with the murine monoclonal antibody fragment HAb18-F(ab')(2) but human anti-mouse antibody (HAMA) response in some patients after administration limited its clinical use. To reduce the immunogenicity of murine antibody, we attempted to humanize HAb18 by variable domain resurfacing based on the three-dimensional structure of Fv fragment. Considering the surface accessibility of non-human like framework residues and the potential to form a molecular hydrogen bond within the context of the homology modeled Fv of HAb18, three residues in a single chain fragment of antibody variable region of HAb18 (HAb18scFv) were replaced by their human counterparts. We fabricated a humanized version of HAb18scFv, HAb18-huscFv, to the human IgG1Fc fragment to form (HAb18-huscFv)(2)-Fc. The reactivity of (HAb18-huscFv)(2)-Fc to the serum of patients with HAMA response was decreased while its specificity and similar binding activity (K(D) = 1.5 x 10(-9) M) were retained compared with its parental antibody. In addition, this antibody is an efficient mediator of antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). These results suggest (HAb18-huscFv)(2)-Fc could be a more efficient antibody fragment with less immunogenicity and additional cytotoxicity function.